Date of Award

5-1-2020

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Department

Biological Sciences

First Advisor

Timothy Ehlinger

Committee Members

Timothy Ehlinger, Charles Wimpee, John Berges, Neal O'Reilly, Erica Young

Keywords

bioindicators, ecotocilogical, indicators, microbial, nutrient metals, toxic stress

Abstract

Rapid population growth has created problems in meeting the goals of the Clean Water Act (CWA) “to restore and maintain the integrity of the nation’s waters”. Approaches for monitoring and analysis have increasingly focused on identifying “biological response signatures” that can characterize the complex patterns of ecological responses to stress occurring across levels of biological, spatial and temporal organization. One productive area of research has employed integrated indices of chemical risk, ecotoxicological risk and ecological risk to assess the impact of human activity across disturbance gradients such as urbanization. Selecting relevant metrics for use in constructing multimetric index requires identifying bioindicator organisms across different trophic levels with capacities to detect signals from anthropogenic disturbances.

This study explored the efficacy of a suite of higher plant ecotoxicological assays and sediment bacterial taxonomic community metrics for use as indicators in ecological risk assessment along a gradient of urbanization. The study was conducted in the Pike River watershed (Racine, Wisconsin USA) in six wetlands selected across a gradient of dominant land use types (agricultural, commercial, residential, undeveloped and industrial). Field measurements were taken and sediment samples collected from 2015 through 2017. MicroBioTest Phytotoxkit TM ecotoxicological assays, based on growth inhibition of three plants (Sinapis, Sorghum and Lepidium) were used to assess sediment toxicity. Likewise, bacterial taxonomical diversity metrics identified with 16S rRNA gene sequences were used to assess of the bacterial community assemblage of sediments. The Phytotox™ and bacterial community metrics were analyzed in relation to pollutant stress, measured by field concentrations of metals (Ag, As, Cd, Hg, Ni, Pb and Zn) in sediments, concentrations of nitrate and phosphate in the water, and predicted pollutant loadings calculated from surrounding landuse. Additionally, a laboratory microcosm experiment was conducted in 2017 that examined the effects of manipulated pollutant levels of phosphate, nitrate, copper and lead on both PhytoTox™ and bacterial community metrics.

Analysis of results from the field study and microcosm experiments indicate that PhytoTox™ assays (Sinapis alba, Sorghum saccharatum and Lepidium sativum) and sediment bacterial taxonomical diversity from16S rRNA gene sequences are responsive to variation in pollutant loadings and concentrations of metals and nutrients. Statistical interactions and patterns of responses demonstrate that a combination of PhytoTox™ and bacterial taxonomic diversity metrics can serve as predictive bioindicators for ecological risk assessment in urbanizing water sheds. In particular, the response patterns of bacterial genera observed in the microcosm experiments suggest directions for future research and the potential for the development pollutant-specific bacterial indicators.

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