Impact of finfish aquaculture on biogeochemical processes in coastal ecosystems and elemental sulfur as a relevant proxy for assessing farming condition

We conducted experiments to investigate the effects of finfish aquaculture and to propose appropriate proxies for assessing their environmental impact. Due to enhanced fish feed input, sulfate reduction (SR) and the resulting metabolic products (H2S, NH4+, PO43-) were significantly greater at the farm than at the control site. Benthic release of dissolved inorganic nitrogen (DIN) and phosphorus (DIP) from farm sediment accounted for 52-837% and 926-1048%, respectively, of the potential DIN and DIP demand for phytoplankton production. The results suggest that excess organic loading in fish farms induces deleterious eutrophication and algal blooms in coastal ecosystems via benthic-pelagic coupling. Direct SR measurement provided the most useful information of all the parameters on organic contamination in fish farms. However, given its abundance, relatively lower chemical reactivity and relative ease of analysis, elemental sulfur was regarded as the most appropriate proxy for assessing the environmental impacts of finfish aquaculture.