EXPLORING THE EFFECTS OF ACID ON AQUATIC MICROORGANISM COMMUNITIES ACROSS TIME AND SPACE: CHANGING COMMUNITY STRUCTURE REFLECTS INCREASING STRESS

Acidification of lakes and oceans is a major problem in conservation efforts. This study examines the response of lacustrine microorganism communities (diatom, rotifer, cladoceran, copepod) to acidification in single basins over time and across acidification gradients in regions with many lakes (United States and Canada). The goal is to analyze modern and subfossil data from lakes that have been acidified using a technique that is appropriate for both modern and fossil data, facilitating future studies on the effects of stress on communities through time and providing a modern baseline for the effects of acid stress. Here, community structure is quantified as rank-abundance curve-shape by calculating kurtosis (peakedness) for each community’s rank-abundance curve. Previous studies have shown species richness and community evenness to be of limited use in cataloguing the effects of acidification, while measures of community structure have met with more success.

Forty-nine lakes provide records of acidification and recovery, through long term monitoring and sediment cores. One hundred and eighteen lakes represent a continuum of acidity levels comparable to the pH change in the forty-nine lakes with long term records. Acid stressed communities tend to be dominated by a few acid-tolerant species, with low abundances of other species that were abundant prior to acidification. Kurtosis values increase with higher acidity levels, reflecting the higher stress levels. As pH returns to pre-acidification levels, community structure recovers and becomes more stable. This meta-analysis of acid stressed communities reveals that community structure changes predictably in response to stress. These results underscore the utility of rank-abundance curves, which allow comparison of modern, subfossil, and fossil data, and provide opportunities for better understanding of how communities respond to and recover from acidification.