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At least 829 records · Page 46Linked to original sources
USGS2013

A national streamflow network gap analysis

The U.S. Geological Survey (USGS) conducted a gap analysis to evaluate how well the USGS streamgage network meets a variety of needs, focusing on the ability to calculate various statistics at locations that have streamgages (gaged) and that do not have streamgages (ungaged). This report presents the results of analysis to determine where there are gaps in the network of gaged locations, how accurately desired statistics can be calculated with a given length of record, and whether the current network allows for estimation of these statistics at ungaged locations. The analysis indicated that there is variability across the Nation’s streamflow data-collection network in terms of the spatial and temporal coverage of streamgages. In general, the Eastern United States has better coverage than the Western United States. The arid Southwestern United States, Alaska, and Hawaii were observed to have the poorest spatial coverage, using the dataset assembled for this study. Except in Hawaii, these areas also tended to have short streamflow records. Differences in hydrology lead to differences in the uncertainty of statistics calculated in different regions of the country. Arid and semiarid areas of the Central and Southwestern United States generally exhibited the highest levels of interannual variability in flow, leading to larger uncertainty in flow statistics. At ungaged locations, information can be transferred from nearby streamgages if there is sufficient similarity between the gaged watersheds and the ungaged watersheds of interest. Areas where streamgages exhibit high correlation are most likely to be suitable for this type of information transfer. The areas with the most highly correlated streamgages appear to coincide with mountainous areas of the United States. Lower correlations are found in the Central United States and coastal areas of the Southeastern United States. Information transfer from gaged basins to ungaged basins is also most likely to be successful when basin attributes show high similarity. At the scale of the analysis completed in this study, the attributes of basins upstream of USGS streamgages cover the full range of basin attributes observed at potential locations of interest fairly well. Some exceptions included very high or very low elevation areas and very arid areas.

Puerto Rico↗
USGS2001

Hydrogeology and ground-water flow in the Memphis and Fort Pillow aquifers in the Memphis area, Tennessee

On the basis of known hydrogeology of the Memphis and Fort Pillow aquifers in the Memphis area, a three-layer, finite-difference numerical model was constructed and calibrated as the primary tool to refine understanding of flow in the aquifers. The model was calibrated and tested for accuracy in simulating measured heads for nine periods of transient flow from 1886-1985. Testing and sensitivity analyses indicated that the model accurately simulated observed heads areally as well as through time. The study indicates that the flow system is currently dominated by the distribution of pumping in relation to the distribution of areally variable confining units. Current withdrawal of about 200 million gallons per day has altered the prepumping flow paths, and effectively captured most of the water flowing through the aquifers. Ground-water flow is controlled by the altitude and location of sources of recharge and discharge, and by the hydraulic characteristics of the hydrogeologic units. Leakage between the Fort Pillow aquifer and Memphis aquifer, and between the Memphis aquifer and the water-table aquifers (alluvium and fluvial deposits) is a major component of the hydrologic budget. The study indicates that more than 50 percent of the water withdrawn from the Memphis aquifer in 1980 is derived from vertical leakage across confining units, and the leakage from the shallow aquifer (potential source of contamination) is not uniformly distributed. Simulated leakage was concentrated along the upper reaches of the Wolf and Loosahatchie Rivers, along the upper reaches of Nonconnah Creek, and the surficial aquifer of the Mississippi River alluvial plain. These simulations are supported by the geologic and geophysical evidence suggesting relatively thin or sandy confining units in these general locations. Because water from surficial aquifers is inferior in quality and more susceptible to contamination than water in the deeper aquifers, high rates of leakage to the Memphis aquifer may be cause for concern. A significant component of flow (12 percent) discharging from the Fort Pillow aquifer was calculated as upward leakage to the Memphis aquifer. This upward leakage was generally limited to areas near major pumping centers in the Memphis aquifer, where heads in the Memphis aquifer have been drawn significantly below heads in the Fort Pillow aquifer. Although the Fort Pillow aquifer is not capable of producing as much water as the Memphis aquifer for similar conditions, it is nonetheless a valuable resource throughout the area.

Water-Resources Investigations Report↗
USGS1998

Peak-discharge frequency and potential extreme peak discharge for natural streams in the Brazos River basin, Texas

The 2-, 5-, 10-, 25-, 50-, and 100-year peak discharges were estimated for 186 streamflow-gaging stations with at least 8 years of data for natural streams in and near the Brazos River Basin, Texas. Multiple regression equations were developed to estimate peak-discharge frequency for the 2-, 5-, 10-, 25-, 50-, and 100-year recurrence intervals for each of three hydrologic regions that compose the Brazos River Basin. The equations for each region are a function of significant basin characteristics (explanatory variables). The significant explanatory variables among six that were tested are the contributing drainage area and stream slope for regions 1 and 2 and the contributing drainage area for region 3. For the three sets of equations, the coefficient of determination ranges from 0.59 to 0.93, and the standard error ranges from 0.184 to 0.391 log units. A larger coefficient of determination and a lower standard error generally are associated with the equations for hydrologic regions 2 and 3. Statistics from the regression analysis allow computation of the prediction interval associated with a given significance level for a peak-discharge frequency estimate. The regression equations can be used to estimate peak discharges for sites at, near, or away from sites with streamflow-gaging stations. The potential extreme peak-discharge curves as related to contributing drainage area were estimated for each of the three hydrologic regions from measured extreme peaks of record at 186 sites with streamflow-gaging stations and from measured extreme peaks at 37 sites without streamflow-gaging stations in and near the Brazos River Basin. The potential extreme peak-discharge curves generally are similar for hydrologic regions 1 and 2, and the curve for region 3 consistently is below the curves for regions 1 and 2, which indicates smaller peak discharges.

Texas↗
USGS1962

Data on uranium and radium in ground water in the United States, 1954 to 1957

This report is one of a series resulting from a study by the U.S. Geological Survey to determine the occurrence and distribution of naturally radioactive substances in water. From 1954-57 uranium and radium concentrations were determined in 561 samples, mainly of ground water, having wide geologic and geographic distribution. These concentrations, together with data on the hydrologic and geologic environment, the beta-gamma activity, and the chemical characteristics of each sample, are tabulated by States. The conterminous United States was subdivided into 10 geotectonic regions to facilitate statistical interpretation of the occurrence of uranium and radium in fresh water in approximately homogeneous geologic provinces. For each geotectonic region, the range and median were determined for the concentrations of radium and uranium; for regions from which sufficient data were available, log-normal frequency distribution curves were calculated and superimposed on histograms of radium and uranium concentrations in the samples. An "anomaly threshold" is suggested for both radioelements for each region analyzed statistically. The western stable region had the greatest median and highest "anomaly threshold" for uranium. This region also had the highest "anomaly threshold" for radium, but the largest median for radium was found for samples collected in the Ozark-Ouachita system. The median concentration for uranium was lowest for the Atlantic and Gulf Coastal Plain and the Pacific orogenic belt. This latter region also had the lowest median-radium content.

Professional Paper↗
USGS1970

Hydrologic implications of solid-water disposal

The disposal of more than 1,400 million pounds of solid wastes in the United States each day is a major problem. This disposal in turn often leads to serious health, esthetic, and environmental problems. Among these is the pollution of vital ground-water resources. Of the six principal methods of solid-waste disposal in general use today, four methods-open dumps, sanitary landfill, incineration, and onsite disposal-carry an inherent potential for pollution of water resources. Seepage of rainwater through the wastes leaches undesirable constituents which reach the ground water in the area. This leachate is generally both biologically and chemically contaminated. The extent of the pollution from this leachate is largely dependent upon the geologic environment in which the solid wastes are deposited. Pollution potential is highest in permeable areas with a shallow water table where the wastes are in direct contact with the ground water. In a relatively impermeable area, the pollution is generally confined locally to the vicinity of the waste-disposal site. Site selection for disposal of solid wastes must be based on adequate water-resources information if pollutional potential is to be minimized. This will require regional as well as localized data on the water resources of the area. Only through such an approach can adequate protection be afforded to the environment in general and the water resources in particular.

Circular↗
USGS2018

Spatial relationships of levees and wetland systems within floodplains of the Wabash Basin, USA

Given the unique biogeochemical, physical, and hydrologic services provided by floodplain wetlands, proper management of river systems should include an understanding of how floodplain modifications influence wetland ecosystems. The construction of levees can reduce river–floodplain connectivity, yet it is unclear how levees affect wetlands within floodplains, let alone the cumulative impacts within an entire watershed. This paper explores spatial relationships between levee and floodplain wetland systems in the Wabash Basin, United States. We used a hydrogeomorphic floodplain delineation technique to map floodplain extents and identify wetlands that may be hydrologically connected to river networks. We then spatially examined the relationship between levee presence, wetland area, and other river network attributes within discrete subbasins. Our results show that cumulative wetland area is relatively constant in subbasins that contain levees, regardless of maximum stream order within the subbasin. In subbasins that do not contain levees, cumulative wetland area increases with maximum stream order. However, we found that wetland distributions around levees can be complex, and further studies on the influence of levees on wetland habitat may need to consider finer resolution spatial scales.

Wabash Basin↗
USGS2017

Prediction of spatially explicit rainfall intensity–duration thresholds for post-fire debris-flow generation in the western United States

Early warning of post-fire debris-flow occurrence during intense rainfall has traditionally relied upon a library of regionally specific empirical rainfall intensity–duration thresholds. Development of this library and the calculation of rainfall intensity-duration thresholds often require several years of monitoring local rainfall and hydrologic response to rainstorms, a time-consuming approach where results are often only applicable to the specific region where data were collected. Here, we present a new, fully predictive approach that utilizes rainfall, hydrologic response, and readily available geospatial data to predict rainfall intensity–duration thresholds for debris-flow generation in recently burned locations in the western United States. Unlike the traditional approach to defining regional thresholds from historical data, the proposed methodology permits the direct calculation of rainfall intensity–duration thresholds for areas where no such data exist. The thresholds calculated by this method are demonstrated to provide predictions that are of similar accuracy, and in some cases outperform, previously published regional intensity–duration thresholds. The method also provides improved predictions of debris-flow likelihood, which can be incorporated into existing approaches for post-fire debris-flow hazard assessment. Our results also provide guidance for the operational expansion of post-fire debris-flow early warning systems in areas where empirically defined regional rainfall intensity–duration thresholds do not currently exist.

Geomorphology↗
USGS2021

Hydrometeorology and hydrology of flooding in Cape Fear River basin during Hurricane Florence in 2018

Hurricanes are the major flood generating mechanism dominating the upper tail of the peak discharge distribution over the Cape Fear River Basin (CFRB). In 2018, Hurricane Florence swamped CFRB as the ninth-most-destructive hurricane ever hit the United States and set new records of peak discharges over the main river channel and three out of five of its major tributaries. In this study, we examined the hydrometeorology and hydrology of this flood via combined observation and numerical experiment analyses. Our results suggest that the slow-motion in combination to the “L-shaped” path was the most distinctive feature of the hurricane that incurred catastrophic and widespread rainfall and flooding over CFRB. The total rainfall from the storm played a controlling role in the magnitude and spatial distribution of the flood peaks at basin scale. Above that, the spatial heterogeneities of rainfall distribution and hydrologic characteristics was responsible for the distinctive flood responses within the basin. The bi-peak shape of the flood hydrograph for the Deep River was due to the combined effects of rainfall distribution, land cover, and topographic gradient. The exceptional unit peak discharge over the Black River basin was associated with its drainage network structure, topographic gradient and rainfall distribution. The floodplain downstream of the Cape Fear River temporarily stored flood water and attenuated both the riverine floods from upstream and the compound flood over the coastal area. Furthermore, numerical analyses found that re-infiltration accounted for 76% of the total infiltration on average. Re-infiltration was superior to local infiltration over CFRB during Hurricane Florence.

North Carolina↗
USGS2022

Estimating detection and occupancy of secretive marsh bird species in low and high saline marshes in southwestern Louisiana using automated recording units

Secretive marsh birds (SMBs) are important indicator species of coastal wetlands but are difficult to detect and monitor. In coastal Louisiana, an important stronghold for these species, climate and hydrological models predict that freshwater and intermediate marshes will expand in the next 50 years, while brackish marshes will shrink. We used a multi-species Bayesian hierarchical occupancy model to estimate detection and occupancy probabilities for 11 SMB species in low and high saline marshes using data from automated recording units at 33 sites in southwestern Louisiana from February–June 2012. A quadratic effect of Julian date, but not minimum daily temperature nor precipitation affected detection of SMB species. King Rail ( Rallus elegans ), American Bittern ( Botaurus lentiginosus ), Common Gallinule ( Gallinula galeata ), and Pied-billed Grebe ( Podilymbus podiceps ) occupied mainly freshwater and intermediate marshes. Clapper Rail ( Rallus crepitans ), Seaside Sparrow ( Ammospiza maritima ), and Sora ( Porzana carolina ) predominantly occupied brackish and salt marshes. American Coot ( Fulica americana ), Purple Gallinule ( Porphyrio martinica ), Least Bittern ( Ixobrychus exilis ), and Marsh Wren ( Cistothorus palustris ) occupied both low and high saline marshes, showing flexibility that could maintain populations of these species as marsh salinities change in the future. If the current distribution of SMB species persists as marsh availability changes under future conditions, populations of the 4 species we found in low saline marshes may increase, whereas populations of at least 2 species found primarily in high saline marshes may decrease. Our modeling indicates that automatic recording units can produce comparable detection probabilities to other studies using traditional SMB sampling methods.

Louisiana↗
USGS2017

Spatiotemporal variability of snow depletion curves derived from SNODAS for the conterminous United States, 2004-2013

Assessment of water resources at a national scale is critical for understanding their vulnerability to future change in policy and climate. Representation of the spatiotemporal variability in snowmelt processes in continental-scale hydrologic models is critical for assessment of water resource response to continued climate change. Continental-extent hydrologic models such as the U.S. Geological Survey National Hydrologic Model (NHM) represent snowmelt processes through the application of snow depletion curves (SDCs). SDCs relate normalized snow water equivalent (SWE) to normalized snow covered area (SCA) over a snowmelt season for a given modeling unit. SDCs were derived using output from the operational Snow Data Assimilation System (SNODAS) snow model as daily 1-km gridded SWE over the conterminous United States. Daily SNODAS output were aggregated to a predefined watershed-scale geospatial fabric and used to also calculate SCA from October 1, 2004 to September 30, 2013. The spatiotemporal variability in SNODAS output at the watershed scale was evaluated through the spatial distribution of the median and standard deviation for the time period. Representative SDCs for each watershed-scale modeling unit over the conterminous United States ( n = 54,104) were selected using a consistent methodology and used to create categories of snowmelt based on SDC shape. The relation of SDC categories to the topographic and climatic variables allow for national-scale categorization of snowmelt processes.

Journal of the American Water Resources Associatio↗
USGS2019

POLARIS properties: 30-meter probabilistic maps of soil properties over the contiguous United States

Soils play a critical role in the cycling of water, energy, and carbon in the Earth system. Until recently, due primarily to a lack of soil property maps of a sufficiently high‐quality and spatial detail, a minor emphasis has been placed on providing high‐resolution measured soil parameter estimates for land surface models and hydrologic models. This study introduces Probabilistic Remapping of SSURGO (POLARIS) soil properties—a database of 30‐m probabilistic soil property maps over the contiguous United States (CONUS). The mapped variables over CONUS include soil texture, organic matter, pH, saturated hydraulic conductivity, Brooks‐Corey and Van Genuchten water retention curve parameters, bulk density, and saturated water content. POLARIS soil properties was assembled by (1) depth harmonizing and aggregating the pedons in the National Cooperative Soil Survey Soil Characterization Database and the components in Soil Survey Geographic Database into a database of 21,481 different soil series, each soil series having its own vertical profiles of different soil properties, (2) pruning the original POLARIS soil series maps using conventional soil maps to improve soil series prediction accuracy, and (3) merging the assembled soil series databases with the pruned POLARIS soil series maps to construct the soil property maps over CONUS. POLARIS soil properties includes 100‐bin histograms for each layer and variable per grid cell and a series of summary statistics at 30‐, 300‐, and 3,000‐m spatial resolution. Evaluation of POLARIS soil properties using in situ measurements shows an average R2 of 0.41, normalized root‐mean‐square error of 12%, and a normalized mean absolute error of 8.8%.

Water Resources Research↗
USGS2017

Widespread occurrence and potential for biodegradation of bioactive contaminants in Congaree National Park, USA

Organic contaminants with designed molecular bioactivity, such as pesticides and pharmaceuticals, originate from human and agricultural sources, occur frequently in surface waters, and threaten the structure and function of aquatic and terrestrial ecosystems. Congaree National Park in South Carolina (USA) is a vulnerable park unit due to its location downstream of multiple urban and agricultural contaminant sources and its hydrologic setting, being composed almost entirely of floodplain and aquatic environments. Seventy-two water and sediment samples were collected from 16 sites in Congaree National Park during 2013 to 2015, and analyzed for 199 and 81 targeted organic contaminants, respectively. More than half of these water and sediment analytes were not detected or potentially had natural sources. Pharmaceutical contaminants were detected (49 total) frequently in water throughout Congaree National Park, with higher detection frequencies and concentrations at Congaree and Wateree River sites, downstream from major urban areas. Forty-seven organic wastewater indicator chemicals were detected in water, and 36 were detected in sediment, of which approximately half are distinctly anthropogenic. Endogenous sterols and hormones, which may originate from humans or wildlife, were detected in water and sediment samples throughout Congaree National Park, but synthetic hormones were detected only once, suggesting a comparatively low risk of adverse impacts. Assessment of the biodegradation potentials of 8 14 C-radiolabeled model contaminants indicated poor potentials for some contaminants, particularly under anaerobic sediments conditions.

South Carolina↗
USGS2005

Primary production in an impounded baldcypress swamp (Taxodium distichum) at the northern limit of the range

The ability of baldcypress (Taxodium distichum)swamps to maintain themselves near the northern limit of their range depends on their levels of production, which is not only are response to climate but also to local environmental factors(e.g., impoundment). We asked if primary production was reduced under impounded conditions and if species' responses to impoundment were individualistic or more generalized. To examine long-term production trends in a permanently impounded baldcypress swamp, a 6-year study of leaf litterfall was conducted in Buttonland Swamp, Illinois, which had been impounded for 10 years before the beginning of the study. Buttonland Swamp is at the northern boundary of the baldcypress swamp region along the Cache River, Illinois, in the Mississippi River Alluvial Valley of the United States. When the litter production of impounded sites was compared to those with natural hydrology in the same region, impounded sites had about half of the total litterfall of natural sites. Overall, leaf litterfall rates declined during the study(201 vs. 113 gm-2 yr-1), but the pattern was negatively correlated with water depth, which explained 97% of the variation in the data. Along the transect with the lowest mean minimum water depth(<0.5 cm), leaf litterfall decreased linearly over 6 years from 377 to 154gm-2 yr-1. Total leaf litterfall rates were lower at the other three depths(5, 43, and 49 cm mean minimum water depths)and remained below 200 gm-2 yr -1 throughout the study. Acer saccharinum, Nyssa aquatica, and Salix nigra were most responsible for the decline in total leaf litterfall. Amounts of leaf litterfall of T. distichum and Liquidambar styraciflua also generally decreased, while that of Cephalanthus occidentalis increased overtime. Because species' responses to environmental factors such as impoundment are individualistic, models should be based on the responses of individual species, rather than on communities. Our study further suggests that the effects of climate change on impounded swamps may differ from those with natural hydrology, since impounded swamps already have reduced production levels. This finding is particularly relevant since the hydrology of the majority of the world's riverine ecosystems has been altered. ?? Springer 2005.

Conference Paper↗
USGS2018

Variability of organic carbon content and the retention and release of trichloroethene in the rock matrix of a mudstone aquifer

Contaminants diffusing from fractures into the immobile porosity of the rock matrix are subject to prolonged residence times. Organic contaminants can adsorb onto organic carbonaceous materials in the matrix extending contaminant retention. An investigation of spatial variability of the fraction of organic carbon ( f oc ) is conducted on samples of rock core from seven closely spaced boreholes in a mudstone aquifer contaminated with trichloroethene (TCE). A total of 378 samples were analyzed at depths between 14 and 36 m below land surface. Mudstone units associated with deep water deposition have the largest f oc , with a maximum value of 0.0396, and units associated with shallow water deposition have the smallest f oc . Even though f oc correlates with depositional conditions, f oc still varies over more than an order of magnitude in continuous mudstone layers between boreholes, and there is large variability in f oc over short distances perpendicular to bedding. Simulations of diffusion and linear equilibrium adsorption of TCE using spatially variable f oc in the rock matrix show order of magnitude variability in the adsorbed TCE over short distances in the matrix and residence times extending to hundreds of years following remediation in adjacent fractures. Simulations using average values of f oc do not capture the range of TCE mass that can be retained in a rock matrix characterized by spatially variable f oc . Bounds on TCE mass within the rock matrix can be obtained by simulations with spatially uniform values of f oc equal to the maximum and minimum values of f oc for a given mudstone unit.

New Jersey↗
USGS2026

A chromosome-level genome assembly of a vernal pool specialist amphibian, the Western Spadefoot, Spea hammondii

We assembled and annotated a chromosome-level genome for the Western Spadefoot, Spea hammondii (Anura, Scaphiopodidae) representing one of only three amphibians included in the California Conservation Genomics Project (CCGP). Spea hammondii is a vernal pool breeding anuran native to California and northwestern Baja California which has undergone both range contractions and local extirpations across its distribution, primarily due to habitat loss and degradation and drought. The species is recognized by the state of California as a Species of Special Concern and is proposed for listing under the United States Endangered Species Act. Using the established CCGP pipeline, this S. hammondii genome was produced using Pacific Biosciences HiFi long-reads and Omni-C proximity ligation, resulting in a de novo genome assembly 1.14 Gb in length, distributed across 479 scaffolds (scaffold N50 = 120.8 Mb; largest scaffold = 183.6 Mb) with a BUSCO completeness score of 90.9% using a conserved tetrapod ortholog set. Our assembly shows high base accuracy (quality value [QV] = 63.7) and low frameshift error in coding regions (QV 50.42). Annotation of this genome yielded 20,434 genes with a BUSCO completeness score of 94.7%. This genome assembly, in combination with range-wide resequencing data from CCGP, will facilitate statewide population genomic assessments to delineate conservation units, quantify inbreeding and genomic load, and test for adaptive variation associated with vernal pool hydrology and drought tolerance, all of which are important considerations in the proposed federal listing.

Journal of Heredity↗
USGS2026

A chromosome-level genome assembly of a vernal pool specialist amphibian, the Western Spadefoot, Spea hammondii

We assembled and annotated a chromosome-level reference genome for the Western Spadefoot, Spea hammondii (Anura, Scaphiopodidae) representing one of only three amphibians included in the California Conservation Genomics Project (CCGP). Spea hammondii is a vernal pool breeding anuran native to California and northwestern Baja California which has undergone both range contractions and local extirpations across its distribution, primarily due to habitat loss and degradation and drought. The species is recognized by the state of California as a Species of Special Concern and is proposed for listing under the United States Endangered Species Act. Using the established CCGP pipeline, this S. hammondii genome was produced using Pacific Biosciences HiFi long-reads and Omni-C proximity ligation, resulting in a de novo genome assembly 1.14 Gb in length, distributed across 479 scaffolds (scaffold N50 = 120.8 Mb; largest scaffold = 183.6 Mb) with a BUSCO completeness score of 90.9% using a conserved tetrapod ortholog set. Our assembly shows high base accuracy (QV = 63.7) and low frameshift error in coding regions (QV 50.42). Annotation of this genome yielded 20,434 genes with a BUSCO completeness score of 94.7%. This reference genome, in combination with range-wide resequencing data from CCGP, will facilitate statewide population genomic assessments to delineate conservation units, quantify inbreeding and genomic load, and test for adaptive variation associated with vernal pool hydrology and drought tolerance, all of which are important considerations in the proposed federal listing.

BioRxiv↗
USGS2020

Regional coordination between riparian dependence and atmospheric demand in willows (Salix L.) of western North America

Aim Plants vary in their hydrological and climatic niches. How these niche dimensions covary among closely related species can help identify co‐adaptations to hydrological and climatic factors, as well as predict biodiversity responses to environmental change. Location Western United States. Methods Relationships between riparian dependence and climate niches of willows ( Salix L.) were assessed, incorporating phylogenetics and functional traits to understand the adaptive nature of those relationships. The riparian dependence niche was estimated as the mean distance between georeferenced occurrence records and the nearest stream based on the National Hydrography Database. Results were compared to oaks ( Quercus L.), a less riparian‐dependent clade, with the expectation of different niche relationships. Results Willows generally occurred closer to streams than expected by chance, but riparian dependence varied substantially among species. Riparian dependence was positively correlated with mean annual temperature and diurnal temperature range niche, both indicators of atmospheric demand on evapotranspiration. Phylogenetic independent contrast correlations for these relationships were significant as well, and the high degree of niche convergence among species indicated evolutionarily labile co‐adaptations to riparian dependence and atmospheric demand. Plant height increased with mean annual temperature niche, and specific leaf area increased with residual variation in height, indicating underlying morphological correlates of niche variation. Oaks, on the other hand, exhibited no relationship between atmospheric demand and riparian dependence, and weaker niche relationships with riparian dependence overall. Main conclusions These results support the assertion that hydric‐adapted, woody riparian plants compensate for increased atmospheric demand on transpiration with a reliable supply of water provided by riparian habitats and that this trade‐off may be unique from mesic–xeric woody plants. Conservation of warm‐adapted riparian trees and shrubs under increasing temperatures and atmospheric demand may necessitate reversal of groundwater depletion. Cool‐adapted species may be best conserved through maintenance or expansion of riparian buffers as they become more riparian obligate with warming.

Diversity and Distributions↗
USGS2008

Trends of pesticides and nitrate in ground water of the Central Columbia Plateau, Washington, 1993-2003

Pesticide and nitrate data for ground water sampled in the Central Columbia Plateau, Washington, between 1993 and 2003 by the U.S. Geological Survey National Water-Quality Assessment Program were evaluated for trends in concentration. A total of 72 wells were sampled in 1993-1995 and again in 2002-2003 in three well networks that targeted row crop and orchard land use settings as well as the regional basalt aquifer. The Regional Kendall trend test indicated that only deethylatrazine (DEA) concentrations showed a significant trend. Deethylatrazine concentrations were found to increase beneath the row crop land use well network, the regional aquifer well network, and for the dataset as a whole. No other pesticides showed a significant trend (nor did nitrate) in the 72-well dataset. Despite the lack of a trend in nitrate concentrations within the National Water-Quality Assessment dataset, previous work has found a statistically significant decrease in nitrate concentrations from 1998-2002 for wells with nitrate concentrations above 10 mg L-1 within the Columbia Basin ground water management area, which is located within the National Water-Quality Assessment study unit boundary. The increasing trend in DEA concentrations was found to negatively correlate with soil hydrologic group using logistic regression and with soil hydrologic group and drainage class using Spearman's correlation. The decreasing trend in high nitrate concentrations was found to positively correlate with the depth to which the well was cased using logistic regression, to positively correlate with nitrate application rates and sand content of the soil, and to negatively correlate with soil hydrologic group using Spearman's correlation. Copyright ?? 2008 by the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America. All rights reserved.

Conference Paper↗