Harmful algal blooms have been found in freshwater and estuarine water bodies across California this summer, informs Newsweek.
High inputs of nutrients like nitrogen and phosphorous from agricultural or human wastes promote excessive growth of cyanobacteria and algae. They in turn may produce harmful toxins which pose a risk for humans, animals, and the environment, and in that case, they are referred to as harmful algal blooms (HAB). In California, the State Water Resources Control Board maintains a HAB Reports Map both for public information and to support coordination among state partners to address HABs. Dangerous levels of algal toxins have been detected in several lakes and reservoirs across the state.
Algal blooms can have a very negative impact on aquatic environments. Although not all blooms are toxic, when dead cells from a bloom die off, the decay process can consume all the oxygen in the water, killing other organisms. Also, gases such as methane and hydrogen sulfide may be released.
Blooms in freshwater are most commonly caused by cyanobacteria, whereas in saltwater, HAB are most commonly caused by diatoms and dinoflagellates. This summer San Francisco Bay is experiencing a red tide algal bloom which is reportedly the largest of its kind in more than ten years. Sewage inputs into the bay area have been blamed for the bloom. In late August as many as 10,000 fish died in Lake Merrit, a tidal lagoon connected to the Bay with both freshwater and salt water areas.
Aside from nutrient input, conditions such as stagnant water, increased sunlight and high temperature also favour the occurrence of HAB. Climate change is expected to make blooms occur more often and be more severe. Recent research has found that both decreases in wind and higher temperatures predicted with climate change would lead to larger blooms of the freshwater cyanobacteria Microcystis; however, the formation of blooms was more sensitive to the decrease in wind – six times more – than to a 2ºC increase in air temperature.
To reduce the incidence of HAB at the local level, the most feasible strategy is to manage the discharge of nutrients, once the source has been established. Non-point sources such as agricultural runoff are the most difficult to manage. In this regard, experts have called for tighter controls on pollution from agriculture in the U.S., as agricultural expansion and intensification has overwhelmed water quality gains from improved agricultural management practices to address nutrient pollution.