Multiple Stressors in an Estuarine Environment: Drivers of changes in the Chesapeake Bay CO2 system

Chair: Heidi Pethybridge

Elizabeth H. Shadwick (1)*, Marjorie A.M. Friedrichs (1), and Raymond G Najjar (2)

1 Virginia Institute of Marine Science, College of William & Mary, Gloucester Point, VA, 23062, USA
2 Pennsylvania State University, University Park, PA, 16802, USA

Understanding the vulnerability of estuarine ecosystems to anthropogenic impacts requires a quantitative assessment of the dynamic drivers of change to the estuarine carbonate system. New and ongoing research in Chesapeake Bay (US Atlantic coast) is yielding observations of the diurnal, seasonal, and interannual variability of the CO2 system in a non-pristine estuary. The data comprise observations from shipboard sampling (dissolved inorganic carbon, and alkalinity), new high-frequency autonomous instrumentation (pH and CO2 partial pressure), and an existing 30-year (1984 – 2014) time-series from a water-quality (pH and alkalinity) monitoring program. This research will combine biogeochemical observations and modelling to examine the relative importance of the following on variations in the regional carbonate chemistry: (1) eutrophication (through changes in riverine nutrient inputs resulting in increased primary production and respiration); (2) changing freshwater carbonate chemistry (through increased alkalinity in riverine end members); (3) increased atmospheric CO2; (4) increased atmospheric temperature; and (5) sea-level rise. Preliminary analysis indicates spatial and interannual variability in the CO2 system consistent with the dynamic nature of the estuary. Significant trends of increasing pH at several locations in Chesapeake Bay large enough to counteract both the increase in atmospheric CO2 and in temperature observed over the past three decades have been identified. While the appropriateness of the long-term monitoring data for the detection and attribution of trends needs to be established, it is clear that the response of the Chesapeake Bay carbonate system to multiple environmental stressors is complex. Distinguishing between local (i.e., eutrophication) and global scale (i.e., increased atmospheric CO2 and temperature) anthropogenic forcing is the focus of ongoing research.