Long-term directional trajectories among lake crustacean zooplankton communities and water chemistry

Abstract

Understanding community responses to disturbance is a long-standing challenge in ecology and will remain a critical issue as human activity continues to alter environmental conditions. This is particularly concerning for freshwater communities, which are often subject to the effects of multiple disturbances on the landscape. With crustacean zooplankton community composition data and associated water chemistry from 19 Ontario lakes, we quantify the relative magnitude and directionality of change over three decades using distances in multivariate ordinations. The data span a gradient of impact from minimally disturbed reference lakes to lakes with known impacts from experimental acidification trials, atmospheric acidification, and regional land-use changes. Most communities exhibited changes from historical conditions, including previously described reference systems. Zooplankton communities in experimentally acidified lakes showed gradual, directional patterns with a return to historical conditions postmanipulation, but have since deviated again from historical conditions. Most zooplankton communities in atmospherically acidified lakes showed gradual, directional trajectories over time. Overall, our results demonstrate that zooplankton communities are changing among both minimally disturbed lake systems and lakes known to be impacted by human activities.