Resilience Limitations and Resistance of Hyporheic Microbial Communities from Chronic Heavy Metal Contamination Environments: Analysis with the Novel Resazurin Resorufin Smart Tracer

摘要

River ecosystems are among the most threatened and rapidly altering systems in the world because of anthropogenic disturbance. Chronic heavy metal contamination of lotic environments is a global concern and a widespread environmental and human health threat. This persistent stressor can shape microbial community structure and function, often selecting for the genotypic and phenotypic characteristics that increase fitness in toxic environments and may encumber the microbial community hosting metal resistance mechanisms with additional energetic costs. This cost should be expressed in heterotrophic aerobic microbial metabolism, a primary ecological process variable and can be estimated through respiration measurements. Hyporheic respiration is a proposed functional indicator of ecosystem health and is sensitive to gradients in environmental quality. The ecological importance and contaminant retention of the hyporheic zone presents these communities as a valuable indicator of natural resource damage.In this study, we illustrate the first documentation of the Resazurin Resorufin Smart Tracer as a functional indicator of lotic ecosystem integrity. This tool was used to quantify metabolism of hyporheic microbial communities from the chronic metal contamination gradient of the Clark Fork River, Montana, USA in column experiments. Communities from low, mid, and high contamination locations of the gradient were paired with pristine reference sites to test hypotheses regarding the use of the Resazurin Resorufin Smart Tracer to estimate ecological functional resilience and resistance to chronic metal stress. We found that acute metal stress inhibits respiration in both communities and that the communities did not differ in metal resistance potential. This research indicates the Resazurin Resorufin Smart Tracer has potential as a functional indicator of ecological integrity and suggests that lotic heavy metal contamination represents a persistent stress from which this ecosystem was not able to recover in over 100 years.