What do algae tell us about the health of our streams and rivers?

Algae are found in almost all streams and they respond rapidly to changes in the environment. An assessment to determine which algal species are present and how abundant they are can be a useful and robust way to measure stream health. Algae react to changes relatively quickly and are therefore particularly useful for characterizing recent changes in stream conditions. They are also more directly responsive to the presence of excess amounts of nutrients (such as nitrogen and phosphorus) than some other organisms. High nutrient levels can cause some algae to grow rapidly, a condition called “eutrophication.” Too much algae can smother other desirable organisms through chemical and physical means. In some cases, algal blooms can release toxins that are harmful to people and animals, or create visual and olfactory nuisance and taint municipal water supplies.

Bioassessment is the characterization of environmental conditions through the observation of biological communities. Two common types of bioassessment are O/E and IBI. O/E stands for observed over expected, and compares of the number of certain species observed at a site to the number of those species that would be expected to occur, based on data from reference sites that are known to be healthy. IBI is an Index of Biotic Integrity, which combines a variety of individual measures of health of a community of organisms, such as species richness (how diverse the community is) and pollution tolerance (how resistant to pollution they are). Preliminary algae IBIs have been developed for the Lahontan region of the state (eastern Sierra Nevada) as well as for coastal watersheds in southern California. Work is ongoing to:

Finalize these IBIs
Develop new IBIs appropriate for application in other portions of the state, and
Produce O/E models

Algae data will be displayed in a future portal update.