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M.Sc. / Mpumalanga, “the place where the sun rises”, sets the scene for one of the rarest wetland types in South Africa. They are formed on one of the last remnants of the ancient African land surface, contain peat and together with a variety of other pan types make up the Mpumalanga Lakes District. Of these approximately 320 pans, only ±2.3% are reed pans. These endorheic wetlands are unique from other pan types and peatlands in South Africa and support an abundant biodiversity. They perform vital functions such as water storage, filtering out impurities and carbon fixation, which prevents an excess release of CO2 into the atmosphere. There is very little known about these endorheic wetlands and thus they are constantly being threatened by various activities such as agriculture, livestock and mining. The objectives of this study were to determine the spatial and temporal variation of macroinvertebrate community structures of reed pans and the environmental factors, such as water quality, responsible for the maintenance of these structures; to determine the best method for sampling aquatic invertebrates in reed pans; as well as to determine the relationship between aquatic invertebrates and the water, sediment and habitat quality of a reed pan. Together with this the amphibian diversity as well as the occurrence of other biotic components was determined. Four reed pans were assessed during four different seasons over a one year period to account for the different hydrological extremes. Sub-surface water samples were analyzed for their suspended solid content, nutrient levels, metals and chlorophyll-a concentrations as well as in situ water quality parameters. Sediment samples were analyzed for metal concentrations, organic carbon and water content, as well as sediment size distribution. Invertebrates were collected using the following sampling techniques: aquatic light trap, terrestrial light trap, emergent trap, sweep net, plankton net, as well as benthic sampling using an Eckman grab.

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Twenty-eight species of zooplankton were identified from Lake Texoma. Seasonal density of the overall microcrustacean community and seasonal cycles of individual species were compared with northern populations and any available literature from the Southwest. Cycles of occurrence and abundance were similar to those observed in northern populations but tended to occur earlier in the year due to higher temperatures. Spatial distributions within the reservoir were heavily influenced by nutrient and salt input from the Red River, which resulted in dense populations in the Red River Arm. In addition, during the summer, the microcrustacean community was restricted to the epilimnion due to anoxic conditions in the hypolimnion of the reservoir.

Community assembly following disturbance is a key process in determining the composition and function of the future community. However, replicated studies of community assembly at whole ecosystem scales are rare. Here is described a series of whole-lake experiments in which the recovery of zooplankton communities is tracked following an ecosystem-scale disturbance. Fourteen lakes in eastern Washington were chosen: seven lakes were treated with rotenone, while the remaining seven were reference. Each lake was monitored up to six months before and one to two years after the rotenone treatments. Zooplankton tows were taken monthly, at a shallow, intermediate, and deep site in each lake, and were later enumerated and identified. A depth profile of environmental variables was taken at the deepest site. Community responses following disturbance were assessed using coarse metrics of abundance and diversity, community composition measures, and the relative importance of species traits was assessed by grouping taxa into functional groups. Communities were considered recovered if there was no significant difference between treatment and reference in zooplankton community metrics of abundance, diversity, and composition. There was a steep decline in the abundance and diversity of the zooplankton community post-treatment. In many of the lakes, cyclopoid copepods, the group with a unique dormancy strategy, were the first group to recover, remained dominant for a few months, and may have exhibited priority effects advantages. Calanoid copepods were the slowest group to recover, perhaps due to their slow rate of development. There were varying recovery times and patterns between lakes, potentially based upon geographic location and severity of the winter season. These findings suggest that dormancy strategies, rate of development, and abiotic conditions following disturbance may be important in helping to understand recovery processes. Results of this study may give insight to disturbance ecology and the relative importance abiotic versus biotic characteristics that structure post-impacted communities.

Phytoplankton communities in fifteen lakes in the Mt. St. Helens area were surveyed to assess the abundance and species present. Eleven of the lakes were inside the blast zone of the 1980 eruption and four were located outside the blast zone as a comparison. The hypothesis is that lakes will cluster together based on the algal species present and that some algae will be correlated with certain environmental conditions. A cluster analysis was performed to determine if the lakes would group together based on algal abundance. There did not appear to be any distinct clustering among the study lakes, but this analysis did help to sort out some similarities of algal species present between lakes. It demonstrated that the lakes outside the blast zone were not functional as control lakes because they were very different from the blast-zone lakes. They had different assemblages of algae and their origin was so different from the blast-zone lakes that there was little overlap between them. The factor analysis was applied to determine the relationships between environmental variables and phytoplankton. The hypothesis is that certain algae are associated with each other and with identifiable environmental factors. Factor analysis should detect these patterns. The factors represent some condition in the environment but the analysis would be virtually meaningless unless these conditions can be recognized and the factors named. From the factor analysis alone, I could not name the factors but returned to the task after the canonical correlation analysis was performed. The canonical correlation analysis gave some clues to identify the environmental conditions that exert control on these algae. The most useful statistical technique used in this study was the canonical correlation analysis. This analysis is a useful tool in community ecology studies where species-environment relationships can be inferred from community composition and environmental data. The environmental data used was nutrient and light attenuation present at the time the phytoplankton samples were taken. From this analysis I summarized a list of algae and with what environmental conditions that they are associated. Trophic state categories were assigned to the lakes from a trophic state index based on phytoplankton biovolume.

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Given the prominent role of nitrogen in the eutrophication of aquatic systems, recent increases in nitrogen loading to freshwaters are of concern. A comparison of nitrogen retention in freshwaters in North America and Europe shows that wetlands retain the greatest proportion of their nitrogen load, followed by lakes and then rivers. A comparison of the relative importance of nitrogen retention mechanisms found denitrification to be responsible for the greatest proportion followed by nitrogen sedimentation and then uptake by aquatic plants. A more in-depth examination of denitrification in the littoral sediments of Lake Memphremagog in Quebec, using the N2 flux technique, found an average denitrification rate of 111 mumol N m-2 h-1. Denitrification rates were positively related to the % organic matter of the sediment, temperature and macrophyte biomass density and negatively related to depth. These results, in combination with a review of the literature indicate that denitrification rates are higher in littoral than profundal sediments.