Biogeographic patterns of benthic microbial communities in metal(loid)-contaminated semi-enclosed bay.

Anthropogenic activities can adversely impact biogeochemical processes essential for maintaining ecosystem health in semi-enclosed bays. However, the influence of anthropogenic contaminants such as potentially toxic elements on microbial communities that regulate biogeochemical cycles in semi-enclosed bays is poorly understood. We determined the concentrations of four potentially toxic elements (Cu, Zn, Pb, and As) in sediments from a typical tropical semi-enclosed bay in Guangdong, China. Source apportionment using Pearson's correlation analysis revealed that aquaculture activities were probably the primary source of Cu, Zn, and Pb. Using high-throughput sediment DNA sequencing, we found that Proteobacteria was the dominant phylum in sediments. There was no evidence suggesting site-specific variation in microbial function even though sediments adjacent to aquaculture discharge points had higher microbial diversity. In contrast, pollutant-specific variations were observed; for example, Zn and Pd showed potential adverse effects on the environmental information processing function, while As showed a negative correlation with metabolic function. Based on different environmental characteristics, future research should consider the impact of multiple factors on the bacterial community in aquaculture systems.

Ecological risk of chlorinated organic pollutants in a semi-enclosed bay impacted by aquaculture.

Semi-enclosed bays are used for critical economic activities such as ports, aquaculture, and human settlement due to their topography and ocean connectivity. However, the role of these geomorphological characteristics on the accumulation of chlorinated organic pollutants in semi-enclosed bays is poorly understood. We investigated the spatiotemporal distribution and potential ecological risk of organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs) in sediments from Shantou Bay, a semi-enclosed bay. The ∑PCB concentration was 258-1297 ng g-1 and 59.6-651 ng g-1 in the dry season and wet season, respectively. Sediments collected downstream and upstream the aquaculture farms had significantly lower DDT concentrations than those collected close to the aquaculture discharge points. The ratio of DDT and its metabolites indicated that there was possible fresh input of DDTs into Shantou Bay. However, no significant spatial trend was observed in the PCB profiles. The concentrations of PCBs and OCPs in Shantou Bay were above the China Marine Sediment Quality Class I suggesting remediation was essential to ensure the aquatic systems could be safely used for fisheries, swimming, or as marine protected areas. Furthermore, the potential ecological risk of DDTs was high as it exceeded the effects thresholds at all sites. Seasonal variations in human activities, resuspension of historical contaminants due to physical oceanographic, climatic and hydrological factors, and contaminant trapping probably contributed to the changes in organic pollutant distribution in the semi-enclosed bay.