Photo of Brewer's Lupine growing in granitic soil.  Lupine are capable of converting naturally occurring nitrogen in the air to a form that is usable to them and other plants, including algae. Photo Credit: Alison Toy

NUTRIENTS IN LAKE TAHOE

Nutrients in a lake are a suite of chemical compounds used by algae (mini lake plants).  These chemicals are natural fertilizers for the algae that are required for growth along with photosynthesis (light + carbon dioxide + water).   Algae are the important base of the lake food web; these algae are consumed by zooplankton and the zooplankton are consumed by fish.  So, nutrients that support algae are supporting most life in a lake.  Another way of saying this is that both algae and certain chemicals in a lake are good.   

UCD scientists measure the naturally occurring forms of nitrogen (algae use these to make proteins) and phosphorus (algae use these to make cell membranes and DNA) over time and from many depths to measure natural and human induced changes in the lake.  

Every lake is different in its concentrations of various nutrients emanating from parent rock, vegetation cover, climate and topography.  Lake Tahoe has a unique natural ratio of nitrogen and phosphorus and other chemicals compared to other lakes creating an environment where a specific mix of algae can thrive.  Lakes can change from human activity creating contemporary sources of N or P (see table below).

Nitrogen and Phosphorus are measured in Lake Tahoe monthly in multiple places and many depths.  We are measuring the forms of N and P that are available as food to algae.  This gives us and idea of whether the N and P are increasing over time.  However, algae are extremely quick at using N and P in the lake water and thus it’s very difficult to measure.  We must also look at the number of algae growing in the same vicinity to put together a complete picture of whether nutrients are increasing in Lake Tahoe.

The above is a table of natural sources vs. contemporary sources of N and P.