Stage‐Discharge Relationships for U‐, A‐, and W‐Weirs in Un‐submerged Flow Conditions1

Thornton, Christopher I., Anthony M. Meneghetti, Kent Collins, Steven R. Abt, and S. Michael Scurlock, 2011. Stage‐Discharge Relationships for U‐, A‐, and W‐Weirs in Un‐submerged Flow Conditions. Journal of the American Water Resources Association (JAWRA) 47(1):169‐178. DOI: 10.1111/j.1752‐1688.2010.00501.x Abstract: Instream rock weirs are routinely placed into stream systems to provide grade control, reduce streambank erosion, provide energy dissipation, and allow fish passage. However, design and performance criteria for site specific applications are often anecdotal or qualitative in nature, and based upon the experience of the design team. A study was conducted to develop generic state‐discharge relationships for U‐, A‐, and W‐weirs. A laboratory testing program was performed in which scaled, near‐prototype U‐, A‐, and W‐rock weir structures were constructed in 11 configurations. Each configuration encompassed a unique weir shape, bed material, and/or bed slope. Thirty‐one tests were conducted in which each structure was subjected to a sequence of predetermined discharges that minimally included the equivalent of 1/3 bankfull, 2/3 bankfull, and bankfull conditions. All tests were performed in subcritical, un‐submerged flow conditions. Stage‐discharge relationships were developed using multivariant, power regression techniques for each of the U‐, A‐, and W‐rock weirs as a function of the effective weir length, flow depth, mean weir height, rock size, and discharge coefficient. Unique coefficient expressions were developed for each weir shape, and a single discharge coefficient was proposed applicable to the weirs for determining the channel stage‐discharge rating.     

Variations in Base‐Flow Nitrate Flux in a First‐Order Stream and Riparian Zone1

Abstract: Nonpoint source pollution, which contributes to contamination of surface waters, is difficult to control. Some pollutants, particularly nitrate (), are predominantly transmitted through ground water. Riparian buffer zones have the potential to remove contaminants from ground water and reduce the amount of that enters surface water. This is a justification for setting aside vegetated buffer strips along waterways. Many riparian zone hydrologic models assume uniform ground‐water flow through organic‐rich soil under reducing conditions, leading to effective removal of ground‐water prior to discharge into a stream. However, in a small first‐order stream in the mid‐Atlantic coastal plain, base‐flow generation was highly variable (spatially and temporally). Average base‐flow loads were greater in winter than summer, and higher during a wetter year than in dryer years. Specific sections of the stream consistently received greater amounts of high ground water than others. Areas within the riparian zone responsible for most of the exported from the watershed are termed “critical areas.” Over this 5‐year study, most of the exported during base flow originated from a critical area comprising less than 10% of the total riparian zone land area. Allocation of resources to address and improve mitigation function in critical areas should be a priority for continued riparian zone research.     

A Side‐by‐Side Comparison of Pervious Concrete and Porous Asphalt1

Welker, Andrea L., James D. Barbis, and Patrick A. Jeffers, 2012. A Side‐by‐Side Comparison of Pervious Concrete and Porous Asphalt. Journal of the American Water Resources Association (JAWRA) 48(4): 809‐819. DOI: 10.1111/j.1752‐1688.2012.00654.x Abstract: This article compares the performance of two permeable pavements, pervious concrete and porous asphalt, that were installed side‐by‐side in fall 2007. Because the pavements are located directly adjacent to one another, they experience the same vehicle loads, precipitation, and pollution loads. These permeable pavements are part of an infiltration stormwater control measure (SCM). This article focuses on the comparison of water quality parameters, maintenance and durability, and user perception. Eleven different water quality parameters were analyzed at this site for 19 different storm events over a one year period: pH, conductivity, total suspended solids, chlorides, total nitrogen, total phosphorus, total dissolved copper, total dissolved lead, total dissolved cadmium, total dissolved chromium, and total dissolved zinc. Results from the two pavement types were compared using the Mann–Whitney U‐test. The only parameter that was found to be statistically different between the two pavements was pH. Periodic inspection of the two pavement types indicated that after two years of use both pavements were wearing well. However, there was some evidence of clogging of both pavements and some evidence of surface wear. A survey of users of the lot indicated that the perception of these permeable pavements was favorable.     

Model Based Nitrate TMDLs for Two Agricultural Watersheds of Southeastern Minnesota1

Abstract: In this study, a set of nitrogen reduction strategies were modeled to evaluate the feasibility of improving water quality to meet total maximum daily loads (TMDLs) in two agricultural watersheds. For this purpose, a spatial‐process model was calibrated and used to predict monthly nitrate losses (1994‐96) from Sand and Bevens Creek watersheds located in south‐central Minnesota. Statistical comparison of predicted and observed flow and nitrate losses gave r² coefficients of 0.75 and 0.70 for Sand Creek watershed and 0.72 and 0.67 for Bevens Creek watershed, respectively. Modeled alternative agricultural management scenarios included: six different N application rates over three application timings and three different percentages of crop land with subsurface drainage. Predicted annual nitrate losses were then compared with nitrate TMDLs assuming a 30% reduction in observed nitrate losses is required. Reductions of about 33 (8.6 to 5.8 kg/ha) and 35% (23 to 15 kg/ha) in existing annual nitrate losses are possible for Sand and Bevens Creek watersheds, respectively, by switching the timing of fertilizer application from fall to spring. Trends towards increases in tile‐drained crop land imply that attaining nitrate TMDLs in future may require other alternative management practices in addition to fertilizer management such as partial conversion of crop land to pasture.     

Modeling the Potential Impact of Seasonal and Inactive Multi‐Aquifer Wells on Contaminant Movement to Public Water‐Supply Wells1

Johnson, R.L., B.R. Clark, M.K. Landon, L.J. Kauffman, and S.M. Eberts, 2011. Modeling the Potential Impact of Seasonal and Inactive Multi‐Aquifer Wells on Contaminant Movement to Public Water‐Supply Wells. Journal of the American Water Resources Association (JAWRA) 47(3):588‐596. DOI: 10.1111/j.1752‐1688.2011.00526.x Abstract: Wells screened across multiple aquifers can provide pathways for the movement of surprisingly large volumes of groundwater to confined aquifers used for public water supply (PWS). Using a simple numerical model, we examine the impact of several pumping scenarios on leakage from an unconfined aquifer to a confined aquifer and conclude that a single inactive multi‐aquifer well can contribute nearly 10% of total PWS well flow over a wide range of pumping rates. This leakage can occur even when the multi‐aquifer well is more than a kilometer from the PWS well. The contribution from multi‐aquifer wells may be greater under conditions where seasonal pumping (e.g., irrigation) creates large, widespread downward hydraulic gradients between aquifers. Under those conditions, water can continue to leak down a multi‐aquifer well from an unconfined aquifer to a confined aquifer even when those multi‐aquifer wells are actively pumped. An important implication is that, if an unconfined aquifer is contaminated, multi‐aquifer wells can increase the vulnerability of a confined‐aquifer PWS well.     

Impacts of Land‐Cover Change on Suspended Sediment Transport in Two Agricultural Watersheds1

Schilling, Keith E., Thomas M. Isenhart, Jason A. Palmer, Calvin F. Wolter, and Jean Spooner, 2011. Impacts of Land‐Cover Change on Suspended Sediment Transport in Two Agricultural Watersheds. Journal of the American Water Resources Association (JAWRA) 47(4):672‐686. DOI: 10.1111/j.1752‐1688.2011.00533.x Abstract: Suspended sediment is a major water quality problem, yet few monitoring studies have been of sufficient scale and duration to assess the effectiveness of land‐use change or conservation practice implementation at a watershed scale. Daily discharge and suspended sediment export from two 5,000‐ha watersheds in central Iowa were monitored over a 10‐year period (water years 1996‐2005). In Walnut Creek watershed, a large portion of land was converted from row crop to native prairie, whereas in Squaw Creek land use remained predominantly row crop agriculture. Suspended sediment loads were similar in both watersheds, exhibiting flashy behavior typical of incised channels. Modeling suggested that expected total soil erosion in Walnut Creek should have been reduced 46% relative to Squaw Creek due to changes in land use, yet measured suspended sediment loads showed no significant differences. Stream mapping indicated that Walnut Creek had three times more eroding streambank lengths than did Squaw Creek suggesting that streambank erosion dominated sediment sources in Walnut Creek and sheet and rill sources dominated sediment sources in Squaw Creek. Our results demonstrate that an accounting of all sources of sediment erosion and delivery is needed to characterize sediment reductions in watershed projects combined with long‐term, intensive monitoring and modeling to account for possible lag times in the manifestation of the benefits of conservation practices on water quality.     

A Benefit‐Cost Analysis of Total Maximum Daily Load Implementation1

Abstract: Total Maximum Daily Load (TMDL) implementation generates benefits and costs from water quality improvements, which are rarely quantified. This analysis examines a TMDL written to address bacteria and aquatic‐life‐use impairments on Abrams and Opequon Creeks in Virginia. Benefits were estimated using a contingent valuation survey of local residents. Costs were based on the number and type of best management practices (BMPs) necessary to achieve TMDL pollution reduction goals. BMPs were quantified using watershed‐scale water quality simulation models (Generalized Watershed Loading Function and Hydrological Simulation Program‐FORTRAN). Based on our projections, the costs to achieve TMDL induced pollution reduction goals outweigh the estimated benefits. Benefit‐cost ratios ranged between 0.1 and 0.3.     

Clogging of an Effluent Dominated Semiarid River: A Conceptual Model of Stream‐Aquifer Interactions1

Abstract: Water managers in arid and semiarid regions increasingly view treated wastewater (effluent) as an important water resource. Artificial recharge basins allow effluent to seep into the ground relieving stressed aquifers, however these basins frequently clog due to physical, chemical, and biological processes. Likewise effluent is increasingly used to maintain perennial base flow for dry streambeds, however, little is known about the impact of effluent on streambed hydraulic conductivity and stream‐aquifer interactions. We address this issue by investigating: if a clogging layer forms, how the formation of a clogging layer alters stream‐aquifer connections, and what hydrologic factors control the formation and removal of clogging layers. We focused on the Upper Santa Cruz River, Arizona where effluent from the Nogales International Waste Water Treatment Plant sustains perennial flow. Monthly sampling, along a 30 km river reach, was done with two foci: physical streambed transformations and water source identification using chemical composition. Historical dataset were included to provide a larger context for the work. Results show that localized clogging occurs in the Upper Santa Cruz River. The clogging layers perch the stream and shallow streambed causing desaturation below the streambed. With these results, a conceptual model of clogging is established in the context of a semiarid hydrologic cycle: formation during the hot premonsoon months when flow is nearly constant and removal by large flood flows (>10 m³/s) during the monsoon season. However, if the intensity of flooding during the semiarid hydrologic cycle is lessened, the dependent riparian area can experience a die off. This conceptual model leads us to the conclusion that effluent dominated riparian systems are inherently unstable due to the clogging process. Further understanding of this process could lead to improved ecosystem restoration and management.     

A Multilevel Model of the Impact of Farm‐Level Best Management Practices on Phosphorus Runoff1

Abstract: Multilevel or hierarchical models have been applied for a number of years in the social sciences but only relatively recently in the environmental sciences. These models can be developed in either a frequentist or Bayesian context and have similarities to other methods such as empirical Bayes analysis and random coefficients regression. In essence, multilevel models take advantage of the hierarchical structure that exists in many multivariate datasets; for example, water quality measurements may be taken from individual lakes, lakes are located in various climatic zones, lakes may be natural or man‐made, and so on. The groups, or levels, may effectively yield different responses or behaviors (e.g., nutrient load response in lakes) that often make retaining group membership more effective when developing a predictive model than when working with either all of the data together or working separately with the individuals. Here, we develop a multilevel model of the impact of farm level best management practices (BMPs) on phosphorus runoff. The result of this research is a model with parameters which vary with key practice categories and thus may be used to evaluate the effectiveness of these practices on phosphorus runoff. For example, it was found that the effect of fertilizer application rate on farm‐scale phosphorus loss is a function of the application method, the hydrologic soil group, and the land use (crop type). Further, results indicate that the most effective method for controlling fertilizer loss is through soil injection. In summary, the resultant multilevel model can be used to estimate phosphorus loss from farms and hence serve as a useful tool for BMP selection.     

POINT‐NONPOINT SOURCE WATER QUALITY TRADING: A CASE STUDY IN THE MINNESOTA RIVER BASIN1

ABSTRACT: Contrary to the general trend of only a few actual trades occurring within point‐nonpoint source water quality trading programs in the United States, two trading projects in the Minnesota River Basin, created under the provisions of National Pollutant Discharge Elimination System (NPDES) permits, have generated five major trades and numerous smaller ones. In this paper, these two projects are described to illustrate their origins, implementation, and results. It was found that several factors contributed to the relatively high number of trades in these projects, including the offsetting nature of the projects (hence a fixed number of credits that the point sources were required to obtain), readily available information on potential nonpoint source trading partners, and an effectively internal trading scheme used by one of the two projects. It was also found that long term structural pollution control measures, such as streambank stabilization, offered substantial cost savings over point source controls. Estimates of transaction costs showed that the total costs of the trading projects were increased by at least 35 percent after transaction costs were taken into account. Evidence also showed that in addition to pollution reduction, these two trading projects brought other benefits to the watershed, such as helping balance environmental protection and regional economic growth.     

EXAMINING LAND USE INFLUENCES ON STREAM HABITATS AND MACROINVERTEBRATES: A GIS APPROACH1

ABSTRACT: Geographic Information Systems (GIS) were used to assess the relationships between land use patterns and the physical habitat and macroinvertebrate fauna of streams within similar sized watersheds. Eleven second or third order watersheds ranging from highly urbanized to heavily forested were selected along Lake Superior's North Shore. Land use patterns within the watersheds were quantified using readily available digital land use/land cover information, with a minimum mapping resolution of 16 ha. Physical habitat features, describing substrate characteristics and stream morphology, were characterized at sample points within each stream. Principle component and correlation analyses were used to identify relationships between macroinvertebrates and stream physical habitat, and between habitat and land use patterns. Substrate characteristics and presence of coarse woody debris were found to have the strongest correlations with macreinvertebrate assemblage richness and composition. Agricultural and urban land use was correlated with substrate characteristics. Algal abundance, associated with macroinvertebrate compositional differences, was correlated with housing density and non-forest land covers. The use of readily available spatial data, even at this relatively coarse scale, provides a means to detect the primary relationships between land use and stream habitat quality; finer-resolution GIS databases are needed to assess more subtle influences, such as those due to riparian conditions.     

The Regionalization of National‐Scale SPARROW Models for Stream Nutrients1

Schwarz, Gregory E., Richard B. Alexander, Richard A. Smith, and Stephen D. Preston, 2011. The Regionalization of National‐Scale SPARROW Models for Stream Nutrients. Journal of the American Water Resources Association (JAWRA) 47(5):1151‐1172. DOI: 10.1111/j.1752‐1688.2011.00581.x Abstract: This analysis modifies the parsimonious specification of recently published total nitrogen (TN) and total phosphorus (TP) national‐scale SPAtially Referenced Regressions On Watershed attributes models to allow each model coefficient to vary geographically among three major river basins of the conterminous United States. Regionalization of the national models reduces the standard errors in the prediction of TN and TP loads, expressed as a percentage of the predicted load, by about 6 and 7%. We develop and apply a method for combining national‐scale and regional‐scale information to estimate a hybrid model that imposes cross‐region constraints that limit regional variation in model coefficients, effectively reducing the number of free model parameters as compared to a collection of independent regional models. The hybrid TN and TP regional models have improved model fit relative to the respective national models, reducing the standard error in the prediction of loads, expressed as a percentage of load, by about 5 and 4%. Only 19% of the TN hybrid model coefficients and just 2% of the TP hybrid model coefficients show evidence of substantial regional specificity (more than ±100% deviation from the national model estimate). The hybrid models have much greater precision in the estimated coefficients than do the unconstrained regional models, demonstrating the efficacy of pooling information across regions to improve regional models.     

Grass‐Shrub Riparian Buffer Removal of Sediment,Phosphorus, and Nitrogen From Simulated Runoff1

Abstract: Riparian buffer forests and vegetative filter strips are widely recommended for improving surface water quality, but grass‐shrub riparian buffer system (RBSs) are less well studied. The objective of this study was to assess the influence of buffer width and vegetation type on the key processes and overall reductions of total suspended solids (TSS), phosphorus (P), and nitrogen (N) from simulated runoff passed through established (7‐year old) RBSs. Nine 1‐m RBS plots, with three replicates of three vegetation types (all natural selection grasses, two‐segment buffer with native grasses and plum shrub, and two‐segment buffer with natural selection grasses and plum shrub) and widths ranging from 8.3 to 16.1 m, received simulated runoff having 4,433 mg/l TSS from on‐site soil, 1.6 mg/l total P, and 20 mg/l total N. Flow‐weighted samples were collected by using Runoff Sampling System (ROSS) units. The buffers were very efficient in removal of sediments, N, and P, with removal efficiencies strongly linked to infiltration. Mass and concentration reductions averaged 99.7% and 97.9% for TSS, 91.8% and 42.9% for total P, and 92.1% and 44.4% for total N. Infiltration alone could account for >75% of TSS removal, >90% of total P removal, and >90% of total N removal. Vegetation type induced significant differences in removal of TSS, total P, and total N. These results demonstrate that adequately designed and implemented grass‐shrub buffers with widths of only 8 m provide for water quality improvement, particularly if adequate infiltration is achieved.     

Development and Use of a Sedimentation Risk Index for Unpaved Road‐Stream Crossings in the Choctawhatchee Watershed1

Abstract: Unpaved road‐stream crossings increase sediment yields in streams and alter channel morphology and stability. Before restoration and sedimentation reduction strategies can be implemented, a priority listing of unpaved road‐stream crossings must be created. The objectives of this study were to develop a sedimentation risk index (SRI) for unpaved road‐stream crossings and to prioritize 125 sites in the Choctawhatchee watershed (southeastern Alabama) using this model. Field surveys involved qualitative and quantitative observations of 73 metrics related to waterway conditions, crossing structures, road approaches, and roadside soil erosion. The road‐stream crossing risk analyses involved elimination of candidate metrics based on redundancy, skewness, lack of data, professional judgment, lack of nonzero values, unbalanced box plots, and limited ranges of values. A final selection of 12 metrics formed the SRI and weighed factors involving soil erodibility, road sedimentation abatement features, and stream morphology alteration. The SRI was organized into narrative categories (excellent, good, fair, poor, and very poor) based on the distribution of scores. No excellent sites (scores ≥55) were found in this study, 17 (20.7%) were good (low sedimentation risk), 37 (45.1%) were fair (moderate sedimentation risk), 26 (31.7%) were poor (high sedimentation risk), and two (2.5%) were very poor (high sedimentation risk). There was no significant difference in SRI scores among crossing structure type (round culverts, box culverts, and bridges) (H = 4.31, df = 2, p = 0.058). A future study of the Choctawhatchee watershed involving the same study sites could assess the success of restoration plans and activities based on site score improvement or decline.     

Assessing the Relationship Between Landscape Patterns and Nonpoint‐Source Pollution in the Danjiangkou Reservoir Basin in China1

Abstract: The constrained ordination method from quantitative ecology was utilized to assess the relationship between landscape patterns and nonpoint‐source (NPS) pollution for the purpose of identifying effective water‐quality improvement practices in Danjiangkou Reservoir (DJKR) basin, China. The soil and water assessment tool (SWAT) was applied to simulate NPS pollution and the Fragstats model was applied to calculate the landscape metrics. The study concluded that organic nutrients formed the main NPS pollutant in the DJKR basin and that most of the NPS pollution occurred along with soil loss. Based on partial redundancy analysis, the conclusion that landscape metrics were significantly correlated to NPS pollution indices was obtained. Specifically, the composition of LULC (land use/land cover) was the most effective factor to estimate NPS pollution. Dry cultivated land was identified as the main source of NPS pollution, and paddy fields were characterized with the most intensive soluble nutrients loss. In addition, the reason that fragmented and complex landscape patterns exacerbate NPS pollution was that natural landscape composed most of this area. Moreover, the fragmented natural landscape indicated intensive agricultural activities that were the crucial trigger for NPS pollution. Combined with the economic condition in China, Conversion of Cropland to Forests Program (CCFP) should be conducted selectively and gradually in the DJKR basin.     

Water-Quality Performance of a Constructed Stormwater Wetland for All Flow Conditions1

Wadzuk, Bridget M., Matthew Rea, Gregg Woodruff, Kelly Flynn, and Robert G. Traver, 2010. Water-Quality Performance of a Constructed Stormwater Wetland for All Flow Conditions. Journal of the American Water Resources Association (JAWRA) 46(2):385-394. DOI: 10.1111/j.1752-1688.2009.00408.x Abstract: Results from a multiyear study demonstrate that a constructed stormwater wetland (CSW) improves urban stormwater runoff quality mitigating downstream impacts. Best management practices, such as CSWs, can comprehensively treat the various scales of stormwater runoff issues. Discrete sample analysis was used to investigate the CSW effect for storm events and base-flow periods on water-quality parameters [i.e., total suspended solids, total dissolved solids, total nitrogen, phosphorous (total and reactive), chloride, heavy metals (zinc, lead, and copper), and Escherichia coli]. The primary finding was that stormwater sediment load was removed through the CSW for all flow conditions during all seasons. The mechanisms responsible for the removal of suspended solids, including slower flow velocity, longer retention times, and vegetative contact, also reduced the mass of nutrients discharged downstream throughout the year. Exceedance probabilities were used to evaluate the expected pollutant reductions of nutrients and to incorporate the effect of natural flow variation on quality. Other findings included the observation that there was no significant difference in the performance of the CSW over two-year-long periods four years apart, indicating that a CSW is effective for an extended period.     

Hydrologic and Phosphorus Export Behavior of Small Streams in Commercial Poultry‐Pasture Watersheds1

Romeis, J. Joshua, C. Rhett Jackson, L. Mark Risse, Andrew N. Sharpley, and David E. Radcliffe, 2011. Hydrologic and Phosphorus Export Behavior of Small Streams in Commercial Poultry‐Pasture Watersheds. Journal of the American Water Resources Association (JAWRA) 1‐19. DOI: 10.1111/j.1752‐1688.2011.00521.x Abstract: Few watershed‐scale studies have evaluated phosphorus export in streamflow from commercial poultry‐pasture operations. Continuous streamflow and mixed‐frequency water quality datasets were collected from nine commercial poultry‐pasture (AG) and three forested (FORS) headwater streams (2.4‐44 ha) in the upper Etowah River basin of Georgia to estimate total P (TP) loads and examine variability of hydrologic response and water quality of storm and nonstorm‐flow regimes. Data collection duration ranged from 18 to 22 months, and approximately 1,600 water quality samples were collected. Significant (p < 0.1) inverse relationships were detected between peak flow response variables and both drainage area and fraction of forest cover. Order‐of‐magnitude differences in TP and dissolved reactive P (DRP) concentration were observed between AG and FORS sites and among AG sites. TP yields of FORS sites ranged from 0.01 to 0.1 kg P/ha. Yields of AG sites ranged from 0.031 to 3.17 kg P/ha (median = 0.354 kg P/ha). With 95% confidence intervals, AG yields ranged from 0.025 to 13.1 kg P/ha. These small‐watershed‐scale yields were similar to field‐scale yields measured in other studies in other regions. TP yields were significantly related to area‐weighted Mehlich‐1 soil test P concentrations (p = 0.0073) and base‐flow water sample P concentrations (p ≤ 0.0005). Water quality sampling during base‐flow conditions may be a useful screening tool for P risk‐based management programs.     

Long‐Term Water Quality and Biological Responses to Multiple Best Management Practices in Rock Creek,Idaho1

Abstract: Water quality and macroinvertebrate assemblage data from 1981 to 2005 were assessed to evaluate the water quality and biological responses of a western trout stream to the implementation of multiple best management practices (BMPs) on irrigated cropland. Data from Rock Creek near Twin Falls, Idaho, a long‐term monitoring site, were assembled from state and federal sources to provide the evaluation. Seasonal loads of the nonpoint source pollutants suspended sediment (SS), total phosphorus (TP), and nitrate‐nitrite (NN) were estimated using a regression model with time‐series streamflow data and constituent concentrations. Trends in the macroinvertebrate assemblages were evaluated using a number of biological metrics and nonmetric multidimensional scaling ordination. Regression analysis found significant annual decreases in TP and SS flow‐adjusted concentrations during the BMP implementation period from 1983 to 1990 of about 7 and 10%, respectively. These results are coincident with the implementation of multiple BMPs on about 75% of the irrigated cropland in the watershed. Macroinvertebrate assemblages during this time also responded with a change in taxa composition resulting in improved biotic index scores. Taxon specific TP and SS optima, empirically derived from a large national dataset, predicted a decrease in SS concentrations of about 37% (52 to 33 mg/l) and a decrease in TP concentrations of about 50% (0.20 to 0.10 mg/l) from 1981 to 1987. Decreasing trends in TP, SS, and NN pollutant loads were primarily the result of naturally low streamflow conditions during the BMP post‐implementation period from 1993 to 2005. Trends in macroinvertebrate responses during 1993 to 2005 were confounded by the introduction of the New Zealand mudsnail (Potamopyrgus  antipodarum), which approached densities of 100,000 per m² in riffle habitat. The occurrence of this invasive species appears to have caused a major shift in composition and function of the macroinvertebrate assemblages.     

“Nutrient Inputs to the Laurentian Great Lakes by Source and Watershed Estimated Using SPARROW Watershed Models” by Dale M. Robertson and David A. Saad2

Richards, R. Peter, Ibrahim Alameddine, J. David Allan, David B. Baker, Nathan S. Bosch, Remegio Confesor, Joseph V. DePinto, David M. Dolan, Jeffrey M. Reutter, and Donald Scavia, 2012. Discussion –“Nutrient Inputs to the Laurentian Great Lakes by Source and Watershed Estimated Using SPARROW Watershed Models” by Dale M. Robertson and David A. Saad. Journal of the American Water Resources Association (JAWRA) 1‐10. DOI: 10.1111/jawr.12006 Abstract: Results from the Upper Midwest Major River Basin (MRB3) SPARROW model and underlying Fluxmaster load estimates were compared with detailed data available in the Lake Erie and Ohio River watersheds. Fluxmaster and SPARROW estimates of tributary loads tend to be biased low for total phosphorus and high for total nitrogen. These and other limitations of the application led to an overestimation of the relative contribution of point sources vs. nonpoint sources of phosphorus to eutrophication conditions in Lake Erie, when compared with direct estimates for data‐rich Ohio tributaries. These limitations include the use of a decade‐old reference point (2002), lack of modeling of dissolved phosphorus, lack of inclusion of inputs from the Canadian Lake Erie watersheds and from Lake Huron, and the choice to summarize results for the entire United States Lake Erie watershed, as opposed to the key Western and Central Basin watersheds that drive Lake Erie’s eutrophication processes. Although the MRB3 SPARROW model helps to meet a critical need by modeling unmonitored watersheds and ranking rivers by their estimated relative contributions, we recommend caution in use of the MRB3 SPARRROW model for Lake Erie management, and argue that the management of agricultural nonpoint sources should continue to be the primary focus for the Western and Central Basins of Lake Erie.     

Streambank Soil and Phosphorus Losses Under Different Riparian Land‐Uses in Iowa1

Abstract: Phosphorus and sediment are major nonpoint source pollutants that degrade water quality. Streambank erosion can contribute a significant percentage of the phosphorus and sediment load in streams. Riparian land‐uses can heavily influence streambank erosion. The objective of this study was to compare streambank erosion along reaches of row‐cropped fields, continuous, rotational and intensive rotational grazed pastures, pastures where cattle were fenced out of the stream, grass filters and riparian forest buffers, in three physiographic regions of Iowa. Streambank erosion was measured by surveying the extent of severely eroding banks within each riparian land‐use reach and randomly establishing pin plots on subsets of those eroding banks. Based on these measurements, streambank erosion rate, erosion activity, maximum pin plot erosion rate, percentage of streambank length with severely eroding banks, and soil and phosphorus losses per unit length of stream reach were compared among the riparian land‐uses. Riparian forest buffers had the lowest streambank erosion rate (15‐46 mm/year) and contributed the least soil (5‐18 tonne/km/year) and phosphorus (2‐6 kg/km/year) to stream channels. Riparian forest buffers were followed by grass filters (erosion rates 41‐106 mm/year, soil losses 22‐47 tonne/km/year, phosphorus losses 9‐14 kg/km/year) and pastures where cattle were fenced out of the stream (erosion rates 22‐58 mm/year, soil losses 6‐61 tonne/km/year, phosphorus losses 3‐34 kg/km/year). The streambank erosion rates for the continuous, rotational, and intensive rotational pastures were 101‐171, 104‐122, and 94‐170 mm/year, respectively. The soil losses for the continuous, rotational, and intensive rotational pastures were 197‐264, 94‐266, and 124‐153 tonne/km/year, respectively, while the phosphorus losses were 71‐123, 37‐122, and 66 kg/km/year, respectively. The only significant differences for these pasture practices were found among the percentage of severely eroding bank lengths with intensive rotational grazed pastures having the least compared to the continuous and rotational grazed pastures. Row‐cropped fields had the highest streambank erosion rates (239 mm/year) and soil losses (304 tonne/km/year) and very high phosphorus losses (108 kg/km/year).