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A new measuring system for the restoration of river systems in post-mining environments has been developed by a United States-based research team.

The long-term research project studied results from four mining-impacted watersheds over a span of 20-29 years, in California, Colorado, Idaho and Montana.

The sites were chosen because they were identified as the most severely polluted in the western United States and had the most potential upside in the case of a positive outcome.

The average term for a river system to properly recover was found to be between 10 and 15 years, with an average of 10.25 years.

Benchmarks were set early on through the tracking of mayflies, stoneflies and caddisflies, as these groups of insects were suitable indicators of the amount of food available from the rivers.

Co-author of the paper Dave Herbst said the study was equally important for flora and fauna, as many plant species never fully disappeared and could slowly be rehabilitated over time.

This way, the regrowth and remediation of food webs could be tracked by the occurrence of the insect population.

The researchers used a value of 7.1 micrograms of cobalt per litre of water as a limit to define toxic levels to aquatic life.

Levels of arsenic were also used in the study.

A surprising find from the study was that all projects across the four watershed environments were remediated along similar timelines with similarly positive results, despite beginning with different levels and different types of toxins.

Herbst hoped the environmental protection agency (EPA) and relevant industries such as mining and minerals could take the findings as a sign that most examples of river pollution could be reversed.

The study was titled ‘Long-term monitoring reveals convergent patterns of recovery from mining contamination across 4 western US watersheds’ and was published in Freshwater Science.