Sparrow modeling to understand water quality conditions in major regions of the United States: A featured collection introduction
No abstract available.
Journal of the American Water Resources Associatio↗
Geology topics
R. B. Alexander
Publications and source records attributed to R. B. Alexander.
Trends in lead concentrations in major U.S. rivers and their relation to historical changes in gasoline-lead consumption
Declines in concentrations of dissolved lead occurred at nearly two-thirds of 306 locations on major U.S. rivers from 1974 to 1985. Declines in dissolved lead concentrations are statistically significant (p < 0.10) at approximately one-third of the sampling locations. Statistically significant increases in dissolved lead concentrations occurred at only 6 percent of the sites, but are clustered in the Texas-Gulf and Lower Mississippi region. Possible explanations for the observed trends in lead concentrations are tested through comparisons with (1) records of lead discharges from major sources including leaded-gasoline consumption and municipal- and industrial-point source discharges, (2) trends in various water-quality constituents such as pH and total alkalinity, and (3) basin characteristics such as drainage area. Statistically significant declines in lead concentrations in streams and gasoline lead (i.e., the largest source of lead at these sites) are highly coincident for the 1979 to 1980 period at most sampling locations. The greatest amount of decline in gasoline lead occurred at sites showing statistically significant downtrends in stream concentrations of lead from 1974 to 1985. No more than 5 percent of the trends in stream lead are influenced by municipal- and industrial-point sources of lead. Factors that affect the transport of dissolved lead, including lead solubility, suspended sediment, and basin characteristics such as drainage basin size, are not significantly related to trends in dissolved lead. Trends in streamflow explain no more than 7 percent of the downtrends in concentrations of lead and may partly explain the frequent increases in lead concentrations in the Texas-Gulf and Lower Mississippi regions.Declines in concentrations of dissolved lead occurred at nearly two-thirds of 306 locations on major US rivers from 1974 to 1985. Declines in dissolved lead concentrations are statistically significant at approximately one-third of the sampling locations. Statistically significant increases in dissolved lead concentrations occurred at only 6 percent of the sites, but are clustered in the Texas-Gulf and Lower Mississippi regions. Possible explanations for the observed trends in lead concentrations are tested through comparisons with records of lead discharges from major sources including leaded-gasoline consumption and municipal- and industrial-point source discharges, trends in various water-quality constituents such as pH and total alkalinity, and basin characteristics such as drainage area. Study results are discussed.
Water Resources Bulletin↗
The role of headwater streams in downstream water quality
Knowledge of headwater influences on the water-quality and flow conditions of downstream waters is essential to water-resource management at all governmental levels; this includes recent court decisions on the jurisdiction of the Federal Clean Water Act (CWA) over upland areas that contribute to larger downstream water bodies. We review current watershed research and use a water-quality model to investigate headwater influences on downstream receiving waters. Our evaluations demonstrate the intrinsic connections of headwaters to landscape processes and downstream waters through their influence on the supply, transport, and fate of water and solutes in watersheds. Hydrological processes in headwater catchments control the recharge of subsurface water stores, flow paths, and residence times of water throughout landscapes. The dynamic coupling of hydrological and biogeochemical processes in upland streams further controls the chemical form, timing, and longitudinal distances of solute transport to downstream waters. We apply the spatially explicit, mass-balance watershed model SPARROW to consider transport and transformations of water and nutrients throughout stream networks in the northeastern United States. We simulate fluxes of nitrogen, a primary nutrient that is a water-quality concern for acidification of streams and lakes and eutrophication of coastal waters, and refine the model structure to include literature observations of nitrogen removal in streams and lakes. We quantify nitrogen transport from headwaters to downstream navigable waters, where headwaters are defined within the model as first-order, perennial streams that include flow and nitrogen contributions from smaller, intermittent and ephemeral streams. We find that first-order headwaters contribute approximately 70% of the mean-annual water volume and 65% of the nitrogen flux in second-order streams. Their contributions to mean water volume and nitrogen flux decline only marginally to about 55% and 40% in fourth- and higher-order rivers that include navigable waters and their tributaries. These results underscore the profound influence that headwater areas have on shaping downstream water quantity and water quality. The results have relevance to water-resource management and regulatory decisions and potentially broaden understanding of the spatial extent of Federal CWA jurisdiction in U.S. waters. ?? 2007 American Water Resources Association.
Journal of the American Water Resources Associatio↗
Section 3. The SPARROW Surface Water-Quality Model—Theory, application and user documentation
SPARROW (SPAtially Referenced Regressions On Watershed attributes) is a watershed modeling technique for relating water-quality measurements made at a network of monitoring stations to attributes of the watersheds containing the stations. The core of the model consists of a nonlinear regression equation describing the non-conservative transport of contaminants from point and diffuse sources on land to rivers and through the stream and river network. The model predicts contaminant flux, concentration, and yield in streams and has been used to evaluate alternative hypotheses about the important contaminant sources and watershed properties that control transport over large spatial scales. This report provides documentation for the SPARROW modeling technique and computer software to guide users in constructing and applying basic SPARROW models. The documentation gives details of the SPARROW software, including the input data and installation requirements, and guidance in the specification, calibration, and application of basic SPARROW models, as well as descriptions of the model output and its interpretation. The documentation is intended for both researchers and water-resource managers with interest in using the results of existing models and developing and applying new SPARROW models. The documentation of the model is presented in two parts. Part 1 provides a theoretical and practical introduction to SPARROW modeling techniques, which includes a discussion of the objectives, conceptual attributes, and model infrastructure of SPARROW. Part 1 also includes background on the commonly used model specifications and the methods for estimating and evaluating parameters, evaluating model fit, and generating water-quality predictions and measures of uncertainty. Part 2 provides a user's guide to SPARROW, which includes a discussion of the software architecture and details of the model input requirements and output files, graphs, and maps. The text documentation and computer software are available on the Web at http://usgs.er.gov/sparrow/sparrow-mod.html .
Techniques and Methods↗
Estimation of nutrient sources and transport for New Zealand using the hybrid mechanistic-statistical model SPARROW
The hybrid mechanistic-statistical catchment model SPARROW was applied to predict the mean annual load of nitrogen and phosphorus in streams throughout New Zealand (270,000 km2). The loads from land areas, point sources, and erosion are routed through the drainage network (576,300 reaches) with first-order stream decay and attenuation in lakes and reservoirs. Model parameters were determined by calibration against loads measured in the national water quality network (77 sites). For nitrogen, the model predicted the measured loads well (R2 of 0.956 and RMSE of 0.33 in natural-log space), while for phosphorus the model fit was not as good (R2 of 0.900 and RMSE of 0.58). The predictions of exported yields for streams with catchments > 20 km2 are broadly comparable with previous compilations of yields for various land-use classes for nitrogen, but are larger than the previous measurements for phosphorus. The calibrated stream attenuation and lake/reservoir rates were broadly consistent with previous measurements. The predicted load of total nitrogen (TN) delivered to the coast was 167,700 t yr-1, which is 45% of the loads entering the streams. For total phosphorus (TP) the predicted load to the coast was 63,100 t yr-1, 44% of the load entering the streams. Reservoir/lake attenuation makes a relatively small contribution to the overall attenuation compared with in-stream attenuation (3.5% for nitrogen and 8.5% for phosphorus). The largest contribution of total nitrogen is from pastoral land uses, together accounting for 70% of the total nitrogen load to the coast. Land used for dairying makes a disproportionately large contribution to the load of total nitrogen in relation to the area of land (37% of the load versus 6.8% of the land). For total phosphorus, the highest contribution of the load to the coast is from erosion (53.2%). Point sources contribute only a small proportion of the load to the coast (3.2% for nitrogen, 1.8% for total phosphorus). The monitoring network does not include streams with catchments smaller than 10 km2, so model predictions for streams smaller than 10 km2 should be used with caution. ?? New Zealand Hydrological Society (2005).
Journal of Hydrology New Zealand↗
Estimates of diffuse phosphorus sources in surface waters of the United States using a spatially referenced watershed model
The statistical watershed model SPARROW (SPAtially Referenced Regression On Watershed attributes) was used to estimate the sources and transport of total phosphorus (TP) in surface waters of the United States. We calibrated the model using stream measurements of TP from 336 watersheds of mixed land use and spatial data on topography, soils, stream hydrography, and land use (agriculture, forest, shrub/grass, urban). The model explained 87% of the spatial variability in log transformed stream TP flux (kg yr -1 ). Predictions of stream yield ( kg ha -1 yr -1 ) were typically within 45% of the observed values at the monitoring sites. The model identified appreciable effects of soils, streams, and reservoirs on TP transport, The estimated aquatic rates of phosphorus removal declined with increasing stream size and rates of water flushing in reservoirs (i.e. areal hydraulic loads). A phosphorus budget for the 2.9 million km2 Mississippi River Basin provides a detailed accounting of TP delivery to streams, the removal of TP in surface waters, and the stream export of TP from major interior watersheds for sources associated with each land-use type.
Water Science and Technology↗
Natural background concentrations of nutrients in streams and rivers of the conterminous United States
Determining natural background concentrations of nutrients in watersheds in the developed world has been hampered by a lack of pristine sampling sites covering a range of climatic conditions and basin sizes. Using data from 63 minimally impacted U.S. Geological Survey reference basins, we developed empirical models of the background yield of total nitrogen (TN) and total phosphorus (TP) from small watersheds as functions of annual runoff, basin size, atmospheric nitrogen deposition rate, and region-specific factors. We applied previously estimated in-stream loss rates to yields from the small watershed models to obtain estimates of background TN and TP yield and concentration throughout the stream/river network in 14 ecoregions of the conterminous United States. Background TN concentration varies from less than 0.02 mg L-1 in the xeric west to more than 0.5 mg L-1 along the southeastern coastal plain. Background TP concentration varies from less than 0.006 mg L-1 in the xeric west to more than 0.08 mg L-1 in the great plains. TN concentrations in U.S. streams and rivers currently exceed natural background levels by a much larger factor (6.4) than do TP concentrations (2.0). Because of local variation in runoff and other factors, the range of background nutrient concentrations is very large within some nutrient ecoregions. It is likely that background concentrations in some streams in these regions exceed proposed nutrient criteria.
Environmental Science & Technology↗
Support of total maximum daily load programs using spatially referenced regression models
The spatially referenced regressions on watershed attributes modeling approach, as applied to predictions of total nitrogen flux in three North Carolina river basins, addresses several information needs identified by a National Research Council evaluation of the total maximum daily load program. The model provides reach-level predictions of the probability of exceeding water-quality criteria, and estimates of total nitrogen budgets. Model estimates of point- and diffuse-source contributions and nitrogen loss rates in streams and reservoirs compared moderately well with literature estimates. Maps of reach-level predictions of nutrient inputs and delivery provide an intuitive and spatially detailed summary of the origins and fate of nutrients within a basin.
Journal of Water Resources Planning and Management↗
Nitrogen retention in rivers: Model development and application to watersheds in the northeastern U.S.A.
A regression model (RivR-N) was developed that predicts the proportion of N removed from streams and reservoirs as an inverse function of the water displacement time of the water body (ratio of water body depth to water time of travel). When applied to 16 drainage networks in the eastern U.S., the RivR-N model predicted that 37% to 76% of N input to these rivers is removed during transport through the river networks. Approximately half of that is removed in 1st through 4th order streams which account for 90% of the total stream length. The other half is removed in 5th order and higher rivers which account for only about 10% of the total stream length. Most N removed in these higher orders is predicted to originate from watershed loading to small and intermediate sized streams. The proportion of N removed from all streams in the watersheds (37-76%) is considerably higher than the proportion of N input to an individual reach that is removed in that reach (generally <20%) because of the cumulative effect of continued nitrogen removal along the entire flow path in downstream reaches. This generally has not been recognized in previous studies, but is critical to an evaluation of the total amount of N removed within a river network. At the river network scale, reservoirs were predicted to have a minimal effect on N removal. A fairly modest decrease (<10 percentage points) in the N removed at the river network scale was predicted when a third of the direct watershed loading was to the two highest orders compared to a uniform loading.
Conference Paper↗
A comparison of models for estimating the riverine export of nitrogen from large watersheds
We evaluated the accuracy of six watershed models of nitrogen export in streams (kg km2 yr-1) developed for use in large watersheds and representing various empirical and quasi-empirical approaches described in the literature. These models differ in their methods of calibration and have varying levels of spatial resolution and process complexity, which potentially affect the accuracy (bias and precision) of the model predictions of nitrogen export and source contributions to export. Using stream monitoring data and detailed estimates of the natural and cultural sources of nitrogen for 16 watersheds in the northeastern United States (drainage sizes = 475 to 70,000 km2), we assessed the accuracy of the model predictions of total nitrogen and nitrate-nitrogen export. The model validation included the use of an error modeling technique to identify biases caused by model deficiencies in quantifying nitrogen sources and biogeochemical processes affecting the transport of nitrogen in watersheds. Most models predicted stream nitrogen export to within 50% of the measured export in a majority of the watersheds. Prediction errors were negatively correlated with cultivated land area, indicating that the watershed models tended to over predict export in less agricultural and more forested watersheds and under predict in more agricultural basins. The magnitude of these biases differed appreciably among the models. Those models having more detailed descriptions of nitrogen sources, land and water attenuation of nitrogen, and water flow paths were found to have considerably lower bias and higher precision in their predictions of nitrogen export.
Biogeochemistry↗
Effect of stream channel size on the delivery of nitrogen to the Gulf of Mexico
An increase in the flux of nitrogen from the Mississippi river during the latter half of the twentieth century has caused eutrophication and chronic seasonal hypoxia in the shallow waters of the Louisiana shelf in the northern Gulf of Mexico. This has led to reductions in species diversity, mortality of benthic communities and stress in fishery resources. There is evidence for a predominantly anthropogenic origin of the increased nitrogen flux, but the location of the most significant sources in the Mississippi basin responsible for the delivery of nitrogen to the Gulf of Mexico have not been clearly identified, because the parameters influencing nitrogen-loss rates in rivers are not well known. Here we present an analysis of data from 374 US monitoring stations, including 123 along the six largest tributaries to the Mississippi, that shows a rapid decline in the average first-order rate of nitrogen loss with channel size-from 0.45 day-1 in small streams to 0.005 day-1 in the Mississippi river. Using stream depth as an explanatory variable, our estimates of nitrogen-loss rates agreed with values from earlier studies. We conclude that the proximity of sources to large streams and rivers is an important determinant of nitrogen delivery to the estuary in the Mississippi basin, and possibly also in other large river basins.
Nature↗
Streamflow-induced variations in nitrate flux in tributaries to the Atlantic coastal zone
Streamflow-related variability in nutrient flux represents an important source of uncertainty in managing nutrient inputs to coastal ecosystems. Quantification of flux variability is of particular interest to coastal resource managers in adopting effective nutrient-reduction goals and monitoring progress towards these goals. We used historical records of streamflow and water-quality measurements for 104 river monitoring stations in an analysis of variability in annual and seasonal flux of nitrate to the Atlantic coastal zone. We present two measures of temporal flux variability: the coefficient of variation (CV) and the exceedence probability (EP) of 1.5 times the median flux. The magnitude of flux variations spans a very wide range and depends importantly upon the season of year and the climatic and land-use characteristics of the tributary watersheds. Year-to-year variations (CV) in annual mean flux range over two orders of magnitude, from 3-200% of the long-term mean flux, although variations more typically range from 20-40% of the long term mean. The annual probability of exceeding the long term median flux by more than 50% (EP) is less than 0.10 in most rivers, but is between 0.10 and 0.35 in 40% of the rivers. Year- to-year variability in seasonal mean flux commonly exceeds that in annual flux by a factor of 1.5 to 4. In western Gulf of Mexico coastal rivers, the year-to- year variability in the seasonal mean flux is larger than in other regions, and is of a similar magnitude in all seasons. By contrast, in Atlantic coastal rivers, the winter and spring seasons, which account for about 70% of the annual flux, display the smallest relative variability in seasonal mean flux. We quantify the elasticity of nutrient flux to hypothetical changes in streamflow (i.e., the percent increase in flux per percentage increase in mean discharge) to allow the approximation of flux variability from streamflow records and the estimation of the effects of future climatically induced changes in streamflow on nutrient flux. Flux elasticities are less than unity (median = 0.93%) at most stations, but vary widely from 0.05 % to 1.59%. Elasticities above unity occur most frequently in the largest rivers and in rivers draining the arid portions of the western Gulf of Mexico Basin. Historical flux variability and elasticity generally increase with the extent of arid conditions and the quantity of nonurban land use in the watershed. We extend the analysis of flux variability to examine several case studies of highly unusual meteorological events capable of significantly elevating nitrate flux and degrading estuarine ecology.
Biogeochemistry↗
State Soil Geographic (STATSGO) Data Base for the Conterminous United States
USSOILS is an Arc 7.0 coverage containing hydrology-relevant information for 10,498 map units covering the entire conterminous United States. The coverage was compiled from individual State coverages contained in the October 1994 State Soil Geographic (STATSGO) Data Base produced on CD-ROM. The geo-dataset USSOILS.PAT relates (on the basis of a map unit identifier) the 10,498 map units to 78,518 polygons. The scale of the geo-dataset is 1:250,000. The INFO attribute table USSOILS.MUID_ATTS contains selected variables from the STATSGO data set for 10,501 map units (an extra 3 map units are contained in the attribute table that are not in the geo-dataset - see the 'Procedures' section below), including: the map unit identifier, a 2-character state abbreviation, available water capacity of the soil, percent clay in the soil, the actual k-factor used in the water erosion component of the universal soil loss equation, the organic material in soil, soil permeability, cumulative thickness of all soil layers, hydrologic characteristics of the soil, quality of drainage, surface slope, liquid limit of the soil, share of a map unit having hydric soils, and the annual frequency of flooding. To facilitate mapping the attribute data, the narrative section below contains instructions for transferring the information contained in the attribute table USSOILS.MUID_ATTS to the polygon attribute table USSOILS.PAT. STATSGO United States Soil Water Capacity Clay Organic material Permeability Infiltration Drainage Hydric Flood frequency Slope
Open-File Report↗
A spatial model to aggregate point-source and nonpoint-source water-quality data for large areas
More objective and consistent methods are needed to assess water quality for large areas. A spatial model, one that capitalizes on the topologic relationships among spatial entities, to aggregate pollution sources from upstream drainage areas is described that can be implemented on land surfaces having heterogeneous water-pollution effects. An infrastructure of stream networks and drainage basins, derived from 1:250,000-scale digital-elevation models, define the hydrologic system in this spatial model. The spatial relationships between point- and nonpoint pollution sources and measurement locations are referenced to the hydrologic infrastructure with the aid of a geographic information system. A maximum-branching algorithm has been developed to simulate the effects of distance from a pollutant source to an arbitrary downstream location, a function traditionally employed in deterministic water quality models. ?? 1992.
Computers & Geosciences↗
Correlations between stream sulphate and regional SO2 emissions
The relationship between atmospheric SO 2 emissions and stream and lake acidification has been difficult to quantify, largely because of the limitations of sulphur deposition measurements. Precipitation sulphate (SO 4 ) records are mostly <5 yr in length 1 and do not account for dry sulphur deposition 2 . Moreover, a variable fraction of wet- and dry-deposited sulphur is retained in soils and vegetation and does not contribute to the acidity of aquatic systems 3,4 . We have compared annual SO 2 emissions for the eastern United States from 1967 to 1980 with stream SO 4 measurements from fifteen predominantly undeveloped watersheds (Figs 1,2). We find that the two forms of sulphur are strongly correlated on a regional basis and that streams in the southeastern United States (SE) receive a smaller fraction (on average, 16%, compared with 24% of regional sulphur emissions than do streams in the northeastern United States (NE). In addition to providing direct empirical evidence of a relationship between sulphur emissions and aquatic chemistry, these results suggest that there are significant regional differences in the fraction of deposited sulphur retained in basin soils and vegetation.
Nature↗