Seabed Resuspension in the Chesapeake Bay: Implications for Biogeochemical Cycling and Hypoxia

Abstract

Sediment processes, including resuspension and transport, affect water quality in estuaries by altering light attenuation, primary productivity, and organic matter remineralization, which then influence oxygen and nitrogen dynamics. The relative importance of these processes on oxygen and nitrogen dynamics varies in space and time due to multiple factors and is difficult to measure, however, motivating a modeling approach to quantify how sediment resuspension and transport affect estuarine biogeochemistry. Results from a coupled hydrodynamic–sediment transport–biogeochemical model of the Chesapeake Bay for the summers of 2002 and 2003 showed that resuspension increased light attenuation, especially in the northernmost portion of the Bay, shifting primary production downstream. Resuspension also increased remineralization in the central Bay, which experienced larger organic matter concentrations due to the downstream shift in primary productivity and estuarine circulation. As a result, oxygen decreased and ammonium increased throughout the Bay in the bottom portion of the water column, due to reduced photosynthesis in the northernmost portion of the Bay and increased remineralization in the central Bay. Averaged over the channel, resuspension decreased oxygen by ~ 25% and increased ammonium by ~ 50% for the bottom water column. Changes due to resuspension were of the same order of magnitude as, and generally exceeded, short-term variations within individual summers, as well as interannual variability between 2002 and 2003, which were wet and dry years, respectively. Our results quantify the degree to which sediment resuspension and transport affect biogeochemistry, and provide insight into how coastal systems may respond to management efforts and environmental changes.

Attributing Controlling Factors of Acidification and Hypoxia in a Deep, Nutrient-Enriched Estuarine Embayment

“…These dynamics may explain the persistent positive AOU, intense O 2 depletion and low pH displayed at the inner Firth, despite its high GPP. A similar recirculation mechanism was described for Chesapeake Bay by Moriarty et al (2020) to explain observations of persistent low O 2 conditions in the mid-to inner-estuary. The validity of this conceptual model for the Firth could be tested with dynamic biogeochemical modelling like that applied by those authors.…”

Advancing estuarine ecological forecasts: seasonal hypoxia in Chesapeake Bay

“…In support of nutrient control efforts, the CBP uses complex airshed, watershed, and water quality models (US EPA 2010) to determine oxygen concentration targets (Irby and Friedrichs 2019), but other predictive models have been used to both forecast and study oxygen dynamics (e.g., Testa et al 2014;Irby et al 2016Irby et al , 2018Da et al 2018;Du et al 2018;Moriarty et al 2020), including the model presented here (Scavia et al 2006).…”

Estuaries as Filters for Riverine Microplastics: Simulations in a Large, Coastal-Plain Estuary

“…ROMS solves the 3-D, hydrostatic, Boussinesq, primitive equations in a structured horizontal grid with terrain-following vertical coordinates McWilliams, 2005, 2009;Haidvogel et al, 2008). The ChesROMS configuration used here is based upon Da et al (2018) and its previous iterations have been extensively used for circulation, biogeochemistry, and sediment transport studies within the Chesapeake Bay (Feng et al, 2015;Irby and Friedrichs, 2019;St-Laurent et al, 2020;Moriarty et al, 2021;Turner et al, 2021). The model has a curvilinear horizontal grid of 150 × 100 cells (Figure 1) and a vertical grid of 20 levels.…”