Global warming’s impact on Tahoe
It is possible that despite all the efforts of conservationists to protect the clarity of Lake Tahoe, global warming may have the greatest impact on the transparency of the basin’s famed waters.
A scientific report released this spring called “The Warming of Lake Tahoe,” alludes to a grim picture of the lake’s future if perceived warming trends of its waters continue.
The report states the “biogeochemical worst case scenario” for Lake Tahoe would be an unprecedented algae bloom. This phenomenon would be a result of a three part series of events: 1) the warming trend of Tahoe’s waters would increase its stability and decrease the frequency to which lake water mixes from top to bottom, 2) this in turn would result in an anaerobic (without oxygen) layer of nutrients on the bottom of the lake, since the oxygen rich waters of the surface would never mix with the less oxygenated water at the bottom of the lake and 3) when a deep mixing event finally does occur this anaerobic and phosphorus rich layer would be dispersed toward the surface stimulating the algae bloom.
No time frame
UC Davis research ecologist Bob Coats helped to research and write the report and emphasized that such a phenomenon is merely long-term speculation based on current data trends. There is no guarantee, Coats said, that such a scenario would ever occur nor is their concurrence as to the time frame required for such a phenomenon to take place.
What is certain is that their is a warming trend of Tahoe’s water’s similar to warming trends in lakes around the world. The warming trend corresponds with a recent estimate of atmospheric warming around the world. That rate is currently 0.017 degrees Celsius each year.
For Tahoe, an oligotrophic lake – meaning a lake that mixes completely every few years – this warming trend has the potential to alter the oligotrophic structure.
“If the lake is at a lower temperature the mixing is easier other things being equal,” Coats explained. “A warmer lake is a more stable lake – as the lake warms it becomes more resistant to mixing.”
Regardless of whether this increased stability leads to the “worst case scenario,” the report points out increased stability of the lakes water column will impact other ecological events. Reduced mixing of water may prolong periods of reduced clarity as sediments do not have a chance to be dispersed through the volume of the lake. This may be especially noticeable after years of heavy runoff when the most sediments and nutrients enter the water.
The increased stability may also affect the population of phytoplankton. Phytoplankton are microscopic plants that live in the ocean and in lakes. UC Davis researcher, Monika Winder has been studying phytoplankton populations in Tahoe. She said phytoplankton are important to study because they are at the bottom of the food chain and therefore changes in their population structure can indicate future changes throughout the ecosystem.
Various species of phytoplankton will be impacted in different ways by increased water stability, some populations increasing and others decreasing – though there is too little information to postulate how these changes will impact other facets of the lake’s ecosystem, Winder said.
Increased stability favors blue green algae, an algae that is usually a “very bad indicator for a lake” because of its toxicity and low nutrient quality, Winder noted. Right now there are very few blue green algae in Tahoe, but that a combination of increased nutrients and increased stability could create more favorable conditions for their populations.
Neither researcher Winder or Coats believe Lake Tahoe is doomed.
Coats pointed out that in so much as there is a correlation between lake warming and global warming there is the possibility that lake warming trends could level off if global warming trends level off.
Slowing those warming trends is a matter, say scientists and conservationist across the world, of reducing global warming pollutants – especially carbon dioxide – into the atmosphere. A report released Wednesday by the U.S. Public Interest Research Group points to Nevada as a state that could work more on reducing the amount of carbon dioxide it releases into the air each year. The report states that Nevada’s global warming pollution is rising faster than almost every other state. Between 1960 and 2001 releases of carbon dioxide into the air in Nevada increased by 835 percent.
Response from local organizations
The Sierra Nevada Alliance, a nonprofit organization based in South Lake Tahoe, is an alliance of conservation groups throughout the Sierra Nevada. The Alliance has made climate change one of their priority programs.
“Climate change is one of the most significant changes our region is going to face in the next 25 years. It impacts everything from species, to watersheds to agriculture to communities,” said Executive Director of the Alliance, Joan Clayburgh.
Clayburgh stressed that there are great opportunities today to make sure doomsday scenarios such as the “greening of lake Tahoe,” are avoided.
Restoration efforts undertaken today are especially important, Clayburgh said, “the healthier we can make our ecosystems now the better they will be able to transition into this new climate.
“If you have a really stressed population and then the population is reduced, it has less likelihood, genetically, to make it next time around.”
Clayburgh said one way of insuring a healthy ecosystem means working to help animal and plant communities operate at their optimum levels.
The Sierra Nevada Alliance offers resources and guidance to individuals and organizations to participate in local and statewide planning efforts aimed to help ecosystems and people adapt to climate change in the Sierra Nevada.
“It is vital that conservation representatives be actively involved in conservation planning, prepared and informed to shape these plans, and have the most cutting-edge tools to engage and ensure smart plans are adopted for the future,” reads a call to action on the Sierra Nevada Alliance Web page.