Tailwater recovery system as a best management practice to improve irrigation water quantity and quality in Louisiana

Changyoon Jeong, 262 Research Station Road, Red River Research Station, LSU AgCenter, Bossier City, LA, 71112: cjeong@agcenter.lsu.edu. Ernest Girouard, 1373 Caffey Road, Rice Research Station, LSU AgCenter, Rayne, LA 70578: EGirouard@agcenter.lsu.edu. Patrick Colyer, 262 Research Station Road, Red River Research Station, LSU AgCenter, Bossier City, LA, 71112: pcolyer@agcenter.lsu.edu.

Tailwater recovery systems conserve irrigation water supplies through capture and reuse for agriculture. To reuse surface runoff for irrigation, runoff or water drained from agricultural fields after rain or irrigation events is collected in constructed wetlands, and then used again to irrigate crop fields. Constructed wetlands function as bio-filters through a combination of various physical, chemical and biological functions and are capable of removing a wide variety of contaminants, including sediment, nutrients, pesticides and bacterial pollutants from field runoff and agricultural waterways. With the aim to develop an efficient Best Management Practice (BMP) using constructed wetlands, the efficacy of constructed wetlands in the control of non-point source pollutants has been demonstrated in constructed wetlands at the Red River Research Station, LSU AgCenter in Northwest Louisiana. The Red River Research Station consists of 232 ha of agricultural land subdivided into 1.62- to 3.24-ha research blocks, where crops such as cotton, soybean, corn, grain sorghum, and wheat are grown. Runoff from approximately 162 ha of the station flows to the southeastern corner, where it enters Lay’s Bayou. It then flows to the Flat River. The Flat River is a tributary to the Red River, which flows south-southeast through Louisiana until it joins the Atchafalaya and Mississippi Rivers. The constructed wetland consists of two connected shallow and deep ponds. At the point where the drainage ditches from crop land enters the wetland, basins were created to allow some of the sediment to settle out before the runoff enters a shallow wetland of approximately 1.82 ha with an average depth of 0.53 m. It collectively contains approximately 1,530 m³ volume of water. The shallow wetland was planted with native wetland plant species and cultivated grass species. The deep wetland is approximately 4.04 ha with a maximum depth of 2.3 m, resulting in an average volume of 17,959 m³. The effectiveness of the constructive wetland system in improving water quality was determined by sampling at three locations using automatic water samplers placed along the edges of the field where runoff flows and in the shallow and deep wetlands. The results during a critical crop season showed that the constructed wetland system was effective in reducing suspended solids and nutrient levels in runoff. The mean concentrations of Total kjeldahl nitrogen (TKN), total phosphorus (TP), soluble reactive phosphorus (SRP), and total suspended solids (TSS) were reduced by 65%, 59%, 45%, and 90% respectively, as runoff moved from the shallow to the deep wetland system. This system will continue to be monitored to determine the longevity of its effectiveness in improving water quality of runoff and it will reduce the amount of ground water used for irrigation from the research station.