Stream Restoration Is Influenced by Details of Engineered Habitats at a Headwater Mine Site

Robert S Arkle,David S Pilliod

doi:10.3390/d13020048

Abstract

A lack of information regarding which ecological factors influence restoration success or failure has hindered scientifically based restoration decision-making. We focus on one headwater site to examine factors influencing divergent ecological outcomes of two post-mining stream restoration projects designed to improve instream conditions following 70 years of mining impacts. One project was designed to simulate natural stream conditions by creating a morphologically complex channel with high habitat heterogeneity (HH-reach). A second project was designed to reduce contaminants and sediment using a sand filter along a straight, armored channel, which resulted in different habitat characteristics and comparatively low habitat heterogeneity (LH-reach). Within 2 years of completion, stream habitat parameters and community composition within the HH-reach were similar to those of reference reaches. In contrast, habitat and community composition within the LH-reach differed substantially from reference reaches, even 7–8 years after project completion. We found that an interaction between low gradient and high light availability, created by the LH-reach design, facilitated a Chironomid-Nostoc mutualism. These symbionts dominated the epilithic surface of rocks and there was little habitat for tailed frog larvae, bioavailable macroinvertebrates, and fish. After controlling for habitat quantity, potential colonizing species’ traits, and biogeographic factors, we found that habitat characteristics combined to facilitate different ecological outcomes, whereas time since treatment implementation was less influential. We demonstrate that stream communities can respond quickly to restoration of physical characteristics and increased heterogeneity, but “details matter” because interactions between the habitats we create and between the species that occupy them can be complex, unpredictable, and can influence restoration effectiveness.

Highlights

Each year resource managers and agencies spend over one billion dollars on >5000 stream or river restoration projects in the United States alone [1]
In addition to being proposed by the U.S Environmental Protection Agency as a “Superfund” site, Meadow Creek is designated critical habitat for three salmonid fish species listed as Threatened under the Endangered Species Act
To assess habitat heterogeneity differences between GROUPs, we examined relative standard error (RSE = standard error/mean) values for each individual quantitative variable measured by GROUP

Summary

Introduction

Each year resource managers and agencies spend over one billion dollars on >5000 stream or river restoration projects in the United States alone [1]. In particular, seek to improve conditions through increasing habitat heterogeneity [10]. This is partly because many streams in need of restoration were simplified (i.e., channelized, armored, or regulated) for human purposes [11,12], and because studies of intact ecosystems have shown positive relationships between particular species, or species diversity as a whole, and habitat complexity or heterogeneity [13]. The ecological effectiveness of intentionally increasing habitat heterogeneity has been mixed in stream restoration studies [10] and increasing habitat heterogeneity does not guarantee use by a particular target species or establishment of desired (pre-disturbance) community composition

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