Analysis of total and methyl mercury as part of continuing monitoring to establish baseline concentrations in the sediments of the ponds comprising the South Bay Salt Pond Restoration Project. Results reported herein summarize efforts from winter 2005 and are presented with summaries from previous sampling conducted during late summer-early fall 2003 and 2004.
We collected sediment cores for analysis of total (THg) and methyl (meHg) mercury during winter 2005 from the Alviso and Eden Landing salt ponds as part of continuing monitoring to establish baseline concentrations in the sediments of the ponds comprising the South Bay Salt Pond Restoration Project. Results reported herein summarize efforts from winter 2005 and are presented with summaries from previous sampling conducted during late summer-early fall 2003 and 2004 (Miles et al. 2005).
The protocol set forth in the proposed scope of work for the monitoring study (Miles and Takekawa 2003, Stallings 2003) identified 2 main objectives: 1) establish a set of baseline concentrations of total and meHg in south bay salt ponds, primarily during late summer – early fall or winter, and 2) conduct additional sampling in ponds with highest baseline meHg concentrations, scheduled for changing water and salinity regimes, or characterized by important physical features. Results from ponds sampled during late summer – fall during 2003 and 2004 were reported previously (Miles et al. 2005) and, along with consultation with FWS, were used to determine ponds for sampling during winter 2005. Specifically,
- Ponds A3N, A12, and A13 were re-sampled because they contained surface sediments with the highest geometric mean concentrations of meHg during late summer – early fall.
- AB1, A5, and A7 are characterized by increasing depth associated with increasing distance from the south bay, causing exposed mudflats as water flow changes and higher methylation potential. Thus, we sampled 3 points (near, midway, and farthest from the bay) in order describe potential within pond variation in Hg concentrations associated with depth.
- Alviso ponds A9, A15, A17, A19, A20, and A21 were sampled to establish baseline Hg concentrations during winter. Water regime changes either have been conducted or soon will be conducted on these ponds.
- Finally, we collected sediment samples to obtain winter baseline THg and meHg concentrations in all Eden Landing Ponds (B1, B2, B4, B5, B6, B7, B8, B9, B10, B11, B12, B14, B1C, B2C, B4C, B5C, B6A, B6B, and B6C). In addition, 4 Eden Landing ponds were sampled in late summer – fall (B1, B2, B4, and B7).
- Concentrations of meHg in surface sediments from Alviso ponds A1, A2E, A2W, A3W, A5, A7, AB1, and AB2 sampled during late summer – fall 2004 were not available for inclusion in the January 2005 Progress Report. Results are included in this report which completes the baseline dataset for late summer – early fall.
