Effects of Urbanization on the Biological Integrity of Puget Sound Lowland Streams: Restoration with a Biological Focus
Abstract
Rapid urbanization threatens the condition of streams and rivers across the Pacific
Northwest. Efforts to protect and control urban streams have traditionally focused on
physical channel conditions and chemical water quality. This study is designed to use
biological attributes of these streamsmeasured with the multimetric index of biological
integrity (B-IBI) based on benthic macroinvertebratesto assess stream condition.
Between 1997 and 1999, invertebrate samples were collected from 45 sites in second and
third order streams of the Puget Sound lowlands of Western Washington. The locations
of 14 sites were chosen to evaluate the placement of large woody debris (LWD) as a
restoration technique on five streams. Urbanization was characterized by a 1998 satellite
land cover classification and was measured across several spatial scales. The
relationships among metrics of the B-IBI and stream substrate and hydrologic features
were also evaluated at a sub-set of sampling sites. B-IBI declined as urban land cover
increased both across the entire basin and within riparian zones. The effectiveness of
localized patches of riparian corridor in maintaining biological integrity varied as a
function of the percentage of urban land cover in the sub-basin. Channel roughness and
hydrologic flashiness were also correlated with B-IBI. Below the five restoration
projects, there was no overall detectable improvement in B-IBI. The aquatic biota is
sensitive to a variety of urban impacts controlled over both large and small spatial scales.
Restoration efforts that deal with only one local impact type without addressing larger
scale issues are unlikely to successfully restore the biota of degraded streams.
Collections
- Fisheries [238]