Toxic Microcystis Blooms in the Sacramento- San Joaquin Delta Watershed

Abstract

The Sacramento-San Joaquin Delta, in Northern California has a watershed that covers more than 40% of California, and has impaired water quality, which is a result of agricultural discharges, urban runoff, wastewater effluents, erosion, the diversion of water to Southern California, and other causes. The Delta watershed supplies drinking water for 25 million people in California. Nutrient enrichment, particularly from agricultural runoff, can promote blooms of algae. During the summer of 2012, there was a very large bloom of the algae Microcystis in the Delta. Microcystis produces microcystin, a liver toxin, which can be harmful to humans, livestock, wildlife, and some crops. The Ecological Engineering Research Program (EERP) at the University of the Pacific completed water quality surveys to study these harmful algae in the south Delta. During the large bloom, the microcystin toxins in the Delta were measured above California EPA recreational advisory limits (800 ng/L) and World Health Organization drinking water limits (1,000 ng/L). These concentrations were more than 10 times higher than nutrient concentrations from previous years (2009 and 2011). The reason for the Microcystis bloom in 2012 is unknown, but factors such as high temperatures and timing of spring flows may have affected the bloom. More studies are needed to determine if the bloom in 2012 was an abnormality or if massive blooms will reoccur in the future. Research is needed to determine the effects that these toxic blooms are having on the Delta’s ecosystem