Baltimore Ecosystem Study Institute of Ecosystem Studies

2016 BES Annual Meeting Presentation and Poster Abstracts

Exploring stream conductivity as a driver of biotic changes associated with impervious cover
Baker, Matthew
Co-Authors: Matthew Baker (UMBC) Jaylen Bos (UMBC) Ellen Woytowitz (UMBC) Joseph Sexton (UMCP)

Abstract: Recent studies continue to confirm that land development measured by impervious cover impacts stream assemblages at lower levels of urbanization than previously suspected. Although the dynamics of the ‘urban stream syndrome’ are well known, like many syndromes the specific mechanisms driving observed impacts remain unclear. Hydrologic studies have failed to implicate flashy flows as a proximal cause, despite their intuitive link to imperviousness. Recent reviews have once again implicated long-term salinization of freshwaters as a potential contributor, but do they explain patterns of biotic change associated with low levels of urbanization? We developed a 25-year time-series of annual impervious cover for the Baltimore-Washington corridor to explore changes in water chemistry associated with incremental urban expansion. We then compared taxon-specific analysis of change across environmental gradients associated with impervious cover and specific conductivity to detect patterns consistent with a mechanistic linkage. We found in larger rivers, impacts from conductivity were more consistent with a proximate signal driving biotic changes when compared to impervious cover, yet in smaller streams conductivity generated a less definitive response. We examined patterns of spatial arrangement and found no evidence that proximity was necessary to explain acute effects of imperviousness, as distal development also appeared to drive biotic impacts. We propose a new theory to explain the role of land use change on degradation of stream assemblage composition and structure.