Beyond the Holy Grail: Adding Browning to the Lake Management Paradigm
The holy grail of lake management can be found in the strong relationship between nutrient loading and chlorophyll concentrations. Increase nutrients enough, and you may get harmful algal blooms, cyanotoxins, and dead zones. These events plague western Lake Erie, coastal oceans, and many other inland waters. Yet a recent survey of 2,913 lakes in the USA shows that overall little has changed with either nutrients or chlorophyll in recent decades. In the meantime, lakes in many parts of the world are turning browner due to up to a doubling of terrestrially derived dissolved organic matter. Hot spots of this lake “browning” include northern Europe and northeastern North America. Lake browning is both a good news story involving recovery from anthropogenic acid deposition in response to the Clean Air Act Amendments of 1990, and a bad news story related to climate change and increases in precipitation and extreme storm events. What are the implications of browning for lake management? Reductions in water transparency can increase surface water temperatures, lead to stronger thermal stratification, and contribute to oxygen depletion. Anoxia can in turn stimulate regeneration of phosphorus from the sediments, and combined with warmer surface water temperatures, increase the potential for harmful algal blooms that further decrease water transparency. Both increases and decreases in dissolved organic matter also have important implications for fisheries management. Understanding the causes and consequences of change in water transparency is essential to effective management of water quality, fisheries, and disinfection of parasites and pathogens in lakes.
Craig Williamson is the Ohio Eminent Scholar of Ecosystem Ecology at Miami University in Ohio where he leads the Global Change Limnology Laboratory. His expertise is in the ecology of UV radiation and climate change, with a current focus on the effects of browning on lakes. His research is based at the Lacawac Sanctuary and Biological Field Station in the Poconos of Pennsylvania but extends worldwide. Research questions range from UV effects on the ecology of zooplankton, larval fish, and infectious diseases, to deploying advanced sensors to decipher the sentinel responses of lakes to climate change. He is the Chief Scientific Adviser of the Pocono Lake Ecological Observatory Network (PLEON), an outreach program on public education and monitoring of Pocono lakes. He is active in the Global Lake Ecological Observatory Network (GLEON) where he leads the Climate Sentinels Working Group, and serves on the United Nations Environment Programme Environmental Effects Assessment Panel (UNEP EEAP).
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