The relationship between microbial communities, processes, and mine waste contamination in upper Clark Fork River alluvial soils

Understanding interactions between ecosystem-level functioning and community structure in contaminated systems will enable us to make better predictions of the consequences of anthropogenic stress. The following work develops, tests, and applies a theory of how contaminants affect ecosystem processes and community structure in the long-term. Field studies were conducted within the mine-waste contaminated floodplain of the Clark Fork River inside Grant-Kohrs Ranch National Historic Area in Deerlodge, Montana. In chapter 2 we evaluate the method of documenting change in microbial community structure (phospholipid fatty acid analysis (PLFA)) used in chapters 3 and 5 and compare its sensitivity to other current methods. We show that PLFA analysis is the most sensitive available method for showing treatment effects on microbial communities. In chapter 3 we report the first study to use an alluvial mine waste contamination gradient in soil to test an hypothesis regarding the relationship between ecosystem functioning and community structure. We show that functional suppression continues in an ecosystem where soil microbial communities have been exposed to mine waste contamination for almost a century and over a range of contamination concentrations where the contaminants do not exert a strong current effect on microbial community structure. In chapter 4, we report the first study to use Quantile Regression (QR) to separate contaminant effects on soil processes from variability in processes due to natural heterogeneity. QR facilitated the analysis of the limiting effects of heavy metals and soil acidity on soil respiration, a measure of soil function. Chapter 5 binds the theory developed in chapter 3 with the statistical approach developed in chapter 4. Microbial and plant community structure were examined along a floodplain scale contamination gradient. Results indicated that soil acidity and organic matter concentration exerted stronger effects on plant and microbial community structure than metals. The theory and findings presented in chapters 3 and 4 are discussed in reference to the decision process regarding environmental remediation of contaminated soil. We assert that removal of the floodplain surface is not necessary for remediation, rather liming and organic matter amendments would alleviate most of the toxic effects of the mine wastes.