Historic and recent trends of cyanobacterial harmful algal blooms and environmental conditions in Clear Lake, California: a 70-year perspective

Clear Lake is the largest, natural lake in northern California, USA with many beneficial uses but also substantive environmental issues. The lake has a long history of water quality problems including mercury contamination, pesticide usage, invasive species, and high rates of primary production. In recent years, an increase in cyanobacterial harmful algal blooms (cyanoHABs) have been documented in the lake, adding to the environmental issues faced by aquatic species present in the lake, and the local community. Extensive observations of various physical, chemical, and biological parameters in Clear Lake began in the mid-1900s. The most pertinent of these datasets and findings have been reviewed and analyzed with the intent of improving our understanding of the causes and drivers of cyanoHABs, toxin production, and identifying data gaps. The findings are published in Smith et al. (2023) at DOI: https://doi.org/10.1525/elementa.2022.00115  Funding for this work, including data acquisition, database assembly and manuscript preparation was provided by the Big Valley Band of Pomo Indians Environmental Protection Agency and the Elem Indian Colony Environmental Protection Agency.

The dataset assembled as a part of Smith et al. (2023) is posted here. It is the master database of 50 lake and climatological parameters (~217,000 individual data points) from the period of 1920 to mid-2020 of environmental parameters within and surrounding the lake. This database and analysis builds upon the efforts of the Big Valley Band of Pomo Indians Environmental Protection Agency to identify the Clear Lake monitoring entities and assemble the available water quality data. More information about this effort, as well as data visualizations can be found here: https://www.bvrancheria.com/water-quality-dashboard 

In 2014, two Tribal Nations, the Big Valley Band of Pomo Indians, and the Elem Indian Colony, developed the Clear Lake Cyanobacteria Monitoring Program (https://www.bvrancheria.com/clearlakecyanotoxins) which includes water quality parameters along with cyanobacterial-specific parameters such as cyanotoxins, phycocyanin, and cyanobacterial genera identifications via microscopy. The vast majority of available cyanotoxin data, which are presented in this database, resulted from these efforts.

Basic climatological and hydrologic data have been collected near and around Clear Lake as early as the 1910s by the U.S. Geological Survey (USGS) and National Oceanic and Atmospheric Administration (NOAA). Multiple agencies have conducted both routine and intermittent monitoring of chemical and physical parameters on Clear Lake since the 1950s, although routine and consistent collection of biological monitoring data began more recently within the last two decades. The California Department of Water Resources, the California State Water Resource Control Board, and Lake County Vector Control District have monitored several water quality parameters beginning in the 1950s.