| dc.description.abstract | The Whycocomagh Basin, located in the Bras d’Or Lakes, Nova Scotia, is a naturally deep and anoxic basin that presently houses a Steelhead Trout (Oncorhynchus mykiss) aquaculture farm operated as an economic resource by the We’koqma’q First Nation. However, the accumulation of free sulfide resulting from anaerobic processes poses challenges for the sustainable management of the fish farm pens. The accumulation of high concentrations of total dissolved free sulfide (TS2−= H2S + HS− + S2−) can be detrimental to the benthic community and have adverse effects on the surrounding biogeochemical environment. It also poses a risk to the farmed fish in the floating pens at the water surface. This study aimed to investigate the levels of sulfide accumulation at the sediment-water interface by conducting horizontal transects, both moving from shallow, nearshore waters toward the middle of the Basin and extending away from the fish farm parallel to the shoreline at similar depths to the fish pen array. Various parameters were measured, including dissolved oxygen (DO), porewater chemistry, microsensor profiling, and CHN analysis of sediment and water properties. Vertical profiles of ammonium (NH4+), dissolved iron (Fe2+), carbon-to-nitrogen (C:N) ratio, nitrate plus nitrite (NO3- + NO2-), pH, and TS2- were analyzed. The results revealed a decrease in DO with water depth at all sites, and anoxia was observed to begin at a depth of approximately 15 meters. Significant impacts were identified in the bottom sediment, with increased TS2- and NH4+ production localized beneath the fish pens, and within a radius of 50-100 meters. Although there was a high level of organic enrichment beneath the fish farm, the water quality remained similar to that of sample sites located away from the farm. The localized effect at the sediment-water interface was evident, as concentrations returned to background levels within 100 meters from the fish farm. A reactive- transport model specific to the Whycocomagh Basin was developed to assess sediment recovery under various stocking scenarios. Observations revealed that the concentrations of TS2- became elevated in the water column near the oxycline when the number of fish pens was increased and when they were located in waters less than ~23 meters deep. In contrast, when the same increased number of fish pens were placed in deeper waters (~48 meters), elevated concentrations were observed near the sediment-water interface. This finding suggests that relocating the farm to the deeper portions of the Basin could be beneficial in avoiding the shoaling of the oxycline. Considering the increasing prevalence of anoxia in aquatic ecosystems, implementing site-specific management strategies to monitor remineralization dynamics would contribute to sustainable practices for future fish farm facilities. To enhance the applications of this study, additional research should focus on the long-term effects of sulfide accumulation, seasonal variations, and the role of microbial communities in mitigating sulfide levels. These insights can inform the development of effective approaches to aquaculture in proximity to anoxic environments. | en_US |
