Mark R. Noel

Can oyster restoration reverse cultural eutrophication in Chesapeake Bay

We investigated the hypothesis that effects of cultural eutrophication can be reversed through natural resource restoration via addition of an oyster module to a predictive eutrophication model. We explored the potential effects of native oyster restoration on dissolved oxygen (DO), chlorophyll, light attenuation, and submerged aquatic vegetation (SAV) in eutrophic Chesapeake Bay. A tenfold increase in existing oyster biomass is projected to reduce system-wide summer surface chlorophyll by approximately 1 mg m−3, increase summer-average deep-water DO by 0.25 g m−3, add 2100 kg C (20%) to summer SAV biomass, and remove 30,000 kg d−1 nitrogen through enhanced denitrification. The influence of osyter restoration on deep extensive pelagic waters is limited. Oyster restoration is recommended as a supplement to nutrient load reduction, not as a substitute.

Three-dimensional Management Model for Lake Washington, Part II: Eutrophication Modeling and Skill Assessment

Abstract The CE-QUAL-ICM 3-dimensional eutrophication model was applied to Lake Washington for the period 1995–1997. Transport processes were obtained from the companion CH3D-WES hydrodynamic model. The model activated 18 state variables in the water column, including physical variables; phytoplankton; multiple forms of carbon, nitrogen, and phosphorus; dissolved oxygen; and fecal coliform. The water column was coupled to a sediment diagenesis model that computed sediment-water fluxes of dissolved oxygen, methane, ammonium, nitrate, and phosphate, based on computed inputs of particulate organic matter. The model successfully computed the annual cycles and spatial distributions of key water quality components. Nutrient loads were calculated and nutrient budgets were constructed as part of the model exercise. Load sources included river inflows, distributed loads, sewer overflows and atmospheric loading. The Sammamish River was identified as the largest source of nutrients to Lake Washington, followed by the Cedar River and other distributed sources. The majority of the nutrient load is deposited in the sediments. A lesser amount leaves via Lake Union. Our nutrient loads were 30% (nitrogen) to 60% (phosphorus) higher than the loads from the late 1970s.

Impact of Reservoir Sediment Scour on Water Quality in a Downstream Estuary.

The Conowingo Reservoir is situated at the lower terminus of the Susquehanna ---River watershed, immediately above Chesapeake Bay. Since construction, the reservoir has been filling with sediment to the point where storage capacity is nearly exhausted. The potential for release of accumulated sediments, organic matter, and nutrients, especially through the action of storm scour, causes concern for water quality in Chesapeake Bay. We used hydrodynamic and eutrophication models to examine the effects of watershed loads and scour loads on bay water quality under total maximum daily load conditions. Results indicate that increased suspended solids loads are not a threat to bay water quality. For most conditions, solids scoured from the reservoir settle out before the season during which light attenuation is critical. The organic matter and nutrients associated with the solids are, however, detrimental. This material settles to the estuary bottom and is mineralized in bed sediments. Carbon diagenesis spurs oxygen consumption in bottom sediments and in the water column via release of chemical oxygen demand. The nutrients are recycled to the water column and stimulate algal production. As a result of a scour event, bottom-water dissolved oxygen declines up to 0.2 g m, although the decline is 0.1 g m or less when averaged over the summer season. Surface chlorophyll increases 0.1 to 0.3 mg m during the summer growing season.