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At least 955 records · Page 53Linked to original sources
USGS2000

Pesticides in the atmosphere of the Mississippi River Valley, part I: Rain

Weekly composite rainfall samples were collected in three paired urban and agricultural regions of the Midwestern United States and along the Mississippi River during April–September 1995. The paired sampling sites were located in Mississippi, Iowa, and Minnesota. A background site, removed from dense urban and agriculture areas, was located near Lake Superior in Michigan. Herbicides were the predominant type of pesticide detected at every site. Each sample was analyzed for 47 compounds and 23 of 26 herbicides, 13 of 18 insecticides, and three of three related transformation products were detected in one or more sample from each paired site. The detection frequency of herbicides and insecticides were nearly equivalent at the paired Iowa and Minnesota sites. In Mississippi, herbicides were detected more frequently at the agricultural site and insecticides were detected more frequently at the urban site. The highest total wet depositional amounts (μg pesticide/m 2 per season) occurred at the agricultural sites in Mississippi (1980 μg/m 2 ) and Iowa (490 μg/m 2 ) and at the urban site in Iowa (696 μg/m 2 ). Herbicides accounted for the majority of the wet depositional loading at the Iowa and Minnesota sites, but methyl parathion (1740 μg/m 2 ) was the dominant compound contributing to the total loading at the agricultural site in Mississippi. Atrazine, CIAT (a transformation product of atrazine and propazine) and dacthal were detected most frequently (76, 53, and 53%, respectively) at the background site indicating their propensity for long-range atmospheric transport.

Mississippi River Valley↗
USGS2025

The US EPA’s National Nutrient Inventory: Critical shifts in US nutrient pollution sources from 1987 to 2017

Efforts to constrain the negative environmental impacts of excess nitrogen (N) and phosphorus (P) are costly and challenging, due in part to inconsistent reporting of nutrient sources at temporal and spatial scales relevant for local decision making. To meet this challenge, the U.S. Environmental Protection Agency’s National Nutrient Inventory provides estimates of major agricultural, urban, atmospheric, and natural nutrient fluxes for the contiguous United States at county and HUC12 scales annually from 1987 (from 1950 for agriculture) to 2017. Since the late 1980s, total N emissions and atmospheric N deposition have declined 22% and 15%, respectively, despite increased agricultural emissions. Over the same period, municipal wastewater N and P loads remained largely stable, despite population increases, through wastewater treatment upgrades and the phaseout of phosphorus-containing detergents. Improved agricultural efficiency allowed for dramatic increases in agricultural production and crop harvest since 1987 (∼25% for N and P), with little change in surplus nutrients left on fields. Overall, a combination of innovative technologies and management has stemmed or even decreased major sources of nutrient pollution to the environment over the last several decades, representing an important shift that, if continued, may contribute to improved air, land, and water quality and human health.

contiguous United States↗
USGS1998

Occurrence of pesticides in shallow groundwater of the United States: initial results from the National Water-Quality Assessment program

The first phase of intensive data collection for the National Water-Quality Assessment (NAWQA) was completed during 1993−1995 in 20 major hydrologic basins of the United States. Groundwater land-use studies, designed to sample recently recharged groundwater (generally within 10 years) beneath specific land-use and hydrogeologic settings, are a major component of the groundwater quality as sessment for NAWQA. Pesticide results from the 41 land-use studies conducted during 1993−1995 indicate that pesticides were commonly detected in shallow groundwater, having been found at 54.4% of the 1034 sites sampled in agricultural and urban settings across the United States. Pesticide concentrations were generally low, with over 95% of the detections at concentrations less than 1 μg/L. Of the 46 pesticide compounds examined, 39 were detected. The compounds detected most frequently were atrazine (38.2%), deethylatrazine (34.2%), simazine (18.0%), metolachlor (14.6%), and prometon (13.9%). Statistically significant relations were observed between frequencies of detection and the use, mobility, and persistence of these compounds. Pesticides were commonly detected in both agricultural (56.4%; 813 sites) and urban (46.6%; 221 sites) settings. Frequent detections of pesticides in urban areas indicate that, as is the case with agricultural pesticide use in agricultural areas, urban and suburban pesticide use significantly contribute to pesticide occurrence in shallow groundwater. Although pesticides were detected in groundwater sampled in urban areas and all nine of the agricultural land-use categories examined, significant variations in occurrence were observed among these categories. Maximum contaminant levels (MCLs) established by the U.S. Environmental Protection Agency for drinking water were exceeded for only one pesticide (atrazine, 3 μg/L) at a single location. However, MCLs have been established for only 25 of the 46 pesticide compounds examined, do not cover pesticide degradates, and, at present, do not take into account additive or synergistic effects of combinations of pesticide compounds or potential effects on nearby aquatic ecosystems.

Environmental Science & Technology↗
USGS2012

Crop classification modelling using remote sensing and environmental data in the Greater Platte River Basin, USA

With an ever expanding population, potential climate variability and an increasing demand for agriculture-based alternative fuels, accurate agricultural land-cover classification for specific crops and their spatial distributions are becoming critical to researchers, policymakers, land managers and farmers. It is important to ensure the sustainability of these and other land uses and to quantify the net impacts that certain management practices have on the environment. Although other quality crop classification products are often available, temporal and spatial coverage gaps can create complications for certain regional or time-specific applications. Our goal was to develop a model capable of classifying major crops in the Greater Platte River Basin (GPRB) for the post-2000 era to supplement existing crop classification products. This study identifies annual spatial distributions and area totals of corn, soybeans, wheat and other crops across the GPRB from 2000 to 2009. We developed a regression tree classification model based on 2.5 million training data points derived from the National Agricultural Statistics Service (NASS) Cropland Data Layer (CDL) in relation to a variety of other relevant input environmental variables. The primary input variables included the weekly 250 m US Geological Survey Earth Observing System Moderate Resolution Imaging Spectroradiometer normalized differential vegetation index, average long-term growing season temperature, average long-term growing season precipitation and yearly start of growing season. An overall model accuracy rating of 78% was achieved for a test sample of roughly 215 000 independent points that were withheld from model training. Ten 250 m resolution annual crop classification maps were produced and evaluated for the GPRB region, one for each year from 2000 to 2009. In addition to the model accuracy assessment, our validation focused on spatial distribution and county-level crop area totals in comparison with the NASS CDL and county statistics from the US Department of Agriculture (USDA) Census of Agriculture. The results showed that our model produced crop classification maps that closely resembled the spatial distribution trends observed in the NASS CDL and exhibited a close linear agreement with county-by-county crop area totals from USDA census data ( R 2 = 0.90).

Greater Platte River Basin↗
USGS2011

Sulfur in the South Florida ecosystem: Distribution, sources, biogeochemistry, impacts, and management for restoration

Sulfur is broadly recognized as a water quality issue of significance for the freshwater Florida Everglades. Roughly 60% of the remnant Everglades has surface water sulfate concentrations above 1 mg l-1, a restoration performance measure based on present sulfate levels in unenriched areas. Highly enriched marshes in the northern Everglades have average sulfate levels of 60 mg l-1. Sulfate loading to the Everglades is principally a result of land and water management in South Florida. The highest concentrations of sulfate (average 60-70 mg l-1) in the ecosystem are in canal water in the Everglades Agricultural Area (EAA). Potential sulfur sourcesin the watershed are many, but geochemical data and a preliminary sulfur mass balance for the EAA are consistent with sulfur presently used in agricultural, and sulfur released by oxidation of organic EAA soils (including legacy agricultural applications and natural sulfur) as the primary sources of sulfate enrichment in the EAA canals. Sulfate loading to the Everglades increases microbial sulfate reduction in soils, leading to more reducing conditions, greater cycling of nutrients in soils, production of toxic sulfide, and enhanced methylmercury (MeHg) production and bioaccumulation. Wetlands are zones of naturally high MeHg production, but the combination of high atmospheric mercury deposition rates in South Florida and elevated sulfate loading leads to increased MeHg production and MeHg risk to Everglades wildlife and human consumers. Sulfate from the EAA drainage canals penetrates deep into the Everglades Water Conservation Areas, and may extend into Everglades National Park. Present plans to restore sheet flow and to deliver more water to the Everglades may increase overall sulfur loads to the ecosystem, and move sulfate-enriched water further south. However, water management practices that minimize soil drying and rewetting cycles can mitigate sulfate release during soil oxidation. A comprehensive Everglades restoration strategy should include reduction of sulfur loads as a goal because of the many detrimental impacts of sulfate on the ecosystem. Monitoring data show that the ecosystem response to changes in sulfate levels is rapid, and strategies for reducing sulfate loading may be effective in the near term. A multifaceted approach employing best management practices for sulfur in agriculture, agricultural practices that minimize soil oxidation, and changes to stormwater treatment areas that increase sulfate retention could help achieve reduced sulfate loads to the Everglades, with resulting benefits.

Florida↗
USGS2017

Adding a nitrogen footprint to Colorado State University’s sustainability plan

As a large land grant university with more than 32,000 students, Colorado State University has both on-campus non-agricultural and agricultural sources of nitrogen (N) released to the environment. We used the Nitrogen Footprint Tool to estimate the amount of N released from different sectors of the university for the CSU 2014 academic year. The largest on campus sources were food production, utilities (heating, cooling, electricity), and research animals. The total on-campus N footprint in 2014 was 287 metric tons. This value was equivalent to the nitrogen footprint of agricultural experiment stations and other agricultural facilities, whose nitrogen footprint was 273 metric tons. CSU has opportunities to reduce its on-campus footprint through educational programs promoting low-meat diets and commuting by bicycle or bus. There is also an opportunity to advance ideas of agricultural best management practices, including precision farming and better livestock management. This article describes the planned and ongoing efforts to educate CSU about how societal activities release nitrogen to the environment, contributing to global change. It offers personal and institutional options for taking action, which would ultimately reduce CSU’s excess reactive nitrogen loss to the environment. The N-footprint for CSU, including scenarios of possible future nitrogen reductions, is also discussed.

Sustainability↗
USGS2023

Conserved grasslands support similar pollinator diversity as pollinator-specific practice regardless of proximal cropland and pesticide exposure

Pollinator diversity and abundance are declining globally. Cropland agriculture and the corresponding use of agricultural pesticides may contribute to these declines, while increased pollinator habitat (flowering plants) can help mitigate them. Here we tested whether the relative effect of wildflower plantings on pollinator diversity and counts were modified by proportion of nearby agricultural land cover and pesticide exposure in 24 conserved grasslands in Iowa, USA. Compared with general grassland conservation practices, wildflower plantings led to only a 5% increase in pollinator diversity and no change in counts regardless of the proportion of cropland agriculture within a 1 km radius. Pollinator diversity increased earlier in the growing season and with per cent flower cover. Unexpectedly, neither insecticide nor total pesticide concentrations on above-ground passive samplers were related to pollinator diversity. However, pollinator community composition was most strongly related to date of sampling, total pesticide concentration, and forb or flower cover. Our results indicate very little difference in pollinator diversity between grassland conservation practices with and without wildflower plantings. Given the relatively high economic costs of wildflower plantings, our research provides initial evidence that investment in general grassland conservation may efficiently conserve pollinator diversity in temperate regions of intensive cropland agriculture.

Iowa↗
USGS2013

Variability and trends in irrigated and non-irrigated croplands in the central U.S

Over 23 million hectares (233 thousand km 2 ) of U.S. croplands are irrigated and there was an overall net expansion of 522 thousand hectares nationally from 2002 to 2007. Most of this expansion occurred across the High Plains Aquifer (HPA) in the central Great Plains. Until recently, there has been a lack of geospatially-detailed irrigation data that are consistent, timely, geographically extensive, and periodic to support studies linking agricultural land use change to crop yields, aquifer water use, and other factors. We employed a modeling approach implemented at two time intervals (2002 and 2007) to map irrigated agriculture across the conterminous U.S. at a sub-county spatial detail (250 m 2 spatial resolution). The model integrated U.S. Department of Agriculture (USDA) county statistics, satellite imagery, and a national land cover map. The geospatial model output, called the Moderate Resolution Imaging Spectroradiometer (MODIS) Irrigated Agriculture Dataset for the United States (MIrAD-US), was then used to depict detailed spatial patterns of irrigation change across the HPA from 2002 to 2007. Spatial changes in irrigation may result in shifts in local and regional climate, groundwater depletion, and higher crop yields and farm income. A closer investigation of irrigated corn across the HPA from 2000 to 2012 revealed even more variability through time, underscoring the need for more frequent periodic mapping of irrigated agriculture.

Conference Paper↗
USGS2005

Impact of land use and land cover change on groundwater recharge and quality in the southwestern US

Humans have exerted large‐scale changes on the terrestrial biosphere, primarily through agriculture; however, the impacts of such changes on the hydrologic cycle are poorly understood. The purpose of this study was to test the hypothesis that the conversion of natural rangeland ecosystems to agricultural ecosystems impacts the subsurface portion of the hydrologic cycle by changing groundwater recharge and flushing salts to underlying aquifers. The hypothesis was examined through point and areal studies investigating the effects of land use/land cover (LU/LC) changes on groundwater recharge and solute transport in the Amargosa Desert (AD) in Nevada and in the High Plains (HP) in Texas, US. Studies use the fact that matric (pore‐water‐pressure) potential and environmental‐tracer profiles in thick unsaturated zones archive past changes in recharging fluxes. Results show that recharge is related to LU/LC as follows: discharge through evapotranspiration (i.e., no recharge; upward fluxes <0.1 mm yr −1 ) in natural rangeland ecosystems (low matric potentials; high chloride and nitrate concentrations); moderate‐to‐high recharge in irrigated agricultural ecosystems (high matric potentials; low‐to‐moderate chloride and nitrate concentrations) (AD recharge: ∼130–640 mm yr −1 ); and moderate recharge in nonirrigated (dryland) agricultural ecosystems (high matric potentials; low chloride and nitrate concentrations, and increasing groundwater levels) (HP recharge: ∼9–32 mm yr −1 ). Replacement of rangeland with agriculture changed flow directions from upward (discharge) to downward (recharge). Recent replacement of rangeland with irrigated ecosystems was documented through downward displacement of chloride and nitrate fronts. Thick unsaturated zones contain a reservoir of salts that are readily mobilized under increased recharge related to LU/LC changes, potentially degrading groundwater quality. Sustainable land use requires quantitative knowledge of the linkages between ecosystem change, recharge, and groundwater quality.

Global Change Biology↗
USGS2006

Does avian species richness in natural patch mosaics follow the forest fragmentation paradigm?

As one approaches the north-eastern limit of pinyon (Pinus spp.) juniper (Juniperus spp.) vegetation on the Colorado Plateau, USA, woodland patches become increasingly disjunct, grading into sagebrush (Artemisia spp.)-dominated landscapes. Patterns of avian species richness in naturally heterogeneous forests may or may not respond to patch discontinuity in the same manner as bird assemblages in fragmented agricultural systems. We used observational data from naturally patchy woodlands and predictions derived from studies of human-modified agricultural forests to estimate the effects of patch area, shape, isolation and distance to contiguous woodland on avian species richness. We predicted that patterns of species richness in naturally patchy juniper woodlands would differ from those observed in fragmented agricultural systems. Our objectives were to (1) estimate the effect of naturally occurring patch structure on avian species richness with respect to habitat affinity and migratory strategy and (2) assess the concordance of the effects to predictions from agricultural forest systems. We used the analogy between populations and communities to estimate species richness, where species are treated as individuals in the application of traditional capture-recapture theory. Information-theoretic model selection showed that overall species richness was explained primarily by the species area relationship. There was some support for a model with greater complexity than the equilibrium theory of island biogeography where the isolation of large patches resulted in greater species richness. Species richness of woodland-dwelling birds was best explained by the equilibrium hypothesis with partial landscape complementation by open-country species in isolated patches. Species richness within specific migratory strategies showed concomitant increases and no shifts in species composition along the patch area gradient. Our results indicate that many patterns of species richness considered to be fragmentation effects may be general consequences of patch discontinuity and are ubiquitous in naturally heterogeneous systems. There was no evidence for the effects of patch shape and distance to contiguous woodland in juniper woodland, suggesting edge effects and dependence upon regional species pools are characteristics of fragmented agricultural systems. Natural patch mosaics may provide benchmarks for evaluating fragmentation effects and managing forests by mimicking natural landscape patterns. ?? 2007 The Zoological Society of London.

Animal Conservation↗
USGS2012

A quantitative assessment of the conservation benefits of the Wetlands Reserve Program to amphibians

The Mississippi Alluvial Valley (MAV) originally consisted of nearly contiguous bottomland hardwood (BLH) forest encompassing approximately 10 million hectares. Currently, only 20–25% of the historical BLH forests remain in small patches fragmented by agricultural lands. The Wetlands Reserve Program (WRP) was established to restore and protect the functions and values of wetlands in agricultural landscapes. To assess the potential benefit of WRP restoration to amphibians, we surveyed 30 randomly selected WRP sites and 20 nearby agricultural sites in the Mississippi Delta. We made repeat visits to each site from May to August 2008 and performed both visual encounter and vocalization surveys. We analyzed the encounter history data for 11 anuran species using a Bayesian hierarchical occupancy model that estimated detection probability and probability of occurrence simultaneously for each species. Nine of the 11 species had higher probabilities of occurrence at WRP sites compared to agriculture. Derived estimates of species richness were also higher for WRP sites. Five anuran species were significantly more likely to occur in WRP than in agriculture, four of which were among the most aquatic species. It appears that the restoration of a more permanent hydrology at the WRP sites may be the primary reason for this result. Although amphibians represent only one group of wildlife species, they are useful for evaluating restoration benefits for wildlife because of their intermediate trophic position. The methods used in this study to evaluate the benefit of restoration could be used in other locations and with other groups of indicator species.

Mississippi↗
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↗
USGS2007

Atrazine and metolachlor occurrence in shallow ground water of the United States, 1993 to 1995: Relations to explanatory factors

Since 1991, the U.S. Geological Survey has been conducting the National Water Quality Assessment (NAWQA) Program to determine the quality of the Nation's water resources. In an effort to obtain a better understanding of why pesticides are found in shallow ground water on a national scale, a set of factors likely to affect the fate and transport of two herbicides in the subsurface were examined. Atrazine and metolachlor were selected for this discussion because they were among the most frequently detected pesticides in ground water during the first phase of the NAWQA Program (1993 to 1995), and each was the most frequently detected compound in its chemical class (triazines and acetanilides, respectively). The factors that most strongly correlated with the frequencies of atrazine detection in shallow ground-water networks were those that provided either: (1) an indication of the potential susceptibility of ground water to atrazine contamination, or (2) an indication of relative ground-water age. The factors most closely related to the frequencies of metolachlor detection in ground water, however, were those that estimated or indicated the intensity of the agricultural use of metolachlor. This difference is probably the result of detailed use estimates for these compounds being available only for agricultural settings. While atrazine use is relatively extensive in nonagricultural settings, in addition to its widespread agricultural use, metolachlor is used almost exclusively for agricultural purposes. As a result, estimates of agricultural applications provide a less reliable indication of total chemical use for atrazine than for metolachlor. A multivariate analysis demonstrated that the factors of interest explained about 50 percent of the variance in atrazine and metolachlor detection frequencies among the NAWQA land-use studies examined. The inclusion of other factors related to pesticide fate and transport in ground water, or improvements in the quality and accuracy of the data employed for the factors examined, may help explain more of the remaining variance in the frequencies of atrazine and metolachlor detection.

Journal of the American Water Resources Associatio↗
USGS2018

Current research in land, water, and agroecosystems: ASABE journals 2017 year in review

This article highlights current research into land and water resources, agroecosystems, and agricultural production systems published by the Natural Resources and Environmental Systems (NRES) community of ASABE journals (Transactions of the ASABE and Applied Engineering in Agriculture) in 2017. This article reviews the context, scope, and key results of the published articles and perhaps more importantly recommends areas for increased research attention. Experimental and modeling advances were described in hydrology, agroecosystems, climate-change effects, soil erosion, irrigation, drainage, forest resources, livestock systems, natural treatment systems, international water issues, and water quality topic areas. Three special collections were published (International Watershed Technology, Crop Modeling to Optimize Water Use, and Advances in Drainage). Other focal areas included 14 articles relating to livestock waste management, 13 concerning irrigated agricultural systems, 8 addressing climate change effects on land and water resources, and 16 on various aspects of soil erosion measurement and modeling. Building on the articles reviewed from 2017 and toward a vision of future agroecosystems research, the NRES community of ASABE journals strives to grow its role in making new knowledge accessible to sustain agricultural and natural systems in a changing world. In this vane, recommendations for future research direction are discussed with an emphasis on increased application of remote sensing data to agroecosystems research, improved assessment of agroecosystem resiliency and vulnerability to land and climate change, development of integrated models of agroecosystem services, meeting stubborn water management challenges in agricultural production systems, and focusing on publishing fully reproducible model results.

Transactions of the ASABE↗
USGS2014

Habitat availability is a more plausible explanation than insecticide acute toxicity for U.S. grassland bird species declines

Grassland bird species have experienced substantial declines in North America. These declines have been largely attributed to habitat loss and degradation, especially from agricultural practices and intensification (the habitat-availability hypothesis). A recent analysis of North American Breeding Bird Survey (BBS) “grassland breeding” bird trends reported the surprising conclusion that insecticide acute toxicity was a better correlate of grassland bird declines in North America from 1980–2003 (the insecticide-acute-toxicity hypothesis) than was habitat loss through agricultural intensification. In this paper we reached the opposite conclusion. We used an alternative statistical approach with additional habitat covariates to analyze the same grassland bird trends over the same time frame. Grassland bird trends were positively associated with increases in area of Conservation Reserve Program (CRP) lands and cropland used as pasture, whereas the effect of insecticide acute toxicity on bird trends was uncertain. Our models suggested that acute insecticide risk potentially has a detrimental effect on grassland bird trends, but models representing the habitat-availability hypothesis were 1.3–21.0 times better supported than models representing the insecticide-acute-toxicity hypothesis. Based on point estimates of effect sizes, CRP area and agricultural intensification had approximately 3.6 and 1.6 times more effect on grassland bird trends than lethal insecticide risk, respectively. Our findings suggest that preserving remaining grasslands is crucial to conserving grassland bird populations. The amount of grassland that has been lost in North America since 1980 is well documented, continuing, and staggering whereas insecticide use greatly declined prior to the 1990s. Grassland birds will likely benefit from the de-intensification of agricultural practices and the interspersion of pastures, Conservation Reserve Program lands, rangelands and other grassland habitats into existing agricultural landscapes.

PLoS ONE↗
USGS2010

Land-use controls on sources and processing of nitrate in small watersheds: Insights from dual isotopic analysis

Studies have repeatedly shown that agricultural and urban areas export considerably more nitrogen to streams than forested counterparts, yet it is difficult to identify and quantify nitrogen sources to streams due to complications associated with terrestrial and in-stream biogeochemical processes. In this study, we used the isotopic composition of nitrate (??15N-NO3- and ??18O- NO3-) in conjunction with a simple numerical model to examine the spatial and temporal variability of nitrate (NO3-) export across a land-use gradient and how agricultural and urban development affects net removal mechanisms. In an effort to isolate the effects of land use, we chose small headwater systems in close proximity to each other, limiting the variation in geology, surficial materials, and climate between sites. The ??15N and ??18Oof stream NO 3- varied significantly between urban, agricultural, and forested watersheds, indicating that nitrogen sources are the primary determinant of the ??15N-NO3-, while the ??18O-NO3- was found to reflect biogeochemical processes. The greatest NO3- concentrations corresponded with the highest stream ??15N-NO3- values due to the enriched nature of two dominant anthropogenic sources, septic and manure, within the urban and agricultural watersheds, respectively. On average, net removal of the available NO3- pool within urban and agricultural catchments was estimated at 45%. The variation in the estimated net removal of NO3- from developed watersheds was related to both drainage area and the availability of organic carbon. The determination of differentiated isotopic land-use signatures and dominant seasonal mechanisms illustrates the usefulness of this approach in examining the sources and processing of excess nitrogen within headwater catchments. ?? 2010 by the Ecological Society of America.

Ecological Applications↗
USGS2011

Multilevel regression models describing regional patterns of invertebrate and algal responses to urbanization across the USA

Multilevel hierarchical regression was used to examine regional patterns in the responses of benthic macroinvertebrates and algae to urbanization across 9 metropolitan areas of the conterminous USA. Linear regressions established that responses (intercepts and slopes) to urbanization of invertebrates and algae varied among metropolitan areas. Multilevel hierarchical regression models were able to explain these differences on the basis of region-scale predictors. Regional differences in the type of land cover (agriculture or forest) being converted to urban and climatic factors (precipitation and air temperature) accounted for the differences in the response of macroinvertebrates to urbanization based on ordination scores, total richness, Ephemeroptera, Plecoptera, Trichoptera richness, and average tolerance. Regional differences in climate and antecedent agriculture also accounted for differences in the responses of salt-tolerant diatoms, but differences in the responses of other diatom metrics (% eutraphenic, % sensitive, and % silt tolerant) were best explained by regional differences in soils (mean % clay soils). The effects of urbanization were most readily detected in regions where forest lands were being converted to urban land because agricultural development significantly degraded assemblages before urbanization and made detection of urban effects difficult. The effects of climatic factors (temperature, precipitation) on background conditions (biogeographic differences) and rates of response to urbanization were most apparent after accounting for the effects of agricultural development. The effects of climate and land cover on responses to urbanization provide strong evidence that monitoring, mitigation, and restoration efforts must be tailored for specific regions and that attainment goals (background conditions) may not be possible in regions with high levels of prior disturbance (e.g., agricultural development).

Journal of the North American Benthological Societ↗
USGS2003

Nitrate distributions and source identification in the Abbotsford-Sumas Aquifer, northwestern Washington State

The Abbotsford–Sumas Aquifer is a shallow, predominantly unconfined aquifer that spans regions in southwestern British Columbia, Canada and northwestern Washington, USA. The aquifer is prone to nitrate contamination because of extensive regional agricultural practices. A 22-month ground water nitrate assessment was performed in a 10-km 2 study area adjacent to the international boundary in northwestern Washington to examine nitrate concentrations and nitrogen isotope ratios to characterize local source contributions from up-gradient sources in Canada. Nitrate concentrations in excess of 10 mg nitrate as nitrogen per liter (mg N L −1 ) were observed in ground water from most of the 26 domestic wells sampled in the study area, and in a creek that dissects the study area. The nitrate distribution was characteristic of nonpoint agricultural sources and consistent with the historical documentation of agriculturally related nitrate contamination in many parts of the aquifer. Hydrogeologic information, nitrogen isotope values, and statistical analyses indicated a nitrate concentration stratification in the study area. The highest concentrations (>20 mg N L −1 ) occurred in shallow regions of the aquifer and were linked to local agricultural practices in northwestern Washington. Nitrate concentrations in excess of 10 mg N L −1 deeper in the aquifer (>10 m) were related to agricultural sources in Canada. The identification of two possible sources of ground water nitrate in northwestern Washington adds to the difficulty in assessing and implementing local nutrient management plans for protecting drinking water in the region.

Washington, British Columbia↗