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TECHNICAL REPORTS

Landscape and Watershed Processes

Predicting Estuarine Sediment Metal Concentrations and Inferred Ecological Conditions: An Information Theoretic Approach

^a USEPA, Office of Research and Development, National Health and Environmental Effects Research Laboratory, Atlantic Ecology Division, 27 Tarzwell Drive, Narragansett, RI 02882
^b Univ. of Rhode Island, Dep. of Natural Resources Science, 1 Greenhouse Road, Kingston, RI 02881
^c USEPA, Office of Research and Development, Mail Code B343-06, Research Triangle Park, NC 27711
^d USEPA, Office of Research and Development, National Health and Environmental Effects Research Lab., Atlantic Ecology Div., 27 Tarzwell Drive, Narragansett, RI 02882

^* Corresponding author (hollister.jeff{at}epa.gov).

Received for publication February 26, 2007. Empirically derived relationships associating sediment metal concentrations with degraded ecological conditions provide important information to assess estuarine condition. Resources limit the number, magnitude, and frequency of monitoring activities to acquire these data. Models that use available information and simple statistical relationships to predict sediment metal concentrations could provide an important tool for environmental assessment. We developed 45 predictive models for the total concentrations of copper, lead, mercury, and cadmium in estuarine sediments along the Southern New England and Mid-Atlantic regions of the United States. Using information theoretic model-averaging approaches, we found total developed land and percent silt/clay of estuarine sediment were the most important variables for predicting the presence of all four metals. Estuary area, river flow, tidal range, and total agricultural land varied in their importance. The model-averaged predictions explained 78.4, 70.5, 56.4, and 50.3% of the variation for copper, lead, mercury, and cadmium, respectively. Overall prediction accuracies of selected sediment benchmark values (i.e., effects ranges) were 83.9, 84.8, 78.6, and 92.0% for copper, lead, mercury, and cadmium, respectively. Our results further support the generally accepted conclusion that sediment metal concentrations are best described by the physical characteristics of the estuarine sediment and the total amount of urban land in the contributing watershed. We demonstrated that broad-scale predictive models built from existing monitoring data with information theoretic model-averaging approaches provide valuable predictions of estuarine sediment metal concentrations and show promise for future environmental modeling efforts in other regions.

Abbreviations: AIC, Akaike Information Criteria • EMAP-E, EPA's Environmental Monitoring and Assessment Program-Estuaries component • ER, effects range • ERL, effects range low • ERM, effects range median • MAIA, Mid-Atlantic Integrated Assessment • NCPDI, National Coastal Pollution Discharge Inventory

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