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LINKAGES AMONG LAND-USE, WATER QUALITY, PHYSICAL HABITAT CONDITIONS AND LOTIC DIATOM ASSEMBLAGES: A MULTI-SPATIAL SCALE ASSESSMENT
Citation:
Pan, Y., A. T. Herlihy, P R. Kaufmann, P. J. WIGINGTON JR, J Van Sickle, AND T. Moser. LINKAGES AMONG LAND-USE, WATER QUALITY, PHYSICAL HABITAT CONDITIONS AND LOTIC DIATOM ASSEMBLAGES: A MULTI-SPATIAL SCALE ASSESSMENT. HYDROBIOLOGIA. Kluwer Academic Publishers, Hingham, MA, 515:59-73, (2004).
Description:
We assessed the importance of spatial scales (catchment, stream network, and sample reach) on the effects of agricultural land-use on lotic diatom assemblages along a land-use gradient in the agricultural Willamette Valley Ecoregion of Oregon. Periphyton, water chemistry, and physical habitat were characterized for 25 wadeable streams during a dry season (July to Sept., 1997). Additional water chemistry samples were collected in the following wet season (Feb. 1998) to assess seasonal effects of land-use on stream water chemistry. Percent agricultural land in the study catchments ranged from 10% to 89% with an average of 52%. Detrended correspondence analysis (DCA) on diatom species data showed that the 1st DCA axis was negatively correlated with % of pollution sensitive taxa (r=-0.89), but positively with diatom taxa richness (r =0.78), % of hypereutrophic taxa (r =0.62), % of a-mesosaprobous taxa (r=0.60), and % of polysaprobous taxa (r=0.60), and % of obligately nitrogen (N)-heterotrophic taxa (r=0.59). The 1st DCA axis did not significantly correlate with % of agricultural land-use regardless of spatial scales. This axis was, however, significantly correlated with both water chemistry variables (e.g., acid neutralizing capacity (r =0.55) and Cl- (r=0.40)) and physical habitat variables (e.g., % substrate as coarse gravels (r=-0.55), channel wet width (r=-0.45)) in the dry season. The correlation was stronger with the same water chemistry variables measured in the wet season (e.g., r anc=0.71, rcl=0.56). Percent of obligately N-heterotrophic taxa was the only diatom autecological metric that showed a significant correlation with % agricultural land-use along the entire stream network (r=0.50), but not at catchment or sample reach scales. Correlation between % agricultural land-use and water chemistry variables varied among the spatial scales and between seasons. Physical habitat variables (log10 erodible substrate diameters and stream reach slope) were significantly correlated with % agriculture along the stream network but not at reach or catchment scales. Our data suggest that spatial scales are important in assessing effects of land-use on stream conditions but the spatial scale effects may vary between seasons. Direct linkages between land-use and lotic diatom assemblages were weak during summer base-flow time regardless of the spatial scales. Summer sampling may underestimate the effects of land-use on stream conditions in areas where seasonal patterns are so distinctive as in the Willamette Valley.