Submitted to: Ecological Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/29/2011
Publication Date: 8/26/2011
Citation: Kroger, R., Moore, M.T. 2011. Phosphorus dynamics within agricultural drainage ditches in the lower Mississippi Alluvial Valley. Ecological Engineering. 37:1905-1909. Interpretive Summary: Drainage ditches are important agricultural landscape features that transport excess water from crops into receiving aquatic systems. A study was conducted collecting samples from agricultural ditches in four states and measuring the presence of phosphorus in both water and sediment. Drainage ditches may serve as sinks for phosphorus-laden agricultural runoff, but they may also serve as sources, depending on the chemical makeup of the ditch sediment. Results indicated that ditch sediments sampled in the Lower Mississippi Alluvial Plain had the capacity to adsorb phosphorus (serve as a sink); however, sediment binding energy was not strong enough to actually attract phosphorus to the sediment.
Technical Abstract: Excessive phosphorus loading from fertilizers in agriculture results in enriched runoff and downstream freshwater and saltwater aquatic system eutrophication. This study evaluated phosphorus dynamics in agricultural drainage ditches across eight sites within the Lower Mississippi Alluvial Valley (LMAV). The objective of the study was to better understand P dynamics spatially across the agricultural landscape, as well as describe temporal changes within the drainage system. Spatially and temporally, all drainage ditch sediments had very low immediately bioavailable phosphorus (Pw), and a very low degree of phosphorus saturation (DPS < 20%) throughout the LMAV. Phosphorus binding energy (K) (0.34 – 0.60 L/mg) and P sorption maxima (17.8 – 26.6 L/mg) were low, with very little variation in space and time. Using these metrics, drainage ditches sampled within the LMAV could be described as P sinks, capable of sorbing varying degrees of P seasonally as a result to changes in the Fe-P pool. Sorption, however, will likely be low due to low P sorption maxima and low binding energies. These results will help in P management within primary aquatic systems (such as drainage ditches) within the agricultural landscape and enhance P mitigation strategies at the source, prior to runoff reaching downstream aquatic systems.