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USGS1996

Lead-isotopic, sulphur-isotopic, and trace-element studies of galena from the Silesian-Cracow Zn-Pb ores, polymetallic veins from the Gory Swietokrzyskie MTS, and the Myszkow porphyry copper deposit, Poland

Lead-isotopic data on galena samples collected from a paragenetically constrained suite of samples from the Silesian-Cracow ore district show no regional or paragenetically controlled lead-isotopic trends within the analytical reproducibility of the measurements. Furthermore, the new lead-isotopic data agree with previously reported lead-isotopic results (R. E. Zartman et al., 1979). Sulfur-isotopic analyses of ores from the Silesian-Cracow district as well as from vein ore from the Gory Swietokrzyskie Mts. and the Myszkow porphyry copper deposit, when coupled with trace-element data from the galena samples, clearly discriminate different hydrothermal ore-forming events. Lead-isotopic data from the Permian and Miocene evaporite deposits in Poland indicate that neither of these evaporite deposits were a source of metals for the Silesian-Cracow district ores. Furthermore, lead-isotopic data from these evaporite deposits and the shale residues from the Miocene halite samples indicate that the crustal evolution of lead in the central and western European platform in southern Poland followed normal crustal lead-isotopic growth, and that the isotopic composition of crustal lead had progressed beyond the lead-isotopic composition of lead in the Silesian-Cracow ores by Permian time. Thus, Mesozoic and Tertiary sedimentary flysch rocks can be eliminated as viable source rocks for the metals in the Silesian-Cracow Mississippi Valley-type (MVT) deposits. The uniformity of the isotopic composition of lead in the Silesian-Cracow ores, when coupled with the geologic evidence that mineralization must post-date Late Jurassic faulting (E. Gorecka, 1991), constrains the geochemical nature of the source region. The source of the metals is probably a well-mixed, multi-cycle molasse sequence of sedimentary rocks that contains little if any Precambrian metamorphic or granitic clasts (S. E. Church, R. B. Vaughn, 1992). If ore deposition was post Late Jurassic (about 150 m. y.) or later as indicated by the geologic evidence, the source rocks probably contained elevated concentrations of Zn and Pb (75-100 ppm), and relatively low concentrations of U and Th (2 and 8 ppm or less, respectively). The Carboniferous coal-bearing molasse rocks of the Upper Silesian Coal Basin are a prime candidate for such a source region. The presence of ammonia and acetate in the fluid inclusions (Viets et al., 1996a) also indicate that the Carboniferous coal-bearing molasse sequence in the Upper Silesian Coal Basin may have been a suitable pathway for the MVT ore fluids. The lead-isotopic homogeneity, when coupled with the sulfur-isotopic heterogeneity of the ores suggests that mixing of a single metal-bearing fluid with waters from separate aquifers containing variable sulfur-isotopic compositions in karsts in the Muschelkalk Formation of Middle Triassic age may have been responsible for the precipitation of the ores of the Silesian-Cracow district.

Prace - Panstwowego Instytutu Geologicznego↗

USGS2026

Using quantitative polymerase chain reaction to assess phytoplankton and indicate eutrophication in freshwater rivers: A multiyear nationwide study across the United States

Phytoplankton are essential primary producers in fresh surface water that are critical to the health of ecosystems. However, phytoplankton overgrowth due to eutrophication threatens ecological, economic, and public health. Therefore, assessing phytoplankton is fundamental for understanding the productivity, health, and trophic status of freshwater ecosystems. Light microscopy and chlorophyll a assessment are common approaches for studying phytoplankton. They are easy to use, cost-effective, and reliable but have significant limitations. Microscopy has a low throughput and is time-consuming and labor-intensive. Chlorophyll a assessment does not reveal phytoplankton community composition and structure. For comparison, quantitative polymerase chain reaction (qPCR) is widely applied in quantifying microorganisms, offering multiple advantages, including high throughput, sensitivity, accuracy, and robustness. However, a research gap remains regarding the feasibility of using qPCR to assess phytoplankton and indicate trophic status of freshwater bodies. We conducted a nationwide, multiyear study in the United States to compare the performance of qPCR, microscopy, and chlorophyll a assessment in assessing phytoplankton and trophic statuses of multiple freshwater rivers. From early summer to late fall in 2017, 2018, and 2019, we assessed phytoplankton, chlorophyll a , pheophytin a , and the overall Trophic Level Index ( TLI Overall ) at the sampling sites in 12 large freshwater rivers in three regions (western, midcontinent, and eastern) across the United States. The seasonal summed abundance of four major phytoplankton taxa [Bacillariophyta (diatoms), Cyanobacteria (blue-green algae), Chlorophyta (green algae), and Dinoflagellates (Dinophyta)] ranged from 6.88 log 10 (GCN·L –1 ) (the Connecticut River, 2017) to 9.29 log 10 (GCN·L –1 ) (the Kansas River, 2019) (GCN: gene or genome copy number). qPCR- and microscopy-based phytoplankton abundance of eight phytoplankton taxa had a significant positive allometric or log-linear correlation (adjusted R 2 = 0.836, p -value < 0.001, n = 815). In addition, qPCR-based phytoplankton abundance had positive allometric or log-linear correlations with chlorophyll a (adjusted R 2 = 0.5437, p -value < 0.001, n = 164), pheophytin a (adjusted R 2 = 0.3378, p -value < 0.001, n = 164), and TLI Overall (adjusted R 2 = 0.4789, p -value < 0.001, n = 164). Therefore, qPCR is a promising alternative to microscopy and chlorophyll a for studying phytoplankton and trophic status in freshwater rivers. Moreover, phytoplankton abundance had limited temporal variation within each sampling season and over the three sampling seasons in 2017, 2018, and 2019 but showed clear spatial variation. The midcontinent sites had significantly higher phytoplankton abundance, chlorophyll a concentrations, pheophytin a concentrations, and TLI Overall values than those in the eastern and western rivers, reflecting the higher trophic statuses of the midcontinent rivers. This work also provides the thresholds of qPCR-based phytoplankton abundance for delineating trophic statuses in freshwater rivers. Overall, this work demonstrates that qPCR is a promising tool for studying phytoplankton and characterizing the trophic status of freshwater rivers.

Book chapter↗

USGS2022

Ungulate migration in a changing climate—An initial assessment of climate impacts, management priorities, and science needs

Executive Summary Migratory behavior among ungulates in the Western United States occurs in response to changing forage quality and quantity, weather patterns, and predation risk. As snow melts and vegetation green-up begins in late spring and early summer, many migratory ungulates leave their winter range and move to higher elevation summer ranges to access high-quality forage and areas with vegetative cover for protection during fawning. Ungulates remain on these ranges until the fall when increasing snowfall and decreasing temperatures trigger them to migrate back to their lower elevation winter ranges. While researchers have begun to assess the effects of physical barriers such as roads and energy infrastructure on migration, less attention has been paid to understanding how changing climate conditions might affect ungulate movements and range habitats. Does earlier spring green-up make ungulates leave their winter ranges sooner? Do persistent drought conditions reduce the carrying capacity of seasonal range habitats or lead to shifts in migration pathways? These and other questions remain largely unanswered but could have cascading effects on ungulate population dynamics and migratory behavior. In February 2018, the Secretary of the Interior signed Department of the Interior Secretarial Order 3362 (SO3362), “Improving Habitat Quality in Western Big-Game Winter Range and Migration Corridors.” The order, which focuses on elk, mule deer, and pronghorn in 11 Western States, directs the Bureau of Land Management (BLM), the U.S. Fish and Wildlife Service (FWS), the National Park Service (NPS), and the U.S. Geological Survey (USGS) to partner with State wildlife agencies on their priorities and objectives for identifying and conserving ungulate migration corridors and winter-range habitat. The USGS Climate Adaptation Science Centers (CASCs) were established to help managers of the Nation’s fish, wildlife, waters, and lands understand the effects of climate change and adapt to changing conditions. To support the recent Department of the Interior (DOI) emphasis on ungulate migration corridors and winter-range habitat, this report assesses current information on how climate change could affect elk, mule deer, and pronghorn migration. The report synthesizes the drivers of migration, outlines what is known about how climate change might affect these drivers, and summarizes management priorities and science needs related to ungulate migration corridors and range habitat. A review of the literature on ungulate migration shows that the core drivers of spring migration are the timing of spring green-up and snowmelt, and the core driver of fall migration is winter severity. After exploring what is known about how these drivers affect or could be affected by climate change, several pathways through which ungulate migration could be altered were identified: (1) ungulates alter migration timing to better track plant phenology or in response to changes in winter conditions; (2) ungulates change their migration route or distance traveled during migration to accommodate changes in environmental conditions; and (3) ungulate populations that are currently migratory may begin to demonstrate interannual variability in whether they migrate, depending on environmental conditions and density-dependence, and may remain resident for sets of consecutive years. Through discussions with managers, physical barriers to movement such as roads and fences were identified as a core concern. In addition, the primary research needs of States are the acquisition and analysis of data on ungulate movements, to refine delineation of winter range, summer range, and corridors, and to support a better understanding of how ungulates use these habitats. When it comes to understanding climate effects, managers were more concerned with understanding the vulnerability of winter- and summer-range habitats than the vulnerability of migration corridors because of the influence of summer and winter forage on ungulate condition and reproductive success. Managers were also concerned about how forage quality and quantity might change because of stressors such as drought, wildfire, and invasive species and how they might need to alter habitat-treatment strategies as a result. More baseline data are needed before effective projections of ungulate migration, at a West-wide scale under climate change, can be made. These data needs include (1) more clearly defined corridors and seasonal range habitats; (2) a comprehensive understanding of the ecological drivers of migration across ungulate species and populations; and (3) the identification of environmental thresholds for key variables that influence migration, above which ungulates alter migratory behavior. The CASCs have several opportunities to play a role in addressing these needs. The CASCs could initiate projects to identify past and potential future changes and trends in key variables known to affect ungulate migration, such as plant phenology, forage quality, or winter severity. However, it would be difficult to use this information to determine what those trends mean for ungulate migration due to the lack of knowledge about environmental thresholds for ungulates. Additional projects would be required to compare multiple years of movement data with key variables to define thresholds. Once available, information on environmental thresholds could be integrated with projections of key variables to forecast the likelihood that the migration routes or the distance traveled could change—another area in which the CASCs could contribute. A more immediate role for the CASCs would be to carry out synthesis projects. One such project could summarize the “state of the science” on the drivers of ungulate migration. Although there are dozens of population- and location-specific studies on this topic, collating this information could help highlight trends in migration drivers that span species and geographies: a necessary first step toward determining the extent to which migration drivers could be affected by climate change. A second project could focus on what is known about how climate variability and change affect ungulate life-histories, population dynamics, and migration in the Western United States. The goal of this effort could be to identify knowledge clusters and information gaps that require further investigation. Together, these synthesized products could focus future scientific activities on the most pressing issues of ungulate migration and climate change in the Western United States.

Arizona, California, Colorado, Idaho, Montana, New↗

USGS2012

Bioaccumulation and toxicity of selenium during a life-cycle exposure with desert pupfish (Cyprinodon macularius)

Populations of desert pupfish ( Cyprinodon macularius ; pupfish), a federally-listed endangered species, inhabit irrigation drains in the Imperial Valley agricultural area of southern California. These drains have varying degrees of selenium (Se) contamination of water, sediment, and aquatic biota. Published Se toxicity studies suggest that these levels of Se contamination may pose risk of chronic toxicity to Se-sensitive fish, but until recently there have been no studies of the chronic toxicity of Se to desert pupfish. A life-cycle Se exposure with pupfish was conducted to estimate dietary and tissue thresholds for toxic effects of Se on all life stages. The dietary exposure was based on live oligochaete worms ( Lumbriculus variegatus ) dosed with Se by a laboratory food chain based on selenized yeast. Oligochaetes readily accumulated Se from mixtures of selenized and control yeasts. The protocol for dosing oligochaetes for pupfish feeding studies included long-term (at least 28 days) feeding of a low-ration of yeast mixtures to large batches of oligochaetes. Oligochaetes were dosed at five Se levels in a 50-percent dilution series. Pupfish were simultaneously fed Se-dosed oligochaetes and exposed to a series of Se concentrations in water (consisting of 85 percent selenate and 15 percent selenite) to produce exposures that were consistent with Se concentrations and speciation in pupfish habitats. The nutritional characteristics of oligochaete diets were consistent across the range of oligochaete Se concentrations tested. The life-cycle exposure started with laboratory-cultured juvenile pupfish that were exposed to Se through sexual maturation and reproduction (150 days; F0 exposure). The Se exposure continued with eggs, larvae, and juveniles produced by Se-exposed parents (79 days; F1 exposure). Selenium exposure (water and diets), Se bioaccumulation (whole-body and eggs), and toxicity endpoints (juvenile and adult survival and growth; egg production and hatching success, larval survival and deformities) were documented throughout the life-cycle study. Selenium concentrations in water (as much as 52 micrograms per liter [μg/L]) and diets (as much as 53 micrograms per gram [μg/g], on a dry weight basis) bracketed concentrations reported in pupfish habitats. Juvenile F0 pupfish rapidly accumulated Se and bioaccumulation models indicated that pupfish had reached more than 97 percent of maximum whole-body Se concentrations by the time they reached reproductive maturity. Adult pupfish accumulated whole-body Se concentrations that averaged about 40 percent of those in the oligochaete diets. Selenium concentrations in eggs and F1 juveniles were similar to or slightly greater than Se concentrations in F0 adults. Juvenile F0 pupfish contained selenomethionine fractions (62–71 percent of whole-body Se) greater than the average reported for wild pupfish from the Imperial Valley (53 percent). Selenium exposure had minimal effects on survival or growth of juvenile and adult pupfish. There was evidence of toxic effects on pupfish in the highest Se treatment (Se–5), including reduced growth of F0 and F1 juvenile pupfish (17–21 percent less than controls) on some sampling dates. These growth reductions did not persist to subsequent sampling dates, but reduced growth of F1 pupfish in the Se–5 treatment was associated with reduced survival (12 percent less than controls). Egg production was greatest in the controls and decreased with increasing Se exposure, reaching a minimum (51 percent less than controls) in the Se–4 treatment, but egg production was reduced by only 24 percent in the Se–5 treatment, a lesser reduction than in other Se treatments except Se–1. There was no statistically significant overall effect of Se treatment on mean pupfish egg production, reflecting large variation among replicates and among sampling dates. However, comparisons of daily mean egg production for 23 sampling dates indicated that egg production in each of 5 Se treatments was significantly less than controls on multiple (3–7) sampling dates, but no mean for any Se treatment was significantly greater than controls on any date. Significant reductions in daily egg production occurred mainly during the middle of the study and egg production increased in several Se treatments during the final 2 weeks of the study. These results suggest that pupfish egg production, although a highly variable endpoint, was adversely affected by elevated Se exposure. Neither egg hatching success nor survival of F1 larvae indicated clear evidence of Se toxicity. Egg hatching success did not differ significantly among treatments, with means ranging from 84–91 percent. The frequency of morphological deformities (primarily spinal deformities) was greater in larvae 10 days post-fertilization (dpf) from a preliminary reproduction study than in older larvae (14 dpf) from the main reproduction study. The frequency of larval deformities was generally greater in Se treatments than controls, but mean frequencies did not differ significantly among treatments. Survival of F1 larvae to 21 dpf was not reduced significantly by parental Se exposure, but the Se–5 treatment had the lowest larval survival (84 percent), and lowest combined egg hatching and larval survival (76 percent). Results of the Se treatments indicate that pupfish were insensitive to Se toxicity through most of their life cycle. Consistent toxic effects on survival and growth of juvenile and adult pupfish (defined as at least 10 percent reduction compared to controls) occurred only in treatment Se–5, which had a mean dietary Se concentration of 52 μg/g and a mean pupfish whole-body Se concentration of 27 μg/g. These apparent toxicity thresholds for growth and survival rank among the least sensitive chronic Se toxicity values reported for nonreproductive endpoints in freshwater fish. Comparisons of these thresholds to surveys of Se concentrations in the Imperial Valley suggest that risks of Se toxicity are low in pupfish habitats. The dietary threshold was about twice as high as the greatest mean Se concentrations reported in midge larvae from seven sites in the Imperial Valley. Whole-body thresholds were greater than mean whole-body Se concentrations reported for field-collected pupfish from three sites and for the sailfin molly (Poecilia latipinna), a potential bioaccumulation surrogate for pupfish, from seven sites. Reduced egg production, although highly variable, was the most sensitive response of pupfish to Se exposure. Toxic effects on egg production (reductions of 24–51 percent relative to controls) occurred in the four highest Se treatments, corresponding to reproductive toxicity thresholds of 7.3 μg/g for Se in diet, 3.4 μg/g in pupfish (whole body), and 4.4 μg/g in pupfish eggs. These thresholds are substantially lower than published Se toxicity values for reproductive effects in other freshwater fish (for example, 17–24 μg/g in eggs). Reduced egg production has not been reported as a sensitive endpoint in Se toxicity studies, although abnormal ovarian development has been reported in Se-exposed fish, and reduced egg production has been reported as a sensitive response of other Cyprinodon pupfish to other environmental stressors. Selenium concentrations in tissues of pupfish, mollies, and diet items from Imperial Valley sites frequently exceeded concentrations associated with reduced pupfish egg production in the laboratory study. Reduced egg production may limit the ability of pupfish populations to persist and recover in Se-contaminated habitats in the Imperial Valley and elsewhere in their limited range. However, these apparent risks of Se toxicity are not supported by recent surveys of desert pupfish populations in the Imperial Valley. These surveys indicated that desert pupfish made up a small, but variable, component of fish communities in Imperial Valley habitats, including sites with increased levels of Se exposure, and that pupfish distribution and population density indicated no clear relationships with Se concentrations in diets or fish tissues. Additional studies could determine the role of egg production in the maintenance and recovery of desert pupfish populations in Se-contaminated habitats.

Scientific Investigations Report↗

USGS2007

Use of chemical analysis and assays of semipermeable membrane devices extracts to assess the response of bioavailable organic pollutants in streams to urbanization in six metropolitan areas of the United States

Studies to assess the effects of urbanization on stream ecosystems are being conducted as part of the U.S. Geological Survey’s National Water-Quality Assessment (NAWQA) Program. The overall objectives of these studies are to (1) determine how hydrologic, geomorphic, water quality, habitat, and biological characteristics respond to land-use changes associated with urbanization in specific environmental settings, and (2) compare these responses across environmental settings. As part of an integrated assessment, semipermeable membrane devices (SPMDs) were deployed in streams along a gradient of urban land-use intensity in and around Atlanta, Georgia; Raleigh-Durham, North Carolina; and Denver-Fort Collins, Colorado, in 2003; and Dallas-Fort Worth, Texas; Milwaukee-Green Bay, Wisconsin; and Portland, Oregon, in 2004. Sites were selected to avoid point-source discharge and to minimize natural variability within each of the six metropolitan areas. In addition to standard chemical analysis for hydrophobic organic contaminants, three assays were used to address mixtures and potential toxicity: (1) Fluoroscan provides an estimate of the total concentration of polycyclic aromatic hydrocarbons (PAHs); (2) the P450RGS assay indicates the presence and levels of aryl hydrocarbon receptor agonists; and (3) Microtox® measures toxicological effects on photo-luminescent bacteria. Of the 140 compounds targeted or identified by gas chromatography/mass spectrometry analysis in this study, 67 were not detected. In terms of numbers and types of compounds, the following were detected: 2 wood preservatives, 6 insecticides (parent compounds), 5 herbicides, 22 polycyclic aromatic hydrocarbons, 2 dibenzofurans, 4 polychlorinated biphenyls, 7 compounds associated with fragrances or personal care products, 4 steroids associated with wastewater, 5 polydibromated diphenyl ethers (flame retardants), 3 plasticizers, 3 antimicrobials/disinfectants, and 3 detergent metabolites. Of the 73 compounds detected and three assays utilized, 29 were detected in 25 percent or more of the streams and were strongly related to increases in urban intensity (defined as having a Spearman’s rho > 0.5 with percent urban land cover) in at least one of the six metropolitan areas investigated. These 29 endpoints included 16 PAHs, a wood preservative (pentachloroanisole), 2 insecticides (chlorpyrifos and chlordane), 3 herbicides (benfluralin, trifluralin, and dacthal), a synthetic musk (hexahydrohexamethylcyclopentabenzopyran, HHCB), 2 furans (methyldibenzofuran and benzo[b]naphtho[2,3-d]furan), and a flame retardant (BDE 47). In addition, the number of compounds detected and results of the Fluoroscan and P450RGS assays were strongly related to urban intensity. Average water concentrations estimated from SPMDs were compared to screening benchmarks for the protection of human health and aquatic life; of the 14 compounds with available benchmarks, 3 compounds (anthracene, dieldrin, and diazinon) exceeded those levels in one or more streams. Both dieldrin and anthracene exceeded their respective benchmarks in seven streams, and diazinon in only one stream. There were more exceedances in Milwaukee-Green Bay and Raleigh-Durham than in the other metropolitan areas, and there were no exceedances in Dallas-Fort Worth. The six metropolitan areas studied differed in the number and types of endpoints related to urban intensity, probably from a combination of factors governing source strength, transport, and fate of hydrophobic compounds. The number of endpoints strongly related to urban intensity ranged from 3 in Dallas-Fort Worth and Portland to 21 in Raleigh-Durham. High frequencies of detection and strong correlations with urban land cover for pyrogenic PAHs (such as unsubstituted 4-ringed PAHs) in all six metropolitan areas indicate that these compounds are an important component of urbanization, regardless of location. Pentachloroanisole, dibenzofurans, and petrogenic PAHs (alkylated PAHs and heterocyclic dibenzothiophenes) were frequently detected and strongly related to urban intensity in Atlanta, Raleigh-Durham, Milwaukee-Green Bay, and Denver-Fort Collins. Two insecticides were related to urban intensity: chlorpyrifos in Atlanta, Raleigh-Durham, and Dallas-Fort Worth; and chlordane in Raleigh-Durham. Three herbicides were strongly related to urban intensity: trifluralin in Atlanta and Raleigh-Durham; benfluralin in Atlanta, and dacthal in Denver-Fort Collins. The detection frequencies for most wastewater indicator compounds were too low to establish relations with urban intensity. Of the wastewater compounds analyzed, HHCB in Raleigh-Durham and Denver-Fort Collins, and BDE 47 in Denver-Fort Collins and Dallas-Forth Worth, had the strongest relations with urban intensity. In addition to pyrogenic PAHs, levels of aryl hydrocarbon receptor agonists (as measured by the P450RGS assay) were strongly related to increasing urban intensity in all six metropolitan areas. PAHs were the only group of aryl hydrocarbon agonists consistently detected and related with urban intensity in all six metropolitan areas. It is unknown which compounds in the SPMDs caused the increased response in the P450RGS assay because the SPMDs likely contained many aryl hydrocarbon receptor agonists not quantified by chemical analysis. It is clear that bioavailable, aryl hydrocarbon receptor agonists increase in streams with increasing urban intensity in the basin. Potential toxicity mediated by this metabolic pathway should be considered in integrated assessments of the response of aquatic biota to urbanization.

Scientific Investigations Report↗

USGS2022

Use case development for earth monitoring, analysis, and prediction (EarthMAP)—A road map for future integrated predictive science at the U.S. Geological Survey

Executive Summary The U.S. Geological Survey (USGS) 21st-century science strategy 2020–30 promotes a bureau-wide strategy to develop and deliver an integrated, predictive science capability that works at the scales and timelines needed to inform societally relevant resource management and protection and public safety and environmental health decisions (U.S. Geological Survey, 2021). This is the overarching goal of the USGS Earth Monitoring, Analysis, and Prediction (EarthMAP) vision, which consists of three components: (1) integrated data and information, (2) integrated predictive science, and (3) actionable information—all designed and delivered to respond to user needs. To launch this vision and help shape the design and implementation of integrated predictive science, the USGS Regional Offices each developed a set of use cases (hereafter Use Cases)—short descriptions of potential science applications that could clearly address high priority decision-making needs of our stakeholders and that align with an integrated science focus. Use Cases are not actionable science planning documents, nor stand-alone scholarly works, but should be considered as innovative, next-generation science ideas that can be considered as potential components of science plans still under development. The goal of Use Case development was to (1) identify and characterize existing USGS scientific capacities and expertise that can support science goals and products, (2) identify opportunities to leverage current capacities for next-generation science, and (3) foster engagement across the entire Bureau to further refine the USGS strategy for EarthMAP and integrated predictive science. The Use Case development effort documented in this report was coordinated by the Use Case Development Team (UCDT), consisting of representatives from each region. The UCDT undertook five tasks: (1) develop a unified approach to engage bureau scientists consistently across all regions in aspirational thinking about what can be accomplished; (2) work with the regions and their Science Centers to generate an initial set of Use Cases, authored directly by scientists; (3) characterize, summarize, and document the initial set of Use Case submissions from authors to illuminate bureau-level demand for integrated science; (4) compare existing and needed capacities from the Use Case descriptions with preliminary results of the EarthMAP Capacity Assessment (Keisman and others, 2021); and (5) describe lessons learned from the Use Case development process and provide recommendations to inform future efforts to generate integrated science activities. This report outlines the approach the UCDT developed to solicit Use Cases from the regions and summarizes the high-level qualitative findings from this first-round effort. The UCDT received 36 Use Cases from the regions and identified potential points of convergence and commonalities considered useful in making connections among the participating scientists. The Southwest (SW) Region and the Rocky Mountain (RM) Region asked scientists to give special consideration to Use Cases with applicability to the Colorado River Basin, and seven of the Use Cases specifically named that geographic area as a focus. Coastal hazards and coastal resilience were identified in Use Cases from the Alaska (AK), Northeast (NE), and Southeast (SE) Regions. Aspects of wildfire and post-wildfire response were part of Uses Cases from AK, RM, and SW Regions. The greatest convergence of Use Case themes was related to conservation of public lands and waters, which is a powerful linkage lending strength to future collaborative efforts. The most common type of stakeholder decisions that would be informed by the Use Case science applications were related to adaptation, mitigation, and response (for example, how to increase the resilience of coastal communities to climate-related stressors and how to prevent or respond to harmful algal blooms). Other common types of decisions included water and land management decisions (including operational water management decisions such as reservoir operations and land use planning in the sagebrush biome), decisions about how to manage and conserve habitats and species, and risk management decisions (such as managing the post-wildfire flood risks). These decision types are not exclusive because many Use Cases cross categories. Use Case authors identified existing and needed science and technology capabilities required for Use Case implementation, which were then aligned to capabilities assessed in the EarthMAP Capacity Assessment (Keisman and others, 2021). Strong alignment was found for data and information integration approaches, modeling and prediction approaches, and capabilities related to delivery of actionable information. A majority of Use Cases indicated insufficient current capacity for needed data collection methods, data integration, and modeling and prediction approaches, whereas only 25 percent indicated insufficient capacity for actionable information delivery. Overall, many Use Case capacity demand gaps could potentially be met by existing bureau-wide capacity. In addition, nearly half of the Use Cases could potentially be implemented within 3 years if funding, capabilities, and personnel impediments were removed and science priorities were realigned. Several challenges emerged during the Use Case development process. The first challenge was developing an approach that was flexible enough to accommodate regional differences in planning and implementation, while also ensuring enough guidance to promote meaningful summary analyses. The UCDT encountered a strong demand for continuous communication and education to improve overall understanding of the integrated predictive science strategy. Another challenge was managing expectations about EarthMAP activities as a design effort that was not aligned to an immediate funding opportunity. Connecting the Use Cases to stakeholder needs without the opportunity for direct stakeholder engagement was also challenging. The last notable challenge was in obtaining consistent interpretation and characterization of the qualitative data housed in the narrative descriptions of Use Cases, written in different styles. Overall, the 36 Use Cases can serve as components of a road map for advancing integrated monitoring and predictive science throughout the USGS by revealing opportunities to (1) encourage cross-region initiatives that address shared interests in common themes by integrating similar Use Cases and through direct involvement of stakeholders in identifying needs and designing effective responses, (2) leverage the Use Cases to target investments that are aligned with the Bureau and Department of the Interior (DOI) priorities, (3) connect Use Cases and the results of the companion EarthMAP Capacity Assessment (Keisman and others, 2021) to identify potential priorities for capacity building investments, and (4) raise awareness of common integrated and interdisciplinary science interests within and across the regions through Use Case and Capacity Assessment summary outreach activities.

Open-File Report↗

USGS2003

Sediment quantity and quality in three impoundments in Massachusetts

As part of a study with an overriding goal of providing information that would assist State and Federal agencies in developing screening protocols for managing sediments impounded behind dams that are potential candidates for removal, the U.S Geological Survey determined sediment quantity and quality at three locations: one on the French River and two on Yokum Brook, a tributary to the west branch of the Westfield River. Data collected with a global positioning system, a geographic information system, and sediment-thickness data aided in the creation of sediment maps and the calculation of sediment volumes at Perryville Pond on the French River in Webster, Massachusetts, and at the Silk Mill and Ballou Dams on Yokum Brook in Becket, Massachusetts. From these data the following sediment volumes were determined: Perryville Pond, 71,000 cubic yards, Silk Mill, 1,600 cubic yards, and Ballou, 800 cubic yards. Sediment characteristics were assessed in terms of grain size and concentrations of potentially hazardous organic compounds and metals. Assessment of the approaches and methods used at study sites indicated that ground-penetrating radar produced data that were extremely difficult and time-consuming to interpret for the three study sites. Because of these difficulties, a steel probe was ultimately used to determine sediment depth and extent for inclusion in the sediment maps. Use of these methods showed that, where sampling sites were accessible, a machine-driven coring device would be preferable to the physically exhausting, manual sediment-coring methods used in this investigation. Enzyme-linked immunosorbent assays were an effective tool for screening large numbers of samples for a range of organic contaminant compounds. An example calculation of the number of samples needed to characterize mean concentrations of contaminants indicated that the number of samples collected for most analytes was adequate; however, additional analyses for lead, copper, silver, arsenic, total petroleum hydrocarbons, and chlordane are needed to meet the criteria determined from the calculations. Particle-size analysis did not reveal a clear spatial distribution pattern at Perryville Pond. On average, less than 65 percent of each sample was greater in size than very fine sand. The sample with the highest percentage of clay-sized particles (24.3 percent) was collected just upstream from the dam and generally had the highest concentrations of contaminants determined here. In contrast, more than 90 percent of the sediment samples in the Becket impoundments had grain sizes larger than very fine sand; as determined by direct observation, rocks, cobbles, and boulders constituted a substantial amount of the material impounded at Becket. In general, the highest percentages of the finest particles, clays, occurred in association with the highest concentrations of contaminants. Enzyme-linked immunosorbent assays of the Perryville samples showed the widespread presence of petroleum hydrocarbons (16 out of 26 samples), polycyclic aromatic hydrocarbons (23 out of 26 samples), and chlordane (18 out of 26 samples); polychlorinated biphenyls were detected in five samples from four locations. Neither petroleum hydrocarbons nor polychlorinated biphenyls were detected at Becket, and chlordane was detected in only one sample. All 14 Becket samples contained polycyclic aromatic hydrocarbons. Replicate quality-control analyses revealed consistent results between paired samples. Samples from throughout Perryville Pond contained a number of metals at potentially toxic concentrations. These metals included arsenic, cadmium, copper, lead, nickel, and zinc. At Becket, no metals were found in elevated concentrations. In general, most of the concentrations of organic compounds and metals detected in Perryville Pond exceeded standards for benthic organisms, but only rarely exceeded standards for human contact. The most highly contaminated samples were

Water-Resources Investigations Report↗

USGS2003

The Tuscarora Au-Ag district: Eocene volcanic-hosted epithermal deposits in the Carlin gold region, Nevada

The Tuscarora mining district contains the oldest and the only productive Eocene epithermal deposits in Nevada. The district is a particularly clear example of association of low-sulfidation deposits with igneous activity and structure, and it is unusual in that it consists of two adjoining but physically and chemically distinct types of low-sulfidation deposits. Moreover, Tuscarora deposits are of interest because they formed contemporaneously with nearby, giant Carlin-type gold deposits. The Tuscarora deposits formed within the 39.9 to 39.3 Ma Tuscarora volcanic field, along and just outside the southeastern margin of the caldera-like Mount Blitzen volcanic center. Both deposit types formed at 39.3 Ma, contemporaneous with the only major intrusive activity in the volcanic field. No deposits are known to have formed during any of the intense volcanic phases of the field. Intrusions were the apparent heat source, and structures related to the Mount Blitzen center were conduits for hydrothermal circulation. The ore-forming fluids interacted dominantly with Eocene igneous rocks. The two deposit types occur in a northern silver-rich zone that is characterized by relatively high Ag/Au ratios (110-150), narrow alteration zones, and quartz and carbonate veins developed mostly in intrusive dacite, and in a southern gold-rich zone that is typified by relatively low Ag/Au ratios (4-14), more widespread alteration, and quartz-fissure and stockwork veins commonly developed in tuffaceous sedimentary rocks. The deposit types have similar fluid inclusion and Pb and S isotope characteristics but different geochemical signatures. Quartz veins from both zones have similar thermal and paragenetic histories and contain fluid inclusions that indicate that fluids cooled from between 260?? and 230??C to less than 200??C. Fluid boiling may have contributed to precious-metal deposition. Veins in both zones have relatively high As and Sb and low Bi, Te, and W. The silver zone has high Ca, Pb, Mn, Zn, Cd, Tl, and Se. The gold zone has high Hg and Mo. A few samples from an area of overlap between the two zones share chemical characteristics of both deposit types. The deposit types could represent a single zoned or evolving system in which hydrothermal fluids rose along structures within the silver zone, preferentially deposited Ag and base metals, and then spread into the gold zone. Alternatively, the deposit types could represent two distinct but temporally indistinguishable hydrothermal cells that only narrowly overlapped spatially. As noted in previous studies, the hydrothermal fluids that generated the Tuscarora and other epithermal deposits could have evolved from Carlin-type fluids by boiling and mixing with meteoric water. If so, the Tuscarora deposit may represent epithermal conditions above Carlin-type deposits, and Carlin-type deposits may lie beneath the district.

Economic Geology↗

USGS2002

Factors related to well yield in the fractured-bedrock aquifer of New Hampshire

The New Hampshire Bedrock Aquifer Assessment was designed to provide information that can be used by communities, industry, professional consultants, and other interests to evaluate the ground-water development potential of the fractured-bedrock aquifer in the State. The assessment was done at statewide, regional, and well field scales to identify relations that potentially could increase the success in locating high-yield water supplies in the fractured-bedrock aquifer. statewide, data were collected for well construction and yield information, bedrock lithology, surficial geology, lineaments, topography, and various derivatives of these basic data sets. Regionally, geologic, fracture, and lineament data were collected for the Pinardville and Windham quadrangles in New Hampshire. The regional scale of the study examined the degree to which predictive well-yield relations, developed as part of the statewide reconnaissance investigation, could be improved by use of quadrangle-scale geologic mapping. Beginning in 1984, water-well contractors in the State were required to report detailed information on newly constructed wells to the New Hampshire Department of Environmental Services (NHDES). The reports contain basic data on well construction, including six characteristics used in this study?well yield, well depth, well use, method of construction, date drilled, and depth to bedrock (or length of casing). The NHDES has determined accurate georeferenced locations for more than 20,000 wells reported since 1984. The availability of this large data set provided an opportunity for a statistical analysis of bedrock-well yields. Well yields in the database ranged from zero to greater than 500 gallons per minute (gal/min). Multivariate regression was used as the primary statistical method of analysis because it is the most efficient tool for predicting a single variable with many potentially independent variables. The dependent variable that was explored in this study was the natural logarithm (ln) of the reported well yield. One complication with using well yield as a dependent variable is that yield also is a function of demand. An innovative statistical technique that involves the use of instrumental variables was implemented to compensate for the effect of demand on well yield. Results of the multivariate-regression model show that a variety of factors are either positively or negatively related to well yields. Using instrumental variables, well depth is positively related to total well yield. Other factors that were found to be positively related to well yield include (1) distance to the nearest waterbody; (2) size of the drainage area upgradient of a well; (3) well location in swales or valley bottoms in the Massabesic Gneiss Complex and Breakfast Hill Granite; (4) well proximity to lineaments, identified using high-altitude (1:80,000-scale) aerial photography, which are correlated with the primary fracture direction (regional analysis); (5) use of a cable tool rig for well drilling; and (6) wells drilled for commercial or public supply. Factors negatively related to well yields include sites underlain by foliated plutons, sites on steep slopes sites at high elevations, and sites on hilltops. Additionally, seven detailed geologic map units, identified during the detailed geologic mapping of the Pinardville and Windham quadrangles, were found to be positively or negatively related to well yields. Twenty-four geologic map units, depicted on the Bedrock Geologic Map of New Hampshire, also were found to be positively or negatively related to well yields. Maps or geographic information system (GIS) data sets identifying areas of various yield probabilities clearly display model results. Probability criteria developed in this investigation can be used to select areas where other techniques, such as geophysical techniques, can be applied to more closely identify potential drilling sites for high-yielding

Professional Paper↗

USGS2003

Ecosystem history of southern and central Biscayne Bay: Summary report on sediment core analyses

During the last century, the environs of Biscayne Bay have been greatly affected by anthropogenic alteration through urbanization of the Miami/Dade County area. The sources, timing, delivery, and quality of freshwater flow into the Bay have been changed by construction of a complex canal system that controls movement of water throughout south Florida. Changes in shoreline and sub-aquatic vegetation and marine organisms have been observed and changes in water delivery are believed to be the cause. Current restoration goals are attempting to restore natural flow of fresh water into Biscayne and Florida Bays and to restore the natural fauna and flora, but first we need to determine pre-alteration baseline conditions in order to establish targets and performance measures for restoration. This research is part of an ongoing study designed to address the needs of the Biscayne Bay Coastal Wetlands Project (BBCW) of the Comprehensive Everglades Restoration Plan (CERP). By establishing the natural patterns of temporal change in salinity, water quality, vegetation, and benthic fauna in Biscayne Bay and the nearby wetlands over the last 100- 500 years the USGS, in collaboration with our partners, will provide the data necessary to set realistic targets to achieve the BBCW Project goals. Six cores from three sites in Biscayne Bay were collected in April 2002 for multidisciplinary multi-proxy analyses. This report details the results of these analyses and compares the 2002 cores to cores collected in 1997. The following are our significant findings to date: The salinity of central Biscayne Bay has become increasingly marine and increasingly stable over the last 100 years. At No Name Bank, prior to approximately 1915, the inter-decadal and decadal salinity fluctuations appear to have been greater than after 1915 when salinities stabilized at that site. Continental shelf/open marine influence on the sites has increased during the 20th century. There is no indication of inter-decadal salinity extremes or periods of hypersalinity. Freshwater and mesohaline salinities have had a minor influence on No Name bank throughout the time of deposition. At Featherbed Bank, the influence is reduced to mesohaline salinities. Card Bank has experienced relatively large swings in salinity over multi-decadal and centennial timescales, compared to central Biscayne Bay, but marine influence at the site has increased over the last century. Indications of regional scale patterns have been found, especially in the shell chemistry data and the pollen assemblages. These regional patterns indicate that the changes are not site specific and may not be limited to Biscayne Bay. Sub-aquatic vegetation has undergone bay-wide patterns of change over the last 200-500 years, which includes expansion prior to 1900 and declines during the last century in central Biscayne Bay. Thalassia appears to have increased at all three core sites sometime between 1550 and 1750 AD. A decline in Thalassia appears to have occurred after 1950 at No Name Bank and slightly earlier in the 20th century at Featherbed Bank. Card Bank does not appear to have experienced any declines in vegetation on an inter-decadal scale during the 20th century. Molluscan faunal abundance and diversity have undergone significant changes in central Biscayne Bay. Indicators of increased organic-rich sediments at No Name occur between 1869 to 1888 and between the 1930’s to 1975. These changes may correlate to human activities (settlement, population growth). These findings represent a first step towards the project’s goal to reconstruct the history of Biscayne Bay and they provide us with a working model to be tested at other sites. It is clear from our findings that Biscayne Bay has been a dynamic environment over the last 500 years, with natural changes occurring in salinity and benthic habitats. However, several significant changes have occurred in the 20th century: 1) increased stabilization of marine salinities; 2) declines in seagrass in central Biscayne Bay; 3) dramatic changes in molluscan abundance and diversity in central Biscayne Bay. The question remains - how do we better differentiate natural cycles of change from anthropogenic change within these observed trends? The preliminary implications from our research are that changes in salinity and benthic habitats have occurred naturally in Biscayne Bay on inter-decadal to centennial scales, perhaps due to climatic changes, changes in sea level, bank migrations, or a combination of factors. However, further work needs to be done to determine which components of change in the 20th century are human-induced and which are natural. By examining the historical records preserved in the sediments of Biscayne Bay, we can provide restoration trust agencies with the information necessary to set realistic targets and performance measures for Biscayne Bay.

Florida↗

USGS2009

Natural offshore oil seepage and related tarball accumulation on the California coastline — Santa Barbara Channel and the southern Santa Maria Basin; source identification and inventory

Oil spillage from natural sources is very common in the waters of southern California. Active oil extraction and shipping is occurring concurrently within the region and it is of great interest to resource managers to be able to distinguish between natural seepage and anthropogenic oil spillage. The major goal of this study was to establish the geologic setting, sources, and ultimate dispersal of natural oil seeps in the offshore southern Santa Maria Basin and Santa Barbara Basins. Our surveys focused on likely areas of hydrocarbon seepage that are known to occur between Point Arguello and Ventura, California. Our approach was to 1) document the locations and geochemically fingerprint natural seep oils or tar; 2) geochemically fingerprint coastal tar residues and potential tar sources in this region, both onshore and offshore; 3) establish chemical correlations between offshore active seeps and coastal residues thus linking seep sources to oil residues; 4) measure the rate of natural seepage of individual seeps and attempt to assess regional natural oil and gas seepage rates; and 5) interpret the petroleum system history for the natural seeps. To document the location of sub-sea oil seeps, we first looked into previous studies within and near our survey area. We measured the concentration of methane gas in the water column in areas of reported seepage and found numerous gas plumes and measured high concentrations of methane in the water column. The result of this work showed that the seeps were widely distributed between Point Conception east to the vicinity of Coal Oil Point, and that they by in large occur within the 3-mile limit of California State waters. Subsequent cruises used sidescan and high resolution seismic to map the seafloor, from just south of Point Arguello, east to near Gaviota, California. The results of the methane survey guided the exploration of the area west of Point Conception east to Gaviota using a combination of seismic instruments. The seafloor was mapped by sidescan sonar, and numerous lines of high -resolution seismic surveys were conducted over areas of interest. Biomarker and stable carbon isotope ratios were used to infer the age, lithology, organic matter input, and depositional environment of the source rocks for 388 samples of produced crude oil, seep oil, and tarballs mainly from coastal California. These samples were used to construct a chemometric fingerprint (multivariate statistics) decision tree to classify 288 additional samples, including tarballs of unknown origin collected from Monterey and San Mateo County beaches after a storm in early 2007. A subset of 9 of 23 active offshore platform oils and one inactive platform oil representing a few oil reservoirs from the western Santa Barbara Channel were used in this analysis, and thus this model is not comprehensive and the findings are not conclusive. The platform oils included in this study are from west to east: Irene, Hildago, Harvest, Hermosa, Heritage, Harmony, Hondo, Holly, Platform A, and Hilda (now removed). The results identify three “tribes” of 13 C-rich oil samples inferred to originate from thermally mature equivalents of the clayey-siliceous, carbonaceous marl, and lower calcareous-siliceous members of the Monterey Formation. Tribe 1 contains four oil families having geochemical traits of clay-rich marine shale source rock deposited under suboxic conditions with substantial higher-plant input. Tribe 2 contains four oil families with intermediate traits, except for abundant 28,30-bisnorhopane, indicating suboxic to anoxic marine marl source rock with hemipelagic input. Tribe 3 contains five oil families with traits of distal marine carbonate source rock deposited under anoxic conditions with pelagic but little or no higher-plant input. Tribes 1 and 2 occur mainly south of Point Conception in paleogeographic settings where deep burial of the Monterey Formation source rock favored generation from all three members or their equivalents. In this area, oil from the clayey-siliceous and carbonaceous marl members (Tribes 1 and 2) may overwhelm that from the lower calcareous-siliceous member (Tribe 3) because the latter is thinner and less oil-prone than the overlying members. Tribe 3 occurs mainly north of Point Conception, where shallow burial caused preferential generation from the underlying lower calcareous-siliceous member or another unit with similar characteristics. It is very desirable to be able to clearly distinguish the naturally occurring seep oils from the anthropogenically derived platform oils. Within the “training set” of oils and tars (388 samples), the biomarker parameters are sometimes sufficient to allow unique discrimination of individual platform oils. More often however, platform samples and seep samples with sources geographically close to each other are too similar to each other, with respect to the biomarker parameters, to definitively differentiate them on that basis alone. In some cases other parameters can be helpful. These other parameters are related to the degree of biogeochemical degradation or weathering that the oils or tars have experienced. These components include the typical oil distribution of n-alkane hydrocarbons and isoprenoids pristane and phytane. All of the platform oils in our sample set contain these components. On the other hand, the seep oils or tars have been exposed to significant biodegradation while in the near subsurface. The majority, but not all of seep oils or tars have been biodegraded up to or beyond the loss of n-alkanes and isoprenoids. Seep oils found in the vicinity of Coal Oil Point or Arroyo Burro are apparently the least weathered and are particularly likely to retain significant n-alkanes and isoprenoids. Therefore the combination of chemometric fingerprinting and the presence or absence of n-alkanes and isoprenoids help to differentiate anthropogenic production oils versus natural seeps oils and tars. The differentiation is not always definitive because of the close chemical similarity of some samples and the variability in the biodegradation progression. This is the case near Coal Oil Point, and near Platform A (Dos Cuadros Field) where seep oils and Platform Holly and Platform A oils are genetically very similar and cannot be definitively distinguished after a period of a few days of weathering. In contrast, oils from the Point Conception platforms can be distinguished on the basis of chemometric fingerprinting alone. In the middle of this spectrum are oils from Platforms Harmony, Heritage, and Hondo, where it is expected that oil weathering would take on the order of two weeks to a month to produce tarballs similar to those seen near Point Conception. In this case there is a much greater degree of weathering needed to proceed from produced oil to the biodegraded tar characteristic of tarball stranded on the beach. Tar deposition on beaches was monitored as part of cooperative with the County of Santa Barbara Energy Division and the U.S. Geological Survey during 2001-2003. We found tar deposition varies on a seasonal basis. In general, tarballs accumulate at a faster rate or remain longer on all beaches during the summer and fall months. The reasons for this are unclear based on our limited observations, however we speculate that factors such as prevailing winds and currents combined with more quiescent wave conditions favors the accumulation and preservation of tarballs on the beach during the summer and fall months. In contrast, winter storms, with much greater wave action remove beach sand and other materials, and stormy seas tend to break up oil that might weather into tarballs. Natural seepage is affected by the spring/neap tidal cycle; however, the link to tar deposition is unclear. Longer periods of monitoring are needed to address the variability in the data and provide a more robust statistical analysis.

California↗

USGS2011

Secondary chaotic terrain formation in the higher outflow channels of southern circum-Chryse, Mars

Higher outflow channel dissection in the martian region of southern circum-Chryse appears to have extended from the Late Hesperian to the Middle Amazonian Epoch. These outflow channels were excavated within the upper 1. km of the cryolithosphere, where no liquid water is expected to have existed during these geologic epochs. In accordance with previous work, our examination of outflow channel floor morphologies suggests the upper crust excavated by the studied outflow channels consisted of a thin (a few tens of meters) layer of dry geologic materials overlying an indurated zone that extends to the bases of the investigated outflow channels (1. km in depth). We find that the floors of these outflow channels contain widespread secondary chaotic terrains (i.e., chaotic terrains produced by the destruction of channel-floor materials). These chaotic terrains occur within the full range of outflow channel dissection and tend to form clusters. Our examination of the geology of these chaotic terrains suggests that their formation did not result in the generation of floods. Nevertheless, despite their much smaller dimensions, these chaotic terrains are comprised of the same basic morphologic elements (e.g., mesas, knobs, and smooth deposits within scarp-bound depressions) as those located in the initiation zones of the outflow channels, which suggests that their formation must have involved the release of ground volatiles. We propose that these chaotic terrains developed not catastrophically but gradually and during multiple episodes of nested surface collapse. In order to explain the formation of secondary chaotic terrains within zones of outflow channel dissection, we propose that the regional Martian cryolithosphere contained widespread lenses of volatiles in liquid form. In this model, channel floor collapse and secondary chaotic terrain formation would have taken place as a consequence of instabilities arising during their exhumation by outflow channel dissection. Within relatively warm upper crustal materials in volcanic settings, or within highly saline crustal materials where cryopegs developed, lenses of volatiles in liquid form within the cryolithosphere could have formed, and/or remained stable.In addition, our numerical simulations suggest that low thermal conductivity, dry fine-grained porous geologic materials just a few tens of meters in thickness (e.g., dunes, sand sheets, some types of regolith materials), could have produced high thermal anomalies resulting in subsurface melting. The existence of a global layer of dry geologic materials overlying the cryolithosphere would suggest that widespread lenses of fluids existed (and may still exist) at shallow depths wherever these materials are fine-grained and porous. The surface ages of the investigated outflow channels and chaotic terrains span a full 500 to 700. Myr. Chaotic terrains similar in dimensions and morphology to secondary chaotic terrains are not observed conspicuously throughout the surface of Mars, suggesting that intra-cryolithospheric fluid lenses may form relatively stable systems. The existence of widespread groundwater lenses at shallow depths of burial has tremendous implications for exobiological studies and future human exploration. We find that the clear geomorphologic anomaly that the chaotic terrains and outflow channels of southern Chryse form within the Martian landscape could have been a consequence of large-scale resurfacing resulting from anomalously extensive subsurface melt in this region of the planet produced by high concentrations of salts within the regional upper crust. Crater count statistics reveal that secondary chaotic terrains and the outflow channels within which they occur have overlapping ages, suggesting that the instabilities leading to their formation rapidly dissipated, perhaps as the thickness of the cryolithosphere was reset following the disruption of the upper crustal thermal structure produced during outflow channel ex

Icarus↗

USGS1984

The evolution of the southern California uplift, 1955 through 1976

The southern California uplift culminated in 1974 as a 150- km-wide crustal swell that extended about 600 km eastward and east-southeastward from Point Arguello to the Colorado River and Salton Sea, respectively; it was characterized by remarkably uniform height changes between 1959 and 1974 of 0.30-0.35 m over at least half of its 60,000-70,000 km 2 area. At its zenith, the uplift included virtually the entire Transverse Ranges geologic province and parts of the Coast Ranges, San Joaquin Valley, Sierra Nevada, Basin and Range, Mojave Desert, Peninsular Ranges, and Salton Trough provinces. The alinement of the western part of the uplift closely paralleled the east-trending Transverse Ranges, whereas the southern flank of the eastern lobe roughly coincided with the west-northwest-trending San Andreas fault. The position and configuration of the uplift associate it with a singularly complex section of the boundary between the North American and Pacific plates that has certainly sustained major modification during the past 5 million years and probably during the past 1 million years. Surface deformation can be categorized as tectonic or nontectonic. Nontectonic vertical displacements associated with the activities of man have overwhelmed natural compaction and areally significant soil expansion in the southern California area. Because tectonic displacements are implicitly defined as those that cannot be otherwise explained, those vertical movements that can be reasonably attributed to artificial processes have been subtracted from our reconstructed configurations of the uplift. Hence this reconstruction has necessarily included the assembly and evaluation of an enormous volume of data on oil-field operations, changes in ground-water levels, and measured subsidence (or rebound) associated with changes in the underground fluid regimen. Measured changes in height at various stages in the evolution of the uplift have been based chiefly on first-order levelings carried out between 1953 and 1976. Exceptions to this generalization consist largely of the results of pre-1953 surveys through the western Transverse Ranges and the eastern Mojave Desert. Errors in measured height differences derive from blunders, systematic survey errors, random survey errors, improperly formulated orthometric corrections, and intrasurvey movement; the last of these has created the most serious problems encountered in our reconstruction of the basic data. A variety of independent tests indicate that survey error associated with the utilized levelings was generally small and fell largely within the predicted random-error range. Moreover, the redundancy and coherence displayed by the entire data set provide convincing evidence of survey accuracy and the virtual absence of height- and slope-dependent error in particular. Our reconstructions of the changing configuration of the uplift derive chiefly from comparisons among sequentially developed observed elevations along the same route. Most of the observed elevations from which the vertical displacements were computed have been reconstructed with respect to bench mark Tidal 8, San Pedro, as invariant in height. Because the San Pedro tide station has been characterized by a history of modest relative uplift, vertical displacements referred to this station are biased slightly toward the appearance of subsidence. Where the observed elevations cannot be conveniently tied to Tidal 8, they have been referred to secondary control points whose history with respect to Tidal 8 can be independently established. Each of the lines of observed elevation changes provides, accordingly, a section athwart or along the axis of the uplift from which the changes in the configuration of the uplift can be roughly generalized. Because relatively few surveys were run in 1955, which we choose as a representative temporal datum, we have commonly incorporated the results of earlier or of somewhat later levelings as the equivalents of 1955 surveys. Although this procedure introduces a certain subjectivity, the probable equivalence between the results of these earlier or later surveys with those that would have been obtained had this leveling been carried out in 1955, usually can be independently tested. Wherever the calculated vertical displacements are based on comparisons between the results of levelings over different routes, the observed elevations have been orthometrically corrected to agree with those that would have been produced had each of these surveys been along the same route. The growth of the southern California uplift consisted of two well-defined spasms of positive movement, the second of which was closely followed by partial collapse. Our reconstruction, although it clearly errs in detail, indicates that the uplift, together with marginal and apparently ephemeral tectonic subsidence, nucleated in the west-central Transverse Ranges near Ozena, sometime between the spring of 1959 and the spring of 1960. The uplift expanded rapidly eastward (and probably westward as well), and by the fall of 1961 much of the Transverse Ranges and the Mojave Desert at least as far east as Twentynine Palms had risen by as much as 0.25 m. Between 1962 and 1972 the area included by the initially developed (1959-61) uplift sustained additional but clearly decelerating uplift accompanied locally by oscillatory displacements. Between 1972/ 73 and 1974 a second crustal spasm extended the uplift eastward to the Colorado River and elevated much of the eastern Mojave Desert by values that equaled or exceeded those developed within the western lobe. Between 1974 and 1976, at least the central part of the uplift sustained partial collapse that nowhere amounted to less than 50 percent of the cumulative uplift since 1959. Whether this collapse affected the entire uplift is conjectural, but we now recognize well-defined evidence of major down-to-the-north tilting that must have occurred within the eastern part of the uplift at some time between 1974 and 1976. Accumulating evidence indicates that nearly all the area included with the southern California uplift underwent similar uplift and partial collapse during the early part of the 20th century. Thus we infer that the recent uplift represents but a single event in an ongoing, more or less cyclic deformational process characterized by a period of about 50 years. Even though less than two full cycles are expressed in the geodetic record, the cumulative rate of uplift near the center of the recent uplift probably has averaged about 5 mm/yr, a value that is roughly consistent with the uplift rates that have been deduced for the late Quaternary emergent marine terraces along the south flank of the Transverse Ranges. Although the evolution of the recent uplift is relatively well defined, its correlation with the regional seismicity is poorly defined. A comparison between the occurrence of southern California earthquakes of magnitude ≥4 during the period 1932 to 1976 with the 1974 configuration of the uplift demonstrates the existence of (1) relatively aseismic areas within the western lobe of the uplift (in the western Transverse Ranges), in the central part of the uplift (in the western Mojave Desert), and along an east-trending zone that extends into the eastern Mojave athwart the south flank of the uplift (north of the Salton Sea) and (2) localized concentrations of seismic activity along the flanks of the uplift. Moreover, 9 of the 10 largest earthquakes recorded within or around the area of the southern California uplift during the period 1932 to 1976 (the 1933 Long Beach, the 1941 Santa Barbara, the 1946 Walker Pass, the 1947 Manix, the 1948 Desert Hot Springs, and the four major 1952 Kern County shocks) occurred before the inception of the uplift in 1959 or 1960. The area embraced by the southern California uplift has been identified with geodetically defined horizontal strain, part of which may have accumulated as a major north-south contractional event that roughly coincided with the first spasm of uplift. Nonetheless, continuing contractional strain associated with regionally developed partial collapse argues that the uplift cannot be fully explained simply as the vertical expression of continuing north-south compression. Consideration of the two well-defined historical episodes of uplift and partial collapse indicate that the southern California uplift may be the product of decoupling and viscous flow beneath the seismogenic zone, presumably driven by continuing motion between the irregularly margined plates south of the great bend of the San Andreas fault. Because the magnitude of the maximum uplift associated with each episode was approximately the same, there may be some threshold value above which collapse (viscous flow) may ensue; the absence of total collapse may be a function of precollapse strain hardening within the postulated subseismogenic viscoelastic layer.

California↗

USGS2017

Geomorphic response of the North Fork Stillaguamish River to the State Route 530 landslide near Oso, Washington

On March 22, 2014, the State Route 530 Landslide near Oso, Washington mobilized 8 million cubic meters of unconsolidated Pleistocene material, creating a valley‑spanning deposit that fully impounded the North Fork Stillaguamish River. The river overtopped the 8-meter high debris impoundment within 25 hours and began steadily incising a new channel through the center of the deposit. Repeat topographic surveys, sediment transport measurements, bedload transport models, and observations of downstream channel change were used to document the establishment of that new channel through the landslide and assess the potential for downstream aggradation or channel change that might increase downstream flood hazards. Efficient erosion of the landslide deposit, associated with the steep knickzone formed by the downstream edge of the deposit, resulted in the re-establishment of a 20–40 meters wide, deeply inset channel through the entire deposit by May 2014, 2 months after the landslide. The mean water-surface elevation of the channel through the landslide decreased 7 meters during that 2-month period, and was about 1 meter above the pre-landslide profile in July 2014. The 2014–15 flood season, which included flows near the 0.5 annual exceedance probability discharge (2-year flood), widened the channel tens of meters, and further lowered the water-surface profile 0.5 meter. The planform position evolved slowly as a result of 5–20-meter high banks predominantly composed of clay-rich, cohesive lacustrine material. Erosion of the landslide deposit delivered a total of 820 thousand metric tons of sediment to the North Fork Stillaguamish River over the 18 months following the landslide. The sediment delivery from the deposit was predominantly fine grained: 77 percent (by mass) of the eroded material was silt or clay (less than 0.063 millimeter [mm]), 19 percent sand (0.063–2 mm), and 4 percent pebbles and cobbles (greater than 2 mm). Over the 18 months following the landslide, the bedload at a site 5 kilometers downstream of the landslide was estimated to be 310±65 thousand metric tons, and the suspended load at that same site was estimated to be 990±110 thousand metric tons. These loads represent the combined input from the landslide and ambient upstream sources; over the study interval, landslide sediment made up about 20–40 percent of the bedload, and 65–85 percent of the suspended-sediment load at this site. At a site 70 kilometers downstream of the landslide, near the mouth of the main‑stem Stillaguamish River, suspended sediment loads were estimated to be about 1,440 thousand metric tons, of which about 600 thousand metric tons, or 30 percent, likely was derived from the landslide. The mass of landslide sediment in suspension at the mouth of the river, and the timing of arrival of that sediment, indicates that about 70 percent of the landslide sediment eroded during the study period was quickly transported through the entire basin, exiting into Puget Sound within weeks of initial entrainment. Empirical bedload transport equations, in conjunction with surficial grain-size data and output from a one‑dimensional hydraulic model, were used to estimate spatial trends in bedload transport capacity, highlighting areas where reach-scale conditions would be most likely to promote deposition of coarse landslide sediment. Transport capacities decreased sharply over a reach about 5 kilometers downstream of the landslide and remained relatively low over the next 10 kilometers downstream. However, the magnitude of calculated transport capacities are large relative to the coarse sediment input from the landslide, suggesting that substantial deposition of landslide sediment was not likely to occur. These assessments were corroborated by observations of channel change, which indicated that the downstream channel response to the landslide was modest and short-lived. The most pronounced downstream effects included a wedge of aggradation just downstream of the landslide, about 1 meter high and extending a kilometer downstream, and a 0.3-meter pulse of aggradation observed 5 kilometers downstream of the landslide. In both locations, peak aggradation and channel response occurred within about a month of the landslide, and both sites had largely recovered to pre-landslide conditions by July 2014. No substantial channel change clearly linked to the landslide was observed after July 2014 except for a modest fining of surficial gravel size distributions and continued recovery and incision of the reach just downstream of the landslide. The muted downstream response of the North Fork Stillaguamish River to the State Route 530 Landslide primarily can be attributed to the cohesive, silt- and clay-rich material that bounded most of the new channel. Although the river efficiently incised a new channel through the deposit, subsequent rates of lateral erosion were slowed by the tall, cohesive banks, limiting the total volume of sediment delivery. Once entrained, however, most landslide material was rapidly transported downstream in suspension with little geomorphic effect. Landslide material coarse enough to travel as bedload was predominantly sand and fine gravel, and sediment transport models and observations of downstream change indicated that the rate of coarse sediment delivery from the landslide did not exceed the rivers ability to transport that material. The generally muted downstream response to sediment delivery from the State Route 530 Landslide, as well as the mechanics of that delivery and response, were generally consistent with observations made following the intentional removal of constructed dams. The rate and efficiency of erosion from the landslide decreased over the period of analysis, as the new channel approached a quasi-equilibrium form. In the absence of additional hillslope activity, rates of erosion from the landslide are likely to be small compared to those over the first 18 months after the landslide. The modest channel response to the highest rates of sediment delivery, and rapid recovery thereafter, indicate that the river should be able to convey the continued supply of landslide-derived sediment effectively with little effect on the downstream morphology and flood risks.

Washington↗

USGS2005

Response curves for phosphorus plume lengths from reactive-solute-transport simulations of onland disposal of wastewater in noncarbonate sand and gravel aquifers

Surface-water resources in Massachusetts often are affected by eutrophication, excessive plant growth, which has resulted in impaired use for a majority of the freshwater ponds and lakes and a substantial number of river-miles in the State. Because supply of phosphorus usually is limiting to plant growth in freshwater systems, control of phosphorus input to surface waters is critical to solving the impairment problem. Wastewater is a substantial source of phosphorus for surface water, and removal of phosphorus before disposal may be necessary. Wastewater disposed onland by infiltration loses phosphorus from the dissolved phase during transport through the subsurface and may be an effective disposal method; quantification of the phosphorus loss can be simulated to determine disposal feasibility. In 2003, the U.S. Geological Survey, in cooperation with the Massachusetts Department of Environmental Protection, initiated a project to simulate distance of phosphorus transport in the subsurface for plausible conditions of onland wastewater disposal and subsurface properties. A coupled one-dimensional unsaturated-zone and three-dimensional saturated-zone reactive-solute-transport model (PHAST) was used to simulate lengths of phosphorus plumes. Knowledge of phosphorus plume length could facilitate estimates of setback distances for wastewater-infiltration sites from surface water that would be sufficient to protect the surface water from eutrophication caused by phosphorus transport through the subsurface and ultimate discharge to surface water. The reactive-solute-transport model PHAST was used to simulate ground-water flow, solute transport, equilibrium chemistry for dissolved and sorbed species, and kinetic regulation of organic carbon decomposition and phosphate mineral formation. The phosphorus plume length was defined for the simulations as the maximum extent of the contour for the 0.015 milligram-per-liter concentration of dissolved phosphorus downgradient from the infiltration bed after disposal cessation. Duration of disposal before cessation was assumed to be 50 years into an infiltration bed of 20,000 square feet at the rate of 3 gallons per square foot per day. Time for the maximum extent of the phosphorus plume to develop is on the order of 100 years after disposal cessation. Simulations indicated that phosphorus transport beyond the extent of the 0.015 milligram-per-liter concentration contour was never more than 0.18 kilogram per year, an amount that would likely not alter the ecology of most surface water. Simulations of phosphorus plume lengths were summarized in a series of response curves. Simulated plume lengths ranged from 200 feet for low phosphorus-concentration effluents (0.25 milligram per liter) and thick (50 feet) unsaturated zones to 3,400 feet for high phosphorus-concentration effluents (14 milligrams per liter) discharged directly into the aquifer (unsaturated-zone thickness of 0 feet). Plume length was nearly independent of unsaturated-zone thickness at phosphorus concentrations in the wastewater that were less than 2 milligrams per liter because little or no phosphorus mineral formed at low phosphorus concentrations. For effluents of high phosphorus concentration, plume length varied from 3,400 feet for unsaturated-zone thickness of 0 to 2,550 feet for unsaturated-zone thickness of 50 feet. Model treatments of flow and equilibrium-controlled chemistry likely were more accurate than rates of kinetically controlled reactions, notably precipitation of iron-phosphate minerals; the kinetics of such reactions are less well known and thus less well defined in the model. Sensitivity analysis indicated that many chemical and physical aquifer properties, such as hydraulic gradient and model width, did not affect the simulated plume length appreciably, but duration of discharge, size of infiltration bed, amount of dispersion, and number of sorption sites on the aquifer sediments did affect plume length appreciably. Because simulation of plume length in carbonate-mineral sediments indicated that the plume would be substantially longer than in noncarbonate-mineral sediments, the application of the response curves in locations with carbonate-mineral sediments would be inappropriate. The effect of carbonate minerals in sediments is to increase pH, which causes decreased sorption of phosphorus on aquifer sediments. Phosphorus removal from solution by precipitation onto aquifer sediments is more efficient at high concentrations of disposed phosphorus than at low concentrations. At very low phosphorus concentrations, the solubility product of phosphorus minerals is not exceeded and no phosphorus mineral forms. An important consequence is that removal of dissolved phosphorus from the plume by processes in the subsurface is decreased the more that removal efforts are applied in treatment before wastewater is disposed. Model simulations indicate that removal of phosphorus from wastewater disposed through septic systems would have the advantage of efficient phosphorus removal in the subsurface because phosphorus concentrations are high in septic-system effluent. Short plume lengths result from wastewater disposal through septic systems because of the efficient phosphorus removal and because of the low volume of wastewater involved. The simulation results for small-volume systems are not quantitative, however, because wastewater-infiltration rates are much lower than those of the higher-volume system that was used to calibrate the model and to create the plume-length response curves. The response curves for phosphorus plume lengths, as defined by the maximum extent of the 0.015 milligram-per-liter concentration contour, is clearly defined in the model simulations, although the relation between simulated plume length and protective setback distance is subject to interpretation. Phosphorus does move beyond the point at which the simulated 0.015 milligram-per-liter concentration contour has stopped, so that a determination of protective setback distance must include a consideration of whether that continued flux, or some other flux amount, is appropriate. Also, simulations indicate that phosphorus plumes do not reach their full extent until 50 to 200 years after disposal cessation, depending on concentration of phosphorus disposed. No phosphorus plume has been monitored for that long after cessation, so there is no way to verify the long-term simulation results.

Massachusetts↗

USGS1993

Flow recommendations for maintaining riparian vegetation along the Upper Missouri River, Montana

Montana Power Company, Inc. (MPC) submitted a final license application to the Federal Energy Regulatory Commission (FERC) on November 30, 1992. In this application, MPC proposed a plan for the protection of fish, wildlife, habitat, and water-quality resources. One concern was maintenance of woody riparian vegetation along the Missouri River, especially along the Wild and Scenic reach of the river, where the riparian forest occurs in relatively small discontinuous stands. The objectives of this project were 1) to recommend flows that would protect and enhance riparian forests along the Missouri River, and 2) to develop elements of an environmental monitoring program that could be used to assess the effectiveness of the recommended flows. Plains cottonwood ( Populus deltoides subsp. monilifera ) is the key structural component of riparian forests along the Missouri River. Therefore, we focused our analysis on factors affecting populations of this species. Previous work had demonstrated that the age structure of cottonwood populations is strongly influenced by aspects of flow that promote successfully establishment. In this study our approach was to determine the precise age of plains cottonwood trees growing along the Upper Missouri River and to relate years of establishment to the flow record. Our work was carried out between Coal Banks Landing and the Fred G. Robinson Bridge within the Wild and Scenic portion of the Missouri River. This segment of the river occupies a narrow valley and exhibits little channel migration. Maps and notes from the journals of Lewis and Clark (1804-1806) suggest that the present distribution and abundance of cottonwoods within the study reach is generally similar to presettlement conditions. Flows in the study reach are influenced by a number of dams and diversions, most importantly, Canyon Ferry and Tiber Dams. Although flow regulation has decreased peak flows and increased low flows, the gross seasonal pattern of flow has not been greatly altered. Most cottonwood establishment in our study reach occurred in years with a peak mean daily flow greater than 1,400 m 3 /s (49,434 cfs), or in the two years following such a flow. These years include 35 out of the 111 years of record, and account for establishment of 47 of 60 trees examined, a highly significant relationship. Infrequent establishment of cottonwood trees is not the result of scarcity of seed or seedlings. In the study reach seedlings become established most years on bare, relatively low surfaces deposited by the river. However, the high elevation of establishment of all trees dating to before 1978 indicates that only individuals established on high flood deposits are able to survive subsequent floods and ice jams. In order to maintain the present abundance of plains cottonwood in the study area we recommend flood flows in excess of 1,400 m 3 /s (49,434 cfs) measures as mean daily discharge at Fort Benton (U.S. Geological Survey gage 06090800) with a recurrence interval of approximately 9 years. Because cottonwood seeds remain viable for only a few weeks, and because seedling require a moist, bare surface, we further recommend maintenance of the historic timing of flooding with peak flood flows occurring between mid-May and late-June. Flow is not the only factor influencing cottonwood regeneration along this reach of the Missouri River. Land management, especially cattle grazing, is clearly having an impact, and changes in cottonwood populations could be expected if these practices were altered. However, the dependence of cottonwood establishment on high flow is clear in this reach in spite of the effects of other factors. Given the value of the resource, we strongly suggest establishment of a monitoring program to determine the effectiveness of the recommended flows and to provide the data necessary for refining them. We recommend a monitoring program that would include: 1) ten permanent, widely space channel cross sections for annual measurement of channel geometry and cottonwood establishment, growth, and survival; 2) five livestock enclosures to monitor the influence of grazing in the study area; and 3) low-elevation aerial photography of the reach every five years and after every flood to detect changes in channel geometry and forested area. Because cottonwood establishment is episodic, a long-term commitment to the monitoring effort is essential. In addition, cross sections and exclosures should be easy enough to access that measurements during flood years are possible.

Montana↗

USGS1997

Historical land-use changes and potential effects on stream disturbance in the Ozark Plateaus, Missouri

Land-use changes have been blamed for creating disturbance in the morphology of streams in the Ozark Plateaus, Missouri (hereafter referred to as the "Ozarks"). Historical evidence and stratigraphic observations document that streams have been aggraded by substantial quantities of gravel beginning sometime at or near the time of European settlement of the Ozarks. Before European settlement, streams were depositing a mixed sediment load of gravel bedload and silty overbank sediment. Observations of early explorers conspicuously lack descriptions of extensive gravel bars; observations of geologists working during the middle to late 1800's before significant landuse disturbance, however, include descriptions of large quantities of gravel in stream banks and beds. The first change in land cover as settlement progressed from the early 1800's to approximately 1880 was replacement of valley-bottom forest with cultivated fields and pastures. At the same time, suppression of wildfires in the uplands caused an increase of woodland with woody understory at the expense of grassland and oak savannah. Valley-bottom clearing probably initiated some direct disturbance of stream channels, but fire suppression would have decreased runoff and sediment yield from uplands. Beginning sometime from 1870 to 1880 and continuing until 1920, commercial timber companies began large operations in the Ozarks to harvest shortleaf pine for sawlogs and oak for railroad ties. Selective cutting of large timber, use of livestock for skidding logs from the forest, and avoidance of the steeper slopes minimized the effect of this phase of logging on runoff and sediment supply of uplands and valley-side slopes. Continued decreases in the erosional resistance of valley bottoms through clearing and road building and the incidence of extreme regional floods from 1895 to 1915 probably caused initiation of moderate stream disturbance. This hypothesis is supported by historical and oral-historical observations that stream instability began before the peak of upland destabilization from 1920 to 1960. The post-Timber-boom period (1920-60) included the institution of annual burning of uplands and cut-over valley-side slopes, increased grazing on open range, and increased use of marginal land for cultivated crops. Models for landuse controls on annual runoff, storm runoff, and soil erosion indicate that this period should have been the most effective in creating stream disturbance. Written historical sources and oral-historical accounts indicate that erosion was notable mainly on lands in row-crop cultivation. Oral-history respondents consistently recall that smaller streams had more discharge for longer periods from 1920 to 1960 than from 1960 to 1993; many additionally observed that floods are "flashier" under present-day (1993) conditions. Changes in the timing of hydrographs probably relate to changes in upland and riparian zone vegetation that decreased storage and flow resistance. Probably the most destabilizing effect on Ozarks stream channels during this period was caused by livestock on the open range that concentrated in valley bottoms and destroyed riparian vegetation in the channels and on banks. Destruction of riparian vegetation in small valleys may have encouraged headward migration of channels, resulting in extension of the drainage network and accelerated release of gravel from storage in the small valleys. This hypothesis is supported by lack of other sources for the large quantity of gravel in Ozarks streams and oral-historical observations that gravel came out of the runs, rather than from slopes. From 1960 to 1993, cultivated fields and total improved land in farms decreased, but cattle populations continued to increase. This increase in grazing density has the potential to maintain runoff and sediment delivery to streams at rates higher than natural background rates. Whereas some riparian zones have been allowed to grow up into bottom-land forest, this stabilizing effect occurs on only a small part of valley-bottom land. Recovery processes aided by riparian vegetation are limited by channel instability and frequent, large floods.

Water Supply Paper↗

USGS2013

Monitoring to assess progress toward meeting the total maximum daily load for phosphorus in the Assabet River, Massachusetts: phosphorus loads, 2008 through 2010

Wastewater discharges to the Assabet River contribute substantial amounts of phosphorus, which support accumulations of nuisance aquatic plants that are most evident in the river’s impounded reaches during the growing season. To restore the Assabet River’s water quality and aesthetics, the U.S. Environmental Protection Agency required the major wastewater-treatment plants in the drainage basin to reduce the amount of phosphorus discharged to the river by 2012. From October 2008 to December 2010, the U.S. Geological Survey, in cooperation with the Massachusetts Department of Environmental Protection and in support of the requirements of the Total Maximum Daily Load for Phosphorus, collected weekly flow-proportional, composite samples for analysis of concentrations of total phosphorus and orthophosphorus upstream and downstream from each of the Assabet River’s two largest impoundments: Hudson and Ben Smith. The purpose of this monitoring effort was to evaluate conditions in the river before enhanced treatment-plant technologies had effected reductions in phosphorus loads, thereby defining baseline conditions for comparison with conditions following the mandated load reductions. The locations of sampling sites with respect to the impoundments enabled examination of the impoundments’ effects on phosphorus sequestration and on the transformation of phosphorus between particulate and dissolved forms. The study evaluated the differences between loads upstream and downstream from the impoundments throughout the sampling period and compared differences during two seasonal periods of relevance to aquatic plants: April 1 through October 31, the growing season, and November 1 through March 31, the nongrowing season, when existing permit limits allowed average monthly wastewater-treatment-plant-effluent concentrations of 0.75 milligram per liter (growing season) or 1.0 milligram per liter (nongrowing season) for total phosphorus. At the four sampling sites during the growing season, median weekly total phosphorus loads ranged from 110 to 190 kilograms (kg) and median weekly orthophosphorus loads ranged from 17 to 41 kg. During the nongrowing season, median weekly total phosphorus loads ranged from 240 to 280 kg and median weekly orthophosphorus loads ranged from 56 to 66 kg. During periods of low and moderate streamflow, estimated loads of total phosphorus upstream from the Hudson impoundment generally exceeded those downstream during the same sampling periods throughout the study; orthophosphorus loads downstream from the impoundment were typically larger than those upstream. When storm runoff substantially increased the streamflow, loads of total phosphorus and orthophosphorus both tended to be larger downstream than upstream. At the Ben Smith impoundment, both total phosphorus and orthophosphorus loads were generally larger downstream than upstream during low and moderate streamflow, but the differences were not as pronounced as they were at the Hudson impoundment. High flows were also associated with substantially larger total phosphorus and orthophosphorus loads downstream than those entering the impoundment from upstream. In comparing periods of growing- and nongrowing-season loads, the same patterns of loads entering and leaving were observed at both impoundments. That is, at the Hudson impoundment, total phosphorus loads entering the impoundment were greater than those leaving it, and orthophosphorus loads leaving the impoundment were greater than those entering it. At the Ben Smith impoundment, both total phosphorus and orthophosphorus loads leaving the impoundment were greater than those entering it. However, the loads were greater during the nongrowing seasons than during the growing seasons, and the net differences between upstream and downstream loads were about the same. The results indicate that some of the particulate fraction of the total phosphorus loads is sequestered in the Hudson impoundment, where particulate phosphorus probably undergoes some physical and biogeochemical transformations to the dissolved form orthophosphorus. The orthophosphorus may be taken up by aquatic plants or transported out of the impoundments. The results for the Ben Smith impoundment are less clear and suggest net export of total phosphorus and orthophosphorus. Differences between results from the two impoundments may be attributable in part to differences in their sizes, morphology, unmonitored tributaries, riparian land use, and processes within the impoundments that have not been quantified for this study.

Massachusetts↗