That lost biodiversity includes fish, macro-invertebrates such as insects, clams and crustaceans, algae, fungi, bacteria, unicellular organisms called protists, and other animal and plant species.
The scientists behind the study analyzed 93 streams along a gradient ranging from heavily mined watersheds to relatively pristine streams across the Appalachian range in West Virginia. They found a clear relationship between the density of mining activities and loss of biodiversity: the more mining there is, the fewer species are found.
According to Marie Simonin and Emily Bernhardt, who led the research, the results highlight another concerning pattern: significant diversity loss was detected in streams whose water was still far below the maximum disturbance standards set by the Environmental Protection Agency (EPA).
“A very small increase in mining activities in the watershed is already too much,” Simonin said in a media statement.
This means that the detrimental effects of pollutants in aquatic species start at much lower concentrations than previously thought.
The expert pointed out that this is the first time that the whole tree of life is analyzed at once in the same streams, at the same time, using environmental DNA (eDNA). This technique measures fragments of genetic materials that organisms leave behind in their environment.
This DNA could originate from excrement, lost bits of skin or scales, or from unicellular organisms. To collect it, the team gathered water samples from each stream and filtered them through extremely fine filters. The DNA stayed stuck on the filters and was later on extracted, sequenced, and sorted.
Simonin explained that groups of organisms, such as algae share common genes or segments of genes. By comparing the DNA obtained from the filters with DNA known to belong to a certain species or groups of species, the scientists were able to determine what is hanging out in each stream.
“eDNA is an inexpensive approach that can provide substantial insights into drivers of biodiversity,” Bernhardt said. “It can open the possibility for monitoring water quality impacts over a much larger number of rivers across the globe.”
The results obtained with eDNA are well in line with those obtained with more traditional methods, with a fraction of the work. As an example, the team detected 28 species of fish in all 93 sampled mined streams by using eDNA. That is comparable with previous studies that had painstakingly collected, counted and identified the fish diversity of the same region. eDNA, thus, provided a much quicker and less invasive method of diversity assessment, with similar results.