The Influence of Storm Events on Metabolism and Water Quality of Riverine and Estuarine Segments of the James, Mattaponi, and Pamunkey Rivers

Abstract

The frequency and magnitude of storm events is expected to increase with climate warming. Tidal freshwaters may be particularly sensitive to these events owing to their proximity to riverine inputs. Continuous and synoptic water quality data from riverine and tidal freshwater segments of the James, Mattaponi, and Pamunkey Rivers (Virginia, USA) were analyzed to characterize their response to high discharge events. Water quality attributes subject to dilution effects (conductivity, pH) showed negative responses to increasing discharge, which were similar in magnitude among riverine and estuarine segments. Variables associated with sediment transport (turbidity, TSS, E. coli, TN, and TP) showed positive responses to discharge, stronger responses in riverine vs. estuarine segments, and relatively linear responses over the full range of discharge. Variables affected by internal biological processes (CHLa, DO) showed negative responses to increasing discharge, greater sensitivity in the low range of discharge, and stronger responses in estuarine segments. High discharge was associated with reduced chlorophyll-a (CHLa), lower dissolved oxygen, and more heterotrophic conditions (lower production relative to respiration). During unusually high discharge in 2018, annual GPP was reduced to 38% (Pamunkey) and 78% (James) of long-term average values. Inter-estuarine differences in their sensitivity to high discharge reflect differences in forms of primary production, as the phytoplankton-dominated James exhibited rapid recovery in CHLa and GPP between storm events.