State of the Lake 2014 report released; Expect longer summers in Lake Tahoe

By the end of the century Lake Tahoe summers may be two months longer than they were in the 1960s and the maximum temperatures may have risen by 8 degrees F. Those were part of the predictions released in the State of the Lake 2014 report.

Data collected over the last 50 years, combined with the monitoring of Lake Tahoe during the 12 months of 2013, was presented at Thursday's unveiling of the report at the Tahoe Center for Environmental Sciences (TERC) in Incline Village by Director Geoff Schladow.

Here is a link to the 91 page report. Highlights are listed below:

- Lake clarity down 5 feet when compared to last year, mainly due to high precipitation in early winter. Year to year fluctuations are the norm. Summer clarity was almost identical to last year at 63.8 feet. It has improved 13 feet in just two years.

- 2013 saw the continuation of dry conditions for the 2nd consecutive year at Lake Tahoe. Air temperatures were colder in winter and warmer in summer than the long term average. Earlier peak in timing of snowmelt, occurring on May 15.

- Lake level rose by 6" during the spring snowmelt, one of the lowest on record. The elevation difference between peak lake level and the lowest lake level in 2013 was 2.73 feet, falling at an average rate of decline of
1.1 inches per week.July water surface temperatures were highest on record in 5 years at 65.6 degrees F, an increase of 1.8 degrees.

- Lake Tahoe did not mix to its full depth in 2013, the 2nd consecutive year. Mixing occurred at a depth of just 590 feet in March.

- Temperature of the water at the dam in Tahoe City have increased significantly since they started collecting data there in 1993. Summer water releases have increased over the last two years even though water levels have decreased.

- Input of stream-born nutrients to the lake was low again in 2013 due to low precipitation and low run-off. Both phosphorus and sediment inputs from the streams were even lower than 2012, although still larger than the loads during the drought years of the early 1990’s.

- Overall in-lake nitrate concentrations have remained relatively constant over the 33 years of record. By contrast, in-lake phosphorus concentrations display a downward trend over the same period, having decreased by almost 50 percent.

- Long term shift towards smaller algal species that can process nutrients faster is helping to biologically increase the lake productivity. Chlorophyll has remained constant but there was a decrease in the abundance of diatom cells. In particular the concentration of Cyclotella was reduced. This small-sized diatom can exert a large influence on lake clarity.

- Nearshore degradation due to algae attaching to rocks is getting more attention from local agencies to control it since it has a direct affect on lake clarity.