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USGS2022

Functional composition of plant communities mediates biomass effects on ecosystem service recovery across an experimental dryland restoration network

Land degradation can result in a loss of critical ecosystem services that we often seek to restore through re-establishment of desired plant communities. Trait-based approaches have the potential to target specific ecosystem services based on associations between the functional composition of plant communities and ecosystem properties that serve as indicators of those services. The effect of functional composition on ecosystem recovery may depend on the amount of restored plant biomass, itself a supporting service frequently targeted in restoration efforts. Yet, interactions between functional composition and biomass are not formally integrated into trait-based analytical frameworks. We tested the hypothesis that functional composition of plant communities both drives, and interacts with, biomass production to influence indicators of soil functioning and weed suppression across a network of degraded dryland restoration experiments. This networked approach allowed us to identify generalized effects of functional composition on ecosystem recovery across a range of dryland climate conditions. Climate had a substantial effect on ecosystem indicators, with weed cover and soil surface stability increasing in more arid climates, water infiltration increasing with precipitation, and aggregate structure increasing with less freezing. After accounting for climate effects across study sites, we found significant effects of community-weighted mean (CWM) trait values on biomass, particularly a positive effect of leaf carbon-to-nitrogen ratio, and of CWM-biomass interactions on other ecosystem indicators. Cover of exotic species was reduced in restored communities with a combination of low leaf dry matter content and high biomass, soil water infiltration increased with lower specific root length and high biomass, and soil aggregate stability increased with higher root dry matter content and high biomass, among other effects. Functional diversity had no significant effects on any ecosystem indicators. Synthesis : The influence of community functional composition on ecosystem properties increases with community biomass, particularly in disturbed or low productivity systems. This suggests that active management should not only focus on trait values that optimize individual ecosystem indicators but also how those functional strategies are complementary or counter to those that increase biomass.

Functional Ecology↗

USGS2004

Delineation of a collapse feature in a noisy environment using a multichannel surface wave technique

A collapse developed at Calvert Cliffs Nuclear Power Plant, Maryland, in early 2001. The location of the collapse was over a groundwater drainage system pipe buried at an elevation of +0??9 m (reference is to Chesapeake Bay level). The cause of the collapse was a subsurface drain pipe that collapsed because of saltwater corrosion of the corrugated metal pipe. The inflow/outflow of sea water and groundwater flow caused soil to be removed from the area where the pipe collapsed. To prevent damage to nearby structures, the collapse was quickly filled with uncompacted sand and gravel (???36000 kg). However, the plant had an immediate need to determine whether more underground voids existed. A high-frequency multichannel surface-wave survey technique was conducted to define the zone affected by the collapse. Although the surface-wave survey at Calvert Cliffs Nuclear Power Plant was conducted at a noise level 50-100 times higher than the normal environment for a shallow seismic survey, the shear (S)-wave velocity field calculated from surface-wave data delineated a possible zone affected by the collapse. The S-wave velocity field showed chimney-shaped low-velocity anomalies that were directly related to the collapse. Based on S-wave velocity field maps, a potential zone affected by the collapse was tentatively defined.

Geotechnique↗

USGS2011

The efficacy of salvage logging in reducing subsequent fire severity in conifer-dominated forests of Minnesota, USA

Although primarily used to mitigate economic losses following disturbance, salvage logging has also been justified on the basis of reducing fire risk and fire severity; however, its ability to achieve these secondary objectives remains unclear. The patchiness resulting from a sequence of recent disturbances—blowdown, salvage logging, and wildfire—provided an excellent opportunity to assess the impacts of blowdown and salvage logging on wildfire severity. We used two fire‐severity assessments (tree‐crown and forest‐floor characteristics) to compare post‐wildfire conditions among three treatment combinations (Blowdown–Salvage–Fire, Blowdown–Fire, and Fire only). Our results suggest that salvage logging reduced the intensity (heat released) of the subsequent fire. However, its effect on severity (impact to the system) differed between the tree crowns and forest floor: tree‐crown indices suggest that salvage logging decreased fire severity (albeit with modest statistical support), while forest‐floor indices suggest that salvage logging increased fire severity. We attribute the latter finding to the greater exposure of mineral soil caused by logging operations; once exposed, soils are more likely to register the damaging effects of fire, even if fire intensity is not extreme. These results highlight the important distinction between fire intensity and severity when formulating post‐disturbance management prescriptions.

Minnesota↗

USGS2002

Genesis of the Doğankuzu and Mortaş Bauxite deposits, Taurides, Turkey: separation of Al, Fe, and Mn and implications for passive margin metallogeny

The Taurides region of Turkey is host to a number of important bauxite, Al-rich laterite, and Mn deposits. The most important bauxite deposits, Doğankuzu and Mortaş, are karst-related, unconformity-type deposits in Upper Cretaceous limestone. The bottom contact of the bauxite ore is undulatory, and bauxite fills depressions and sinkholes in the footwall limestone, whereas its top surface is concordant with the hanging-wall limestone. The thickness of the bauxite varies from 1 to 40 m and consists of böhmite, hematite, pyrite, marcasite, anatase, diaspore, gypsum, kaolinite, and smectite. The strata-bound, sulfide- and sulfate-bearing, low-grade lower part of the bauxite ore bed contains pyrite pseudomorphs after hematite and is deep red in outcrop owing to supergene oxidation. The lower part of the bauxite body contains local intercalations of calcareous conglomerate that formed in fault-controlled depressions and sinkholes. Bauxite ore is overlain by fine-grained Fe sulfide-bearing and calcareous claystone and argillaceous limestone, which are in turn overlain by massive, compact limestone of Santonian age. That 50-m-thick limestone is in turn overlain by well-bedded bioclastic limestone of Campanian or Maastrichtian age, rich with rudist fossils. Fracture fillings in the bauxite orebody are up to 1 m thick and consist of bluish-gray-green pyrite and marcasite (20%) with böhmite, diaspore, and anatase. These sulfide veins crosscut and offset the strata-bound sulfide zones. Sulfur for the sulfides was derived from the bacterial reduction of seawater sulfate, and Fe was derived from alteration of oxides in the bauxite. Iron sulfides do not occur within either the immediately underlying or overlying limestone. The platform limestone and shale that host the bauxite deposits formed at a passive margin of the Tethys Ocean. Extensive vegetation developed on land as the result of a humid climate, thereby creating thick and acidic soils and enhancing the transport of large amounts of organic matter to the ocean. Alteration of the organic matter provided CO 2 that contributed to formation of a relatively 12 C-rich marine footwall limestone. Relative sea-level fall resulted from strike-slip faulting associated with closure of the ocean and local uplift of the passive margin. That uplift resulted in karstification and bauxite formation in topographic lows, as represented by the Doğankuzu and Mortaş deposits. During stage 1 of bauxite formation, Al, Fe, Mn, and Ti were mobilized from deeply weathered aluminosilicate parent rock under acidic conditions and accumulated as hydroxides at the limestone surface owing to an increase in pH. During stage 2, Al, Fe, and Ti oxides and clays from the incipient bauxite (bauxitic soil) were transported as detrital phases and accumulated in the fault-controlled depressions and sinkholes. During stage 3, the bauxitic material was concentrated by repeated desilicification, which resulted in the transport of Si and Mn to the ocean through a well-developed karst drainage system. The transported Mn was deposited in offshore muds as Mn carbonates. The sulfides also formed in stage 3 during early diagenesis. Transgression into the foreland basin resulted from shortening of the ocean basin and nappe emplacement during the latest Cretaceous. During that time bioclastic limestone was deposited on the nappe ramp, which overlapped bauxite accumulation.

Taurides Region↗

USGS2015

Feasibility and potential effects of the proposed Amargosa Creek Recharge Project, Palmdale, California

Historically, the city of Palmdale and vicinity have relied on groundwater as the primary source of water, owing, in large part, to the scarcity of surface water in the region. Despite recent importing of surface water, groundwater withdrawal for municipal, industrial, and agricultural use has resulted in groundwater-level declines near the city of Palmdale in excess of 200 feet since the early 1900s. To meet the growing water demand in the area, the city of Palmdale has proposed the Amargosa Creek Recharge Project (ACRP), which has a footprint of about 150 acres along the Amargosa Creek 2 miles west of Palmdale, California. The objective of this study was to evaluate the long-term feasibility of recharging the Antelope Valley aquifer system by using infiltration of imported surface water from the California State Water Project in percolation basins at the ACRP. Three monitoring sites were constructed, and geophysical surveys (gravity, seismic, and resistivity) were completed to define the thickness of valley-fill deposits, depth to water, and location of faults that could influence groundwater flow. Data collected at the monitoring sites, and results from the geophysical surveys, were used to identify three northwest-southeast trending faults in the vicinity of the proposed recharge facility; these faults are probably related to the nearby San Andreas fault zone. Water levels collected from wells at the monitoring sites showed water-level altitude differences as much as 230 feet between the upgradient and downgradient sides of the faults, indicating that these faults are barriers to groundwater flow. Lithologic and geophysical logs indicated the presence of a coarse gravel and sand unit extending from land surface to about 150 feet below land surface that did not appear to be disrupted by faulting. Water samples collected from the monitoring wells were analyzed for major ions, nutrients, trace elements, dissolved organic carbon, volatile organic compounds, stable isotopes of oxygen (oxygen-18) and hydrogen (hydrogen-2, or deuterium), and the radioactive isotopes of hydrogen (hydrogen-3, or tritium) and carbon (carbon-14, or 14 C) to determine the water quality of the aquifer system and to help determine the source and age of the groundwater. Results of the water-quality analysis indicated that the source of natural recharge is Amargosa Creek near the ACRP, but that the creek does not provide modern-day recharge downstream of the ACRP. Potential effects of artificial recharge at the ACRP were evaluated by using a local-scale model of groundwater flow. On the basis of geologic samples collected during drilling, the hydraulic conductivity of the sand and gravel unit in the upper 150 feet was assumed to range from 10 to 100 feet per day. To address the goal of minimizing the potential for liquefaction during an earthquake from water-table rise associated with groundwater recharge at the ACRP, simulated water levels were constrained to remain at least 50 feet below land surface, except beneath the proposed artificial-recharge facility. The hydraulic conductivities of faults were estimated on the basis of water-level data and an estimate of natural recharge along Amargosa Creek. With assumed horizontal hydraulic conductivities of 10 and 100 feet per day in the upper 150 feet, the simulated maximum artificial recharge rates to the regional flow system at the ACRP were 3,400 and 9,400 acre-feet per year, respectively. These maximum recharge rates were limited primarily by the horizontal hydraulic conductivity in the upper 150 feet and by the liquefaction constraint. Future monitoring of water-level and soil-water content changes during the proposed project would allow improved estimation of aquifer hydraulic properties, the effect of the faults on groundwater movement, and the overall recharge capacity of the ACRP.

California↗

USGS2019

Monitoring drought impact on annual forage production in semi-arid grasslands: A case study of Nebraska sandhills

Land management practices and disturbances (e.g. overgrazing, fire) have substantial effects on grassland forage production. When using satellite remote sensing to monitor climate impacts, such as drought stress on annual forage production, minimizing land management practices and disturbance effects sends a clear climate signal to the productivity data. This study investigates the effect of this climate signal by: (1) providing spatial estimates of expected biomass under specific climate conditions, (2) determining which drought indices explain the majority of interannual variability in this biomass, and (3) developing a predictive model that estimates the annual biomass early in the growing season. To address objective 1, this study uses an established methodology to determine Expected Ecosystem Performance (EEP) in the Nebraska Sandhills, US, representing annual forage levels after accounting for non-climatic influences. Moderate Resolution Imaging Spectroradiometer (MODIS)-based Normalized Difference Vegetation Index (NDVI) data were used to approximate actual ecosystem performance. Seventeen years (2000–2016) of annual EEP was calculated using piecewise regression tree models of site potential and climate data. Expected biomass (EB), EEP converted to biomass in kg*ha −1 *yr −1 , was then used to examine the predictive capacity of several drought indices and the onset date of the growing season. Subsets of these indices were used to monitor and predict annual expected grassland biomass. Independent field-based biomass production data available from two Sandhills locations were used for validation of the EEP model. The EB was related to field-based biomass production (R 2 = 0.66 and 0.57) and regional rangeland productivity statistics of the Soil Survey Geographic Database (SSURGO) dataset. The Evaporative Stress Index (ESI), the 3- and 6-month Standardized Precipitation Index (SPI), and the U.S. Drought Monitor (USDM), which represented moisture conditions during May, June and July, explained the majority of the interannual biomass variability in this grassland system (three-month ESI explained roughly 72% of the interannual biomass variability). A new model was developed to use drought indices from early in the growing season to predict the total EB for the whole growing season. This unique approach considers only climate-related drought signal on productivity. The capability to estimate annual EB by the end of May will potentially enable land managers to make informed decisions about stocking rates, hay purchase needs, and other management issues early in the season, minimizing their potential drought losses. View Full-Text

Nebraska↗

USGS2003

Synergy of agroforestry and bottomland hardwood afforestation

Afforestation of bottomland hardwood forests has historically emphasized planting heavy-seeded tree species such as oak (Quercus spp.) and pecan (Caryaillinoensis) with little or no silvicultural management during stand development. Slow growth of these tree species, herbivory, competing vegetation, and limited seed dispersal, often result in restored sites that are slow to develop vertical vegetation structure and have limited tree diversity. Where soils and hydrology permit, agroforestry can provide transitional management that mitigates these historical limitations on converting cropland to forests. Planting short-rotation woody crops and intercropping using wide alleyways are two agroforestry practices that are well suited for transitional management. Weed control associated with agroforestry systems benefits planted trees by reducing competition. The resultant decrease in herbaceous cover suppresses small mammal populations and associated herbivory of trees and seeds. As a result, rapid vertical growth is possible that can 'train' under-planted, slower-growing, species and provide favorable environmental conditions for naturally invading trees. Finally, annual cropping of alleyways or rotational pulpwood harvest of woody crops provides income more rapidly than reliance on future revenue from traditional silviculture. Because of increased forest diversity, enhanced growth and development, and improved economic returns, we believe that using agroforestry as a transitional management strategy during afforestation provides greater benefits to landowners and to the environment than does traditional bottomland hardwood afforestation.

Book chapter↗

USGS1982

A 40-foot static cone penetrometer

The Navy needs a lightweight device for testing seafloor soils to sub bottom depths of 12 meters in water depths to 60 meters. To meet this need a quasistatic cone penetration device that uses water jetting to reduce friction on the cone rod has been developed. This device is called the XSP-40. The 5-ton XSP-40 stands 15 meters tall and pushes a standard 5-ton cone into the seafloor. It is remotely controlled with an electronic unit on the deck of the support vessel. All cone outputs are recorded directly as a function of penetration depth with a strip chart recorder. A full suite of gauges is provided. on the electronic unit for monitoring the XSP-40's performance during a test .. About 40 penetration tests have been performed with very good success. The XSP-40 was field tested in Norton Sound, off the west coast of Alaska. The general objective, in addition to evaluation of the device, was to gather geotechnical information on sediments that may be involved in processes potentially hazardous to offshore development. Four example penetration records are presented from gas charged sediment zones and areas near the Yukon River delta. In general it was determined that soil classification from cone data agreed well with classifications from core samples. Relative densities of the silt-sand to sandy-silt soils were usually very high. The significance of these results are discussed with respect to storm wave, liquefaction. It is concluded that the XSP-40 is a durable and reliable piece of equipment capable of achieving penetration beyond that possible when not using the water jet system.

Proceedings of the Offshore Technology Conference↗

USGS1976

Hydrologic evaluation of salinity control and reclamation projects in the Indus Plain, Pakistan--A summary

This report summarizes the observations and findings of a team of four specialists from the U.S. Geological Survey assigned to Pakistan under the auspices of the U.S. Agency for International Development during May to August 1972 for a hydrologic evaluation of Salinity Control and Reclamation Projects in the Indus Plain Individual members of the team undertook comprehensive studies related to climatology, surface-water hydrology, and the canal system; streamflow and sediment yields of the rivers; computer applications to hydrologic data; aquifer characteristics; hydrologic evaluation of Salinity Control and Reclamation Projects (SCARPs); tubewell performance; hydrology of shallow versus deep tubewells; well and well-screen design in the Indus Plain; evaluation of observed and anticipated trends in both private and public tubewell development; evaluation of water-quality programs, data analysis, and records, and computer coding of special water-quality data; and evaluation of water-level data, well discharge and specific-capacity tests and aquifer tests. The reclamation program, by pumping from tubewells, has been notably successful in lowering the water table, in providing supplemental water for irrigation and for leaching of salinized soils, and in improving crop production. Some changes in water quality have been observed in SCARP-I and the Mona Scheme of SCARP-II, but these have not as yet (1972) significantly affected the utility of the water for irrigation. Problems associated with reclamation include control of deterioration in performance of tubewells and their rehabilitation, local brackish or saline-water encroachment, and maintenance of a favorable salt balance in the ground-water system. Rapid and as yet (1972) unregulated growth of shallow private tubewell development in the past decade has introduced complicating factors to the reclamation planning of the early 1960's which had emphasized public tubewell development through the SCARP program. In comparing shallow (0-200 feet) with deep (200-400 feet} tubewell development, it is concluded that long-term response of the water table is the same, whether many shallow wells of small capacity or fewer deeper wells of large capacity pump the same total volume of water in the same area. Moreover, it is concluded that there is no definite advantage for either type of pumping regime with respect to water quality. Utilization of the Punjab aquifer could be greatly enhanced by recharge of high-quality water diverted from the Chenab and Jhelum Rivers to the Ravi and Sutlej Rivers by way of the link and irrigation canals during periods of surplus flow. Recharge to the aquifer could also be improved by diversion of high-quality water from the Chenab and the Jhelum to natural nalas and other surface drainageways during periods of surplus flow. Such recharge would be of much better quality than water leaching downward from irrigated fields. Continued monitoring of the hydrologic system and research on problems engendered by reclamation are essential to the viability of the SCARP program and related water-resources development in the Indus River Basin.

Water Supply Paper↗

USGS2019

Long-term nitrogen addition shifts the soil nematode community to bacterivore-dominated and reduces its ecological maturity in a subalpine forest

Nitrogen deposition from anthropogenic sources is a global problem that reaches even the most remote ecosystems. Responses belowground vary by ecosystem, and have feedbacks to geochemical processes, including carbon storage. A long-term nitrogen addition study in a subalpine forest has shown carbon loss over time, atypical for a forest ecosystem. Loss of microbial biomass is likely linked to lower soil carbon, but the mechanism behind this is still unknown. One possible explanation is through increased turnover due to grazing by soil fauna. Because nematodes occupy many trophic levels and are sensitive to trophic and environmental changes, assessing their communities helps reveal belowground responses. In this study, we tested the hypothesis that long-term nitrogen fertilization affects nematode community structure and maturity beneath coniferous forests in the Rocky Mountains, indicating a faster cycling, bacterial-driven system. We identified and enumerated nematodes by trophic group and family from experimental plots. Total nematode abundance was 40–96% greater in fertilized plots compared to the control, but richness, diversity, and ecological maturity were lower. The differences in abundance were driven by opportunistic bacterivores (e.g., Rhabditidae) and plant parasites (e.g., Tylenchidae), which made up 23 and 13% of the community in fertilized compared to 7 and 5% in control plots, respectively. Nematode maturity indices showed that the nematode food webwas enriched (indicating high nutrient/resource status) and structured (all trophic levels present, including long-lived predators) in both treatments, but significantly more enriched in the fertilized treatment. Nonmetric multidimensional scaling of the relative abundance of nematode families demonstrated that nematode community composition differed between treatments, driven largely by opportunistic bacterivores (e.g., Rhabditidae) in the fertilized plots. The mechanism of the aboveground–belowground link between nitrogen deposition and nematode community composition is likely through increased microbial turnover, and sustained high-quality food for microbial grazing nematodes.

Soil Biology and Biochemistry↗

USGS2010

Water-budget methods

A water budget is an accounting of water movement into and out of, and storage change within, some control volume. Universal and adaptable are adjectives that reflect key features of water-budget methods for estimating recharge. The universal concept of mass conservation of water implies that water-budget methods are applicable over any space and time scales (Healy et al ., 2007). The water budget of a soil column in a laboratory can be studied at scales of millimeters and seconds. A water-budget equation is also an integral component of atmospheric general circulation models used to predict global climates over periods of decades or more. Water-budget equations can be easily customized by adding or removing terms to accurately portray the peculiarities of any hydrologic system. The equations are generally not bound by assumptions on mechanisms by which water moves into, through, and out of the control volume of interest. So water-budget methods can be used to estimate both diffuse and focused recharge, and recharge estimates are unaffected by phenomena such as preferential flow paths within the unsaturated zone. Water-budget methods represent the largest class of techniques for estimating recharge. Most hydrologic models are derived from a water-budget equation and can therefore be classified as water-budget models. It is not feasible to address all water-budget methods in a single chapter. This chapter is limited to discussion of the “residual” water-budget approach, whereby all variables in a water-budget equation, except for recharge, are independently measured or estimated and recharge is set equal to the residual. This chapter is closely linked with Chapter 3, on modeling methods, because the equations presented here form the basis of many models and because models are often used to estimate individual components in water-budget studies. Water budgets for streams and other surface-water bodies are addressed in Chapter 4. The use of soil-water budgets and lysimeters for determining potential recharge and evapotranspiration from changes in water storage is discussed in Chapter 5. Aquifer water-budget methods based on the measurement of groundwater levels are described in Chapter 6.

Book chapter↗

USGS2013

Toxic exposure of songbirds to lead in the Southeast Missouri Lead Mining District

Mining and smelting in the Southeast Missouri Lead Mining District has caused widespread contamination of soils with lead (Pb) and other metals. Soils from three study sites sampled in the district contained from approximately 1,000–3,200 mg Pb/kg. Analyses of earthworms [33–4,600 mg Pb/kg dry weight (dw)] collected in the district showed likely high Pb exposure of songbirds preying on soil organisms. Mean tissue Pb concentrations in songbirds collected from the contaminated sites were greater (p < 0.05) than those in songbirds from reference sites by factors of 8 in blood, 13 in liver, and 23 in kidney. Ranges of Pb concentrations in livers (mg Pb/kg dw) were as follows: northern cardinal (Cardinalis cardinalis) = 0.11–3.0 (reference) and 1.3–30 (contaminated) and American robin (Turdus migratorius) = 0.43–8.5 (reference) and 7.6–72 (contaminated). Of 34 adult and juvenile songbirds collected from contaminated sites, 11 (32 %) had hepatic Pb concentrations that were consistent with adverse physiological effects, 3 (9 %) with systemic toxic effects, and 4 (12 %) with life-threatening toxic effects. Acid-fast renal intranuclear inclusion bodies, which are indicative of Pb poisoning, were detected in kidneys of two robins that had the greatest renal Pb concentrations (952 and 1,030 mg/kg dw). Mean activity of the enzyme delta-aminolevulinic acid dehydratase (ALAD) in red blood cells, a well-established bioindicator of Pb poisoning in birds, was decreased by 58–82 % in songbirds from the mining sites. We conclude that habitats within the mining district with soil Pb concentrations of ≥1,000 mg Pb/kg are contaminated to the extent that they are exposing ground-feeding songbirds to toxic concentrations of Pb.

Missouri↗

USGS2012

Environmental and physical controls on northern terrestrial methane emissions across permafrost zones

Methane (CH 4 ) emissions from the northern high-latitude region represent potentially significant biogeochemical feedbacks to the climate system. We compiled a database of growing-season CH 4 emissions from terrestrial ecosystems located across permafrost zones, including 303 sites described in 65 studies. Data on environmental and physical variables, including permafrost conditions, were used to assess controls on CH 4 emissions. Water table position, soil temperature, and vegetation composition strongly influenced emissions and had interacting effects. Sites with a dense sedge cover had higher emissions than other sites at comparable water table positions, and this was an effect that was more pronounced at low soil temperatures. Sensitivity analysis suggested that CH 4 emissions from ecosystems where the water table on average is at or above the soil surface (wet tundra, fen underlain by permafrost, and littoral ecosystems) are more sensitive to variability in soil temperature than drier ecosystems (palsa dry tundra, bog, and fen), whereas the latter ecosystems conversely are relatively more sensitive to changes of the water table position. Sites with near-surface permafrost had lower CH 4 fluxes than sites without permafrost at comparable water table positions, a difference that was explained by lower soil temperatures. Neither the active layer depth nor the organic soil layer depth was related to CH 4 emissions. Permafrost thaw in lowland regions is often associated with increased soil moisture, higher soil temperatures, and increased sedge cover. In our database, lowland thermokarst sites generally had higher emissions than adjacent sites with intact permafrost, but emissions from thermokarst sites were not statistically higher than emissions from permafrost-free sites with comparable environmental conditions. Overall, these results suggest that future changes to terrestrial high-latitude CH 4 emissions will be more proximately related to changes in moisture, soil temperature, and vegetation composition than to increased availability of organic matter following permafrost thaw.

Global Change Biology↗

USGS2010

Effects of Groundwater Development on Uranium: Central Valley, California, USA

Uranium (U) concentrations in groundwater in several parts of the eastern San Joaquin Valley, California, have exceeded federal and state drinking water standards during the last 20 years. The San Joaquin Valley is located within the Central Valley of California and is one of the most productive agricultural areas in the world. Increased irrigation and pumping associated with agricultural and urban development during the last 100 years have changed the chemistry and magnitude of groundwater recharge, and increased the rate of downward groundwater movement. Strong correlations between U and bicarbonate suggest that U is leached from shallow sediments by high bicarbonate water, consistent with findings of previous work in Modesto, California. Summer irrigation of crops in agricultural areas and, to lesser extent, of landscape plants and grasses in urban areas, has increased Pco2 concentrations in the soil zone and caused higher temperature and salinity of groundwater recharge. Coupled with groundwater pumping, this process, as evidenced by increasing bicarbonate concentrations in groundwater over the last 100 years, has caused shallow, young groundwater with high U concentrations to migrate to deeper parts of the groundwater system that are tapped by public-supply wells. Continued downward migration of U-affected groundwater and expansion of urban centers into agricultural areas will likely be associated with increased U concentrations in public-supply wells. The results from this study illustrate the potential longterm effects of groundwater development and irrigation-supported agriculture on water quality in arid and semiarid regions around the world.

California↗

USGS2015

Hydrogeologic framework, hydrology, and refined conceptual model of groundwater flow for Coastal Plain aquifers at the Standard Chlorine of Delaware, Inc. Superfund Site, New Castle County, Delaware, 2005-12

From 1966 to 2002, activities at the Standard Chlorine of Delaware chemical facility in New Castle County, Delaware resulted in the contamination of groundwater, soils, and wetland sediment. In 2005, the U.S. Geological Survey (USGS), in partnership with the U.S. Environmental Protection Agency, Region 3, and the Delaware Department of Natural Resources and Environmental Control began a multi-year investigation of the hydrogeologic framework and hydrology of the confined aquifer system. The goals of the ongoing study at the site (the Potomac Aquifer Study) are to determine the hydraulic connection between the Columbia and Potomac aquifers, determine the direction of groundwater flow in the Potomac aquifer, and identify factors affecting the fate of contaminated groundwater. This report describes progress made towards these goals based on available data collected through September 2012. The regional hydrogeologic framework indicates that the site is underlain by Coastal Plain sediments of the Columbia, Merchantville, and Potomac Formations. Two primary aquifers underlying the site, the Columbia and the upper Potomac, are separated by the Merchantville Formation confining unit. Local groundwater flow in the surficial (Columbia) aquifer is controlled by topography and generally flows northward and discharges to nearby surface water. Regional flow within the Potomac aquifer is towards the southeast, and is strongly influenced by major water withdrawals locally. Previous investigations at the site indicated that contaminants, primarily benzene and chlorinated benzene compounds, were present in the Columbia aquifer in most locations; however, there were only limited detections in the upper Potomac aquifer as of 2004. From 2005 through 2012, the USGS designed a monitoring network, assisted with exploratory drilling, collected data at monitoring wells, conducted geophysical surveys, evaluated water-level responses in wells during pumping of a production well, and evaluated major aquifer withdrawals. Data collected through these efforts were used to refine the local conceptual flow system. The refined conceptual flow system for the site includes: (a) identification of gaps in confining units in the study area, (b) identification and correlation of multiple water-bearing sand intervals within the upper Potomac Formation, (c) connections between groundwater and surface water, (d) connections between shallow and deeper groundwater, (e) new water-level (or potentiometric surface) maps and inferred flow directions, and (f) identification of major local pumping well influences. The implications of the revised conceptual flow system on the occurrence and movement of site contaminants are that the resulting detection of contaminants in the upper Potomac aquifer at specific well locations can be attributed primarily to either advective lateral transport, direct vertical contaminant transport, or a combination of vertical and lateral movement resulting from changes in water withdrawal rates over time.

Delaware↗

USGS2020

A newly emerging thermal area in Yellowstone

Yellowstone is a large restless caldera that contains many dynamic thermal areas that are the surface expression of the deeper magmatic system. In 2018, using a Landsat 8 nighttime thermal infrared image, we discovered the emergence of a new thermal area located near Tern Lake on the northeast margin of the Sour Creek dome. A high-spatial-resolution airborne visible image from August 2017 revealed a large (~33,000 m2) area of recently fallen trees, mostly devoid of vegetation, with bright soil, similar to other nearby thermal areas. Field observations in August 2019 confirmed that this was a steam-heated acid-sulfate thermal area, with an arc-shaped zone of hydrothermally altered soil and heated ground, with surface temperatures of 60-80 °C, several steaming fumaroles, and boiling temperatures (93 °C) just beneath the surface. Fallen trees in contact with warm ground were being carbonized, yet there were some cooler areas with new trees growing. Observations of stressed or dying vegetation from archived satellite and airborne remote sensing data going back to 1994 indicated that this thermal area started emerging around 2000. It increased in size slowly until around 2005, when the radiative heat output started measurably increasing. From 2005 to 2012 it grew more rapidly; and from 2012 through 2019 the growth rate slowed and the heat output stabilized. We predict that this stabilizing trend will continue in the coming years. The initial formation of this new thermal area was not clearly linked to any distinct seismic or geodetic events, although the period of rapid growth partly coincided with a period of rapid local uplift, possibly suggesting a causative relationship. The identification of this emerging thermal area illustrates the importance of satellite thermal infrared imaging combined with high-spatial-resolution remote sensing data and field observations for mapping, measuring, and monitoring Yellowstone's thermal areas. It is also an example of the dynamics we expect to observe within large caldera systems like Yellowstone, where changes in the size and distribution of thermal areas are normal and do not indicate an impending eruption nor any significant changes in the broader magmatic system.

Wyoming↗

USGS2010

Management intensity alters decomposition via biological pathways

Current conceptual models predict that changes in plant litter chemistry during decomposition are primarily regulated by both initial litter chemistry and the stage-or extent-of mass loss. Far less is known about how variations in decomposer community structure (e.g., resulting from different ecosystem management types) could influence litter chemistry during decomposition. Given the recent agricultural intensification occurring globally and the importance of litter chemistry in regulating soil organic matter storage, our objectives were to determine the potential effects of agricultural management on plant litter chemistry and decomposition rates, and to investigate possible links between ecosystem management, litter chemistry and decomposition, and decomposer community composition and activity. We measured decomposition rates, changes in litter chemistry, extracellular enzyme activity, microarthropod communities, and bacterial versus fungal relative abundance in replicated conventional-till, no-till, and old field agricultural sites for both corn and grass litter. After one growing season, litter decomposition under conventional-till was 20% greater than in old field communities. However, decomposition rates in no-till were not significantly different from those in old field or conventional-till sites. After decomposition, grass residue in both conventional- and no-till systems was enriched in total polysaccharides relative to initial litter, while grass litter decomposed in old fields was enriched in nitrogen-bearing compounds and lipids. These differences corresponded with differences in decomposer communities, which also exhibited strong responses to both litter and management type. Overall, our results indicate that agricultural intensification can increase litter decomposition rates, alter decomposer communities, and influence litter chemistry in ways that could have important and long-term effects on soil organic matter dynamics. We suggest that future efforts to more accurately predict soil carbon dynamics under different management regimes may need to explicitly consider how changes in litter chemistry during decomposition are influenced by the specific metabolic capabilities of the extant decomposer communities.

Biogeochemistry↗

USGS2013

Characterisation of the Permafrost Carbon Pool

The current estimate of the soil organic carbon (SOC) pool in the northern permafrost region of 1672 Petagrams (Pg) C is much larger than previously reported and needs to be incorporated in global soil carbon (C) inventories. The Northern Circumpolar Soil Carbon Database (NCSCD), extended to include the range 0–300 cm, is now available online for wider use by the scientific community. An important future aim is to provide quantitative uncertainty ranges for C pool estimates. Recent studies have greatly improved understanding of the regional patterns, landscape distribution and vertical (soil horizon) partitioning of the permafrost C pool in the upper 3 m of soils. However, the deeper C pools in unconsolidated Quaternary deposits need to be better constrained. A general lability classification of the permafrost C pool should be developed to address potential C release upon thaw. The permafrost C pool and its dynamics are beginning to be incorporated into Earth System models, although key periglacial processes such as thermokarst still need to be properly represented to obtain a better quantification of the full permafrost C feedback on global climate change.

Permafrost and Periglacial Processes↗