UNDERSTANDING AND PREDICTING THE IMPACT OF AGRICULTURE ON THE ENVIRONMENTAL INTEGRITY OF MANAGED WATERSHEDS
Location: Water Quality and Ecology Research
Title: Concentrated standing tailwater: a mechanism for nutrient delivery to downstream aquatic ecosystems
Submitted to: Journal of Agricultural Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 1, 2011
Publication Date: September 20, 2011
Citation: Kroger, R., Moore, M.T., Farris, J.L. 2011. Concentrated standing tailwater: a mechanism for nutrient delivery to downstream aquatic ecosystems. Journal of Agricultural Science and Technology Part B. 1:773-777.
Interpretive Summary: Drainage ditches efficiently move water off the production landscape and into receiving aquatic systems. Unfortunately, this rapid transport can also result in significant amounts of sediment, nutrients, and pesticides being delivered to streams and lakes. Two independent studies confirmed that background levels of nutrients in water were flushed through the system following an experimental dose. To help reduce the impacts of this "first flush," the use of controlled drainage is recommended. By reducing the amount of nutrients and pesticides through controlled drainage, water quality will be improved in downstream lakes and rivers. This information will be of benefit to farmers, landowners, conservationists, and regulators.
Contribution of first flush runoff events from intense rainfall to downstream aquatic ecosystems are often reported in terms of sediment and nutrient delivery, with hardly any consideration to the contribution that standing, concentrated tailwater in primary aquatic systems makes to downstream nutrient loads. Two geographically distinct studies (Jonesboro Arkansas, and Stoneville Mississippi; 4 studies, n = 30) evaluated the effectiveness of drainage ditch systems to mitigate nutrient concentrations and loads. Within each independent study all experimental ditches had elevated background nutrient concentrations as a result of standing water, prior to the start of each simulated runoff experiment. These concentrations remained elevated 15-30 minutes post the start of each simulation as the concentrated, impounded water was pushed out through each system. In both these systems, it was hypothesized that water had accumulated in the respective drainage ditches and had been concentrated though evaporation and aquatic macrophyte transpiration. It is theorized that additional controlled drainage could decrease the potential of concentration toxicity downstream with improved dilution and hydraulic residence management.