Response of macroinvertebrate assemblages of boreal streams to acid stress

Abstract

1. Use of ecological criteria to exclude streams affected by stressors not of interest here (e.g. nutrient enrichment, liming) resulted in a strong acidity gradient as exemplified by principal component analysis. For example, the first PC axis explained 31.1% of the variance and was clearly related to acidity, e.g. pH buffering capacity and the ratio ANC/H+ were strongly correlated with this axis (loadings > 0.20). 2. Linear and multivariate regression techniques were used to assess the effects of land use and water chemistry (in particular acidity variables) on macroinvertebrate community structure. 3. Correlation revealed a number of significant predictor variables. Stepwise regression of four selected biological metrics (taxon richness, diversity EPT taxa and the Henrikson & Medin acid index) showed that, with the exception of one metric (Shannon diversity), acidity variables were selected as the first explanatory variable. For example, for richness and the acid index minimum ANC was the first variable selected and explained 37.4% and 68.6%, respectively, of the among-stream variance. Similarly, CCA ordination of community composition and environmental variables showed the importance of acidity variables, in particular in the southernmost (Central Plain) ecoregion. 4. Use of lag responses of acidity variables or modeled (flood) minimum pH or ANC did not improve explanatory power. 5. Plots of the Henrikson & Medin acid index showed significant relationships with in-stream measures of acidity. For pH, the first three classes (i.e. class 1 to 3) showed gradual increases in acid index scores. The latter two classes (class 4 and 5), on the other hand, were not as clearly defined (higher variability). Regarding buffering capacity (ANC), the two highest classes (class 4 and 5) showed high among-site variability, in particular when acid scores were regressed against mean ANC. At ANC 100 μg/L indicating biological impairment.

Published in

Rapport / Sveriges lantbruksuniversitet, Miljöanalys
2005, number: 2005:26
Publisher: Department of Environmental Assessment, Swedish University of Agricultural Sciences

SLU Authors

• Johnson, Richard

  • Department of Aquatic Sciences and Assessment, Swedish University of Agricultural Sciences
    

UKÄ Subject classification

Fish and Aquacultural Science

Permanent link to this page (URI)

https://res.slu.se/id/publ/8390