Responses of benthic-pelagic coupling to climate change in a temperate estuary

This article reports the first demonstration of the impact of climate change on benthic-pelagic coupling and the biogeochemical cycles of a coastal marine system. Over the last 30 years Narragansett Bay, a 328-km² temperate estuary on the east coast of the United States, has undergone a variety of ecological changes. Building on a robust data set that spans three decades, we present a link between warming (+1.7°C in annual mean water temperature) in the bay and a marked decrease in sediment oxygen consumption, in the fluxes of ammonium and phosphate from sediments to the overlying water, and in sediment denitrification. We attribute this reduction in biogeochemical exchange to a dramatic drop in the standing crop of water-column chlorophyll as the system has shifted from one characterized by a dominant winter-spring bloom to one supported by more ephemeral and less intense summer-autumn blooms. The recent climate-induced oligotrophication of the bay will be further exacerbated by forthcoming nitrogen reductions due to tertiary sewage treatment.