Comparison of Sedimentation, Aquatic Vegetation, Benthic Invertebrates, and Wild Brook and Brown Trout Twenty Years after Dredging in Wisconsin Spring Ponds

The purpose of this study was to evaluate two spring ponds, Krause Springs and Sunshine Springs, before, shortly after, and 20 years after dredging. The ponds, whose major water source was springs, were dredged in 1970 and 1971 to increase depth, remove dense vegetation, and uncover trout spawning beds. A third pond, Maxwell Springs, was never dredged and served as a reference. Pond morphometry, sedimentation rates, aquatic macrophyte coverage and density, benthic invertebrate density, and trout biomass and density were compared among time periods. The undredged pond decreased 3% in area, 32% in volume, and 30% in mean depth from 1971-1992. Krause Springs had external springs, organic soils, and no change in discharge after dredging. It decreased 19% in area, 15% in volume, and 0% in mean depth. Sunshine Springs had few external springs, loamy and sandy soils, and increased discharge after dredging. Area, volume, and mean depth did not change in the 20 years since it was dredged. The ponds before dredging had over 50% of the pond bottom covered by Chara vulgaris (L.) and Elodea canadensis (Michx.). Aquatic plants covered less than 20% of the pond bottom in both ponds 20 years after dredging. Aquatic plant density appeared to increase from 1200 g/m2 before dredging to 5000 g/m2 by 1992, a density similar to the undredged pond (4556 g/m2) but sampling methods may be responsible for the difference. Invertebrate densities and taxa eaten by trout seemed to be lower shortly after dredging, but by 1992 appeared to be similar to predredging levels. Brook trout densities appeared to increase or remain similar after dredging, however total biomass increased after dredging, indicating average weight increased for trout in these dredged ponds. Brook trout density and biomass appeared to decline in the undredged pond. Brown trout were abundant by 1991-1992 in Sunshine Springs whereas they were uncommon in the pond from 1968- 1975. The results from this study suggest that spring pond dredging projects will have long-term success in enhancing trout fisheries if ground water flow increases, surrounding topography allows for drainage through loamy or sandy soils, and trout spawning habitat in the pond can be sustained or improved.Wisconsin Cooperative Fishery Research Unit; the Wisconsin Department of Natural Resources; Central Wisconsin Chapter of Trout Unlimited; University of Wisconsin-Stevens Point College of Natural Resources, Biology Department, and Student Research Fund; and the American SportFishing Association Fund