Causes and Consequences of Ecosystem Service Regionalization in a Coastal Suburban Watershed

The demand for ecosystem services and the abil- ity of natural ecosystems to provide those services evolve over time as population, land use, and management prac- tices change. Regionalization of ecosystem service activity, or the expansion of the area providing ecosystem services to a population, isa commonresponse in densely populated coastal regions, with important consequences for watershed water and nitrogen (N) fluxes to the coastal zone. We link biophysical and historical information to explore the causes and consequences of change in ecosystem service activity—focusing on water provi- sioning and N regulation—from 1850 to 2010 in a coastal suburban watershed, the Ipswich River watershed in northeast- ern Massachusetts, USA. Net interbasin water transfers started in the late 1800s due to regionalization of water supply for use by larger populations living outside the Ipswich watershed boundaries, reaching a peak in the mid-1980s. Over much of the twentieth century, about 20 % of river runoff was diverted from reaching the estuary, with greater proportions during drought years. Ongoing regionalization of water supply has contributed to recent declines in diversions, influenced by socioecological feedbacks resulting from the river drying and fish kills. Similarly, the N budget has been greatly perturbed since the suburban era began in the 1950s due to food and lawn fertilizer imports and human waste release. However, natural ecosystems are able to remove most of this anthropogenic N, mitigating impacts on the coastal zone. We propose a conceptual model whereby the amount and type of ecosystem services provided by coastal watersheds in urban regions expand and contract over time as regional population expands and ecosys- tem services are regionalized. We hypothesize that suburban watersheds can be hotspots of ecosystem service sources be- cause they retain sufficient ecosystem function to still produce services that meet increasing demand from the local population andnearbyurbancenters.Historical reconstructionofecosystem service activity provides a perspective that may help to better understandcoupledhuman-natural system processes and lead to more sustainable management of coastal ecosystems.