Threats and opportunities for freshwater conservation under future land use change scenarios in the United States
Freshwater ecosystems provide vital resources for humans and support high levels of biodiversity, yet are severelythreatened throughout the world. The expansion of human land uses, such as urban and crop cover, typicallydegrades water quality and reduces freshwater biodiversity, thereby jeopardizing both biodiversity and ecosystemservices. Identifying and mitigating future threats to freshwater ecosystems requires forecasting where land usechanges are most likely. Our goal was to evaluate the potential consequences of future land use on freshwater eco-systems in the coterminous United States by comparing alternative scenarios of land use change (2001–2051) withcurrent patterns of freshwater biodiversity and water quality risk. Using an econometric model, each of our landuse scenarios projected greater changes in watersheds of the eastern half of the country, where freshwater ecosys-tems already experience higher stress from human activities. Future urban expansion emerged as a major threat inregions with high freshwater biodiversity (e.g., the Southeast) or severe water quality problems (e.g., the Midwest).Our scenarios reflecting environmentally oriented policies had some positive effects. Subsidizing afforestation forcarbon sequestration reduced crop cover and increased natural vegetation in areas that are currently stressed bylow water quality, while discouraging urban sprawl diminished urban expansion in areas of high biodiversity. Onthe other hand, we found that increases in crop commodity prices could lead to increased agricultural threats inareas of high freshwater biodiversity. Our analyses illustrate the potential for policy changes and market factors toinfluence future land use trends in certain regions of the country, with important consequences for freshwater eco-systems. Successful conservation of aquatic biodiversity and ecosystem services in the United States into the futurewill require attending to the potential threats and opportunities arising from policies and market changes affectingland use.