Mercury residues and productivity in osprey and grebes from a mine-dominated ecosystem.

Mercury (Hg) and reproduction and status of Western and Clark's Grebes (Aechmophorus sp.) and Osprey (Pandion haliaetus) were studied from 1992 through 2001 and then less intensely through 2006 at Clear Lake, California, USA. Remediation to reduce Hg loading from the Sulphur Bank Mercury Mine was initiated in 1992. Mercury in grebe feathers declined monotonically from approximately 23 mg/kg dry mass (DM) in 1967-1969 to 1 mg/kg in 2003, but then increased to 7 mg/kg in 2004-2006. Mercury in Osprey feathers varied similarly, with mean values of 20 mg/kg DM in 1992, declining to a low of 2 mg/kg in 1998, but increasing to 23 mg/kg in 2003, and 12 mg/kg in 2006. Mercury in Osprey feathers at our reference site (Eagle Lake, California) remained low (1-8 ppm) throughout the entire period, 1992-2003. Grebe productivity at Clear Lake improved from approximately 0.1 to 0.5 fledged young per adult during the latter part of the study when human disturbance was prevented. At that period in time, improved productivity did not differ from our reference site at Eagle Lake. Human disturbance, however, as a co-factor made it impossible to evaluate statistically subtle Hg effects on grebe productivity at Clear Lake. Osprey reproduced sufficiently to maintain increasing breeding numbers from 1992 to 2006. Mercury in Clear Lake water, sediments, invertebrates, and fish did not decline from 1992 to 2003, but a shift in trophic structure induced by an introduced planktivorous fish species may have caused significant alterations in Hg concentrations in several species of prey fishes that may have produced concomitant changes in Osprey and grebe Hg exposure. The temporary declines observed in grebe and Osprey feather residues in the late 1990s, with coincidental improvements in reproductive performance, however, could not be attributed to remediation at the mine site.

The legacy of mercury cycling from mining sources in an aquatic ecosystem: from ore to organism.

Clear Lake is the site of an abandoned mercury (Hg) mine (active intermittently from 1873 to 1957), now a U.S. Environmental Protection Agency Superfund Site. Mining activities, including bulldozing waste rock and tailings into the lake, resulted in approximately 100 Mg of Hg entering the lake's ecosystem. This series of papers represents the culmination of approximately 15 years of Hg-related studies on this ecosystem, following Hg from the ore body to the highest trophic levels. A series of physical, chemical, biological, and limnological studies elucidate how ongoing Hg loading to the lake is influenced by acid mine drainage and how wind-driven currents and baroclinic circulation patterns redistribute Hg throughout the lake. Methylmercury (MeHg) production in this system is controlled by both sulfate-reducing bacteria as well as newly identified iron-reducing bacteria. Sediment cores (dated with dichlorodiphenyldichlorethane [DDD], 210pb, and 14C) to approximately 250 cm depth (representing up to approximately 3000 years before present) elucidate a record of total Hg (TotHg) loading to the lake from natural sources and mining and demonstrate how MeHg remains stable at depth within the sediment column for decades to millenia. Core data also identify other stresses that have influenced the Clear Lake Basin especially over the past 150 years. Although Clear Lake is one of the most Hg-contaminated lakes in the world, biota do not exhibit MeHg concentrations as high as would be predicted based on the gross level of Hg loading. We compare Clear Lake's TotHg and MeHg concentrations with other sites worldwide and suggest several hypotheses to explain why this discrepancy exists. Based on our data, together with state and federal water and sediment quality criteria, we predict potential resulting environmental and human health effects and provide data that can assist remediation efforts.

Seabird diets provide early warning of sardine fishery declines in the Gulf of California.

Small pelagic fisheries show wide fluctuations, generally attributed to oceanographic anomalies. Most data on these fisheries come from landings, often reporting sustained catches-per-unit-effort (CPUEs) until a decline occurs. Fishery-independent data are important as management tools. In this study we show that the proportions of Pacific Sardine and Northern Anchovy in the diet of three seabird species (California Brown Pelicans, Heermann's Gulls, and Elegant Terns) nesting in spring in the Gulf of California show significant relationships with CPUEs during the following season in gulls and terns, or during the same season in pelicans. As sardine availability for seabirds declines, CPUEs remain high until the fishery falls, one or two seasons later. A declining proportion of sardines in the seabirds' diet, combined with the status of the Pacific warm-phase anomaly (El Niño), give a reliable forecast of diminishing CPUEs and signals the need to reduce fishing efforts in the ensuing season.

East versus West: organic contaminant differences in brown pelican (Pelecanus occidentalis) eggs from South Carolina, USA and the Gulf of California, Mexico.

Brown pelicans (Pelecanus occidentalis) were listed as endangered in the United States in 1970, largely due to reproductive failure and mortality caused by organochlorine contaminants, such as DDT. The southeast population, P.o. carolinensis, was delisted in 1985, while the west coast population, P.o. californicus, was not delisted until 2009. As fish-eating coastal seabirds, brown pelicans may serve as a biomonitors. Organic contaminants were examined in brown pelican eggs collected from the Gulf of California in 2004 and South Carolina in 2005 using gas chromatography/mass spectrometry (GC/MS). Contaminants were compared using all individual data as well as statistically pooled samples to provide similar sample sizes with little difference in results. Principal components analysis separated the Gulf of California brown pelican eggs from the South Carolina eggs based on contaminant patterns. The South Carolina population had significantly (P<0.05) higher levels of polychlorinated biphenyls (PCBs), chlordanes, dieldrin and mirex, while the Gulf of California eggs had higher levels of dichlorodiphenyltrichloroethanes (DDTs) and hexachlorocyclohexanes (HCHs). With the exception of dieldrin and brominated diphenyl ether (BDE) 47, this pattern was observed for mussel and oyster tissues from these regions, indicating the need for further study into the differences between east and west coast brown pelican populations and ecosystem contamination patterns.