Wastewater discharges alter microbial community composition in surface waters of the canadian prairies.

Microbial communities are an important component of freshwater biodiversity that is threatened by anthropogenic impacts. Wastewater discharges pose a particular concern by being major sources of anthropogenic contaminants and microorganisms that may influence the composition of natural microbial communities. Nevertheless, the effects of wastewater treatment plant (WWTP) effluents on microbial communities remain largely unexplored. In this study, the effects of wastewater discharges on microbial communities from five different WWTPs in Southern Saskatchewan were investigated using rRNA gene metabarcoding. In parallel, nutrient levels and the presence of environmentally relevant organic pollutants were analyzed. Higher nutrient loads and pollutant concentrations resulted in significant changes in microbial community composition. The greatest changes were observed in Wascana Creek (Regina), which was found to be heavily polluted by wastewater discharges. Several taxa occurred in greater relative abundance in the wastewater-influenced stream segments, indicating anthropogenic pollution and eutrophication, especially taxa belonging to Proteobacteria, Bacteroidota, and Chlorophyta. Strong decreases were measured within the taxa Ciliphora, Diatomea, Dinoflagellata, Nematozoa, Ochrophyta, Protalveolata, and Rotifera. Across all sample types, a significant decline in sulfur bacteria was measured, implying changes in functional biodiversity. In addition, downstream of the Regina WWTP, an increase in cyanotoxins was detected which was correlated with a significant change in cyanobacterial community composition. Overall, these data suggest a causal relationship between anthropogenic pollution and changes in microbial communities, possibly reflecting an impairment of ecosystem health.

Cold spots and cold moments: The potential for sediment freezing to depress denitrification in wetland sediments.

Within the north-temperate zone, winters can be long and are associated with conditions of low temperature and potential for sediment freezing. There are critical gaps in our knowledge of biogeochemical cycling during winter and inadequate knowledge of how warming winters and changing snowpack might affect biogeochemistry. Here, we assessed the impacts of sediment freeze-thaw cycling and nitrate amendment on denitrification rates in the littoral fringe of four urban wetlands. We demonstrate the potential for experimental sediment freezing to suppress denitrification, although freezing effects were not observed at all sites. Multiple freeze-thaw cycles were assessed, and, although subsequent cycles may affect denitrification, the first instance of our experimental freezing seems the most critical. Although this work demonstrates potential sensitivity of wetland denitrification rates to changing winter conditions, we note nitrate availability has a larger impact upon denitrification rates. This suggests nitrification rates and changing nitrate loads may be more important determinants of nitrate retention than sediment freeze-thaw history. Although there has been great interest in hot spots and moments for biogeochemical cycling, we suggest there is similar need to understand cold spots and moments, as evidenced here. This is particularly important where cold moments may correspond with critical periods of nitrate transport, such as snowmelt.

Mercury methylation in high and low-sulphate impacted wetland ponds within the prairie pothole region of North America.

Using enriched stable (201)Hg injections into intact sediment cores, we provide the first reported Hg methylation potential rate constants (km) in prairie wetland ponds (0.016-0.17 d(-1)). Our km values were similar to other freshwater wetlands and did not differ in ponds categorized with high compared to low surface water concentrations of sulphate. Sites with high sulphate had higher proportions of methylmercury (MeHg) in sediment (2.9 ± 1.6% vs. 1.0 ± 0.3%) and higher surface water MeHg concentrations (1.96 ± 1.90 ng L(-1)vs. 0.56 ± 0.55 ng L(-1)). Sediment-porewater partitioning coefficients were small, and likely due to high ionic activity. Our work suggests while km measurements are useful for understanding mercury cycling processes, they are less important than surface water MeHg concentrations for assessing MeHg risks to biota. Significant differences in MeHg concentrations between sites with high and low sulphate concentrations may also inform management decisions concerning wetland remediation and creation.