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Inflows affect water quality, food web dynamics, and even the incidence of harmful algal blooms. It may be that inflows can be manipulated to create refuge habitat for biota trying to escape poor environmental conditions, such as fish populations in lakes during times of toxic Prymnesium parvum blooms. Water availability sometimes can be an issue, especially in arid climates, which limits this approach to management. Utilizing source water from deeper depths to displace surface waters, however, might effectively mimic inflow events. I test this notion by conducting in-lake mesocosm experiments with natural plankton communities where I manipulate hydraulic flushing. Results show that P. parvum cell density is reduced by 69%, and ambient toxicity completely ameliorates during pre-bloom conditions in the lake. During conditions of bloom development, population density is reduced by 53%, toxicity by 57%, and bloom proportions are never reached. There is minimal effect of these inflows on total phytoplankton and zooplankton biomass, and little effect on water quality. Shifts toward more rapidly growing phytoplankton taxa are observed, as are enhanced copepod nauplii. In other words, while inflows using deep waters suppress P. parvum bloom initiation and development, they are benign to other aspects of the lower food web and environment. The results from using deep lake water to suppress harmful algal blooms indicate this may be a promising management approach and further studies are recommended to test whether this mitigating effect can translate to a large-scale in-lake treatment.

Freshwater ecosystems face unprecedented levels of human-induced stresses and it is expected that the invasion of non-indigenous species will cause the greatest loss of biodiversity in lakes and rivers worldwide. Bythotrephes longimanus is a predatory invertebrate that invaded North America in the early 1980s, first being detected in the Great Lakes, and then moving to a number of inland lakes in Ontario and the northern United States. Using experimental and survey-based approaches, I tested several hypotheses concerning the effects of Bythotrephes on native zooplankton community structure and function. My results indicate that Bythotrephes reduces total abundance, biomass, and richness of zooplankton, especially cladoceran taxa, throughout the ice-free season. As a result of high predation pressure by the invader, total seasonal and epilimnetic zooplankton production was also substantially reduced in invaded lakes, which may have important consequences for the transfer of energy to fish and other taxa that feed on zooplankton. Interestingly, there was some evidence that zooplankton shifted their reproduction in time and space to avoid Bythotrephes, which may buffer the effects of the invader on food web functioning. Other measures of ecosystem function were relatively unaffected by the invasion of Bythotrephes. In addition, Bythotrephes may interact in unexpected ways with other anthropogenic stressors, and act to slow down the process of recovery by preying on species that maintain community abundance during acidification, but also affecting species attempting to recolonize historically acidified lakes. Although dispersal of zooplankton may maintain some of the ecosystem functions provided by zooplankton communities, loss of biodiversity may be a permanent result of invasion. The effects of the continued spread of invasive species across the landscape may be profound, as the invader Bythotrephes has demonstrably altered zooplankton communities and may reduce the ability of freshwater ecosystems to respond to future environmental change and maintain ecosystem functioning. / Thesis (Ph.D, Biology) -- Queen's University, 2007-07-19 14:56:57.102

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The period of ice break-off in spring is a key event for many biogeochemical processes in lakes globallly. The biogeochemical processes occurring at ice break-off have the potential of influencing characteristics of lakes throughout spring and summer, including algal blooms and greenhouse gas emission. This makes it important to study lakes in the period of ice break-off. At ice break-off, soil bacteria from the catchment area usually enter the lake via spring floods and mix with the bacteria already occurring in the lake water. In this study, the effects of mixing soil- and lake microbial communities during ice break-off-like conditions were tested by performing an experiment under controlled conditions in the laboratory. In the experiment, light, microbial community composition and concentration of soil-derived organic matter were manipulated to simulate different conditions associated with ice break-off. The variables investigated were bacterial activity and functionality, measured as cell abundance and enzymatic activity, as well as primary production and concentration of dissolved organic matter. The results showed that a mix of soil and lake microbial communities had enzymatic activity patterns resembling lake communities, and then shifted to being more similar to soil communities. The experiment also showed that degradation of measured dissolved organic matter was not linked to biotic processes, and that the observed decrease was most likely due to photo degradation. Finally, the experiment showed that primary production, here measured as chlorophyll a, was only stimulated by the mixed community with light and added soil dissolved organic matter. The results found in this study are important as they show that microbial communities do alter their function and enzymatic activity based on composition. Furthermore, the result that primary production was only seen in the presence of light, soilderived organic matter and a mixed community of lake and soil bacteria may be seen as an indication that primary producers in lake ecosystems to some extent depend on the inflow of terrestrial microbes and organic matter. It also possible that the coalescence of microbial communities enables the communities to perform tasks they were unable to prior to coalescence (i.e. perform tasks that allows primary production to take place). These results give the basis for further, more detailed studies.

The Fairy shrimp Branchinecta gaini Daday, 1910 is the largest freshwater invertebrate in Antarctica and the top-level consumer of local freshwater food webs. Ecological demands of B. gaini that are accompanied by 'ruderal' life strategy together with its spatial distribution that exceeds to Patagonia indicate that it had survived last glacial period in South America and expanded to Antarctica shortly after this epoch endeed. On James Ross Island that is the most extreme environment where B. gaini occurs today was this fairy shrimp considered extinct until year 2008. Its disappearance was based on paleolimnological analysis of several lake sediment cores according to which it inhabited this island between years 4200 to approximately 1500 before present when it died out because of changes in lake catchments caused by harsh neoglacial conditions. Paleolimnological analysis of Monolith Lake presented in this study has shown that this assumption was wrong and B. gaini has lived on James Ross Island throughout neoglacial period up to recent time. Phylogeographic analysis of 16S rDNA of specimens from Patagonia, South Orkneys, South Shetlands and James Ross Island revealed that its high morphological diversity is not supported by this gene and that all examined populations of B. gaini is one species with very few...

Depuis la découverte d’archées capables d’oxyder l’ammoniac en milieu aérobie, de nombreuses études ont mesuré en simultané les taux de nitrification et la diversité des organismes oxydant l’ammoniac dans la colonne d’eau des milieux marins. Malgré l’importance globale des lacs d’eau douce, beaucoup moins d’études ont fait la même chose dans ces milieux. Dans cette étude, nous avons évalué l’importance de la nitrification et caractérisé la communauté microbienne responsable de la première étape limitante de la nitrification dans un lac tempéré durant une année entière. L’utilisation de traceur isotopique 15NH4 nous a permis de mesurer des taux d’oxydation d’ammoniac à deux profondeurs dans la zone photique tout au long de l’année. Les taux d’oxydation d’ammoniac varient de non détectable à 333 nmol L-1 j-1 avec un pic d’activité sous la glace. De toutes les variables environnementales mesurées, la concentration d’ammonium dans la colonne d’eau semble avoir le plus grand contrôle sur les taux d’oxydation d’ammoniac. Nous avons détecté la présence d’archées (AOA) et de bactéries oxydante d’ammoniac (BOA) à l’aide de tests par réaction en chaîne de la polymérase (PCR) ciblant une partie du gène ammoniac monoxygénase (amoA). Les AOA et les BOA ont été détectées dans la zone photique du lac, cependant seules les AOA étaient omniprésentes durant l’année. Le séquençage du gène amoA des archées révèle que la majorité des AOA dans le lac sont membres du groupe phylogénétique Nitrosotalea (également appelé SAGMGC-1 ou groupe I.1a associé), ce qui confirme la pertinence écologique de ce groupe dans les eaux douces oligotrophes. Globalement, nos résultats indiquent l’hiver comme étant un moment propice pour l’oxydation de l’ammoniac dans les lacs tempérés. Cette étude fournit un point de référence pour la compréhension du processus d’oxydation de l’ammoniac dans les petits lacs oligotrophes. / Since the discovery that some archaea are able to oxidize ammonia aerobically, several studies have focused on measuring nitrification rates and identifying the diversity of planktonic ammonia oxidizers in marine systems. Despite the global importance of freshwater lakes, far fewer studies have done the same in these ecosystems. Here we investigated the importance of nitrification and characterize the microbial community catalyzing the first rate-limiting step of nitrification over an annual cycle in a temperate lake. The measurements of ammonia oxidation rates, using the 15NH4+ isotope tracer method, at two depths in the photic zone show that this process occurred throughout the entire year in the lake. Rates of ammonia oxidation ranged from undetectable to 333 nmol L-1 d-1 with a peak of activity during winter. Off all environmental variables measured, ammonium concentrations in the water-column seem to have the strongest effect on the magnitude of ammonia oxidation rates. We detected the presence of ammonia-oxidizing archaea (AOA) and bacteria (AOB) using polymerase chain reaction (PCR) assays targeting part of the ammonia monooxygenase (amoA) gene. Both AOA and AOB were detected in the photic zone of the lake, although only AOA were omnipresent over the year. The sequencing of archaeal amoA genes reveals that most of the AOA in the lake are members of the Nitrosotalea cluster (also referred as SAGMGC-1 or group I.1a associated), which confirms the ecological relevance of this cluster in oligotrophic freshwaters. Altogether, our results indicate that winter may be a critical time for ammonia oxidation in temperate lakes and provide a baseline for the understanding of ammonia oxidation in small oligotrophic lakes.

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