History of land cover change and biogeochemical impacts in the Choptank River basin in the mid-Atlantic region of the US

The Choptank River basin lies on the Atlantic coastal plain of North America. A terrestrial basin (1756 km(2)) surrounds a tributary of Chesapeake Bay (280 km(2)) with degrading water quality. Land use is dominated by agriculture (65%) and forest (26%); urban areas are small (6%), and the human population density is low (59 km(-2)). Reconstruction of the land cover history showed deforestation and agriculturalization by colonizing Europeans during 1650-1850, with relatively stable patterns thereafter. In the twentieth century, slow urbanization and loss of agriculture occurred as human populations increased, accompanied by mechanization and application of commercial fertilizers. We modelled the effects of these changes using the hydrochemical model GWLF, which showed that, despite relatively stable land cover after 1850, nutrient export increased primarily due to application of fertilizers and human wastewater discharges. As a result of increased inputs to the estuary, algal biomass and turbidity have increased, indicative of eutrophication. Although land cover conversion is often considered an important driver of eutrophication, the intensity of land use (i.e. land use modifications such as application of fertilizers and human population density) can also produce eutrophication in areas with a relatively stable land cover.