A great deal of work has been done by our lab on the Qu'Appelle Valley. The University is located within minutes of one site (Wascana lake), and the furthest site sampled is only two hours away. For the past three years, surveys and experiments have been conducted on six of the Qu'Appelle Valley lakes.
Map of the Qu'appelle Valley
Research has included work on Omnivory/stable isotopes (M.Graham); DOC biogeochemistry (C.Teichreb); Leptodora kindtii diel vertical migration (T. Cobb); paleolimnology (P. Leavitt, R. Hall); zooplankton (J. Sweetman); UV radiation (R. Vinebrooke, J. Hobdevo); Macrophytes (M. Zurowski); and Hg contamination (P. Leavitt, K. Kidd, FW Institute); Zooplankton Population Dynamics (Curtis Brock)
Temporal changes in the gut pigment and ratios of nitrogen isotopes (15N/14N) of zooplankton were measured in five lakes to determine if zooplankton occupied discrete or variable trophic positions along a gradient of lake production. Mean del15N (±SD) of a presumed herbivore Daphnia galeata mendotae (10.1± 2.7o/oo) and predator Diacyclops thomasi (11.2 ± 2.8o/oo) were not significantly different (t-test, P > 0.05, n = 13) regardless of lake trophic status, measured as N, phosphorus (P) , or chlorophyll (Chl). This suggested that these species occupied the same tropic position relative to particulate organic matter (POM; del 15N=3.8 ± 2.8o/oo). Also, analyses suggested that Daphnia and Diacyclops occupied a trophic position intermediate to that of an absolute herbivore or carnivore suggesting that both species were omnivorous. However, temporal changes in invertebrate del15N in the two most productive lakes (Katepwa, Crooked) indicated that Daphnia and Diacyclops became progressively more herbivorous over the summer, with Diacyclops showing a greater decline in trophic position relative to POM.
High performance liquid chromatography (HPLC) was used to quantify carotenoid and chlorophyll content in zooplankton, determine the ratio of algal:animal pigments in their diets and infer omnivory. Algal:animal carotenoid ratios were similar across lakes, but differed between species. Diacyclops had a higher relative abundance of animal-specific astaxanthin than did Daphnia, suggesting a more carnivorous habit. Analysis of gut pigments also showed that Diacyclops actively selected (Ivlev's electivity index, Ei>0.75) filamentous cyanobacteria (as myxoxanthophyll) in eutrophic lakes, which were represented mainly by N2-fixing Anabaena spiroides and Aphanizomenon flos-aquae. In contrast, Daphnia was a generalist herbivore, consuming algae in direct proportion to phytoplankton composition (Ei= -0.5 to 0.5).
Selective feeding by copepods on N2-fixing cyanobacteria likely lowered their tissue del15N because cyanobacteria in the Qu'Appelle Valley lakes were isotopically light (-1.6o/oo) relative to eukaryotic algae (6.9o/oo). Diacyclops may have actively selected N2-fixing cyanobacteria to avert a N-dificiency. Elemental ratios of C:N in Diacyclops from eutrophic Crooked Lake were much higher prior to feeding on cyanobacteria (approx. 13:1, by moles) than afterwards (5:1-7:1), indicating that copepods may have been N-limited. In general, Qu'Appelle lakes exhibited low ratios of dissolved N:P (2:1- 5:1, by mass), consistent with overall N-limitation of algal growth. In most lakes, bottle assays revealed that algal growth was colimited by N and P and was not solely P-limited. Overall, these patterns suggest that omnivory and selective feeding were common in pelagic zooplankton and that species did not occupy discrete trophic positions perhaps in an effort to maintain elemental ratios in tissues.
| The cladoceran Leptodora kindtii is a successful and voracious predator in large freshwater lakes. However Leptodora's lack of pigmentation make it potentially susceptible to damaging ultraviolet radiation (UVR), and it exhibits behavioural adaptations to avoid exposure. The combination of these two factors creates a situation where zooplankton at lower trophic levels may be controlled by the direct effects of UVR, predation by Leptodora or by complex interactions of UVR and Leptodora. This hypothesis was tested in a temperate eutrophic lake using in-situ mesocosms arranged in a factorial design with two levels of UVR (+UV, -UV) and Leptodora density (ambient, 5x). |  |
Leptodora predation directly reduced rotifer density by suppressing both Keratella quadrata and K. cochlearis. Rotifers also experienced a combined effect of UVR and Leptodora density, where UVR reduced the impact of Leptodora predation. Populations of cladocerans also declined slightly as a result of Leptodora predation. Direct effects of UVR on Leptodora could not be determined as populations declined rapidly following introduction to the mesocosms. UVR had no direct effect on the density of other zooplankton species. This study supports previous findings that Leptodora are important consumers in aquatic food webs, and that UV irradiance poses little direct risk to large zooplankton in eutrophic systems with high DOC. Instead this study identified the potential for complex trophic interactions in which UVR exposure reduced predation by Leptodora on small-bodied, soft zooplankton prey.
Quantifying the degree and patterns of zooplankton synchrony among lakes connected in a watershed can contrast the relative roles of climatic and landscape processes in controlling invertebrate population abundance. Here I investigated the temporal coherence (degree of synchrony among populations in a region) of interannual abundances for common freshwater zooplankton in five lakes situated in the Qu'Appelle Valley, Saskatchewan, Canada, from 1994 to 1999. The average correlation coefficient of time series data was used to estimate temporal coherence of individual species of copepods (Diacyclops thomasi, Leptodiaptomus siciloides), cladocerans (Bosmina longirostris, Daphnia retrocurva, Daphnia pulex, Daphnia galeata mendota, Leptodora kinditi) and algae (total chlorophyll). Spatial patterns were also examined by regressing inter-lake synchrony against a measure of lake separation between five Qu'Appelle lakes. Although the Qu'Appelle lakes are connected in the landscape, I hypothesised that zooplankton should exhibit uniform spatial variations of inter-lake synchrony regardless of the distance between lakes; implicating climate as the most important regional control of zooplankton populations.
Average temporal coherence for common cladoceran and copepod zooplankton were relatively low and variable among taxa (range = -0.134 to 0.802). Only one species, Leptodiaptomus siciloides, showed a statistically significant (P lt 0.05) average temporal coherence (r = 0.802) in this analysis. Spatial patterns of inter-lake synchrony varied among species. In general, inter-lake synchrony of large-bodied Daphnia increased with the degree of lake separation, whereas, that of copepods declined or remained constant, although patterns were not always statistically significant. Leptodiaptomus siciloides, was the only species that exhibited a uniform and synchronous pattern of spatial coherence, indicating that some proportion of interannual fluctuations in abundance was due to regional regulators such as climate. Analysis of the lake-pair synchrony and the average lake-pair synchrony for all taxa revealed that differences in lake morphology appeared to contribute to differences in the average synchrony measures among lake-pairs. Overall, synchrony of zooplankton populations appeared to be regulated mainly by site-specific processes, leading to high coherence when lakes exhibited similar physical, chemical, and biological properties.