Evaluating long-term effects of destructive flooding on in-stream riparian characteristics and macroinvertebrate abundance in low order headwater streams

Abstract

In August of 2009 a flashflood scoured an assemblage of fourteen 1st -- 3rd- order headwater streams surrounding Zoar Valley Canyon in western New York State USA. Macroinvertebrate composition, watershed variables, and habitat features of these streams were quantitated in 2006 and reported in the peer-reviewed literature. The objective of this study was to determine long-term disturbance effects within these impacted streams, particularly as relation to meta-community assembly. Biotic and environmental assessments from 2011, 2012, and 2013 mirrored those from 2006, with biota collected from riffle/cobble segments by Surber net, and environmental/habitat variables quantified by a widely used Qualitative Habitat Evaluation Index (QHEI) that assesses in-stream and riparian characteristics. In- stream environmental variables such as substrate diversity and in-stream cover initially declined in quality and converged leading to homogenization of stream patches. Dissimilarity among stream communities for both biotic and environmental characteristic from year to year (assessed by Non-metric Multidimensional Scaling ordination) revealed that streams were differentially impacted and also suggested changes in meta-community composition in response to the disturbance. In 2006, partial correlations suggested a niche-based species sorting of organisms, whereas by 2011, this structuring was lost, suggesting a switch to either equivalence based neutral theory or homogenous patch dynamics. By 2013, although QHEI numbers were reaching pre-flood values, an environmental/biotic partial correlation (as seen in 2006) had yet to re-emerge, suggesting that macroinvertebrate communities were still facing the effects of this disturbance.