Abstract
Metal sedimentary profiles are archives of past metal leaching and acid rock drainage (ML/ARD). Research reported that DNA can be preserved in sediments for several decades. The objective of this study was to investigate if historical metal profiles could be associated with shifts in microbial, benthic invertebrates and fish DNA. To this end, we collected sediment cores and extruded these at 1-cm intervals in an exposed and unexposed lake downstream of silver and copper operations in the Cobalt area in Ontario. Each sediment layer was digested by aqua regia to obtain concentrations of arsenic, cobalt and silver. About 0.1-0.2g of each layer of dried sediment were submitted to the University of Ottawa for 210Pb radioisotopic analysis. Dating of sections was interpreted with the constant rate of supply model. We extracted environmental DNA using the DNeasy® PowerSoil® Pro Kit and quantified it using the Qubit 3 BR Assay. For eDNA sequencing, agarose gels were prepared using Thermo Fisher Scientific Owl Easy Cast, and the gels were analyzed using the UVP GelSolo by Analytik Jena. Sediment profiles reconstructed past exposure of arsenic, cobalt and silver exposures resulting from ML/ARD historical releases from mining activities since 1920. Using environmental DNA, we were able to demonstrate changes in microbial communities in response to exposure to ML/ARD during historical mining operations when compared to older sediment layers. For instance. loose DNA indicates the number of microbial orders in the upper layers of sediments are reduced compared to older and less contaminated layers of sediments. Similarly, tight DNA show significant differences in microbial diversity and whole communities as suggested by the number of microbial orders in the upper layers of sediments significantly reducing to 5 orders compared to deeper and less contaminated sediment layers, and compared to control lake sediment samples that contain up to 11 orders. Next step is to determine if these changes could also be observed for benthic invertebrates and fish communities. The implication of this research is that environmental DNA could be used as a proxy of freshwater ecosystem diversity, which could reduce cost of environmental effects monitoring programs and also avoid the lethal surveys required for fish and benthic communities.