Comparison of sediment in watersheds with varying amounts of conservation lands

Background/Question/Methods

Increased suspended sediment commonly is associated with agricultural land use.  Agricultural land retirement (Conservation Reserve, Conservation Reserve Enhancement, ReInvest in Minnesota, and other conservation programs) began in the 1990s with the goal of reducing sediment and nutrient transport to streams.  The U.S. Geological Survey, Minnesota Board of Water and Soil Resources, Hawk Creek Watershed Project, and the Minnesota Pollution Control Agency have cooperated on monitoring studies of varying duration and drainage size to investigate the effects of conservation land on water quality in Minnesota River watersheds.  A three year paired watershed study, including watersheds (<15km^2) with and without conservation land along the riparian corridor, began in 2011 to assess sediment and nutrient concentrations in relation to contributions from agricultural fields and instream processes (bank sloughing, storage, or cycling). Samples of field and riparian soil, suspended sediment, and water were collected in 2011 and 2012.  A second ongoing study focuses on the relation of sediment and nutrients to conservation land over time. This study includes data collected between 1998 and 2012 and identifies long-term trends in sediment and nutrient abundance not evident in shorter duration studies. 

Results/Conclusions

Results from the two ongoing studies and two completed studies will be reported. In a 2005-08 study of three paired watersheds (about 250 km^2) with varying degrees of conservation lands (Christensen and others, 2009), the watershed with the most land retirement had the lowest suspended-sediment concentrations.  A 2001-03 study of 82 watersheds (from 4 to 2,190 km^2; Christensen and others, 2012) indicated correlation between lower total suspended solids concentrations and greater conservation land area within 100 m (p= .03) to 400 m (p=.02) of a stream. This study indicated that when conservation lands are concentrated less than 100 m from a stream or more than 400 m of a stream, they may not be effective at reducing the amount of sediment reaching the stream.