Lake Chemical Processes: Nutrients & Cycling
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 foundation of the lake's food web; these algae are consumed by zooplankton, which are in turn consumed by fish. So, nutrients that support algae support 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 differs in the concentrations of various nutrients derived from parent rock, vegetation cover, climate, and topography. Lake Tahoe has a unique natural ratio of nitrogen, 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 monthly in Lake Tahoe at multiple locations and at various depths. We are measuring the forms of N and P that are available to algae as food. This gives us an idea of whether the N and P are increasing over time. However, algae are extremely quick to use N and P in lake water, making it very difficult to measure. We must also consider the number of algae in the same vicinity to build a complete picture of whether nutrients are increasing in Lake Tahoe.