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Risk Assessment of Exposure to Lead for Mottled Ducks on National Wildlife Refuge of the Upper Texas Gulf Coast

Investigators:
Brian Kearns, Ph.D Student
Dr. Jena Moon
Stephen McDowell, M.S.

Project Supervisors:
Dr. David Haukos

Funding:
U.S. Fish and Wildlife Service
U.S. Geological Survey
Stephen F. Austin State University

Cooperators:
Texas Chenier Plain NWR Complex
Stephen F. Austin State University
Dr. Dan Collins
Patrick Walther

Location: Texas Chenier Plain NWR Complex

Completion: May 2015

Status: Completed


Mottled ducks are being studied to determine potential impacts of lead exposure on populations of the Texas Gulf Coast

Objectives:
Develop body condition and fat indices for Texas Gulf Coast mottled ducks

Determine ratios of Pb isotopes in bone and blood tissue from mottled ducks, and examine environmental ratios of Pb isotopes from vegetation and soil samples to determine contamination sources, potential bioavailability, and exposure pathways.

Create a predictive surface for high risk areas of Pb contamination in the Texas Chenier Plain and Midcoast NWR Complexes using spatial interpolation techniques.

Use Species Distribution Modeling (SDM) technology to create distribution maps of mottled ducks at an ecosystem scale for the Texas Chenier Plain NWR complex, and assess potential effects Pb contamination on habitat use.

Develop a formal Environmental Risk Assessment report for risk of exposure to environmental Pb for mottled ducks and other waterbirds on the Upper Texas Gulf Coast.

Results:
The mottled duck (Anas fulvigula) is a dabbling waterfowl species native to coastal wetlands of the Gulf of Mexico of the United States and Mexico. Although closely related to common waterfowl species such as the mallard (A. platyrhynchos) and American black duck (A. rubrip es), the mottled duck exhibits unique behavior, mainly in its life history as a non-migratory species. As such, because of population declines caused by predation, habitat destruction, and environmental contaminants, this species requires specialized conservation concerns and species-specific management to protect population numbers. The goal of this study was to assess the ongoing effect of observed lead (Pb) contamination and exposure issues in mottled ducks and their habitats, which I achieved by conducting assessments that will provide managers habitat and organism level metrics to detect and mitigate Pb in mottled ducks and their environments.

Field data were gathered at the Texas Chenier Plain National Wildlife Refuge Complex (TCPC), which was the area of greatest mottled duck density on the Texas Coast. First, a body condition index was created to provide managers a tool to monitor population health, and a proxy for Pb exposure and avian health without destructively sampling individuals. Presence-only maximum entropy (MaxENT) and multivariate statistical modeling procedures were then used in conjunction with mottled duck movement data to elucidate sets of habitat conditions that were conducive to predicting the occurrence of mottled ducks and environmental Pb "hot spots". MaxENT analyses suggested that Pb in the top portion of the soil column is similarly related to all environmental variables considered, may be increasingly available after large-scale environmental disturbances. Lack of variation in coarse-scale habitat use between breeding and non-breeding seasons may further point to a food-based exposure pathway for Pb as mottled ducks switch from an invertebrate to plant diet, either as a result of changing age classes or normal adult phenology, during the period of increased Pb exposure.

Using stable isotope ratio analysis, I then tested environmental samples of soil and vegetation as well as mottled duck blood to determine isotopic signatures that were consistent with particular sources of Pb deposition (e.g., Pb shot pellets, leaded fossil fuel combustion, industrial effluents). Comparisons suggested a great deal of similarity to Pb shot reference values in vegetation and blood samples, especially in blood samples with higher concentrations of Pb present.

Last, I conducted a formal Ecological Risk Assessment (ERA) procedure to quantify the risk to mottled ducks from Pb exposure in their current habitat and direct managers towards effective mitigation and habitat management strategies to reduce future exposure. One scenario suggested that mottled ducks were at greatest risk from eating an invertebrate-based diet, but Pb content values at the TCPC suggest that a plant-based diet may provide a higher Pb exposure risk for mottled ducks, depending on true levels of bioavailability in environmental media. Overall, I determined that mottled ducks experience greatest Pb exposure risk from Pb shot pellets on the TCPC or in nearby habitat, while potentially also experiencing low levels of exposure from several other sources. Additionally, management strategies such as phytoremediation that focus on plants that do not provide food resources for mottled ducks as a potential environmental sink for Pb contamination may prove effective in reducing the overall Pb load from historical activities that likely deposited much of the Pb in this ecosystem.

Products:
Kearns, Brian (Ph.D., 2015; advisor Haukos) Patterns and pathways of lead contamination in mottled ducks (Anas fulvigula) and their habitat, Kansas State University.

Publications:
Kearns, B., P. Walther, W. Conway, and D. Haukos. 2015. Factors affecting fat content in mottled ducks on upper Texas Gulf Coast. Journal of the Southeastern Association of Fish and Game Agencies 2:274-280.

McDowell, P.K., W.C. Conway, D.A. Haukos, J.A. Moon, C.E. Comer, and I.K. Hung. 2015. Blood lead exposure concentrations in mottled ducks (Anas fulvigula) on the upper Texas coast. Journal of the Southeastern Association of Fish and Game Agencies 2:221-228.

Professional Presentations:
Kearns, B., P. Walther, W. Conway, and D. Haukos. 2014. A body condition index for non-breeding mottled ducks on the upper Texas Gulf Coast. Mottled Duck Symposium, Annual Conference of the Southeastern Association of Fish and Wildlife Agencies, Destin, Florida.

Brian Kearns, Stephen McDowell, Jena Moon, Elizabeth Rigby, and David Haukos. 2014. Identifying Landscape-level indicators of environmental contaminants that affect wildlife: a species distribution approach. Graduate Student Research Forum, Division of Biology, Kansas State University.

Kearns, B., P. Walther, and D. Haukos. 2014. Developing a body condition index for mottled ducks on the upper Texas Gulf Coast. Annual meeting of the Texas Chapter of The Wildlife Society, Austin, TX.

Kearns, B., S. McDowell, J. Moon, W. Conway, and D. Haukos. 2014. The legacy of lead: developing new methods for assessing lead contamination and wildlife exposure risks in Gulf Coast wetland habitats. Annual meeting of the Texas Chapter of The Wildlife Society, Austin, TX.

Kearns, B.V., McDowell, S., Moon, J., Rigby E., Haukos, D. 2014. Identifying landscape-level indicators of environmental contaminants that affect wildlife: a species distribution approach. Midwest Fish and Wildlife Conference, Kansas City, MO.

Kearns, B., D. Haukos, J. Moon, and E. Rigby. 2013. Species distribution in environmental decision-making: characterizing the efficacy of different models for use in habitat and wildlife management. Annual Meeting of the Society for Conservation GIS. Monterey, California.

Kearns, B., S. McDowell, J. Moon, and D. Haukos. 2013. Spatial analysis and ecological risk assessment for lead exposure in Gulf Coast waterfowl: does environmental lead represent an ecological trap? Annual Meeting of the Ecological Society of America. Minneapolis, Minnesota.