TNT Degradation by Natural Microbial Assemblages at Frontal Boundaries Between Water Masses in Coastal Ecosystems (ER-2124)

Abstract

Abstract : This limited scope, three year SERDP project involves determining the primary biogeochemical factors that control energetics metabolism by natural microbial assemblages in coastal systems. By correlating standard water quality measurements with degradation rates, we can predict turnover times and ecosystem capacity for energetics released into hydrodynamically similar, UXO-impacted ecosystems where access to site samples may be limited. During samplings in the Florida Keys and Lower Outer Banks, NC, USA, we found that mixing experiments between coastal end members (mangrove lagoon or Cypress bog water, respectively) and open ocean seawater 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. Energetics and PAH mineralization rates in areas adjacent to Key West DoD sites suggest that contaminants in surface runoff from shoreside areas should be rapidly metabolized (i.e., hours to weeks) in the adjacent seawater and sediment. Ecosystem capacities for contaminant biodegradation were also determined for three North Carolina coastal estuarine systems: Newport River Estuary, New River Estuary and Bogue Sound. The analyses predicted how much energetics or phenanthrene could be released into the headwaters or DoD site of each system and be attenuated before exiting the estuary into adjacent ecosystems. Taken together, this work supports a site conceptual model where PAHs and energetics would be rapidly biodegraded by natural microbial assemblages were they to migrate from mangrove- or Cypress-dominated coastal systems to adjacent waterways in both tropical and temperate ecosystems, respectively.