Water quality improvements in Grand Lake St. Marys watershed with the region’s first saturated buffer

Abstract

Saturated buffers are an edge-of-field best management practice designed to reduce nutrient loading into streams. Acting as an extension to drainage water management, these systems use a multichamber control box to raise the water table in the field (i.e., controlled drainage) and then route a portion of the subsurface drainage that does leave the field along the riparian zone using distribution tiles (i.e., saturated buffer), providing an opportunity for biological and chemical processes to reduce nitrogen (N) and phosphorus (P). Saturated buffers are inexpensive and suitable on a wide spatial scale, yet monitoring studies are lacking for many areas of the United States. This study outlines the monitoring of the first saturated buffer in Grand Lake St. Marys Watershed, Ohio. A combination of water samples from groundwater wells, depth loggers in the control box, and area velocity sensors on a comparably sized free-flowing reference site facilitated a complete hydrologic and nutrient budget for the saturated buffer study site’s subsurface drainage over two years. Using data from the free-flowing reference site as a comparison point, controlled drainage was found to have reduced runoff by ~48%. Of the water that did leave the field, ~57% of this was intercepted by the buffer where nutrient concentration reductions of ~85% soluble reactive phosphorus (SRP) and ~59% nitrate (NO3–) were noted comparing field tile to monitoring wells. Routing water through the buffer resulted in annual load reductions of 34.2 kg of N (34%) and 1.27 kg of P (52%) from the 11 ha subwatershed. Compared to previous studies, NO3– load reductions were on the lower end, likely due to the buffer tile only running an average of 35 days (buffer subwatershed) versus 245 days (free-flowing subwatershed) a year; however, SRP load reductions were higher than in previous studies. Evidence of denitrification, chemical adsorption of nutrients to sediment, as well as biological uptake in plants caused these reductions. This saturated buffer study is one of the first in Ohio and suggests additional utilization could reduce nutrient loading in the Great Lakes and Ohio River watersheds.