Methyl and Total Mercury Spatial and Temporal Trends in Surficial Sediments of the San Francisco Bay-Delta Assessment of Ecological and Human Health Impacts of Mercury in the Bay-Delta Watershed CALFED Bay-Delta Mercury Project Final Report Submitted to: Mark Stephenson California Department of Fish and Game Moss Landing Marine Labs 7544 Sandholdt Road Moss Landing, CA 95039 Submitted by: Wesley A. Heim Moss Landing Marine Laboratories 8272 Moss Landing Rd Moss Landing, CA 95039 [email protected](email) 831-771-4459 (voice) Dr. Kenneth Coale Moss Landing Marine Laboratories 8272 Moss Landing Rd Moss Landing, CA 95039 Mark Stephenson California Department of Fish and Game Moss Landing Marine Labs 7544 Sandholdt Road Moss Landing, CA 95039
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Methyl and Total Mercury Spatial and Temporal …...2001). As a result, the fish, water, and sediment of the central valley and Bay-Delta have elevated levels of mercury. The primary
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Methyl and Total Mercury Spatial and Temporal Trends in
Surficial Sediments of the San Francisco Bay-Delta
Assessment of Ecological and Human Health Impacts of Mercury in the Bay-Delta Watershed
CALFED Bay-Delta Mercury Project Final Report
Submitted to:
Mark Stephenson
California Department of Fish and Game Moss Landing Marine Labs
EXECUTIVE SUMMARY Recent studies indicate significant amounts of mercury are transported into the Bay-Delta from the Coastal and Sierra mountain ranges. In response to mercury contamination of the Bay-Delta and potential risks to humans, health advisories have been posted in the estuary, recommending no consumption of large striped bass and limited consumption of other sport fish. The major objective of the CALFED Bay-Delta Mercury Project “Assessment of Ecological and Human Health Impacts of Mercury in the Bay-Delta Watershed” is to reduce mercury levels in fish tissue to levels that do not pose a health threat to humans or wildlife. This report summarizes the accomplishments of the Moss Landing Marine Laboratories (MLML) and California Department of Fish and Game (CDF&G) at Moss Landing as participants in the CALFED Bay-Delta Mercury Project. Specific objectives of MLML and CDF&G include: 1. Determination of the spatial distribution of total mercury and methyl mercury in surficial sediments of the Bay-Delta. Identify locations within the Bay-Delta having high mercury methylation potentials (as indicated by the methyl mercury to total mercury ratio) (Task 4A1 & 4A2). 2. Determination of the temporal changes in total mercury, methyl mercury, and the methyl mercury to total mercury ratio at six locations within the Bay-Delta (Task 4A1 & 4A2). 3. Determination of the mercury methylation potentials in Coastal and Sierra Range river and lake sediments (Task 4A1 & 4A2). 4. Determination of the mercury methylation potential of wetland areas within the Delta (Task 4A1 & 4A2 Phase 2). The initial survey of Bay-Delta sediments was conducted October, 1999. Samples were collected for the determination of total mercury, methyl mercury, percent Loss on Ignition (LOI), and grain size, as well as water column measurements of temperature and pH. Sediment samples were collected monthly from May, 2000 – November, 2001 at six locations in the Bay-Delta. Samples were analyzed for total and methyl mercury, and LOI. Sediment collections were made in October, 2001 from the Coastal Range and Sierra Range for the determination of mercury methylation potentials. Transects across three wetlands were conducted May 2001. Sediments were collected from the interior, middle, exterior, and control site of each wetland area for the determination of total mercury, methyl mercury, and LOI. All raw data is given in Appendix B. Major Findings (Working Hypotheses):
• In the Bay-Delta, total mercury concentrations decreased north to south and increased east to west while methyl mercury concentrations increased north to south. The highest methyl mercury sediment concentrations were found in the
central Delta. The central Delta had the greatest mercury methylation potential when compared to the surrounding tributaries.
• Solid phase methyl mercury concentrations varied seasonally with highest
concentrations occurring during late spring/summer.
• Coastal mountain streams had two orders of magnitude higher total mercury concentrations than Sierra mountain streams and the methyl mercury concentrations were equivalent. Sediments from lakes of the Coastal Range and Sierra Range were equivalent in total mercury and methyl mercury.
• Inner areas of wetlands consistently had higher solid phase methyl mercury
concentrations and methyl mercury to total mercury ratios when compared to outer areas of wetlands and the control site.
(Figure 19). LOI was significantly correlated to both methyl mercury (p< 0.001) and the
methyl mercury to total mercury ratio (p< 0.001) (Data not shown).
Numerous studies have shown wetland areas to be areas of high methyl mercury
production (St. Louis et al. 1994, Hurley et al. 1995, Rudd 1995, St. Louis et al. 1995,
Krabbenhoft et al. 1999). The common features of these areas are limited circulation,
proximity to agricultural areas, and lack of peat in the sediments. The LOI levels in the
sediment in the interior of these wetlands appeared to be high (7-50%) relative to those in
the main, well flushed, part of the Delta (usually <5%). Water circulation in the interior
of the wetland areas was limited and led to increased water temperature and residence
time. The large amount of organic material present and the limited circulation of the
water likely led to hypoxic water conditions. The combination of these environmental
conditions set the ideal stage for mercury methylation in the presence of reactive mercury
(Kelly et al. 1997). Clearly the wetland areas within the Bay-Delta have a high potential
for production of methyl mercury. Further research is needed to quantify the production
of methyl mercury in the wetland habitats and determine the contribution these habitats
make with respect to the mercury budget of the entire Bay-Delta.
CONCLUSIONS In brief summary, the major findings of the study are listed below.
• The highest methyl mercury sediment concentrations were found in the central
Delta. The central Delta had the greatest mercury methylation potential when compared to the surrounding tributaries.
• Solid phase methyl mercury concentrations varied seasonally with highest
concentrations occurring during late spring/summer.
• Coastal mountain streams had two orders of magnitude higher total mercury concentrations than Sierra mountain streams and the methyl mercury concentrations were equivalent.
• Interiors of wetlands consistently had higher solid phase methyl mercury
concentrations and methyl mercury to total mercury ratios than fringes of wetlands.
ACKNOWLEDGEMENTS This work would not have been possible without the field assistance and/or analytical work of Sean Mundell, Bettina Sohst, Lisa Berrios, Susan Von Thun, Myah Gunn, John Haskins, Elizabeth Sassone, Susan Coale, Autumn Bonnema, Amy Byington, Tam Voss, and the MPSL clean lab crew. In addition, Dylan Service was largely responsible for the flawless operation of the many small boats used to sample the Bay-Delta.Special thanks to the reviewers Dr C. Gilmour, Dr. D. Krabbenhoft,Dr. J. Wiener, and Dr. J. Rudd for all of their good advice and recommendations.
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Picture 1. A picture showing the fringe marsh habitat along rip-rap waterways at Mandeville Island located near Franks Tract in the central Bay-Delta. (Photo by W. Heim)
Picture 2. This picture of Tower Park marina in the Bay-Delta illustrates the subsidence of croplands and the necessity of levees for prevention of flooding. (Photo by W. Heim)
Picture 3. An assembled Sludge O Matic with attached shutter trigger line. The door is shown in the closed position. The attachment of the pulley system with plastic ties is clearly shown as is the handle configurations and aircraft pin. (Photo by W. Heim)
Picture 4. Close-up photo of the topmost 0.5 cm of sediment captured cleanly using the SOM. The trap door of the sampler is shown in the open position with sediment ready to be transferred into sample jars. (Photo by W. Heim)
Picture 5. Field team employing “clean hand techniques” at Sherman Island. Sediment is being sub-sampled from the SOM using a plastic scoop to transfer samples. “Clean hands” person is wearing clean room gloves during all sub-sampling. “Dirty hands” person never comes into contact with the sample but aids “clean hands” person as necessary. (Photo by R. Lehman)
Picture 6. Shallow water environment of East Columbia Cut characterized by a mixed sediment type of sand and silt with an abundance of floating and submerged aquatic vegetation.
Figure 2. Total mercury surficial (0-0.5 cm) sediment concentrations of San Francisco Bay are indicated by purple scale bars with the key given in the lower left. The Key to Features shown in the upper right gives a color code for different habitat types found in the Bay as described by the National Wetlands Inventory. Sampling locations are represented as red circles.
Figure 3. Methyl mercury surficial (0-0.5 cm) sediment concentrations of San Francisco Bay are indicated by red scale bars with the key given in the lower left. The Key to Features shown in the upper right gives a color code for different habitat types found in the Bay as described by the National Wetlands Inventory. Sampling locations are represented as purple circles.
Figure 4. Methyl mercury to total mercury ratios (as a percent) in surficial (0-0.5 cm) sediment of San Francisco Bay are indicated by aqua scale bars with the key given in the lower left. The Key to Features shown in the upper right gives a color code for different habitat types found in the Bay as described by the National Wetlands Inventory. Sampling locations are represented as pink circles.
Figure 5. A map of the San Francisco Bay-Delta showing the surrounding tributaries and Bays. The six seasonal sampling stations are shown with asterisks and the following names: Prospect Slough, Cosumnes River, White Slough, Franks Tract, Connection Slough, and Sherman Island. The dashed line circle represents the approximate boundary of an area within the study area operationally defined as the “central delta”.
Figure 7. Small scale variation in methyl mercury concentrations at East Columbia Cut in the central Bay-Delta. Field Replicates are shown with error bars as the standard deviation of analytical triplicates.
Figure 8. Total mercury surficial (0-0.5 cm) sediment concentration for locations within the Delta and surrounding tributaries and bays. Mercury concentration for each location sampled is represented by a scale bar and the key is given in ppm dry weight sediment. Sampled locations with mercury values less than the method detection limit of 0.10 ppm are represented by solid black circles.
Figure 9. Correlation between total mercury concentration and longitude (R2 = 0.34) for samples collected from the Bay-Delta between 38.00° and 38.15° latitude.
Figure 10. Methyl mercury surficial (0-0.5 cm) sediment concentration for locations within the Delta and surrounding tributaries and bays. Methyl mercury concentration for each location sampled is represented by a scale bar and the key is given in ppb dry weight sediment. Two sites are shown with the methyl mercury concentrations explicitly expressed (in ppb) as the concentration of methyl mercury was large in comparison to all other samples. Sampled locations with methyl mercury values less than the method detection limit of 0.019 ppb are represented by solid black circles. The dashed line circle represents the approximate boundary of the study area operationally defined as the “central delta”.
Figure 11. Methyl mercury to total mercury ratios (as a percent) in surficial (0-0.5 cm) sediment for locations within the Delta and surrounding tributaries and Bays. Grey scale bars are indicative of an upper limit ratio, as the methyl mercury to total mercury ratio was calculated using the method detection limit for total mercury. Solid black circles were used to indicate locations with methyl mercury values and total mercury values less than method detection limits. The dashed line circle represents the approximate boundary of the study area operationally defined as the “central delta”.
Figure 13. Correlation between methyl mercury and total mercury in Delta sediment samples collected during the winter of 1999 (R2 = 0.19). Circled triangles were considered as outliers and were left out of the correlation analysis.
Figure 14. Seasonal changes in methyl mercury (▲), total mercury (■), and the methyl mercury to total mercury ratio (as a percent)(♦) in surficial sediment (0-0.5 cm) of the Bay-Delta. Methyl mercury (ppb) and methyl mercury to total mercury ratio (as %) share the primary y-axis. Total mercury is on the second y-axis (log scale). Error bars represent analytical uncertainty rather than field duplication.
Figure 15. Methyl mercury and total mercury concentration of surficial sediment samples collected at Franks Tract (□), White Slough (∆), Connection Slough (x), Prospect Slough (○), Cosumnes River ( ), and Sherman Island (●). Red markers indicate samples collected during the seasonal peak of in situ methyl mercury production. A positive correlation between methyl mercury and total mercury is shown only for samples collected at Sherman Island (regression coefficient of R2 = 0.40).
Figure 16. Three panels showing total mercury concentration, methyl mercury concentration, and the methyl mercury to total mercury ratio (as a percent) in unsieved surficial sediments collected from coastal and Sierra lakes, mountain streams, and valley streams. Dark colored bars are from the coastal range and light colored bars are from the Sierra range. Each bar is the averaged value of many locations within a particular classification. The error bars are the standard error of samples within a particular classification.
Figure 17. Three panels showing total mercury concentration, methyl mercury concentration, and the methyl mercury to total mercury ratio (as a percent) in sieved surficial sediments collected from coastal and Sierra lakes, mountain streams, and valley streams. Dark colored bars are from the coastal range and light colored bars are from the Sierra range. Each bar is the averaged value of many locations within a particular classification. The error bars are the standard error of samples within a particular classification.
Figure 18. Methyl mercury concentrations in surficial sediments collected from three wetland areas and one control area outside the wetland area. Dark colored bars are from the interior of the wetlands, medium colored bars are mid way between the interior and fringe of the wetland, and the light colored bars are from the outer fringe of the wetland areas. The bars represent the average of field duplicates and the error bars are the range of field duplicates.
Mandeville Cut 14 mile Slough Webber Point Control
MM
Hg/
HgT
(%)
Figure 19. Methyl mercury to total mercury ratio as a percent in surficial sediments collected from three wetland areas and one control area outside the wetland area. Dark colored bars are from the interior of the wetlands, medium colored bars are mid way between the interior and fringe of the wetland, and light colored bars are from the outer fringe of the wetland areas. The bars represent the average of field duplicates and the error bars are the range of field duplicates.