In response to continuing water quality issues in the Chesapeake Bay, the U.S. Environmental Protection Agency (EPA) in collaboration with the six watershed states and the District of Columbia has finalized the Chesapeake Bay Total Maximum Daily Load (TMDL) for nitrogen, phosphorus and sediment and the jurisdiction-specific clean up plans to attain these limits. The present study evaluates the ecosystem service benefits that would accrue in the Chesapeake Watershed as a result of implementing these clean up plans.
We focus on the dollar value of eight ecosystem services originating, and largely enjoyed, in the Chesapeake Bay watershed region: food production (crops, livestock, and fish), climate stability, gas regulation, water supply, water regulation, waste treatment, aesthetics, and recreation. These we evaluated for baseline, TMDL, and business-as-usual scenarios. Ecosystem service benefits accrue in the TMDL scenario in two complementary ways. First, land use shift from less to more ecosystem-service-productive uses. Second, land in any land use can become more productive as a result of management actions designed to reduce nutrient and sediment pollution.
We employed a four-step process to estimate these benefits: 1) Assign land and water in the Chesapeake Bay watershed to one of seven land uses (forest, wetlands, open water, urban open space, other urban land, agriculture, and other) based on EPA Chesapeake Bay Program data and remotely sensed land cover data. Land use was estimated for each of the three scenarios. 2) Adjust baseline (2009) health / productivity for land use based on a spatially explicit index derived from pollution, population density and other indicators of human impacts on ecosystems. 3) Estimate changes from baseline ecosystem health for the TMDL and BAU scenarios, using projected changes in total suspended solids loads as a proxy for improvement/degradation for the non-tidal portion of the watershed. For the Tidal portion, improvement in attainment of dissolved oxygen standards serves as the proxy. 4) Calculate the dollar value of eight ecosystem services in each scenario using the benefits transfer met hod with region-specific values drawn from thousands of possible source studies.
Relative to both the baseline and business-as-usual scenario, estimated benefits of full implementation of the TMDL is approximately $20 billion per year, beginning in 2025 (2013 dollars). Detailed estimates by land use, state and ecosystem service will be publicly released in the fall and presented at the conference, but in general, the majority of benefits involve the water supply and regulation, and aesthetic services. For land uses, forests, open water and lands supply the majority of these benefits. Relative to the size of the region economy, the magnitude of these estimates compares well with previous studies. And relative to the projected cost of TMDL implementation, these estimates suggest that complete implementation is a worthwhile financial investment.