Mountaintop removal coal mining impacts on structural and functional indicators in Central Appalachian streams

Abstract

Mountaintop removal coal mining (MTR) has been a major source of landscape change in the Central Appalachians of the United States (US). Changes in stream hydrology, channel geomorphology and water quality caused by MTR coal mining can lead to severe impairment of stream ecological integrity. The objective of the Clean Water Act (CWA) is to restore and maintain the ecological integrity of the Nation's waters. Sensitive, readily measured indicators of ecosystem structure and function are needed for the assessment of stream ecological integrity. Most CWA assessments rely on structural indicators; inclusion of functional indicators could make these assessments more holistic and effective. The goals of this study were: (1) test the efficacy of selected carbon (C) and nitrogen (N) cycling and microbial structural and functional indicators for assessing MTR coal mining impacts on streams; (2) determine whether indicators respond to impacts in a predictable manner; and (3) determine if functional indicators are less likely to change than are structural indicators in response to stressors associated with MTR coal mining. The structural indicators are water quality and sediment organic matter concentrations, and the functional indicators relate to microbial activity and biofilm production. Seasonal measurements were conducted over the course of a year in streams draining small MTR-impacted and forested watersheds in the Twentymile Creek watershed of West Virginia (WV). Five of the eight structural parameters measured had significant responses, with all means greater in the MTR-impacted streams than in the forested streams. These responses resulted from changes in source or augmentation of the original source of the C and N structural parameters because of MTR coal mining. Nitrate concentration and the stable carbon isotopic ratio of dissolved inorganic carbon were the most effective indicators evaluated in this study. Only three of the fourteen functional indicators measured had significant responses to MTR coal mining, with all means greater in the forested streams than in the MTR-impacted streams. These results suggest that stressors associated with MTR coal mining caused reduction in some aspects of microbial cycling, but resource subsidies may have counterbalanced some of the inhibition leading to no observable change in most of the functional indicators. The detritus base, which is thought to confer functional stability, was likely sustained in the MTR-impacted streams by channel storage and/or leaf litter inputs from their largely intact riparian zones. Overall, our results largely support the hypothesis that certain functional processes are more resistant to stress induced change than structural properties but also suggest the difficulty of identifying suitable functional indicators for ecological integrity assessment.