Geology Seminar Series - Ms. Luisa Patino - Aquatic ecosystems’ responses to past human activities in the neotropics

Speaker 1: Jamie Schmidt, Master Student, Dept. of Geology, University of Regina

Title: Geological controls on mercury methylation and sulphur cycling in Prairie Pothole Region wetland complexes

Abstract: Fossil fuel combustion and industrial emissions have contributed to increased levels of atmospheric mercury (Hg) globally. Deposition of atmospheric Hg in aquatic ecosystems can lead to the generation of methylmercury (MeHg), a neurotoxin that may bioaccumulate in food webs. Methylmercury in wetland ecosystems is formed as a by-product of various anaerobic metabolic processes, including bacterial sulphate reduction (BSR). Yet, the formation of MeHg in the Prairie Pothole Region (PPR) wetland complexes remains poorly understood due to variability in hydrology and biogeochemistry.

Title: Aquatic ecosystems’ responses to past human activities in the neotropics

Abstract: Lake systems are essential for the environment and human populations. Nevertheless, human activities have strongly modified aquatic ecosystems, and many lakes have been affected by anthropogenic stressors, including eutrophication, acidification, increased sediment loading, among others. In the last years, the study of the environmental history of lakes has increased, as well as the need for assessing the changes due to anthropogenic activities on aquatic systems. However, the information about how freshwater ecosystems in the neotropics have respond to climate variations and anthropogenic activities, is still scarce. Sediments accumulated in lakes provide a useful archive that can be used to reconstruct past responses to changes in climate and anthropogenic activities. In this study, the diatom assemblages of two lakes located in areas with histories of human influence, are used as proxies to reconstruct the limnological conditions of these neotropical ecosystems to trace back the extent of the impacts of climate variability and anthropogenic activities. The outcomes of this study shows that the diatom assemblages of both lakes respond to variations in the physical and chemical parameters of the lake, such as turbidity, pH, and nutrient content. Natural factors, possible precipitation, appear to have had influence on the variations in the diatom assemblages of both lakes, especially on the older zones. Furthermore, in both lakes was possible to identify changes related to the European arrival that occurred around 1500 CE. The differences in the nature of the changes in both lakes could be suggesting an influence of the lake morphometry in the response of diatoms to environmental changes as, while in the deep lake, Tota, the dominant species are found throughout the entire record with the changes between assemblages corresponding mainly to variations in the diatoms abundance, in the shallow lake, La Encantada, the diatoms found in the assemblages of the older zone are nearly completely different to the assemblage of the most recent zone. It is hope that this study serves to support the management and conservation policies of aquatic ecosystems and give insights on the possible responses to climate change that are expected to occur in the future.