Integrating water quality monitoring and diatom community trends to determine landscape-level change in protected lakes

Abstract

Lakes in protected or remote regions are not immune to anthropogenic impacts and face a variety of stressors ranging from atmospheric deposition of pollutants to global climate change. Monitoring programs in these lakes can be limited in scope due to sampling logistics, leaving an incomplete picture of how the systems may be impacted by environmental stressors. Here, we used diatoms as early indicators of change in relatively undisturbed lakes from five national park units in the US Great Lakes region. Surface sediment samples were collected repeatedly over more than a decade to analyze the diatom community turnover. This diatom community assemblage data were compared with the measured water quality data collected over the same period in order to identify the predominant drivers of ecological change. Even though the parks in this study span two biomes, and lake characteristics vary between and within parks, we found synchronicity in measured water quality trends and diatom responses. Changes in the thermal regime and water-column mixing appeared to drive much of the change across parks, although much of the diatom turnover also followed a sulfate or pH gradient. Nutrients did not appear to play a major role in diatom community change. This method of using diatoms in conjunction with water quality monitoring allows for an integrated response over a number of years and provides managers with a complementary tool to determine which environmental parameters are having the biggest effect on lake ecology.