TNT Degradation by Natural Microbial Assemblages at Frontal Boundaries Between Water Masses in Coastal Ecosystems (ER-2124 Interim Report)
Memorandum rept. 1 Jan-31 Dec 2013
NAVAL RESEARCH LAB WASHINGTON DC CHEMICAL DYNAMICS AND DIAGNOSTICS BRANCH
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This limited scope, three year SERDP project involves determining the primary biogeochemical factors that control TNT metabolism by natural microbial assemblages in coastal systems. By correlating standard water quality measurements with degradation rates, we can predict turnover times for energetics released into hydrodynamically similar, UXO-impacted ecosystems where access to site samples may be limited. During this first year of sampling in the Florida Keys, USA, we found that mixing experiments between mangrove lagoon water and open ocean Gulf of Mexico water resulted in more rapid rates of bacterial growth and aromatic contaminant mineralization i.e., TNT, RDX, HMX and phenanthrene than would have been predicted by interpolation of unmixed end members. This line of evidence supports the hypothesis that coastal mixing zones may lead to more rapid energetic and PAH biodegradation than would be expected using standard measures and techniques. Surveys of energetic and PAH mineralization rates in areas adjacent to DoD sites in the Key West area suggest that contaminants in surface runoff from shoreside areas would be rapidly metabolized i.e., hours to weeks in the adjacent seawater and surface sediment. Rapid intrinsic biodegradation rates of such contaminants would potentially mitigate the ecological risk associated with exposure of marine biota to these compounds. In addition, as part of these surveys, the most rapid RDX and HMX mineralization rates associated with any natural assemblage to date were found in the tropical sediment at some stations around Key West. Taken together, this work supports a site conceptual model where PAH and energetics would be rapidly biodegraded by natural microbial assemblages were they to migrate from mangrove-dominated lagoon systems to adjacent coastal waterways in tropical ecosystems.
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