MEPS 538:81-98 (2015)  -  DOI: https://doi.org/10.3354/meps11448

ABSTRACT: The impact of climate warming on shallow tributary estuaries will be influenced by the complex cycling of nutrients and organic matter, diversity of primary producers, and enhanced benthic-pelagic coupling typical of these systems, along with advection of nutrients, organic matter, and hypoxic water from adjacent systems. This study utilized a parsimonious, reduced-complexity model that combines mechanistic equations with robust, data-driven, empirical formulations to predict how phytoplankton net primary production (NPP), net ecosystem metabolism (NEM), and hypoxia will change under a range of warmer conditions in the York River Estuary, VA, USA, a sub-estuary of Chesapeake Bay. Modeled NPP peaked earlier and responded positively to warming in the winter and spring throughout most of the system due to increased rates of nutrient remineralization; NPP remained elevated during summer and fall in the upper estuary under warming but decreased in the lower estuary. These changes caused the upper estuary to become more autotrophic, while NEM decreased in the lower estuary due to greater stimulation of respiration relative to NPP. Warming increased the predicted temporal and spatial extent of hypoxia, with the upper estuary experiencing a relatively constant increase in the number of hypoxic days with increasing temperature. Hypoxia in the lower estuary increased more rapidly with temperature. Offsetting this increase in hypoxia with climate warming will require additional nutrient and organic matter load reductions from the surrounding watershed and Chesapeake Bay in order to achieve the same level of improvement predicted in the absence of a warming climate.

KEY WORDS: York River · Ecosystem model · Climate warming · Primary production · Net ecosystem metabolism · Hypoxia