Date Approved

5-2009

Graduate Degree Type

Thesis

Degree Name

Biology (M.S.)

Degree Program

Biology

Abstract

Extreme environments can create ecotones with uncharacteristic physicochemical conditions and ecological communities. Recently, several submerged sinkholes were discovered in Lake Huron where hypoxic groundwater that is rich with dissolved ions intrudes into surrounding lake water. Researchers have documented large growths of cyanobacteria and chemosynthetic bacteria surrounding these groundwater vents, but little is known if this production is utilized by upper trophic level organisms and how the environmental conditions affect local community density and diversity. My objectives were threefold: (1) I wanted to confirm the presence and describe the nature and extent of chemical and physical gradients in the sublacustrine sinkhole environments; (2) I wanted to determine the distribution and abundance of higher trophic level organisms surrounding these sinkholes; (3) I wanted to trace the nutrient and energy flow through the food web from groundwater to primary producers to heterotrophic invertebrates and fish using stable isotopes. I used sonde measurements and chemical analyses to determine the extent of the environmental gradients, after which I set up random transects in the sinkholes to sample plankton, benthic macroinvertebrates, and fish. These data were compared to samples from local areas without groundwater input that I used as control sites. Lastly, I collected 126 samples from different components of the food web at both groundwater and control sites to compare stable isotope rations of the food webs. Distinct environmental gradients of dissolved oxygen, specific conductance, and temperature were observed at the sinkhole sites, and all of these parameters were significantly different from control sites. These environmental conditions affected the density and community composition of both the benthic macroinvertebrate and fish communities, although I did not observe any significant patterns in the plankton communities. Moreover, stable isotope analysis showed significantly different carbon isotope signatures of the benthic communities (algae, macroinvertebrates, fish). The results suggest that the inflow of groundwater moves across the benthos and creates a unique environmental zone, and that the biological communities within this area are affected by and partially reliant on the intruding groundwater as a source of inorganic nutrients for primary production.

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