Land Use and Climate Change Impacts on Streamflow and Sediment Transport in a Groundwater-Dominated Watershed

The Jordan River Watershed in Michigan is an excellent natural laboratory to examine the influences of changes in land cover and climate on a stream ecosystem. Discharge in this river is dominated by groundwater inflows through coarse-textured glacial sediments that promote groundwater recharge and allow little overland runoff. Due to high recharge and a thick unconsolidated aquifer underlying the watershed, the Jordan River has one of the highest baseflow indexes of any gaged watershed in the US. Anthropogenic land use disturbances began in the late 19th century, involving extensive clearcut logging, forest fires, agricultural development of marginal lands, subsequent abandonment, followed by reforestation. Prior to development, local accounts indicate that the Jordan River was primarily gravel-bottomed, supplying ideal spawning grounds for a population of Grayling trout. The channel is now a mixed gravel-sand bottom, which transports large quantities of sand, particularly in its upper reaches. Like most streams in the region, it no longer supports Grayling. We simulate sediment and water fluxes within the Jordan River watershed using the Integrated Landscape Hydrology Model (ILHM) to test hypotheses about the causes of changes in the sediment transport regime related to land use (including deforestation, fires, landslides, agricultural development, etc.) and climate change during the last century. Simulations representing land use and climate conditions circa 1900 are compared to modern conditions and forecast scenarios driven by statistically-downscaled climate model outputs. These backcast and forecast simulations offer context for the current state of the system and its trajectory during the coming century.