Mercury in Western Mountains

1. Mercury in Western Mountains Mark Williams, CU-Boulder

2. Problem Statement • Concern for mercury arose from human health effects caused by mercury ingestion from freshwater and marine fish, in which mercury bioaccumulates • Documented bioaccumulation of mercury in fish has occurred in many high elevation lakes in Sweden (Johansson et al., 1995) • In 1998, five water bodies in Colorado were put on the EPA section 303(d) list for impaired water bodies – Hg content in fish exceeded advisory levels of 0.5mg kg-1

3. MERCURY and BRAIN FOOD • Mercury is toxic to the developing fetal brain • Exposure to mercury in the womb can cause learning deficiencies and delay mental development in children

5. Mercury in the Environment • In a recent EPA report to Congress (1994), they pointed to coal fired utilities as the major anthropogenic source of mercury • It is suggested that deposition of mercury and organochlorines may increase with elevation because of cold condensation and orographic precipitation (grasshopper effect) • This may be cause for concern in warm mid-latitude climates where water resources fall mainly in the form of snow (70%)

6. MeHg is toxic form

7. Forms of Mercury (Hg) • Elemental (inorganic) mercury • Total mercury • Dissolved mercury (Hg content after filtering) • Less toxic form of mercury • Methylmercury (MeHg) • Toxic • Produced by bacterial transformations of inorganic Hg to MeHg • Anoxic conditions appear to increase rate of MeHg

8. NOT A PROBLEM IN THE WEST?

9. Mercury Loading in Wetfall

10. Mast et al. 2006: ROMO Hg

11. Mercury Deposition • 10 g m-2 yr-1 • Higher than Buffalo Pass MDN for 2001-02 • Similar to midwest, NE US with Hg warnings • Summer deposition 3-4 times > winter • Basin export about 2 g m-2 yr-1 • Basin accumulation about 80% of wet dep • MeHg: little export

12. Hg export greatest on rising limb

13. Total Hg concentrations in stream waters track DOC • Little MeHg export • What does occur is on rising limb • Loch Vale catchment

14. High correlation between THg and DOC (Loch outlet)

15. Summary • Atmospheric dep of Hg high because of moderate concentrations with high precip • 80% of atm dep retained in basin • Basins accumulating mercury • Hg export limited by DOC production • > 50% of annual Hg export during first 6 weeks of snowmelt from flushing of soils • -Flowpaths important! • MeHg production (the bad stuff) appears limited

16. Paleorecords: Mercury Accumulation in Alpine Lakes, Colorado David Manthorne, USGS Mark Williams, CU-Boulder

17. MOUNTAINS ENHANCE MERCURY PROBLEMS • Snowfall increases with elevation • Mercury deposition may increase with altitude • Mercury transport associated with carbon • Carbon transport increases during snow melt • Mercury transport from soils to lakes may be greater than in catchments without snow melt • Increasing nitrogen deposition • May increase lake productivity • May increase mercury sequestration in lakes

18. Study Objectives • To compare wet vs. freeze-dried methods • To evaluate trends in mercury accumulation in alpine lakes of Colorado • Place these results in context by comparing to other sites • Evaluate other factors that may worsen Hg accumulation in Colorado lakes: • Cold-condensation • Increasing Hg deposition with elevation • Snow melt • Increased carbon production from N deposition • Fires

20. Pristine Lake Hayden, Craig Black Lake Green 4,5 Denver Navajo Lake Navajo, San Juan PP Sulfate deposition Sulfate/Mercury emissions (1,000/yr SO2)

21. Lake Sediment Cores - Sample Collection • Lake sediment cores were collected with gravity corer from each lakes deepest point • Samples were extruded in the field in .5 to 1cm intervals • Samples were kept cold until they could be frozen • Wet and freeze-dried samples were digested and analyzed with CVAFS

22. Methods • Lake sediments were dated with 210Pb activity • Sediment mass accumulation was calculated as the dry weight per section and years each section represented • Hg mass flux per section calculated as Hg concentration times sediment accumulation • Hg flux ratios were calculated as surface Hg flux divided by background Hg flux

23. Navajo Lake Concentrations Black Lake Concentrations Digestion Comparison - Concentrations

24. Dating sediments • What we have is the depth where the sediments were collected • Use lead-210 (210Pb) values to date the various depths of each individual core • Correlate lead-210 values with sediment depth for each core • Convert sediment depth in core to age

25. Hg Concentrations in Sediment

26. Sediment Accumulation Rates

27. 1825 Hg Flux Ratio = 4.4

28. 1821 Hg Flux Ratio = 4.0

29. Hg Flux Ratio = 3.8 1841

30. 1984 Hg Flux Ratio = 3.2 1856

31. 1988 1968 1856 Hg Flux Ratio = 3.0

32. Mass Flux Ratios • Divide present-day mercury fluxes by pre-industrial mass fluxes • Pre-industrial defined as prior to 1850 • Take average of pre-1850 fluxes • Present-day harder to say; maybe last ten years? • Normalizing the percent increase in mercury fluxes against background values

35. Front Range Lakes – Historical trends

36. MERCURY DEPOSITION INCREASING IN FRONT RANGE • Highest rates of mercury accumulation in history are now • Mercury accumulation will get worse before it gets better • Front Range lakes and reservoirs at risk • Brown cloud?

37. West Side Lakes – Recent Decline?

38. POWER PLANTS ??? • Unclear why max rates have declined since mid-60’s • Difficult to obtain information on emissions • Stack heights increased? • Future trends unclear

39. SOUTHWEST CO: COMPROMISED DATA • Mining activity comprised data • USGS snow survey: highest mercury content in SW CO • Need additional samples

40. NUTRIENT ENRICHMENT PRISTINE LAKE

41. NUTRIENT ENRICHMENT ENHANCES Hg IN LAKES

42. POWER PLANT EMISSIONS • Mercury sources • Nitrogen sources • Stimulate algal production in lakes • Enhanced lake productivity increases mercury sequestration • More mercury enters the food chain

43. Mast (unpublished), 2001 Mercury and DOC in Streamwaters

44. CARBON and MERCURY • TOC/DOC increases mercury transport to lakes and reservoirs • DOC increases production of MMHg • DOC mobility increases during snow melt • Alpine areas at risk

45. MERCURY AND WILDFIRES: A SMOKING GUN? • 95% of mercury stored in biomass volatilized • 90% as elemental Hg • 10% with aerosols • Biomass burning may account for 25% of global emissions • Large increase after wildfires?

46. CABALLO RESERVOIR: NM • 2,930 ha burned in ’95 • THg increased 650% • MMHg up 3,000 % • TOC up 600% • Ratio of MMHg to THg up 1,000 % • FIRES INCREASE DELIVERY OF Hg TO RESERVOIRS

47. Summary • Mercury loadings are elevated in alpine lakes geographically distributed throughout Colorado • Mercury loadings in all 5 lakes are more than 2x current global background • Mercury loadings in lake sediments are comparable to impacted states such as Minnesota and Wisconsin

48. Summary 2 • Mercury accumulation in Front Range lakes is increasing with time • Mercury accumulation on Western Slope more difficult to evaluate

49. Summary 3 • Snow melt runoff increases mercury and DOC transport to lakes • Nitrogen fertilization from atmospheric deposition increases lake production of DOC • DOC is coupled with mercury transport to lakes, mercury sequestration in lakes, and production of MMHg

50. Summary 4: FIRE • Increases mercury availability • Produces DOC • Produces nutrients: N, P • Changes hydrologic flowpaths to increase transport of DOC, N, P, and Hg to lakes • Causes lake eutrophication, enhancing MMHg production and THg sequestration