Efficacy of Constructed Wetland Systems to Improve the Water Quality of Surface Runoff from Agricultural Fields.

Non-point sources of pollution, which are primarily from agricultural activities, have become the major cause of water quality impairment. For instance, the National Water Quality Inventory of the USA shows that approximately half of impaired water bodies in this country are impacted by nutrients, sediments, pesticides and microbial pathogens from crop production, animal operations, pastures, and rangeland. Constructed wetlands or constructed field wetlands are ecologically engineered systems that are built using quantitative approaches based on ecological principles, and the systems are akin to natural wetlands. Several studies have shown the overall effectiveness of constructed wetlands in removing pollutants from agricultural runoff water. Constructed field wetlands are one such edge-of-field option available to farmers for reducing the loss of sediment and nutrients from agricultural lands, in addition to providing other ecosystem services. However, the efficacy of constructed wetlands in the control of non-point sources pollutants has not been fully demonstrated although their nutrient-removing functions have been shown in numerous studies. The other reason constructed wetlands are not yet widely used in this region is partly because of the perception that they need to be large to be effective. In addition, there is little information on recommended ratio of wetlands to agricultural land in the catchment area. This study was compared two different sets of constructed wetlands with different occupying ratio; a wetland located on the edge of multi-crop fields at the LSU AgCenter Red River Research Station in the Red River Basin, of northwestern Louisiana, and another wetland located at the edge of rice and soybean fields in the Mermentau River Basin at Kaplan, southwestern Louisiana. The overall goal of this project was to demonstrate treatment effectiveness and efficiency for nonpoint source pollution and recycling nutrients from agricultural runoff using an innovative constructed field wetland system, including reusing surface runoff water in rice fields as an additional filtering wetland system. We will quantify the water quality benefits of the constructed wetlands from two unique agricultural settings, and specifically the potential to increase N and P reduction efficiency by managing the constructed wetlands adjoined at the edge of fields before draining to watersheds.