Submitted to: Mississippi Water Resources Research Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 8/15/2005
Publication Date: 12/29/2005
Citation: Kroger, R., M.M. Holland, M.T. Moore, and C.M. Cooper. 2005. Duplicity of wetland plants in nutrient flux within agricultural drainage ditches in Mississippi. Proceedings of the Mississippi Water Resources Conference, Jackson, MS. pp. 185-192. Interpretive Summary: Plants in agricultural drainage ditches sorb nutrients from storm runoff events during the growing season. When these plants die back during the winter months, it is assumed the vegetation releases these nutrients back to the water. A decomposition study examined the nutrient assimilation and subsequent leaching from plant material collected during these two critical time periods. One particular plant species accumulated significantly higher nitrogen and phosphorus concentrations in the biomass. When plant material began to die back, a significant amount of phosphorus was released into the water. This indicates the potential for effects on downstream aquatic receiving systems following plant die back.
Technical Abstract: Drainage ditches, as integral components of the agricultural landscape, remove surface runoff and act as major conduits of nutrients from agricultural lands to receiving waters. These ditches are filled with wetland plants, providing additional surface area for microbial interactions as well as acting in a small, yet important assimilatory capacity. However, their assimilatory function is negated in winter with seasonal die-back and the release of assimilated nutrients into the system. We tested the hypotheses of whether plants, given the opportunity, will firstly assimilate higher concentrations of nutrients, such as nitrogen and phosphorus, and whether with subsequent decomposition these concentrations are released back into the water column. Given the opportunity, Leersia oryzoides, a dominant wetland ditch plant species, will assimilate significantly higher concentrations of nitrogen and phosphorus in aboveground biomass. Subsequently, the senescence of aboveground biomass yielded significantly higher levels of phosphorus. However, there were no significant differences in nitrate, nitrite or ammonia levels between treated and untreated treatments, suggesting that denitrification and microbial processes were removing these products from the system. Using Leersia oryzoides as our model the seasonal dieback and duplicity of drainage ditch vegetation in nutrient assimilation during the growing season and re-release of phosphorus in the winter will have effects on downstream environments.