Characterization and analysis of a natural wetland receiving agricultural runoff

A natural wetland at Purdue’s Agronomy Center for Research and Education in West Lafayette, Indiana was studied to see how it is functioning while receiving a large amount of subsurface tile drainage from nearby agricultural fields. It is important to study wetlands in agricultural settings as nutrients from these settings can make their way downstream, eventually reaching the Gulf of Mexico where seasonal hypoxia from nutrients has become a concern. To understand how the wetland performs at reducing the load of nutrients carried in by the subsurface tile drainage, this initial study investigated the hydrology and chemistry of the water. From July 2007 to July 2008, the wetland was monitored for stage in the two main inlet channels and outlet channel, piezometers were installed and monitored on the western side of the wetland, and water samples were collected and analyzed for nutrients. The natural watershed for the wetland is 129,433 m2, while the area of tile drainage is a combined 708,200 m2 for both main tile drain systems. The water balance is dominated by the amount of water coming in through the tile drainage. Over the course of nearly a year the wetland reduced the load of nitrate by 10% the load of total ammonia by 34%. However, the wetland also appears to be a source of phosphates with an increase in annual load of 39%. The anaerobic conditions in the wetland are able to reduce nitrogen but may be contributing to the increase in phosphorous through the reduction of iron in the soils and subsequent release of phosphorous