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Results for “Journal of the American Statistical Association”

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USGS2007

Problems and methods involved in relating land use to ground-water quality

Efforts to relate shallow ground-water quality to the land use near a well lead to several statistical difficulties. These include potential uncertainty in land-use categorical data due to misclassification, data closure, distributional skewing, and spatial autocorrelation. Methods of addressing these problems are, respectively, the establishment of limits on minimum buffer radius, the estimation of contrasts, rank-based tests of association, and sub-sampling to prevent buffer overlap. Relations between the presence of purgeable organic compounds in ground water and land use are used to illustrate these problems and methods.

Journal of the American Water Resources Associatio↗

USGS2014

Assessment of endocrine-disrupting chemicals attenuation in a coastal plain stream prior to wastewater treatment plant closure

The U.S. Geological Survey is conducting a combined pre/post-closure assessment at a long-term wastewater treatment plant (WWTP) site at Fort Gordon near Augusta, Georgia. Here, we assess select endocrine-active chemicals and benthic macroinvertebrate community structure prior to closure of the WWTP. Substantial downstream transport and limited instream attenuation of endocrine-disrupting chemicals (EDCs) was observed in Spirit Creek over a 2.2-km stream segment downstream of the WWTP outfall. A modest decline (less than 20% in all cases) in surface water detections was observed with increasing distance downstream of the WWTP and attributed to partitioning to the sediment. Estrogens detected in surface water in this study included estrone (E1), 17β-estradiol (E2), and estriol (E3). The 5 ng/l and higher mean estrogen concentrations observed in downstream locations indicated that the potential for endocrine disruption was substantial. Concentrations of alkylphenol ethoxylate (APE) metabolite EDCs also remained statistically elevated above levels observed at the upstream control site. Wastewater-derived pharmaceutical and APE metabolites were detected in the outflow of Spirit Lake, indicating the potential for EDC transport to aquatic ecosystems downstream of Fort Gordon. The results indicate substantial EDC occurrence, downstream transport, and persistence under continuous supply conditions and provide a baseline for a rare evaluation of ecosystem response to WWTP closure.

Georgia↗

USGS2004

The new GFDL global atmosphere and land model AM2-LM2: Evaluation with prescribed SST simulations

The configuration and performance of a new global atmosphere and land model for climate research developed at the Geophysical Fluid Dynamics Laboratory (GFDL) are presented. The atmosphere model, known as AM2, includes a new gridpoint dynamical core, a prognostic cloud scheme, and a multispecies aerosol climatology, as well as components from previous models used at GFDL. The land model, known as LM2, includes soil sensible and latent heat storage, groundwater storage, and stomatal resistance. The performance of the coupled model AM2-LM2 is evaluated with a series of prescribed sea surface temperature (SST) simulations. Particular focus is given to the model's climatology and the characteristics of interannual variability related to El Nin??o-Southern Oscillation (ENSO). One AM2-LM2 integration was perfor med according to the prescriptions of the second Atmospheric Model Intercomparison Project (AMIP II) and data were submitted to the Program for Climate Model Diagnosis and Intercomparison (PCMDI). Particular strengths of AM2-LM2, as judged by comparison to other models participating in AMIP II, include its circulation and distributions of precipitation. Prominent problems of AM2-LM2 include a cold bias to surface and tropospheric temperatures, weak tropical cyclone activity, and weak tropical intraseasonal activity associated with the Madden-Julian oscillation. An ensemble of 10 AM2-LM 2 integrations with observed SSTs for the second half of the twentieth century permits a statistically reliable assessment of the model's response to ENSO. In general, AM2-LM2 produces a realistic simulation of the anomalies in tropical precipitation and extratropical circulation that are associated with ENSO. ?? 2004 American Meteorological Society.

Journal of Climate↗

USGS2005

Response of seismicity to Coulomb stress triggers and shadows of the 1999 Mw=7.6 Chi-Chi, Taiwan, earthquake

The correlation between static Coulomb stress increases and aftershocks has thus far provided the strongest evidence that stress changes promote seismicity, a correlation that the Chi-Chi earthquake well exhibits. Several studies have deepened the argument by resolving stress changes on aftershock focal mechanisms, which removes the assumption that the aftershocks are optimally oriented for failure. Here one compares the percentage of planes on which failure is promoted after the main shock relative to the percentage beforehand. For Chi-Chi we find a 28% increase for thrust and an 18% increase for strike-slip mechanisms, commensurate with increases reported for other large main shocks. However, perhaps the chief criticism of static stress triggering is the difficulty in observing predicted seismicity rate decreases in the stress shadows, or sites of Coulomb stress decrease. Detection of sustained drops in seismicity rate demands a long catalog with a low magnitude of completeness and a high seismicity rate, conditions that are met at Chi-Chi. We find four lobes with statistically significant seismicity rate declines of 40-90% for 50 months, and they coincide with the stress shadows calculated for strike-slip faults, the dominant faulting mechanism. The rate drops are evident in uniform cell calculations, 100-month time series, and by visual inspection of the M ??? 3 seismicity. An additional reason why detection of such declines has proven so rare emerges from this study: there is a widespread increase in seismicity rate during the first 3 months after Chi-Chi, and perhaps many other main shocks, that might be associated with a different mechanism. Copyright 2005 by the American Geophysical Union.

Journal of Geophysical Research B: Solid Earth↗

USGS2020

Spatiotemporal variability of modeled watershed scale surface-depression storage and runoff for the conterminous United States

This study uses the explores the viability of a proxy model calibration strategy through assessment of the spatiotemporal variability of surface-depression storage and runoff generated with the U.S. Geological Survey’s National Hydrologic Model (NHM) infrastructure for hydrologic response units (HRUs; n=109,951) across the conterminous United States (CONUS). Simulated values for each HRU of daily surface-depression storage (treated as a decimal fraction of total possible volume) and monthly normalized runoff (0 to 1) values were calculated using Spearman’s rho at monthly and annual aggregations. Locations where values are correlated show where previously-developed proxy calibration strategies are likely to be effective. In addition, differences in the correlation for monthly and annual time scale aggregations show which time scale drives surface-depression storage processes in the NHM. Results show overall long-term (annual) correlation is more common than short-term (monthly) correlation over the CONUS; however, summary statistics for eighty-six ecoregions show five with higher ranges of monthly relative to annual Spearman’s rank coefficient values. This landscape-scale analysis shows simulations aggregated to an annual time scale are generally more dominant for the CONUS; however, simulations aggregated to monthly, short-term time scales are more dominant in focused areas where surface-depression storage processes are investigated.

Journal of the American Water Resources Associatio↗

USGS2007

A comparison of delta change and downscaled GCM scenarios for three mountainous basins in the United States

Simulated daily precipitation, temperature, and runoff time series were compared in three mountainous basins in the United States: (1) the Animas River basin in Colorado, (2) the East Fork of the Carson River basin in Nevada and California, and (3) the Cle Elum River basin in Washington State. Two methods of climate scenario generation were compared: delta change and statistical downscaling. The delta change method uses differences between simulated current and future climate conditions from the Hadley Centre for Climate Prediction and Research (HadCM2) General Circulation Model (GCM) added to observed time series of climate variables. A statistical downscaling (SDS) model was developed for each basin using station data and output from the National Center for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis regridded to the scale of HadCM2. The SDS model was then used to simulate local climate variables using HadCM2 output for current and future conditions. Surface climate variables from each scenario were used in a precipitation-runoff model. Results from this study show that, in the basins tested, a precipitation-runoff model can simulate realistic runoff series for current conditions using statistically downscaled NCEP output. But, use of downscaled HadCM2 output for current or future climate assessments are questionable because the GCM does not produce accurate estimates of the surface variables needed for runoff in these regions. Given the uncertainties in the GCMs ability to simulate current conditions based on either the delta change or downscaling approaches, future climate assessments based on either of these approaches must be treated with caution.

California, Colorado, Nevada, Washington↗

USGS2011

Digital hydrologic networks supporting applications related to spatially referenced regression modeling

Digital hydrologic networks depicting surface-water pathways and their associated drainage catchments provide a key component to hydrologic analysis and modeling. Collectively, they form common spatial units that can be used to frame the descriptions of aquatic and watershed processes. In addition, they provide the ability to simulate and route the movement of water and associated constituents throughout the landscape. Digital hydrologic networks have evolved from derivatives of mapping products to detailed, interconnected, spatially referenced networks of water pathways, drainage areas, and stream and watershed characteristics. These properties are important because they enhance the ability to spatially evaluate factors that affect the sources and transport of water-quality constituents at various scales. SPAtially Referenced Regressions On Watershed attributes (SPARROW), a process-based &frasl; statistical model, relies on a digital hydrologic network in order to establish relations between quantities of monitored contaminant flux, contaminant sources, and the associated physical characteristics affecting contaminant transport. Digital hydrologic networks modified from the River Reach File (RF1) and National Hydrography Dataset (NHD) geospatial datasets provided frameworks for SPARROW in six regions of the conterminous United States. In addition, characteristics of the modified RF1 were used to update estimates of mean-annual streamflow. This produced more current flow estimates for use in SPARROW modeling.

Journal of the American Water Resources Associatio↗

USGS1987

Habitat suitability index curves for paddlefish, developed by the delphi technique

A Delphi exercise conducted with a panel of 11 experts on paddlefish (Polyodon spathula) and an evaluator resulted in 14 riverine habitat suitability index curves associating various life stages or activities of paddlefish with four variables: velocity, depth, substrate type, and temperature. The panel reached a consensus on six of the curves and eight to 10 panelists agreed on the others. Several panelists reported that they found the Delphi exercise to be a good learning experience, and they believed the technique is an appropriate interim method for developing suitability index curves when available data are inadequate for more conventional statistical analyses. Documentation of good paddlefish spawning habitat was the data need most commonly identified by the panelists.

North American Journal of Fisheries Management↗

USGS2007

Presence and distribution of chlorinated organic compounds in streambed sediments, New Jersey

ABSTRACT: Concentrations of 18 hydrophobic chlorinated organic compounds in streambed sediments from 100 sites throughout New Jersey were examined to determine (1) which compounds were detected most frequently, (2) whether detection frequencies differed among selected drainage basins, and (3) whether concentrations differed significantly among selected drainage basins. Twelve drainage basins across New Jersey that contain a range of land-use patterns and population densities were selected to represent various types and degrees of development. To ensure an adequate number of samples for statistical comparison among drainage basins, the 12 selected basins were consolidated into seven drainage areas on the basis of similarities in land-use patterns and population densities. Additionally, data for three classes of chlorinated organic compounds in streambed sediments from 255 sites throughout New Jersey were examined to determine whether the presence of these compounds in streambed sediments is related to the type and degree of development within the drainage area of each sampling site.

Journal of the American Water Resources Associatio↗

USGS2007

Relation between fish communities and riparian zone conditions at two spatial scales

The relation offish community composition to riparian cover at two spatial scales was compared at 18 streams in the agricultural Minnesota River Basin. The two spatial scales were: (1) local riparian zone (a 200 meter wide buffer extending 2 to 3 kilometers upstream of the sampling reach); and (2) the upstream riparian zone (a 200 m wide buffer on the mainstem and all perennial tributaries upstream of the sampling reach). Analysis of variance indicated that streams with wooded-local riparian zones had greater fish species richness (means = 20 and 15, respectively) and Index of Biotic Integrity (IBI) scores (means = 40 and 26, respectively) than streams with open-local riparian zones. Streams with wooded-upstream riparian zones tended (were not statistically significant) to have greater numbers of species (means = 19 and 15, respectively) and IBI scores (means = 33 and 28, respectively) than streams with open-upstream riparian zones. There was no significant interaction between the riparian zone conditions at the two scales. This study suggests that maintenance of wooded riparian cover along streams could be effective in maintaining or improving fish community composition in streams draining heavily agricultural areas.

Journal of the American Water Resources Associatio↗

USGS2018

A database of natural monthly streamflow estimates from 1950 to 2015 for the conterminous United States

Quantifying and understanding the natural streamflow regime, defined as expected streamflow that would occur in the absence of anthropogenic modification to the hydrologic system, is critically important for the development of management strategies aimed at protecting aquatic ecosystems. Water balance models have been applied frequently to estimate natural flows, but are limited in the number of predictor variables that can be included. Here, a statistical machine learning technique — random forest modeling — was applied to estimate natural flows at a monthly time‐step from 1950 to 2015 for >2.5 million stream reaches in the conterminous United States (U.S.) using 200 potential predictor variables. We describe the development and documentation of this dataset and assess model performance. Model fit statistics (mean Nash–Sutcliffe efficiency = 0.85; observed/expected ratio = 0.94) indicate good correspondence between predicted and observed flows at nearly 2,000 streamgages. As an example application of the dataset, the observed streamflow record at a site prior to and after the construction of an upstream reservoir was compared with estimated natural flows to demonstrate the magnitude of seasonal depletions in streamflow due to the reservoir. This dataset can be applied to quantify natural and anthropogenic processes contributing to streamflow depletion or augmentation, and assess associated ecological effects.

Journal of the American Water Resources Associatio↗

USGS2019

Phosphorus and nitrogen transport in the binational Great Lakes Basin estimated using SPARROW watershed models

Eutrophication problems in the Great Lakes are caused by excessive nutrient inputs (primarily phosphorus, P, and nitrogen, N) from various sources throughout its basin. In developing protection and restoration plans, it is important to know where and from what sources the nutrients originate. As part of a binational effort, Midcontinent SPARROW (SPAtially Referenced Regression On Watershed attributes) models were developed and used to estimate P and N loading from throughout the entire basin based on nutrient inputs similar to 2002; previous SPARROW models only estimated U.S. contributions. The new models have a higher resolution (~2‐km 2 catchments) enabling improved descriptions of where nutrients originate and the sources at various spatial scales. The models were developed using harmonized geospatial datasets describing the stream network, nutrient sources, and environmental characteristics affecting P and N delivery. The models were calibrated using loads from sites estimated with ratio estimator and regression techniques and additional statistical approaches to reduce spatial correlation in the residuals and have all monitoring sites equally influence model development. SPARROW results, along with interlake transfers and direct atmospheric inputs, were used to quantify the entire P and N input to each lake and describe the importance of each nutrient source. Model results can be used to compare loading and yields from various tributaries and jurisdictions.

Great Lakes↗

USGS2026

Estimating baseline flow resistance parameters for remote sensing river discharge (RSQ) from river morphology characteristics

This study demonstrates that flow resistance in rivers, quantified via calibration of a modified Manning equation, can be estimated from channel hydrometric information available from globally derived data sets for a subset of river reaches in Alaska and with less certainty in a subset of river reaches in the contiguous United States. The channel morphometry data sets tested include the National Aeronautics and Space Administration (NASA) Surface Water Ocean Topography (SWOT) river database (SWORD) and U.S. Geological Survey (USGS) Scale Specific Sinuosity (S3) river channel morphometry metrics. It is found that for the subset of rivers considered, the meander length, number of active channels, maximum width, width variance, and slope of the channel are strongly correlated with the flow resistance term in the Manning equation. Analytical machine learned models were derived, and a statistical multiple regression model developed to map the flow resistance in rivers across Alaska that are contained in the SWORD data base. The study points to the possibility of global a priori estimation of flow resistance in rivers for application in remote sensing of river discharge from river water surface-width, slope and height measurements made by SWOT and other satellites.

Journal of the American Water Resources Associatio↗

USGS2007

Year-class formation of upper St. Lawrence River northern pike

Variables associated with year-class formation in upper St. Lawrence River northern pike Esox lucius were examined to explore population trends. A partial least-squares (PLS) regression model (PLS 1) was used to relate a year-class strength index (YCSI; 1974-1997) to explanatory variables associated with spawning and nursery areas (seasonal water level and temperature and their variability, number of ice days, and last day of ice presence). A second model (PLS 2) incorporated four additional ecological variables: potential predators (abundance of double-crested cormorants Phalacrocorax auritus and yellow perch Perca flavescens), female northern pike biomass (as a measure of stock-recruitment effects), and total phosphorus (productivity). Trends in adult northern pike catch revealed a decline (1981-2005), and year-class strength was positively related to catch per unit effort (CPUE; R2 = 0.58). The YCSI exceeded the 23-year mean in only 2 of the last 10 years. Cyclic patterns in the YCSI time series (along with strong year-classes every 4-6 years) were apparent, as was a dampening effect of amplitude beginning around 1990. The PLS 1 model explained over 50% of variation in both explanatory variables and the dependent variable, YCSI first-order moving-average residuals. Variables retained (N = 10; Wold's statistic ??? 0.8) included negative YCSI associations with high summer water levels, high variability in spring and fall water levels, and variability in fall water temperature. The YCSI exhibited positive associations with high spring, summer, and fall water temperature, variability in spring temperature, and high winter and spring water level. The PLS 2 model led to positive YCSI associations with phosphorus and yellow perch CPUE and a negative correlation with double-crested cormorant abundance. Environmental variables (water level and temperature) are hypothesized to regulate northern pike YCSI cycles, and dampening in YCSI magnitude may be related to a combination of factors, including wetland habitat changes, reduced nutrient loading, and increased predation by double-crested cormorants. ?? Copyright by the American Fisheries Society 2007.

North American Journal of Fisheries Management↗

USGS2012

Watershed regressions for pesticides (warp) models for predicting atrazine concentrations in Corn Belt streams

Watershed Regressions for Pesticides (WARP) models, previously developed for atrazine at the national scale, are improved for application to the United States (U.S.) Corn Belt region by developing region-specific models that include watershed characteristics that are influential in predicting atrazine concentration statistics within the Corn Belt. WARP models for the Corn Belt (WARP-CB) were developed for annual maximum moving-average (14-, 21-, 30-, 60-, and 90-day durations) and annual 95th-percentile atrazine concentrations in streams of the Corn Belt region. The WARP-CB models accounted for 53 to 62% of the variability in the various concentration statistics among the model-development sites. Model predictions were within a factor of 5 of the observed concentration statistic for over 90% of the model-development sites. The WARP-CB residuals and uncertainty are lower than those of the National WARP model for the same sites. Although atrazine-use intensity is the most important explanatory variable in the National WARP models, it is not a significant variable in the WARP-CB models. The WARP-CB models provide improved predictions for Corn Belt streams draining watersheds with atrazine-use intensities of 17 kg/km 2 of watershed area or greater.

Corn Belt↗

USGS2007

Relative influence of streamflows in assessing temporal variability in stream habitat

The effects of streamflows on temporal variation in stream habitat were analyzed from the data collected 6-11 years apart at 38 sites across the United States. Multiple linear regression was used to assess the variation in habitat caused by streamflow at the time of sampling and high flows between sampling. In addition to flow variables, the model also contained geomorphic and land use factors. The regression model was statistically significant (p < 0.05; R 2 = 0.31-0.46) for 5 of 14 habitat variables: mean wetted stream depth, mean bankfull depth, mean wetted stream width, coefficient of variation of wetted stream width, and the percent frequency of bank erosion. High flows between samples accounted for about 16% of the total variation in the frequency of bank erosion. Streamflow at the time of sampling was the main source of variation in mean stream depth and contributed to the variation in mean stream width and the frequency of bank erosion. Urban land use (population change) accounted for over 20% of the total variation in mean bankfull depth, 15% of the total variation in the coefficient of variation of stream width, and about 10% of the variation in mean stream width. ?? 2007 American Water Resources Association.

Journal of the American Water Resources Associatio↗

USGS2007

Influence of different temporal sampling strategies on estimating total phosphorus and suspended sediment concentration and transport in small streams

Various temporal sampling strategies are used to monitor water quality in small streams. To determine how various strategies influence the estimated water quality, frequently collected water quality data from eight small streams (14 to 110 km2) in Wisconsin were systematically subsampled to simulate typically used strategies. These subsets of data were then used to estimate mean, median, and maximum concentrations, and with continuous daily flows used to estimate annual loads (using the regression method) and volumetrically weighted mean concentrations. For each strategy, accuracy and precision in each summary statistic were evaluated by comparison with concentrations and loads of total phosphorus and suspended sediment estimated from all available data. The most effective sampling strategy depends on the statistic of interest and study duration. For mean and median concentrations, the most frequent fixed period sampling economically feasible is best. For maximum concentrations, any strategy with samples at or prior to peak flow is best. The best sampling strategy to estimate loads depends on the study duration. For one-year studies, fixed period monthly sampling supplemented with storm chasing was best, even though loads were overestimated by 25 to 50 percent. For two to three-year load studies and estimating volumetrically weighted mean concentrations, fixed period semimonthly sampling was best.

Wisconsin↗

USGS2007

Use of a wetland index to evaluate changes in riparian vegetation after livestock exclusion

A method was developed to characterize ecological integrity of riparian sites based on the abundance of hydric species. This wetland index can be calculated with species data, or with community type data as performed here. Classified riparian community types were used to describe vegetation at 14 livestock exclosures and adjacent grazed areas. Community type wetland index values were generated and used to calculate site wetland index values. It was hypothesized that removal of livestock would result in higher wetland index values because of release from herbivory and decreased physical disturbance of vegetation, streambanks, and soil. The wetland index for exclosures was about 12% higher than grazed sites; differences were statistically significant (p < 0.01) based on paired t-tests. The increase in hydric vegetation after livestock exclusion may have contributed to the greater bank stability (p = 0.002) and smaller width-to-depth ratio (p = 0.005) in exclosures. Challenges were encountered in using community types to describe and compare site vegetation, which could be avoided with species data collection. The wetland index can be a tool to monitor sites over time, compare sites with similar environments, or compare sites for which environmental differences can be accounted.

Journal of the American Water Resources Associatio↗