Limnological Assessment of Mine Pit Lakes for Aquaculture Use

Abstract

This study addresses water quality issues associated with current and future uses of mine pit lakes for intensive aquaculture. In current net pen aquaculture operations (Minnesota Aquafarms, Inc.), metabolic wastes and uneaten food are dispersed into the lakewater. Intensive aquaculture at Twin City-South and Sherman increased levels of phosphorus (P) and nitrogen (N) and reduced dissolved oxygen (DO) in the water column, and increased the deposition of organic matter to the bottom relative to their previous conditions and to unused mine pit lakes. Numerous trophic status indices suggest that TC-S and Sherman have shifted (or are shifting) from an oligotrophic state to a more eutrophic one. However, due to MAPs intensive aeration, and circulation, conditions necessary for algal blooms (typical of eutrophication) have been infrequent, due to light limitation from vertical mixing. Blooms of scum-forming bluegreen algae have never been observed.