Implications of Future Bioenergy Production for Water Quality and Quantity in the Mississippi River Basin

Excess nutrients from agriculture in the Mississippi River drainage, USA have degraded water quality in freshwaters and contributed to anoxic conditions in downstream estuaries. This study sought to understand how projected land use changes associated with future cellulosic bioenergy might influence downstream water quality. We focused on  Arkansas-White-Red (AWR) and Tennessee river basins, two of five major river basins draining to the Mississippi River. The AWR has a strong precipitation gradient from east to west, and advanced cellulosic feedstocks are projected to become economically feasible within normal-to-wet areas of the region. We compared simulated water quality in rivers draining projected future landscapes with and without cellulosic-bioenergy for 2030 with an assumed farmgate price of $50 per dry ton. Changes in simulated water yield, nutrient loadings, and sediment yield varied among subbasins and years, but median loadings decreased by 2030. Spatially, decreased loadings prevailed in the transitional ecotone between 97° and 100° longitude, where switchgrass, Panicum virgatum L., was projected to compete against alternative crops and land uses. Preliminary results for the Tennessee River basin were promising as well. Our modeling identified large regions where bioenergy production would be sustainable, both in terms of both economic feasibility and water-quality protection.