Presentation on theme: "2.1 Triangle Marsh What is the impact of mining on Hg concentrations in estuary? What is natural concentration of Hg? Hg-P Hg- DOC Project designed to."— Presentation transcript:
2.1 Triangle Marsh What is the impact of mining on Hg concentrations in estuary? What is natural concentration of Hg? Hg-P Hg- DOC Project designed to measure historic Hg contamination in southern reach Effects of the weathering of naturally rich Hg mineralization in the Santa Clara Valley?
2.2 Background Worldwide –20 –200 ng/g uncontaminated soils San Francisco Bay Area –50 –100 ng/g Northern Coast Range streams (Domagalski 2001) –1 –20 ng/g Pacific Coast Ranges (Kerin 2002) Downstream of New Almaden –200 ng/g upstream of New Almaden –Modern surface sediments of estuary 200–600 ng/g (Hornberger et al., 1999; Conaway et al., 2003, Marvin-DiPasquale et al., 2003)
2.3 Methods San Francisco Bay –3 cores in South Bay Triangle Marsh –Tidal marsh where Coyote Creek and Guadalupe River enter estuary Chronology AMS 14 C dating of shell and organic material Appearance of non-native pollen –Eucalyptus, Plantago lanceolata Abundance of Cyperaceae (sedge family) pollen related to ENSO events
2.4 Results Bay Mud Inter- tidal peat Tidal marsh Low impact High impact
2.5 Results Gap in time of greatest Hg production and deposition in core! High impact means high sedimentation... Rising sea level Subsiding basin Land use –Hydrologic modifications –Dam building …drive transport and deposition of sediment m m m m m > 2.4 m Subsidence (m) 1934 to 1967 from Poland (1984)
2.6 Conclusion What is the impact of mining on background Hg? What is a natural concentration of Hg in SFB? Pre-mining [Hg] is similar in all SFB cores (~80 ng/g) Little evidence of contamination from natural weathering Contamination reflects mining activity and watershed hydrology Hg-P Hg-DOC Bay mud Intertidal peat Tidal marsh Low impact High impact Rock Peak [Hg]