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ELEVATED LEVELS OF DISSOLVED SULFIDES IN SURFICIAL SEDIMENTS OF YAQUINA BAY ESTUARY, OREGON
Citation:
Young, D R., R. C. Caldwell, AND J O. Lamberson. ELEVATED LEVELS OF DISSOLVED SULFIDES IN SURFICIAL SEDIMENTS OF YAQUINA BAY ESTUARY, OREGON. Presented at Pacific Estuarine Research Society meeting, Tacoma, WA, May 18-19, 2001.
Description:
Concentrations of dissolved sulfides were measured via the standard colorimetric method in porewater of surficial sediments collected during 2000 from two sites in Yaquina Bay estuary, Oregon. The first site, Idaho Point, is an area where drift green macroalgae (principally Ulva spp. and Enteromorpha spp.) is known to accumulate, and the odor of hydrogen sulfide gas (H2S) on the mudflat is common in late summer and fall. The second site, Coquille Point, is located about one km to the east across the channel; H2S odor is uncommon here. Color infrared aerial photos taken in June 2000 indicated an expanding bed of green macroalgae off Idaho Point but not off Coquille Point. Thus, surficial (0 - 5 cm) sediment samples were collected monthly between June and December from 30-m wide band transects at each site, extending between the low-intertidal beds of the seagrass Zostera marina and the high-intertidal rockweed Fucus zone. Density and biomass of seagrass and green macroalgae, and bulk sediment concentrations of total organic carbon, also were measured at random intervals along the 17 sampling lines constituting each study zone. Dissolved sulfides were detected only occasionally off Coquille Point, and at low levels (< 50 ?M). However, beginning at the end of August and extending through November, clearly-measurable levels of dissolved sulfides commonly were observed in porewater of surficial sediment from the Idaho Point transect. Levels peaked at more than 4000 ?M, two orders-of-magnitude above the reported threshold of toxic effects for intertidal infauna. Excessive accumulations of green macroalgae off Idaho Point is a possible cause of the relatively high concentrations of dissolved sulfides measured at this site.