The ecosystem effects of fish introduction and the recovery from acid rain: A story of fish and macrophytes
Lake Minnewaska, located within Minnewaska State Park, southeastern New York, is a historically clear, acidic, and fishless lake. Recently, an increase in pH and the introduction of Notemigonus crysoleucas (Golden Shiner) and Micropterus salmoide (Large Mouth Bass) into the system, have affected the water clarity, and the species in the lake, particularly the macrophytes. We use Lake Minnewaska as a study system to test the combined effects of internal and external drivers on environmental change in a managed ecosystems. The presence of Sphagnum trinitense, a globally rare macrophyte and acid sensitive species, was negatively impacted by both the pH change and regime shift that occurred with the trophic level changes. We analyzed pH change in Lake Minnewaska over 30 years with more spatial and temporal resolution 2012-2014. We hypothesized that the macrophyte coverage would not dominate the littoral zone of the lake due to the regime shift following the loss of S. trinitense. The coverage of macrophyte in the lake was estimated by a transect method. With the addition of zooplanktivory, we predicted phytoplankton population booms were causing decreasing water clarity through increased algal biomass production. We have also been tracking Secchi depths as a metric for water clarity.
pH has continued to increase in Lake Minnewaska from acidic (4.5) to neutral (7) over the past 30 years. S. trinitense was not found during our macrophyte surveys but 3 other species of macrophytes were found in the shallow littoral zone at or below 3m deep. The Secchi depth dropped to less than 3 m following the introduction of N. crysoleucas but water clarity has increased (Secchi depth to 6m) following the extirpation of the N. crysoleucas in 2014. The pH change is a result of increased runoff of hiking trail shale, loss of S. trinitense, and improvements in acid rain to the Northeastern U.S. Lake Minnewaska will likely not return to its original ecosystem state before the introduction of N. crysoleucas despite some recovery of water clarity. 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 in three parks and preserves.