Large-Scale Spatial and Temporal Patterns and Importance of Sediment-Water Oxygen and Nutrient Fluxes in the Chesapeake Bay Region

Measurements of sediment-water fluxes of O-2, NO23, NH4, and PO4 and water column and sediment variables were conducted at 348 sites in Chesapeake Bay and Maryland Coastal Bays with most (similar to 76%) of the 1746 sets of measurements collected during warm seasons when these processes were most active. We performed a system-wide synthesis of these spatially extensive, long-term data to identify the primary controlling factors on sediment-water fluxes over seasonal and interannual time periods and assess the relative contribution of sediment-water fluxes to nutrient cycling across distinct regions of Chesapeake Bay and the Maryland Coastal Bays. Bay-wide spatial patterns revealed hotspots for sediment-water fluxes, and statistical models were able to explain 46% (O-2), 23% (NH4), 25% (NO23), and 38% (PO4) of variability in fluxes, with solute-specific controlling variables including temperature, bottom water oxygen and nutrient concentration, and sediment organic matter. An analysis of long-term variations in fluxes at six locations in the Bay (12-17 year time series) exhibited only weak evidence of long-term trends, but interannual variability was related to both water column and sediment variables, depending on the solute of interest. Finally, we compared external loads of new total nitrogen and phosphorus (TN and TP) to system-wide sediment-water fluxes of NH4 and PO4 at 22 Bay tributary and Coastal Bays sites, finding that similar to 64% of sites had annual sediment recycling rates that exceeded annual external loading rates, revealing the importance of recycled nutrients in these shallow systems.

Automated summary

This study conducted measurements of sediment-water fluxes in Chesapeake Bay and Maryland Coastal Bays, and analyzed the primary controlling factors and relative contribution of sediment-water fluxes to nutrient cycling. Hotspots for sediment-water fluxes were identified, and statistical models showed that temperature, bottom water oxygen and nutrient concentration, and sediment organic matter were important controlling variables. Long-term variations in fluxes exhibited weak evidence of trends, while interannual variability was related to water column and sediment variables. Additionally, the importance of recycled nutrients in these shallow systems was revealed.