Restoration of a Mine Pit Lake from Aquacultural Nutrient Enrichment

Abstract

Minnesota, the land of 10,000 lakes, also has more than 4000 abandoned quarry pits and over 200 deep, exhausted iron ore pits. In the past 25 years the iron ore pits have gradually filled with groundwater and surface water, forming lakes on the Cuyuna, Mesabi, and Vermillion Iron Ranges in northeastern Minnesota. Most remain abandoned, but besides creating a small number of recreational parks and fisheries, the regional economic development agency promoted approximately 20 of the pit lakes for economic reclamation by using them for salmonid aquaculture. Intensive net‐pen aquaculture was carried out from 1988 to 1995 in the Twin City–South and Sherman pit lakes on the Mesabi Range. A water quality controversy resulted over the potential for long‐term degradation of the lakes and regional aquifer. The Minnesota Pollution Control Agency then mandated that aquaculture be terminated in Twin City–South in May 1993 and the lake restored to preaquaculture conditions by 1996. With no management other than artificial aeration for one summer, the lake rapidly recovered to near baseline water quality and returned to an oligomesotrophic (unproductive) status. Within 18 months the phosphorus budget was typical of reference pit lakes in the area and dissolved oxygen in bottom water remained above ∼4 mg O2/L without artificial aeration. Algal growth was low in 1993, due to light limitation from artificial mixing, but it remained low in 1994 without any management due to renewed phosphorus limitation. Inorganic nitrogen initially decreased faster than expected, at a rate similar to its increase during intensive aquaculture. More rapid reductions in water column nutrients might have occurred in 1993 by reducing aeration to allow anoxia in the lower hypolimnion, promoting denitrification and minimizing sediment resuspension, but this was precluded by water quality standards. The “natural” burial of solid wastes under inorganic sediment eroded from the basin walls effectively minimized transport of sediment nutrients to the overlying water. Fallowing for several years provided a simple, effective method for restoration of these pit lakes from aquacultural impacts. No change attributable to aquaculture was observed in the water quality of three nearby pit lakes, including a drinking water source. This fact suggests that there were few or no impacts from off‐site migration of aquaculturally enriched water into the regional aquifer.

Understanding Abiotic and Biotic Conditions in Post-Mining Pit Lakes for Efficient Management: A Case Study (Poland)

“…Post-mining lakes can be used for recreational purposes (Doupé and Lymbery 2005), can provide new habitats in areas where human activity has degraded wetlands (Brenner et al 1987;Doupé and Lymbery 2005;Klapper and Geller 2001), and can be used for fish farming (Axler et al 1996a, b). Such uses can affect lake water quality, Abstract This study was aimed at determining whether the origin, morphometry, and hydrology of post-mining lakes affect their hydrochemical and hydrobiological parameters (i.e.…”

Environmental Risks Associated with Beneficial End Uses of Mine Lakes in Southwestern Australia

“…Aquaculture -aquaculture species may be grown in cages or pens within the lake, or in ponds or tanks using water extracted from the lake (Axler et al 1996a, b;Viadero and Tierney 2003;Whisson and Evans 2003).…”

“…In addition, there may be increases in soil erosion and impacts on biodiversity of terrestrial ecosystems if greater water availability leads to an expansion of agricultural land. Aquaculture 11 Aquaculture has the potential to pollute water by nutrient enrichment (Axler et al 1996a, b;Viadero and Tierney 2003). Aquaculture also poses a potential threat to aquatic biodiversity if exotic species are farmed and can escape into natural waterways (Starcevich et al 2003).…”

“…In recent years, however, increasingly stringent reclamation rules and regulations have caused mining companies to undertake more judicious operational planning and more thorough mine void restoration (Axler et al 1996a;Cloke et al 1996;Johnson and Wright 2003;Norton 1992). The preferred restoration method for final mine voids is often backfilling and rehabilitation to pre-mining or adjacent 'reference' ecosystems (Bell 2001;Cloke et al 1996;Ludwig et al 2003;Schuman et al 1990).…”

“…The preferred restoration method for final mine voids is often backfilling and rehabilitation to pre-mining or adjacent 'reference' ecosystems (Bell 2001;Cloke et al 1996;Ludwig et al 2003;Schuman et al 1990). With very large voids, however, backfilling is not economically viable, and both mining companies and land management agencies have recently focused on potential beneficial end uses for mine lakes (Axler et al 1996a;Johnson and Wright 2003). Following Johnson and Wright (2003), we define beneficial end uses to be goods or services provided by the mine lake, or any element or segment of the mine lake, that provide economic, health, welfare, safety, or aesthetic benefits to the community.…”