Linking Watershed Subbasin Characteristics to Water Quality Parameters in War Eagle Creek Watershed

A short-term sampling program was conducted to assess watershed-scale influences such as catchment land use, seasonal variability, and catchment size in War Eagle Creek in northwest Arkansas. The objective was to identify strategic subbasin sampling locations in War Eagle Creek watershed that would minimize the number of sampling sites while fully characterizing seasonal water quality. Additionally, we compared result from each sampling station (subbasin) to suggested ecoregion nutrient and sestonic chlorophyll-a criteria. Thirteen subbasins were identified within War Eagle Creek watershed for sampling and assessment. The effects of the WWTP effluent discharge (subbasin 8) were evident, as all constituent concentrations (conductivity, SRP, TP, NO2-N, NO3-N, and TN) were significantly greater (p < 0.10) downstream from the effluent discharge site compared with the majority of the other subbasins. NO3-N plus NO2-N and TN median concentrations for pasture-dominated subbasins 10 and 12 were greater than most other values. Similarly, regression analyses indicated a strong correlation between TN and % pasture cover in the subbasin (r = 0.912) and between NO3-N and % pasture cover in the subbasin (r = 0.925). Chlorophyll-a median concentration was greatest for subbasin 11, which was above median ecoregion criteria values. Sites and constituents varied seasonally, with lowest concentrations often measured in the winter-spring season and greatest loads calculated for winter-spring and fall seasons. Results indicated that a reduction of over 50% in the number of sites sampled can be made without losing information on the variability of the selected water quality parameters. By monitoring the reduced set of sampling sites, a more focused and frugal water quality monitoring program can be developed to determine the quality of water in War Eagle Creek for assessing designated uses.