Budy, P. , C. Pennock, A. Giblin, C. Luecke, D. White, and G. Kling. 2021. Understanding the effects of climate change via disturbance on pristine arctic lakes; multi-trophic level response and recovery to a twelve-year, low-level fertilization experiment. To be submitted to Limnology and Oceanography, Special Issue on “Nonlinear dynamics, resilience, and regime shifts in aquatic communities and ecosystems.” 2021: 1-18. doi: 10.1002/lno.11893. USGS FSP IP-129828.
Effects of climate change-driven disturbance on lake ecosystems can be subtle; indirect effects include increased nutrient loading that could impact ecosystem function. We designed a low-level fertilization experiment to mimic persistent, climate change-driven disturbances (deeper thaw, greater weathering, or thermokarst failure) delivering nutrients to arctic lakes. We measured responses of pelagic trophic levels over 12 years in a fertilized deep lake with fish and a shallow fishless lake, compared to paired reference lakes, and monitored recovery for six years. Relative to pre-fertilization in the deep lake, we observed a maximum pelagic response in chl a (+201%), dissolved oxygen (DO, -43%), and zooplankton biomass (+88%) during the fertilization period (2001-2012). Other responses to fertilization, such as water transparency and fish relative abundance, were delayed, but both ultimately declined. Phyto- and zoo-plankton biomass and community composition shifted with fertilization. The effects of fertilization were less pronounced in the paired shallow lakes, because of a natural thermokarst failure likely impacting the reference lake. In the deep lake there was (a) moderate resistance to change in ecosystem functions at all trophic levels, (b) eventual responses were often non-linear, and (c) post-fertilization recovery (return) times were most rapid at the base of the food web (2-4 years) while higher trophic levels failed to recover after 6 years. The timing and magnitude of responses to fertilization in these arctic lakes were similar to responses in other lakes, suggesting indirect effects of climate change that modify nutrient inputs may affect many lakes in the future.