Phytoplankton Monitoring of Discovery Lake (San Marcos, California) in 2022:

CSUSM Undergraduate Student Project

Abstract

Discovery Lake is a small shallow man-made recreational lake located in the suburbs of the City of San Marcos and used as field sampling station for the CSUSM undergraduate course Biol 387L Aquatic Ecology Laboratory since 2011. We studied the phytoplankton dynamics of Discovery Lake from March to November 2022 as a community engagement project mastering our new field and lab research skills developed during the Spring 2022 class of Biol 387L. Our study provides the first data on phytoplankton composition and dynamics of Discovery Lake. Dinoflagelatte species belonging to Ceratium are the most characteristic for the lake phytoplankton and determine the brownish color of the lake water. They grow continuously since the beginning of phytoplankton monitoring in 2011, probably favored by the increased water salinity (492-1204 ppm in 2022). Ceratium forms extensive and prolonged blooms in the fall months, recently continuing until late November in 2022. In the summer months (July and August), filamentous N2-fixing cyanobacteria belonging to Dolichospermum and Aphanizomen form dense blooms, co-dominated by the chrysophyte colonial flagellate Dinobryon in 2022. Although summer cyanobacterial blooms are not confirmed to be toxic, they deplete the oxygen, sometimes causing fish kills.