Impact of Riparian Buffers and Agricultural Drainage Management On Water Quality and Ecosystems of Small Minnesota Streams.

Agriculture in southern Minnesota requires management of poorly drained soils in a climate with a distinct spring-snowmelt runoff signature.  Topographic tile drainage has been in place in this landscape since the late 1800s.  More recently, patterned tile drainage has been implemented, with as little as 50 feet between tiles that are integrated before emptying into a managed drainage ditch system.  Beginning in the 1990s, land retirement was a management practice implemented in these basins in order to reduce runoff and sediment loads from fields into streams.  Lands were retired either permanently or for an extended period of time through federal and local conservation efforts such as Re-invest In Minnesota, Conservation Reserve Program, and Conservation Reserve Enhancement Program.  These programs differ in their directives, resulting in basins with a mix of retired riparian buffers that range from approximately 30 to 300 feet, some of which have intact tile-drain systems that continue to empty into the adjacent ditches.  A recent U.S. Geological Survey (USGS) study of streams draining this agricultural setting in the Minnesota River basin found statistically significant decreases in stream concentrations of nitrogen and sediment, but not phosphorus, as area of retired lands increased.  Additionally, stream health improved as retired land area increased, as documented by several biological metrics.  The USGS, in cooperation with local Soil Water and Conservation District and Natural Resources Conservation Service personnel, began a three-year study in 2011 of small (about 1.5 mi²) paired basins with a range of retired riparian land and tile-drain distributions in a southern Minnesota River basin with a long-term water-quality record.  Agricultural field and riparian soil, suspended sediment, and stream water were sampled for nutrients, trace elements, and organic content in the fall 2011 and spring 2012, in order to quantify the abundance and source of nutrients.  Aquatic biota also were sampled in order to get an initial understanding of diversity, organism health, and trophic resources.  This study evaluates the interaction of retired riparian corridor with tile-drained fields and the variation in resultant biological community structure, food-chain length, and organism health through influences on water quality, sediment sources and characteristics, and habitat.