Controls on Water-Column Respiration Rates in a Coastal Plain Estuary: Insights from Long-Term Time-Series Measurements

Abstract

Rates of ecosystem metabolic properties, such as plankton community respiration, can be used as an assessment of the eutrophication state of a waterbody and are the primary biogeochemical rates causing oxygen depletion in coastal waters. However, given the additional labor involved in measuring biogeochemical rate processes, few monitoring programs regularly measure these properties, and thus, few long-term monitoring records of plankton respiration exist. An 8-year, biweekly plankton community respiration rate time series was analyzed as part of a monitoring program situated in the lower Patuxent River estuary, a tributary of Chesapeake Bay. We found that particulate nutrients (nitrogen and phosphorus) were the most highly correlated covariates with respiration rate. Additionally, statistical and kinetic models including variables both water temperature and particulate nitrogen were able to explain 74% of the variability in respiration. Over the long-term record, both particulate nutrients and respiration rate were elevated when measured at higher tides. Separate measurements of respiration rate during 10 consecutive days and during high and low tide on three separate days also support the enhancement of respiration with high tide. The enhancement was likely due to the import of particulate nutrients from the highly productive mid-bay region. This analysis of the longest consistently measured community respiration rate dataset in Chesapeake Bay has implications for how to interpret long-term records of measurements made at fixed locations in estuaries.