Location: Water Quality and Ecology ResearchTitle: Understanding nitrogen and organic carbon contents of agricultural drainage ditches of the Lower Mississippi Alluvial Valley Author
Submitted to: Wetlands
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/15/2017
Publication Date: N/A
Citation: N/A Interpretive Summary: Nutrients leaving agricultural fields in runoff can cause damage to nearby rivers, lakes, and streams. Drainage ditches surrounding agricultural fields have the potential to clean up nutrients in runoff, but certain conditions must be present. In order to decrease the nitrogen concentration in water, not only must there be anaerobic conditions, but organic carbon must also be available in the system to drive the microbial process of denitrification. An experiment in the lower Mississippi Alluvial Valley examined variability in nitrogen and organic carbon content in ditch water and sediment. Results showed ditch conditions that were most favorable, and when conditions were not met, the study offered suggestions on different organic carbon amendments to help foster these microbial processes to potentially improve water quality. By driving denitrification in drainage waters, less nitrate will travel to the Gulf of Mexico, thereby decreasing the size of the annual hypoxic zone.
Technical Abstract: Application of agricultural fertilizers as a means of increasing production have resulted in excessive nutrient loading to agricultural drainage ditches, contributing to the Gulf of Mexico hypoxic zone. Drainage ditches can have wetland characteristics and functionality, including the capacity to remediate nutrient loading, promotable using management practices. The purpose of this study was to assess relationships between organic carbon and nitrogen contents of drainage ditch sediment and waters, evaluating the spatial scope in which organic carbon amendments may be used in remediating nutrient loading throughout the Lower Mississippi Alluvial Valley. Water and sediment samples were obtained from agricultural drainage ditches in Missouri, Arkansas, Mississippi, and Louisiana. Nitrate, nitrite, ammonium, and total nitrogen concentrations were determined in overlying and pore water, along with characterizing dissolved organic carbon aromaticity (spectral absorbance at 254 nm) and molecular weight (ratio of spectral absorbance at 254:365 nm). A significant correlation was observed between sediment percent nitrogen and percent total organic carbon (r = 0.944, P < 0.001). Sediment percent organic carbon ranged from 0.253% to 6.04%, well below values observed in restored and natural wetlands. Results of this study show there is spatial variability in nitrogen species and organic carbon content of ditch water and sediment throughout the Lower Mississippi Alluvial Valley. The study vastly expands on the degree of knowledge available on the organic carbon content of agricultural drainage ditches in the LMAV and emphasizes the importance of evaluating agricultural drainage ditches in which organic carbon may be limiting denitrification and would thus benefit from organic carbon amendments.