Managing Salt Ponds to Increase Waterbird Nesting Habitat While Minimizing Methyl Mercury Biomagnification: Implications for the South Bay Salt Pond Restoration Project Josh Ackerman 1, Collin Eagles-Smith 1, Mark Marvin-DiPasquale 2, Cheryl Strong 3, and Eric Mruz 3 1 U.S. Geological Survey, University of California, Davis, CA; 2 U.S. Geological Survey, Menlo Park, CA; 3 U.S. Fish and Wildlife Service, San Francisco Bay National Wildlife Refuge Complex, Newark, CA (16 September 2009)
South Bay Salt Pond Restoration Project Plans to convert 50-90% of salt ponds (~25,000 acres ) into tidal marsh Salt ponds are preferred habitat for waterbirds Need to enhance remaining salt ponds to maintain current waterbird populations But unclear how to manage salt ponds to increase waterbird foraging and nesting opportunities while minimizing methyl mercury production
Waterbird Nesting Colonies in South San Francisco Bay 27 13 183 2005-2008 46 5 N=5,874 nests 236 85 16 30 4 Avocet Stilt Forster s tern 59 5 29% of nests in A8/A7 which will be flooded for restoration 93 392 115 2 99 23 121 20 5 3 21 245 4 18 101 462 812 8 352 29 108 262 595 756 474
Pond Bathymetry Foxgrover et al. 2007 A9 A14 A15 A17 A10 A11 A13 A16 A5 A7 current A8 A12 future?
Pond A12 Water Management Before After High-salinity Water levels lowered Deep water Substrate exposed suitable No nesting habitat for nesting islands No prior history of nesting
Pond A12 Nesting Islands Monitored: waterbird nesting response Hg in water over time Hg in fish over time Hg in waterbird eggs
Waterbird Nesting Effort A8 and A12 Avocet Stilt Forster s s tern A8 Avocet=211 Stilt=6 Tern=69 A12 Avocet=321 Stilt=5 Tern=73
Waterbird Abundance Over Time 2007 2008 10000 A11 10000 A11 1000 1000 of Wate erbirds Number 100 10 Jan Mar May Jul Sep Nov Jan Mar May July Sept Nov 10000 A12 1000 100 10000 1000 A12 2008 2007 100 100 Jan Mar May Jul Sep Nov water lowered 10 Jan Mar May July Sept Nov water lowered Athearn & Takekawa
THg (ng g/l) 6 5 4 3 2 1 0 Total Mercury A. Filtered THg B. Particulate THg 160 THg (ng/ /L) 120 80 40 0 A11 A A11 B A12 A A12 B Most THg in the particulate fraction THg higher in A12 (July peak)
Methylmercury MeHg (n ng/l) 1.6 1.2 0.8 0.4 A. Filtered MeHg B. Particulate MeHg A11 A A11 B A12 A A12 B MeHg (n ng/l) 30 20 10 0.0 0 Most MeHg in the particulate fraction Higher MeHg in A12 (July peak)
Mercury Bioaccumulation in Fish Muds sucker THg (µ µg/g dw) 1.2 1.0 0.8 0.6 0.4 Pond da11 Pond da12 Pond da13 0.2 Jan Feb Mar Apr May Jun Jul Aug 2005-2006 Fish mercury concentrations before altered water management
Mercury Bioaccumulation in Waterbird Eggs 7 Forster s Tern Stilt Avocet 7 6 5 4 3 2 1 0 2.5 dw) 6 5 4 3 20 2.0 1.5 1.0 0.5 0.0 A12 A8 A7 B4 A16 A1 AB1 Pond 2 A12 NCM AB1 A16 A2W N4/N5 A7 A12 A8 NCM N4/N5 R1 A2W AB1 A1 Eggg THg (µg/g Wetland Site Photos by Ken Phenicie
What Drives These Trends in MeHg? 1) Salinity was higher in 2) Total Suspended Solids A12 and peaked in July and chlorophyll track salinity Co onductivity (m ms) 300 200 100 0 A11 A A11 B A12 A A12 B TS SS (mg/l) 2000 1500 1000 500 R² = 0.76 July Peak in A12 3) Particulate MeHg tracks 40 salinity (ng/l) )30 0 250 200 0 200 400 Conductivity (ms) R² = 0.80 ulate MeHg Partic 20 10 0 R² = 0.87 July Peak in A12 0 200 400 Conductivity (ms) hl-a (mg/m 3 ) C 150 100 50 0 July Peak in A12 0 200 400 Conductivity (ms)
3.5 3.0 25 2.5 Fish Mercury Among Habitats N=3,033 fish 10 species Moffet West Alviso Central Alviso East Alviso Newark South Bay Sloughs North Bay <0.50 ppm dw 0.50-0.75 ppm dw 0.75-1.0 ppm dw >1.0 ppm dw Fish THg (µg/g dw)* A1 A2W A2E AB1 AB2 A5 A7 A8 A12 A13 A16 A17 A18 New Chicago Marsh A19 A20 A21 M1 M2 N2A N4A N6 N9 Alviso Sl. Charleston Sl. Coyote Cr. South Bay Pond 1 Pond 2 Pond 3 Pond 4 North Bay Mowry 2.0 1.5 1.0 0.5 0.0 *least-square means controlling for species, year, date, site, length, & body condition *0.8=fish effects; 1.2=bird effects
Fish Mercury Correlated Pond Salinity? N=16 ponds over 4 years Fish TH Hg (µg/g dw w) 1.0 0.8 0.6 04 0.4 0.2 0.0 Mudsucker Stickleback R 2 =0.06 006 R 2 =0.14 014 0 20 40 60 0 20 40 60 Pond Salinity (ppt)
Mercury Bioaccumulation in Waterbird Eggs 7 Forster s Tern Stilt Avocet 7 6 5 4 3 2 1 0 2.5 dw) 6 5 4 3 20 2.0 1.5 1.0 0.5 0.0 A12 A8 A7 B4 A16 A1 AB1 Pond 2 A12 NCM AB1 A16 A2W N4/N5 A7 A12 A8 NCM N4/N5 R1 A2W AB1 A1 Eggg THg (µg/g Wetland Site Photos by Ken Phenicie
Percent of Population at Risk Breeding Birds Only Risk Factor: High + Extra High Avocet 6% Stilt 5% Caspian tern 10% Forster s tern 58% 0 20 40 60 80 100 Percent of Breeding Population at Risk *B Based on breeding adult ltblood dhg concentrations ti Low Risk Moderate Risk High Risk Extra-High Risk
Effects of Mercury on Egg Hatchability Forster s Terns fww) 2.0 1.8 2005-2007 P<0.001* F 2,341 =13.58 N=73 failed eggs in successful nests Egg [T THg] (μg/g 1.6 1.4 1.2 1.0 *Statistically controlled for effects of colony site and year
Summary We successfully created waterbird nesting habitat (+400 nests) by lowering water levels But, methyl mercury production was elevated Methyl mercury subsequently biomagnified ifi up the food web, with waterbird egg concentrations highest in Pond A12 than in other ponds Further study is necessary to determine if similar water management actions will increase methyl mercury bioaccumulation within other salt pond habitats as the South Bay Salt Pond Restoration Project proceeds
Funding U.S. Fish and Wildlife Service U.S. Fish and Wildlife Service Coastal Program U.S. Geological Survey Support Staff of Don Edwards San Francisco Bay National Wildlife Refuge Contact jackerman@usgs.gov