Simulation of high-frequency dissolved oxygen dynamics in a shallow estuary, the Corsica River, Chesapeake Bay

Abstract

Understanding shallow water biogeochemical dynamics is a challenge in coastal regions, due to the presence of highly variable land-water interface fluxes, tight coupling with sediment processes, tidal dynamics, and diurnal variability in biogeochemical processes. While the deployment of continuous monitoring devices has improved our understanding of high-frequency (12 - 24 hours) variability and spatial heterogeneity in shallow regions, mechanistic modeling of these dynamics has lagged behind conceptual and empirical models. The inherent complexity of shallow water systems is represented in the Corsica River estuary, a small basin within the Chesapeake Bay ecosystem, where abundant monitoring data have been collected from long-term monitoring stations, continuous monitoring sensors, synoptic sensor surveys, and measurements of sediment-water fluxes. A state-of-the-art modeling system, the Semi-implicit Cross-scale Hydroscience Integrated System Model (SCHISM), was applied to the Corsica domain with a high-resolution grid and nutrient loads from the most recent version of the Chesapeake Bay watershed model. The Corsica SCHISM model reproduced observed high-frequency variability in dissolved oxygen, as well as seasonal variability in chlorophyll-a and sediment-water fluxes. Time-series signal analyses using Empirical Model Decomposition and spectral analysis revealed that the diurnal and M2 tide frequencies are the dominant high-frequency modes and physical transport contributes a larger share to dissolved oxygen budgets than biogeochemical processes on an hourly time scale. Heterogeneity and patchiness in dissolved oxygen resulting from phytoplankton distributions and geometry-driven eddies amplify the physical transport effect, and on longer time scales oxygen is controlled more by photosynthesis and respiration. Our simulation demonstrates that interactions among physical and biological dynamics generate complex high-frequency variability in water quality and non-linear reposes to nutrient loading and environmental forcing in shallow water systems.

High-frequency Dissolved Oxygen Dynamics in an Urban Estuary, the Long Island Sound

“…The relative importance of resolving high-frequency fluctuations in DOb therefore depends on the duration of hypoxia as well as Ai, which varies as a function of tidal current speed and spatial DOb gradient. Tian et al (2022) similarly showed for the Corsica River estuary that tidal advection accounts for a larger percentage of DO variability at hourly timescales compared to yearly timescales. As shown here, approaches to evaluating continuous and discrete data together are relevant to recent efforts in LIS and other systems (e.g., Chesapeake Bay, Murphy et al, 2019) to develop empirical predictive models for hypoxia.…”

“…In other estuaries, highfrequency fluctuations in DO have been examined most often in shallow areas, where dielcycling dynamics are typically dominated by diurnal cycles of daytime net production and nighttime net respiration (D'Avanzo and Kremer 1994;Beck and Bruland 2000;Shen et al, 2008). Diel-cycling DO has also been associated with advection and mixing by tides (Simpson et al, 1990;Breitburg, 1990;Tian et al, 2022), and wind-driven mixing associated with sea-breeze dynamics (Duvall et al, 2022). Determining biophysical processes driving high-frequency fluctuations in DO is fundamental to our understanding of water quality dynamics.…”

Simulation of benthic microalgae impacts on water quality in shallow water systems, Corsica River, Chesapeake Bay

“…This means that there was a physical signal in the DO flux time series. Tian et al (2022) reported significant tidal impact on water quality in shallow water systems, and Kwon et al (2014) observed tidal signals in benthic microalgal production, which ultimately affected DO flux. Tide influences benthic microalgal production mostly through altering environmental conditions, such as temperature, nutrient abundance, water depth, and light availability.…”

“…Electronic sensor-based continuous monitoring often shows high-frequency and large amplitude variability in DO and chlorophyll in shallow water systems (Shen et al, 2008;Graziano and Jones, 2017;Duvall et al, 2022). The understanding and modeling of these large high-frequency variations represent a challenge for the modeling community (Xia et al, 2010;Xia et al, 2011;Xia and Jiang, 2015;Tian, 2019;Tian, 2020;Tian et al, 2022). The objective of this study is to investigate the mechanisms controlling benthic microalgal dynamics and their impact on water quality high-frequency variability in shallow water systems using this fully coupled physical, water quality, and benthic microalga modeling system.…”

“…FIGURE 3Model physical conditions for the calendar year 2006, including (A) total freshwater discharge (blue line) and DIN load (red dashed line), (B) air temperature (blue line) and wind speed (red line), and (C) PAR(Tian et al, 2022).…”