Capacity of freshwater marsh to process nutrients in diverted Mississippi River water

The loss of Louisiana\u27s coastal wetlands has mandated the construction of diversion structures for reintroduction of a portion of the Mississippi River into Louisiana\u27s coastal region for slowing or reversing marsh deterioration. The Davis Pond Freshwater Diversion Structure allows for a section of the Mississippi River water to be reintroduced into Louisiana\u27s Barataria Basin. The reintroduced Mississippi River water contains elevated levels of nitrate and other nutrients from agricultural runoff primarily from the upper reaches of the Mississippi River drainage basin. These elevated nitrate levels have raised questions of possible eutrophication effects on Louisiana estuaries. The purpose of this study is to monitor changes in concentration of nutrients as the diverted Mississippi River input moves across a 9300 acre (3800ha) of ponded, freshwater marsh. Three sampling sites, inlet, outlet, and Lake Cataouatche, were established at the Davis Pond diversion and samples were collected during various discharge or pulsing events. Change in nutrient concentrations were measured between the inlet and the outlet of the ponded freshwater marsh. Results of the study show efficiency that NO3-N removal was affected by discharge rate entering the ponded marsh. Discharge rates of 35m3/s showed that the system effectively removed NO3-N concentrations in diverted river water that were greater than 1 ppm. In contrast, in the month of December, a high discharge rate, even thought nitrate was removed, a significant portion of the NO3-N passed straight through the ponded system introducing a large amount of Nitrate-N into the lake Cataouatche. Results of the study indicate that the Davis Pond Freshwater Diversion acted conservatively in relation to phosphorus with only a small amount removed. The ponded wetland system acted as a source for ammonia and organic carbon. ICP and Standard Tests for Irrigation Water analyses proved all tested nutrient elements to fall within the low to medium or high to medium when compared to threshold range. Assessments of the capacity of the system to process and assimilate nutrients in diverted Mississippi River water is multifold and longer term evaluations must be performed in order to adequately assess the future capacity of freshwater marsh to process nutrients