TSS AND NITRATE MONITORING IN SEVEN MILE CREEK, MN, TO INSPIRE INCREASED BEST MANAGEMENT PRACTICES

Agricultural sustainability is the fundamental starting spot for local, regional, and global successes in food and clean water technologies. It is imperative that changes in land-management are monitored in water bodies so that if they successfully imnprove water quality while maintaining agricultural integrity, best management practices (BMP) can be implemented at larger scale. In the Seven Mile Creek watershed in south-central Minnesota, we monitored at the sub-watershed scale to search for evidence of intermediate improvements during a years-long effort to reduce nutrient and sediment loads. The watershed is 9300 hectares with approximately 95% committed to corn and soybeans. Subwatershed 1 (SW1) is 4030 hectares and subwatershed 2 (SW2) is 3690 hectares (43% and 40% of the watershed area, respectively). In both subwatersheds, ubiquitous subsurface drain tile quickly drains water from the land, shunting it into tributaries and the mainstem which then have flashy storm responses.

Although the SW1 and SW2 comprise 83% of the entire watershed, in 2016-2017 together they only contributed about half of the mainstem discharge during peak storm events. Also, the tributaries had the highest total suspended solids (TSS) concentrations in the spring, while the mainstem had the highest TSS concentrations following summer storms. Therefore, to reduce TSS loading downstream BMPs must address field erosion in the spring and ravine/bluff erosion during the summer. Structural and incentive projects are being targeted to those hotspots.

Nitrate concentrations have been increasing in recent years (2015-2017 relative to 2001-2003), most likely due to expanded corn production. New BMPs like bioreactors and buffer strips installed in the past two years may reduce nitrate in the near future as monitoring continues. Continued sub-watershed monitoring and new field-scale monitoring will help identify such changes.