Impacts of Engineered De-stratification on Estuarine Biogeochemistry

University Of Maryland Center For Environmental Sciences, Cambridge MD

Investigators

Abstract

Lakes, reservoirs, and coastal estuaries are all susceptible to poor water quality as a result of nutrient pollution. In some cases, aquatic "dead zones" are created where dissolved oxygen concentrations become so low that it negatively impacts the abundance of organisms, the availability of nutrients, and the organization of food webs. Engineered de-stratification is a technological solution that includes the use of large scale aerators to mix the water column and to force atmospheric oxygen into deep waters, thereby improving oxygen conditions in these systems. This research project seeks to determine both the intended and unintended consequences of engineered de-stratification, especially in terms of its effects on oxygenation and the chemical cycles that control greenhouse gas and toxin production. For example, changes to the oxygen concentrations may affect the availability of mercury and methane in the environment. Another objective of the research project is to collaborate with county government and citizen scientists interested in studying and restoring the Rock Creek estuary, which is connected to the Chesapeake Bay in Maryland. A critical step in understanding the tradeoffs associated with engineered de-stratification is to document the impacts of de-stratification on biogeochemistry and associated ecosystem responses. Large engineered aeration systems have rarely been installed in tidal waters. This research study capitalizes on a system installed in the Rock Creek estuary, where this technology has been applied for nearly thirty years. The responses of nitrogen, phosphorus, mercury, and methane pools to aeration is being comprehensively documented, and both the ecosystem services (e.g., denitrification) and unintended consequences (e.g. greenhouse gas emissions) associated with engineered de-stratification are being quantified. The researchers are using a novel, user-controlled estuarine-scale de-stratification system for testing dose-response relationships. They are focusing on understanding the effects of aeration time and tidal timing on biogeochemical responses. In optimizing aeration protocols the study will provide insights into the effects of cycled oxygen depletion on nutrient and greenhouse gas cycling. Data from the experiments will be used to enhance a modeling tool to extend findings to other aquatic systems with chronic oxygen depletion. These new efforts will reveal a new and comprehensive picture of how engineered de-stratification can be efficiently utilized to alleviate oxygen depletion and enhance nutrient removal services.