A US-based research team has developed a new measurement system for the renaturation of river systems in post-mining environments.
The long-term research project examined the results of four mining-affected watersheds over a period of 20 to 29 years in California, Colorado, Idaho and Montana.
The sites were chosen because they were identified as the most polluted in the western United States and, if positive, had the greatest potential.
The average time for a river system to recover properly has been found to be between 10 and 15 years, with an average of 10.25 years.
By tracking down mayflies, stone flies and caddis flies, benchmarks were set at an early stage, as these groups of insects were suitable indicators of the food supply in the rivers.
The paper’s co-author Dave Herbst said the study was important for flora and fauna alike, as many plant species never completely disappeared and could be slowly restored over time.
In this way, the regrowth and restoration of food webs could be tracked based on the occurrence of the insect population.
The researchers used 7.1 micrograms of cobalt per liter of water as a limit to define toxic levels for aquatic life.
Arsenic concentrations were also used in the study.
A surprising result of the study was that all projects in the four catchment areas were remediated along similar schedules with similar positive results, although starting with different concentrations and different types of toxins.
Herbst hoped the Environmental Protection Agency (EPA) and relevant industries like mining and minerals could take the results as a sign that most examples of river pollution could be reversed.
The study was titled “Long-term Monitoring Shows Convergent Recovery Patterns From Mining Pollution In Four Western US Watersheds” and was published in was Freshwater science.