CLIMATE CHANGE IMPACTS ON ADIRONDACK LAKES: ASSESSING THE THRESHOLD AND SYNERGISTIC RESPONSES OF ENVIRONMENTAL STRESSORS

Adirondack (ADK) lakes are grappling with climate change, acid rain recovery, and the aftermath of past watershed disturbances. They serve as a case study for understanding how ecosystem functioning of human impacted, mid-latitude lakes are affected by interactions of multiple human-driven disturbances. The project provides a transformative understanding of 1) the role that collective stressors play in initiating regime shifts in trophic status and 2) how climate change will interact with a mixture of legacy human impacts. Additionally, light is shed on how legacy disturbances can hinder ecological restoration, while exploring the little-understood area of interactions among disturbances. We hypothesize that interactions among disturbances can lead to synergistic, not merely additive, impacts and regime shifts. Using sediment core records from three ADK lakes that experienced increasing human disturbances, we assessed past rates of primary productivity and shifts in trophic status. Trace metal concentrations were paired with historical records of forest disturbance and water chemistry as indicators of timing and magnitude of human impact. Ratios and stable isotopic compositions of carbon and nitrogen were used to assess the rate of productivity and organic matter source in each lake. Pre-European impact, these lakes displayed resilience to natural climate variability. However, the sequential impacts of land use change, acid rain, and current warming have led to synergistic interactions, resulting in regime shifts in the lakes' trophic states. Our evidence suggests these lakes have reached a tipping point, transitioning to an irreversible ecological state as long as the ecosystem is stressed by future warming.