Research Technical Reports

Effects of Entrainment and Thermal Increase on Bacteria and Phytoplankton in the Moss Landing Power Plant: What Blooms in the Plume?

Wagner, G. and N. Welschmeyer (March 2005)

Poster presentation at the 2005 Sanctuary Currents Symposium, Seaside, CA

ABSTRACT

Seawater from Moss Landing Harbor is pumped through Moss Landing Power Plant for cooling purposes (4.56 billion L/day); the heated seawater is discharged into Monterey Bay. To evaluate potential effects on plankton, samples were collected along the cooling flow path from the intake source, through the power plant, to the final discharge site in Monterey Bay. Maximum temperatures (27.2 degrees C; roughly 13 degrees C above ambient) were measured in the surge chamber where water collects in the power plant before being discharged into the Bay. Surface water directly over the Monterey Bay discharge site was ca. 4 degrees C warmer than ambient Bay water. Bacterial abundance (DAPI stained direct counts) was similar at all sampling sites. However, bacterial growth activity (culture plating and frequency of dividing cells) was significantly higher (3x) for surge chamber samples. Phytoplankton biomass, estimated from algal pigments, was variable along the sampling track, with lowest concentrations generally found in the surge chamber. Phytoplankton physiological state (fluorescence-based photochemical yield) was lowest in the surge chamber, reflecting values similar to heat-stressed laboratory samples. Phytoplankton pigment degradation products were also highest at the surge chamber site. The results suggest differential effects of entrainment on plankton: bacterial growth is augmented after thermal entrainment, but phytoplankton are negatively impacted.