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USGS2011

From agricultural intensification to conservation: Sediment transport in the Raccoon River, Iowa, 1916-2009

Fluvial sediment is a ubiquitous pollutant that negatively aff ects surface water quality and municipal water supply treatment. As part of its routine water supply monitoring, the Des Moines Water Works (DMWW) has been measuring turbidity daily in the Raccoon River since 1916. For this study, we calibrated daily turbidity readings to modern total suspended solid (TSS) concentrations to develop an estimation of daily sediment concentrations in the river from 1916 to 2009. Our objectives were to evaluate longterm TSS patterns and trends, and relate these to changes in climate, land use, and agricultural practices that occurred during the 93-yr monitoring period. Results showed that while TSS concentrations and estimated sediment loads varied greatly from year to year, TSS concentrations were much greater in the early 20th century despite drier conditions and less discharge, and declined throughout the century. Against a backdrop of increasing discharge in the Raccoon River and widespread agricultural adaptations by farmers, sediment loads increased and peaked in the early 1970s, and then have slowly declined or remained steady throughout the 1980s to present. With annual sediment load concentrated during extreme events in the spring and early summer, continued sediment reductions in the Raccoon River watershed should be focused on conservation practices to reduce rainfall impacts and sediment mobilization. Overall, results from this study suggest that eff orts to reduce sediment load from the watershed appear to be working. ?? 2011 by the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America.

Journal of Environmental Quality↗

USGS2012

U.S. Geological Survey, National Wildlife Health Center, 2011 report of selected wildlife diseases

The National Wildlife Health Center (NWHC) was founded in 1975 to provide technical assistance in identifying, controlling, and preventing wildlife losses from diseases, conduct research to understand the impact of diseases on wildlife populations, and devise methods to more effectively manage these disease threats. The impetus behind the creation of the NWHC was, in part, the catastrophic loss of tens of thousands of waterfowl as a result of an outbreak of duck plague at the Lake Andes National Wildlife Refuge in South Dakota during January 1973. In 1996, the NWHC, along with other Department of Interior research functions, was transferred from the U.S. Fish and Wildlife Service to the U.S. Geological Survey (USGS), where we remain one of many entities that provide the independent science that forms the bases of the sound management of the Nation’s natural resources. Our mission is to provide national leadership to safeguard wildlife and ecosystem health through dynamic partnerships and exceptional science. The main campus of the NWHC is located in Madison, Wis., where we maintain biological safety level 3 (BSL–3) diagnostic and research facilities purposefully designed for work with wildlife species. The NWHC provides research and technical assistance on wildlife health issues to State, Federal, and international agencies. In addition, since 1992 we have maintained a field station in Hawaii, the Honolulu Field Station, which focuses on marine and terrestrial natural resources throughout the Pacific region. The NWHC conducts diagnostic investigations of unusual wildlife morbidity and mortality events nationwide to detect the presence of wildlife pathogens and determine the cause of death. This is also an important activity for detecting new, emerging and resurging diseases. The NWHC provides this crucial information on the presence of wildlife diseases to wildlife managers to support sound management decisions. The data and information generated also allows for further indepth analyses for determining the biological and ecological significance of disease events, detecting disease trends over time and space, as well as detecting any significant changes to how diseases manifest in the field. Moreover, this information allows us to gain insight into the significance of future wildlife disease events. The purpose of this report is to provide a sample of NWHC data that are available from our Laboratory Information Management System (LIMS). These data are presented in summary format with minimal statistical analysis and interpretation. The goal is to share these data with wildlife managers and other stakeholders, promote the use of NHWC data, and encourage the sharing of wildlife disease data to improve temporal and geographic surveillance coverage. Continued national surveillance for wildlife diseases is essential for providing early detection and warning of events that have the potential to result in harm to human health, economic losses, declines in wildlife populations, and subsequent ecological disturbances. Increased collaboration, coordination, and sharing of surveillance data will enhance this Nation’s ability to detect and respond to wildlife disease threats.

Scientific Investigations Report↗

USGS2010

Using the Sonoran and Libyan Desert test sites to monitor the temporal stability of reflective solar bands for Landsat 7 enhanced thematic mapper plus and Terra moderate resolution imaging spectroradiometer sensors

Remote sensing imagery is effective for monitoring environmental and climatic changes because of the extent of the global coverage and long time scale of the observations. Radiometric calibration of remote sensing sensors is essential for quantitative & qualitative science and applications. Pseudo-invariant ground targets have been extensively used to monitor the long-term radiometric calibration stability of remote sensing sensors. This paper focuses on the use of the Sonoran Desert site to monitor the radiometric stability of the Landsat 7 (L7) Enhanced Thematic Mapper Plus (ETM+) and Terra Moderate Resolution Imaging Spectroradiometer (MODIS) sensors. The results are compared with the widely used Libya 4 Desert site in an attempt to evaluate the suitability of the Sonoran Desert site for sensor inter-comparison and calibration stability monitoring. Since the overpass times of ETM+ and MODIS differ by about 30 minutes, the impacts due to different view geometries or test site Bi-directional Reflectance Distribution Function (BRDF) are also presented. In general, the long-term drifts in the visible bands are relatively large compared to the drift in the near-infrared bands of both sensors. The lifetime Top-of-Atmosphere (TOA) reflectance trends from both sensors over 10 years are extremely stable, changing by no more than 0.1% per year (except ETM+ Band 1 and MODIS Band 3) over the two sites used for the study. The use of a semi-empirical BRDF model can reduce the impacts due to view geometries, thus enabling a better estimate of sensor temporal drifts.

Journal of Applied Remote Sensing↗

USGS2014

The long-term trends (1982-2006) in vegetation greenness of the alpine ecosystem in the Qinghai-Tibetan Plateau

The increased rate of annual temperature in the Qinghai-Tibetan Plateau exceeded all other areas of the same latitude in recent decades. The influence of the warming climate on the alpine ecosystem of the plateau was distinct. An analysis of alpine vegetation under changes in climatic conditions was conducted in this study. This was done through an examination of vegetation greenness and its relationship with climate variability using the Advanced Very High Resolution Radiometer satellite imagery and climate datasets. Vegetation in the plateau experienced a positive trend in greenness, with 18.0 % of the vegetated areas exhibiting significantly positive trends, which were primarily located in the eastern and southwestern parts of the plateau. In grasslands, 25.8 % of meadows and 14.1 % of steppes exhibited significant upward trends. In contrast, the broadleaf forests experienced a trend of degradation. Temperature, particularly summer temperature, was the primary factor promoting the vegetation growth in the plateau. The wetter and warmer climate in the east contributed to the favorable conditions for vegetation. The alpine meadow was mostly sensitive to temperature, while the steppes were sensitive to both temperature and precipitation. Although a warming climate was expected to be beneficial to vegetation growth in the alpine region, the rising temperature coupled with reduced precipitation in the south did not favor vegetation growth due to low humidity and poor soil moisture conditions.

Qinghai-tibetan Plateau↗

USGS2015

Patterns and predictability in the intra-annual organic carbon variability across the boreal and hemiboreal landscape

Factors affecting total organic carbon (TOC) concentrations in 215 watercourses across Sweden were investigated using parameter parsimonious regression approaches to explain spatial and temporal variabilities of the TOC water quality responses. We systematically quantified the effects of discharge, seasonality, and long-term trend as factors controlling intra-annual (among year) and inter-annual (within year) variabilities of TOC by evaluating the spatial variability in model coefficients and catchment characteristics (e.g. land cover, retention time, soil type). Catchment area (0.18–47,000 km 2 ) and land cover types (forests, agriculture and alpine terrain) are typical for the boreal and hemiboreal zones across Fennoscandia. Watercourses had at least 6 years of monthly water quality observations between 1990 and 2010. Statistically significant models (p < 0.05) describing variation of TOC in streamflow were identified in 209 of 215 watercourses with a mean Nash-Sutcliffe efficiency index of 0.44. Increasing long-term trends were observed in 149 (70%) of the watercourses, and intra-annual variation in TOC far exceeded inter-annual variation. The average influences of the discharge and seasonality terms on intra-annual variations in daily TOC concentration were 1.4 and 1.3 mg l − 1 (13 and 12% of the mean annual TOC), respectively. The average increase in TOC was 0.17 mg l − 1 year − 1 (1.6% year − 1 ). Multivariate regression with over 90 different catchment characteristics explained 21% of the spatial variation in the linear trend coefficient, less than 20% of the variation in the discharge coefficient and 73% of the spatial variation in mean TOC. Specific discharge, water residence time, the variance of daily precipitation, and lake area, explained 45% of the spatial variation in the amplitude of the TOC seasonality. Because the main drivers of temporal variability in TOC are seasonality and discharge, first-order estimates of the influences of climatic variability and change on TOC concentration should be predictable if the studied catchments continue to respond similarly.

Science of the Total Environment↗

USGS2024

ECCOE Landsat quarterly Calibration and Validation report—Quarter 3, 2023

Executive Summary The U.S. Geological Survey Earth Resources Observation and Science Calibration and Validation (Cal/Val) Center of Excellence (ECCOE) focuses on improving the accuracy, precision, calibration, and product quality of remote-sensing data, leveraging years of multiscale optical system geometric and radiometric calibration and characterization experience. The ECCOE Landsat Cal/Val Team continually monitors the geometric and radiometric performance of active Landsat missions and makes calibration adjustments, as needed, to maintain data quality at the highest level. This report provides observed geometric and radiometric analysis results for Landsats 7, 8, and 9 for quarter 3 (July–September) of 2023. All data used to compile the Cal/Val analysis results presented in this report are freely available from the U.S. Geological Survey EarthExplorer website: https://earthexplorer.usgs.gov . This is the first quarterly report to include analysis results for Landsat 9, which was launched in September 2021. The inclusion of Landsat 9 analysis results was dependent on two factors: a complete reprocessing of the Landsat 9 data archive and enough time elapsing to begin formulating lifetime trends. In April 2023, all Landsat 9 image data acquired since the satellite’s launch were reprocessed to take advantage of calibration updates identified by the ECCOE Landsat Cal/Val Team. Additional information about the Landsat 9 reprocessing effort is available at https://www.usgs.gov/landsat-missions/news/upcoming-reprocessing-all-landsat-9-data .

Open-File Report↗

USGS2024

ECCOE Landsat quarterly Calibration and Validation report—Quarter 4, 2023

Executive Summary The U.S. Geological Survey Earth Resources Observation and Science Calibration and Validation (Cal/Val) Center of Excellence (ECCOE) focuses on improving the accuracy, precision, calibration, and product quality of remote-sensing data, leveraging years of multiscale optical system geometric and radiometric calibration and characterization experience. The ECCOE Landsat Cal/Val Team continually monitors the geometric and radiometric performance of active Landsat missions and makes calibration adjustments, as needed, to maintain data quality at the highest level. This report provides observed geometric and radiometric analysis results for Landsats 7, 8, and 9 for quarter 4 (October–December) of 2023. All data used to compile the Cal/Val analysis results presented in this report are freely available from the U.S. Geological Survey EarthExplorer website: https://earthexplorer.usgs.gov . This is the second quarterly report to include analysis results for Landsat 9, which was launched in September 2021. The inclusion of Landsat 9 analysis results was dependent on two factors: a complete reprocessing of the Landsat 9 data archive and enough time elapsing to begin formulating lifetime trends. In April 2023, all Landsat 9 image data acquired since the satellite’s launch were reprocessed to take advantage of calibration updates identified by the ECCOE Landsat Cal/Val Team. Additional information about the Landsat 9 reprocessing effort is available at https://www.usgs.gov/landsat-missions/news/upcoming-reprocessing-all-landsat-9-data . Additional information about Landsat 9 prelaunch, commissioning, and early on-orbit imaging performance is available at https://www.mdpi.com/journal/remotesensing/special_issues/15B4V2K92K .

Open-File Report↗

USGS2022

The statistical power to detect regional temporal trends in riverine contaminants in the Chesapeake Bay Watershed, USA

Chemical contamination of riverine ecosystems is largely a result of urbanization, industrialization, and agricultural activities occurring on adjacent terrestrial landscapes. Land management activities (e.g., Best Management Practices) are an important tool used to reduce point and non-point sources of pollution. However, the ability to confidently make inferences about the efficacy of land management activities on reducing in-stream chemical concentrations is poorly understood. We estimated regional temporal trends and components of variation for commonly used herbicides (atrazine and metolachlor), total estrogenicity, and riverine sediment concentrations of total PCBs for rivers in the Chesapeake Bay Watershed, USA. We then used the estimated variance components to perform a power analysis and evaluated the statistical power to detect regional temporal trends under different monitoring scenarios. Scenarios included varying the magnitude of the annual contaminant decline, the number of sites sampled each year, the number of years sampled, and sampling frequency. Monitoring for short time periods (e.g., 5 years) was inadequate for detecting regional temporal trends, regardless of the number of sites sampled or the magnitude of the annual declines. Even when monitoring over a 20-year period, sampling a relatively large number of sites each year was required (e.g., > 50 sites) to achieve adequate statistical power for smaller trend magnitudes (declines of 5 – 7%/year). Annual sampling frequency had little impact on power for any monitoring scenario. All sampling scenarios were underpowered for sediment total PCBs. Power was greatest for total estrogenicity, suggesting that this aggregate measure of estrogenic activity may be a useful indicator. This study provides information that can be used to help (1) guide the development of monitoring programs aimed at detecting regional declines in riverine chemical contaminant concentrations in response to land management actions, and (2) set expectations for the ability to detect changes over time.

Chesapeake Bay watershed↗

USGS2014

Links between N deposition and nitrate export from a high-elevation watershed in the Colorado Front Range

Long-term patterns of stream nitrate export and atmospheric N deposition were evaluated over three decades in Loch Vale, a high-elevation watershed in the Colorado Front Range. Stream nitrate concentrations increased in the early 1990s, peaked in the mid-2000s, and have since declined by over 40%, coincident with trends in nitrogen oxide emissions over the past decade. Similarities in the timing and magnitude of N deposition provide evidence that stream chemistry is responding to changes in atmospheric deposition. The response to deposition was complicated by a drought in the early 2000s that enhanced N export for several years. Other possible explanations, including forest disturbance, snow depth, or permafrost melting, could not explain patterns in N export. Our results show that stream chemistry responds rapidly to changes in N deposition in high-elevation watersheds, similar to the response observed to changes in sulfur deposition.

Colorado↗

USGS2015

Concentrations and distributions of metals associated with dissolved organic matter from the Suwannee River (GA, USA)

Concentrations and distributions of metals in Suwannee River (SR) raw filtered surface water (RFSW) and dissolved organic matter (DOM) processed by reverse osmosis (RO), XAD-8 resin (for humic and fulvic acids [FA]), and XAD-4 resin (for “transphilic” acids) were analyzed by asymmetrical flow field-flow fractionation (AsFlFFF). SR samples were compared with DOM samples from Nelson's Creek (NLC), a wetland-draining stream in northern Michigan; previous International Humic Substances Society (IHSS) FA and RO samples from the SR; and an XAD-8 sample from Lake Fryxell (LF), Antarctica. Despite application of cation exchange during sample processing, all XAD and RO samples contained substantial metal concentrations. AsFlFFF fractograms allowed metal distributions to be characterized as a function of DOM component molecular weight (MW). In SR RFSW, Fe, Al, and Cu were primarily associated with intermediate to higher than average MW DOM components. SR RO, XAD-8, and XAD-4 samples from May 2012 showed similar MW trends for Fe and Al but Cu tended to associate more with lower MW DOM. LF DOM had abundant Cu and Zn, perhaps due to amine groups that should be present due to its primarily algal origins. None of the fractograms showed obvious evidence for mineral nanoparticles, although some very small mineral nanoparticles might have been present at trace concentrations. This research suggests that AsFlFFF is important for understanding how metals are distributed in different DOM samples (including IHSS samples), which may be key to metal reactivity and bioavailability.

Georgia↗

USGS2022

Elevating human dimensions of amphibian and reptile conservation, a USA perspective

Increasing threats to amphibian and reptile species raise the urgency of their conservation. However, relative to other vertebrate groups at risk, amphibians and reptiles have low and more variable social capital; they are not generally high-priority natural goods and services valued by people. Consequently, relative to other groups such as birds, mammals, and economically important fish, they garner fewer conservation resources. With increasing risks, their situation degrades. We examine five societal sectors with herpetofaunal conservation interests in the United States (local communities, people in defined geographies and jurisdictions, species and threat specialists and advocates, associated researchers, managers, and policy makers) to understand challenges of low and variable social capital for herpetofauna. With current trends of US public values changing from traditionalist consumerism of wildlife to mutualist coexistence philosophies, a refocus of outreach and inreach efforts could help reframe priorities toward species at greatest risk, rather than broad taxonomic biases. Integrated teams of engaged natural resource managers, researchers, and the interested public can help promote species- and issue-based programs to forestall losses, hence programmatically raising social capital. Heightened recognition of the importance of human relationships and herpetofaunal diversity among researchers, managers, policy makers, educators, artists, authors, citizens, and children could provide inertia to reframe conservation program effectiveness at local-to-national scales.

Conservation Science and Practice↗

USGS2024

The state of the bats in North America

The world's rich diversity of bats supports healthy ecosystems and important ecosystem services. Maintaining healthy biological systems requires prompt identification of threats to biodiversity and immediate action to protect species, which for wide-ranging bat species that span geopolitical boundaries warrants international coordination. Anthropogenic forces drive the threats to bats throughout North America and the world. We conducted an international expert elicitation to assess the status of 153 bat species in Canada, the United States, and Mexico. We used expert assessment to determine the conservation status, highest impact threats, and recent population trends for these species. We found that 53% of North American bat species have moderate to very high risk of extinction in the next 15 years. The highest impact threats varied with species and country, and four IUCN threat categories had the greatest overall impacts: Climate Change, Problematic Species (including disease), Agriculture, and Energy Production. Experts estimated that 90% of species assessed had decreasing population trends over the past 15 years, demonstrating the need for conservation action. Although the state of North American bats is concerning, we identify threats that can be addressed through internationally collaborative, proactive, and protective actions to support the recovery and resilience of North American bat species.

Annals of the New York Academy of Sciences↗

USGS2008

Occurrence, distribution and transport of pesticides into the Salton Sea Basin, California, 2001-2002

The Salton Sea is a hypersaline lake located in southeastern California. Concerns over the ecological impacts of sediment quality and potential human exposure to dust emissions from exposed lakebed sediments resulting from anticipated shrinking of shoreline led to a study of pesticide distribution and transport within the Salton Sea Basin, California, in 2001-2002. Three sampling stations-upriver, river mouth, and offshore-were established along each of the three major rivers that discharge into the Salton Sea. Large-volume water samples were collected for analysis of pesticides in water and suspended sediments at the nine sampling stations. Samples of the bottom sediment were also collected at each site for pesticide analysis. Sampling occurred in October 2001, March-April 2002, and October 2002, coinciding with the regional fall and spring peaks in pesticide use in the heavily agricultural watershed. Fourteen current-use pesticides were detected in water and the majority of dissolved concentrations ranged from the limits of detection to 151 ng/l. Diazinon, EPTC and malathion were detected at much higher concentrations (940-3,830 ng/l) at the New and Alamo River upriver and near-shore stations. Concentrations of carbaryl, dacthal, diazinon, and EPTC were higher in the two fall sampling periods, whereas concentrations of atrazine, carbofuran, and trifluralin were higher during the spring, which matched seasonal use patterns of these pesticides. Current-use pesticides were also detected on suspended and bed sediments in concentrations ranging from detection limits to 106 ng/g. Chlorpyrifos, dacthal, EPTC, trifluralin, and DDE were the most frequently detected pesticides on sediments from all three rivers. The number of detections and concentrations of suspended sediment-associated pesticides were often similar for the river upriver and near-shore sites, consistent with downstream transport of pesticides via suspended sediment. While detectable suspended sediment pesticide concentrations were more sporadic than detected aqueous concentrations, seasonal trends were similar to those for dissolved concentrations. Generally, the pesticides detected on suspended sediments were the same as those on the bed sediments, and concentrations were similar, especially at the Alamo River upriver site. With a few exceptions, pesticides were not detected in suspended or bed sediments from the off-shore sites. The partitioning of pesticides between water and sediment was not predictable from solely the physical-chemical properties of individual pesticide compounds, but appear to be a complicated function of the quantity of pesticide applied in the watershed, residence time of sediments in the water, and compound solubility and hydrophobicity. Sediment concentrations of most pesticides were found to be 100-1,000 times lower than the low-effects levels determined in human health risk assessment studies. However, maximum concentrations of chlorpyrifos on suspended sediments were approximately half the low-effects level, suggesting the need for further sediment characterization of lake sediments proximate to riverine inputs. ?? 2008 Springer Science+Business Media B.V.

Hydrobiologia↗

USGS2012

Over 100 years of environmental change recorded by foraminifers and sediments in a large Gulf of Mexico estuary, Mobile Bay, AL, USA

The marine microfauna of Mobile Bay has been profoundly influenced by the development and expansion of the primary shipping channel over the last ∼100 years. Foraminifers and sediments from seven box cores with excess lead-210 chronology document that channel dredging and spoil disposal have altered circulation, reduced estuarine mixing, changed sedimentation patterns, and caused a faunal turnover within the bay. Beginning in the late 1800s, changes in estuarine mixing allowed for greater low-pH freshwater influence in the bay, and ultimately began environmental changes that resulted in the loss of calcareous foraminifers. By the early 1900s, box cores throughout Mobile Bay record a ∼100-year trend of increasing calcareous test dissolution that continues to the present. Since the completion of the current shipping channel in the 1950s, restricted tidal flushing and increased terrestrial organic matter, documented by carbon-to-nitrogen ratios, stimulated an increase in agglutinated foraminiferal densities. However, in deeper areas of the bay, hypoxic water has negatively impacted the marine microfauna. Comparisons of the present-day foraminiferal assemblage with foraminifers collected in the early 1970s indicate that the continued biologic loss of calcareous foraminifers in the bay has allowed the introduction of a new agglutinated foraminiferal species into the bay.

Alabama↗

USGS2018

Chesapeake Bay's water quality condition has been recovering: Insights from a multimetric indicator assessment of thirty years of tidal monitoring data

To protect the aquatic living resources of Chesapeake Bay, the Chesapeake Bay Program partnership has developed guidance for state water quality standards, which include ambient water quality criteria to protect designated uses (DUs), and associated assessment procedures for dissolved oxygen (DO), water clarity/underwater bay grasses, and chlorophyll-a. For measuring progress toward meeting the respective states' water quality standards, a multimetric attainment indicator approach was developed to estimate combined standards attainment. We applied this approach to three decades of monitoring data of DO, water clarity/underwater bay grasses, and chlorophyll-a data on annually updated moving 3-year periods to track the progress in all 92 management segments of tidal waters in Chesapeake Bay. In 2014–2016, 40% of tidal water segment-DU-criterion combinations in the Bay (n = 291) are estimated to meet thresholds for attainment of their water quality criteria. This index score marks the best 3-year status in the entire record. Since 1985–1987, the indicator has followed a nonlinear trajectory, consistent with impacts from extreme weather events and subsequent recoveries. Over the period of record (1985–2016), the indicator exhibited a positive and statistically significant trend ( p < 0.05), indicating that the Bay has been recovering since 1985. Patterns of attainment of individual DUs are variable, but improvements in open water DO, deep channel DO, and water clarity/submerged aquatic vegetation have combined to drive the improvement in the Baywide indicator in 2014–2016 relative to its long-term median. Finally, the improvement in estimated Baywide attainment was statistically linked to the decline of total nitrogen, indicating responsiveness of attainment status to the reduction of nutrient load through various management actions since at least the 1980s.

Chesapeake Bay watershed↗

USGS2019

Recent trends in nutrient and sediment loading to coastal areas of the conterminous U.S.: Insights and global context

Coastal areas in the U.S. and worldwide have experienced massive population and land use changes contributing to significant degradation of coastal ecosystems. Excess nutrient pollution causes coastal ecosystem degradation, and both regulatory and management efforts have targeted reducing nutrient and sediment loading to coastal rivers. Decadal trends in flow-normalized nutrient and sediment loads were determined for 95 monitoring locations on 88 U.S. coastal rivers, including tributaries of the Great Lakes, between 2002 and 2012 for nitrogen (N), phosphorus (P), and sediment. N and P loading from urban watersheds generally decreased between 2002 and 2012. In contrast, N and P trends in agricultural watersheds were variable indicating uneven progress in decreasing nutrient loading. Coherent decreases in N loading from agricultural watersheds occurred in the Lake Erie basin, but limited benefit is expected from these changes because P is the primary driver of degradation in the lake. Nutrient loading from undeveloped watersheds was low, but increased between 2002 and 2012, possibly indicating degradation of coastal watersheds with a lower intensity of anthropogenic influence. Regional differences in trends were evident, with stable nutrient loads from the Mississippi River to the Gulf of Mexico, but commonly decreasing N loads and increasing P loads in Chesapeake Bay. Compared to global rivers, coastal rivers of the conterminous U.S have somewhat lower TN yields and slightly higher TP yields, but similarities exist among land use, nutrient sources, and changes in nutrient loads. Despite widespread decreases in N loading in coastal watersheds, recent N:P ratios remained elevated compared to historic values in many areas. Additional progress in reducing N and P loading to U.S. coastal waters, particularly outside of urban areas, would benefit coastal ecosystems.

Science of the Total Environment↗

USGS1999

Variation in net trophic transfer efficiencies among 21 PCB congeners

We tested the hypothesis that the efficiency with which fish retain polychlorinated biphenyl (PCB) congeners from their food strongly depends on K ow and degree of chlorination of the congener. We used diet information, determinations of concentrations of individual PCB congeners in both coho salmon ( Oncorhynchus kisutch ) and their prey, and bioenergetics modeling to estimate the efficiencies with which Lake Michigan coho salmon retain various PCB congeners from their food. The retention efficiency for the tetrachloro congeners averaged 38%, whereas retention efficiencies for higher chlorinated congeners ranged from 43 to 56%. Not including tetrachloro congeners, we found neither decreasing nor increasing trends in the efficiencies with which the coho salmon retained the PCB congeners from their food with either increasing K ow or increasing degree of chlorination of the PCB congeners. We concluded that (a) for PCB congeners with 5−8 chlorine atoms/molecule, K ow and degree of chlorination had little influence on the efficiency with which coho salmon retained the various PCB congeners in their food, and (b) the efficiency with which coho salmon retained tetrachloro PCB congeners in their food appeared to be slightly lower than that for higher chlorinated PCB congeners.

Environmental Science & Technology↗

USGS2024

The dominance and growth of shallow groundwater resources in continuous permafrost environments

Water is a limited resource in Arctic watersheds with continuous permafrost because freezing conditions in winter and the impermeability of permafrost limit storage and connectivity between surface water and deep groundwater. However, groundwater can still be an important source of surface water in such settings, feeding springs and large aufeis fields that are abundant in cold regions and generating runoff when precipitation is rare. Whether groundwater is sourced from suprapermafrost taliks or deeper regional aquifers will impact water availability as the Arctic continues to warm and thaw. Previous research is ambiguous about the role of deep groundwater, leading to uncertainty regarding Arctic water availability and changing water resources. We analyzed chemistry and residence times of spring, stream, and river waters in the continuous permafrost zone of Alaska, spanning the mountains to the coastal plain. Water chemistry and age tracers show that surface waters are predominately sourced from recent precipitation and have short (<50 y) subsurface residence times. Remote sensing indicates trends in the areal extent of aufeis over the last 37 y, and correlations between aufeis extent and previous year summer temperature. Together, these data indicate that surface waters in continuous permafrost regions may be impacted by short flow paths and shallow suprapermafrost aquifers that are highly sensitive to climatic and hydrologic change over annual timescales. Despite the lack of connection to regional aquifers, continued warming and permafrost thaw may promote deepening of the shallow subsurface aquifers and creation of shallow taliks, providing some resilience to Arctic freshwater ecosystems.

Proceedings of the National Academy of Sciences↗