Seasonal changes of benthic macroinvertebrate communities in Southwestern British Columbia
Creators: name: Dymond, Pamela F.
Publisher: name: University of British Columbia
Year: 2009

description: Two main goals of community ecology are to recognise patterns in species composition and to understand the processes affecting those patterns. The first goal of this study was to identify patterns of benthic macroinvertebrate composition between both different classes of streams and seasons in southwestern British Columbia. As well, life cycles and environmental conditions were examined to determine which processes were associated with patterns of community composition. The second goal of this study was to determine whether seasonal changes of the benthic community were large enough to affect the accuracy of predictions made by predictive models used for biomonitoring. Predictive models cannot extrapolate beyond the range of variability included within a reference data set. Because of seasonal variation, these models may only provide accurate predictions for the season when reference samples were collected. In the Fraser River Basin, reference samples to be used for biomonitoring with predictive models were collected only once a year - in the autumn. This study established the applicability of test samples collected outside of the reference-sample season. To address the goals of this study, benthic macroinvertebrate samples and associated environmental data were collected over five sampling dates during the course of one year, 1995-1996 (late spring, summer, autumn, winter, early spring). The samples were collected from eight streams that comprised three different classes of streams: 1) coastal streams, 2) interior plateau streams, and 3) large rivers. Each of the stream classes has a different climate, elevation, riparian vegetation, and discharge regime. Seasonal change of the benthic invertebrate community was small relative to the spatial change i.e., between the three stream classes. Correlation analysis indicated that spatial change of the invertebrate community in southwestern British Columbia was related to the environmental factors channel width, mean depth, maximum depth, maximum velocity, discharge, conductivity, alkalinity, nitrite and nitrate nitrogen, and total Kjeldahl nitrogen. Seasonal change of the community was not directly related to the seasonal change of any of the individual environmental variables measured. It was however, related to changes in the environment through effects of the environment on invertebrate life cycles. Of the environmental conditions measured, temperature had the greatest influence on the timing of insect life cycles. Abundance patterns in the small coastal and interior streams were related to the timing of invertebrate life cycles whereas abundance was related to life cycles and the spring freshet in the large rivers. Although seasonal variation of the invertebrate community in ordination space was less than spatial variation, this study found that test samples should be collected during the same season as when the biomonitoring reference samples were collected, or over multiple sampling dates. This strategy reduces the possibility of seasonal shifts or stochastic events leading to erroneous conclusions about the state of a test site.