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Food Web Structures in Lake Superior Revealed by Stable Isotopes Help to Trace Bioaccumulation Pathways of PCBs

Libia Hazra, PhD Candidate, Environmental Engineering, Michigan Tech

Abstract:

Polychlorinated biphenyl (PCB) compounds are the persistent organic contaminant (POPs) found in highest concentrations in Lake Superior fishes. Fish consumption is a health risk, especially for local communities such as the Keweenaw Bay Indian Community (KBIC), since these fishes are a staple part of their diet. 
PCBs enter Lake Superior primarily through air-water exchange and enter food webs through the base of the food web (plankton) as well as through benthic macroinvertebrates.  The degree of bioaccumulation in the fish species consumed by humans depends on the structure of the food web.  Existing data for Lake Superior show that PCB concentrations in fish vary spatially, and thus the risk to humans varies with the location of fish harvest. We hypothesize that this variation in contaminant concentrations is due to spatially variable food web structures across the lake. 
To test this hypothesis, we analyzed stable isotopes in three fish species (lean lake trout, lake whitefish, cisco) from a region with high PCB concentrations in lake trout and from a region with low PCB concentrations.  Values of δ13C were used to infer profundal vs. pelagic components in the diet, and δ15N was used to assign trophic positions.  We use the results to evaluate whether length of food chain or extent of benthic feeding in food webs explain the spatial disparity in PCB concentrations in top predators.
 

Restoration is repairing relationships: Bridging Indigenous and Western Sciences to Assess Wild Rice (Zizania palustris) Restoration Efforts in Keweenaw Bay Indian Community Homelands

Cassandra Reed-VanDam, MS Student, Applied Ecology, Michigan Tech

Abstract:

Wild rice (Zizania palustris) is an ecologically and culturally significant species for the Keweenaw Bay Indian Community (KBIC), an Ojibwe Tribe located on the L’Anse Reservation as established by the Treaty of 1854. This annual aquatic grass is an important food source for many beings, including humans and waterfowl, and the roots hold sediment in place contributing to high water quality. Historically, manoomin was present across much of the northern Great Lakes area, however their lake presence has declined since the early 1900s. Much of this loss is attributed to factors caused by human development such as hydrologic changes due to damming, sulfate pollution from mining, introduction of invasive species, and rising winter temperatures caused by climate change. This study determined what socio-ecological factors are impacting wild rice restoration efforts within KBIC homelands and what the appropriate restoration assessment metrics are for the systematic evaluation of these ecosystems. Ethnographic research methods were applied through participant observation at community workshops, written surveys, and informal interviews with 5 Ojibwa knowledge holders to develop KBIC-specific attributes of successful restoration, including ecological and cultural metrics. These attributes were transformed into a holistic framework for assessing wild rice restoration, using both the SER Ecosystem Recovery Wheel and the Ojibwe Medicine Wheel as foundations for this work. Surface water, sediment, and pore water samples at 6 different rice beds were analyzed to contribute to a comprehensive database on wild rice conditions and to test the feasibility of the framework developed. This seminar introduces the framework, challenges, and applications for the future of bridging Western and Indigenous knowledge systems for wild rice restoration.