Sedimentary cladoceran remains, a key to interpreting past changes in nutrients and trophic interactions

Aquatic community structure and lake trophic status are two important components in assessing aquatic ecosystem health. However, lags in response to environmental perturbations and complex trophic interactions make it necessary to have long-term records in order to understand changes in trophy and community structure in response to environmental stressors. Paleolimnological reconstructions using the remains of organisms preserved in sediments can provide a long-term record, as well as information on historical variability and background conditions.; The Cladocera occupy an important intermediate position in aquatic food webs that makes them interesting for investigating changes in lake trophy and fisheries. However, difficulties in taxonomy and the paucity of ecological data for many cladoceran species have slowed the development of cladocerans as paleoenvironmental indicators. This thesis presents data on sedimentary cladoceran assemblages from forty-nine lakes from central British Columbia, Canada, that span a wide gradient of nutrient status (total phosphorus range = 5 to 146 μg/L). Detailed morphological descriptions are presented for the sedimentary remains of 43 cladoceran species. Cladoceran species composition from surface sediments (top 1 cm) was related to environmental conditions using Canonical Correspondence Analysis (CCA). CCA showed that total phosphorus (TP), take depth and surface water temperature best described the variation in species composition among the lakes. Predictive models to estimate TP from species abundance data were developed using weighted averaging techniques. These models produced relatively good inference models (r2 _boot = 0.61, n = 49), which can now be used to assess changes in lake trophic state.; Two lakes from central British Columbia with known changes in nutrient and fisheries status were investigated to further assess the TP model and to investigate the potential of using size changes in Daphnia remains to reconstruct changes in fish planktivory. Reconstructions from Tabor Lake show that it has undergone cultural eutrophication and that size changes in Daphnia correspond to a recorded fish kill in 1993. Reconstructions from Cicuta Lake show that changes in Daphnia size record the introduction of rainbow trout into this formerly fishless lake. The Cladocera have considerable potential in providing information valuable to lake managers and for investigating long-term species-environment relationships.