Management practices used in agricultural drainage ditches to reduce Gulf of Mexico hypoxia

Authors: Faust, Derek; KROGER, ROBERT - Covington Civil And Environmental; Moore, Matthew; RUSH, SCOTT - Mississippi State University

Submitted to: Bulletin of Environmental Contamination and Toxicology
Publication Type: Review Article
Publication Acceptance Date: 10/30/2017
Publication Date: 1/22/2018
Publication URL: http://handle.nal.usda.gov/10113/5888015
Citation: Faust, D.R., Kroger, R., Moore, M.T., Rush, S.A. 2018. Management practices used in agricultural drainage ditches to reduce Gulf of Mexico hypoxia. Bulletin of Environmental Contamination and Toxicology. 100:32-40.

Interpretive Summary: In 2017, the hypoxic zone in the Gulf of Mexico was the largest ever recorded at about the size of New Jersey. In the Lower Mississippi Alluvial Valley, reducing nutrient loading from agricultural drainage ditches is a primary strategy for reducing the size of the hypoxic zone in the Gulf of Mexico. This paper summarized studies examining changes in nutrient and total suspended solid concentrations and loads associated with riser and slotted pipes, two-stage ditches, vegetated ditches, low-grade weirs, and organic carbon amendments. Percent change in concentrations and loads were quantified for each management practice and information gaps regarding water quality associated with these management practices and research needs in this area were identified. Management practices used in drainage ditches were able to reduce losses of total suspended solids, N, and P. Management practices (e.g., weirs, two-stage ditches, vegetated ditches) were often unable to achieve reductions during large, intense storm events, which is concerning when considering these types of events are predicted to increase in frequency and intensity under future climatic conditions. Both in-field and in-ditch management practices will likely be necessary to achieve effective nutrient and sediment reductions to meet the goals for a much reduced hypoxic zone in the Gulf of Mexico. Several of the management practices examined (e.g., riser and slotted pipes, two-stage ditches, organic carbon amendments) need to be further studied to increase nutrient and sediment reduction efficacies. Furthermore, studies on combined effects of management practices, along with research towards improved nutrient and sediment reduction efficiency during intense storm events in drainage ditches are urgently needed.

Technical Abstract: Agricultural non-point sources of nutrients and sediments have caused eutrophication and other water quality issues in aquatic and marine ecosystems, such as the annual occurrence of hypoxia in the Gulf of Mexico. Management practices have been implemented adjacent to and in agricultural drainage ditches to promote their wetland characteristics and functions, including reduction of nitrogen, phosphorus, and sediment losses downstream. This review: 1) summarized studies examining changes in nutrient and total suspended solid concentrations and loads associated with management practices in drainage ditches (i.e., riser and slotted pipes, two-stage ditches, vegetated ditches, low-grade weirs, and organic carbon amendments) with emphasis on the Lower Mississippi Alluvial Valley, 2) quantified management system effects on nutrient and total suspended solid concentrations and loads and, 3) identified information gaps regarding water quality associated with these management practices and research needs in this area. In general, management practices used in drainage ditches at times reduced losses of total suspended solids, N, and P. However, management practices were often ineffective during storm events that were uncommon and intense in duration and volume, although these types of events could increase in frequency and intensity with climate change. Studies on combined effects of management practices on drainage ditch water quality, along with research towards improved nutrient and sediment reduction efficiency during intense storm events are urgently needed.