Effect of temperature and dissolved oxygen on sediment-water nutrient flux

A series of experiments was conducted in order to determine the influence of water-column temperature and dissolved oxygen on sediment-water nutrient flux. Three nutrients were considered: ammoniurn nitrogen, nitrate nitrogen, and ortho phosphorus. Results of the experiments indicated that nutrient concentration in the overlying water had to be considered, as well as temperature and dissolved oxygen, as an independent variable which affected sediment-water nutrient flux

Influence of Reservoir Infill on Coastal Deep Water Hypoxia

Ecological restoration of the Chesapeake through the Chesapeake Bay total maximum daily load (TMDL) requires the reduction of nitrogen, phosphorus, and sediment loads in the Chesapeake watershed because of the tidal water quality impairments and damage to living resources they cause. Within the Chesapeake watershed, the Conowingo Reservoir has been filling in with sediment for almost a century and is now in a state of near‐full capacity called dynamic equilibrium. The development of the Chesapeake TMDL in 2010 was with the assumption that the Conowingo Reservoir was still effectively trapping sediment and nutrients. This is now known not to be the case. In a TMDL, pollutant loads beyond the TMDL allocation, which are brought about by growth or other conditions, must be offset. Using the analysis tools of the Chesapeake TMDL for assessing the degree of water quality standard attainment, the estimated nutrient and sediment loads from a simulated dynamic equilibrium infill condition of the Conowingo Reservoir were determined. The influence on Chesapeake water quality by a large storm and scour event of January 1996 on the Susquehanna River was estimated, and the same storm and scour events were also evaluated in the more critical living resource period of June. An analysis was also made on the estimated influence of more moderate high flow events. The infill of the Conowingo reservoir had estimated impairments of water quality, primarily on deep‐water and deep‐channel dissolved oxygen, because of increased discharge and transport of organic and particulate inorganic nutrients from the Conowingo Reservoir

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

Eutrophication and hypoxia represent an ever-growing stressor to estuaries and coastal ecosystems due to population growth and climate change. Understanding water quality dynamics in shallow water systems is particularly challenging due to the complex physical and biogeochemical dynamics and interactions among them. Within shallow waters, benthic microalgae can significantly contribute to autotrophic primary production, generate organic matter, increase dissolved oxygen consumption, and alter nutrient fluxes at the sediment–water interface, yet they have received little attention in modeling applications. A state-of-the-art modeling system, the Semi-Implicit Cross-Scale Hydroscience Integrated System Model (SCHISM), coupled with the Integrated Compartment Model (ICM) of water quality and benthic microalgae, has been implemented in the Corsica River estuary, a tributary to Chesapeake Bay, to study benthic microalgal impact on water quality in shallow water systems. The model simulation has revealed a broad impact of benthic microalgae, ranging from sediment–water interface fluxes to water column dynamics, and the effects are observed from near-field to far-field monitoring stations. High-frequency variability and non-linearity dominate benthic microalgal dynamics, sediment oxygen demand, and nutrient fluxes at the sediment–water interface. Resource competition and supply determine the spatial scope of benthic microalgal impacts on far-field stations and the whole estuary system. Our study shows that benthic microalgae are a significant factor in shallow water dynamics that needs adequate attention in future observation and modeling applications

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

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

Passaic River Tunnel Diversion Model Study. Report 5: Water Quality Modeling

Source: https://erdc-library.erdc.dren.mil/jspui/The Passaic River and Newark Bay form part of the complex New York-New Jersey harbor system. A diversion tunnel has been proposed to alleviate flooding in the upper portion of the Passaic River basin. The tunnel will divert flow from the headwaters of the Passaic directly to the upper end of Newark Bay. The objective of the study is to provide information required to evaluate the effect of the diversion tunnel on living resources in the vicinity of the tunnel outlet. Three living-resource parameters were selected for examination: salinity, water temperature, and dissolved-oxygen concentration. Impacts were examined through use of the CE-QUAL-ICM water quality model. State variables in the model included salinity, temperature, dissolved oxygen, ultimate biochemical oxygen demand, and chemical oxygen demand. The model was calibrated to field data collected from July to September 1994. Hydrodynamics for the water quality model were supplied by the CH3D hydrodynamic model. A matrix of scenarios was constructed to examine the impact of tunnel discharge on receiving waters. Base scenarios specified future conditions without the tunnel. Wet-tunnel scenarios examined future conditions with the tunnel in operation and with floodwater remaining in the tunnel between flood events. Dry-tunnel scenarios examined future conditions with the tunnel in operation and with the tunnel pumped dry between flood events. Three flood conditions were considered: 2-year storm, 25-year storm, and 100-year storm. Scenarios were designed to illustrate the worst-case impact of the discharge tunnel on salinity, temperature, and dissolved oxygen. Under worst-case conditions, impact of the tunnel on dissolved oxygen and temperature was minimal in magnitude, short-lived, and of limited spatial extent. Impact of the tunnel on salinity was indiscernible