Estimating benthic secondary production from aquatic insect emergence in streams affected by mountaintop removal coal mining, West Virginia, USA
Johnson, Brent R.; Fritz, Ken M.; Price, Rachel
published: Mar 1, 2013
ArtNo. ESP141018203001, Price: 29.00 €
Mountaintop removal and valley fill (MTR/VF) coal mining recontours the Appalachian landscape, buries headwater stream channels, and degrades downstream water quality. The goal of this study was to compare benthic community production estimates, based on seasonal insect emergence, between mined and forested streams in the Twentymile Creek watershed, WV (USA). We also assessed the relationship between structural and functional indicators by comparing traditional structural bioassessment measures with our secondary production estimates. Emergence traps were deployed seasonally for 2-4 weeks beginning in Autumn 2007 along 100-m reaches in each of five mined and five forested streams. The study reaches in the mined streams were located at varying distances downstream of their respective valley fills. Benthic community production was calculated using published length-mass equations and emergence:production ratios. No differences in seasonal emergent density (indiv. m-2 d-1), biomass (mg m-2 d-1) or estimated annual secondary production (g AFDM m-2 y-1) were detected between treatments. Annual secondary production estimates for mined streams were highly variable and averaged 29.6 g AFDM m-2 y-1, but ranged from 1.51 g AFDM m-2 y-1 in the stream nearest to its valley fill to 65.69 g AFDM m-2 y-1 in another stream that was 1 km downstream from its fill. Production of forested streams was more consistent with an average of 20.42 g AFDM m-2 y-1 and ranged only from 13.81-27.17 g AFDM m-2 y-1. Annual production estimates were not correlated with benthic community index scores, component metrics, or habitat assessment scores. Only EPT production estimates were significantly correlated with structural endpoints. Conductivity of mined streams was > 30× greater than forested streams and contributed to strong differences in emergence composition. Chironomids alone accounted for > 80% of production in mined streams while forested streams had significantly higher EPT production. Measures of stream ecosystem function, including secondary production, can provide more holistic stream assessments. Prior to their widespread application as indicators of stream health, however, studies are needed to further develop robust response functions across disturbance gradients from multiple stressors.