Effects of mining effluents on species composition and stress gene activation in aquatic macroinvertebrates in Finland

Contamination of the ecosystem resulting from anthropogenic activities is a major ecological concern. Mining activities cause great environmental modifications of the landscape outline, chemistry and biology. The abandoned or inactive mines are of particular concern and require continuous control and monitoring. In Finland, the effluent discharges into the aquatic environment of the mines are often heavy metals (Cr, Cu, Pb, Mo, Ni, Zn, V, U, Fe or Al), salts (e.g. sulphates, chlorides) or organic compounds, and the run-off waters are often acidic. The highest environmental risks are presumably linked to the metallic sulfides, causing acidification of the surrounding environment. An ecotoxicological characterization of the aquatic environment is among important tasks to better understand the toxic effects and consequences of the chemicals on aquatic biota.

The non-biting midges (Chironomidae, Diptera) are one of the most dominant groups among the aquatic macroinvertebrates and they are commonly used in biomonitoring or -assessments of aquatic ecosystems. The reason for using these species lies in their ubiquity, species richness, high ecological diversity and very high number of individuals in all kind of lotic systems. Especially the larvae can survive extreme temperatures, pH values, oxygen concentrations or pollution. Furthermore, temporal and spatial variability in the composition of the chironomid community has been observed together with a high adaptability of the community for changing environmental conditions. Several studies have shown that a chironomid community is a very suitable and accurate model in biomonitoring programs. On the other hand, many groups have also excluded them from the analyses, since the species determination above the family level is highly demanding, leaving a lot of room for errors. The reasons for the earlier exclusion of the chironomids from the biomonitoring programs have mainly been based on the low cost affectivity due to the highly demanding determination on the species level with the traditional methods.

Another aquatic macroinvertebrate group commonly used as a target species in the biomonitoring of aquatic environment is the crayfish. In North America, crayfish densities have been shown to decrease in the contaminated areas due to the mining derived metals. The crayfish-based biomonitoring has been mainly concentrating to study the bioaccumulation of heavy metals, but also the stress related gene activation due to toxic exposure have been recently studied with transcriptomics approach. In Finland, the highly sensitive native noble crayfish (Astacus astacus) stocks, considered as an indicator of superior water quality, have been mostly disappeared from the sphere of mining influence. The main reasons for the population declines are considered to be the aquatic effluents on the area, but also the disease crayfish plague, caused by the oomycete Aphanomyces astaci, has been playing a role in the crayfish declines on those areas.

During the recent years, next generation sequencing (NGS) techniques have become a new powerful tool for environmental monitoring. The taxonomic expertise previously needed for the species identification of aquatic macroinvertebrates, has often been lacking in organizations performing the environmental monitoring programs. The DNA based assays to monitor the species abundance and biodiversity in aquatic ecosystems has been shown to be a rapid and efficient tool in biomonitoring. In the metabarcoding technique, a standard gene fragment is amplified in a polymerase chain reaction (PCR) and the samples are barcoded before a high-throughput sequencing run. The species present in the identified based on databank searches.

The transcriptional effects of environmental stress have been widely studied in Drosophila melanogaster and a high number of genes and regulatory mechanisms involved in maintaining heavy metal homeostasis, metal export and import have been recognized. Interestingly, the transcriptomics studies conducted on red-swamp crayfish (Procambarus clarkii) have shown, that the heavy metal stress induced pathways are enriched in the crayfish hepatopancreatic tissue. Furthermore, it has been shown that the transcriptomic effects-based monitoring reflects chemical pollution gradients, thus holding promise for assessment of relative contributions of point sources to pollution and the efficacy of pollution remediation. The crayfish, being one of the most sensitive aquatic macroinvertebrate in Finnish lakes, could act as an excellent target species in transcriptomics-based biomonitoring of the aquatic environment.

This study will focus to understand the effects of mining effluents on aquatic macroinvertebrates in Finnish lakes. The detailed aims are:

1. To apply the metabarcoding technique of chironomids to biomonitoring of the aquatic environments sustaining the effects of mining effluents.

2. To explore the composition of the chironomid communities in the affected and unaffected aquatic environments.

3. To find out the genetic background of stress reactions caused by mine-derived toxins in native crayfish species of Finland and to determine the genetic responses and tolerance limits.

4. To apply the transcriptomics-based environmental monitoring into crayfish.

This study focuses on the characterization of the aquatic environment under the influence of the mining industry. The two macroinvertebrate species selected as target organisms are representing the opposite heads in respect to the tolerance to the mining-derived pollution. The chironomids, being highly tolerant against the toxic effects of mining effluents, can even be found from the close locations of the mines and mining derived pollutants. The crayfish, on the other hand, as a highly sensitive species can reflect the effects of the mining-derived substances on transcriptional level even from far distances of the actual mining industry.

This study will be conducted by Dr. Jenny Makkonen, University of Eastern Finland, Kuopio, Finland.