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Ludwig, Andrea, Marty Matlock, Brian Haggard, and Indrajeet Chaubey, 2012. Periphyton Nutrient Limitation and Maximum Potential Productivity in the Beaver Lake Basin, United States. Journal of the American Water Resources Association (JAWRA) 48(5): 896-908. DOI: 10.1111/j.1752-1688.2012.00657.x Abstract: The objectives of this study were to measure periphytic growth responses to enrichment with nitrogen (N), phosphorus (P), and simultaneous N and P using in situ bioassays in streams draining Beaver Reservoir Basin, Northwest Arkansas; compare periphytic growth responses measured with in situ bioassays with a range of land use and point sources; and test the lotic ecosystem trophic status index (LETSI) as a simplifying metric to compare effects of nonpoint-source pollutant-limiting variables of N, P, and sediment across the basin. P limitation was observed at sites across a transect of stream orders throughout the basin; however, at the two sites with highest ambient nitrogen concentrations, limitation was often coupled with nitrogen limitation. Nutrients were at nonlimiting levels at both of two sites below wastewater treatment plants in all seasonal deployments. A Michaelis-Menten growth equation described LETSI as a function of ambient PO4-P concentrations ( p < 0.05); the midpoint (LETSI of 0.50) corresponded with a PO4-P concentration of approximately 3 μg/l. Change-point analysis indicated a threshold point at LETSI of 0.80 and 15 μg/l PO4-P. These low values show that the periphytic community has a high affinity for available P, and that the watershed as a whole is sensitive to available nutrient inputs. [ABSTRACT FROM AUTHOR]

An increased loss of agricultural nutrients is a growing concern for water quality in Arkansas. Several studies have shown that best management practices (BMPs) are effective in controlling water pollution. However, those affected with water quality issues need water management plans that take into consideration BMPs selection, placement, and affordability. This study used a nondominated sorting genetic algorithm (NSGA-II). This multiobjective algorithm selects and locates BMPs that minimize nutrients pollution cost-effectively by providing trade-off curves (optimal fronts) between pollutant reduction and total net cost increase. The usefulness of this optimization framework was evaluated in the Lincoln Lake watershed. The final NSGA-II optimization model generated a number of near-optimal solutions by selecting from 35 BMPs (combinations of pasture management, buffer zones, and poultry litter application practices). Selection and placement of BMPs were analyzed under various cost solutions. The NSGA-II provides multiple solutions that could fit the water management plan for the watershed. For instance, by implementing all the BMP combinations recommended in the lowest-cost solution, total phosphorous (TP) could be reduced by at least 76% while increasing cost by less than 2% in the entire watershed. This value represents an increase in cost of $5.49 ha−1 when compared to the baseline. Implementing all the BMP combinations proposed with the medium- and the highest-cost solutions could decrease TP drastically but will increase cost by $24,282 (7%) and $82,306 (25%), respectively. [ABSTRACT FROM AUTHOR]

There has been a steady shift towards modeling and model-based approaches as primary methods of assessing watershed response to hydrologic inputs and land management, and of quantifying watershed-wide best management practice (BMP) effectiveness. Watershed models often require some degree of calibration and validation to achieve adequate watershed and therefore BMP representation. This is, however, only possible for gauged watersheds. There are many watersheds for which there are very little or no monitoring data available, thus the question as to whether it would be possible to extend and/or generalize model parameters obtained through calibration of gauged watersheds to ungauged watersheds within the same region. This study explored the possibility of developing regionalized model parameter sets for use in ungauged watersheds. The study evaluated two regionalization methods: global averaging, and regression-based parameters, on the SWAT model using data from priority watersheds in Arkansas. Resulting parameters were tested and model performance determined on three gauged watersheds. Nash-Sutcliffe efficiencies (NS) for stream flow obtained using regression-based parameters (0.53-0.83) compared well with corresponding values obtained through model calibration (0.45-0.90). Model performance obtained using global averaged parameter values was also generally acceptable (0.4 ≤ NS ≤ 0.75). Results from this study indicate that regionalized parameter sets for the SWAT model can be obtained and used for making satisfactory hydrologic response predictions in ungauged watersheds. [ABSTRACT FROM AUTHOR]

A study was conducted to quantify land use and management changes and their effects on water quality as part of an effort to evaluate the effects of best management practices under the Conservation Effects Assessment Project. This study was focused on the Lincoln Lake watershed, a primarily pastured watershed in northwest Arkansas and one of the watersheds funded under the Conservation Effects Assessment Project competitive grants program. As with a number of other Conservation Effects Assessment Project watersheds, this watershed has undergone substantial land-use change over the past few years. These changes have occurred concurrently with best management practice implementation. Thus, the need has arisen to determine their impacts on watershed water quality. Land-use analyses covering a 12-year period revealed a rapidly changing landscape, with the various land uses experiencing gains and losses at different times. Furthermore, a systematic trend for pastured areas to be replaced by urban land uses was identified, with pastures experiencing a net decline of about 12% during the analyses period. With regard to water quality downward trends were observed under base and storm flow conditions in the upper reaches (Upper Moores Creek) with significant changes in total phosphorus and total suspended solids (p-valpes = 0.0153 and 0.0135,respectively). Significant increases in flow and nitrate-nitrogen (p-values = 0.0465 and 0.0927, respectively) were observed in the lower reaches (Lower Moores Creek), while no appreciable changes were observed in one part of the watershed. We conclude that the concurrent implementation of best management practices served to protect water quality from otherwise adverse effects that might have occurred due to a rapid urbanization in the watershed. [ABSTRACT FROM AUTHOR]

Successful nonpoint source pollution control using best management practice placement is a complex process that requires in-depth knowledge of the locations of runoff source areas in a watershed. Currently, very few simulation tools are capable of identifying critical runoff source areas on hillslopes and those available are not directly applicable under all runoff conditions. In this paper, a comparison of two geographic information system (GIS)-based approaches: a topographic index model and a likelihood indicator model is presented, in predicting likely locations of saturation excess and infiltration excess runoff source areas in a hillslope of the Savoy Experimental Watershed located in northwest Arkansas. Based on intensive data collected from a two-year field study, the spatial distributions of hydrologic variables were processed using GIS software to develop the models. The likelihood indicator model was used to produce probability surfaces that indicated the likelihood of location of both saturation and infiltration excess runoff mechanisms on the hillslope. Overall accuracies of the likelihood indicator model predictions varied between 81 and 87% for the infiltration excess and saturation excess runoff locations respectively. On the basis of accuracy of prediction, the likelihood indicator models were found to be superior (accuracy 81-87%) to the predications made by the topographic index model (accuracy 69.5%). By combining statistics with GIS, runoff source areas on a hillslope can be identified by incorporating easily determined hydrologic measurements (such as bulk density, porosity, slope, depth to bed rock, depth to water table) and could serve as a watershed management tool for identifying critical runoff source areas in locations where the topographic index or other similar methods do not provide reliable results. [ABSTRACT FROM AUTHOR]

The article presents a study on the delineation of critical runoff source areas and runoff mechanisms in a pasture hillslope of Ozark Highlands Trail in Arkansas. The objective of the study is to understand the complexity of runoff production from pasture watershed using a field-scale approach. Runoffs of the three adjacent hillslope plots situated at the Savoy Experimental Watershed in north-west Arkansas were isolated, and each plot was equipped with paired subsurface saturation and surface runoff sensors, shallow groundwater wells, H-flumes and rain gauges. Results show that there is variance in infiltration excess and saturation excess runoff processes. It states that the methodology presented can be used in locating areas for best management practice (BMP) implementation.

The Soil and Water Assessment Tool (SWAT) was implemented in Northwest Arkansas to investigate flow and sediment predictive ability at multiple subbasin and hydrologic response units (HRU) distributions. The objectives of this study were to use SWAT and identify differences in annual predicted flow and sediment response of a watershed considering two subbasin delineations with six different HRU distributions each; quantify the uncertainty in SWAT output when sensitive model parameters are considered to have stochastic distribution; and evaluate the ability of the model to describe flow and sediment predictions of an ungauged watershed by stochastically validating the model. Flow results from the Single-Factor Between-Subjects Analysis of Variance test (α=0.05) indicated that predicted flow means were not significantly different from each other for all SWAT subbasin/HRU combinations; however, predicted flow means and measured flow mean were significantly different. Sediment simulation results suggested significant differences were present amongst the different model subbasin/HRU delineations and measured values. The Monte Carlo simulation of the model, using curve number (CN), soil evaporation compensation factor (ESCO), groundwater revap coefficient (GW_REVAP), and peak rate adjustment factor for sediment routing in the subbasin (AMP) as uncertain parameters, indicated that generally ESCO induced most uncertainty in predicted flow. However, sediment prediction uncertainty was affected most by uncertainty in AMP. Results indicated that SWAT applications on ungauged watersheds should include small subbasin sizing (∼2% of watershed area), HRUs that reflect actual land cover composition, a check to evaluate surface runoff and ground water contributions and modification of parameters as needed to reflect site conditions, sensitivity analysis, and uncertainty analysis that includes several sensitive parameters. [ABSTRACT FROM AUTHOR]

The Ecological Engineering Group within the Biological and Agricultural Engineering Department at the University of Arkansas applies the principles of ecology and engineering to prepare students to investigate and restore ecosystems degraded by human activity, focusing on the smallest unit of ecosystem management--the watershed. Ecological engineering teaching intertwined with research activities include investigation of the response of aquatic systems to nutrient enrichment from diffuse and point sources, control of biotic and abiotic processes on water quality, combining these investigations to enhance ecosystem management and develop decision support systems. Students are given an opportunity to apply their classroom knowledge to real-world watershed projects. Integration of teaching and research has enabled students to fully publish their research findings in undergraduate research journals. [ABSTRACT FROM AUTHOR]

Phosphorus (P) release from bottom sediments can be a significant source to the overlying water column, potentially maintaining and enhancing algal growth and eutrophic conditions in lakes and reservoirs. Thus, the objectives of this study were to: (1) measure P flux under aerobic and anaerobic conditions from intact sediment cores collected at Beaver Reservoir, northwest Arkansas, (2) evaluate the spatial variability in measured sediment P flux under aerobic and anaerobic conditions along the reservoir, and (3) compare external and internal P loads to Beaver Reservoir. Six intact sediment cores were collected at three sites representing the lacustrine, transitional, and riverine zones during June 2003, September 2003 and February 2004 and incubated for 21 days in the dark at ∼22°C. Three cores from each site were incubated under aerobic conditions and anaerobic conditions. Water samples were collected from the overlying water column in each core daily for the first five days and every other day thereafter and analyzed for soluble reactive phosphorus (SRP). Water removed from the core was replaced with filtered lake water, maintaining a constant overlying water volume of 1 l. Sediment P flux under anaerobic conditions (<0.01–1.77 mg m−2 day−1) was generally greater than that measured under aerobic conditions (<0.01–0.89 mg m−2 day−1). Some spatial variability existed in sediment P flux where P flux was generally greatest at the sites in the riverine and transitional zones. Maximum sediment P flux was observed under anaerobic conditions in cores collected from the transitional zone during September 2003. Average sediment P flux under aerobic conditions (0.09 mg m−2 day−1) and anaerobic conditions (0.31 mg m−2 day−1) was greater than the external P flux (0.05 mg m−2 day−1) estimated from the Beaver Reservoir tributaries. Results showed that the annual internal P load (7 Mg year−1) from bottom sediments in Beaver Reservoir was less than 10% of the annual external P load (∼81 Mg P year−1). The internal P load was significant, but it would not currently be cost effective to manage this P source given the large surface area of Beaver Reservoir. [ABSTRACT FROM AUTHOR]

Even though agricultural land use is a principal source of nonpoint-source pollution, the in-stream movement and transport of nutrients and their interaction with benthic sediments are not well understood. The objectives of this study were to: (1) assess if nutrients were limiting algal growth, (2) assess equilibrium between sediments and water column phosphorus (P), (3) evaluate spatial and temporal variability in P buffering capacity and easily exchangeable P, and (4) evaluate variations in stream nutrient retention efficiency in Moore's Creek, a pasture-dominated watershed in northwest Arkansas. This study used nutrient limitation bioassays, sediment nutrient extractions, and short-term nutrient injections to accomplish the study objectives. Results suggested that light, not nutrients, was limiting algal growth in Moore's Creek. Sediment equilibrium P concentration measurements suggested that sediments may be releasing dissolved inorganic P during winter and spring; however, sediments were a potential temporary sink of dissolved inorganic P during summer and fall. Exchangeable P concentrations varied between 0.4 and 1.0 mg kg-1 of dry sediments, and P sorption index varied between 3.2 and 5. Concentrations of ammonia nitrogen (NO4-N) and ortho P (PO4-P) generally decreased between sampling stations during nutrient injections at all three sites; however, nitrate N (NO3-N) concentrations increased downstream. A significant retention of NO3-N was not observed in any of the experiments, indicating that agricultural headwater streams may be a source of downstream NO3-N transport. The results indicated that a riparian cover should be maintained in nutrient-rich headwater streams in order to minimize algal production in the streams. Even nutrient-rich streams may continue to assimilate, to some extent, increased loads of P, altering the timing and magnitude of downstream transport of P. [ABSTRACT FROM AUTHOR]

The project team was successful in gaining voluntary stakeholder participation in the effort to evaluate the effectiveness of best management practices at reducing sediment and nutrient runoff and the factors that influence the adoption of best management practices by farmers. The Lincoln Lake watershed, a primarily agricultural subbasin of the politically embattled Illinois River watershed, lies within a designated nutrient surplus area of the state of Arkansas. The team initially faced a watershed population whose trust needed to be gained before any progress could be made. Successful stakeholder participation was fostered through the use of techniques taught to and used by extension agents of the University of Arkansas Division of Agriculture Cooperative Extension Service. The results of this stakeholder-guided collaborative approach allowed the collection of high-quality farm data, perceptions of stakeholders regarding water quality, and reasons why farmers adopt or refuse to adopt best management practices. [ABSTRACT FROM AUTHOR]

Phosphorus (P)-based management strategies have been adopted in state planning standards nationwide, as most states have modified and adapted the original P index approach to better assess local landscape characteristics and management practices. However, P-based management strategies and environmental issues have become the focus of legal action within and between the states of Arkansas and Oklahoma due to differing management strategies in trans-boundary watersheds. A court settlement agreement was reached between parties in July 2003 requiring the development of a new P index by January 1, 2004 for use in writing nutrient management plans throughout the entire Eucha/Spavinaw watershed. The University of Arkansas found it most appropriate to modify the existing P index already in use in Arkansas to meet terms of the settlement agreement and to better reflect landscape characteristics and management practices specific to the Eucha/Spavinaw watershed. Hence, the Eucha/Spavinaw P index was developed and submitted to the court. By court decree, nutrient management plans in the watershed were written using the Eucha/Spavinaw P index beginning in February 2004. The Court issued further modifications to the Eucha/Spavinaw P index prior to release because the court felt that the specific P index did not fully comply with the settlement agreement. Through 2004, it was reported that the implementation of the Eucha/Spavinaw P index resulted in recommended litter application rates that were approximately one-third the rates that were common before the implementation of the Eucha/Spavinaw P index. Litter application rates recommended by the Eucha/Spavinaw p index were as much as 60 percent lower than application rates that would be recommended with the Arkansas phosphorus index for pastures as currently used. [ABSTRACT FROM AUTHOR]