Lake Minnewaska is a historically acidic and fishless lake located in Minnewaska State Park, New York. A popular tourist attraction, Lake Minnewaska has recently experienced successive introductions of a zooplantivorous minnow (Notemigonus crysoleucas) and then the piscivorous fish species Largemouth Bass (Micropterus salmoides). The new presence of M. salmoides has reversed a trophic cascade caused by N. crysoleucas in the lake resulting in decreased algal biomass. The main objective of this study was to examine the effects of fish population on the lake ecosystem, especially dissolved oxygen. Two other lakes in the area, Lake Mohonk and Lake Awosting, were used as comparison to Lake Minnewaska. Like Minnewaska, there are fish species present in Lake Mohonk. However, Lake Awosting is a clear acidic, oligotrophic lake with no fish. Over multiple years, we made multiple sampling trips to all three lakes to collect a range of physical, biological, and chemical data. The fish population size of Lake Minnewaska was estimated using a mark and recapture method via electrofishing. We measured the dissolved oxygen concentration at the deepest point of each lake at 1 m intervals to examine the effect of the trophic cascade on dissolved oxygen profiles.
Results/Conclusions
We found that the dissolved oxygen concentration in Lake Minnewaska has decreased in the hypolimnion since the introduction of fish. This is similar to Lake Mohonk which is anoxic below the thermocline. With no life present, the dissolved oxygen concentration in Lake Awosting is higher at the bottom than at the surface with temperature regulating dissolved oxygen concentrations. In Lake Minnewaska, we found increased algal production and biomass in the epilimnion as a result of a trophic cascade with the introduction of the additional zooplanktivore trophic level. During warm months, the aerobic respiration of the increased algal biomass has decreased the dissolved oxygen concentration in the hypolimnion. The M. salmoides has facilitated a second trophic cascade – we now see less algal biomass in the epilimnion but still hypoxic and anoxic hypolimnion during the summer. The additional trophic level of a piscivore has alleviated some ecosystem wide changes but has ultimately shifted the food web structure. The research from this project is a result of strong collaboration with stakeholders, governmental agencies, and non-profits and will ultimately inform conservation and management efforts across landowners and stakeholders.