Non-wadeable river bioassessment: spatial variation of benthic diatom assemblages in Pacific Northwest rivers,USA |
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Authors: | Yangdong Pan Robert M Hughes Alan T Herlihy Philip R Kaufmann |
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Institution: | (1) Environmental Science and Management, Portland State University, Portland, OR 97207, USA;(2) Amnis Opes Institute, Corvallis, OR 97333, USA;(3) Departmento de Biologia, Universidade Federal de Lavras, Lavras, MG, 37200-000, Brasil;(4) Department of Fisheries and Wildlife, Oregon State University, c/o US Environmental Protection Agency, Corvallis, OR 97333, USA;(5) US Environmental Protection Agency, 200 SW 35th Street, Corvallis, OR 97333, USA |
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Abstract: | Current bioassessment efforts are focused on small wadeable streams, at least partly because assessing ecological conditions
in non-wadeable large rivers poses many additional challenges. In this study, we sampled 20 sites in each of seven large rivers
in the Pacific Northwest, USA, to characterize variation of benthic diatom assemblages among and within rivers relative to
environmental conditions. Analysis of similarity (ANOSIM) indicated that diatom assemblages were significantly different among
all the seven rivers draining different ecoregions. Longitudinal patterns in diatom assemblages showed river-specific features.
Bray–Curtis dissimilarity index values did not increase as a function of spatial distance among the sampled reaches within
any river but the Malheur. Standardized Mantel r of association between assemblage similarity and spatial distance among sites
ranged from a high of 0.69 (Malheur) to a low of 0.18 (Chehalis). In the Malheur River, % monoraphids, nitrogen-tolerant taxa,
and beta-mesosaprobous taxa all decreased longitudinally while % motile taxa, especially Nitzschia, showed an opposite trend, reflecting a strong in-stream water quality gradient. Similar longitudinal trends in water quality
were observed in other rivers but benthic diatom assemblages showed either weak response patterns or no patterns. Our study
indicated that benthic diatom assemblages can clearly reflect among-river factors. The relationships between benthic diatom
assemblages and water quality within each river may depend on the strength of the water quality gradients, interactive effects
of water quality and habitat conditions, and diatom sampling design. |
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