Limnocorrals, experimental enclosures which physically isolate a known volume of water and allow for the testing of various experimental manipulations at a relatively low cost, deployed in the Berkeley Pit. Photo by Nicholas Tucci.

Limnocorrals, experimental enclosures which physically isolate a known volume of water and allow for the testing of various experimental manipulations at a relatively low cost, deployed in the Berkeley Pit.

What started off as small experiments in the laboratory studying Berkeley Pit water in small flasks, has transformed into a much larger, bench-scale field experiment using the Berkeley Pit lake as the laboratory and limnocorrals as giant test tubes suspended in the contaminated water.

For most of the past decade, Dr. Grant Mitman, a Montana Tech biology professor, has been studying the ability of algae to remove heavy metal contaminants from Berkeley Pit water. Through various metabolic, physiological, and biochemical processes, algae have the potential to reduce soluble metal ions in acid mine waters. Dr. Mitman, along with his graduate student, Nicholas Tucci, have applied this potential bioremediation solution in the Berkeley Pit.

Algae occur naturally in the Berkeley Pit, but they lack one essential nutrient for growth-nitrate-a common nutrient found in most fertilizers. If nitrate is added to pit water, the naturally occurring algae can potentially reach a concentration of millions of cells per milliliter, a virtual green soup of suspended organisms that have an ability to permanently remove dissolved metals from the pit. These organisms have been used to remediate other pit lakes around the world, and may one day lead to the natural restoration of the Berkeley Pit.

In the spring of 2004, Mitman and Tucci deployed nine acid- and metal-resistant cylindrical limnocorrals along the eastern edge of the Berkley Pit Lake. Limnocorrals are experimental enclosures which physically isolate a known volume of water, and allow for the testing of various experimental manipulations at a relatively low cost. In this case, 500 gallons of pit water were used to fill the limnocorrals, and varying concentrations of nitrate were added as the experimental variable. Each limnocorral, open at the top and closed at the bottom, measured three feet in width and 10 feet in depth.

Throughout the course of a year, water-quality criteria and algal populations in nutrified limnocorrals were continually monitored and compared with those in non-nutrified limnocorrals to determine if algal growth had an effect on Berkeley Pit water. After the first year of data collection, concentration of algae in the nutrified limnocorrals had increased from undetectable levels to two million cells per milliliter. Additionally, as a result of algal growth, both iron and arsenic concentrations in the pit water were significantly reduced in the nutrified limnocorrals. No significant changes in water-quality or algal growth were detected in the non-nutrified limnocorrals.

The researchers are planning longer term experiments testing the ability of algae to clean Berkeley Pit Water. Algae, like any other biological organisms, need time to achieve a substantial and healthy population. Long term experiments are necessary to fully determine the bioremediation potential in the Berkeley Pit.

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