TEMPORAL VARIATION OF NUTRIENTS AND CHLOROPHYLL IN HUMBOLDT BAY, CALIFORNIA: IMPLICATIONS FOR WATER QUALITY
Courtney Brown, Mathew Hurst.
Humboldt State University, Arcata, CA.
Humboldt Bay is the ancestral land of the Wiyot people and California’s largest producer of oysters. The relatively good water quality in Humboldt Bay provides habitat for both wildlife and aquaculture. The focus of our research was achieving a better understanding of the Humboldt Bay ecosystem, which depends on the availability of nutrients and the production of phytoplankton to support the food web. From October 2012 through February 2015, bimonthly samples were collected from 5 locations within Humboldt Bay in an attempt to understand the sources and sinks of nutrients and measure the amount of phytoplankton. Laboratory water-quality analyses were conducted and included total suspended solids (TSS), turbidity, nutrients (nitrate, phosphate, and silicate), and chlorophyll. We observed that the main source of nutrients throughout the annual cycle was from the ocean. This occurs through upwelling events in the spring and summer, which allow the phytoplankton to bloom during this period. In the summer of 2013, a massive phytoplankton bloom in the main channel of Humboldt Bay caused drawdown of nitrate and silicate to a point that they likely limited further growth. In the summer of 2014, a smaller bloom was observed, and nutrient levels stayed elevated. Although nutrients are present during the winter, reduced sunlight and lower temperatures inhibit phytoplankton growth. Runoff played a minor role in nutrient inputs. Overall, baseline levels of nutrients and phytoplankton were established for Humboldt Bay and will support future work on these waters.