Nutrient retention efficiency in streams receiving inputs from wastewater treatment plants

We tested the effect of nutrient inputs from wastewater treatment plants (WWTPs) on stream nutrient retention efficiency by examining the longitudinal patterns of ammonium, nitrate, and phosphate concentrations downstream of WWTP effluents in 15 streams throughout Catalonia (Spain). We hypothesized that large nutrient loadings would saturate stream communities, lowering nutrient retention efficiency (i.e., nutrient retention relative to nutrient flux) relative to less polluted streams. Longitudinal variation in ambient nutrient concentration reflected the net result of physical, chemical, or biological uptake and release processes. Therefore, gradual increases in nutrient concentration indicate that the stream acts as a net source of nutrients to downstream environments, whereas gradual declines indicate that the stream acts as a net sink. In those streams where gradual declines in nutrient concentration were observed, we calculated the nutrient uptake length as an indicator of the stream nutrient retention efficiency. No significant decline was found in dilution-corrected concentrations of dissolved inorganic nitrogen (DIN) and phosphate in 40 and 45% of streams, respectively. In the remaining streams, uptake length (estimated based on the decline of nutrient concentrations at ambient levels) ranged from 0.14 to 29 km (DIN), and from 0.14 to 14 km (phosphate). Overall, these values are longer (lower retention efficiency) than those from nonpolluted streams of similar size, supporting our hypothesis, and suggest that high nutrient loads affect fluvial ecosystem function. This study demonstrates that the efficiency of stream ecosystems to remove nutrients has limitations because it can be significantly altered by the quantity and quality of the receiving water.     

NUTRIENT AND HEAVY METAL TRANSPORT CAPABILITIES OF SEDIMENT IN THE SOUTHWESTERN UNITED STATES1

ABSTRACT: Most studies of nutrient loss from small study watersheds ignore a potentially important loss transported by the suspended sediment load. We proposed that the geology and vegetation of a watershed are predictors of the nutrient and heavy metal transporting capacity of its suspended sediment. Analyses of acid-digestable and extractable nutrients showed differences for sediments derived from ponderosa pine forests in the Southwest on different geologies. These differences were similar for soil, stream bank, and stream channel material for a given site. Suspended sediment collections had nutrient concentrations similar to those of stream channel collections. Different vegetation on a given geology affected primarily the organic matter content, cation exchange capacity, total P, and levels of extractable nutrients in sediment.     

EFFECT OF A POINT SOURCE INPUT ON STREAM NUTRIENT RETENTION1

ABSTRACT: We examined the effect of a point source (PS) input on water chemistry and nutrient retention in Spavinaw Creek, Arkansas, during summer baseflows in 1998 and 1999. The nutrient uptake length (S_w) concept was used to quantify the impact of nutrient inputs in the receiving stream. We used an artificial injection upstream of the PS inputs to estimate background S and used the natural decline in nutrient concentrations below the PS to estimate the net nutrient uptake length (S_net). S_w for soluble reactive phosphorus (SRP) in the upstream reference section was O.75 km, but S_net ranged from 9.0 to 31 km for SRP and 3.1 to 12 km for NO₃‐N in the reach below the PS. S_net‐SRP was significantly correlated with discharge whereas S_net‐NO₃‐N was correlated with the amount of NO₃‐N enrichment from the PS. In order to examine specific mechanisms of P retention, loosely exchangeable P and P Sorption Index (PSI) of stream sediments were measured. Sediments exhibited little natural P buffering capacity (low PSI) above the PS, but P loading from the PS further reduced PSI. Loosely exchangeable P in the sediments also increased three fold below the PS, indicating sediments removed some water column P. The physical process of flow and sediment sorption apparently regulated P retention in Spavinaw Creek, whereas the level of N enrichment and possibly biotic uptake and denitrification influenced N retention. Regardless of the mechanism, Spavinaw Creek demonstrated little ability to retain PS‐added nutrients because net nutrient uptake lengths were in the km range.     

ANALYSIS OF WASTE LOAD ALLOCATION PROCEDURES1

A study was made to analyze and modify procedures used for stream assimilation capacity and point source wasteload allocation calculations. This paper describes the sources and types of information collected and the analysis of alternative computation methods developed during the study. The calculation of stream assimilation capacity or Total Maximum Daily Load (TMDL), will depend upon assumed stream flows, quality standards, reaction rates, and modeling procedures. The “critical conditions” selected for TMDL calculations usually are low flows and warm temperatures. The complexity of water quality models used for TMDL and allocation calculations can range from simple, complete mixing to calibrated and verified mathematical models. A list of 20 wasteload allocation (WLA) methods was developed. Five of these WLA's were applied to an example stream to permit comparisons based on cost, equity, efficient use of stream assimilation capacity, and sensitivity to fundamental stream quality data. Based on insensitivity to data errors and current use by several states, the WLA method of “equal percent treatment” was preferable in the example stream.     

THE IMPORTANCE OF SOIL IN EVALUATING POTENTIAL WASTE WATER DISPOSAL SITES IN THE MISSOURI OZARKS1

ABSTRACT: A number of criteria can be used in the selection of an area for the irrigation disposal of secondary treated waste water. The inherent capacity of the surface soil to retain, or at least detain, the various nutrient ions passing through the profile in the percolating waters becomes the prime consideration in regions with shallow water tables or in Karst areas such as the Missouri Ozarks where the risk of ground water supply contamination is high. A comprehensive study of the nutrient renovation potential of several soils was undertaken at a proposed effluent irrigation site along the Ozark National Scenic Riverways in south central Missouri. The surface soil hydrology was evaluated employing selected soil water parameters. Exchange equilibria studies determined the retention capacity for Ca and Mg while the concentrations of other selected ions were analyzed in the soil water to measure their retention time and net removal. The movement of a bromine tracer was monitored as an index of the renovation capacity of these soils for the more mobile anions such as nitrate. Neutron activation analysis proved to be a useful tool in the water quality analyses. All surface soil profiles demonstrated some degree of nutrient renovation for the various nutrients studied.     

EFFECTS OF A DAIRY LOAFING LOT-BUFFER STRIP ON STREAM WATER QUALITY1

ABSTRACT: A loafing or sacrifice lot is an area located outside of the free stall barn, where a dairy herd spends several hours per day. Sacrifice lots are usually denuded of vegetation and have high concentrations of manure and urine that can contribute significant amounts of sediment, nutrients, and pathogens to nearby surface waters. In this study, stream water quality impacted by direct runoff from a sacrifice lot was monitored for a period of 20 months. Ambient stream water quality was monitored by grab sampling upstream and downstream of the sacrifice lot. During runoff events, stream water quality downstream of the sacrifice lot was monitored with an automatic sampler. Laboratory analyses were conducted for total suspended solids and nutrients (nitrogen and phosphorus compounds). A grass filter strip (GFS) was installed as a buffer downslope of the sacrifice lot 10 months into the study period. The impact of the buffer strip on the standardized pollutant concentrations and loads was evaluated using the non-parametric Wilcoxon test. The Wilcoxon test indicated that there was no significant difference (α= 0.05) in the standardized yield of sediment and dissolved pollutants before and after the GFS installation, except for phosphate-phosphorus and filtered total phosphorus concentrations, and sediment-bound total phosphorus and total kjeldahl nitrogen loads that decreased significantly. However, load decrease could have been partially caused by the smaller rainfall volumes after the GFS installation as compared to the existing condition.     

TRANSIENT WATER QUALITY MODELING IN STREAMS1

ABSTRACT. A general planning model for simulation of water quality in streams and canals is formulated and verified. The model simulates the temporal and spatial variations in conservative and nonconservative constituents. The nitrogen cycle and its interaction with other nutrients and the dissolved oxygen resources of the stream are included. A fully implicit finite difference approximation is used to solve the mass transport equations describing variations in constituent concentrations throughout the stream systems. The model is applied to the Truckee River in northern California. Results indicate the applicability of the model for assessing the impact of alternative water quality management strategies on the stream system.     

Ecological Responses to Trout Habitat Rehabilitation in a Northern Michigan Stream

Monitoring of stream restoration projects is often limited and success often focuses on a single taxon (e.g., salmonids), even though other aspects of stream structure and function may also respond to restoration activities. The Ottawa National Forest (ONF), Michigan, conducted a site-specific trout habitat improvement to enhance the trout fishery in Cook’s Run, a 3^rd-order stream that the ONF determined was negatively affected by past logging. Our objectives were to determine if the habitat improvement increased trout abundances and enhanced other ecological variables (overall habitat quality, organic matter retention, seston concentration, periphyton abundance, sediment organic matter content, and macroinvertebrate abundance and diversity) following rehabilitation. The addition of skybooms (underbank cover structures) and k-dams (pool-creating structures) increased the relative abundance of harvestable trout (>25 cm in total length) as intended but not overall trout abundances. Both rehabilitation techniques also increased maximum channel depth and organic matter retention, but only k-dams increased overall habitat quality. Neither approach significantly affected other ecological variables. The modest ecological response to this habitat improvement likely occurred because the system was not severely degraded beforehand, and thus small, local changes in habitat did not measurably affect most physical and ecological variables measured. However, increases in habitat volume and in organic matter retention may enhance stream biota in the long term.     

THE FRESHWATER STREAM,A COMPLEX ECOSYSTEM1

A stream is set apart from all other aquatic ecosystems in that the water is continually entering and leaving the stream and is in almost constant motion. Thus, there is essentially a unidirectional flow, a constant mixing of the watery medium, a continuous erosion of the substrate with concomitant changes in the characteristics of the stream bed, and little or no opportunity for the accumulation and retention of the dissolved nutrients. The physical and chemical characteristics of the stream are largely reflections of the physical and chemical makeup of the watershed. Because of the constant replacement of the water as it flows away, new nutrients must be brought into the stream continually in order to support the biotic communities. The kinds and amounts of nutrients that enter the stream determine, to a large extent, the numbers and kinds of organisms in the different communities. The organisms that comprise those communities may be categorized as representative species indigenous to springs, riffles, and pools. Most plants in streams are sessile whereas most of the animals are vagile, at least during some phase of their life cycle. All sessile organisms must depend on the current bringing their foodstuffs to them, but the vagile forms may seek out their foods in different parts of the stream and may even move from one community to another. Each community is adapted to its particular environment. Spring communities, because of the constancy of the physical and chemical environment, may reach what is essentially a “climax” situation and remain stable over long periods of time. Communities that occupy riffle and pool habitats may change from season to season and from year to year depending on changes in temperature, volume of flow, and the character of the substrate. Between each of these kinds of communities there are transitional areas that may be occupied by wider varieties of organisms than any of the three principal kinds of communities. In any event, the continuity of these communities in time and space is determined by the speed of the current which in turn depends upon the volume of flow. On this basis it becomes evident that the characteristics of the biotic communities are different at the source of a stream than at any other location. Similarly, riffle communities are different than those living in pools. The most difficult evaluation to be made in studying a stream ecosystem is that of the interlocking relationships among the many kinds of organisms. The plants, whatever kind they may be, fix carbon and other elements into organic compounds that can be utilized as food by the animals. The multitude of organisms that make up the bottom fauna of any stream are largely supported by the food formed directly by the plants. Such animals as small crustaceans, insect larvae, worms, turbellarians, mollusks, and the like serve as food for the carnivorous species. To determine the role of each organism in maintaining such a complex structure is a tremendous challenge. Many tools and methods are at the disposal of the biologist who dares to undertake such a project. Still, the greatest of all these is the dedication to spending long hours of tedious and, frequently, very hard work.     

Regional characteristics of land use in Northeast and Southern Blue Ridge Province: Associations with acid rain effects on surface-water chemistry

The Direct/Delayed Response Project (DDRP) is one of several studies being conducted by the United States Environmental Protection Agency to assess risk to surface waters from acidic deposition in the eastern United States. In one phase of DDRP, land use, wetland, and forest cover data were collected for statistical samples of 145 Northeast lake and 35 Southern Blue Ridge Province stream watersheds in the United States. Land-use and other data then were extrapolated from individual to target watershed populations. Project statistical design allows summarization of results for various subsets of the target population. This article discusses results and implications of the land-use and land-cover characterization for both regions. Forest cover was the primary land use in both regions. In the Northeast, developed (agriculture and urban) land was positively associated with surface-water chemistry values for acid neutralizing capacity, Ca plus Mg, pH, and sulfate in the Pocono/Catskill subregion. Extensive wetlands and beaver activity occur in parts of the Northeast region, whereas topography limits wetland and riparian development in the Southern Blue Ridge Province. Northeast soils have low sulfate adsorption capacity, most watersheds are near sulfur steady state, and lake sulfate concentrations are controlled principally by levels of sulfur deposition. Net annual sulfur retention in Northeast watersheds is positively correlated with occurrence of wetlands and beaver impoundments. In contrast, most Southern Blue Ridge Province soils have high sulfate adsorption capacities, resulting in high net watershed sulfur retention. At the present time, stream sulfate concentrations and percent sulfur retention are controlled principally by soil chemical properties related to adsorption rather than atmospheric deposition and land use. The information in this document has been funded wholly by the United States Environmental Protection Agency. It has been subjected to the agency's peer and administrative review, and it has been approved for publication as an EPA document. Mention of trade names or commercial products does not constitute endorsement or recommendation for use.     

Research Gaps Related to Forest Management and Stream Sediment in the United States

Water quality from forested landscapes tends to be very high but can deteriorate during and after silvicultural activities. Practices such as forest harvesting, site preparation, road construction/use, and stream crossings have been shown to contribute sediment, nutrients, and other pollutants to adjacent streams. Although advances in forest management accompanied with Best Management Practices (BMPs) have been very effective at reducing water quality impacts from forest operations, projected increases in demand for forest products may result in unintended environmental degradation. Through a review of the pertinent literature, we identified several research gaps related to water yield, aquatic habitat, sediment source and delivery, and BMP effectiveness that should be addressed for streams in the United States to better understand and address the environmental ramifications of current and future levels of timber production. We explored the current understanding of these topics based on relevant literature and the possible implications of increased demand for forest products in the United States.     

Assessment of a turfgrass sod best management practice on water quality in a suburban watershed

The disposal of manure on agricultural land has caused water quality concerns in many rural watersheds, sometimes requiring state environmental agencies to conduct total maximum daily load (TMDL) assessments of stream nutrients, such as nitrogen (N) and phosphorus (P). A best management practice (BMP) has been developed in response to a TMDL that mandates a 50% reduction of annual P load to the North Bosque River (NBR) in central Texas. This BMP exports composted dairy manure P through turfgrass sod from the NBR watershed to urban watersheds. The manure-grown sod releases P slowly and would not require additional P fertilizer for up to 20 years in the receiving watershed. This would eliminate P application to the sod and improve the water quality of urban streams. The soil and water assessment tool (SWAT) was used to model a typical suburban watershed that would receive the sod grown with composted dairy manure to assess water quality changes due to this BMP. The SWAT model was calibrated to simulate historical flow and estimated sediment and nutrient loading to Mary's Creek near Fort Worth, Texas. The total P stream loading to Mary's Creek was lower when manure-grown sod was transplanted instead of sod grown with inorganic fertilizers. Flow, sediment and total N yield were the same for both cases at the watershed outlet. The SWAT simulations indicated that the turfgrass BMP can be used effectively to import manure P into an urban watershed and reduce in-stream P levels when compared to sod grown with inorganic fertilizers.     

Relationships between water quality, habitat quality, and macroinvertebrate assemblages in Illinois streams

The influence of specific stressors, such as nutrient enrichment and physical habitat degradation, on biotic integrity requires further attention in Midwestern streams. We sampled 53 streams throughout Illinois and examined relationships between macroinvertebrate community structure and numerous physicochemical parameters. Streams were clustered into four major groups based on taxa dissimilarity. Habitat quality and dissolved nutrients were responsible for separating the major groups in a nonmetric multidimensional scaling ordination. Furthermore, the alignment of environmental factors in the ordination suggested there was a habitat quality-nutrient concentration gradient such that streams with high-quality habitats usually had low concentrations of nutrients. Discrimination by community measures further validated the major stream groups and indicated that forested streams had generally higher biological integrity than agricultural streams, which in turn had greater integrity than urban streams. Our results demonstrate that physical habitat degradation and nutrient pollution are important and often confounded determinants of biotic integrity in Illinois streams. In addition, we suggest that management of Midwestern streams could benefit from further implementation of multivariate data exploration and stream classification techniques.     

Dry Weather Water Quality Loadings in Arid,Urban Watersheds of the Los Angeles Basin,California, USA1

Abstract: Dry weather runoff in arid, urban watersheds may consist entirely of treated wastewater effluent and/or urban nonpoint source runoff, which can be a source of bacteria, nutrients, and metals to receiving waters. Most studies of urban runoff focus on stormwater, and few have evaluated the relative contribution and sources of dry weather pollutant loading for a range of constituents across multiple watersheds. This study assessed dry weather loading of nutrients, metals, and bacteria in six urban watersheds in the Los Angeles region of southern California to estimate relative sources of each constituent class and the proportion of total annual load that can be attributed to dry weather discharge. In each watershed, flow and water quality were sampled from storm drain and treated wastewater inputs, as well as from in‐stream locations during at least two time periods. Data were used to calculate mean concentrations and loads for various sources. Dry weather loads were compared with modeled wet weather loads under a range of annual rainfall volumes to estimate the relative contribution of dry weather load. Mean storm drain flows were comparable between all watersheds, and in all cases, approximately 20% of the flowing storm drains accounted for 80% of the daily volume. Wastewater reclamation plants (WRP) were the main source of nutrients, storm drains accounted for almost all the bacteria, and metals sources varied by constituent. In‐stream concentrations reflected major sources, for example nutrient concentrations were highest downstream of WRP discharges, while in‐stream metals concentrations were highest downstream of the storm drains with high metals loads. Comparison of wet vs. dry weather loading indicates that dry weather loading can be a significant source of metals, ranging from less than 20% during wet years to greater than 50% during dry years.     

Transport and metabolic fate of sewage particles in a recipient stream

Although the implementation of wastewater treatment plants (WWTP) has dramatically increased the quality of surface waters in urbanized areas, WWTPs can still discharge noticeable amounts of solutes and particles to recipient streams. Although the fate of WWTP nutrients has received considerable attention, transport and in-stream transformation of sewage-derived particulate organic matter (SDPOM) have not. To investigate the transport and transformation of SDPOM in recipient streams, we experimentally injected fluorescently labeled SDPOM into a headwater stream and tracked its downstream fate at baseflow. Most SDPOM disappeared from the streamwater within a 160-m long reach with an average deposition velocity of 0.14 mm s(-1). We further coupled hydrometric measurements of specific water fluxes through the streambed interface with a mixing model to estimate streambed oxygen removal, and found significantly higher oxygen removal in the deposition (0.75 g O2 m(-2) d(-1)) than in the downstream post-deposition (0.36 g O2 m(-2) d(-1)) subreach. Contrary to our expectations, we did not detect any apparent effect of SDPOM deposition on streambed clogging. Our results show the capacity of a recipient stream to retain SDPOM and to reduce its downstream export, and thus contribute to a better understanding of ecosystem services of human-altered streams.     

Effects of dredging on benthic diatom assemblages in a lowland stream

The objective of this study was to assess the effects of dredging on the structure and composition of diatom assemblages from a lowland stream and to investigate whether the response of diatom assemblages to the dredging is also influenced by different water quality. Three sampling sites were established in Rodríguez Stream (Argentina); physico-chemical variables and benthic diatom assemblages were sampled weekly in spring 2001. Species composition, cell density, diversity and evenness were estimated. Diatom tolerance to organic pollution and eutrophication were also analyzed. Differences in physico-chemical variables and changes in benthic diatom assemblages were compared between the pre- and post-dredging periods using a t-test. Data were analyzed using Principal Components Analysis (PCA), non-metric multidimensional scaling (MDS) ordination and cluster analysis. The effects of dredging in the stream involve two types of disturbances: (i) in the stream bed, by the removal and destabilization of the substrate and (ii) in the water column, by generating chemical changes and an alteration of the light environment of the stream. Suspended solids, soluble reactive phosphorus and dissolved inorganic nitrogen were significantly higher in post-dredging periods. Physical and chemical modifications in the habitat of benthic diatoms produced changes in the assemblage; diversity and species numbers showed an immediate increase after dredging, decreasing at the end of the study period. Changes in the tolerance of the diatom assemblage to organic pollution and eutrophication were also observed as a consequence of dredging; in the post-dredging period sensitive species were replaced by either tolerant or most tolerant species. These changes were particularly noticeable in site 1 (characterized by its lower amount of nutrients and organic matter previous to dredging), which showed an increase in the amount of nutrients and oxygen demand as a consequence of sediment removal. However, these changes were not so conspicuous in sites 2 and 3, which already presented a marked water quality deterioration before the execution of the dredging works.     

Restoration of Riparian Buffer Function in Reclaimed Surface Mine Soils

Ecosystem processes such as water infiltration and denitrification largely determine how riparian buffers function to protect surface water quality. Reclaimed mine areas offer a unique opportunity to study the restoration of riparian function without the confounding influence of past land use. Between 1980 and 2000 in southern Illinois, agricultural fields with forest buffers were established along three restored stream reaches in reclaimed mine land. Our research objective was to compare common indicators of soil quality (infiltration, soil C and N, bulk density, and soil moisture) between forest and cultivated riparian zones to determine if riparian function was being restored. Soil bulk density was significantly lower in the forest buffers compared to the agricultural fields. The forest buffers had greater soil total C, total N, and moisture levels than agricultural fields likely due to greater organic matter inputs. Soil total C and N levels in forest buffers were positively related to age of restoration, indicating soil quality is gradually being restored in the buffers. Restoration success of riparian buffers should not be estimated by the return of structure alone; it also includes reestablishment of functions such as nutrient cycling and water retention that largely determine water quality benefits. Watershed planning efforts can expect a lag time on the order of decades between riparian restoration activities and surface water quality improvement.     

The Role of Periphyton in Mediating the Effects of Pollution in a Stream Ecosystem

The effects of pollutants on primary producers ramify through ecosystems because primary producers provide food and structure for higher trophic levels and they mediate the biogeochemical cycling of nutrients and contaminants. Periphyton (attached algae) were studied as part of a long-term biological monitoring program designed to guide remediation efforts by the Department of Energy’s Y-12 National Security Complex on East Fork Poplar Creek (EFPC) in Oak Ridge, Tennessee. High concentrations of nutrients entering EFPC were responsible for elevated periphyton production and placed the stream in a state of eutrophy. High rates of primary production at upstream locations in EFPC were associated with alterations in both invertebrate and fish communities. Grazers represented >50% of the biomass of invertebrates and fish near the Y-12 Complex but <10% at downstream and reference sites. An index of epilithic periphyton production accounted for 95% of the site-to-site variation in biomass of grazing fish. Analyses of heavy metals in EFPC periphyton showed that concentrations of zinc, cadmium, copper and nickel in periphyton decreased exponentially with distance downstream from Y-12. Zinc uptake by periphyton was estimated to reduce the concentration of this metal in stream water ~60% over a 5-km reach of EFPC. Management options for mitigating eutrophy in EFPC include additional reductions in nutrient inputs and/or allowing streamside trees to grow and shade the stream. However, reducing periphyton growth may lead to greater downstream transport of contaminants while simultaneously causing higher concentrations of mercury and PCBs in fish at upstream sites.     

Simulated effects of sulfur deposition on nutrient cycling in class I wilderness areas

We predicted the effects of sulfate (SO(4)) deposition on wilderness areas designated as Class I air quality areas in western North Carolina using a nutrient cycling model (NuCM). We used three S deposition simulations: current, 50% decrease, and 100% increase. We measured vegetation, forest floor, and root biomass and collected soil, soil solution, and stream water samples for chemical analyses. We used the closest climate stations and atmospheric deposition stations to parameterize NuCM. The areas were: Joyce Kilmer (JK), Shining Rock (SR), and Linville Gorge (LG). They differ in soil acidity and nutrients, and soil solution and stream chemistry. Shining Rock and LG have lower soil solution base cation and higher acidic ion concentrations than JK. For SR and LG, the soil solution Ca/Al molar ratios are currently 0.3 in the rooting zone (A horizon), indicating Al toxicity. At SR, the simulated Ca/Al ratio increased to slightly above 1.5 after the 30-yr simulation regardless of S deposition reduction. At LG, Ca/Al ratios ranged from 1.6 to 2.4 toward the end of the simulation period, the 100% increase scenario had the lower value. Low Ca/Al ratios suggest that forests at SR and LG are significantly stressed under current conditions. Our results also suggest that SO(4) retention is low, perhaps contributing to their high degree of acidification. Their soils are acidic, low in weatherable minerals, and even with large reductions in SO(4) and associated acid deposition, it may take decades before these systems recover from depletion of exchangeable Ca, Mg, and K.     

Factors Affecting Stream Nutrient Loads: A Synthesis of Regional SPARROW Model Results for the Continental United States1

Preston, Stephen D., Richard B. Alexander, Gregory E. Schwarz, and Charles G. Crawford, 2011. Factors Affecting Stream Nutrient Loads: A Synthesis of Regional SPARROW Model Results for the Continental United States. Journal of the American Water Resources Association (JAWRA) 47(5):891‐915. DOI: 10.1111/j.1752‐1688.2011.00577.x Abstract: We compared the results of 12 recently calibrated regional SPARROW (SPAtially Referenced Regressions On Watershed attributes) models covering most of the continental United States to evaluate the consistency and regional differences in factors affecting stream nutrient loads. The models – 6 for total nitrogen and 6 for total phosphorus – all provide similar levels of prediction accuracy, but those for major river basins in the eastern half of the country were somewhat more accurate. The models simulate long‐term mean annual stream nutrient loads as a function of a wide range of known sources and climatic (precipitation, temperature), landscape (e.g., soils, geology), and aquatic factors affecting nutrient fate and transport. The results confirm the dominant effects of urban and agricultural sources on stream nutrient loads nationally and regionally, but reveal considerable spatial variability in the specific types of sources that control water quality. These include regional differences in the relative importance of different types of urban (municipal and industrial point vs. diffuse urban runoff) and agriculture (crop cultivation vs. animal waste) sources, as well as the effects of atmospheric deposition, mining, and background (e.g., soil phosphorus) sources on stream nutrients. Overall, we found that the SPARROW model results provide a consistent set of information for identifying the major sources and environmental factors affecting nutrient fate and transport in United States watersheds at regional and subregional scales.