Western Maine Coastal Current reduces primary production rates, zooplankton abundance and benthic nutrient fluxes in Massachusetts Bay

Abstract

Primary production was measured from 1992-2010 in Massachusetts Bay and just outside Boston Harbor for the Massachusetts Water Resources Authority’s outfall monitoring program. In 2003, annual primary production decreased by 221-278 g C m-2 year-1, with decreased rates continuing through 2010. Based on a conceptual model, oceanographic and meteorological variables were analyzed with production rates to determine if concurrent environmental changes were responsible for the reduced primary production in Massachusetts Bay. Results indicated that stronger influx of low salinity water from the western Maine Coastal Current (WMCC) in recent years might be responsible for the decreases. The WMCC appeared to have become fresher from increased river discharge in the western Gulf of Maine. Northeasterly winds in recent years promoted WMCC intrusion into Massachusetts Bay. Correlation between primary production and surface salinities suggested the impact of the WMCC on production rates. We hypothesized that increased stratification resulted in reduced vertical mixing and nutrient concentrations in surface waters for phytoplankton growth. However, no significant correlations were observed between the annual primary production and nutrient concentrations in Massachusetts Bay. Reduced production rates in Massachusetts Bay have been associated with reduced zooplankton abundances, benthic ammonium fluxes and sediment oxygen demand in summer months.