Epsilon Open Archive

Abstract

This thesis describes the spatial and temporal variability of benthic macroinvertebrate
communities in Swedish streams and its implications for environmental assessment. One
of the challenges for environmental assessment is to separate change caused by
anthropogenic stress from natural variability, therefore it is essential to have insight in the
effects of temporal and spatial variability on the benthic macroinvertebrates. The thesis is
based on two stream riffle datasets; one spatial (694 streams) and one temporal (6-11
years sampling of five streams). Classification of macroinvertebrate community
composition showed a gradual change in community composition in Sweden. A
geographical (ecoregional) classification was tested as a starting point for biomonitoring,
but I found that local-scale variables such as stream velocity and substratum type were
important descriptors and must be taken into account in assessments of running waters.
Despite that temporal variability was small relative to the spatial variability, I argue that
the temporal variability is of importance and that the inherent cyclic and seasonal factors
affecting benthic macroinvertebrates has to be accounted for in environmental assessment.
Surprisingly, the stream macroinvertebrate community composition did not show a largescale
pattern (correlation with the limes norrlandicus ecotone, found at ~60° north),
whereas a lake dataset showed such a pattern. I speculate that differences between the two
ecosystems are caused by differences in detrital retention and stability. Richness indicator
measures generally had low variability and high statistical power and needed few samples
to detect changes caused by perturbation. In environmental assessment it is important to
know what effect size and variability (spatial and temporal) one can expect from an
indicator metric (and hence the macroinvertebrate community) so that the money spent in
impact studies is used in a cost-effective way.