Professor S. Geoffrey Schladow, University of California Davis, Director, UC Davis Tahoe Environmental Research Center |

Title: Large Lakes in the 19th, 20th & 21st Centuries: Shifting Perceptions on Potential Threats and Management at Lake Tahoe, USA

Abstract: Lake Tahoe, USA, has only been identified on maps for 170 years, yet in this short period it has undergone tremendous changes in how it has been perceived and managed. In the first few decades it was considered an ethereal water body, capturing the imaginations of both artists and the founders of the new field of limnology. The subsequent thirty years saw the clear cutting of its watershed and a precipitous decline in water quality, a period that was followed by an equally rapid, natural recovery of the lake’s natural physical and ecological integrity. Since that time, however, the lake has seen a steady succession of environmental threats. These have included species extirpation due to overfishing, the introduction of new species in all trophic levels, the impacts of increased urbanization and associated eutrophication, and most recently the impacts of climate change. Each of these threats has been met with a range of responses that include diversion of sewage outside the watershed, stringent land development codes, mandatory boat inspections, and prescribed pollutant reduction targets. Many of these measures have been successful, in part because they were based on an understanding of the physical and ecological cycles at play within the lake. However, with climate change, these physical and ecological processes are showing signs of greater change than has previously been experienced, and shifts toward regimes that have never been experienced. These changes will be described using a combination of field measurements and numerical modeling results, and the range of potential management responses will be discussed.