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USGS2005

Evaluating water management strategies with the Systems Impact Assessment Model: SIAM version 4

Water from many of California's coastal rivers has been used for a wide variety of development ventures, including major agricultural diversions, hydropower generation, and contaminant assimilation from industry, agriculture and logging. Anthropogenic impacts often degrade water quality and decrease the quantity and quality of aquatic habitat. Reallocating streamflow away from uses that degrade water quality to uses that foster higher water quality is a critical step in restoring riverine habitat and the anadromous fish that rely on that habitat for a portion of their life cycle. Reallocation always brings with it the need to examine the economic efficiency of the proposed changes. If the dollar benefits of improving water quality are greater than the costs, the criterion of improving economic efficiency is satisfied, a fact that can be highly persuasive to decision makers contemplating reallocation. Previous related studies have examined nonmarket benefits of the Trinity River in northern California (Douglas and Taylor, 1998; Douglas and Taylor, 1999abc) but nothing of this kind had been done on the Klamath River, another system with numerous uses for and competition over water in times of drought. An economic survey is nearing completion for the mid- to lower Klamath River, including the Scott, Shasta, and Salmon Rivers, but excluding the Trinity River. This survey provides valuable insights about the magnitude of the benefits and nature of the costs of reallocating water from market uses to instream flows that improve water quality and assist in the recovery of Klamath River fish stocks. Preliminary survey results (Douglas and Johnson, 2002; Douglas and Sleeper, In Prep.) indicate that about 234,000 California, Oregon, and Nevada households made recreation trips to the Klamath River Basin 1997-1998 and that these users spent about $372 million on trip related expenditures. Clearly the prosperity of the region is closely linked to the demand for mid- and lower Klamath River Basin recreation trips. Further, respondents indicated that they would make roughly 36% more recreational trips per annum to the Klamath if the water quality and the fishery were restored to an unspoiled condition. Using two distinct types of survey data, these additional trips would yield benefits with a present value of approximately $9.6 billion (at a discount rate of 7.5%). Calculating costs to restore the fishery and raise water quality involved five major hypothetical restoration activities: (1) purchasing Klamath project farmland and environmentally sensitive forest lands, (2) allocating more water down the Trinity River to enhance the quantity and quality of Klamath flows below the confluence, (3) removing four mainstem dams along the Klamath River and losing their associated hydropower production, (4) eliminating all harvest of Klamath-Trinity fish stocks for a 12-year period including the acquisition of fishing rights from both tribal and commercial marine fishermen, and (5) operating all Klamath-Trinity fish hatcheries to restore self-reproducing stocks. In total, restoration costs were estimated to be about $1.7 to $2.3 billion. If the assumptions used in this study are valid, it is clear that the benefits ($9.6B) outweigh the costs of restoring water quality and the fishery. The apparent disparity between restoration benefits and costs for the Klamath River may suggest to some that water resources on the Klamath be reallocated to environmentally friendly nonmarket uses. The economic analysis rests in part on the information made available to the survey designers by the biological, hydrologic, and water quality data incorporated in The System Impact Assessment Model (SIAM). It is our hope that SIAM can be used to improve the river's water quality and fishery, and strengthen the important regional economy.

Open-File Report↗

USGS2016

Development and assessment of indices to determine stream fish vulnerability to climate change and habitat alteration

Understanding the future impacts of climate and land use change are critical for long-term biodiversity conservation. We developed and compared two indices to assess the vulnerability of stream fish in Missouri, USA based on species environmental tolerances, rarity, range size, dispersal ability and on the average connectivity of the streams occupied by each species. These two indices differed in how environmental tolerance was classified (i.e., vulnerability to habitat alteration, changes in stream temperature, and changes to flow regimes). Environmental tolerance was classified based on measured species responses to habitat alteration, and extremes in stream temperatures and flow conditions for one index, while environmental tolerance for the second index was based on species’ traits. The indices were compared to determine if vulnerability scores differed by index or state listing status. We also evaluated the spatial distribution of species classified as vulnerable to habitat alteration, changes in stream temperature, and change in flow regimes. Vulnerability scores were calculated for all 133 species with the trait association index, while only 101 species were evaluated using the species response index, because 32 species lacked data to analyze for a response. Scores from the trait association index were greater than the species response index. This is likely due to the species response index's inability to evaluate many rare species, which generally had high vulnerability scores for the trait association index. The indices were consistent in classifying vulnerability to habitat alteration, but varied in their classification of vulnerability due to increases in stream temperature and alterations to flow regimes, likely because extremes in current climate may not fully capture future conditions and their influence on stream fish communities. Both indices showed higher mean vulnerability scores for listed species than unlisted species, which provided a coarse measure of validation. Our indices classified species identified as being in need of conservation by the state of Missouri as highly vulnerable. The distribution of vulnerable species in Missouri showed consistent patterns between indices, with the more forest-dominated, groundwater fed streams in the Ozark subregion generally having higher numbers and proportions of vulnerable species per site than subregions that were agriculturally dominated with more overland flow. These results suggest that both indices will identify similar habitats as conservation action targets despite discrepancies in the classification of vulnerable species. Our vulnerability assessment provides a framework that can be refined and used in other regions.

Ecological Indicators↗

USGS2017

Multiscale guidance and tools for implementing a landscape approach to resource management in the Bureau of Land Management

The Bureau of Land Management (BLM) is implementing a landscape approach to resource management (hereafter, landscape approach) to more effectively work with partners and understand the effects of management decisions. A landscape approach is a set of concepts and principles used to guide resource management when multiple stakeholders are involved and goals include diverse and sustainable social, environmental, and economic outcomes. Core principles of a landscape approach include seeking meaningful participation of diverse stakeholders, considering diverse resource values in multifunctional landscapes, acknowledging the tradeoffs needed to meet diverse objectives in the context of sustainable resource management, and addressing the complexity of social and ecological processes by embracing interdisciplinarity and considering multiple and broad spatial and temporal perspectives. In chapter 1, we outline the overall goal of this report: to provide a conceptual foundation and framework for implementing a landscape approach to resource management in the BLM, focusing on the role of multiscale natural resource monitoring and assessment information. In chapter 2, we describe a landscape approach to resource management. BLM actions taken to implement a landscape approach include a major effort to compile broad-scale data on natural resource status and condition across much of the west. These broadscale data now provide a regional context for interpreting monitoring data collected at individual sites and informing decisions made for local projects. We also illustrate the utility of using multiscale data to understand potential effects of different resource management decisions, define relevant terms in landscape ecology, and identify spatial scales at which planning and management decisions may be evaluated. In chapter 3, we describe how the BLM Rapid Ecoregional Assessment program and Assessment, Inventory and Monitoring program may be integrated to provide the multiscale monitoring data needed to inform a landscape approach. We propose six core, broad-scale indicators of natural resource status and condition: the amount, spatial distribution, patch size and connectivity of ecosystems and wildlife habitats, and the pattern of existing development across the landscape. Additional supplemental broad-scale indicators may include fire return intervals, distributions of invasive species, and vulnerability of ecosystems to a changing climate. Landscape intactness is an additional derived indicator that is calculated from one or more of the core and supplemental broad-scale indicators. We then outline a process for assessing broad-scale indicators that is consistent with the overall BLM Assessment, Inventory, and Monitoring process, facilitating development of a multiscale natural resource monitoring program. Finally, we describe how broad-scale indicators of natural resource status and condition may guide field monitoring implemented through the BLM Assessment, Inventory and Monitoring program and help address complex management questions. In chapter 4, we consider the specific question of assessing the ecological integrity of rangelands across the western United States. We first define ecological integrity and its relation to land health. We then suggest that a combination of six local-scale indicators collected through field sampling at individual sites and five complementary broad-scale indicators together provide information on the composition, structure, and function of rangelands. The terrestrial monitoring indicators collected at the level of individual field sites are the amount of bare ground, vegetation composition (including invasive plants and plants of management concern), vegetation height, and the proportion of the soil surface in large intercanopy gaps. The broad-scale indicators are vegetation amount, distribution, patch size, connectivity, and productivity, along with the pattern of terrestrial development. Our suggested approach to quantifying ecological integrity focuses specifically on informing management of public lands for multiple resource uses, and illustrates how existing data collected through BLM monitoring and assessment programs may be used together to provide multiscale information on land condition across broad extents. In chapter 5, we develop a method for quantifying landscape intactness and apply this method to the western United States. Our multiscale index of landscape intactness is designed to be defensible, decomposable, and easy to understand. The foundation of the multiscale index of landscape intactness is the surface disturbance footprint of anthropogenic development, including energy and urban development, roads and railroads, cultivated croplands, surface mines and quarries, and energy transmission lines and pipelines. The index represents a gradient of anthropogenic influence as represented by development summarized at two spatial scales of analysis: 2.5 and 20 kilometers. We provide several example applications of the index, illustrating how these data may inform natural resource decisions at the spatial extent of BLM field and district offices, states, ecoregions, and the western United States. We find that 19.2 percent of lands managed by the BLM across the 17 western states of the conterminous United States had the highest landscape intactness. The largest intact areas occur on public lands at high elevations or in the Great Basin. We believe the frameworks, processes, and analyses provided in this report will improve the ability of the BLM to identify and evaluate potential direct and indirect effects of management actions (such as habitat restoration and renewable energy development), and assist the BLM in further implementing a landscape approach to resource management.

Open-File Report↗

USGS2014

Temperature effects induced by climate change on the growth and consumption by salmonines in Lakes Michigan and Huron

We used bioenergetics models to investigate temperature effects induced by climate change on the growth and consumption by Chinook salmon Oncorhynchus tshawytscha , lake trout Salvelinus namaycush , and steelhead O. mykiss in Lakes Michigan and Huron. We updated biological inputs to account for recent changes in the food webs and used temperature inputs in response to regional climate observed in the baseline period (1964–1993) and projected in the future period (2043–2070). Bioenergetics simulations were run across multiple age-classes and across all four seasons in different scenarios of prey availability. Due to the increased capacity of prey consumption, future growth and consumption by these salmonines were projected to increase substantially when prey availability was not limited. When prey consumption remained constant, future growth of these salmonines was projected to decrease in most cases but increase in some cases where the increase in metabolic cost can be compensated by the decrease in waste (egestion and excretion) loss. Consumption by these salmonines was projected to increase the most during spring and fall when prey energy densities are relatively high. Such seasonality benefits their future growth through increasing annual gross energy intake. Our results indicated that lake trout and steelhead would be better adapted to the warming climate than Chinook salmon. To maintain baseline growth into the future, an increase of 10 % in baseline prey consumption was required for Chinook salmon but considerably smaller increases, or no increases, in prey consumption were needed by lake trout and steelhead.

Lake Huron, Lake Michigan↗

USGS2004

The National Assessment of Shoreline Change: A GIS Compilation of Vector Shorelines and Associated Shoreline Change Data for the U.S. Gulf of Mexico

Introduction The Coastal and Marine Geology Program of the U.S. Geological Survey has generated a comprehensive database of digital vector shorelines and shoreline change rates for the U.S. Gulf of Mexico. These data, which are presented herein, were compiled as part of the U.S. Geological Survey's National Assessment of Shoreline Change Project. Beach erosion is a chronic problem along most open-ocean shores of the United States. As coastal populations continue to grow and community infrastructures are threatened by erosion, there is increased demand for accurate information including rates and trends of shoreline migration. There is also a critical need for shoreline change data that is consistent from one coastal region to another. One purpose of this work is to develop standard repeatable methods for mapping and analyzing shoreline movement so that periodic updates regarding coastal erosion and land loss can be made nationally that are systematic and internally consistent. This data compilation for open-ocean, sandy shorelines of the Gulf of Mexico is the first in a series that will eventually include the Atlantic Coast, Pacific Coast, and parts of Hawaii and Alaska. Short- and long-term shoreline change evaluations are based on merging three historical shorelines with a modern shoreline derived from lidar (light detection and ranging) topographic surveys. Historical shorelines generally represent the following time periods: 1800s, 1920s-1930s, and 1970s. The most recent shoreline is derived from data collected over the period of 1998-2002. Long-term rates of change are calculated by linear regression using all four shorelines. Short-term rates of change are simple end-point rate calculations using the two most recent shorelines. Please refer to our full report on shoreline change in the Gulf of Mexico, National Assessment of Shoreline Change: Part 1, Historical Shoreline Changes and Associated Coastal Land Loss Along the U.S. Gulf of Mexico (USGS Open File Report 2004-1043) for additional information regarding methods and results. Data in this report are organized into data layers by state and are provided as single-point vector datasets with metadata. Vector shorelines may represent a compilation of data from one or more sources and these sources are attributed in the dataset. All data are intended to be GIS-ready inasmuch as the data should not require any additional cleanup, formatting, or renaming of fields in order to use the data in a Geographic Information System (GIS). This project employs the Environmental Systems Research Institute's (ESRI) ArcView as its GIS mapping tool and contains several data layers (or themes) that are used to create a geographic view of the margin off the U.S. Gulf of Mexico. These vector data form a basemap comprised of polygon and line themes that include a U.S. coastline (1:80,000), U.S. cities, and state boundaries.

Open-File Report↗

USGS1974

Influence of recharge basins on the hydrology of Nassau and Suffolk Counties, Long Island, New York

An investigation of recharge basins on Long Island was made by the U.S. Geological Survey in cooperation with the New York State Department of Environmental Conservation, Nassau County Department of Public Works, Suffolk County Department of Environmental Control, and Suffolk County Water Authority. The major objectives of the study were to (1) catalog basic physical data on the recharge basins in use on Long Island, (2) measure quality and quantity of precipitation and inflow, (3) measure infiltration rates at selected recharge basins, and (4) evaluate regional effects of recharge basins on the hydrologic system of Long Island. The area of study consists of Nassau and Suffolk Counties -- about 1,370 square miles -- in eastern Long Island, N.Y. Recharge basins, numbering more than 2,100 on Long Island in 1969, are open pits in moderately to highly permeable sand and gravel deposits. These pits are used to dispose of storm runoff from residential, industrial, and commercial areas, and from highways, by infiltration of the water through the bottom and sides of the basins. The hydrology of three recharge basins on Long Island -- Westbury, Syosset, and Deer Park basins -- was studied. The precipitation-inflow relation showed that the average percentages of precipitation flowing into each basin were roughly equivalent to the average percentages of impervious areas in the total drainage areas of the basins. Average percentages of precipitation flowing into the basins as direct runoff were 12 percent at the Westbury basin, 10 percent at the Syosset basin, and 7 percent at the Deer Park basin. Numerous open-bottomed storm-water catch basins at Syosset and Deer Park reduced the proportion of inflow to those basins, as compared with the Westbury basin, which has only a few open-bottomed catch basins. Inflow hydrographs for each basin typify the usual urban runoff hydrograph -- steeply rising and falling limbs, sharp peaks, and short time bases. Unit hydrographs for the Westbury and the Syosset basins are not expected to change; however, the unit hydrograph for the Deer Park basin is expected to broaden somewhat as a result of additional future house construction within the drainage area. Infiltration rates averaged 0.9 fph (feet per hour) for 63 storms between July 1967 and May 1970 at the Westbury recharge basin, 0.8 fph for 22 storms from July 1969 to September 1970 at the Syosset recharge basin, and 0.2 fph for 24 storms from March to September 1970 at the Deer Park recharge basin. Low infiltration rates at Deer Park resulted mainly from (1) a high percentage of eroded silt, clay, and organic debris washed in from construction sites in the drainage area, which partly filled the interstices of the natural deposits, and (2) a lack of a well-developed plant-root system on the floor of the younger basin, which would have kept the soil zone more permeable. The apparent rate of movement of storm water through the unsaturated zone below each basin averaged 5.5 fph at Westbury, 3.7 fph at Syosset, and 3.1 fph at Deer Park. The rates of movement for storms during the warm months (April through October) were slightly higher than average, probably because the recharging water was warmer than it was during the rest of the year, and therefore, was slightly less viscous. On the average, a 1-inch rainfall resulted in a peak rise of the water table directly below each basin of 0.5 foot; a 2-inch rainfall resulted in a peak rise of about 2 feet. The mound commonly dissipated within 1 to 4 days at Westbury, 7 days to more than 15 days at Syosset, and 1 to 3 days at Deer Park, depending on the magnitude of the peak buildup. Average annual ground-water recharge was estimated to be 6.4 acre-feet at the Westbury recharge basin, 10.3 acre-feet at the Syosset recharge basin, and 29.6 acre-feet at the Deer Park recharge basin. Chemical composition of precipitation at Westbury, Syosset, and Deer Park drainage areas was similar:

Water Supply Paper↗

USGS2023

Changes in habitat suitability for wintering dabbling ducks during dry conditions in the Central Valley of California

In arid and Mediterranean regions, landscape-scale wetland conservation requires understanding how wildlife responds to dynamic freshwater availability and conservation actions to enhance wetland habitat. Taking advantage of Landsat satellite data and structured and community science bird survey data, we built species distribution models to describe how three duck species, the Northern Pintail ( Anas acuta ), Green-winged Teal ( Anas crecca ), and Northern Shoveler ( Anas clypeata ), respond to freshwater supply and food resources on different flooded land cover types in the Central Valley of California. Specifically, our models compared duck habitat suitability between the wettest and driest conditions in each month from September through April. Using abundance-weighted boosted regression trees, we created three sets of species occurrence models based on different covariates: (1) near real-time (hereafter “real-time”) covariates in which duck observations were matched to the water availability within the 16-day window of a Landsat observation, (2) a combination of real-time covariates and waterfowl food resource covariates describing annual corn and rice biomass and managed wetland moist soil seed yield estimates derived from Landsat data, and (3) long-term average covariates—the most common approach to species distribution modeling—in which long-term average surface water availability was used. We modeled the monthly occurrence of three duck species as a function of surface water availability, land cover type, road density, temperature, and bird data source. We found that dry conditions result in reduced habitat suitability, with the biggest reductions in November through January and in agricultural fields; in contrast, suitability of flooded wetland habitat was relatively robust to surface water availability. When models of habitat suitability based on long-term average climate conditions were compared to models based on real-time conditions, the highest long-term suitability values occurred in areas where suitability was high regardless of whether it was a wet or a dry year. While all models performed well, the inclusion of crop and wetland plant yield covariates resulted in slightly higher model performance. Overall, species distribution models created using data on the environmental conditions present at the time of bird observations can aid conservation efforts under extreme conditions over large spatial scales.

California↗

USGS2007

Suspended sediment and sediment-associated contaminants in San Francisco Bay

Water-quality managers desire information on the temporal and spatial variability of contaminant concentrations and the magnitudes of watershed and bed-sediment loads in San Francisco Bay. To help provide this information, the Regional Monitoring Program for Trace Substances in the San Francisco Estuary (RMP) takes advantage of the association of many contaminants with sediment particles by continuously measuring suspended-sediment concentration (SSC), which is an accurate, less costly, and more easily measured surrogate for several trace metals and organic contaminants. Continuous time series of SSC are collected at several sites in the Bay. Although semidiurnal and diurnal tidal fluctuations are present, most of the variability of SSC occurs at fortnightly, monthly, and semiannual tidal time scales. A seasonal cycle of sediment inflow, wind-wave resuspension, and winnowing of fine sediment also is observed. SSC and, thus, sediment-associated contaminants tend to be greater in shallower water, at the landward ends of the Bay, and in several localized estuarine turbidity maxima. Although understanding of sediment transporthas improved in the first 10 years of the RMP, determining a simple mass budget of sediment or associated contaminants is confounded by uncertainties regarding sediment flux at boundaries, change in bed-sediment storage, and appropriate modeling techniques. Nevertheless, management of sediment-associated contaminants has improved greatly. Better understanding of sediment and sediment-associated contaminants in the Bay is of great interest to evaluate the value of control actions taken and the need for additional controls.

Environmental Research↗

USGS2019

Climate and disturbance influence self-sustaining stand dynamics of aspen (Populus tremuloides) near its range margin

Species that are primarily seral may form stable (self-sustaining) communities under certain disturbance regimes or environmental conditions, yet such populations may also be particularly vulnerable to ecological change. Aspen (Populus spp.) are generally considered seral throughout the northern hemisphere, including P. tremuloides, the most widely distributed tree species in North America. Recent declines in aspen populations have occurred, especially along drought-sensitive margins of its range and where fire exclusion and herbivory have promoted community transition. However, aspen also forms stable stands, and examination of the mechanisms that influence persistence can offer conservation insights, especially where populations are vulnerable to changing climate or altered disturbance dynamics. We sampled tree age and stand characteristics of isolated aspen forests in the arid Great Basin (USA) to determine if: (1) aspen communities are more fire-dependent and seral or fire-independent and stable; (2) ungulate browsing inhibits aspen stability; and (3) temporal patterns of vegetative reproduction (i.e., ramet establishment or “suckering”) are correlated with climate. Aspen size and age class densities strongly fit negative exponential distributions, whether grouped geographically or by functional type, suggesting landscape-scale persistence. Continuous age distributions and high proportions of recruitment-sized to overstory trees suggest stability at stand-scales, with exceptions including stands with higher browsing pressure. Few stands had evidence of fire, and relationships between dead tree size and variability in live tree size suggest a lack of fire-dependency. Several five-year averaged climate variables and one sea surface temperature index were correlated with aspen ramet establishment densities over time, with strongest relationships occurring ~5 years prior to establishment year, often followed by inverse relationships ~1 year after. Indeed, aspen establishment density for a recent 41-year period was reliably reconstructed using antecedent climate conditions derived from a single drought index. Temporally synchronized aspen ramet establishment across the study region may be due to climate-driven storage of nonstructural carbohydrate reserves in clonal root systems later used for regeneration. Complex regeneration dynamics of these self-sustaining aspen stands, especially sensitivity to climate variability, suggest they may serve as harbingers of ecological change in the arid Great Basin and in other aspen populations near their range margin.

Ecological Applications↗

USGS2006

Integrating human impacts and ecological integrity into a risk-based protocol for conservation planning

Conservation planning aims to protect biodiversity by sustainng the natural physical, chemical, and biological processes within representative ecosystems. Often data to measure these components are inadequate or unavailable. The impact of human activities on ecosystem processes complicates integrity assessments and might alter ecosystem organization at multiple spatial scales. Freshwater conservation targets, such as populations and communities, are influenced by both intrinsic aquatic properties and the surrounding landscape, and locally collected data might not accurately reflect potential impacts. We suggest that changes in five major biotic drivers—energy sources, physical habitat, flow regime, water quality, and biotic interactions—might be used as surrogates to inform conservation planners of the ecological integrity of freshwater ecosystems. Threats to freshwater systems might be evaluated based on their impact to these drivers to provide an overview of potential risk to conservation targets. We developed a risk-based protocol, the Ecological Risk Index (ERI), to identify watersheds with least/most risk to conservation targets. Our protocol combines risk-based components, specifically the frequency and severity of human-induced stressors, with biotic drivers and mappable land- and water-use data to provide a summary of relative risk to watersheds. We illustrate application of our protocol with a case study of the upper Tennessee River basin, USA. Differences in risk patterns among the major drainages in the basin reflect dominant land uses, such as mining and agriculture. A principal components analysis showed that localized, moderately severe threats accounted for most of the threat composition differences among our watersheds. We also found that the relative importance of threats is sensitive to the spatial grain of the analysis. Our case study demonstrates that the ERI is useful for evaluating the frequency and severity of ecosystemwide risk, which can inform local and regional conservation planning.

Tennessee↗

USGS2011

The role of the Everglades Mangrove Ecotone Region (EMER) in regulating nutrient cycling and wetland productivity in South Florida

The authors summarize the main findings of the Florida Coastal Everglades Long-Term Ecological Research (FCE-LTER) program in the EMER, within the context of the Comprehensive Everglades Restoration Plan (CERP), to understand how regional processes, mediated by water flow, control population and ecosystem dynamics across the EMER landscape. Tree canopies with maximum height <3 m cover 49% of the EMER, particularly in the SE region. These scrub/dwarf mangroves are the result of a combination of low soil phosphorus (P < 59 μg P g dw −1 ) in the calcareous marl substrate and long hydroperiod. Phosphorus limits the EMER and its freshwater watersheds due to the lack of terrigenous sediment input and the phosphorus-limited nature of the freshwater Everglades. Reduced freshwater delivery over the past 50 years, combined with Everglades compartmentalization and a 10 cm rise in coastal sea level, has led to the landward transgression (∼1.5 km in 54 years) of the mangrove ecotone. Seasonal variation in freshwater input strongly controls the temporal variation of nitrogen and P exports (99%) from the Everglades to Florida Bay. Rapid changes in nutrient availability and vegetation distribution during the last 50 years show that future ecosystem restoration actions and land use decisions can exert a major influence, similar to sea level rise over the short term, on nutrient cycling and wetland productivity in the EMER.

Florida↗

USGS2020

Boreal blazes: Biomass burning and vegetation types archived in the Juneau Icefield

The past decade includes some of the most extensive boreal forest fires in the historical record. Warming temperatures, changing precipitation patterns, the desiccation of thick organic soil layers, and increased ignition from lightning all contribute to a combustive combination. Smoke aerosols travel thousands of kilometers, before blanketing the surfaces on which they fall, such as the Juneau Icefield. However, many aerosols found in smoke plumes are also produced by other processes and therefore can be ambiguous indicators of fire activity. Here, we use the monosaccharide anhydrides levoglucosan, mannosan, and galactosan as specific indicators of biomass burning to unambiguously demonstrate that fire aerosols reach the Juneau Icefield and are integrated into the snowpack. Back trajectories and satellite observations demonstrate that smoke plumes originating in central Alaska and eastern Siberia affect the Juneau Icefield. These regional sources of fire differ from other combustion aerosols deposited on the Juneau Icefield, such as black carbon, that originate from local fossil fuel burning. Ratios of levoglucosan/mannosan (L/M) and levoglucosan/(mannosan + galactosan) (L/(M + G)) demonstrate that while the majority of fire aerosols reaching the Juneau Icefield originate from softwood burning, grasslands and hardwood forests are also sources. The presence of these hardwoods suggests that fire aerosols may reach the Juneau Icefield from locations as far away as East Asia.

Alaska↗

USGS2017

Structural equation model of total phosphorus loads in the Red River of the North Basin, USA and Canada

Attribution of the causes of trends in nutrient loading is often limited to correlation, qualitative reasoning, or references to the work of others. This paper represents efforts to improve causal attribution of water-quality changes. The Red River of the North basin provides a regional test case because of international interest in the reduction of total phosphorus loads and the availability of long-term total phosphorus data and ancillary geospatial data with the potential to explain changes in water quality over time. The objectives of the study are to investigate structural equation modeling methods for application to water-quality problems and to test causal hypotheses related to the drivers of total phosphorus loads over the period 1970 to 2012. Multiple working hypotheses that explain total phosphorus loads and methods for estimating missing ancillary data were developed, and water-quality related challenges to structural equation modeling (including skewed data and scaling issues) were addressed. The model indicates that increased precipitation in season 1 (November–February) or season 2 (March–June) would increase total phosphorus loads in the basin. The effect of agricultural practices on total phosphorus loads was significant, although the effect is about one-third of the effect of season 1 precipitation. The structural equation model representing loads at six sites in the basin shows that climate and agricultural practices explain almost 60% of the annual total phosphorus load in the Red River of the North basin. The modeling process and the unexplained variance highlight the need for better ancillary long-term data for causal assessments.

Red River of the North Basin↗

USGS2016

Conifer density within lake catchments predicts fish mercury concentrations in remote subalpine lakes

Remote high-elevation lakes represent unique environments for evaluating the bioaccumulation of atmospherically deposited mercury through freshwater food webs, as well as for evaluating the relative importance of mercury loading versus landscape influences on mercury bioaccumulation. The increase in mercury deposition to these systems over the past century, coupled with their limited exposure to direct anthropogenic disturbance make them useful indicators for estimating how changes in mercury emissions may propagate to changes in Hg bioaccumulation and ecological risk. We evaluated mercury concentrations in resident fish from 28 high-elevation, sub-alpine lakes in the Pacific Northwest region of the United States. Fish total mercury (THg) concentrations ranged from 4 to 438 ng/g wet weight, with a geometric mean concentration (±standard error) of 43 ± 2 ng/g ww. Fish THg concentrations were negatively correlated with relative condition factor, indicating that faster growing fish that are in better condition have lower THg concentrations. Across the 28 study lakes, mean THg concentrations of resident salmonid fishes varied as much as 18-fold among lakes. We used a hierarchal statistical approach to evaluate the relative importance of physiological, limnological, and catchment drivers of fish Hg concentrations. Our top statistical model explained 87% of the variability in fish THg concentrations among lakes with four key landscape and limnological variables: catchment conifer density (basal area of conifers within a lake's catchment), lake surface area, aqueous dissolved sulfate, and dissolved organic carbon. Conifer density within a lake's catchment was the most important variable explaining fish THg concentrations across lakes, with THg concentrations differing by more than 400 percent across the forest density spectrum. These results illustrate the importance of landscape characteristics in controlling mercury bioaccumulation in fish.

Environmental Pollution↗

USGS2025

Predictors of mercury and pesticide fluxes by emerging adult aquatic insects from prairie pothole wetlands

Aquatic and terrestrial food webs are linked by movements of aquatic insects during their development from larvae to adults. Contaminants can affect these linkages by reducing insect survival and increasing tissue contaminant concentrations through adult metamorphosis, thus changing contaminant flux from water to land. Most anthropogenically influenced freshwater ecosystems are exposed to multiple contaminants. To better understand the combined effects of contaminants on aquatic–terrestrial linkages, we investigated how adult aquatic insect emergence and tissue contaminant concentrations affect insect-mediated contaminant flux of mercury and pesticides from wetlands. In a field survey of 15 wetlands in the Prairie Pothole Region, an important agricultural region of North America, we found that insect-mediated mercury flux was 3.5 times more strongly predicted by emergence biomass than tissue mercury concentration. Thus, factors that were previously found to influence aquatic insect emergence biomass in this system—including insecticide tissue concentrations in adult insects, open water surface area, and agricultural land use—were the most likely to drive insect-mediated mercury flux. Pesticide flux, however, was 3.3 times more strongly predicted by the tissue pesticide concentration than by emergence. Thus, factors that influence pesticide exposure and, to a smaller extent, emergence biomass were the most likely to drive pesticide flux. Our results show how factors driving contaminant fluxes by adult aquatic insects differ by contaminant class, and they suggest one mechanism by which toxic effects of one contaminant (pesticides) could influence the flux of another (mercury). Predicting contaminant fluxes in areas where different mixtures of contaminants are present can aid in identifying risk to insectivores.

Prairie Pothole Region↗

USGS2014

Hydrosalinity studies of the Virgin River, Dixie Hot Springs, and Littlefield Springs, Utah, Arizona, and Nevada

The Virgin River contributes a substantial amount of dissolved solids (salt) to the Colorado River at Lake Mead in the lower Colorado River Basin. Degradation of Colorado River water by the addition of dissolved solids from the Virgin River affects the suitability of the water for municipal, industrial, and agricultural use within the basin. Dixie Hot Springs in Utah are a major localized source of dissolved solids discharging to the Virgin River. The average measured discharge from Dixie Hot Springs during 2009–10 was 11.0 cubic feet per second (ft 3 /s), and the average dissolved-solids concentration was 9,220 milligrams per liter (mg/L). The average dissolved-solids load—a measurement that describes the mass of salt that is transported per unit of time—from Dixie Hot Springs during this period was 96,200 tons per year (ton/yr). Annual dissolved-solids loads were estimated at 13 monitoring sites in the Virgin River Basin from streamflow data and discrete measurements of dissolved-solids concentrations and (or) specific conductance. Eight of the sites had the data needed to estimate annual dissolved-solids loads for water years (WYs) 1999 through 2010. During 1999–2010, the smallest dissolved-solids loads in the Virgin River were upstream of Dixie Hot Springs (59,900 ton/yr, on average) and the largest loads were downstream of Littlefield Springs (298,200 ton/yr, on average). Annual dissolved-solids loads were smallest during 2002–03, which was a period of below normal precipitation. Annual dissolved-solids loads were largest during 2005—a year that included a winter rain storm that resulted in flooding throughout much of the Virgin River Basin. An average seepage loss of 26.7 ft 3 /s was calculated from analysis of monthly average streamflow from July 1998 to September 2010 in the Virgin River for the reach that extends from just upstream of the Utah/Arizona State line to just above the Virgin River Gorge Narrows. Seepage losses from three river reaches in the Virgin River Gorge containing known fault zones accounted for about 48 percent of this total seepage loss. An additional seepage loss of 6.7 ft 3 /s was calculated for the reach of the Virgin River between Bloomington, Utah, and the Utah/Arizona State line. This loss in flow is small compared to total flow in the river and is comparable to the rated error in streamflow measurements in this reach; consequently, it should be used with caution. Littlefield Springs were studied to determine the fraction of its discharge that originates as upstream seepage from the Virgin River and residence time of this water in the subsurface. Geochemical and environmental tracer data from groundwater and surface-water sites in the Virgin River Gorge area suggest that discharge from Littlefield Springs is a mixture of modern (post-1950s) seepage from the Virgin River upstream of the springs and older groundwater from a regional carbonate aquifer. Concentrations of the chlorofluorocarbons (CFCs) CFC-12 and CFC-113, chloride/fluoride and chloride/bromide ratios, and the stable isotope deuterium indicate that water discharging from Littlefield Springs is about 60 percent seepage from the Virgin River and about 40 percent discharge from the regional carbonate aquifer. The river seepage component was determined to have an average subsurface traveltime of about 26 ±1.6 years before discharging at Littlefield Springs. Radiocarbon data for Littlefield Springs suggest groundwater ages from 1,000 to 9,000 years. Because these are mixed waters, the component of discharge from the carbonate aquifer is likely much older than the groundwater ages suggested by the Littlefield Springs samples. If the dissolved-solids load from Dixie Hot Springs to the Virgin River were reduced, the irrigation water subsequently applied to agricultural fields in the St. George and Washington areas, which originates as water from the Virgin River downstream of Dixie Hot Springs, would have a lower dissolved-solids concentration. Dissolved-solids concentrations in excess irrigation water draining from the agricultural fields are about 1,700 mg/L higher than the concentrations in the Virgin River water that is currently (2014) used for irrigation that contains inflow from Dixie Hot Springs; this increase results from evaporative concentration and dissolution of mineral salts in the irrigated agricultural fields. The water samples collected from drains downgradient from the irrigated areas are assumed to include the dissolution of all available minerals precipitated in the soil during the previous irrigation season. Based on this assumption, a change to more dilute irrigation water will not dissolve additional minerals and increase the dissolved-solids load in the drain discharge. Following the hypothetical reduction of salts from Dixie Hot Springs, which would result in more dilute Virgin River irrigation water than is currently used, the dissolution of minerals left in the soil from the previous irrigation season would result in a net increase in dissolved-solids concentrations in the drain discharge, but this increase should only last one irrigation season. After one (or several) seasons of irrigating with more dilute irrigation water, mineral precipitation and subsequent re-dissolution beneath the agricultural fields should be greatly reduced, leading to a reduction in dissolved-solids load to the Virgin River below the agricultural drains. A mass-balance model was used to predict changes in the dissolved-solids load in the Virgin River if the salt discharging from Dixie Hot Springs were reduced or removed. Assuming that 33.4 or 26.7 ft 3 /s of water seeps from the Virgin River to the groundwater system upstream of the Virgin River Gorge Narrows, the immediate hypothetical reduction in dissolved-solids load in the Virgin River at Littlefield, Arizona is estimated to be 67,700 or 71,500 ton/yr, respectively. The decrease in dissolved-solids load in seepage from the Virgin River to the groundwater system is expected to reduce the load discharging from Littlefield Springs in approximately 26 years, the estimated time lag between seepage from the river and discharge of the seepage water, after subsurface transport, from Littlefield Springs. At that time, the entire reduction in dissolved solids seeping from the Virgin River is expected to be realized as a reduction in dissolved solids discharging from Littlefield Springs, resulting in an additional reduction of 24,700 ton/yr (based on 33.4 ft 3 /s of seepage loss) or 21,000 ton/yr (based on 26.7 ft 3 /s of seepage loss) in the river’s dissolved-solids load at Littlefield.

Arizona, Nevada, Utah↗

USGS2020

Contaminant subsidies to riparian food webs in Appalachian streams impacted by mountaintop removal coal mining

Selenium is highly elevated in Appalachian streams and stream organisms that receive alkaline mine drainage from mountaintop removal coal mining compared to unimpacted streams in the region. Adult aquatic insects can be important vectors of waterborne contaminants to riparian food webs, yet pathways of Se transport and exposure of riparian organisms are poorly characterized. We investigated Se concentrations in stream and riparian organisms to determine whether mining extent increased Se uptake in stream biofilms and insects and if these insects were effective Se biovectors to riparian spiders. Biofilm Se concentration increased (p = 0.006) with mining extent, reaching a maximum value of 16.5 μg/g of dw. Insect and spider Se increased with biofilm Se (p = 0.004, p = 0.003), reaching 95 and 26 μg/g of dw, respectively, in mining-impacted streams. Adult insect biomass was not related to mining extent or Se concentrations in biofilm. Even though Se concentrations in aquatic insects were significantly and positively related to mining extent, aquatic insect Se flux was not associated with mining extent because the mass of emerging insects did not change appreciably over the mining gradient. Insect and spider Se concentrations were among the highest reported in the literature, regularly exceeding the bird Se dietary risk threshold of 5 μg/g of dw. Risks of Se exposure and toxicity related to mining are thus not constrained to aquatic systems but extend to terrestrial habitats and food webs.

Environmental Science & Technology↗

USGS2015

The climate space of fire regimes in north-western North America

Aim. Studies of fire activity along environmental gradients have been undertaken, but the results of such studies have yet to be integrated with fire-regime analysis. We characterize fire-regime components along climate gradients and a gradient of human influence. Location. We focus on a climatically diverse region of north-western North America extending from northern British Columbia, Canada, to northern Utah and Colorado, USA. Methods. We used a multivariate framework to collapse 12 climatic variables into two major climate gradients and binned them into 73 discrete climate domains. We examined variation in fire-regime components (frequency, size, severity, seasonality and cause) across climate domains. Fire-regime attributes were compiled from existing databases and Landsat imagery for 1897 large fires. Relationships among the fire-regime components, climate gradients and human influence were examined through bivariate regressions. The unique contribution of human influence was also assessed. Results. A primary climate gradient of temperature and summer precipitation and a secondary gradient of continentality and winter precipitation in the study area were identified. Fire occupied a distinct central region of such climate space, within which fire-regime components varied considerably. We identified significant interrelations between fire-regime components of fire size, frequency, burn severity and cause. The influence of humans was apparent in patterns of burn severity and ignition cause. Main conclusions. Wildfire activity is highest where thermal and moisture gradients converge to promote fuel production, flammability and ignitions. Having linked fire-regime components to large-scale climate gradients, we show that fire regimes – like the climate that controls them – are a part of a continuum, expanding on models of varying constraints on fire activity. The observed relationships between fire-regime components, together with the distinct role of climatic and human influences, generate variation in biotic communities. Thus, future changes to climate may lead to ecological changes through altered fire regimes.

Journal of Biogeography↗