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At least 1,243 records · Page 69Linked to original sources
USGS2004

Methods for the preparation and analysis of solids and suspended solids for total mercury

The methods documented in this report are utilized by the Wisconsin District Mercury Lab for analysis of total mercury in solids (soils and sediments) and suspended solids (isolated on filters). Separate procedures are required for the different sample types. For solids, samples are prepared by room-temperature acid digestion and oxidation with aqua regia. The samples are brought up to volume with a 5 percent bromine monochloride solution to ensure complete oxidation and heated at 50C in an oven overnight. Samples are then analyzed with an automated flow injection system incorporating a cold vapor atomic fluorescence spectrometer. A method detection limit of 0.3 ng of mercury per digestion bomb was established using multiple analyses of an environmental sample. Based on the range of masses processed, the minimum sample reporting limit varies from 0.6 ng/g to 6 ng/g. Suspended solids samples are oxidized with a 5 percent bromine monochloride solution and held at 50?C in an oven for 5 days. The samples are then analyzed with an automated flow injection system incorporating a cold vapor atomic fluorescence spectrometer. Using a certified reference material as a surrogate for an environmental sample, a method detection limit of 0.059 ng of mercury per filter was established. The minimum sample reporting limit varies from 0.059 ng/L to 1.18 ng/L, depending on the volume of water filtered.

Techniques and Methods↗
USGS2024

Variability in weather and site properties affect fuel and fire behavior following fuel treatments in semiarid sagebrush-steppe.

Fuel-treatments targeting shrubs and fire-prone exotic annual grasses (EAGs) are increasingly used to mitigate increased wildfire risks in arid and semiarid environments, and understanding their response to natural factors is needed for effective landscape management. Using field-data collected over four years from fuel-break treatments in semiarid sagebrush-steppe, we asked 1) how the outcomes of EAG and sagebrush fuel treatments varied with site biophysical properties, climate, and weather, and 2) how predictions of fire behavior using the Fuel Characteristic Classification System fire model related to land-management objectives of maintaining fire behavior expected of low-load, dry-climate grasslands. Generalized linear mixed effect modeling with build-up model selection was used to determine best-fit models, and marginal effects plots to assess responses for each fuel type. EAG cover decreased as antecedent-fall precipitation increased and increased as antecedent-spring temperatures and surface soil clay contents increased. Herbicides targeting EAGs were less effective where pre-treatment EAG cover was >40 % and antecedent spring temperatures were >9.5 °C. Sagebrush cover was inversely related to soil clay content, especially where clay contents were >17 %. Predicted fire behavior exceeded management objectives under 1) average fire weather conditions when EAG or sagebrush cover was >50 % or >26 %, respectively, or 2) extreme fire weather conditions when EAG or sagebrush cover was >10 % or >8 %, respectively. Consideration of the strong effects of natural variability in site properties and antecedent weather can help in justifying, planning and implementing fuel-treatments.

Idaho, Oregon↗
USGS2016

Conditional vulnerability of plant diversity to atmospheric nitrogen deposition across the United States

Atmospheric nitrogen (N) deposition has been shown to decrease plant species richness along regional deposition gradients in Europe and in experimental manipulations. However, the general response of species richness to N deposition across different vegetation types, soil conditions, and climates remains largely unknown even though responses may be contingent on these environmental factors. We assessed the effect of N deposition on herbaceous richness for 15,136 forest, woodland, shrubland, and grassland sites across the continental United States, to address how edaphic and climatic conditions altered vulnerability to this stressor. In our dataset, with N deposition ranging from 1 to 19 kg N⋅ha−1⋅y−1, we found a unimodal relationship; richness increased at low deposition levels and decreased above 8.7 and 13.4 kg N⋅ha−1⋅y−1 in open and closed-canopy vegetation, respectively. N deposition exceeded critical loads for loss of plant species richness in 24% of 15,136 sites examined nationwide. There were negative relationships between species richness and N deposition in 36% of 44 community gradients. Vulnerability to N deposition was consistently higher in more acidic soils whereas the moderating roles of temperature and precipitation varied across scales. We demonstrate here that negative relationships between N deposition and species richness are common, albeit not universal, and that fine-scale processes can moderate vegetation responses to N deposition. Our results highlight the importance of contingent factors when estimating ecosystem vulnerability to N deposition and suggest that N deposition is affecting species richness in forested and nonforested systems across much of the continental United States.

PNAS↗
USGS2022

What is a biocrust? A refined, contemporary definition for a broadening research community

Studies of biological soil crusts (biocrusts) have proliferated over the last few decades. The biocrust literature has broadened, with more studies assessing and describing the function of a variety of biocrust communities in a broad range of biomes and habitats and across a large spectrum of disciplines, and also by the incorporation of biocrusts into global perspectives and biogeochemical models. As the number of biocrust researchers increases, along with the scope of soil communities defined as ‘biocrust’, it is worth asking whether we all share a clear, universal, and fully articulated definition of what constitutes a biocrust. In this review, we synthesize the literature with the views of new and experienced biocrust researchers, to provide a refined and fully elaborated definition of biocrusts. In doing so, we illustrate the ecological relevance and ecosystem services provided by them. We demonstrate that biocrusts are defined by four distinct elements: physical structure, functional characteristics, habitat, and taxonomic composition. We describe outgroups, which have some, but not all, of the characteristics necessary to be fully consistent with our definition and thus would not be considered biocrusts. We also summarize the wide variety of different types of communities that fall under our definition of biocrusts, in the process of highlighting their global distribution. Finally, we suggest the universal use of the Belnap, Büdel & Lange definition, with minor modifications: Biological soil crusts (biocrusts) result from an intimate association between soil particles and differing proportions of photoautotrophic (e.g. cyanobacteria , algae , lichens , bryophytes) and heterotrophic (e.g. bacteria , fungi , archaea) organisms , which live within , or immediately on top of , the uppermost millimetres of soil. Soil particles are aggregated through the presence and activity of these often extremotolerant biota that desiccate regularly , and the resultant living crust covers the surface of the ground as a coherent layer. With this detailed definition of biocrusts, illustrating their ecological functions and widespread distribution, we hope to stimulate interest in biocrust research and inform various stakeholders (e.g. land managers, land users) on their overall importance to ecosystem and Earth system functioning.

Biological Reviews↗
USGS2004

Water quality in Big Cypress National Preserve and Everglades National Park — Trends and spatial characteristics of selected constituents

Seasonal changes in water levels and flows in Big Cypress National Preserve (BICY) and Everglades National Park (EVER) affect water quality. As water levels and flows decline during the dry season, physical, geochemical and biological processes increase the breakdown of organic materials and the build-up of organic waste, nutrients, and other constituents in the remaining surface water. For example, concentrations of total phosphorus in the marsh are less than 0.01 milligram per liter (mg/L) during much of the year. Concentrations can rise briefly above this value during the dry season and occasionally exceed 0.1 mg/L under drought conditions. Long-term changes in water levels, flows, water management, and upstream land use also affect water quality in BICY and EVER, based on analysis of available data (1959-2000). During the 1980's and early 1990's, specific conductance and concentrations of chloride increased in the Taylor Slough and Shark River Slough. Chloride concentrations more than doubled from 1960 to 1990, primarily due to greater canal transport of high dissolved solids into the sloughs. Some apparent long-term trends in sulfate and total phosphorus were likely attributable, at least in part, to high percentages of less-than and zero values and to changes in reporting levels over the period of record. High values in nutrient concentrations were evident during dry periods of the 1980's and were attributable either to increased canal inflows of nutrient-rich water, increased nutrient releases from breakdown of organic bottom sediment, or increased build-up of nutrient waste from concentrations of aquatic biota and wildlife in remaining ponds. Long-term changes in water quality over the period of record are less pronounced in the western Everglades and the Big Cypress Swamp; however, short-term seasonal and drought-related changes are evident. Water quality varies spatially across the region because of natural variations in geology, hydrology, and vegetation and because of differences in water management and land use. Nutrient concentrations are relatively low in BICY and EVER compared with concentrations in parts of the northern Everglades that are near agricultural and urban lands. Concentrations of total phosphorus generally are higher in BICY (median values, 1991-2000, were mostly greater than 0.015 mg/L) than in EVER (median values, 1991-2000, less than 0.01 mg/L), probably because of higher phosphorus in natural sources such as shallow soils, rocks, and ground water in the Big Cypress region than in the Everglades region. Conversely, concentrations of chloride and sulfate are higher in EVER (median values in Shark River Slough, 1991-2000, mostly greater than 2 mg/L sulfate and 50 mg/L chloride) than in BICY (median values, 1991-2000, less than 1 mg/L sulfate and at most sites less than 20 mg/L chloride), probably because of the canal transport system, which conveys more water from an agricultural source into EVER than into BICY. Trace elements and contaminants such as pesticides and other toxic organic compounds are in relatively low concentrations in BICY and EVER compared with concentrations in parts of the northern Everglades near agricultural and urban sources. Concentrations rarely exceeded aquatic life criteria in BICY and EVER. Atrazine was the only pesticide found in water that exceeded the criteria (in 2 out of 304 samples). The pesticides heptachlor expoxide, lindane, and p,p?-DDE exceeded criteria in canal bed sediments in 1, 2, and 16 percent of the samples, respectively.

Florida↗
USGS2009

Introduction to special section on impacts of land use change on water resources

Changes in land use have potentially large impacts on water resources, yet quantifying these impacts remains among the more challenging problems in hydrology. Water, food, energy, and climate are linked through complex webs of direct and indirect effects and feedbacks. Land use is undergoing major changes due not only to pressures for more efficient food, feed, and fiber production to support growing populations but also due to policy shifts that are creating markets for biofuel and agricultural carbon sequestration. Hydrologic systems embody flows of water, solutes, sediments, and energy that vary even in the absence of human activity. Understanding land use impacts thus necessitates integrated scientific approaches. Field measurements, remote sensing, and modeling studies are shedding new light on the modes and mechanisms by which land use changes impact water resources. Such studies can help deconflate the interconnected influences of human actions and natural variations on the quantity and quality of soil water, surface water, and groundwater, past, present, and future.

Water Resources Research↗
USGS2009

The changing global carbon cycle: Linking plant-soil carbon dynamics to global consequences

Most current climate-carbon cycle models that include the terrestrial carbon (C) cycle are based on a model developed 40 years ago by Woodwell & Whittaker (1968) and omit advances in biogeochemical understanding since that time. Their model treats net C emissions from ecosystems as the balance between net primary production (NPP) and heterotrophic respiration (HR, i.e. primarily decomposition). Under conditions near steady state, geographic patterns of decomposition closely match those of NPP, and net C emissions are adequately described as a simple balance of NPP and HR (the Woodwell-Whittaker model). This close coupling between NPP and HR occurs largely because of tight coupling between C and N (nitrogen) cycles and because NPP constrains the food available to heterotrophs. Processes in addition to NPP and HR become important to understanding net C emissions from ecosystems under conditions of rapid changes in climate, hydrology, atmospheric CO 2 , land cover, species composition and/or N deposition. Inclusion of these processes in climate-C cycle models would improve their capacity to simulate recent and future climatic change. Processes that appear critical to soil C dynamics but warrant further research before incorporation into ecosystem models include below-ground C flux and its partitioning among roots, mycorrhizas and exudates; microbial community effects on C sequestration; and the effects of temperature and labile C on decomposition. The controls over and consequences of these processes are still unclear at the ecosystem scale. Carbon fluxes in addition to NPP and HR exert strong influences over the climate system under conditions of rapid change. These fluxes include methane release, wildfire, and lateral transfers of food and fibre among ecosystems. Water and energy exchanges are important complements to C cycle feedbacks to the climate system, particularly under non-steady-state conditions. An integrated understanding of multiple ecosystem-climate feedbacks provides a strong foundation for policies to mitigate climate change. Synthesis . Current climate systems models that include only NPP and HR are inadequate under conditions of rapid change. Many of the recent advances in biogeochemical understanding are sufficiently mature to substantially improve representation of ecosystem C dynamics in these models.

Journal of Ecology↗
USGS1996

Regional evaluation of evapotranspiration in the Everglades

Understanding the water budget of the Everglades system is crucial to the success of restoration and management strategies. Although the water budget is simple in concept, it is difficult to assess quantitatively. Models used to simulate changes in water levels and vegetation resulting from management strategies need to accurately simulate all components of the water budget. One of the most important components of the Everglades water budget is evapotranspiration (ET). ET is water removed from the surface and soils by direct evaporation and plant transpiration. In South Florida, ET rates may exceed 40 in/yr (inches per year) on the average; during dry years, the ET could exceed rainfall (about 50 in/yr). Thus, most of the water that falls on the land surface as rainfall is returned to the atmosphere by ET. Despite the importance of ET in the Everglades water budget, our knowledge of ET is, at present, only semi-quantitative. Recent advances in instrumentation and measurement techniques have made it possible to continuously measure ET, so that an accurate evaluation of ET in the Everglades can be made.

Florida↗
USGS2007

An Online Interactive Map Service for Displaying Ground-Water Conditions in Arizona

Monitoring the availability of the nation's ground-water supplies is of critical importance to planners and water managers. The general public also has an interest in understanding the status of ground-water conditions, especially in the semi-arid Southwestern United States where much of the water used by municipalities and agriculture comes from the subsurface. Unlike surface-water indicators such as stage or discharge, ground-water conditions may be more difficult to assess and present. Individual well observations may only represent conditions in a limited area surrounding the well and wells may be screened over single or multiple aquifers, further complicating single-well measurement interpretations. Additionally, changes in ground-water conditions may involve time scales ranging from days to many years, depending on recharge, soil properties and depth to the water table. This lack of an easily identifiable ground-water property indicative of current conditions combined with differing time scales of water-level changes makes the presentation of ground-water conditions a difficult task, particularly on a regional basis. One approach is to spatially present several indicators of ground-water conditions that address different time scales and attributes of the aquifer systems. In this report, we describe a publicly-available online interactive map service that presents several different layers of ground-water-conditions information for the alluvial basins in the Lower Colorado River Basin in Arizona (http://montezuma.wr.usgs.gov/website/azgwconditions/). These data layers include wells experiencing water-level decline, wells experiencing water-level rise, recent trends in ground-water levels, change in water level since predevelopment and change in storage since predevelopment. Recent pumpage totals and projected population numbers are also provided for ground-water basins and counties in the region of the Lower Colorado River in Arizona along with a bibliography of U.S. Geological Survey reports for those seeking further information. The methods used to create these data layers are explained with illustrations of example information available on the Web site.

Open-File Report↗
USGS2006

Vulnerability of recently recharged ground water in the High Plains aquifer to nitrate contamination

Nitrate concentrations greater than background levels have been detected in ground water of the High Plains aquifer. Empirically based models and corresponding maps were developed that predict the vulnerability of the aquifer to nonpoint-source nitrate contamination. The models predict the probability of detecting nitrate concentrations larger than 4 milligrams per liter in ground water of the High Plains aquifer that was recharged during the last 50 years. The models were calibrated by correlating concentrations of nitrate in ground water from 336 wells that intercept recently recharged (less than 50 years) water with anthropogenic and hydrogeologic explanatory variables. Particle-tracking simulations delineated well-contributing areas and determined well-screen depths that intercept recently recharged ground water. The models were developed using multivariate logistic regression, and a map was generated from these models using a geographic information system. Two multivariate logistic regression models of vulnerability were found to have the most statistical significance and the best model fit and predictive ability. The two models represent the Northern High Plains and the combined Central and Southern High Plains, and they indicate that ground-water vulnerability of the entire High Plains aquifer is best explained by the spatial distribution of nonirrigated and irrigated agricultural lands, organic matter of the soil, depth to the regional water table, and clay content of the unsaturated zone. Vulnerability of the Northern High Plains is greater in areas that have more nonirrigated and irrigated agricultural lands and less organic matter in the soil. The vulnerability of the Central and Southern High Plains also is greater in areas that have more nonirrigated and irrigated agricultural lands and also in areas with shallow depths to water table and less clay in the unsaturated zone. The majority (53.3 percent) of the High Plains aquifer has less than a 40-percent predicted probability of nitrate concentrations larger than 4 milligrams per liter. Approximately 21.1 percent of the High Plains aquifer has a relatively high (greater than 60 percent) predicted probability of nitrate concentrations greater than or equal to 4 milligrams per liter. Areas with relatively high predicted probability are located in the southwestern, southern, and eastern areas of the Northern High Plains, in the eastern arm of the Central High Plains, and in southern areas of the Southern High Plains. Areas of the aquifer with relatively low (less than 40 percent) predicted vulnerability to nitrate concentrations greater than or equal to 4 milligrams per liter are located in the northwestern and north-central areas of the Northern High Plains, the central and southern areas of the Central High Plains, and a band across the north-central part of the Southern High Plains. Uncertainty of these vulnerability predictions was estimated by Latin hypercube sampling to address propagation of model and data errors inherently associated with estimates of model coefficients and explanatory variables. Results of the Latin hypercube sampling simulations are presented as uncertainty maps of the lower 5th and upper 95th percentile of the output probability distribution, which represents the 90-percent prediction interval that contains the true probability of detecting nitrate greater than or equal to 4 milligrams per liter. Generally, these uncertainty maps show greater prediction uncertainty in areas with relatively higher predicted vulnerability and lower uncertainty in areas with relatively lower predicted vulnerability.

Scientific Investigations Report↗
USGS2004

Contemporary carbon dynamics in terrestrial ecosystems in the Southeastern Plains of the United States

Quantifying carbon dynamics over large areas is frequently hindered by the lack of consistent, high-quality, spatially explicit land use and land cover change databases and appropriate modeling techniques. In this paper, we present a generic approach to address some of these challenges. Land cover change information in the Southeastern Plains ecoregion was derived from Landsat data acquired in 1973, 1980, 1986, 1992, and 2000 within 11 randomly located 20-km × 20-km sample blocks. Carbon dynamics within each of the sample blocks was simulated using the General Ensemble Biogeochemical Modeling System (GEMS), capable of assimilating the variances and covariance of major input variables into simulations using an ensemble approach. Results indicate that urban and forest areas have been increasing, whereas agricultural land has been decreasing since 1973. Forest clear-cutting activity has intensified, more than doubling from 1973 to 2000. The Southeastern Plains has been acting as a carbon sink since 1973, with an average rate of 0.89 Mg C/ha/yr. Biomass, soil organic carbon (SOC), and harvested materials account for 56%, 34%, and 10% of the sink, respectively. However, the sink has declined continuously during the same period owing to forest aging in the northern part of the ecoregion and increased forest clear-cutting activities in the south. The relative contributions to the sink from SOC and harvested materials have increased, implying that these components deserve more study in the future. The methods developed here can be used to quantify the impacts of human management activities on the carbon cycle at landscape to global scales.

Environmental Management↗
USGS2000

Sources and haloacetic acid/trihalomethane formation potentials of aquatic humic substances in the Wakarusa River and Clinton Lake near Lawrence, Kansas

Gram quantities of aquatic humic substances (AHS) were extracted from the Wakarusa River−Clinton Lake Reservoir system, near Lawrence, KS, to support nuclear magnetic resonance (NMR) experimental studies, report concentrations of dissolved organic carbon (DOC) and AHS, define sources of the AHS, and determine if the AHS yield sufficient quantities of haloacetic acids (HAA5) and trihalomethanes (THM4) that exceed U.S. Environmental Protection Agency (EPA) Maximum Contaminant Levels (MCL) in drinking water. AHS from the Wakarusa River and Clinton Lake originated from riparian forest vegetation, reflected respective effects of soil organic matter and aquatic algal/bacterial sources, and bore evidence of biological degradation and photodegradation. AHS from the Wakarusa River showed the effect of terrestrial sources, whereas Clinton Lake humic acid also reflected aquatic algal/bacterial sources. Greater amounts of carbon attributable to tannin-derived chemical structures may correspond with higher HAA5 and THM4 yields for Clinton Lake fulvic acid. Prior to appreciable leaf-fall from deciduous trees, the combined (humic and fulvic acid) THM4 formation potentials for the Wakarusa River approached the proposed EPA THM4 Stage I MCL of 80 μg/L, and the combined THM4 formation potential for Clinton Lake slightly exceeded the proposed THM4 Stage II MCL of 40 μg/L. Finally, AHS from Clinton Lake could account for most (>70%) of the THM4 concentrations in finished water from the Clinton Lake Water Treatment Plant based on September 23, 1996, THM4 results.

Environmental Science & Technology↗
USGS2025

American alligators (Alligator mississippiensis) as wetland ecosystem carbon stock regulators

Blue carbon refers to organic carbon sequestered by oceanic and coastal ecosystems. This stock has gained global attention as a high organic carbon repository relative to other ecosystems. Within blue carbon ecosystems, tidally influenced wetlands alone store a disproportionately higher amount of organic carbon than other blue carbon systems. North America harbors 42% of tidally influenced global wetland area, which has been identified as a critical carbon stock in the context of climate change mitigation. However, quantified associations between vertebrate biota and carbon sequestration within ecosystems are in their infancy and have been incidental, given that microbial trophic levels are thought to drive nutrient dynamics. Here, we assess the relationship between American alligator ( Alligator mississippiensis ) demography and tidally influenced wetland soil carbon stock among habitats at continental, biogeographically-relevant, and local scales. We used soil core profile data from the Smithsonian’s Coastal Carbon Network and filtered for continuous core profiles in tidally influenced wetland areas along the Gulf and Atlantic Coasts of the United States. Results indicate that American alligator presence is positively correlated with soil carbon stock across habitats within their native distribution. Further, American alligator demographic variables are positively correlated with soil carbon stock at local scales. These conclusions are concordant with previous findings that apex predators, through trophic cascade theory, play a key role in regulating soil carbon stock and that alligators are functional apex predators in carbon dynamics and a key commercialized natural resource.

Connecticut, Delaware, Florida, Georgia, Louisiana↗
USGS2014

A precipitation-runoff model for simulating natural streamflow conditions in the Smith River watershed, Montana, water years 1996-2008

This report documents the construction of a precipitation-runoff model for simulating natural streamflow in the Smith River watershed, Montana. This Precipitation-Runoff Modeling System model, constructed in cooperation with the Meagher County Conservation District, can be used to examine the general hydrologic framework of the Smith River watershed, including quantification of precipitation, evapotranspiration, and streamflow; partitioning of streamflow between surface runoff and subsurface flow; and quantifying contributions to streamflow from several parts of the watershed. The model was constructed by using spatial datasets describing watershed topography, the streams, and the hydrologic characteristics of the basin soils and vegetation. Time-series data (daily total precipitation, and daily minimum and maximum temperature) were input to the model to simulate daily streamflow. The model was calibrated for water years 2002–2007 and evaluated for water years 1996–2001. Though water year 2008 was included in the study period to evaluate water-budget components, calibration and evaluation data were unavailable for that year. During the calibration and evaluation periods, simulated-natural flow values were compared to reconstructed-natural streamflow data. These reconstructed-natural streamflow data were calculated by adding Bureau of Reclamation’s depletions data to the observed streamflows. Reconstructed-natural streamflows represent estimates of streamflows for water years 1996–2007 assuming there was no agricultural water-resources development in the watershed. Additional calibration targets were basin mean monthly solar radiation and potential evapotranspiration. The model estimated the hydrologic processes in the Smith River watershed during the calibration and evaluation periods. Simulated-natural mean annual and mean monthly flows generally were the same or higher than the reconstructed-natural streamflow values during the calibration period, whereas they were lower during the evaluation period. The shape of the annual hydrographs for the simulated-natural daily streamflow values matched the shape of the hydrographs for the reconstructed-natural values for most of the calibration period, but daily streamflow values were underestimated during the evaluation period for water years 1996–1998. The model enabled a detailed evaluation of the components of the water budget within the Smith River watershed during the water year 1996–2008 study period. During this study period, simulated mean annual precipitation across the Smith River watershed was 16 inches, out of which 14 inches evaporated or transpired and 2 inches left the basin as streamflow. Per the precipitation-runoff model simulations, during most of the year, surface runoff rarely (less than 2 percent of the time during water years 2002–2008) makes up more than 10 percent of the total streamflow. Subsurface flow (the combination of interflow and groundwater flow) makes up most of the total streamflow (99 or more percent of total streamflow for 71 percent of the time during water years 2002–2008).

Montana↗
USGS2003

Stream Bank Stability in Eastern Nebraska

Dredged and straightened channels in eastern Nebraska have experienced degradation leading to channel widening by bank failure. Degradation has progressed headward and affected the drainage systems upstream from the modified reaches. This report describes a study that was undertaken to analyze bank stability at selected sites in eastern Nebraska and develop a simplified method for estimating the stability of banks at future study sites. Bank cross sections along straight reaches of channel and geotechnical data were collected at approximately 150 sites in 26 counties of eastern Nebraska. The sites were categorized into three groups based on mapped soil permeability. With increasing permeability of the soil groups, the median cohesion values decreased and the median friction angles increased. Three analytical methods were used to determine if banks were stable (should not fail even when saturated), at risk (should not fail unless saturated), or unstable (should have already failed). The Culmann and Agricultural Research Service methods were based on the Coulomb equation and planar failure; an indirect method was developed that was based on Bishop's simplified method of slices and rotational failure. The maximum angle from horizontal at which the bank would be stable for the given soil and bank height conditions also was computed with the indirect method. Because of few soil shear-strength data, all analyses were based on the assumption of homogeneous banks, which was later shown to be atypical, at least for some banks. Using the Culmann method and assuming no soil tension cracks, 67 percent of all 908 bank sections were identified as stable, 32 percent were at risk, and 1 percent were unstable; when tension cracks were assumed, the results changed to 58 percent stable, 40 percent at risk, and 1 percent unstable. Using the Agricultural Research Service method, 67 percent of all bank sections were identified as stable and 33 percent were at risk. Using the indirect method, 62 percent of all bank sections were identified as stable and 31 percent were at risk; 3 percent were unstable, and 3 percent were outside of the range of the tables developed for the method. For each of the methods that were used, the largest percentage of stable banks and the smallest percentage of at risk banks was for the soil group with the lowest soil permeability and highest median cohesion values. A comparison of the expected stable bank angles for saturated conditions and the surveyed bank angles indicated that many of the surveyed bank angles were considerably less than the maximum expected stable bank angles despite the banks being classified as at risk or unstable. For severely degraded channels along straight reaches this was not expected. It was expected that they would have angles close to the maximum stable angle as they should have been failing from an oversteepened condition. Several explanations are possible. The channel reaches of some study sites have not yet been affected to a significant degree by degradation; study sites were selected throughout individual basins and severe degradation has not yet extended to some sites along upper reaches; and some reaches have experienced aggradation as degradation progresses upstream. Another possibility is that some bank sections have been affected by lateral migration processes, which typically result in shallow bank angles on the inside bend of the channel. Another possibility is that the maximum expected stable bank angles are too steep. The stability methods used were well established and in essential agreement with each other, and there was no reason to question the geometry data. This left non-representative soil data as a probable reason for computed stable bank angles that, at least in some cases, are overly steep. Based on an examination of the cohesion data, to which the stable bank-angle calculations were most sensitive, both vertical and horizontal variability in soil properti

Water-Resources Investigations Report↗
USGS2013

Influence of multi-source and multi-temporal remotely sensed and ancillary data on the accuracy of random forest classification of wetlands in northern Minnesota

Wetland mapping at the landscape scale using remotely sensed data requires both affordable data and an efficient accurate classification method. Random forest classification offers several advantages over traditional land cover classification techniques, including a bootstrapping technique to generate robust estimations of outliers in the training data, as well as the capability of measuring classification confidence. Though the random forest classifier can generate complex decision trees with a multitude of input data and still not run a high risk of over fitting, there is a great need to reduce computational and operational costs by including only key input data sets without sacrificing a significant level of accuracy. Our main questions for this study site in Northern Minnesota were: (1) how does classification accuracy and confidence of mapping wetlands compare using different remote sensing platforms and sets of input data; (2) what are the key input variables for accurate differentiation of upland, water, and wetlands, including wetland type; and (3) which datasets and seasonal imagery yield the best accuracy for wetland classification. Our results show the key input variables include terrain (elevation and curvature) and soils descriptors (hydric), along with an assortment of remotely sensed data collected in the spring (satellite visible, near infrared, and thermal bands; satellite normalized vegetation index and Tasseled Cap greenness and wetness; and horizontal-horizontal (HH) and horizontal-vertical (HV) polarization using L-band satellite radar). We undertook this exploratory analysis to inform decisions by natural resource managers charged with monitoring wetland ecosystems and to aid in designing a system for consistent operational mapping of wetlands across landscapes similar to those found in Northern Minnesota.

Minnesota↗
USGS2012

Modeling a thick unsaturated zone at San Gorgonio Pass, California: lessons learned after five years of artificial recharge

The information flow among the tasks of framework assessment, numerical modeling, model forecasting and hind casting, and system-performance monitoring is illustrated. Results provide an understanding of artificial recharge in high-altitude desert settings where large vertical distances may separate application ponds from their target aquifers. Approximately 3.8 million cubic meters of surface water was applied to spreading ponds from 2003–2007 to artificially recharge the underlying aquifer through a 200-meter thick unsaturated zone in the San Gorgonio Pass area in southern California. A study was conducted between 1997 and 2003, and a numerical model was developed to help determine the suitability of the site for artificial recharge. Ongoing monitoring results indicated that the existing model needed to be modified and recalibrated to more accurately predict artificial recharge at the site. The objective of this work was to recalibrate the model by using observation of the application rates, the rise and fall of the water level above a perching layer, and the approximate arrival time to the water table during the 5-yr monitoring period following initiation of long-term artificial recharge. Continuous monitoring of soil-matric potential, temperature, and water levels beneath the site indicated that artificial recharge reached the underlying water table between 3.75 and 4.5 yr after the initial application of the recharge water. The model was modified to allow the simulation to more adequately match the perching layer dynamics and the time of arrival at the water table. The instrumentation also showed that the lag time between changes in application of water at the surface and the response at the perching layer decreased from about 4 mo to less than 1 mo due to the wet-up of the unsaturated zone and the increase in relative permeability. The results of this study demonstrate the importance of iteratively monitoring and modeling the unsaturated zone in layered alluvial systems in the context of artificial recharge. They show that adequate geologic and hydraulic-property data on perching layers are critical to success. Continuous monitoring in the unsaturated and saturated zones beneath a site provides data to develop and constrain numerical models, better understand local unsaturated zone process, manage artificial recharge operations, and to determine the timing and volume of recoverable water for consumptive use.

California↗
USGS2011

Hydrology and biogeochemistry linkages

This chapter provides an overview of the linkages between hydrology and biogeochemistry in terrestrial and aquatic systems. Selected topics include hydrological pathways on drainage basin slopes, mountain environments, within-river (or in-stream) processes, wetlands, groundwater (and groundwater–surface water interactions), and lakes. Beginning from catchment headwaters, This chapter introduces mechanisms delivering water from hillslopes to stream channels, highlighting the relative importance of biogeochemical processes along hydrological pathways. It considers processes affecting components of the water budget, including snow formation and ablation processes, and interactions with the soil below snow cover and during snowmelt. It presents the concept of nutrient spiraling and the importance of temperature and stream flow variability on biogeochemistry, as well as groundwater–surface water interactions through hyporheic and riparian zones. This chapter contrasts important processes in hydrologically isolated wetlands with those temporally connected to streams and rivers. It addresses stream and groundwater inputs, stratification, and within-lake processes, interactions with sediments, and a discussion about limiting nutrients. This chapter presents information about typical reactions controlled by hydrological pathways, lithology (mineralogy) and biota, the importance of residence time in biogeochemical evolution, and linkages between groundwater Acidic atmospheric deposition

Book chapter↗