Changes to water quality and sediment phosphorus forms in a shallow, eutrophic lake after removal of common carp (Cyprinus carpio)

摘要

ABSTRACT Pickerel Lake (Minnesota, USA) is a shallow, polymictic lake that has had eutrophication problems for decades. Although excess nutrient loading has been a problem in the past, the dominance of common carp (Cyprinus carpio) was considered to be a substantial factor driving and sustaining eutrophic conditions. To remove carp and restore the fish community, the lake was treated with rotenone in late 2009 and then restocked with native species. All water quality variables improved after carp removal, with mean values (May–Sep) for chlorophyll a, total phosphorus, and turbidity decreasing by 80% to 93% and Secchi disk transparency increasing nearly 600% when comparing means of pre- to post-treatment years. Macrophyte coverage also improved, from means of 4.6% before treatment to 90% after treatment, indicating a shift from an algal- to a macrophyte-dominated system. Sediment phosphorus (P) storage increased significantly after carp removal as well, with labile (releasable) forms of P increasing in the upper 10 cm of sediment in all cores (n = 7). The decrease in water column P equaled the increase in labile sediment P forms after treatment, indicating carp were a key driver of P transport from sediment to water. The results of this study indicate that an ecological (i.e., both abiotic and biotic) approach is needed when managing eutrophic lakes because management of nutrients alone will not likely be adequate to restore water quality in systems dominated by carp or other large benthic feeding fish.