Using Diatom Assemblages to Assess Urban Stream Conditions |
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Authors: | Christopher E Walker Yangdong Pan |
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Institution: | (1) Environmental Sciences and Resources, Portland State University, Portland, OR 97207, USA;(2) USGS, Columbia River Research Lab, Cook-Underwood Rd, 5501-AWA, 98605-9717, USA |
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Abstract: | We characterized changes in diatom assemblages along an urban-to-rural gradient to assess impacts of urbanization on stream
conditions. Diatoms, water chemistry, and physical variables of riffles at 19 urban and 28 rural stream sites were sampled
and assessed during the summer base flow period. Near stream land use was characterized using GIS. In addition, one urban
and one rural site were sampled monthly throughout a year to assess temporal variation of diatom assemblages between the urban
and rural stream sites. Canonical correspondence analysis (CCA) showed that the 1st ordination axis distinctly separated rural
and urban sites. This axis was correlated with conductivity (r = 0.75) and % near-stream commercial/industrial land use (r = 0.55). TWINSPAN classified all sites into four groups based on diatom assemblages. These diatom-based site groups were
significantly different in water chemistry (e.g., conductivity, dissolved nutrients), physical habitat (e.g., % stream substrate
as fines), and near-stream land use. CCA on the temporal diatom data set showed that diatom assemblages had high seasonal
variation along the 2nd axis in both urban and rural sites, however, rural and urban sites were well separated along the 1st
ordination axis. Our results suggest that changes in diatom assemblages respond to urban impacts on stream conditions. |
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Keywords: | canonical correspondence analysis TWINSPAN urban-to-rural gradient bioassessment diatoms |
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