Sigleo, A. C. EPA/OSU,
, . C. ,

Silica is a critical element required for diatom skeletal growth. The apparent decrease in dissolved silica relative to P and N is cited as a reason for increases in flagellates resulting in toxic algal blooms. Silica deficiencies also may stimulate toxin production in diatom species found in the Pacific Northwest (PNW). Spatial and seasonal silica distributions were measured in the Yaquina Watershed, OR and the Willapa Watershed, WA. PNW dissolved silica concentrations varied from 240 microM in the freshwater portion of the Willapa River to an averge of 51 (n=69) microM in Willapa Bay. The higher values within the bay, i.e. >70 microM, occurred after major rainfall events. Dissolved silica in the surf zone of coastal waters outside Willapa Bay averaged 32 microM, and beyond the surf zone, the dissolved silica concentrations decreased to less than 1 microM within one km from shore. Data for Yaquina Bay were similar, averaging 40 microM both within the bay and the surf zone outside the bay. Dissolved silica values up to 120 microM occurred in the bay after major storm events. The Yaquina Bay data correspond to dissolved silica values of 121 to 231 microM in the freshwater Yaquina River to 43 microM in the bay reported in the 1970s.
Day: Friday, Feb. 5
Time: 04:15 - 04:30pm
Location: Sweeney Center
Code: SS13FR0415S