Environmental Controls of Denitrification in
Estuarine Sediments
The overabundance in Bay waters of nitrogen compounds contributes to the heavy growth of algae. Algae not consumed by young fish and other organisms decay, a phenomenon that often leads to conditions of poor water quality, particularly low levels of dissolved oxygen and sometimes its absence (hypoxia). Oxygen depletion traditionally occurs throughout the upper Bay during warm months. An important factor in regulating these processes resides in sediments, which can either recycle nitrogen compounds or serve as a repository (sink) and sequester them. Understanding the cycling processes in sediments is critical to determining how much nitrogen in the form of nitrate and ammonia is available for uptake by algae and how much is converted to nitrogen gas, and released from the ecosystem into the atmosphere. Though scientists have now characterized recycling processes in the Bay's mainstem, they know far less about the biochemical processes that regulate the availability of nitrogen compounds in marshes and rivers because of the difficulty in measuring them accurately and the complexity of their fate. Over these last two years, Jeffrey Cornwell and Todd Kana have been using a new methodology they developed to take rapid and accurate measurements of denitrification, the process by which microbes in sediments metabolize nitrate and nitrite and release them as nitrogen gas. In an intensive field sampling program in the Choptank River on Maryland's Eastern Shore, they have found marked differences in the mobilization of nitrate and ammonia and denitrification between upriver (low salinity) and down river (high salinity) regions. This project is helping to develop a more sophisticated understanding of nitrogen cycling that will, in the long run, be of considerable importance in assessing the implications of nutrient reduction goals for improving water quality in the Chesapeake ecosystem.
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Jeffrey Cornwell
Todd Kana
Horn Point Laboratory
University of Maryland Center for Environmental Science
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