Abstract: Nutrients and Phytoplankton Productivity in the Sacramento River and San Francisco Bay Delta Region Under Drought Conditions (2016 Ocean Sciences Meeting)

Nutrients and Phytoplankton Productivity in the Sacramento River and San Francisco Bay Delta Region Under Drought Conditions

Frances Wilkerson¹, Sarah Blaser², Edmund Antell², Richard C Dugdale¹, Curtiss O Davis³, Steven G Ackleson^4,5, W. Joe Rhea⁶, Alexander Parker⁷ and Jamie Lee², (1)San Francisco State University, San Francisco, CA, United States, (2)San Francisco State University, CA, United States, (3)Oregon State University, Corvallis, OR, United States, (4)S A Ocean Services, Falls Church, VA, United States, (5)Naval Research Laboratory, Washington, DC, United States, (6)Naval Research Laboratory, Remote Sensing Division, Washington, DC, United States, (7)CSU Maritime Academy, Sciences and Mathematics, Vallejo, CA, United States

Abstract:

California experienced extreme drought conditions during 2014 and 2015, that followed below average precipitation years in 2012 and 2013. The effects of these extreme drought conditions on the lower trophic levels of the pelagic food web of the northern San Francisco Estuary (nSFE) were investigated. A series of seasonal field campaigns were conducted between June 2014 and October 2015, in which nutrient concentrations, phytoplankton productivity (using ¹³C, ¹⁵NO₃ and ¹⁵NH₄ uptake) and community composition (using HPLC pigment analysis) were measured. These measurements were made in collaboration with investigators that characterized the particulate and dissolved matter, in situ spectral light scatter and absorption, and analyzed remotely sensed radiometric measurements. It was hypothesized that the nSFE would be characterized by 1) elevated nutrients during the drought, a result of reduced dilution of nutrient point sources. 2) phytoplankton blooms enabled by increased water residence times. 3) elevated nitrification rates associated with warm water temperatures. Relative to historical data, elevated nitrate concentrations were observed in the nSFE during the drought period along with spring phytoplankton blooms that were dominated by diatoms. These results support the idea that the nSFE is strongly influenced by interannual variation in precipitation and that drought conditions will likely alter the nutrient field and lower trophic level response.

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