Prepared in cooperation with the Bureau of Land Management

Environmental Assessment of Water, Sediment, and Biota 

Collected from the Bear Creek Watershed, Colusa County, 

California

By James J. Rytuba, Roger L. Hothem, Brianne E. Brussee, Daniel N. Goldstein, and Jason T. May

Open-File Report 2013–1070

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

SALLY JEWELL, Secretary

U.S. Geological Survey

Suzette M. Kimball, Acting Director

U.S. Geological Survey, Reston, Virginia: 2015

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Suggested citation:

Rytuba, J.J., Hothem, R.L., Brussee, B.E., Goldstein, D.N., and May, J.T., 2015, Environmental assessment of 

water, sediment, and biota collected from the Bear Creek watershed, Colusa County, California: U.S. Geological 

Survey Open-File Report 2013–1070, 83 p., http://dx.doi.org/10.3133/ofr20131070.

ISSN 2331-1258 (online)
iii

Contents

Introduction................................................................................................................................................................. 1

Background and Objectives .................................................................................................................................... 1

Mining History and Geology........................................................................................................................................ 2

Rathburn-Petray Mine............................................................................................................................................. 2

Sample Locations and Methods.................................................................................................................................. 2

Sample Locations and Conditions: Water and Sediment ........................................................................................ 2

Sample Locations and Conditions: Biota................................................................................................................. 3

Field Sampling Methods ............................................................................................................................................. 3

Sediments ............................................................................................................................................................... 3

Water ...................................................................................................................................................................... 4

Biota........................................................................................................................................................................ 4

Invertebrates ....................................................................................................................................................... 5

Fish ..................................................................................................................................................................... 5

Sample Shipment.................................................................................................................................................... 6

Analytical Methods...................................................................................................................................................... 6

Sediments ............................................................................................................................................................... 6

Waters..................................................................................................................................................................... 6

Biota........................................................................................................................................................................ 7

Statistics.................................................................................................................................................................. 9

Results and Discussion .............................................................................................................................................. 9

Hg and MMeHg in waters........................................................................................................................................ 9

Hg and MMeHg in sediments................................................................................................................................ 10

Water Chemistry and Stable Isotopes................................................................................................................... 12

Biota...................................................................................................................................................................... 13

Invertebrates ..................................................................................................................................................... 13

Fish ................................................................................................................................................................... 14

Conclusions .............................................................................................................................................................. 15

Acknowledgments..................................................................................................................................................... 16

References Cited...................................................................................................................................................... 16

Tables

 1. Sample locations and selected parameters for waters collected from Bear Creek, Colusa County, 

California. .................................................................................................................................................... 19

 2. Sampling sites for biota within the Bear Creek watershed (NAD 83)........................................................... 21

 3. Mercury and monomethylmercury concentrations in waters and sediment collected from Bear Creek, 

Colusa County, California............................................................................................................................ 22

 4. Concentration of anions and selected cations in filtered water collected from Bear Creek, Colusa County, 

California. .................................................................................................................................................... 24

 5. Mercury and associated major and minor elements in sediment, precipitates, Bear Creek, Colusa County, 

California. .................................................................................................................................................... 26

 6. Major- and minor-element concentrations in unfiltered waters collected from Bear Creek, Colusa County, 

California. ICP-MS results (ICP-AES for major elements). .......................................................................... 30

 7. Major- and minor-element concentrations in filtered waters collected from Bear Creek, Colusa County 

California. ICP-MS results (ICP-AES for major elements). .......................................................................... 37
iv

 8. Enrichment of stable isotopes in unfiltered waters collected from Bear Creek, Colusa County, California. . 44

 9. Wet weight concentrations of total mercury (HgT) and monomethyl mercury (MMeHg) in invertebrates from 

sites in the Bear Creek Watershed, June and September 2010. ................................................................. 45

10. Wet weight concentrations of total mercury (HgT) and monomethyl mercury (MMeHg) in California roach 

(Hesperoleucus symmetricus) from sites in the Bear Creek Watershed, June and September 2010.......... 48

Figures

 1. Bear Creek Watershed with locations of mines, springs, and locations of samples sites for water, sediment, 

and biota. Locations of figures 3 and 4 are indicated on this figure. ............................................................ 53

 2. Geological map and ore deposits and geothermal springs located in the Clear Lake volcanic field, including 

the Bear Creek watershed. Wilbur Springs and adjacent Hg and Au deposits and geothermal springs in the 

Sulphur Creek tributary are significant sources of Hg to Bear Creek........................................................... 54

 3. Geology and Hg and Au deposits located in the Sulphur Creek tributary to Bear Creek. Geothermal springs 

adjacent to the ore deposits are actively depositing Hg and Au and are sources of Hg-enriched sediment to 

Bear Creek. ................................................................................................................................................. 55

 4. Location of the Rathburn and Petray Hg mines and tributaries 15 that drain the mine area and release Hgenriched sediment into Bear Creek. Some saline cold springs along the Bear Fault release Hg into Bear 

Creek. Cold carbonate springs east of the Petray Mine have relatively low concentrations of Hg as does 

the saline Cain Spring located east of Bear Creek. Sample site 2 located upstream of the mine input and 

sample site 3 located downstream from the mine area are shown by red dots............................................ 56

 5. View of sample site BC1 located under Brim Road bridge during low flow conditions sampling on 

September 16, 2010. Biota were not collected at this site in 2010............................................................... 57

 6. View of sample site BC2 located at the bridge upstream from the Rathburn and Petray mines. Samples 

were collected under this bridge during low conditions during the September 16, 2010 sampling event. 

Biota were collected here on June 29 and September 15, 2010.................................................................. 58

 7. View of Bear Creek during low conditions on September 16, 2010 of sample site BC3 located downstream 

from the Rathburn and Petray mines. Biota were collected here on June 29 and September 15, 2010...... 59

 8. View of Bear Creek at water/sediment site BC4 during low conditions on September 16, 2010. The biota 

site BC4, located about 800 m upstream of the water/sediment site, was sampled on June 29 and 

September 15, 2010. Both sites are downstream from the Rathburn and Petray mines and upstream from 

Sulphur Creek.............................................................................................................................................. 60

 9. Water/sediment sample site BC5 located in Sulphur Creek where several hot spring vents occur in and 

adjacent to the creek. The white material is elemental sulfur, and the black sediment is fine grained iron 

sulfide that contains HgS, which is deposited from the thermal water. View is during low conditions on 

September 16, 2010. ................................................................................................................................... 61

10. Biota sites BC5 and BC6, sampled on June 29 and September 17, 2010................................................... 62

11. View of Bear Creek downstream during low conditions on September 16, 2010 at sample site BC7 located 

downstream from the confluence with Sulphur Creek. Biota were collected at this site on June 29 and 

September 15, 2010. ................................................................................................................................... 63

12. View of Bear Creek during low conditions on June 15, 2010 at the water/sediment sample site BC8, 

located 300 m upstream from Highway 20 bridge crossing. The biota BC8 sample site is located at the 

bridge and was sampled on June 15 and September 15, 2010................................................................... 64

13. View of Bear Creek during low flow conditions on June 15, 2010 at water/sediment sample site BC9. Biota 

were sampled at a site about 80 m downstream near the Thompson Canyon bridge on June 15 and 

September 15, 2010. ................................................................................................................................... 65
v

14. View of Bear Creek during low conditions on September 16, 2010 at sample site BC10 about 60 m 

upstream from confluence with Cache Creek. Exposures of bedded siltstone and shale of the Great Valley 

Sequence occur in the creek. Biota were also collected at this site and further upstream on June 15 and 

September 15, 2010. ................................................................................................................................... 66

15. Plot showing Mean daily flows in Cache Creek in cubic feet per second over a three-year period beginning 

in January 2009. Flows were measured at the USGS Gaging Station in Cache Creek, downstream of Bear 

Creek at the Rumsey Bridge........................................................................................................................ 67

16. Logarithmic-scale plot showing concentrations of total mercury (HgT) in water collected from sample sites 

in Bear Creek watershed, Colusa County, California, moving downstream to the right on the x-axis.......... 68

17. Logarithmic-scale plot showing concentrations of filtered mercury (HgF) in water collected from sample 

sites in Bear Creek watershed, Colusa County, California, moving downstream to the right on the x-axis.. 69

18. Logarithmic-scale plot showing concentrations of MMeHg in water collected from sample sites in Bear 

Creek watershed, Colusa County, California, moving downstream to the right on the x-axis. ..................... 70

19. Map showing concentrations of Hg in sediment collected from Bear Creek and Sulphur Creek, Colusa 

County, California, in June 2010. The increase in Hg in Bear Creek sediment downstream from Sulphur 

Creek is about five times greater than the increase in Hg in sediment downstream from the RathburnPetray Input. ................................................................................................................................................ 71

20. Map showing concentrations of Hg in sediment collected from Bear Creek and Sulphur Creek, Colusa 

County, California, in September 2010. The increase in Hg in sediment is significantly greater after the 

Sulphur Creek saline input enters Bear Creek than the increase associated with the mine input at sample 

site BC3....................................................................................................................................................... 72

21. Map showing MMeHg levels in sediments collected from Bear Creek and Sulphur Creek, Colusa County, 

California, in June 2010. Figure shows high rates of methylation occurring downstream from the mine, and 

further downstream in Bear Creek at sites BC8 and 9................................................................................. 73

22. Map showing MMeHg levels in sediments collected from Bear Creek and Sulphur Creek, Colusa County, 

California, in September 2010. Figure shows high rates of methylation at sample site BC4 downstream 

from the mine input, as well as at sample site BC9 in downstream Bear Creek. ......................................... 74

23. Logarithmic-scale plot showing concentrations of Hg and MMeHg in sediment collected from sample sites 

in Bear Creek watershed, Colusa County, California, moving downstream to the right on the x-axis.......... 75

24. Logarithmic scale plot showing concentrations of Chloride, Sulfate, and Filtered Mercury moving 

downstream in Bear Creek and Sulphur Creek, Colusa County, California. ................................................ 76

25. Logarithmic scale plot showing concentrations of Chloride, Sulfate, and Filtered Mercury moving 

downstream in Bear Creek and Sulphur Creek, Colusa County, California. ................................................ 77

26. Plot of isotopic composition of waters in Bear Creek and Sulphur Creek, Colusa County, California, which 

shows that the waters do not fall along the meteoric water line and are, thus, a mixture of connate water, 

thermal water, and meteoric water............................................................................................................... 78

27. Plot showing changes in groundwater input and HgT and HgF concentration in low-flow condition waters 

collected from Bear Creek, Colusa County, California................................................................................. 79

28. Seasonal comparisons for damselfly and dragonfly larvae collected from Bear Creek during June and 

September 2010. ......................................................................................................................................... 80

29. Monomethyl mercury concentrations in three families of dragonflies collected from Bear Creek in 

September 2010. ......................................................................................................................................... 81

30. Adjusted mean HgT concentrations and 95% confidence limits by site and season for California Roach 

collected from the Bear Creek Watershed during 2010. .............................................................................. 82

31. Adjusted mean MMeHg concentrations and 95% confidence limits by site and season for California Roach 

collected from the Bear Creek Watershed during 2010. . ............................................................................ 83
vi

Conversion Factors

Inch/Pound to International System of Units

Multiply By To obtain

Length

inch (in) 2.54 centimeter (cm)

inch (in) 25.4 millimeter (mm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Area

acre 4,047 square meter (m2)

acre 0.004047 square kilometer (km2)

square mile (mi2) 259.0 hectare (ha)

square mile (mi2) 2.590 square kilometer (km2) 

Volume

cubic inch (in3) 0.01639 cubic centimeter (cm3) 

cubic foot (ft3) 28.32 cubic decimeter (dm3) 

cubic foot (ft3) 0.02832 liter (L)

cubic yard (yd3) 0.7646 cubic decimeter (dm3) 

cubic mile (mi3) 4.168 cubic meter (m3) 

acre-foot (acre-ft) 1,233 cubic meter (m3) 

acre-foot (acre-ft) 0.001233 cubic kilometer (km3) 

Mass

gram (g) 0.03527 ounce, avoirdupois (oz)

Kilogram (kg) 2.205 pound, avoirdupois (lb)

microgram (μg) 0.0000000353 ounce, avoirdupois (oz)

milligram (mg) 0.0000353 ounce, avoirdupois (oz)

nanogram (ng) 0.0000000000353 ounce, avoirdupois (oz)

ounce, avoirdupois (oz) 28.35 gram (g) 

pound, avoirdupois (lb) 0.4536 kilogram (kg) 

Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as °F = (1.8 × °C) + 32.

Temperature in degrees Fahrenheit (°F) may be converted to degrees Celsius (°C) as °C = (°F – 32) / 1.8

Concentrations of chemical constituents are given in micrograms per gram (μg /g).

Datum

Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83).
vii

Abbreviations

μg Micrograms

ANCOVA Analysis of covariance

Au Gold

B Boron

BaSO4 Barium sulfate (barite)

C Celsius (degrees)

CaCO3 Calcium carbonate 

Calcines Products of roasting ore

CDFG California Department of Fish and Game

CERCLA Comprehensive Environmental Response, Compensation, and Liability Act

Cl- Chloride

CRM Certified reference material

CVAAS Cold vapor atomic absorption spectroscopy

CVAFS Cold vapor atomic fluorescence spectroscopy

CV-GC-AFS cold vapor-gas chromatography-atomic fluorescence spectrometry

CVRWQCB Central Valley Regional Water Quality Control Board

DOC Dissolved organic carbon

Fe Iron

GC Gas chromatographic

GMWL Global meteoric water line

HCl Hydrochloric acid

HDPE High-density polyethylene

Hg Mercury; generic shorthand for mercury; does not denote speciation.

Hg(II) Mercury salt

HgF Total mercury (inorganic plus organic) in a filtered sample (either 0.1 μm or 0.45 μm, as 

specified in text)

HgS Mercury sulfide (cinnabar)

HgT Total mercury (inorganic plus organic)

H2SO4 Sulfuric acid 

HCl Hydrochloric acid

HNO3 Nitric acid 

ICP-AES Inductively couple plasma-atomic emission spectrometry

ICP-MS Inductively coupled plasma-mass spectrometry

K Potassium

Li Lithium

LCS Laboratory control samples

MDL Mean detection limit

MMeHg Monomethylmercury (also known as methylmercury and monomethyl mercury 

(CH3Hg+))

N Number of samples

Na Sodium

NAWQA National Water-Quality Assessment

NBS National Bureau of Statistics

NIST National Institute of Standards and Technology
viii

ng/g Nanogram per gram, equivalent to one (1) part per billion

ng/L Nanogram per liter, approximately equivalent to one (1) part per billion

ORP Oxidative-reductive potential

ppm Parts per million, equivalent to mg/kg or μg/g

QAQC Quality assurance/Quality Control

Rb Rubidium

RPD Relative percent difference

RSI Removal Site Investigation

S Sulfur

SC Specific (electrical) conductivity, reported in units of millisiemens per centimeter 

(mS/cm) or microsiemens per centimeter (μS/cm).

Sc Scandium

Se Selenium

SLAP Standard Light Antarctic Precipitation

SnCl2 Stannous chloride

SO4 Sulfate

SOP Standard Operation Procedure

Sr Strontium

TSS Total Suspended Sediment

USBLM U.S. Bureau of Land Management

USBM U.S. Bureau of Mines

USEPA U.S. Environmental Protection Agency

USGS U.S. Geological Survey

VSMOW Vienna Standard Mean Ocean Water

W Tungsten

ww Wet weight
Environmental Assessment of Water, Sediment, and Biota 

Collected from the Bear Creek Watershed, Colusa County, 

California

By James J. Rytuba,1 Roger L. Hothem,2 Brianne E. Brussee,

2 Daniel N. Goldstein,1 and Jason T. May3

Introduction

Background and Objectives

The Cache Creek watershed lies within California’s North Coast Range, an area with abundant 

geologic sources of mercury (Hg) and a long history of Hg contamination (Rytuba, 2000). Bear Creek, 

Cache Creek, and the North Fork of Cache Creek are the major streams of the Cache Creek watershed, 

encompassing 2978 km2 (fig. 1). The Cache Creek watershed contains soils naturally enriched in Hg as 

well as natural springs (both hot and cold) with varying levels of aqueous Hg (Domagalski and others,

2004, Suchanek and others, 2004, Holloway and others 2009). All three tributaries are known to be 

significant sources of anthropogenically derived Hg from historic mines, both Hg and gold (Au), and 

associated ore storage/processing sites and facilities (Slotton and others, 1995, 2004; CVRWQCB,

2003; Schwarzbach and others, 2001; Gassel and others, 2005; Suchanek and others., 2004, 2008a, 

2009) (fig. 2). Historically, two of the primary sources of mercury contamination in the upper part of

Bear Creek have been the Rathburn and Petray Hg Mines.

The Rathburn Hg mine was discovered and initially mined in the early 1890s. The Rathburn and 

the more recently developed Petray open pit mines are localized along fault zones in serpentinite that 

has been altered and cut by quartz and chalcedony veins (fig. 3). Cold saline-carbonate springs are 

located perepheral to the Hg deposits and effluent from the springs locally has high concentrations of 

Hg (Slowey and Rytuba, 2008). Several ephemeral tributaries to Bear Creek drain the mine area which 

is located on federal land managed by the U.S. Bureau of Land Management (USBLM). The USBLM 

requested that the U.S. Geological Survey (USGS) measure and characterize Hg and other geochemical 

constituents in sediment, water, and biota to establish baseline information prior to remediation of the 

Rathburn and Petray mines. Samples sites were established in Bear Creek upstream and downstream 

from the mine area. This report is made in response to the USBLM request, the lead agency mandated to 

conduct a Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) -

Removal Site Investigation (RSI). The RSI applies to the possible removal of Hg-contaminated mine 

waste from Bear Creek. 

 1

U.S. Geological Survey, Menlo Park, California.

2

U.S. Geological Survey, Dixon, California.

3

U.S. Geological Survey, Sacramento, California.
2

This report summarizes data obtained from field sampling of water, sediment, and biota in Bear 

Creek, above input from the mine area and downstream from the Rathburn-Petray mine area to the 

confluence with Cache Creek. Our results permit a preliminary assessment of the chemical constituents 

that could elevate levels of monomethyl Hg (MMeHg) in Bear Creek and its uptake by biota and 

provide baseline information for comparison to conditions after mine remediation is completed.

Mining History and Geology

Rathburn-Petray Mine

The Rathburn Hg mine was discovered and initially mined in the early 1890s. The Rathburn and 

the more recently developed Petray open pit mines are localized along fault zones in serpentinite that 

has been altered and cut by quartz and chalcedony veins. Cinnabar is the primary ore mineral, and 

metacinnabar has been identified in sediment derived from the Petray mine. The Hg ores formed in a hot 

spring system in the steam-heated environment present above a boiling groundwater table. However, no 

active hot springs are present in the deposits but cold saline-carbonate springs are present adjacent to the 

northeast of the Petray Hg mine and may reflect the waning stage of the mercury hydrothermal system 

(Slowey and Rytuba, 2008). The Rathburn Hg mine is relatively small, having produced 100 flasks of 

Hg. Mining in the late 1960s and early 1970s recovered about 400 flasks of Hg from the Petray open pit 

mine (USBM, 1965). At the Rathburn Mine, Hg ores were processed in a brick retort, and small 

amounts of calcines are present that contain up to 1,020 ppm Hg (Churchill and Clinkenbeard, 2002; 

Slowey and Rytuba, 2008). Waste rock derived from open cuts (in altered serpentinite) contains less 

than 39 ppm total Hg (HgT). Ores from the Petray Mine were processed offsite in a rotary furnace at the 

Abbott Mine, and, as a result, there are no mine tailings at the Petray mine. 

Sample Locations and Methods

Sample Locations and Conditions: Water and Sediment

Samples were collected to assess the concentration of Hg and biogeochemically relevant 

constituents in water and sediment in Bear Creek. Water and sediment were sampled from Bear Creek 

both upstream and downstream from the Rathburn and Petray mine sites (fig. 4). In addition, samples 

were collected from Sulphur Creek, a tributary to Bear Creek (fig. 3). Sample-site locations are shown 

in figures 1 and 4 and listed in table 1. Sample site BC1 is located in Bear Creek at the Brim Road 

bridge upstream of the tributary input from the mine area and is representative of background conditions 

in the watershed (figs. 1 and 5). The collection site was under the county road bridge on public land. 

Sample site BC2 is located in Bear Creek just upstream of the tributary input from the Rathburn-Petray 

mine area (figs. 4 and 6). Sample sites BC3 (figs. 4 and 7) and BC4 (figs. 1 and 8) are located in Bear 

Creek downstream from the mine input but upstream from the confluence with Sulphur Creek. Sample 

sites BC5 and BC6 are located in Sulphur Creek (figs. 1, 9-10). Sample site BC7 is located in Bear 

Creek, just downstream from the confluence with Sulphur Creek (figs. 1 and 11). Sample sites BC8 (fig. 

12), BC9 (fig. 13), and BC10 (fig. 14) are in the lower reach of Bear Creek, with sample site BC10 

located just upstream from the confluence with Cache Creek. Water and sediment were collected during 

five sampling events from 2009 to 2011 (table 1).

Samples were collected under low- and high-flow conditions in 2009, 2010, and 2011 during 

five separate sampling events. Site numbers in 2009 differed from those in 2010 and 2011. 09BC1 was 
3

the same site as 10BC2, 09BC2 was the same site as 10BC3, and 09BC5 was the same site as 10BC4. 

Flows in Cache Creek at Rumsey Bridge, just downstream from the confluence with Bear Creek are 

shown in figure 15. Upper Cache Creek and Bear Creek account for most of the flow in Cache Creek at 

Rumsey Bridge, thus we use Cache Creek flows as measured at Rumsey Bridge to give an indication of 

flows in Bear Creek. The first sampling event in this study occurred in January 2009 under low-flow 

conditions—flows during this sampling event were the lowest of the five events in this study. Flows

were high during the second sampling event, in June 2010, as the Cache Creek watershed experienced 

an extended rainy season from winter 2009 through summer 2010. The third sampling event occurred 

during September 2010, and flows during this event were considerably lower than flows during the June 

2010 event. The fourth sampling event occurred in March of 2011 during a severe storm, and the flows

in upper Cache Creek were among the highest recorded since 2006. The fifth and final sampling event 

took place in June 2011 under high-flow conditions, as the watershed experienced another extended wet 

period in early summer 2011.

Sample Locations and Conditions: Biota

Samples were collected to assess the concentration of Hg and MMeHg in biological samples 

collected from Bear Creek, both upstream and downstream from the Rathburn and Petray mine sites, 

and from Sulphur Creek during June and September 2010. Sample-site locations are shown in figure 1 

and listed in table 2. Biological samples were not collected from BC1 because the landowner refused to 

allow access to the site. Sample site BC2 is co-located with the water and sediment sampling site in 

Bear Creek at a bridge just upstream of the tributary input from the Rathburn-Petray mine area (fig. 6).

Biological sample site BC3 (fig. 7) is co-located with the water and sediment sampling site downstream 

of the input from the Rathburn and Petray mines and cold saline springs. Biological site BC4 (fig. 8) is 

located in Bear Creek about 2.9 km downstream from BC3 and about 2.2 km upstream from the 

confluence with Sulphur Creek. The biota BC4 site was about 800 m upstream from the BC4 site 

sampled for water and sediment. Biota sample site BC5 is located in Sulphur Creek, about 420 m 

upstream from the water/sediment site BC5. BCUS is a biota sample site located at a pool on Sulphur 

Creek about 230 m upstream of biota sample site BC5 (no water or sediment sampled there), and BC6 is

a site co-located in Sulphur Creek with a water/sediment site (fig. 10). Sample site BC7 is located in 

Bear Creek, just downstream from the confluence with Sulphur Creek (fig. 11). Sample sites BC8 (fig. 

12), BC9 (fig. 13), and BC10 (fig. 14) are downstream in Bear Creek (fig. 1), and all were within 300 m 

or less of the water and sediment sites. 

Field Sampling Methods

Sediments

Wet-sediment samples were collected from Bear Creek sites and placed in polycarbonate jars 

(100 ml capacity) for analysis of total Hg (HgT) and MMeHg. The samples were frozen with dry ice 

immediately after collection (freezing time approximately 10–20 minutes) and kept frozen until shipped 

overnight on dry ice to the analytical laboratory. The temperature of samples arriving at the analytical 

facilities remained below freezing, which is within the limits specified in USEPA Method 1631E.

Another sediment sample was collected in a Ziploc® bag for analysis of major and minor elements and 

was stored at ambient temperature. 
4

Water

Stream-water samples were collected in the field with a peristaltic pump using ultraclean tubing 

and an inline filter with 0.45 μm openings. Filtered water samples were collected for analysis of anions 

by ion chromatography, alkalinity by titration, and major and minor elements using inductively coupled 

plasma-mass spectrometry (ICP-MS) and inductively coupled plasma-atomic emission spectrometry 

(ICP-AES) analysis. An unfiltered sample also was analyzed using both ICP-MS and ICP-AES. 

Samples for major and minor element determinations were acidified to pH<2 with trace-metal 

(Ultrex, J.T. Baker)-grade HNO3 and were stored in acid-washed, high-density polyethylene (HDPE) 

bottles. Subsamples for anion and alkalinity measurements were filtered, stored in HDPE bottles, and 

chilled to approximately 4 °C until analysis, in accordance with USGS protocols for trace metals 

(http://pubs.water.usgs.gov/twri9A).

Samples for DOC analysis were filtered using 0.45-micron disposable borosilicate filters and 

stored in 40-mL amber ICHEM glass vials. Shortly after collection, DOC samples were acidified to pH 

less than 2 with HCl and kept on ice and refrigerated until analyzed.

Samples for stable-isotope analysis were collected as a grab sample directly from the stream into 

clear 40-mL ICHEM glass vials and were stored at ambient temperature until analyzed. 

Water variables, including pH, conductivity, temperature, dissolved oxygen, and oxidationreduction potential (ORP), were measured in the field by placing the probe of a battery-powered 

Hydrolab sonde directly into the flowing stream water.

Samples for HgT and MMeHg analyses were collected with no headspace in trace-metal-freecertified 250-mL bottles Nalgene HDPE). The MMeHg bottles contained a preservative of certified 

ultra-clean HCl provided by the analytical laboratories, Frontier Global Sciences and Brooks Rand 

Labs. Sampling for HgT analysis followed ultra-clean sampling and handling protocols (Bloom, 1995;

Gill and Fitzgerald, 1987) during the collection of field samples and analysis to avoid introduction of 

Hg. Samples were kept on ice until shipped. Samples were shipped on ice packs and arrived the next 

morning at the analytical facilities at temperatures ranging from 1 to 4oC, as specified by USEPA 

Method 1631E to minimize biologically induced phase changes and MMeHg degradation. During every 

sampling event, a field blank was collected by processing ultra-clean water provided by the analytical 

laboratories and collecting the same subsamples (except for alkalinity) following the same procedures as 

used for the field samples. Laboratory blanks and acid blanks were processed periodically to determine 

whether the equipment, containers, reagents, and procedures introduced any significant contamination. 

Biota

Biological samples were collected similar to procedures outlined by Suchanek and others (2010). 

Field forms, sample labels, and laboratory submission forms were prepared and printed prior to 

collecting samples. For examples of such forms, see Scudder and others (2008). California scientific 

collection permits for collections of invertebrates and fish were obtained from the California 

Department of Fish and Game. Landowner permissions were obtained for access to sites located on 

private property or when site access required crossing private property. 

Clean techniques were essential to minimize potential contamination, including contact with 

personnel and equipment. The field methods described here are based on guidelines developed in 

conjunction with the National Water-Quality Assessment (NAWQA) Program, the Toxic Substances 

Hydrology Programs, and researchers from other disciplines in the USGS as described by Scudder and 

others (2008).
5

Biological samples were collected within a short time period (2 weeks or less for invertebrates 

and forage fish) to minimize changes that might affect relative Hg concentrations. In addition, sample 

collection of biota was coordinated with the collection of water and sediment to minimize risk of site 

disturbance and potential water or sediment sample contamination. 

Invertebrates

Aquatic invertebrates can serve as excellent bioindicators of metals contamination (Cain and 

others, 1992). The invertebrates sampled for this study (Merritt and Cummins, 1995) were predatory 

insects, depending on their abundance and availability at sampling sites: larval dragonflies (Order 

Odonata, Suborder Anisoptera, family Gomphidae, Aeshnidae, and Libellulidae), larval damselflies 

(Order Odonata, Suborder Zygoptera, family Calopterygidae, Lestidae, and Coenagrionidae), and adult 

water striders (Order Hemiptera, family Gerridae). Invertebrates were sorted to family and processed as 

single-taxon composites. Alternate species of invertebrates were collected where available to serve as 

functionally equivalent substitutes in case adequate numbers of the primary target invertebrates were not 

available. Field duplicate samples were collected where individuals were sufficiently abundant.

Invertebrate sampling was conducted in June and September to evaluate seasonal differences in 

Hg bioaccumulation. Invertebrates were collected using dip nets and by hand. Samples were separated 

by taxon and placed into Ziploc® bags with native water on wet ice for later sorting. Within 24 hours, 

individuals were sorted by family and placed in disposable dishes using Teflon®-coated forceps or 

gloved-hand. Organisms were rinsed with DI water and patted dry with a clean paper towel. The total 

mass of the composite samples, consisting of 1–120 individuals of the same family, was determined (± 

0.01 g) with an electronic balance. Samples were placed into chemically cleaned glass jars with 

Teflon®-lined lids, stored frozen for no more than 30 days, and were then shipped to Frontier Global 

Sciences for analyses. Composites of whole-body aquatic invertebrates were analyzed for both HgT and 

MMeHg because the ratios of MMeHg to HgT tend to be inconsistent among invertebrate taxa, among 

sites, and among years (Mason and others, 2000; Haines and others, 2003; Wiener and others, 2007).

Fish

Fish were collected using backpack electrofishing techniques described elsewhere (Meador and 

others, 1993; Moulton and others, 2002). Seven to fifteen individual California roach (Hesperoleucus 

symmetricus) of similar length were collected in both spring and fall from the vicinity of sites on Bear 

Creek also sampled for water, sediments, and invertebrates. After capture, fish were placed in a large 

plastic bucket in native water until they could be processed. Guidelines for live specimen handling and 

care are provided in Walsh and Meador (1998); detailed procedures for processing fish are provided by 

Scudder and others (2008). 

Captured fish were held in buckets of native water and were anesthetized using clove oil, placed 

in clean zip-lock bags on wet ice, and then stored frozen until they could be processed, usually within 

24 hours. Individual fish were measured for standard and total length (± 0.5 mm) and the total mass 

determined (± 0.01 g) with an electronic balance. The contents of the gastrointestinal tract were 

removed, and the mass of the remaining sample was determined (± 0.01 g). Each sample was then 

placed in a chemically cleaned glass jar with a Teflon®-lined lid and stored frozen. Seven similar-sized 

fish from each site and both seasons were selected for analysis and sent to the contract laboratory, 

Frontier Global Sciences in Seattle, Washington for HgT and MMeHg analyses within 30 days of 

collection. Fish not selected for analysis were stored frozen as potential backups. 
6

Sample Shipment

Before samples were shipped to the contract laboratory for analysis, all sample data were entered 

on the appropriate sample chain-of-custody forms (included in the packaging), and the analytical 

laboratory was notified to ensure that they could receive the samples. Frozen samples were shipped for 

next-day delivery via FedEx®. A sufficient amount of dry ice was included in the packaging so that a 1-

day delay would not adversely affect the samples. Samples were shipped on 14 July (June samples) and 

7 October (September samples). 

Analytical Methods

Sediments

Multi-element analyses for all sediments were performed in the laboratories of ALS Chemex. 

Bulk samples were ground in a zirconia ring mill and subjected to a near-total four-acid digestion. 

Major elements were determined by ICP-AES. Minor elements, other than Hg, were determined by 

ICP–MS. Hg was determined by cold vapor atomic absorption spectroscopy (CVAAS) following 

methods similar to those described by Crock (1996) and O’Leary and others (1996).

Hg and MMeHg analyses for all wet sediments were done at Frontier Global Sciences and 

Brooks Rand LABS. For total Hg, the sediment was leached with cold aqua regia, followed by stannous 

chloride (SnCl2) reduction, two-stage gold amalgamation, and cold vapor atomic fluorescence 

spectroscopy (CVAFS) detection. MMeHg was obtained by acid bromide/methyl chloride extraction 

followed by aqueous phase ethylation, isothermal gas chromatographic (GC) separation, and CVAFS 

detection (Horvat and others, 1993). Results were reported on both a wet- and dry-weight basis and are 

listed in table 3.

Waters

Alkalinity as CaCO3 was determined in the laboratory by titration with H2SO4, using Gran’s 

technique (Orion Research, Inc., 1978), within 2–4 days after sample collection. Sulfate, chloride, 

nitrate, and fluoride concentrations were determined by ion chromatography (Fishman and Pyen, 1979) 

by the USGS analytical laboratory at the Denver Federal Center. Cations were analyzed by ICP–AES 

and ICP–MS at USGS laboratories at the Denver Federal Center in Denver, Colorado. Duplicate water 

samples, blank samples, and USGS Water Resource Division standard reference waters were analyzed 

with the data set.

At both Frontier Global Sciences and Brooks Rand Labs, samples were handled in a Class-100 

clean-air station that was monitored routinely for low levels of total gaseous Hg. An ultra-clean Hg 

trace-metal protocol was followed, including the use of rigorously cleaned and tested Teflon® equipment 

and sample bottles and prescreened and purified reagents. Laboratory atmosphere and water supply also 

were routinely monitored for low levels of Hg. Primary standards used in the laboratory were NISTcertified, or traceable to NIST-certified materials. Following USEPA Method 1631, MMeHg standards 

were made from pure powder and calibrated against an NBS-3133 certified Hg(II) standard. Standards 

were cross-verified by daily analysis of Certified reference material (CRM) DORM-2 (National 

Research Council of Canada Institute for National Measurement Standards, 1999). Total Hg was 

determined by bromine monochloride (BrCl) oxidation followed by tin(II) chloride (SnCl2) reduction, 

two-stage gold amalgamation, and detection by CVAFS (Bloom and others, 1988). MMeHg was 

liberated from water using an all-Teflon® distillation system. Distilled samples were analyzed using 
7

aqueous phase ethylation with purging onto CarbotrapTM, isothermal GC separation, and CVAFS 

detection (Bloom, 1989). To address accuracy and precision, quality assurance measures were employed 

with the following minimum frequencies: laboratory duplicates, one per ten samples; method blanks, 

three per analytical batch; filtration blanks, one per ten samples; and spike recovery or standard 

reference material, one per ten samples.

Since May 1, 1990, hydrogen-isotope-ratio analyses have been performed using a hydrogen 

equilibration technique (Coplen and others, 1991; Révész and Coplen, 2008a), rather than the zinc 

technique used prior to that date (Kendall and Coplen, 1985). The hydrogen equilibration technique 

measures deuterium activity, whereas the zinc technique measures deuterium concentration.

For the majority of the isotopic samples, the difference in reported isotopic compositions 

between the two techniques is not significant. However, in brines, the difference may be significant 

(Sofer and Gat, 1972, 1975). Reported delta H-2 values of activity are more positive than delta H-2 

values of concentration, and this difference is proportional to molalities of the major dissolved solids. 

Some examples of the differences between activity ratios and concentration ratios for delta H-2 in 1 

molal salt solutions are provided by Horita and others (1993). The data for individual salts may be 

multiplied by molality to obtain adjustments to delta values based on concentration. Water samples are 

measured for delta O-18 using the CO2 equilibration technique of Epstein and Mayeda (1953), which 

has been automated (Révész and Coplen, 2008b). Therefore, both oxygen and hydrogen isotopic ratio 

measurements are reported as activities. Oxygen and hydrogen isotopic results are reported in per mil

relative to VSMOW (Vienna Standard Mean Ocean Water) and normalized (Coplen, 1994) on scales 

such that the oxygen and hydrogen isotopic values of SLAP (Standard Light Antarctic Precipitation) are 

-55.5 per mil and -428 per mil, respectively. The 2-sigma uncertainties of oxygen and hydrogen isotopic 

results are 0.2 per mil and 2 per mil, respectively, unless otherwise indicated. 

Biota

Samples were analyzed for HgT and MMeHg at Frontier Global Sciences, in Seattle, 

Washington. Invertebrate samples were rinsed with reagent water, and blotted with clean laboratory 

wipes prior to being homogenized. Fish were homogenized as whole body fish. Homogenized samples 

were digested for total mercury analysis with concentrated sulfuric and nitric acids according to method 

FGS-011, a modified EPA method 1631, Digestion I. Homogenized samples were digested for 

monomethyl mercury analysis by a heated 25% KOH solution, followed by dilution with methanol, 

according to FGS-010.

Total mercury in digested tissues was analyzed by SnCl2 reduction, dual gold amalgamation, and 

cold vapor atomic fluorescence spectrometry (CVAFS) detection according to FGS-069, a modified 

EPA1631 method. 

Monomethyl mercury in digested tissues was analyzed by gas chromatography-cold vaporatomic fluorescence spectrometry (GC-CV-AFS) (aqueous phase ethylation, isothermal GC separation, 

and CVAFS detection) according to Frontier’s SOP FGS-070, a modified EPA method 1630.

Duplicate samples were analyzed at a rate of 5%, with at least one duplicate per matrix per 

analytical run to estimate the precision of the methods. The range of relative percent differences (RPD) 

for the HgT duplicates (n=8) in spring-season samples was 1.23 to 38.4 percent; one RPD was outside 

the acceptable criterion (RPD <25%). The range of RPD for the invertebrate MMeHg duplicates (n=8) 

in spring samples was 9.27 to 38.7 percent; two results fell outside the acceptable criterion of an RPD < 

25%. In the fall-season samples, the RPDs for HgT (n=6) ranged from 0.663 to 28.4 percent, with one 

sample outside the acceptable criterion. The RPDs for MMeHg in the fall samples (n=6) ranged from 

7.53 to 34.6 percent, with one sample outside the acceptable criterion. The QA/QC results for those 
8

batches with values outside acceptable limits were deemed acceptable based on matrix spike/matrix 

spike duplicate (MS/MSD) and/or laboratory control sample/laboratory control sample duplicate 

(LCS/LCSD) RPD values within control limits.

To assure the accuracy of the methods, procedural blanks, spiked samples, and laboratory 

control samples were analyzed. To assure that no analyte was added during the processing of the 

sample, procedural blanks were analyzed at a rate of 5% of the total samples, with at least one per 

matrix per analytical run. In all blanks for HgT in the spring (n=21) and fall (n=15), and for MMeHg in 

the spring (n=24) and fall (n=21) the analyte was undetected, although included in the analysis. All 

blank results were less than the acceptable criterion of twice the method detection limit.

Matrix spikes were used to verify that the matrix characteristics did not interfere with the 

analytical results. Matrix spike samples and matrix spike duplicates of HgT and MMeHg were analyzed 

at a rate of 5%, with at least one spike per matrix per analytical run. Spiked samples were fortified with 

a known quantity of analyte and analyzed as part of the run. The results were compared with an analysis 

of the original sample with no added spike. If there was no matrix interference, the result of the matrix 

spike should be equivalent to the result of the parent sample plus the amount of chemical added to the 

matrix spike sample.

In the spring samples, the HgT matrix spike and matrix spike duplicate recoveries (n=9) ranged 

from 52.6 to 119 percent, with one sample outside the acceptable criteria of 75-125%. The relative 

percent differences (RPDs) (n=9) ranged from 0.31 to 54.9 percent, with two exceeding the 25% 

criterion. In the fall samples, the HgT spike recoveries (n=8) ranged from 13.4 to 201 percent, with six 

samples outside the acceptable criteria of 75-125%. The RPDs (n=8) ranged from 0.837 to 43.1 percent, 

with only one exceeding the 25% criterion.

In the spring samples, one of the spike recoveries and one of the RPDs were outside acceptance 

limits because the spike concentration was less than one-half the sample concentration, the target spike 

ratio. In the fall samples, the percent recovery for both the matrix and the duplicate were outside the 

established criteria for three samples. Only one of these sets, however, had an RPD > 25. The other two 

sets of recoveries were outside acceptance limits because the spike concentrations were less than onehalf the sample concentration. The analyses that did not meet the target spike ratio were excluded from 

the results. The remaining acceptable matrix spike and matrix spike duplicates were sufficient to verify 

that the matrix did not interfere with the analytical results.

For MMeHg, the matrix spike and matrix spike duplicate recoveries in the spring (n=15) ranged 

from 12.2 to 2560 percent, with RPDs (n=13) ranging from 4.27 to 179 percent. Nine spike or duplicate 

recoveries and six RPD values were outside the acceptable limits (65-130%, and < 25%, respectively). 

The MMeHg spike and matrix duplicate recoveries (n=9) for the fall samples ranged from -1060 to 285 

percent, with 7 falling outside the acceptable criteria of 65-135%. RPDs (n=9) ranged from -75.2 to 75.1 

percent, with 4 exceeding the acceptable criterion of 25%.

The reason that the matrix spike or duplicates (9 in the spring and 7 in the fall) and the RPDs (6 

in the spring and 4 in the fall) were outside the acceptance limits was that spike concentrations were less 

than one-half the sample concentration. The analyses that did not meet the target spike ratio were 

excluded from the results. The remaining acceptable matrix spike and matrix spike duplicates were 

sufficient to verify that the matrix did not interfere with the analytical results.

LCS were analyzed at a rate of 5% to insure that the method worked with naturally incorporated 

mercury. For spring samples, the recovery for HgT in the LCSs (n=14) was 83.1 to 105 percent, within 

the criterion of 75 to 125; for MMeHg, recovery was 70 to 128 percent, within the criterion of 70 to 130 

percent. LCS duplicates (n=7) ranged from 0.25 to 19.9 percent RPD for HgT, and 0.47 to 5.92 percent 

for MMeHg, all within the acceptable criterion of less than 25 percent. For fall samples, recovery for 
9

HgT in the LCSs (n=12) was 104 to 114 percent, within the criterion of 75 to 125; for MMeHg, LCS 

recovery (n=10) was 84.4 to 110 percent, within the criterion of 70 to 130 percent. LCS duplicates 

ranged from 0.438 to 6.61 percent for HgT (n=6), and 0.264 to 13.9 percent for MMeHg (n=5), all less 

than the acceptable limit of 25 percent. 

Statistics

Total Hg and MMeHg concentrations in all matrices (water, sediments, invertebrates, and fish) 

were compared statistically among sites and seasons. Concentrations of MMeHg were compared 

graphically by site and season for composite samples of invertebrates.

All data for both HgT and MMeHg in California roach from Bear Creek were transformed using 

Box-Cox transformations. We used a maximum likelihood method for statistically determining the best 

Box-Cox transformation for a particular dependent variable. Since HgT and MMeHg had different 

distributions, we chose one family of transformations that was flexible enough to accommodate both. 

For the statistical analyses of fish data, we began with a generalized analysis of covariance 

(ANCOVA) that included site, season, total length (TL), and all possible interaction effects. A backward 

selection was performed to remove interaction effects that were not significant for either dependent 

variable. Site, season, TL, and the interaction between TL and site effects were significant. Due to the 

significance of the TL*site interaction, the relationship between TL and mercury varied depending on 

site.

To compensate for the various effects of TL on mercury, sites were compared by adjusting the 

mercury concentrations for TL. A TL of 70 mm was chosen because the median for all the fish was 70.5 

mm and the range of fish sizes at all sites and seasons, except site 7 in the fall, captured this value. 

When all sites were pooled, the mean TL was 71.7 mm, but the site-specific means varied greatly across 

sites, ranging from 53.6 to 82.7 mm. Although fish from site 7 in the fall were all < 60 mm, the 

estimates of HgT and MMeHg concentrations were adjusted to project a mercury value for a 70-mm 

fish. However, since the range of TLs for site-7 data did not capture 70mm, the estimated value is an 

extrapolation. 

Results and Discussion

Hg and MMeHg in waters

HgT levels in unfiltered water under high-flow conditions are generally higher than Hg levels in 

water during low-flow conditions, due to contribution of Hg-contaminated geothermal water and 

sediment from Sulphur Creek, as well as surface runoff from Rathburn-Petray mine wastes that are 

enriched in Hg (fig. 15). HgT levels during the high-flow sampling event in March 2011 exceeded lowflow levels by orders of magnitude at all sample sites in Bear Creek (fig. 16). Flows during this highflow sampling event were unusually high (fig. 15). HgT levels generally increase from a local minimum 

at the background site (BC1) to a local maximum in Sulphur Creek at sites BC5 and BC6, then decrease 

downstream in Bear Creek towards the final sample site BC10. However, HgT levels at downstream 

sample sites (BC7-10) were significantly higher than levels at the upstream sample site (BC1). HgT

concentrations in and downstream from Sulphur Creek were orders of magnitude higher than other HgT

concentrations measured upstream from Sulphur Creek during low-flows.

HgF levels in water under high-flow conditions are comparable to or lower than HgF levels under 

low-flow conditions at most of the sample sites (fig. 17). HgF levels were high during the high-flow 

sampling events in the summer of 2010 and 2011, compared to low-flow HgF levels measured at sites 
10

BC2-4 during the initial sampling event in January 2009. Due to extreme flows and high total suspended

sediment in Bear Creek during the highest-flow sampling event in March 2011, Hg present in the waters

during this event was predominantly particulate. During both high- and low-flow conditions, HgF levels 

generally increased from sample site BC1 to a local maximum at sample sites BC4 and BC7, then 

decreased farther downstream to sample site BC10. HgF levels were significantly higher in Sulphur 

Creek than in Bear Creek. The value of 44 ng/L of dissolved Hg at sample site BC1 during the Sept. 

2010 sampling event is anomalous. Because it is orders of magnitude greater than the result for total Hg 

at the same site, its reliability is questionable.

MMeHg levels in water under high-flow conditions are comparable to MMeHg levels under 

low-flow conditions in the upper part of Bear Creek at sample sites BC1-4 (fig. 18). In the lower part of 

Bear Creek, at sample sites BC7-10, MMeHg levels are considerably higher under high-flow conditions 

than under low-flow conditions. In the upper reach of the watershed, MMeHg levels tend to increase 

from sample site BC1 to sample site BC4. During high-flow conditions, MMeHg levels were highest at 

sample sites BC3 and BC9. Within Sulphur Creek, MMeHg levels are highly elevated at both sample 

sites BC5 and BC6, and MMeHg levels are also elevated in Bear Creek immediately downstream from 

the Sulphur Creek input at sample site BC7. As a percentage of HgT, MMeHg levels are highest during 

low-flow conditions compared to MMeHg levels measured during high-flow conditions. Conditions that 

favor MMeHg production occur during low-flow, warm conditions. During the high-flow sampling 

event in March 2011, MMeHg levels were elevated at sample site BC4, just downstream from the 

Rathburn-Petray mine input.

Hg and MMeHg in sediments

Hg and MMeHg levels in sediments collected from Bear Creek are listed in table 3 and shown in 

figs 19-23. Hg levels in sediments are elevated both downstream from the mine input and more so

downstream from the confluence with Sulphur Creek. During the low-flow sampling event in January 

2009, Hg levels in sediment upstream from the mine area at sample site BC2 were low (80.3 ng/g) (table 

3). However, Hg levels in sediment downstream from the mine area, at sample site BC3, were highly 

elevated (9,290 ng/g for a 0.2 g sample) but decreased downstream in Bear Creek at site BC3. A larger 

BC3 sample, 20 g, has a lower but still high Hg concentration of 1,780 ng/g (table 5) and indicates that 

the 0.2 g sample is anomalously high. Downstream to BC4 the Hg concentration decreased to 

background level.

During the high-flow sampling event in June 2010, Hg levels in sediments collected at sample 

sites BC1 (Brim Road upstream from mine area) and BC2 (upstream from mine area) were both low 

(40.6 and 40.1 ng/g, respectively) (fig. 19). However, sediment collected from Bear Creek at sample site 

BC4, just upstream from the confluence with Sulphur Creek, contained high levels of Hg (2,750 ng/g)

(table 3). Sediments collected in the active channel in Sulphur Creek were very highly elevated in Hg. 

Upstream from the Wilbur hot springs, Hg levels were elevated (2,960 ng/g) in sediments at sample site 

BC5, but downstream from the hot springs Hg levels were extraordinarily high (332,000 ng/g) in 

sediments at sample site BC6 (fig. 19). In Bear Creek downstream from the confluence with Sulphur 

Creek, Hg levels in sediments were elevated at sample sites BC7 and BC8 (1,220 and 1,840 ng/g, 

respectively), but decreased significantly farther downstream at sites BC9 and BC10 but remained 

above background concentrations (171 and 355 ng/g, respectively). 

During the low-flow sampling event in September 2010, the Hg level in sediments collected at 

sample site BC1 (Brim Road upstream from mine area) was low (57.2 ng/g), and the Hg level in 

sediments collected just upstream from the mine area at sample site BC2 were higher but still low (126 

ng/g) (fig. 20). Sediment collected from Bear Creek at sample sites BC3 and BC4, downstream from the 
11

tributaries that drain the Rathburn and Petray mines but upstream from the confluence with Sulphur 

Creek, contained moderately elevated levels of Hg (221 and 254 ng/g, respectively) compared to 

concentrations upstream from the mine area. At sample site BC5, upstream from the Wilbur hot springs 

in Sulphur Creek, Hg levels were elevated (1,920 ng/g). Downstream from the hot springs in Sulphur 

Creek at sample site BC6, the Hg level in sediment was very high (33,500 ng/g), but it was an order of 

magnitude lower than Hg levels measured under June 2010 high-flow conditions at the same sample 

site. Downstream from the confluence with Sulphur Creek, Hg levels in sediments in Bear Creek were 

elevated at sample sites BC7-9 (620-942 ng/g) before decreasing to lower levels at the most downstream 

sample site, BC10 (228 ng/g) (fig. 20). No data were collected for Hg or MMeHg in sedments during 

high-flow sampling in 2011.

MMeHg levels were only measured in Bear Creek sediments during two sampling events in 

2010. In June 2010, under high-flow conditions, MMeHg levels in sediments in upper Bear Creek at 

sites BC1 and BC2 were low (0.067 and 0.069 ng/g, respectively, table 3) (fig. 21). MMeHg levels then 

increased in sediments collected at sample sites BC3 and BC4, downstream from the mine area (0.275 

and 0.591 ng/g, respectively, table 3). Within Sulphur Creek, MMeHg levels were highly elevated. At 

sample site BC5, MMeHg levels in sediment were high (1.52 ng/g), but at sample site BC6, downstream 

from the hot springs, MMeHg levels were extraordinarily high (145 ng/g). MMeHg levels in sediments 

collected in Bear Creek downstream from the confluence with Sulphur Creek were highly variable

depending on the flow conditions. Immediately downstream from the confluence at sample site BC7 and 

in one downstream sample at site BC9, MMeHg levels in sediment were low (0.072 and 0.103 ng/g, 

respectively) (fig. 21). However, at downstream sample sites BC8 and BC10, MMeHg levels in 

sediments were elevated (1.48 and 0.679 ng/g). Under low-flow conditions in September 2010 when 

MMeHg production was expected to be at a maximum, MMeHg levels were low in sediments collected 

at background sample site BC1 upstream from the mine area (0.015 ng/g) (fig. 21). MMeHg levels in 

sediments just above and downstream from the mine area increased at sites BC2 and BC3 (0.245 and 

0.372 ng/g, respectively, table 3) and were highly elevated at sample site BC4 (3.08 ng/g). MMeHg 

levels were elevated in sediments collected at sample sites BC5 and BC6 in Sulphur Creek (0.774 and 

1.17 ng/g respectively), but were orders of magnitude lower than levels measured within Sulphur Creek 

during high-flow conditions. Downstream from the confluence with Sulphur Creek at sample sites BC7-

10, sediments in Bear Creek have moderate to high concentrations of MMeHg (0.222-0.982 ng/g) (fig. 

22).

The percentage of MMeHg relative to total Hg (%MMeHg) in sediments is indicative of the 

overall rate of MMeHg production in the watershed. We calculate %MMeHg as:

%MMeHg = [MMeHg in sediment in ng/g] / [Hg in sediment in ng/g] × 100

The %MMeHg in samples collected in June 2010 from Bear Creek under high-flow conditions was 

highly variable (table 3). Because MMeHg was less variable than Hg, the highest %MMeHg values 

occurred at sample sites where the total Hg in sediment was low. Although MMeHg levels were highly 

elevated in Sulphur Creek, the %MMeHg in these samples was relatively constant. Downstream from 

the confluence with Sulphur Creek, the %MMeHg generally trended to higher concentrations 

downstream to sample site BC10, where %MMeHg was highest during the high-flow sampling event 

(0.19 percent). 

%MMeHg values were similarly variable under low-flow conditions in September 2010. Above 

the mine area, at sample site BC1, %MMeHg values were low (0.03 percent). %MMeHg values 

increased significantly downstream from the mine area in Bear Creek at sample sites BC2 to BC4 (0.19 

to 1.21 percent). Within Sulphur Creek, Hg levels in sediments were high, and thus, %MMeHg levels 

remained as low as 0.003 percent. In Bear Creek downstream from the confluence with Sulphur Creek, 
12

%MMeHg values increased downstream from sample sites BC7 to BC9-10 (0.04 to 0.12-0.16 percent, 

table 3).

Water Chemistry and Stable Isotopes

Bear Creek waters are predominantly Mg-CO3 waters with elevated levels of boron (B), chloride 

(Cl), lithium (Li), sodium (Na), potassium (K), rubidium (Rb), selenium (Se), sulfate (SO4), strontium 

(Sr), and tungsten (W) resulting from input from both hot and cold saline springs from multiple sources 

(tables 4–7). Waters are slightly alkaline (pH 7.6–8.55) due to buffering from interaction with 

serpentinite bedrock. Waters are saline in Bear Creek, both above and below the inputs from the mines

and saline springs, with conductivity ranging from 822 μS/cm above the mine input to 2,723 μS/cm just 

below the confluence with the highly saline geothermal waters derived from hot springs in Sulphur 

Creek (table 1) (figs. 24 and 25).

Cold carbonate springs are present along several faults in the Bear Creek watershed. A large 

number of these springs are localized along the Bear Fault, which is located to the west of Bear Creek 

and east of the Rathburn-Petray mines (fig. 4). These springs consist of variable mixtures of meteoric 

water and saline groundwater derived from connate fluids in sedimentary rocks of the Great Valley 

Sequence. The cold spring waters have a highly variable proportion of saline groundwater, ranging from 

13 to 100 %, with the largest component of saline ground water occurring along the central part of the 

Bear Fault (Slowey and Rytuba, 2008). The springs have exceptionally high conductivities (9,400 to

19,000 μS). The most saline cold spring waters, 6,065 mg/L Cl-, are comparable to saline geothermal 

hot spring waters located in the Sulphur Creek watershed. The cold springs are characterized by high 

concentration of the cations Na, K, Rb, Li, Se, Sr, and W, as well as nitrate, sulfate, and DOC. Plots of 

these cations against Cl- for the various cold springs in the Bear Creek watershed define two-component 

linear mixing lines, indicating that the spring waters are mixtures of meteoric and saline ground water.

Chloride, sulfate, and filtered mercury concentrations in waters are shown in figure 24. Alkalinity is 

relatively high in cold carbonate springs and surface waters that drain the Rathburn-Petray mine area. 

This results from release of carbonate from saline groundwater, and interaction of groundwater with

serpentinite and mafic bedrock of the Coast Range ophiolite and the Franciscan Formation. The 

presence of alkaline pH (> 8.0) indicates that the cold carbonate springs, and some surface waters, with 

a significant component of saline ground water are in aqueous equilibrium with calcium carbonate. At 

Wilbur Springs, several hot spring vents form a coalescing hot spring terrace along the north bank of 

Sulphur Creek. The temperature of the Wilbur Hot Springs geothermal waters ranges as high as 56 oC, 

and the waters have very high concentrations of Cl- (approx.. 13,800 ppm) and B (approx. 275,000

ppb). The concentration of HgT in Sulphur Creek are typically very high but variable seasonally, ranging 

from 3.55 to 11,400 ng/L (fig. 25). However, the value of 3.55 reported for HgT during June 2010 

sampling was less than the value reported for HgF, so we disregard this result as erroneous.

Stable-isotope data from samples collected in the 2011 sampling event indicate that stream water 

in Bear Creek under high-flow conditions is isotopically lighter than under low-flow conditions,

measured in summer of 2010 (table 8 and fig. 26) Because meteoric water is light in δ2

H and δ 18O, 

stream water dominated by meteoric input under the high-flow conditions will be lighter isotopically. 

During the dry summer season, the creek receives an influx of isotopically-heavy saline groundwater

and minimal runoff of meteoric water. The overall trend of these data represents a two-end-member 

mixing system between the isotopically-light meteoric water and the isotopically-heavy saline 

groundwater (figs. 26 and 27). At any given time, the water isotopic chemistry in Bear Creek represents 

a point along this mixing line, depending on the relative dominance of each input. During the summer 
13

season, saline groundwater input exceeds meteoric input, and the water in Bear Creek is isotopically 

heavy as a result. During winter and spring, meteoric input dominates the water chemistry of Bear 

Creek, resulting in isotopically-light water. Under low-flows, Bear Creek appears to receive a gradual 

input of saline groundwater throughout the study area, with the heaviest waters sampled at downstream 

site BC10 (fig. 27).

Biota

Bacteria can convert naturally occurring inorganic Hg to its most toxic form, MMeHg, which is 

a neurotoxin. MMeHg may affect several physiological functions, including vision, response to stimuli, 

growth, and reproduction in both vertebrates and invertebrates, and in some cases, can cause mortality. 

It is important to understand what concentrations of Hg are present, and evaluate whether corrective 

measures are feasible to lessen the impacts of Hg to wildlife and humans in this region.

Invertebrates

Aquatic invertebrates were collected during spring (June 16 and 30) and fall (September 15 and 

17) of 2010 to evaluate differences in MMeHg bioaccumulation for multiple taxa among sites and 

between seasons. Forty-four composite samples were collected in spring, and 35 of them were analyzed 

for HgT and MMeHg, including larval dragonflies (families Aeshnidae, Libellulidae, and Gomphidae) 

and damselflies (family Coenagrionidae), and adult water striders (family Gerridae), back swimmers 

(family Notonectidae), and water boatmen (family Corixidae) (table 9). In the fall, we collected 44 

composite samples, and analyzed 40, including larval dragonflies (families Aeshnidae, Libellulidae, and 

Gomphidae) and damselflies (families Calopterygidae and Lestidae), and adult water striders (family 

Gerridae), back swimmers (family Notonectidae), and water boatmen (family Corixidae) (table 9). The 

only taxa that could be collected in the fall from site BC6 on Sulphur Creek were larval soldier flies 

(family Stratiomyidae) and larval horse flies (family Tabanidae). 

Only one site (BC2) was sampled for biota upstream from known mining inputs to Bear Creek. 

All nine composite invertebrate samples collected from site BC2 had MMeHg concentrations <0.10 

μg/g, ww. Only one other sample, a composite sample of larval dragonflies (family Gomphidae) from 

site BC10 collected in spring was less than 0.10 μg/g MMeHg. The HgT concentration in only one of the 

nine samples from BC2 (water striders from June 2010) exceeded 0.10 μg/g. Water striders were 

collected at eight of the nine biota sites in the spring, but they were present in sufficient numbers for 

analysis at only two sites in the fall. MMeHg concentrations ranged from 0.09 μg/g at the reference site 

(BC2) to a high of 0.618 μg/g at BC6 on Sulphur Creek, about 6.7 times that recorded at the reference. 

MMeHg concentrations in water striders at sites BC7, BC9, and BC10 were similar in the spring, with 

all about three times greater than the reference. The MMeHg concentration in water striders at site BC5 

in Sulphur Creek in the fall (0.482 μg/g) was about 40% greater than the sample collected from BC5 in 

the spring. Two composite samples of 25 water striders each were collected from BC9 in the fall. Both 

samples were nearly identical in mass, percent moisture, HgT, MMeHg, and % MMeHg (table 9). The 

mean MMeHg concentration was about twice that of the highest sample from the spring, while the mean 

HgT concentration was only 0.11 μg/g higher than the highest strider concentration in the spring. 

However, although the percent MMeHg should normally be less than 100%, the average percent 

MMeHg for these two strider samples was 176%. This discrepancy may be the result of a problem with 

precision of the analytical method or difficulty in producing a homogeneous sample for analysis. 

The taxa most consistently collected at the most sites in both spring and fall were two families of 

dragonfly larvae, Libellulidae and Aeshnidae, and damselfly larvae, Coenagrionidae in the spring and 
14

Calopterygidae in the fall (fig. 28). In both seasons, MMeHg concentrations in these invertebrates from 

BC2, above mine inputs, were lower than any other site sampled in the study. Differences between sites 

BC2 and BC3 were especially great, ranging from 4 to 10 times higher at BC3 located below the mine 

area than in BC2 for the individual taxa. A trend that was apparent in these taxa was higher site-specific 

concentrations of MMeHg in the spring above the confluence of Sulphur Creek and Bear Creek and 

higher concentrations in the fall below Sulphur Creek (fig. 28). This difference is likely related to the 

relative composition of water entering Bear Creek during each of the seasons. The impact of the Sulphur 

Creek inflow on lower Bear Creek is apparently more significant in the fall. 

Three families of dragonfly larvae, Aeshnidae, Gomphidae, and Libellulidae, were collected at 

most Bear Creek sites in September. While there was variability among the families in their relative 

concentrations of MMeHg at each site, the general trends were similar, especially related to the low 

concentrations at BC2 and the elevated concentrations just downstream from Sulphur Creek at site BC7 

(fig. 29). 

Slotton and others (1997) found the highest HgT concentrations in the Bear Creek Watershed 

were from Sulphur Creek, with lower concentrations above the confluence with Sulphur Creek, but with 

one site about 0.4 km above the confluence of Sulphur Creek with Bear Creek (near sample site BC4) 

having elevated Hg in invertebrates. Their data also revealed that as soon as Sulphur Creek waters 

entered Bear Creek, invertebrate Hg concentrations increased. Further studies conducted from 1999-

2003 by Slotton and others (2004) provided additional Hg data for invertebrates at three sites in the Bear 

Creek watershed. As found in the current study, the average MMeHg concentrations in aquatic insects 

were low at the Upper Bear Creek site, moderately high at the Middle Bear Creek site and especially 

high at the Sulphur Creek site. Schwarzbach and others (2001) found a pattern of lower HgT

concentrations in insects in Bear Creek upstream of Sulphur Creek, but much higher concentrations at 

sites in Bear Creek downstream of Sulphur Creek and in Sulphur Creek proper. Neither Slotton and 

others (1997; 2004) nor Schwarzbach and others (2001) sought to evaluate the contribution of the 

Rathburn and Petray mines to the Hg contamination of Bear Creek. 

Fish

Species of fish that have been collected in previous studies (Slotton and others, 1997, 2004; 

Schwarzbach and others, 2001) include Sacramento pikeminnow (Ptychocheilus grandis), Sacramento 

sucker (Catostomus occidentalis), and California roach. Although predatory fish can serve as good 

bioindicators of metals contamination in the long term (Wiener and Spry, 1996), considering the 

ephemeral nature of the streams in the Bear Creek watershed, the preferred fish for collection was the 

California roach, primarily because of its availability and resident status. Smaller fish provide a more 

short-term representation of changes in Hg concentrations of prey species, which in turn will reflect 

short-term changes in Hg in water and sediments. Slotton and others (2004) found that only California 

roach were abundant enough within the Bear Creek watershed to obtain sufficient samples to analyze 

trends. No fish were found in Sulphur Creek. Total Hg and MMeHg were analyzed in individual wholebody samples of fish, and comparisons were made among sites and between seasons.

Adjusted mean HgT and MMeHg concentrations and 95% confidence limits were calculated for 

the 7 sites where California roach could be collected (fig. 30 and 31). Comparisons among sites revealed 

that for both seasons, sites BC4, BC7, BC8, and BC9 were not different from one another. Sites BC3, 

BC4, BC7, BC9, and BC10 were also not different from one another. However, site BC8 was higher 

than sites BC3 and BC10, and site BC2 was lower than all other sites.

Previous studies have shown that about 95 percent of HgT in fish muscle tissue is MMeHg 

(Huckabee and others, 1979; Bloom, 1992; Wiener and Spry, 1996). In this study, however, chemical 
15

analyses from the 98 fish resulted in 58 with MMeHg determinations higher than the HgT

determinations in the same fish. Despite this anomaly, the comparisons among sites using HgT and 

MMeHg produced the same outcomes. There was a significant difference in fish between seasons for 

Hg (September higher than June), but not for MMeHg. Sampling variation could be a factor, and a 

larger sample size might have revealed more of a separation.

Back-transformed means (and standard errors, and lower and upper confidence limits]) for each 

of the 7 sites and 2 seasons are not necessarily good estimates of mean mercury. However, it is fair to 

call them estimates of median mercury, adjusted for fish length. 

Conclusions

There are three main sources of Hg to Bear Creek: mine wastes from the Rathburn-Petray Hg 

mines; cold saline springs that occur along the Bear Fault in Bear Valley; and Sulphur Creek where Hg 

is released from from several hot springs along with a minor release from mines. These sources 

contribute Hg to Bear Creek by means of two processes: surface runoff in which Hg-enriched mine 

waste is transported from the mine area and released into the tributaries that flow into Bear Creek, and 

upwelling of groundwater, in which both cold- and hot-spring fluids rise to the surface and enter Bear 

Creek through its tributaries. The data show that the relative contribution of Hg to Bear Creek by each 

distinct water source is controlled by several factors; the most important is seasonal variation related to 

dilution by precipitation. 

During the dry season, mine wastes at the Rathburn-Petray mine area do not release Hg to the 

tributaries that drain the mine area and flow into Bear Creek. The increase in HgT in Bear Creek stream 

waters downstream from the mine area BC3, compared to upstream sites at BC1 and 2, is measureable 

but minor compared to the levels of Hg contributed to Bear Creek by Sulphur Creek from the 

geothermal springs at Wilbur Hot Springs and other thermal springs in the tributary (fig. 16). Under 

low-flow conditions, these geothermal saline spring waters contribute significant amounts of Hg to Bear 

Creek, as observed in samples collected downstream from Sulphur Creek in Sept. 2010 (fig. 16). During 

the storm season, Hg-contaminated waste materials in the Rathburn-Petray mine area are eroded and 

released into several small tributaries to Bear Creek. Under these high-flow conditions, significant 

concentrations of Hg are released from the mine area, as indicated by the increase in Hg concentrations 

in Bear Creek immediately downstream from the mine area at sites BC3 and BC4, as compared to Hg 

concentrations upstream from the mine area ( sites BC1 and 2, fig16). However Hg concentrations in the 

March 2011 high flow were comparable above and below the mine area. 

However, saline springs, especially those emanating from the Wilbur Springs area in Sulphur

Creek, also contribute significant levels of Hg to Bear Creek during high-flow conditions. Under highflow conditions in June 2010, the highest measured HgT levels in Bear Creek stream water were 

observed at sample site BC7, just downstream from the confluence with Sulphur Creek and remainded 

elevated downstream to the confluence with Cache Creek. This demonstrates that even during periods of 

large input of surface runoff, the natural source of Hg emanating from Wilbur Springs and other hot 

springs in Sulphur Creek dominates the Hg released into the segment of Bear Creek downstream from 

the confluence with Suphur Creek. The concentration of Hg in sediment are also very high in this 

segment of Bear Creek and decrease systematically downstream to site BC10 (figs. 19 and 20. The 

magnitude of the Hg input from Sulphur Creek far exceeds upstream inputs of Hg from the Rathburn 

and Petray mines and cold springs along the Bear Fault. As a result, Hg in the Bear Creek watershed 

below the confluence with Sulphur Creek is dominated by geothermal inputs of Hg from hot springs in 
16

Sulphur Creek. Above the confluence with Sulphur Creek, Hg in Bear Creek is dominated by inputs 

from the Rathburn and Petray Hg mines and cold springs located along the Bear Fault. 

Mercury and MMeHg concentrations in water and sediment were considerably lower at the 

background sites BC1 and BC2 compared to sites below the mine area, and Hg and MMeHg 

concentrations in biota were lower at BC2, than sites BC3–4 downstream from the Rathburn and Petray 

mine areas. Thus, there is a measurable impact on biota in the reach of Bear Creek below the mine area 

downstream to site BC4, located just above the confluence with Sulphur Creek (figs. 16, 19, and 20). In 

this reach of Bear Creek, baseline concentrations of HgT and MMeHg in water, sediment, and biota have 

been established and provide a basis for monitoring changes resulting from the clean-up of the Rathburn 

and Petray Hg mine areas. However downstream from the confluence of Sulphur Creek with Bear 

Creek, monitoring of changes of Hg input from the Rathburn and Petray mine areas would not be 

detectable because of the large input of Hg from the Sulphur Creek tributary. This source of Hg 

dominates both Hg and MMeHg in water, sediment, and biota in the reach of Bear Creek below its 

confluence with Sulphur Creek.

Acknowledgments

Funding for this study was provided by the Ukiah Field Office of the Bureau of Land 

Management. We appreciate the cooperation and assistance provided by Gary Sharpe, Steve Arriaza, 

and the staff of the Field Office during the course of this study. We acknowledge the cooperation of the 

landowners, Jim Owen of the Bear Valley Ranch and Dr. Richard Miller of Wilbur Hot Springs Resort. 

Julie Yee conducted the statistical analyses. The California Department of Fish and Game granted 

permission to collect biological specimens for this study under Scientific Collecting Permit No. SC1243, issued to Roger Hothem.

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19

Table 1. Sample locations and selected parameters for waters collected from Bear Creek, Colusa County, California.

Field Conductivity Temperature Dissolved

number Latitude Longitude Date Sample site description mS/cm pH oC O2, ppm

Low Flow Jan. 2009

09BC2 39.09766 -122.41359 1/12/2009 Bear Ck upstream Rathburn Petray Mines 803 8.02 12.19 nr

09BC3 39.08046 -122.41339 1/12/2009 Bear Ck downstream Rathburn Petray Mines 1027 7.92 12.28 nr

09BCA 39.10952 -122.44063 1/13/2009 Spring N of Prater Ranch 224 8.24 17.86 nr

09BCB 39.09733 -122.44911 1/13/2009 Trout Creek Tributary 704 8.16 9.18 nr

09BC4 39.04146 -122.40914 1/13/2009 Bear Ck upstream Sulphur Ck input 1213 8.72 9.21 nr

High Flow Jun. 2010

10BC1 39.16320 -122.44724 6/15/2010 Brim Road just upstream of bridge 822 8.05 22.75 9.00

10BC2 39.09762 -122.41358 6/15/2010 Upstream of bridge 817 7.98 22.10 7.99

10BC3 39.08030 -122.41329 6/15/2010 In restricted flowing channel 987 8.17 24.19 10.12

10BC4 39.04967 -122.40948 6/15/2010 Fast flowing section between stagnant ponds 1045 8.05 24.59 8.01

10BC5 39.03467 -122.42733 6/15/2010 Upstream of Wilbur Spring, below foot bridge 8430 8.01 28.68 6.55

10BC6 39.03876 -122.41936 6/15/2010 Downstream USGS Gaging Station on Sulphur Creek 10950 8.02 29.40 3.60

10BC7 39.03983 -122.40792 6/15/2010 Downstream confluence w Sulphur Creek 2723 8.20 25.89 7.37

10BC8 39.01247 -122.36462 6/15/2010 300 m upstream from Hwy 20 Bridge 2522 8.43 25.88 8.59

10BC9 38.97247 -122.34123 6/15/2010 Upstream of Thompson Canyon Bridge 2327 8.55 28.00 8.05

10BC10 38.92704 -122.33356 6/15/2010 60 m upstream confluence with Cache Creek 2357 8.55 29.45 8.04

Low Flow Sept. 2010

10BC1-2 39.16320 -122.44724 9/16/2010 Brim Road just upstream of bridge 913 7.72 22.69 5.14

10BC2-2 39.09762 -122.41358 9/16/2010 At bridge upstream 777 7.62 20.20 4.79

10BC3-2 39.08030 -122.41329 9/16/2010 In restricted flowing channel 1008 7.60 21.47 4.50

10BC4-2 39.04967 -122.40948 9/16/2010 Fast flowing section between stagnant ponds 1050 7.69 20.60 5.20

10BC5-2 39.03467 -122.42733 9/16/2010 Upstream of Wilbur Spring, below foot bridge 32000 7.48 31.52 4.57

10BC6-2 39.03876 -122.41936 9/16/2010 Downstream USGS Gaging Station on Sulphur Creek 33307 7.69 29.88 2.56

10BC7-2 39.03983 -122.40792 9/17/2010 Downstream confluence w Sulphur Creek 3933 7.96 19.62 4.61

10BC8-2 39.01247 -122.36462 9/15/2010 300 m upstream from Hwy 20 Bridge 3730 8.13 23.94 6.36

10BC9-2 38.97247 -122.34123 9/15/2010 Upstream of Thompson Canyon Bridge 3992 8.24 26.16 4.79

10BC10-2 38.92704 -122.33356 9/15/2010 60 m upstream confluence of Cache Creek 3942 8.25 25.38 5.22
20

Table 1.—Continued

Field Conductivity Temperature Dissolved

number Latitude Longitude Date Sample site description mS/cm pH o C O2, ppm

High Flow Mar. 2011

11BC1 39.16320 -122.44724 3/23/2011 Brim Road just upstream of bridge 242.9 7.47 22.69 nr

11BC4 39.04967 -122.40948 3/23/2011 Fast flowing section between stagnant ponds 384.8 7.46 20.60 nr

11BC5 39.03467 -122.42733 3/24/2011 Upstream Wilbur Spring, below foot bridge 497.6 7.49 31.52 nr

11BC6 39.03876 -122.41936 3/24/2011 Downstream USGS Gaging Station on Sulphur Creek 469.3 7.39 29.88 nr

11BC7 39.03983 -122.40792 3/24/2011 Downstream confluence w Sulphur Creek 499.2 7.58 19.62 nr

11BC8 39.01247 -122.36462 3/24/2011 300 m upstream from Hwy 20 Bridge 420.6 7.43 23.94 nr

11BC9 38.97247 -122.34123 3/24/2011 Upstream of Thompson Canyon Bridge 320.4 7.42 26.16 nr

11BC10 38.92704 -122.33356 3/24/2011 60 m upstream confluence of Cache Creek 425.0 7.44 25.38 nr

High flow Jun. 2011

11BC2-2 39.09762 -122.41358 6/6/2011 Upstream of bridge 736 8.35 17.2 nr

11BC3-2 39.08030 -122.41329 6/6/2011 In restricted flowing channel 898 8.45 16.9 nr

11BC4-2 39.04967 -122.40948 6/6/2011 Fast flowing section between stagnant ponds 905 8.23 16.9 nr

11BC10-2 38.92704 -122.33356 6/6/2011 60 m upstream confluence of Cache Creek 1311 8.51 17.2 nr
21

Table 2. Sampling sites for biota within the Bear Creek watershed (NAD 83).

Site no. Site description Latitude Longitude Sampling 

dates

Distance from Cache 

Creek (km)

BC1 Milk Creek at Brim Rd; water and sediment 

only

39.16320 - 122.44724 Not sampled for 

biota

34.80

BC2 Bear Creek at bridge; coincides with 

water/sediment site

39.09761 - 122.41358 6/29, 9/15 25.78

BC3 Bear Creek downstream of BC2; coincides 

with water/sediment site

39.08063 - 122.41336 6/29, 9/15 23.65

BC4 Bear Creek 2.11 km upstream of Sulphur 

Creek; 800 m upstream from 

water/sediment site

39.05667 - 122.41139 6/29, 9/15 20.74

BC5 Sulphur Creek above Wilbur Hot Springs 

and most mines(stream habitat); 420 m 

upstream from water/sediment site

39.03344 - 122.43050 6/29, 9/17 21.41

BCUS Sulphur Creek 230 m above BC5 (pool 

habitat); no water/sediment collected here

39.03436 - 122.43272 9/17 21.64

BC6 Sulphur Creek at USGS Gauge; coincides 

with water/sediment site

39.03861 - 122.41889 6/29, 9/17 19.92

BC7 Bear Creek downstream of Sulphur Creek;

coincides with water/sediment site

39.03972 - 122.40778 6/29, 9/15 18.56

BC8 Bear Creek at Highway 20 Bridge; 300 m 

downstream from water/sediment site

39.01161 - 122.36121 6/15, 9/15 12.33

BC9 Bear Creek at Thompson Canyon Bridge; 

80 m downstream from water/sediment 

site

38.97183 - 122.34072 6/15, 9/15 6.73

BC10 Bear Creek just upstream of the 

confluence with Cache Creek; coincides 

with water/sediment site

38.92694 - 122.33333 6/15, 9/15 0.08
22

Table 3. Mercury and monomethylmercury concentrations in waters and sediment collected from Bear Creek, Colusa County, California.

Water Water Water T.S.S. Sediment Sediment % MMeHg

Hg Total Hg Filtered MMeHg total DOC Hg MMeHg (MMeHg/Hg)

Sample site Date ng/L ng/L ng/L mg/L mg/L ng/g ng/g in sediment

Low Flow Jan. 20091

BC2 1/12/2009 0.45 0.42 0.094 nr nr 80.3 nr nr

BC3 1/12/2009 2.21 1.74 0.140 nr nr 9290.0 nr nr

BCA 1/13/2009 0.81 0.82 0.095 nr nr 69.7 nr nr

BCB 1/13/2009 0.26 0.23 0.020 nr nr 165.0 nr nr

BC4 1/13/2009 1.83 1.91 0.098 nr nr 83.9 nr nr

High Flow June 2010

BC1 6/15/2010 0.79 0.49 0.036 nr 1.2 40.6 0.067 0.165

BC2 6/15/2010 41.30 1.24 0.242 nr nr 40.1 0.069 0.172

BC3 6/15/2010 6.11 257.00 0.903 nr 1.9 101.0 0.275 0.272

BC4 6/15/2010 5.10 4.13 1.030 nr 2.2 2750.0 0.591 0.021

BC5 6/15/2010 3.55 250.00 0.627 nr 5.8 2960.0 1.520 0.051

BC6 6/15/2010 496.00 442.00 0.650 nr 5.5 332000.0 145.000 0.044

BC7 6/15/2010 49.60 56.00 0.357 nr 2.7 1220.0 0.072 0.006

BC8 6/15/2010 34.00 20.20 0.690 nr 3.0 1840.0 1.480 0.080

BC9 6/15/2010 26.80 23.40 2.170 nr 3.3 171.0 0.103 0.060

BC10 6/15/2010 10.70 17.00 0.832 nr 3.3 355.0 0.679 0.191

Low Flow Sept. 2010

BC1 9/16/2010 1.37 44.00 0.080 nr 2.06 57.2 0.015 0.026

BC2 9/16/2010 7.82 1.86 0.146 nr 1.53 126.0 0.245 0.194

BC3 9/16/2010 2.67 1.53 0.302 nr 1.67 221.0 0.372 0.168

BC4 9/16/2010 3.87 1.19 0.259 nr 1.63 254.0 3.080 1.213

BC5 9/16/2010 1360.00 555.00 0.499 nr 6.57 1920.0 0.774 0.040

BC6 9/16/2010 2030.00 517.00 2.250 nr 4.81 33500.0 1.170 0.003

BC7 9/17/2010 47.40 16.40 0.025 nr 3.55 620.0 0.222 0.036

BC8 9/15/2010 36.50 25.80 0.023 nr 3.17 942.0 0.501 0.053

BC9 9/15/2010 10.40 7.97 0.023 nr 4.20 634.0 0.982 0.155

BC10 9/15/2010 2.72 2.34 0.023 nr 4.38 228.0 0.265 0.116
23

Table 3.—Continued

Water Water Water T.S.S. Sediment Sediment % MMeHg

Hg Total Hg Filtered MMeHg total DOC Hg MMeHg (MMeHg/Hg)

Sample site Date ng/L ng/L ng/L mg/L mg/L ng/g ng/g in sediment

High Flow Mar. 2011

BC1 3/24/2011 204 3.19 0.157 72.2 5.17 nr nr nr

BC4 3/23/2011 104 4.47 0.361 412.0 4.93 nr nr nr

BC5 3/23/2011 9590 111.00 2.260 1700.0 4.76 nr nr nr

BC6 3/23/2011 11400 91.60 3.220 2440.0 4.75 nr nr nr

BC7 3/23/2011 156 4.05 0.411 202.0 4.70 nr nr nr

BC8 3/23/2011 1670 16.80 1.130 607.0 5.06 nr nr nr

BC9 3/23/2011 927 5.62 0.734 593.0 5.05 nr nr nr

BC10 3/23/2011 1750 9.23 0.743 569.0 5.17 nr nr nr

High Flow June 2011

BC2 6/1/2011 1.89 1.24 0.108 nr 2.84 nr nr nr

BC3 6/1/2011 8.66 6.56 0.295 nr 4.63 nr nr nr

BC4 6/1/2011 6.84 22.80 0.295 nr 3.63 nr nr nr

BC10 6/1/2011 49.40 31.10 0.539 nr 4.24 nr nr nr

1

Refer to table 1 for locations of sites BC1–BC5 in 2009.
24

Table 4. Concentration of anions and selected cations in filtered water collected from Bear Creek, Colusa County, California.

Sample Cl F NO3 SO4 CaCO3 HCO3 Ca Fe K Li Mg Na

site ppm ppm ppm ppm ppm ppm mg/L μg/L mg/L μg/L mg/L mg/L

Low Flow Jan. 2009

BC2 30.2 < 0.08 < 0.08 18.5 405.8 nr 17.2 < 20 0.372 < 5.0 88.7 20.50

BC3 93.8 < 0.08 2.20 17.2 403.1 nr 17.7 < 20 4.940 194.0 88.0 65.30

BCA 1.7 0.25 2.00 4.2 112.0 nr 4.30 < 20 < 0.10 5.4 29.0 1.12

BCB 13.5 < 0.08 < 0.08 13.7 392.7 nr 8.77 < 20 0.341 8.4 96.7 7.27

BC4 150.0 < 0.08 2.50 19.1 415.0 nr 23.4 < 20 4.780 202.0 96.4 83.50

High Flow Jun. 2010

10BC1 63.5 < 0.08 < 0.08 7.8 403.5 nr 16.3 < 50 0.56 3.6 89.9 29.6

10BC2 40.4 < 0.08 < 0.08 12.5 438.5 nr 17.8 < 50 1.00 20.1 93.0 27.9

10BC3 88.2 < 0.08 < 0.08 11.9 448.0 nr 18.3 < 50 4.26 171.0 91.4 59.6

10BC4 93.0 < 0.08 < 0.08 16.2 463.0 nr 19.8 < 50 4.13 168.0 95.0 64.1

10BC5 1990.0 1.15 50.10 158.3 1240.5 nr 32.8 151 96.40 1560.0 91.1 nr

10BC6 2195.0 < 0.08 < 0.08 180.0 1517.5 nr 31.5 95 132.00 1980.0 90.2 nr

10BC7 518.2 < 0.08 < 0.08 37.0 629.5 nr 23.8 < 50 23.00 572.0 92.2 nr

10BC8 467.1 < 0.08 14.40 37.2 631.5 nr 22.7 < 50 18.70 534.0 96.3 nr

10BC9 463.0 < 0.08 5.20 41.9 621.5 nr 22.3 < 50 16.30 458.0 95.3 nr

10BC10 460.0 < 0.08 4.40 52.7 628.0 nr 24.8 < 50 16.50 457.0 98.9 nr

Low Flow Sept. 2010

10BC1-2 98.8 0.06 < 0.08 2.6 297.0 362.2 14.9 < 20.0 0.476 < 5.0 90.3 27.90

10BC2-2 37.0 0.06 < 0.08 9.0 278.9 340.1 16.4 37.4 0.862 19.5 88.7 26.00

10BC3-2 121.5 < 0.04 < 0.08 9.0 298.0 363.3 17.1 40.9 3.890 168.0 90.2 57.50

10BC4-2 124.7 < 0.04 < 0.08 9.0 289.5 353.0 17.4 32.0 3.820 163.0 94.4 57.50

10BC5-2 13710.0 < 0.04 < 0.08 460.7 2943.0 3588.2 26.3 136.0 85.800 2180.0 94.6 1520.00

10BC6-2 13934.0 < 0.04 < 0.08 470.1 3347.4 4081.3 10.5 13300.0 1.180 < 5.0 8.23 4.19

10BC7-2 778.3 < 0.04 1.10 46.5 519.9 633.9 < 0.1 < 20.0 0.406 < 5.0 < 0.1 < 0.10

10BC8-2 1032.3 < 0.04 3.50 47.2 473.9 577.8 18.3 < 20.0 16.700 536.0 96.6 337.00

10BC9-2 1178.0 < 0.04 3.40 48.2 541.1 659.8 < 0.1 < 20.0 2.390 < 5.0 < 0.1 0.763

10BC10-2 1228.0 < 0.04 < 0.08 50.2 542.9 661.9 21.6 < 20.0 15.900 504.0 103 325.00
25

Table 4.—Continued

Sample Cl F NO3 SO4 CaCO3 HCO3 Ca Fe K Li Mg Na

site ppm ppm ppm ppm ppm ppm mg/L μg/L mg/L μg/L mg/L mg/L

High Flow Mar. 2011

11BC1 12.9 <0.04 <0.08 4.8 nr nr 11.7 120 1.5 < 0.1 17.3 10.5

11BC4 18.8 <0.04 0.40 7.1 nr nr 10.1 223 1.8 25.5 38.9 16.3

11BC5 42.8 <0.04 0.40 15.8 nr nr 10.5 697 5.7 69.4 19.6 52.7

11BC6 44.2 <0.04 0.40 17.5 nr nr 10.3 179 6.2 68.3 18.5 59.8

11BC7 30.6 <0.04 0.40 9.4 nr nr 11.0 148 2.5 55.4 44.6 25.9

11BC8 22.1 <0.04 0.40 9.0 nr nr 9.62 207 2.5 33.7 33.5 21.8

11BC9 19.6 <0.04 0.40 11.0 nr nr 9.86 <20 2.4 29.0 30.7 20.7

11BC10 21.7 <0.04 0.40 14.1 nr nr 12.6 <20 2.6 34.5 36.1 23.6

High Flow June 2011

11BC2 34.1 <0.04 <0.08 8.5 339.1 413.4 15.3 <20 1.78 23.3 91.1 24.5

11BC3 29.6 0.40 <0.08 210.2 322.2 392.9 16.2 <20 4.46 141.0 95.5 55.2

11BC4 74.6 <0.04 0.80 12.7 333.5 406.7 15.4 <20 4.64 146.0 88.6 51.3

11BC10 161.5 <0.04 0.80 44.9 373.0 454.2 23.0 22 9.30 264.0 94.2 136.0
26

Table 5. Mercury and associated major and minor elements in sediment, precipitates, Bear Creek, Colusa County, California.

Sample Hg Ag Al As Ba Be Bi Ca Cd Ce Co Cr

site ppm ppm % ppm ppm ppm ppm % ppm ppm ppm ppm

Low Flow Jan. 2009

09BC3S 1.78 0.05 2.61 3.8 210 0.32 0.04 1.01 0.09 8.94 83.6 2150

09BCBS 0.08 0.05 3.38 3.0 230 0.47 0.06 0.86 0.07 12.80 70.0 1630

09BC4S 0.59 0.12 4.86 6.1 370 0.65 0.10 1.35 0.10 18.15 54.1 5510

High Flow June 2010

10BC1S2 0.06 0.07 3.56 2.0 170 0.30 0.03 2.02 0.07 10.15 86.1 6020

10BC2S2 0.08 0.09 3.64 3.1 280 0.47 0.06 0.79 0.08 13.20 76.3 1780

10BC3S2 1.90 0.12 3.11 3.7 240 0.31 0.04 1.31 0.09 10.45 85.5 4970

10BC4S2 1.20 0.09 5.18 6.7 350 0.63 0.08 1.17 0.10 19.30 60.7 2020

10BC5S2 5.66 0.16 6.69 8.6 510 1.02 0.11 1.46 0.14 27.70 34.8 638

10BC6S2 228.00 0.18 7.00 8.9 580 1.00 0.11 1.59 0.13 28.80 38.4 1850

10BC7S2 9.97 0.11 4.55 6.5 330 0.63 0.09 0.94 0.12 19.30 63.8 1100

10BC8S2 5.47 0.13 4.43 5.1 410 0.65 0.08 1.28 0.10 18.30 54.6 1060

10BC9S2 1.60 0.10 4.09 6.3 290 0.43 0.05 1.78 0.10 15.45 68.7 1630

10BC10S2 0.43 0.17 7.84 16.0 560 1.23 0.17 1.17 0.18 34.10 31.6 345

Low Flow Sept. 2010

10BC1-2S 0.1 0.07 3.10 3.7 140 0.28 0.04 1.68 0.08 9.15 73.3 3860

10BC2-2S 0.1 0.10 3.76 2.8 260 0.51 0.06 1.18 0.08 14.4 72.1 5010

10BC3-2S 9.5 0.10 3.86 2.9 250 0.41 0.06 1.25 0.09 14.6 77.7 10000

10BC4-2S 2.4 0.10 4.84 4.3 300 0.52 0.07 1.67 0.08 20.6 51.7 8210

10BC5-2S 21.7 0.16 6.09 8.0 480 1.04 0.10 1.31 0.14 26.6 26.9 445

10BC6-2S 33.1 0.27 5.90 5.9 460 0.92 0.11 1.18 0.14 27.3 27.6 681

10BC7-2S 5.9 0.12 4.94 8.1 310 0.82 0.10 0.98 0.15 21.9 45.8 1370

10BC8-2S 23.1 0.14 4.66 9.0 420 0.72 0.09 1.40 0.12 23.1 54.7 1940

10BC9-2S 17.6 0.10 3.83 8.1 480 0.45 0.05 2.95 0.11 15.1 60.4 2610

10BC10-2S 0.5 0.15 7.12 11.9 850 1.11 0.15 4.03 0.15 30.7 23.9 251
27

Table 5.—Continued

Sample Cs Cu Fe Ga Ge Hf In K La Li Mg Mn

site ppm ppm % ppm ppm ppm ppm % ppm ppm % ppm

Low Flow Jan. 2009

09BC3S 9.19 29.0 5.54 5.48 0.16 0.6 0.022 0.33 4.1 31.7 15.50 1025

09BCBS 1.89 28.8 5.32 7.38 0.13 1.0 0.028 0.55 6.2 27.1 14.30 801

09BC4S 8.86 35.9 5.10 10.3 0.13 1.4 0.050 0.68 8.6 43.4 8.93 1035

High Flow June 2010

10BC1S2 1.58 30.2 6.27 8.12 0.15 1.1 0.030 0.31 4.5 14.8 13.70 1120

10BC2S2 22.50 29.8 5.99 8.28 0.17 1.1 0.030 0.61 6.2 36.1 15.20 803

10BC3S2 10.10 26.3 6.43 6.84 0.16 0.9 0.025 0.36 4.5 27.9 15.50 1000

10BC4S2 10.10 40.2 5.89 11.55 0.16 1.5 0.042 0.75 8.5 50.3 10.55 914

10BC5S2 76.60 51.4 5.71 16.00 0.22 2.3 0.055 1.34 12.6 112.5 4.64 678

10BC6S2 72.10 51.5 5.96 16.45 0.16 2.3 0.057 1.26 13.0 110.0 4.73 739

10BC7S2 14.65 39.2 5.78 9.95 0.18 1.4 0.041 0.76 8.7 49.8 12.60 884

10BC8S2 21.20 36.3 5.30 9.88 0.16 1.5 0.037 0.74 8.4 56.9 11.65 758

10BC9S2 17.25 33.9 6.25 8.95 0.17 1.2 0.036 0.53 6.7 45.9 12.75 1060

10BC10S2 16.65 66.0 5.00 18.15 0.18 2.7 0.060 1.39 16.1 77.5 4.08 622

Low Flow Sept. 2010

10BC1-2S 1.20 27.7 5.60 6.73 0.24 0.8 0.024 0.30 4.0 15.5 13.35 973

10BC2-2S 22.90 28.4 6.01 8.50 0.25 1.0 0.027 0.57 7.0 43.2 11.70 804

10BC3-2S 14.40 25.8 5.86 8.81 0.24 1.1 0.028 0.48 7.0 38.8 10.45 1250

10BC4-2S 9.61 26.6 5.25 10.30 0.22 1.4 0.036 0.57 9.7 44.7 7.48 846

10BC5-2S 101.00 42.7 5.11 13.75 0.20 1.9 0.048 1.26 12.5 138.5 3.84 672

10BC6-2S 116.00 43.5 4.42 13.40 0.18 1.8 0.047 1.20 12.7 146.0 3.84 496

10BC7-2S 28.20 38.7 5.25 11.25 0.22 1.5 0.041 0.88 10.5 66.1 9.64 636

10BC8-2S 23.60 36.0 5.54 10.65 0.25 1.4 0.039 0.76 11.0 66.3 10.30 827

10BC9-2S 15.85 26.9 6.11 8.24 0.24 1.0 0.031 0.46 6.8 49.2 11.25 1080

10BC10-2S 16.65 52.3 4.20 15.65 0.16 2.1 0.053 1.34 14.6 83.5 2.94 615
28

Table 5.—Continued

Sample Mo Na Nb Ni P Pb Rb Re S Sb Sc Sn

site ppm % ppm ppm ppm ppm ppm ppm % ppm ppm ppm

Low Flow Jan. 2009

09BC3S 0.37 0.54 1.6 1685 220 4.6 20.3 < 0.002 0.08 0.27 14.5 0.5

09BCBS 0.33 0.43 2.6 1325 260 5.0 23.9 < 0.002 0.03 0.35 12.9 0.5

09BC4S 0.49 0.92 3.2 836 430 8.9 31.7 < 0.002 0.05 0.51 16.6 0.6

High Flow June 2010

10BC1S2 0.22 0.72 2.3 1445 270 2.9 17.9 < 0.002 0.01 0.18 16.9 0.7

10BC2S2 0.27 0.49 2.9 1550 230 5.1 42.5 < 0.002 0.01 0.32 13.6 0.6

10BC3S2 0.26 0.59 2.1 1610 220 4.0 22.8 < 0.002 0.06 0.27 14.4 0.4

10BC4S2 0.43 0.91 3.6 1050 360 6.2 41.5 < 0.002 0.04 0.50 17.2 1.0

10BC5S2 0.64 1.46 5.7 390 780 8.9 64.8 0.002 0.41 5.63 19.8 1.5

10BC6S2 0.63 1.47 5.7 398 650 10.8 71.6 0.002 0.35 6.14 21.0 2.8

10BC7S2 0.46 0.80 3.4 1290 440 6.6 43.0 < 0.002 0.04 0.62 15.3 0.7

10BC8S2 0.51 0.82 3.7 1040 470 6.1 41.9 < 0.002 0.12 2.80 14.8 1.0

10BC9S2 0.44 0.80 2.8 1250 360 5.0 31.1 < 0.002 0.05 0.87 17.2 0.6

10BC10S2 0.92 1.09 5.9 362 560 13.6 68.4 < 0.002 0.22 1.54 20.1 1.3

Low Flow Sept. 2010

10BC1-2S 0.24 0.73 1.8 1330 200 2.8 13.3 < 0.002 0.01 0.45 15.3 0.6

10BC2-2S 0.20 0.60 3.3 1240 230 4.7 41.2 < 0.002 0.03 0.36 15.3 0.6

10BC3-2S 0.29 0.74 2.9 1065 320 4.3 31.0 < 0.002 0.05 0.42 15.2 0.5

10BC4-2S 0.33 1.19 3.3 684 300 5.3 30.0 < 0.002 0.03 0.38 17.1 0.7

10BC5-2S 0.56 2.13 4.8 322 670 7.3 68.0 < 0.002 0.93 12.55 17.5 1.1

10BC6-2S 0.53 1.95 4.7 324 500 7.9 67.8 < 0.002 0.31 5.95 16.4 1.2

10BC7-2S 0.53 0.90 4.0 871 480 7.1 48.3 < 0.002 0.04 1.00 15.7 3.5

10BC8-2S 0.54 0.91 3.7 947 440 6.7 43.4 < 0.002 0.08 1.29 15.9 0.8

10BC9-2S 0.51 0.85 2.6 1030 370 4.6 24.5 < 0.002 0.10 7.99 15.7 0.5

10BC10-2S 0.80 1.11 5.5 225 470 12.2 60.9 < 0.002 0.22 1.47 16.4 1.1
29

Table 5.—Continued

Sample Sr Ta Te Th Ti Tl U V W Y Zn Zr

site ppm ppm ppm ppm % ppm ppm ppm ppm ppm ppm ppm

Low Flow Jan. 2009

09BC3S 76.4 0.11 0.08 1.0 0.144 0.08 0.4 86 2.9 7.3 65 22.2

09BCBS 44.0 0.17 < 0.05 2.0 0.164 0.15 0.7 87 0.5 7.6 72 30.5

09BC4S 154.5 0.20 0.07 2.4 0.265 0.16 0.8 132 1.9 11.5 112 43.3

High Flow June 2010

10BC1S2 160.5 0.15 < 0.05 1.0 0.255 0.08 0.4 127 0.4 9.3 98 39.3

10BC2S2 32.0 0.19 < 0.05 2.0 0.170 0.16 0.7 97 7.7 7.6 79 39.5

10BC3S2 61.3 0.14 < 0.05 1.1 0.198 0.09 0.5 117 2.9 7.9 96 32.5

10BC4S2 93.0 0.25 0.06 2.5 0.275 0.18 0.9 131 2.2 11.6 94 54.1

10BC5S2 203.0 0.40 0.06 3.3 0.393 0.39 1.2 166 43.7 17.3 112 83.5

10BC6S2 212.0 0.37 0.06 3.5 0.409 0.37 1.2 173 41.8 18.3 120 85.3

10BC7S2 112.0 0.23 0.06 2.5 0.234 0.21 0.9 116 6.0 11.0 87 50.2

10BC8S2 166.5 0.24 < 0.05 2.4 0.246 0.21 0.9 108 11.0 10.8 83 53.3

10BC9S2 121.5 0.19 < 0.05 1.6 0.239 0.14 0.7 115 10.4 10.8 80 44.5

10BC10S2 181.0 0.42 0.08 5.5 0.370 0.38 2.0 140 6.0 16.9 111 93.2

Low Flow Sept. 2010

10BC1-2S 134.5 0.11 nr 0.9 0.213 0.05 0.4 107 0.3 8.4 74 31.1

10BC2-2S 49.2 0.20 nr 2.2 0.214 0.14 0.7 109 4.8 9.5 98 37.9

10BC3-2S 89.5 0.17 nr 1.9 0.244 0.12 0.7 146 2.9 10.0 139 39.5

10BC4-2S 124.5 0.20 nr 2.0 0.303 0.12 0.8 140 1.6 11.7 110 46.6

10BC5-2S 189.0 0.30 nr 3.4 0.351 0.31 1.1 138 31.8 16.2 92 66.6

10BC6-2S 222.0 0.28 nr 3.2 0.316 0.27 1.0 121 22.2 14.9 89 65.4

10BC7-2S 128.5 0.25 nr 3.2 0.258 0.23 1.1 121 6.1 12.7 89 56.0

10BC8-2S 146.5 0.23 nr 3.3 0.252 0.20 1.0 117 11.5 13.1 86 54.3

10BC9-2S 446.0 0.16 nr 1.5 0.235 0.11 0.6 115 10.3 11.5 82 38.3

10BC10-2S 1250.0 0.33 nr 5.8 0.333 0.31 2.0 114 6.9 15.4 95 79.0
30

Table 6. Major- and minor-element concentrations in unfiltered waters collected from Bear Creek, Colusa 

County, California. ICP-MS results (ICP-AES for major elements).

Field Ag Al As B Ba Be Bi Ca Cd

number μg/L μg/L μg/L μg/L μg/L μg/L μg/L mg/L μg/L

Sampling Event 1: Jan. 2009

BC2 < 1 18.2 1 77.60 99.9 < 0.05 < 0.2 17.20 < 0.02

BC3 < 1 5.3 2 2830.00 184.0 < 0.05 < 0.2 17.60 < 0.02

BCA < 1 123.0 2 8.05 23.0 < 0.05 < 0.2 4.04 < 0.02

BCB < 1 < 2.0 < 1 98.60 18.3 < 0.05 < 0.2 8.17 < 0.02

BC4 < 1 13.5 2 3270.00 200.0 < 0.05 < 0.2 23.70 < 0.02

Sampling Event 2: Jun. 2010

10BC1A < 1 7.3 1.0 132 65.5 < 0.05 < 0.2 13.8 < 0.02

10BC2A < 1 10900.0 2.0 339 206.0 0.30 < 0.2 19.9 0.08

10BC3A < 1 25.3 2.0 1910 185.0 < 0.05 < 0.2 16.6 < 0.02

10BC4A < 1 18.3 2.0 2000 204.0 < 0.05 < 0.2 17.7 < 0.02

10BC5A < 1 82.9 13.8 43300 384.0 < 0.05 < 0.2 25.1 < 0.02

10BC6A < 1 40.8 16.1 65300 496.0 < 0.05 < 0.2 23.9 < 0.02

10BC7A < 1 35.8 4.5 13500 259.0 < 0.05 < 0.2 21.4 < 0.02

10BC8A < 1 31.0 4.5 12300 244.0 < 0.05 < 0.2 21.3 < 0.02

10BC9A < 1 10.6 4.1 10400 230.0 < 0.05 < 0.2 20.9 < 0.02

10BC10A < 1 10.1 3.8 9350 205.0 < 0.05 < 0.2 21.3 < 0.02

Sampling Event 3: Sep. 2010

10BC1A < 1 9.2 < 1.0 183 74.2 < 10 < 0.2 16.3 < 0.02

10BC2A < 1 20.5 < 1.0 138 127.0 < 10 < 0.2 15.6 < 0.02

10BC3A < 1 42.8 < 1.0 2850 222.0 < 10 < 0.2 17.2 < 0.02

10BC4A < 1 136.0 < 1.0 2630 228.0 < 10 < 0.2 17.4 < 0.02

10BC5A < 1 197.0 10.9 204000 1770.0 < 10 < 0.2 17.0 0.05

10BC6A < 1 29.8 9.5 250000 1620.0 < 10 < 0.2 14.3 0.02

10BC7A < 1 32.0 1.4 19800 335.0 < 10 < 0.2 18.9 < 0.02

10BC8A < 1 33.4 2.4 20500 333.0 < 10 < 0.2 20.4 < 0.02

10BC9A < 1 10.5 2.8 21100 325.0 < 10 < 0.2 21.6 < 0.02

10BC10A < 1 5.8 2.6 19400 171.0 < 10 < 0.2 16.6 < 0.02

Sampling Event 4: Mar. 2011

11BC1A < 1 4850 < 1.0 25.9 146 0.13 < 0.2 13.1 0.05

11BC4A < 1 6470 < 1.0 435.0 144 0.12 < 0.2 12.2 0.05

11BC5A < 1 50800 3.4 1740.0 769 1.00 < 0.2 49.2 0.52

11BC6A < 1 38600 2.3 1640.0 674 0.78 < 0.2 31.7 0.33

11BC7A < 1 2980 4.5 897.0 146 0.07 < 0.2 11.5 0.03

11BC8A < 1 10100 < 1.0 612.0 222 0.26 < 0.2 15.0 0.09

11BC9A < 1 10100 1.0 553.0 189 0.22 < 0.2 14.8 0.07

11BC10A < 1 12100 1.4 655.0 203 0.21 < 0.2 17.6 0.08

Sampling Event 5: Jun. 2011

11BC2A < 1 115.0 < 1.0 220 87.4 < 0.05 < 0.2 14.6 < 0.02

11BC3A < 1 11.6 < 1.0 966 94.4 < 0.05 < 0.2 62.5 < 0.02

11BC4A < 1 23.1 < 1.0 1810 144.0 < 0.05 < 0.2 16.0 < 0.02

11BC10A < 1 54.6 1.6 4260 153.0 < 0.05 < 0.2 22.0 < 0.02
31

Table 6.—Continued

Field Ce Co Cr Cs Cu Dy Er Eu

number μg/L μg/L μg/L μg/L μg/L μg/L μg/L μg/L

Sampling Event 1: Jan. 2009

BC2 0.03 0.18 7.9 < 0.02 0.59 0.009 0.005 0.030

BC3 0.02 0.15 8.9 2.02 0.68 0.010 0.007 0.052

BCA 0.16 0.30 7.6 < 0.02 0.91 0.040 0.009 0.020

BCB <0.01 0.03 22.0 < 0.02 0.56 0.006 < 0.005 0.008

BC4 0.03 0.11 9.0 0.56 0.89 0.010 0.010 0.058

Sampling Event 2: Jun. 2010

10BC1A 0.01 0.13 7.9 < 0.02 < 0.50 < 0.005 0.005 0.007

10BC2A 5.66 61.5 807.0 10.70 27.20 0.880 0.390 0.300

10BC3A 0.02 0.29 5.1 1.97 0.59 0.006 0.005 0.030

10BC4A 0.02 0.17 4.6 1.55 0.74 0.006 0.005 0.020

10BC5A 0.08 0.43 11.1 140.00 3.00 0.030 0.020 0.052

10BC6A 0.09 0.44 15.0 262.00 2.40 0.040 0.020 0.050

10BC7A 0.05 0.26 6.0 26.20 1.40 0.020 0.020 0.020

10BC8A 0.04 0.30 6.0 26.20 1.40 0.020 0.010 0.030

10BC9A 0.03 0.24 6.5 19.60 1.40 0.020 0.010 0.020

10BC10A 0.02 0.21 5.2 15.70 1.40 0.007 0.009 0.020

Sampling Event 3: Sep. 2010

10BC1A 0.01 0.23 < 1.0 < 0.02 < 0.50 0.030 < 0.005 < 0.005

10BC2A 0.02 0.19 < 1.0 0.04 < 0.50 0.020 < 0.005 < 0.005

10BC3A 0.04 0.28 1.4 2.70 < 0.50 0.020 0.009 < 0.005

10BC4A 0.09 0.43 2.2 1.40 0.71 0.030 0.010 < 0.005

10BC5A 0.24 0.61 4.8 905.00 1.80 0.130 0.110 < 0.005

10BC6A 0.17 0.37 4.8 1000.00 1.50 0.097 0.068 < 0.005

10BC7A 0.04 0.17 1.1 68.70 0.77 0.020 0.010 < 0.005

10BC8A 0.04 0.26 < 1.0 55.80 1.10 0.020 0.020 0.010

10BC9A 0.02 0.26 < 1.0 37.00 1.50 < 0.005 0.008 0.010

10BC10A 0.01 0.26 < 1.0 21.70 1.50 0.009 0.008 0.008

Sampling Event 4: Mar. 2011

11BC1A 4.2 13.0 81 0.37 13.9 0.64 0.35 0.25

11BC4A 4.1 23.7 149 2.10 17.7 0.69 0.38 0.23

11BC5A 53.6 115.0 635 56.20 141.0 7.70 3.60 2.50

11BC6A 36.6 87.2 421 33.20 106.0 5.10 2.40 1.70

11BC7A 2.6 11.0 67.8 2.10 9.6 0.43 0.24 0.15

11BC8A 9.1 36.5 220 6.60 31.3 1.40 0.68 0.46

11BC9A 7.9 33.9 202 4.80 28.3 1.20 0.64 0.43

11BC10A 8.7 32.9 194 7.00 30.8 1.40 0.67 0.47

Sampling Event 5: Jun. 2011

11BC2A 0.31 11.80 15.7 0.64 1.1 0.094 0.066 0.30

11BC3A 0.27 0.83 < 1.0 <0.02 1.8 0.099 0.064 0.30

11BC4A 0.26 6.70 6.5 3.80 1.0 0.094 0.064 0.29

11BC10A 0.30 7.10 5.1 6.50 1.6 0.098 0.066 0.29
32

Table 6.—Continued

Field Fe Ga Gd Ge Ho K La Li

number μg/L μg/L μg/L μg/L μg/L mg/L μg/L μg/L

Sampling Event 1: Jan. 2009

BC2 43.8 < 0.05 0.010 < 0.05 < 0.005 0.43 0.01 4.8

BC3 < 20.0 < 0.05 0.010 < 0.05 < 0.005 5.78 0.01 206.0

BCA 249.0 < 0.05 0.052 < 0.05 0.006 0.08 0.05 4.5

BCB < 20.0 < 0.05 0.005 < 0.05 < 0.005 0.42 0.01 7.2

BC4 30.0 < 0.05 0.008 < 0.05 < 0.005 5.67 0.02 220.0

Sampling Event 2: Jun. 2010

10BC1A < 20.0 < 0.05 < 0.005 < 0.05 < 0.005 0.52 < 0.01 2.8

10BC2A 37.4 2.90 1.130 1.30 0.170 1.45 3.16 52.3

10BC3A 40.9 < 0.05 0.009 < 0.05 < 0.005 3.95 0.02 170.0

10BC4A 32.0 < 0.05 0.006 < 0.05 < 0.005 3.94 0.02 173.0

10BC5A 136.0 0.05 0.030 3.10 0.010 88.20 0.04 1,560.0

10BC6A 13,300.0 < 0.05 0.040 6.40 0.009 121.00 0.04 2,020.0

10BC7A < 20.0 < 0.05 0.010 0.94 < 0.005 23.90 0.03 610.0

10BC8A < 20.0 < 0.05 0.020 0.58 < 0.005 18.00 0.03 551.0

10BC9A < 20.0 < 0.05 0.010 0.28 < 0.005 16.20 0.02 494.0

10BC10A < 20.0 < 0.05 0.009 0.20 < 0.005 15.80 0.01 469.0

Sampling Event 3: Sep. 2010

10BC1A 20 < 0.05 < 0.005 nr 0.006 0.462 < 0.01 < 5

10BC2A 50 < 0.05 0.006 nr 0.006 0.498 0.01 14

10BC3A 110 < 0.05 < 0.005 nr < 0.005 5.570 0.01 218

10BC4A 293 0.05 0.010 nr 0.009 4.760 0.04 193

10BC5A 884 0.39 0.096 nr 0.030 394 0.07 10,400

10BC6A 253 0.43 0.072 nr 0.020 486 0.05 12,700

10BC7A 75 0.09 0.020 nr 0.020 33.5 0.02 908

10BC8A 65 0.07 < 0.005 nr 0.010 33.4 0.02 939

10BC9A < 20 0.10 0.020 nr < 0.005 32.2 < 0.01 934

10BC10A < 20 0.07 0.020 nr 0.020 29.1 < 0.01 876

Sampling Event 4: Mar. 2011

11BC1A 9,490 1.8 0.85 nr 0.120 1.9 1.90 5.8

11BC4A 13,900 2.4 0.84 nr 0.130 2.5 1.70 35.9

11BC5A 102,000 21.8 9.50 nr 1.400 12.5 21.10 254.0

11BC6A 73,200 16.2 6.50 nr 0.940 11.6 14.30 197.0

11BC7A 6230 1.2 0.54 nr 0.084 2.9 0.96 65.5

11BC8A 21,400 4.3 1.80 nr 0.260 3.7 3.50 59.1

11BC9A 20,800 3.9 1.70 nr 0.220 3.4 3.10 47.1

11BC10A 23,800 4.3 1.60 nr 0.250 3.8 3.40 56.6

Sampling Event 5: Jun. 2011

11BC2A 218.0 < 0.05 < 0.005 nr 0.02 1.12 < 0.01 18.6

11BC3A < 20.0 < 0.05 < 0.005 nr 0.02 2.49 < 0.01 68.3

11BC4A 56.6 < 0.05 < 0.005 nr 0.02 4.21 < 0.01 141.0

11BC10A 99.7 < 0.05 < 0.005 nr 0.02 8.60 < 0.01 244.0
33

Table 6.—Continued

Field Lu Mg Mn Mo Na Nb Nd Ni

number μg/L mg/L μg/L μg/L mg/L μg/L μg/L μg/L

Sampling Event 1: Jan. 2009

BC2 < 0.1 91.1 39.8 < 2 21.2 < 0.2 0.03 3.8

BC3 < 0.1 87.0 32.6 < 2 66.5 < 0.2 0.02 3.8

BCA < 0.1 27.4 6.2 < 2 1.23 < 0.2 0.15 4.2

BCB < 0.1 92.8 0.4 < 2 7.6 < 0.2 0.03 2.2

BC4 < 0.1 98.1 7.3 < 2 86.6 < 0.2 0.03 3.8

Sampling Event 2: Jun. 2010

10BC1A < 0.1 90.3 5.1 < 2 27.9 < 0.2 < 0.01 2.6

10BC2A < 0.1 88.7 842.0 < 2 26.0 < 0.2 4.27 1,400

10BC3A < 0.1 90.2 31.5 < 2 57.5 < 0.2 0.02 4.9

10BC4A < 0.1 94.4 13.6 < 2 57.5 < 0.2 0.02 4.2

10BC5A < 0.1 94.6 47.6 < 2 1520.0 < 0.2 0.06 5.9

10BC6A < 0.1 8.23 57.2 < 2 4.19 < 0.2 0.08 5.6

10BC7A < 0.1 < 0.10 15.5 < 2 < 0.10 < 0.2 0.05 5.2

10BC8A < 0.1 96.6 13.8 < 2 337.0 < 0.2 0.04 5.1

10BC9A < 0.1 < 0.10 9.2 < 2 0.763 < 0.2 0.03 4.8

10BC10A < 0.1 103.0 4.9 < 2 325.0 < 0.2 0.02 3.8

Sampling Event 3: Sep. 2010

10BC1A nr 103.0 33.6 < 2 32.4 < 0.2 < 0.01 2.4

10BC2A nr 88.2 33.5 < 2 21.1 < 0.2 0.02 2.4

10BC3A nr 91.0 41.8 < 2 66.8 < 0.2 0.01 4.3

10BC4A nr 89.3 28.9 < 2 63.8 < 0.2 0.07 6.9

10BC5A nr 78.5 185.0 < 2 5,060.0 0.27 0.20 9.3

10BC6A nr 80.1 108.0 < 2 5,560.0 < 0.2 0.11 8.0

10BC7A nr 93.9 20.3 < 2 624.0 < 0.2 0.04 3.9

10BC8A nr 104.0 9.0 < 2 627.0 < 0.2 0.04 4.3

10BC9A nr 115.0 10.2 < 2 644.0 < 0.2 < 0.01 4.9

10BC10A nr 120.0 8.1 < 2 631.0 0.27 0.02 3.6

Sampling Event 4: Mar. 2011

11BC1A nr 28.0 237 < 2 10.1 < 0.2 2.9 192

11BC4A nr 58.4 380 < 2 15.8 < 0.2 2.9 359

11BC5A nr 142.0 2,600 < 2 57.8 < 0.2 35.6 1,440

11BC6A nr 101.0 1,930 < 2 56.9 < 0.2 24.1 1,040

11BC7A nr 50.5 196 < 2 24.9 < 0.2 1.8 162

11BC8A nr 67.2 665 < 2 21.2 < 0.2 6.2 531

11BC9A nr 62.4 590 < 2 20.1 < 0.2 5.4 480

11BC10A nr 68.3 621 < 2 22.7 < 0.2 5.8 465

Sampling Event 5: Jun. 2011

11BC2A nr 86.8 226.0 < 2 22.3 < 0.2 0.50 5.8

11BC3A nr 140.0 < 0.2 < 2 64.1 < 0.2 0.48 < 0.4

11BC4A nr 92.3 34.8 < 2 53.2 < 0.2 0.47 0.4

11BC10A nr 89.2 94.5 < 2 130.0 < 0.2 0.48 < 0.4
34

Table 6.—Continued

Field P Pb Pr Rb Sb Sc Se SiO2

number mg/L μg/L μg/L μg/L μg/L μg/L μg/L mg/L

Sampling Event 1: Jan. 2009

BC2 0.04 < 0.05 < 0.01 0.14 < 0.3 5.5 1.3 24.4

BC3 0.04 < 0.05 < 0.01 10.30 < 0.3 5.3 2.2 25.4

BCA 0.03 0.09 0.03 0.10 < 0.3 8.9 < 1.0 44.4

BCB < 0.01 < 0.05 < 0.01 0.28 < 0.3 6.5 < 1.0 32.2

BC4 0.02 0.91 < 0.01 6.90 < 0.3 4.6 2.7 23.0

Sampling Event 2: Jun. 2010

10BC1A < 0.01 1.6 < 0.01 0.30 < 0.3 2.8 1.3 32.8

10BC2A 0.20 5.8 0.94 7.67 < 0.3 15.3 1.2 100.0

10BC3A 0.01 1.5 < 0.01 8.94 < 0.3 2.3 2.1 29.1

10BC4A < 0.01 1.5 < 0.01 8.34 < 0.3 2.4 1.9 29.5

10BC5A < 0.01 1.2 0.01 189.0 5.39 1.4 36.5 23.0

10BC6A 0.02 0.6 0.01 262.0 6.22 2.3 47.0 39.9

10BC7A < 0.01 2.0 0.01 55.2 0.85 2.1 9.6 30.9

10BC8A < 0.01 1.6 < 0.01 40.1 0.84 1.8 8.7 24.0

10BC9A < 0.01 1.5 < 0.01 35.2 0.75 1.6 7.9 22.1

10BC10A < 0.01 1.4 < 0.01 33.2 0.68 1.2 7.5 16.2

Sampling Event 3: Sept. 2010

10BC1A < 0.01 < 0.05 < 0.01 0.28 < 0.3 1.1 < 1.0 31

10BC2A 0.03 < 0.05 < 0.01 0.46 < 0.3 1.1 1.1 28

10BC3A 0.03 < 0.05 < 0.01 12.6 < 0.3 0.9 5.0 29

10BC4A 0.04 1.87 0.01 10.1 < 0.3 1.1 3.9 30

10BC5A 0.40 0.40 0.04 899.0 31.1 4.4 611.0 58

10BC6A 0.40 0.09 0.02 919.0 20.2 6.3 686.0 96

10BC7A 0.07 < 0.05 < 0.01 70.4 1.3 2.5 76.3 35

10BC8A 0.03 < 0.05 0.01 65.4 1.3 1.9 65.9 29

10BC9A 0.04 < 0.05 < 0.01 61.3 1.2 1.4 75.6 21

10BC10A 0.04 < 0.05 < 0.01 50.6 1.0 1.2 71.4 10

Sampling Event 4: Mar. 2011

11BC1A 0.2 1.64 0.66 3.0 < 0.3 8.1 < 1.0 55

11BC4A 0.2 1.83 0.62 6.2 < 0.3 11.5 < 1.0 82

11BC5A 1.7 23.5 8.0 77.8 0.46 44.8 2.0 190

11BC6A 1.1 16.80 5.4 60.4 0.39 34.5 2.4 180

11BC7A 0.1 1.24 0.4 6.1 < 0.3 5.6 < 1.0 46

11BC8A 0.3 4.21 1.4 12.3 < 0.3 14.3 1.0 100

11BC9A 0.3 3.55 1.2 10.4 < 0.3 12.8 < 1.0 100

11BC10A 0.3 3.96 1.3 12.3 < 0.3 14.4 < 1.0 110

Sampling Event 5: Jun. 2011

11BC2A 0.04 0.14 0.22 2.2 < 0.3 3.4 1.2 33

11BC3A 0.03 0.17 0.22 1.2 < 0.3 2.0 1.8 17

11BC4A 0.02 0.13 0.22 9.2 < 0.3 3.6 1.9 32

11BC10A 0.02 0.14 0.22 16.4 0.39 3.1 4.8 26
35

Table 6.—Continued

Field Sm SO4 Sr Ta Tb Th Ti Tl

number μg/L mg/L μg/L μg/L μg/L μg/L μg/L μg/L

Sampling Event 1: Jan. 2009

BC2 < 0.01 18 320.0 < 0.02 < 0.005 < 0.2 < 0.5 < 0.1

BC3 < 0.01 17 428.0 < 0.02 < 0.005 < 0.2 < 0.5 < 0.1

BCA 0.03 3 34.6 < 0.02 0.008 < 0.2 < 0.5 < 0.1

BCB 0.01 9 97.4 < 0.02 < 0.005 < 0.2 < 0.5 < 0.1

BC4 < 0.01 18 768.0 < 0.02 < 0.005 < 0.2 < 0.5 < 0.1

Sampling Event 2: Jun. 2010

10BC1A < 0.01 4 450 < 0.02 < 0.005 < 0.2 0.6 < 0.1

10BC2A 1.12 11 395 < 0.02 0.170 0.34 231.0 < 0.1

10BC3A < 0.01 11 428 < 0.02 < 0.005 < 0.2 1.0 < 0.1

10BC4A < 0.01 12 518 < 0.02 < 0.005 < 0.2 0.8 < 0.1

10BC5A 0.02 107 915 0.03 0.006 < 0.2 4.3 < 0.1

10BC6A 0.03 134 1,000 0.04 0.006 < 0.2 5.0 < 0.1

10BC7A < 0.01 29 690 < 0.02 < 0.005 < 0.2 2.0 < 0.1

10BC8A 0.01 29 679 < 0.02 < 0.005 < 0.2 1.7 < 0.1

10BC9A 0.01 33 678 < 0.02 < 0.005 < 0.2 1.2 < 0.1

10BC10A < 0.01 45 664 < 0.02 < 0.005 < 0.2 1.6 < 0.1

Sampling Event 3: Sep. 2010

10BC1A < 0.01 < 2.0 510 0.04 < 0.005 < 0.2 < 0.5 < 0.1

10BC2A < 0.01 5.9 328 0.03 < 0.005 < 0.2 < 0.5 < 0.1

10BC3A < 0.01 2.9 418 0.03 < 0.005 < 0.2 < 0.5 < 0.1

10BC4A 0.03 6.2 460 0.03 < 0.005 < 0.2 3.2 < 0.1

10BC5A 0.07 240.0 1,460 0.42 0.020 < 0.2 13.6 < 0.1

10BC6A 0.09 280.0 1,600 0.22 0.006 < 0.2 14.4 < 0.1

10BC7A < 0.01 31.0 640 0.04 < 0.005 < 0.2 3.6 < 0.1

10BC8A < 0.01 32.0 689 0.03 < 0.005 < 0.2 2.0 < 0.1

10BC9A 0.03 41.0 767 0.04 < 0.005 < 0.2 2.7 < 0.1

10BC10A 0.04 49.0 498 0.09 < 0.005 < 0.2 3.4 < 0.1

Sampling Event 4: Mar. 2011

11BC1A 0.65 2.7 256 < 0.02 0.13 0.31 91.4 < 0.10

11BC4A 0.72 4.4 210 < 0.02 0.14 0.32 136.0 < 0.10

11BC5A 8.80 15.0 690 < 0.02 1.40 3.23 1070.0 0.53

11BC6A 6.30 14.0 530 < 0.02 0.98 1.81 483.0 0.34

11BC7A 0.42 5.6 239 < 0.02 0.088 0.25 37.9 < 0.10

11BC8A 1.60 6.2 275 < 0.02 0.28 0.40 120.0 0.11

11BC9A 1.40 7.2 255 < 0.02 0.25 0.42 152.0 0.10

11BC10A 1.50 11.0 279 < 0.02 0.27 0.62 226.0 0.12

Sampling Event 5: Jun. 2011

11BC2A 0.35 9.9 350 < 0.02 0.006 0.38 2.7 0.28

11BC3A 0.34 220.0 940 < 0.02 < 0.005 0.39 3.5 0.43

11BC4A 0.34 13.0 397 < 0.02 < 0.005 0.37 1.0 0.29

11BC10A 0.36 51.0 540 < 0.02 < 0.005 0.38 3.7 0.30
36

Table 6.—Continued

Field Tm U V W Y Yb Zn Zr

number μg/L μg/L μg/L μg/L μg/L μg/L μg/L μg/L

Sampling Event 1: Jan. 2009

BC2 < 0.005 < 0.1 4.3 < 0.50 0.10 0.005 2.3 < 0.2

BC3 < 0.005 < 0.1 5.2 3.06 0.12 0.006 2.0 < 0.2

BCA < 0.005 < 0.1 3.7 < 0.50 0.15 < 0.005 2.4 < 0.2

BCB < 0.005 < 0.1 1.7 < 0.50 0.06 < 0.005 2.4 < 0.2

BC4 < 0.005 < 0.1 5.1 1.47 0.14 0.007 2.2 < 0.2

Sampling Event 2: Jun. 2010

10BC1A < 0.005 < 0.10 5.0 < 0.50 0.04 < 0.005 0.6 < 0.2

10BC2A 0.053 0.18 36.7 0.88 3.54 0.280 52.6 0.2

10BC3A < 0.005 < 0.10 4.0 2.66 0.08 0.005 1.5 < 0.2

10BC4A < 0.005 < 0.10 3.8 2.61 0.08 < 0.005 1.0 < 0.2

10BC5A < 0.005 0.31 12.5 509.0 0.30 0.020 1.7 0.2

10BC6A < 0.005 0.28 12.4 782.0 0.30 0.020 1.9 0.3

10BC7A < 0.005 < 0.10 6.4 136.0 0.15 0.009 3.0 < 0.2

10BC8A < 0.005 < 0.10 5.4 105.0 0.14 0.007 1.2 < 0.2

10BC9A < 0.005 < 0.10 5.8 87.1 0.12 0.008 1.4 < 0.2

10BC10A < 0.005 0.11 5.6 84.6 0.10 0.010 2.0 < 0.2

Sampling Event 3: Sep. 2010

10BC1A 0.005 < 0.10 1.9 nr 0.04 0.01 < 3 nr

10BC2A < 0.005 < 0.10 < 0.5 nr 0.05 < 0.01 < 3 nr

10BC3A < 0.005 < 0.10 1.4 nr 0.08 < 0.01 < 3 nr

10BC4A < 0.005 < 0.10 1.8 nr 0.13 0.04 < 3 nr

10BC5A 0.010 0.19 5.0 nr 1.00 0.10 3.5 nr

10BC6A 0.010 0.13 2.2 nr 0.60 0.06 < 3 nr

10BC7A 0.007 < 0.10 1.7 nr 0.11 0.04 < 3 nr

10BC8A < 0.005 < 0.10 2.2 nr 0.14 0.02 < 3 nr

10BC9A 0.005 < 0.10 4.3 nr 0.11 0.05 < 3 nr

10BC10A 0.006 0.11 5.0 nr 0.04 0.04 < 3 nr

Sampling Event 4: Mar. 2011

11BC1A 0.070 < 0.10 19.9 < 0.5 35.1 2.60 295.0 nr

11BC4A 0.077 < 0.10 27.2 < 0.5 24.4 1.60 230.0 nr

11BC5A 0.440 0.62 263.0 2.0 1.9 0.14 20.4 nr

11BC6A 0.310 0.41 169.0 1.2 6.4 0.47 65.5 nr

11BC7A 0.052 < 0.10 15.1 < 0.5 5.8 0.45 57.1 nr

11BC8A 0.120 0.14 47.5 < 0.5 6.1 0.40 60.5 nr

11BC9A 0.110 0.14 43.3 < 0.5 nr nr nr nr

11BC10A 0.110 0.17 47.7 0.56 nr nr nr nr

Sampling Event 5: Jun. 2011

11BC2A 0.03 < 0.10 3.9 1.9 0.10 < 0.01 < 3 nr

11BC3A 0.03 0.88 3.3 2.0 0.13 < 0.01 < 3 nr

11BC4A 0.03 < 0.10 4.0 3.8 0.09 < 0.01 < 3 nr

11BC10A 0.03 < 0.10 4.9 20.0 0.12 < 0.01 < 3 nr
37

Table 7. Major- and minor-element concentrations in filtered waters collected from Bear Creek, Colusa 

County California. ICP-MS results (ICP-AES for major elements).

Field Ag Al As B Ba Be Bi Ca

number μg/L μg/L μg/L μg/L μg/L μg/L μg/L mg/L

Sampling Event 1: Jan. 2009

BC2 < 1 < 2 1 77.7 100 < 0.05 < 0.2 17.2

BC3 < 1 < 2 2 2,790 179 < 0.05 < 0.2 17.7

BCA < 1 < 2 2 6.21 20.5 < 0.05 < 0.2 4.30

BCB < 1 < 2 < 1 96.7 18.0 < 0.05 < 0.2 8.77

BC4 < 1 < 2 2 3,100 195 < 0.05 < 0.2 23.4

Sampling Event 2: Jun. 2010

10BC1B < 1 < 2.0 1.0 116 66 < 0.05 < 0.2 14.9

10BC2B < 1 14.3 1.0 273 111 < 0.05 < 0.2 16.4

10BC3B < 1 15.0 2.0 1,920 176 < 0.05 < 0.2 17.1

10BC4B < 1 13.4 2.0 2,030 193 < 0.05 < 0.2 17.4

10BC5B < 1 84.1 14.8 46,600 375 < 0.05 < 0.2 26.3

10BC6B < 1 38.7 16.6 < 5 488 < 0.05 < 0.2 10.5

10BC7B < 1 10.7 4.7 < 5 249 < 0.05 < 0.2 < 0.1

10BC8B < 1 < 2.0 4.0 10,600 248 < 0.05 < 0.2 18.3

10BC9B < 1 8.6 3.4 90.5 220 < 0.05 < 0.2 < 0.1

10BC10B < 1 < 2.0 3.9 9,990 203 < 0.05 < 0.2 21.6

Sampling Event 3: Sep. 2010

10BC1B < 1 < 2.0 3.2 96.7 98.3 < 10 < 0.2 14.6

10BC2B < 1 < 2.0 2.8 90.1 175 < 10 < 0.2 15.4

10BC3B < 1 < 2.0 3.2 2,660 299 < 10 < 0.2 16.3

10BC4B < 1 < 2.0 3.3 2,660 307 < 10 < 0.2 17.4

10BC5B < 1 45.6 20.5 198,000 2,320 < 10 < 0.2 16.8

10BC6B < 1 7.4 15.1 275,000 2,110 < 10 < 0.2 15.4

10BC7B < 1 < 2.0 5.4 19,800 429 < 10 < 0.2 18.9

10BC8B < 1 2.7 4.3 19,600 435 < 10 < 0.2 19.2

10BC9B < 1 < 2.0 3.2 21,000 407 < 10 < 0.2 21.3

10BC10B < 1 < 2.0 5.8 19,500 223 < 10 < 0.2 16.5

Sampling Event 4: Mar. 2011

11BC1B < 1 80.9 < 1 26.7 56.7 < 0.05 < 0.2 11.7

11BC4B < 1 155.0 < 1 449 51.8 < 0.05 < 0.2 10.1

11BC5B < 1 485.0 < 1 1,560 33.7 < 0.05 < 0.2 10.5

11BC6B < 1 115.0 < 1 1,620 32.1 < 0.05 < 0.2 10.3

11BC7B < 1 96.9 < 1 868 71.3 < 0.05 < 0.2 11.0

11BC8B < 1 134.0 < 1 593 49.8 < 0.05 < 0.2 9.62

11BC9B < 1 3.7 < 1 537 44.6 < 0.05 < 0.2 9.86

11BC10B < 1 3.1 < 1 679 47.5 < 0.05 < 0.2 12.6

Sampling Event 5: Jun. 2011

11BC2B < 1 < 2 < 1.0 252 88.2 < 0.05 < 0.2 15.3

11BC3B < 1 < 2 < 1.0 1,820 143 < 0.05 < 0.2 16.2

11BC4B < 1 < 2 < 1.0 1,870 145 < 0.05 < 0.2 15.4

11BC10B < 1 < 2 1.6 4,480 156 < 0.05 < 0.2 23.0
38

Table 7.—Continued

Field Cd Ce Co Cr Cs Cu Dy Er

number μg/L μg/L μg/L μg/L μg/L μg/L μg/L μg/L

Sampling Event 1: Jan. 2009

BC2 < 0.02 < 0.01 0.13 7.8 < 0.02 0.63 0.007 0.006

BC3 < 0.02 0.01 0.14 9.6 1.95 0.67 0.008 0.007

BCA < 0.02 0.03 0.12 6.4 < 0.02 0.54 0.009 < 0.005

BCB < 0.02 < 0.01 0.03 23.4 < 0.02 0.53 0.008 < 0.005

BC4 < 0.02 0.02 0.07 9.4 0.53 0.85 0.010 0.009

Sampling Event 2: Jun. 2010

10BC1B < 0.02 < 0.01 0.12 6.5 < 0.02 0.50 < 0.005 < 0.005

10BC2B < 0.02 0.01 0.20 4.3 0.20 0.62 0.010 0.005

10BC3B < 0.02 0.02 0.24 4.8 1.90 0.66 < 0.005 < 0.005

10BC4B < 0.02 0.02 0.16 4.2 1.46 0.81 < 0.005 0.007

10BC5B < 0.02 0.07 0.48 10.8 143.0 3.0 0.020 0.020

10BC6B < 0.02 0.09 0.50 10.2 259.0 2.5 0.040 0.020

10BC7B < 0.02 0.02 0.22 4.7 35.6 1.2 0.010 0.010

10BC8B < 0.02 0.02 0.22 4.0 26.8 1.2 0.009 0.007

10BC9B < 0.02 0.02 0.29 3.5 19.1 1.4 0.010 0.010

10BC10B < 0.02 0.01 0.19 3.3 15.8 1.5 0.008 0.009

Sampling Event 3: Sep. 2010

10BC1B 0.03 < 0.01 0.15 1.1 0.02 < 0.5 0.02 0.020

10BC2B 0.06 0.01 0.15 1.4 0.12 < 0.5 0.02 0.010

10BC3B 0.06 < 0.01 0.14 1.5 3.20 < 0.5 0.02 0.008

10BC4B 0.04 0.01 0.10 1.2 1.60 0.54 0.02 0.009

10BC5B 0.04 0.15 0.38 4.6 1,070 1.3 0.11 0.079

10BC6B 0.03 0.12 0.26 4.6 1,220 1.3 0.06 0.040

10BC7B 0.03 0.01 0.15 1.5 81.7 0.9 0.01 0.020

10BC8B 0.04 0.02 0.20 1.3 66.2 1.1 0.01 0.020

10BC9B 0.03 0.01 0.20 1.2 42.1 1.3 0.03 0.020

10BC10B 0.03 < 0.01 0.21 1.3 26.1 1.4 0.008 0.020

Sampling Event 4: Mar. 2011

11BC1B < 0.02 0.18 1.40 1.9 < 0.02 1.7 0.073 0.072

11BC4B < 0.02 0.15 3.40 6.2 0.14 1.8 0.078 0.063

11BC5B < 0.02 0.48 4.60 7.5 0.74 2.8 0.110 0.084

11BC6B < 0.02 0.27 0.41 3.5 0.54 2.0 0.074 0.066

11BC7B < 0.02 0.12 1.40 5.7 0.33 1.4 0.063 0.056

11BC8B < 0.02 0.18 3.80 6.3 0.30 2.1 0.071 0.067

11BC9B < 0.02 0.07 0.22 3.5 0.16 1.5 0.052 0.063

11BC10B < 0.02 0.07 0.24 3.6 0.22 1.6 0.056 0.061

Sampling Event 5: Jun. 2011

11BC2B < 0.02 0.25 4.9 6.6 0.55 0.89 0.089 0.064

11BC3B < 0.02 0.25 5.4 6.2 4.10 0.96 0.088 0.063

11BC4B < 0.02 0.25 5.6 6.1 3.80 1.20 0.097 0.063

11BC10B 0.11 0.26 5.8 4.8 6.60 1.60 0.097 0.065
39

Table 7.—Continued

Field Eu Fe Ga Gd Ge Ho K La

number μg/L μg/L μg/L μg/L μg/L μg/L mg/L μg/L

Sampling Event 1: Jan. 2009

BC2 0.030 < 20 < 0.05 0.006 < 0.05 < 0.005 0.44 < 0.01

BC3 0.061 < 20 < 0.05 0.008 < 0.05 < 0.005 5.58 0.01

BCA 0.009 < 20 < 0.05 0.010 < 0.05 < 0.005 0.06 0.01

BCB 0.007 < 20 < 0.05 0.007 < 0.05 < 0.005 0.41 0.01

BC4 0.059 < 20 < 0.05 0.008 < 0.05 < 0.005 5.58 0.01

Sampling Event 2: Jun. 2010

10BC1B 0.01 < 20 < 0.05 < 0.005 < 0.05 < 0.005 0.56 < 0.01

10BC2B 0.02 37.4 < 0.05 0.006 < 0.05 < 0.005 1.00 0.02

10BC3B 0.04 40.9 < 0.05 0.010 < 0.05 < 0.005 4.26 0.01

10BC4B 0.02 32.0 < 0.05 0.006 < 0.05 < 0.005 4.13 0.01

10BC5B 0.04 136 < 0.05 0.040 3.40 0.008 96.4 0.03

10BC6B 0.051 13,300 < 0.05 0.030 6.60 0.008 132.0 0.05

10BC7B 0.03 < 20 < 0.05 0.010 1.10 < 0.005 23.0 0.02

10BC8B 0.05 < 20 < 0.05 0.007 0.52 < 0.005 18.7 0.02

10BC9B 0.02 < 20 < 0.05 0.006 0.32 < 0.005 16.3 0.01

10BC10B 0.02 < 20 < 0.05 0.005 0.10 < 0.005 16.5 < 0.01

Sampling Event 3: Sep. 2010

10BC1B 0.010 < 20 0.10 0.02 nr < 0.005 0.373 < 0.01

10BC2B 0.007 < 20 0.10 0.02 nr 0.009 0.510 0.01

10BC3B < 0.005 < 20 0.09 0.03 nr 0.005 5.330 < 0.01

10BC4B 0.010 < 20 0.10 0.01 nr 0.005 5.130 < 0.01

10BC5B < 0.005 301 0.46 0.087 nr 0.020 385.0 0.04

10BC6B 0.009 241 0.48 0.067 nr 0.020 539.0 0.03

10BC7B 0.010 < 20 0.10 0.03 nr 0.008 32.5 < 0.01

10BC8B < 0.005 < 20 0.20 0.02 nr 0.007 32.7 0.01

10BC9B < 0.005 < 20 0.20 0.02 nr 0.009 32.6 < 0.01

10BC10B 0.007 < 20 0.20 0.02 nr 0.009 29.9 < 0.01

Sampling Event 4: Mar. 2011

11BC1B 0.04 120 < 0.05 0.092 nr 0.01 1.5 0.10

11BC4B 0.04 223 < 0.05 0.072 nr 0.01 1.8 0.06

11BC5B 0.04 697 0.10 0.130 nr 0.02 5.7 0.18

11BC6B 0.04 179 < 0.05 0.094 nr 0.01 6.2 0.10

11BC7B 0.04 148 < 0.05 0.062 nr 0.01 2.5 0.05

11BC8B 0.03 207 < 0.05 0.071 nr 0.01 2.5 0.07

11BC9B 0.03 < 20 < 0.05 0.056 nr 0.01 2.4 0.02

11BC10B 0.04 < 20 < 0.05 0.053 nr 0.01 2.6 0.03

Sampling Event 5: Jun. 2011

11BC2B 0.3 < 20 < 0.05 < 0.005 nr 0.02 1.78 < 0.01

11BC3B 0.3 < 20 < 0.05 < 0.005 nr 0.02 4.46 < 0.01

11BC4B 0.3 < 20 < 0.05 < 0.005 nr 0.02 4.64 < 0.01

11BC10B 0.3 22 < 0.05 < 0.005 nr 0.02 9.30 < 0.01
40

Table 7.—Continued

Field Li Lu Mg Mn Mo Na Nb Nd

number μg/L μg/L mg/L μg/L μg/L mg/L μg/L μg/L

Sampling Event 1: Jan. 2009

BC2 4.2 < 0.1 88.7 24.8 < 2 20.50 < 0.2 0.01

BC3 203.0 < 0.1 88.0 28.5 < 2 65.30 < 0.2 0.02

BCA 3.9 < 0.1 29.0 5.2 < 2 1.12 < 0.2 0.03

BCB 7.2 < 0.1 96.7 0.2 < 2 7.27 < 0.2 0.02

BC4 217.0 < 0.1 96.4 5.5 < 2 83.50 < 0.2 0.02

Sampling Event 2: Jun. 2010

10BC1B 3.6 < 0.1 90.3 3.2 < 2 27.9 < 0.2 < 0.01

10BC2B 20.1 < 0.1 88.7 26.6 < 2 26.0 < 0.2 0.02

10BC3B 171 < 0.1 90.2 27.0 < 2 57.5 < 0.2 0.02

10BC4B 168 < 0.1 94.4 12.8 < 2 57.5 < 0.2 0.02

10BC5B 1,560 < 0.1 94.6 50.8 < 2 1,520 < 0.2 0.06

10BC6B 1,980 < 0.1 8.23 60.5 < 2 4.19 < 0.2 0.08

10BC7B 572 < 0.1 < 0.10 19.3 < 2 < 0.1 < 0.2 0.02

10BC8B 534 < 0.1 96.6 7.7 < 2 337 < 0.2 0.02

10BC9B 458 < 0.1 < 0.10 7.7 < 2 0.763 < 0.2 0.03

10BC10B 457 < 0.1 103 3.4 < 2 325 < 0.2 0.01

Sampling Event 3: Sep. 2010

10BC1B 8 nr 91.0 19.9 < 2 33.0 < 0.2 0.02

10BC2B 10 nr 86.2 14.6 < 2 20.7 < 0.2 0.04

10BC3B 200 nr 85.9 22.0 < 2 65.5 < 0.2 0.02

10BC4B 196 nr 88.3 3.8 < 2 70.1 < 0.2 0.03

10BC5B 10,100 nr 77.6 140 < 2 < 0.1 < 0.2 0.14

10BC6B 14,000 nr 85.9 84.8 < 2 < 0.1 < 0.2 0.09

10BC7B 880 nr 90.7 12.3 < 2 596.0 < 0.2 0.05

10BC8B 915 nr 101.0 3.3 < 2 633.0 < 0.2 0.02

10BC9B 939 nr 115.0 3.1 < 2 648.0 < 0.2 0.01

10BC10B 890 nr 122.0 2.7 < 2 654.0 < 0.2 0.01

Sampling Event 4: Mar. 2011

11BC1B < 0.1 nr 17.3 3.6 < 2 10.5 < 0.2 0.22

11BC4B 25.5 nr 38.9 11.7 < 2 16.3 < 0.2 0.18

11BC5B 69.4 nr 19.6 24.7 < 2 52.7 < 0.2 0.43

11BC6B 68.3 nr 18.5 10.9 < 2 59.8 < 0.2 0.24

11BC7B 55.4 nr 44.6 6.8 < 2 25.9 < 0.2 0.17

11BC8B 33.7 nr 33.5 12.6 < 2 21.8 < 0.2 0.21

11BC9B 29.0 nr 30.7 3.3 < 2 20.7 < 0.2 0.14

11BC10B 34.5 nr 36.1 3.1 < 2 23.6 < 0.2 0.14

Sampling Event 5: Jun. 2011

11BC2B 23.3 nr 91.1 < 0.2 < 2 24.5 < 0.2 0.45

11BC3B 141.0 nr 95.5 < 0.2 < 2 55.2 < 0.2 0.46

11BC4B 146.0 nr 88.6 < 0.2 < 2 51.3 < 0.2 0.46

11BC10B 264.0 nr 94.2 < 0.2 < 2 136.0 < 0.2 0.46
41

Table 7.—Continued

Field Ni P Pb Pr Rb Sb Sc Se

number μg/L mg/L μg/L μg/L μg/L μg/L μg/L μg/L

Sampling Event 1: Jan. 2009

BC2 3.0 0.03 0.4 < 0.01 0.14 < 0.3 5.5 1.2

BC3 3.4 0.04 0.3 < 0.01 10.10 < 0.3 5.5 2.2

BCA 2.1 0.02 < 0.05 < 0.01 0.03 < 0.3 9.8 < 1.0

BCB 2.1 < 0.01 0.2 < 0.01 0.27 < 0.3 6.8 < 1.0

BC4 3.4 0.02 0.4 < 0.01 6.82 < 0.3 5.1 2.8

Sampling Event 2: Jun. 2010

10BC1B 1.9 0.02 0.8 < 0.01 0.29 < 0.3 3.1 1.3

10BC2B 3.9 0.04 0.5 < 0.01 1.28 < 0.3 2.8 1.2

10BC3B 4.3 0.05 0.7 < 0.01 9.16 < 0.3 2.6 2.0

10BC4B 3.9 0.04 0.6 < 0.01 8.52 < 0.3 2.6 1.9

10BC5B 6.4 0.09 0.8 0.01 199 5.37 1.7 38.0

10BC6B 5.9 0.04 0.4 0.01 275 6.18 2.4 45.8

10BC7B 4.3 < 0.01 1.4 < 0.01 51.7 0.88 2.1 9.2

10BC8B 3.9 < 0.01 1.1 < 0.01 41.4 0.86 1.7 8.3

10BC9B 4.5 0.02 0.9 < 0.01 34.8 0.72 1.5 7.2

10BC10B 3.7 < 0.01 0.9 < 0.01 33.8 0.74 1.1 7.5

Sampling Event 3: Sep. 2010

10BC1B 1.8 0.03 < 0.05 < 0.01 0.22 < 0.3 3.6 42.2

10BC2B 1.5 0.04 0.06 < 0.01 0.43 < 0.3 3.5 44.1

10BC3B 2.2 0.03 < 0.05 < 0.01 11.8 < 0.3 3.2 40.1

10BC4B 1.7 0.03 < 0.05 < 0.01 9.7 < 0.3 3.0 36.9

10BC5B 5.1 0.10 0.12 0.02 873 48.2 4.3 624.0

10BC6B 4.6 0.07 0.07 0.01 896 31.1 5.8 662.0

10BC7B 2.6 0.04 0.08 < 0.01 67.8 2.1 3.4 92.1

10BC8B 3.2 0.03 0.05 < 0.01 63.1 2.0 2.9 86.3

10BC9B 4.0 0.02 < 0.05 < 0.01 57.9 1.6 2.7 95.0

10BC10B 3.4 0.03 0.05 < 0.01 47.8 1.5 2.4 84.7

Sampling Event 4: Mar. 2011

11BC1B 4.4 0.07 < 0.05 0.07 0.17 < 0.30 1.6 < 1.0

11BC4B 10.3 0.08 0.39 0.05 1.8 0.86 2.4 < 1.0

11BC5B 18.5 0.07 0.34 0.09 8.5 1.30 2.3 2.3

11BC6B 8.1 0.06 0.10 0.07 8.9 0.47 1.9 2.2

11BC7B 7.9 0.07 0.18 0.05 3.2 < 0.30 2.4 1.5

11BC8B 27.1 0.07 0.47 0.06 3.1 2.10 2.3 1.1

11BC9B 6.6 0.07 < 0.05 0.04 2.6 < 0.30 2.0 1.3

11BC10B 6.6 0.07 < 0.05 0.04 3.0 < 0.30 2.1 1.1

Sampling Event 5: Jun. 2011

11BC2B < 0.4 0.02 0.11 0.22 2.3 < 0.30 3.5 < 1.0

11BC3B < 0.4 0.02 0.12 0.22 9.5 < 0.30 3.5 2.7

11BC4B < 0.4 0.04 0.12 0.22 9.3 < 0.30 3.5 1.8

11BC10B < 0.4 0.01 0.13 0.22 16.9 0.36 2.9 4.8
42

Table 7.—Continued

Field SiO2 Sm SO4 Sr Ta Tb Th Ti

number mg/L μg/L mg/L μg/L μg/L μg/L μg/L μg/L

Sampling Event 1: Jan. 2009

BC2 23.2 < 0.01 16 331 < 0.02 < 0.005 < 0.2 < 0.5

BC3 24.1 < 0.01 16 417 < 0.02 < 0.005 < 0.2 < 0.5

BCA 42.3 < 0.01 3 33.7 < 0.02 < 0.005 < 0.2 < 0.5

BCB 31.2 < 0.01 8 94 < 0.02 < 0.005 < 0.2 < 0.5

BC4 23.6 < 0.01 19 755 < 0.02 < 0.005 < 0.2 < 0.5

Sampling Event 2: Jun. 2010

10BC1B 34.6 < 0.01 6 469 < 0.02 < 0.005 < 0.2 < 0.5

10BC2B 30.7 < 0.01 11 393 < 0.02 < 0.005 < 0.2 0.8

10BC3B 30.6 < 0.01 12 445 < 0.02 < 0.005 < 0.2 0.8

10BC4B 30.4 < 0.01 13 517 < 0.02 < 0.005 < 0.2 0.6

10BC5B 25.5 0.02 108 963 0.04 0.005 < 0.2 4.6

10BC6B 39.7 0.03 133 1,040 0.04 0.007 < 0.2 4.8

10BC7B 31.6 < 0.01 27 676 < 0.02 < 0.005 < 0.2 1.2

10BC8B 23.8 < 0.01 25 692 < 0.02 < 0.005 < 0.2 0.9

10BC9B 20.7 < 0.01 28 653 < 0.02 < 0.005 < 0.2 1.1

10BC10B 15.2 < 0.01 43 667 0.02 < 0.005 < 0.2 1.0

Sampling Event 3: Sept. 2010

10BC1B 15 0.03 13 504 0.04 0.005 < 0.2 4.3

10BC2B 14 0.04 18 343 < 0.02 < 0.005 < 0.2 5.2

10BC3B 15 0.05 14 440 < 0.02 < 0.005 < 0.2 4.3

10BC4B 15 0.05 12 486 < 0.02 0.006 < 0.2 3.8

10BC5B 28 0.07 110 1,550 0.29 0.020 < 0.2 12.2

10BC6B 49 0.07 130 1,690 0.20 0.010 < 0.2 11.9

10BC7B 17 0.04 19 676 0.03 0.006 < 0.2 5.4

10BC8B 15 0.04 21 728 0.03 < 0.005 < 0.2 5.2

10BC9B 10 0.02 22 773 0.02 0.007 < 0.2 5.2

10BC10B 5.4 0.04 26 510 0.03 0.005 < 0.2 5.5

Sampling Event 4: Mar. 2011

11BC1B 16 < 0.01 4.2 231 < 0.02 0.03 < 0.2 3.3

11BC4B 23 < 0.01 5.4 161 < 0.02 0.02 0.20 3.4

11BC5B 22 0.03 15.0 195 < 0.02 0.03 0.21 7.2

11BC6B 19 < 0.01 16.0 190 < 0.02 0.03 < 0.2 2.6

11BC7B 23 < 0.01 8.2 216 < 0.02 0.02 < 0.2 1.9

11BC8B 23 < 0.01 7.5 192 < 0.02 0.03 < 0.2 2.9

11BC9B 20 < 0.01 9.5 189 < 0.02 0.02 < 0.2 < 0.5

11BC10B 21 < 0.01 13.0 219 < 0.02 0.02 < 0.2 < 0.5

Sampling Event 5: Jun. 2011

11BC2B 32 0.34 10 345 < 0.02 < 0.005 0.37 < 0.5

11BC3B 32 0.35 11 393 < 0.02 < 0.005 0.37 < 0.5

11BC4B 32 0.34 14 394 < 0.02 < 0.005 0.38 < 0.5

11BC10B 27 0.34 52 554 < 0.02 < 0.005 0.38 1.1
43

Table 7.—Continued

Field Tl Tm U V W Y Yb Zn Zr

number μg/L μg/L μg/L μg/L μg/L μg/L μg/L μg/L μg/L

Sampling Event 1: Jan. 2009

BC2 < 0.1 < 0.005 < 0.1 4.4 < 0.5 0.09 0.005 3.0 < 0.2

BC3 < 0.1 < 0.005 < 0.1 5.3 3.01 0.11 < 0.005 2.2 < 0.2

BCA < 0.1 < 0.005 < 0.1 3.5 < 0.5 0.05 < 0.005 1.8 < 0.2

BCB < 0.1 < 0.005 < 0.1 2.2 < 0.5 0.06 < 0.005 2.6 < 0.2

BC4 < 0.1 < 0.005 < 0.1 5.2 1.74 0.13 0.008 2.6 < 0.2

Sampling Event 2: Jun. 2010

10BC1B < 0.1 < 0.005 < 0.1 5.1 < 0.5 0.03 < 0.005 0.6 < 0.2

10BC2B < 0.1 < 0.005 < 0.1 3.6 < 0.5 0.07 < 0.005 0.8 < 0.2

10BC3B < 0.1 < 0.005 < 0.1 4.1 2.07 0.07 < 0.005 0.7 < 0.2

10BC4B < 0.1 < 0.005 < 0.1 4.1 2.09 0.07 0.006 0.7 < 0.2

10BC5B < 0.1 < 0.005 0.30 12.8 506 0.29 0.020 1.6 0.3

10BC6B < 0.1 < 0.005 0.28 12.3 779 0.30 0.020 2.9 0.2

10BC7B < 0.1 < 0.005 < 0.1 5.4 122 0.13 0.010 1.0 < 0.2

10BC8B < 0.1 < 0.005 < 0.1 5.2 105 0.12 < 0.005 1.3 < 0.2

10BC9B < 0.1 < 0.005 < 0.1 5.1 83.5 0.12 0.005 0.9 < 0.2

10BC10B < 0.1 < 0.005 0.1 5.2 81.2 0.10 < 0.005 1.0 < 0.2

Sampling Event 3: Sept. 2010

10BC1B < 0.1 0.007 < 0.1 4.3 nr 0.05 0.03 < 3 nr

10BC2B < 0.1 0.007 < 0.1 3.4 nr 0.07 0.04 < 3 nr

10BC3B < 0.1 0.006 < 0.1 3.4 nr 0.07 0.02 < 3 nr

10BC4B < 0.1 0.010 < 0.1 4.2 nr 0.08 0.03 < 3 nr

10BC5B < 0.1 0.010 0.26 4.9 nr 1.10 0.07 3.2 nr

10BC6B < 0.1 0.010 0.19 4.5 nr 0.65 0.05 < 3 nr

10BC7B < 0.1 0.010 < 0.1 3.7 nr 0.12 0.02 < 3 nr

10BC8B < 0.1 0.009 < 0.1 4.2 nr 0.15 0.02 < 3 nr

10BC9B < 0.1 0.010 0.11 4.8 nr 0.14 0.04 < 3 nr

10BC10B < 0.1 0.010 0.17 6.6 nr 0.04 0.01 < 3 nr

Sampling Event 4: Mar. 2011

11BC1B < 0.1 0.04 < 0.1 2.9 < 0.5 0.20 0.03 < 3 nr

11BC4B < 0.1 0.04 < 0.1 3.4 0.52 0.14 0.03 < 3 nr

11BC5B < 0.1 0.04 < 0.1 4.7 7.7 0.34 0.04 4.5 nr

11BC6B < 0.1 0.04 < 0.1 4.0 9.9 0.22 0.02 < 3 nr

11BC7B < 0.1 0.03 < 0.1 3.0 1.1 0.14 0.02 < 3 nr

11BC8B < 0.1 0.04 < 0.1 3.6 1.5 0.18 0.03 < 3 nr

11BC9B < 0.1 0.04 < 0.1 3.3 2.0 0.10 0.02 < 3 nr

11BC10B < 0.1 0.03 < 0.1 3.2 2.2 0.10 0.02 < 3 nr

Sampling Event 5: Jun. 2011

11BC2B 0.28 0.03 < 0.1 3.6 2.0 0.06 < 0.01 < 3 nr

11BC3B 0.28 0.03 < 0.1 4.0 4.0 0.07 < 0.01 < 3 nr

11BC4B 0.28 0.03 < 0.1 4.0 4.1 0.08 < 0.01 < 3 nr

11BC10B 0.29 0.03 < 0.1 4.9 20 0.10 < 0.01 < 3 nr
44

Table 8. Enrichment of stable isotopes in unfiltered waters collected from 

Bear Creek, Colusa County, California.

Sample site δ18H δ2H

per mil per mil

Low Flow Sept. 2010

BC1 -8.12 -58.68

BC2 -7.92 -57.12

BC3 -7.75 -57.99

BC4 -7.64 -55.74

BC5 -5.21 -48.65

BC6 -4.20 -45.84

BC7 -7.02 -55.29

BC8 -6.88 -53.79

BC9 -6.65 -52.64

BC10 -6.48 -51.80

High Flow Mar. 2011

BC1 -10.04 -71.06

BC4 -8.94 -61.38

BC5 -10.03 -67.00

BC6 -9.79 -66.00

BC7 -8.96 -61.76

BC8 -9.10 -61.45

BC9 -9.17 -62.48

BC10 -9.11 -62.30

High Flow June 2011

BC2 -8.80 -63.42

BC3 -8.73 -61.92

BC4 -8.73 -62.32

BC10 -8.47 -61.48
45

Table 9. Wet weight concentrations of total mercury (HgT) and monomethyl mercury (MMeHg) in invertebrates from sites in the Bear Creek 

Watershed, June and September 2010.

Sample code

Order Family

Sample 

size Mass (g)

Ave. mass 

(g) % Moisture

HgT (μg/g 

ww)

MMeHg 

(μg/g ww) % MMeHg

Collection siteCollection dateSample number Common name

BC2-062910-002 Larval dragonflies Odonata Aeshnidae 3 5.79 1.930 78.2 0.072 0.067 93.1

BC2-062910-001 Larval damselflies Odonata Coenagrionidae 30 1.15 0.038 80.8 0.058 0.073 126.9

BC2-062910-005 adult water striders Hemiptera Gerridae 25 1.38 0.055 67.1 0.121 0.091 75.2

BC2-062910-004 Larval dragonflies Odonata Gomphidae 4 1.45 0.363 71.5 0.045 0.040 89.7

BC2-062910-003 Larval dragonflies Odonata Libellulidae 7 3.83 0.547 81.6 0.059 0.068 115.7

BC3-062910-003 Larval dragonflies Odonata Aeshnidae 1 2.17 2.170 53.7 0.442 0.543 122.9

BC3-062910-002 Larval damselflies Odonata Coenagrionidae 30 1.37 0.046 NA 0.237 0.365 154.0

BC3-062910-007 Adult water striders Hemiptera Gerridae 20 1.01 0.051 55.9 0.139 0.157 112.9

BC3-062910-005 Larval dragonflies Odonata Libellulidae 4 2.33 0.583 80.1 0.351 0.397 113.1

BC4-062910-001 Larval dragonflies Odonata Aeshnidae 2 3.51 1.755 78.6 0.293 0.344 117.4

BC4-062910-003 Larval damselflies Odonata Coenagrionidae 30 1.13 0.038 NA 0.376 0.472 125.5

BC4-062910-004 Adult water striders Hemiptera Gerridae 13 0.58 0.045 NA 0.385 0.259 67.3

BC4-062910-002 Larval dragonflies Odonata Libellulidae 3 1.67 0.557 80.0 0.271 0.339 125.1

BC5-062910-002 Larval damselflies Odonata Coenagrionidae 30 1.32 0.044 NA 0.429 0.248 57.8

BC5-062910-006 Adult water boatmen Hemiptera Corixidae 28 1.24 0.044 71.5 0.235 0.124 52.8

BC5-062910-003 Adult water striders Hemiptera Gerridae 20 1.02 0.051 NA 0.317 0.344 108.5

BC5-062910-001 Larval dragonflies Odonata Libellulidae 4 1.97 0.493 80.5 0.334 0.170 50.9

BC5-062910-004 Adult backswimmers Hemiptera Notonectidae 17 1.73 0.102 NA 0.298 0.255 85.6

BC6-062910-001 Larval damselflies Odonata Coenagrionidae 17 0.74 0.044 NA 4.660 0.331 7.1

BC6-062910-002 Adult water striders Hemiptera Gerridae 24 1.16 0.048 NA 0.597 0.618 103.5

BC7-062910-002 Larval dragonflies Odonata Aeshnidae 1 2.18 2.180 73.7 0.353 0.205 58.1

BC7-062910-003 Larval damselflies Odonata Coenagrionidae 30 1.41 0.047 80.4 0.284 0.185 65.1

BC7-062910-004 Adult water striders Hemiptera Gerridae 30 1.58 0.053 71.9 0.327 0.298 91.1

BC7-062910-001 Larval dragonflies Odonata Gomphidae 7 2.07 0.296 72.6 0.253 0.140 55.3

BC8-061510-002 Larval dragonflies Odonata Aeshnidae 3 4.97 1.657 77.7 0.286 0.207 72.4

BC8-061510-005 Larval damselflies Odonata Coenagrionidae 40 1.79 0.045 64.4 0.239 0.201 84.1

BC8-061510-003 Larval dragonflies Odonata Libellulidae 5 2.91 0.582 79.6 0.278 0.282 101.4

BC9-061510-001 Larval damselflies Odonata Coenagrionidae 30 1.35 0.045 84.0 0.264 0.238 90.2
46

Table 9. Wet weight concentrations of total mercury (HgT) and monomethyl mercury (MMeHg) in invertebrates from sites in the Bear Creek Watershed, 

June and September 2010.—Continued

Sample code

Order Family

Sample 

size Mass (g)

Ave. mass 

(g) % Moisture

HgT 

(μg/g ww)

MMeHg 

(μg/g ww) % MMeHg

Collection siteCollection dateSample number Common name

BC9-061510-004 Adult water striders Hemiptera Gerridae 25 1.23 0.049 NA 0.260 0.281 108.1

BC9-061510-003 Larval dragonflies Odonata Libellulidae 4 2.25 0.563 80.7 0.270 0.181 67.0

BC10-061510-004 Larval dragonflies Odonata Aeshnidae 2 4.47 2.235 77.7 0.257 0.299 116.3

BC10-061510-005 Larval damselflies Odonata Coenagrionidae 50 2.15 0.043 82.3 0.171 0.140 81.9

BC10-061510-006 Adult water striders Hemiptera Gerridae 19 0.88 0.046 NA 0.152 0.290 190.8

BC10-061510-002 Larval dragonflies Odonata Gomphidae 5 1.89 0.378 74.6 0.100 0.086 86.2

BC10-061510-001 Larval dragonflies Odonata Libellulidae 3 1.88 0.627 77.4 0.132 0.142 107.6

BC2-091510-003 Larval dragonflies Odonata Aeshnidae 2 1.15 0.575 NA 0.019 0.020 107.0

BC2-091510-005 Larval damselflies Odonata Calopterygidae 10 1.07 0.107 87.1 0.023 0.020 87.7

BC2-091510-001 Larval dragonflies Odonata Gomphidae 5 1.66 0.332 77.0 0.064 0.040 62.0

BC2-091510-002 Larval dragonflies Odonata Libellulidae 7 1.90 0.271 84.6 0.082 0.052 63.4

BC3-091510-001 Larval dragonflies Odonata Aeshnidae 10 3.50 0.350 80.4 0.186 0.216 116.1

BC3-091510-004 Larval damselflies Odonata Calopterygidae 14 1.05 0.075 84.5 0.095 0.083 87.0

BC3-091510-003 Larval dragonflies Odonata Gomphidae 3 0.49 0.163 NA 0.372 0.308 82.8

BC3-091510-002 Larval dragonflies Odonata Libellulidae 7 3.38 0.483 87.6 0.304 0.240 78.9

BC4-091510-001 Larval dragonflies Odonata Aeshnidae 16 5.11 0.319 85.0 0.387 0.338 87.3

BC4-091510-004 Larval damselflies Odonata Calopterygidae 13 1.33 0.102 84.4 0.132 0.108 81.8

BC4-091510-003 Larval dragonflies Odonata Gomphidae 8 1.80 0.225 75.7 0.248 0.200 80.6

BC4-091510-002 Larval dragonflies Odonata Libellulidae 9 2.65 0.294 85.9 0.272 0.273 100.4

BC5-091710-004 Adult water boatmen Hemiptera Corixidae 9 0.45 0.050 NA 0.401 0.220 54.9

BC5-091710-005 Adult water striders Hemiptera Gerridae 17 0.98 0.058 NA 0.482 0.482 100.0

BC5-091710-006 Larval damselflies Odonata Lestidae 120 1.14 0.010 85.7 0.182 0.245 134.6

BC5-091710-003 Larval dragonflies Odonata Libellulidae 3 0.98 0.327 NA 0.175 0.144 82.3

BC5-091710-001 Adult backswimmers Hemiptera Notonectidae 20 2.17 0.109 68.6 0.373 0.344 92.2

BCUS-091710-002 Larval dragonflies Odonata Aeshnidae 5 0.95 0.190 NA 0.199 0.259 130.2

BCUS-091710-001 Larval dragonflies Odonata Libellulidae 10 1.21 0.121 85.4 0.054 0.052 95.6

BC6-091710-002 Larval soldier flies Diptera Stratiomyidae 10 2.43 0.243 74.5 1.110 0.072 6.5

BC6-091710-001 Larval horse flies Diptera Tabanidae 5 0.89 0.178 NA 0.670 0.100 14.9
47

Table 9. Wet weight concentrations of total mercury (HgT) and monomethyl mercury (MMeHg) in invertebrates from sites in the Bear Creek 

Watershed, June and September 2010.—Continued

Sample code

Order Family

Sample 

size Mass (g)

Ave. mass 

(g) % Moisture

HgT (μg/g 

ww)

MMeHg 

(μg/g ww) % MMeHg

Collection siteCollection dateSample number Common name

BC7-091510-003 Larval dragonflies Odonata Aeshnidae 15 4.58 0.305 NA 1.010 0.369 36.5

BC7-091510-005 Larval damselflies Odonata Calopterygidae 15 1.62 0.108 88.3 1.090 0.591 54.2

BC7-091510-004 Larval dragonflies Odonata Gomphidae 9 3.06 0.340 76.3 0.583 0.599 102.7

BC7-091510-001 Larval dragonflies Odonata Libellulidae 4 1.76 0.440 84.0 1.200 0.347 28.9

BC8-091510-001 Larval dragonflies Odonata Aeshnidae 4 2.38 0.595 78.6 0.240 0.216 90.0

BC8-091510-002 Larval dragonflies Odonata Aeshnidae 10 3.14 0.314 79.8 0.286 0.179 62.6

BC8-091510-005 Larval damselflies Odonata Calopterygidae 19 1.89 0.099 81.7 0.183 0.128 69.9

BC8-091510-003 Larval dragonflies Odonata Libellulidae 9 3.59 0.399 82.7 0.573 0.504 88.0

BC9-091510-002 Larval dragonflies Odonata Aeshnidae 14 4.17 0.298 81.4 0.236 0.271 114.8

BC9-091510-005 Larval damselflies Odonata Calopterygidae 20 0.91 0.046 83.9 0.212 0.224 105.7

BC9-091510-006 Adult water striders Hemiptera Gerridae 25 1.25 0.050 63.1 0.718 1.250 174.1

BC9-091510-007 Adult water striders Hemiptera Gerridae 25 1.22 0.049 62.7 0.694 1.230 177.2

BC9-091510-001 Larval dragonflies Odonata Gomphidae 3 1.04 0.347 NA 0.477 0.534 111.9

BC9-091510-003 Larval dragonflies Odonata Libellulidae 10 4.39 0.439 82.9 0.537 0.589 109.7

BC9-091510-004 Larval dragonflies Odonata Libellulidae 13 2.37 0.182 85.2 0.288 0.291 101.0

BC10-091510-001 Larval dragonflies Odonata Aeshnidae 14 3.40 0.243 79.0 0.299 0.330 110.4

BC10-091510-004 Larval damselflies Odonata Calopterygidae 6 0.36 0.060 NA 0.129 0.149 115.5

BC10-091510-003 Larval dragonflies Odonata Gomphidae 5 1.70 0.340 78.0 0.106 0.131 123.6

BC10-091510-002 Larval dragonflies Odonata Libellulidae 15 2.86 0.191 82.6 0.103 0.145 140.8
48

Table 10. Wet weight concentrations of total mercury (HgT) and monomethyl mercury (MMeHg) in California roach (Hesperoleucus symmetricus) 

from sites in the Bear Creek Watershed, June and September 2010.

Sample code

Total length 

(mm)

Standard 

length (mm)

Fresh 

mass (g)

Sample 

mass (g)

% 

moisture

HgT

(μg/g, ww)

Geometric 

mean HgT 

(μg/g)

MMeHg 

(μg/g, ww)

Geometric mean 

MMeHg (μg/g)

Collection siteCollection dateSample number % MMeHg

BC2-062910-005F 104 90 14.83 13.03 73.8 0.273 0.161 0.384 0.204 140.7

BC2-062910-007F 93 80 9.98 8.41 74.4 0.238 0.280 117.6

BC2-062910-010F 76 65 5.96 4.89 74.3 0.124 0.135 108.9

BC2-062910-011F 85 71 7.17 6.11 75.6 0.107 0.093 86.7

BC2-062910-012F 70 59 4.62 4.01 72.8 0.277 0.374 135.0

BC2-062910-013F 66 56 3.13 2.58 75.6 0.104 0.161 154.8

BC2-062910-019F 55 46 2.08 1.70 67.2 0.113 0.181 160.2

BC3-062910-001F 82 70 8.35 6.67 76.3 0.220 0.326 0.375 0.413 170.5

BC3-062910-003F 79 67 6.97 5.23 77.0 0.245 0.410 167.3

BC3-062910-006F 75 64 6.09 4.79 74.4 0.424 0.503 118.6

BC3-062910-007F 71 61 5.19 4.11 75.9 0.309 0.281 90.9

BC3-062910-008F 67 56 4.32 3.62 69.6 0.355 0.372 104.8

BC3-062910-010F 71 60 3.87 3.38 76.8 0.475 0.558 117.5

BC3-062910-015F 56 48 2.34 1.82 69.8 0.326 0.455 139.6

BC4-062910-001F 77 65 6.31 4.93 74.6 0.479 0.482 0.628 0.505 131.1

BC4-062910-002F 80 67 6.34 5.20 75.2 0.617 0.761 123.3

BC4-062910-004F 75 65 5.42 4.34 73.3 0.523 0.531 101.5

BC4-062910-007F 71 60 4.65 3.59 74.5 0.327 0.324 99.1

BC4-062910-008F 68 57 3.96 3.19 72.8 0.392 0.475 121.2

BC4-062910-009F 65 54 3.26 2.69 72.1 0.494 0.442 89.5

BC4-062910-014F 60 50 2.67 2.10 66.9 0.614 0.483 78.7
49

Table 10. Wet weight concentrations of total mercury (HgT) and monomethyl mercury (MMeHg) in California roach (Hesperoleucus symmetricus) 

from sites in the Bear Creek Watershed, June and September 2010.—Continued

Sample code

Total length 

(mm)

Standard 

length (mm)

Fresh 

mass (g)

Sample 

mass (g)

% 

moisture

HgT

(μg/g, ww)

Geometric 

mean HgT 

(μg/g)

MMeHg 

(μg/g, ww)

Geometric mean 

MMeHg (μg/g)

Collection siteCollection dateSample number % MMeHg

BC7-062910-001F 80 67 7.19 5.80 68.2 0.436 0.457 0.463 0.481 106.2

BC7-062910-002F 71 60 5.29 4.01 74.9 0.407 0.407 100.0

BC7-062910-004F 67 56 4.36 3.40 74.1 0.488 0.453 92.8

BC7-062910-005F 68 56 4.06 3.20 75.2 0.532 0.393 73.9

BC7-062910-009F 62 54 3.26 2.65 75.6 0.577 0.575 99.7

BC7-062910-012F 60 51 2.97 2.25 74.8 0.410 0.610 148.8

BC7-062910-015F 57 49 2.29 1.63 81.0 0.383 0.505 131.9

BC8-061510-003F 75 65 5.66 4.40 75.4 0.501 0.523 0.390 0.554 77.8

BC8-061510-005F 67 56 3.91 3.14 78.1 0.427 0.628 147.1

BC8-061510-006F 61 52 3.13 2.63 75.4 0.405 0.504 124.4

BC8-061510-007F 59 49 2.61 2.04 78.1 0.488 0.639 130.9

BC8-061510-009F 50 42 1.62 1.22 77.7 0.461 0.441 95.7

BC8-062910-001F 72 62 5.68 4.38 75.9 0.820 0.602 73.4

BC8-062910-002F 69 59 4.79 3.59 75.4 0.672 0.767 114.1

BC9-061510-001F 67 57 4.14 3.19 75.8 0.363 0.437 0.457 0.456 125.9

BC9-061510-003F 51 43 1.86 1.49 74.3 0.359 0.397 110.6

BC9-062910-001F 96 81 11.08 9.39 72.5 0.663 0.587 88.5

BC9-062910-002F 71 60 4.84 3.84 75.1 0.407 0.519 127.5

BC9-062910-003F 70 60 4.59 3.45 74.0 0.660 0.568 86.1

BC9-062910-007F 62 54 3.29 2.36 75.9 0.357 0.355 99.4

BC9-062910-008F 62 52 2.88 2.31 76.7 0.367 0.369 100.5
50

Table 10. Wet weight concentrations of total mercury (HgT) and monomethyl mercury (MMeHg) in California roach (Hesperoleucus symmetricus) from 

sites in the Bear Creek Watershed, June and September 2010.—Continued

Sample code

Total length 

(mm)

Standard 

length (mm)

Fresh 

mass (g)

Sample 

mass (g)

% 

moisture

HgT 

(μg/g, ww)

Geometric 

mean HgT 

(μg/g)

MMeHg 

(μg/g, ww)

Geometric mean 

MMeHg (μg/g)

Collection siteCollection dateSample number % MMeHg

BC10-062910-001F 96 81 11.41 9.96 76.0 0.750 0.433 0.879 0.521 117.2

BC10-062910-002F 88 75 8.64 7.26 74.3 0.436 0.551 126.4

BC10-062910-004F 84 70 8.19 6.59 74.0 0.454 0.585 128.9

BC10-062910-007F 83 71 7.12 5.92 77.6 0.365 0.447 122.5

BC10-062910-008F 80 65 6.21 5.33 75.8 0.449 0.584 130.1

BC10-062910-010F 67 55 3.48 2.88 78.5 0.376 0.402 106.9

BC10-062910-011F 62 51 3.20 2.57 77.8 0.314 0.352 112.1

BC2-091510-001F 80 66 5.21 4.43 75.7 0.184 0.164 0.301 0.213 163.6

BC2-091510-003F 78 65 5.05 4.55 74.0 0.114 0.165 144.7

BC2-091510-004F 75 62 4.26 3.68 74.7 0.109 0.204 187.2

BC2-091510-005F 68 56 3.40 2.92 73.8 0.177 0.168 94.9

BC2-091510-006F 66 55 3.03 2.62 74.9 0.285 0.280 98.2

BC2-091510-008F 66 56 3.40 2.81 73.2 0.281 0.384 136.7

BC2-091510-009F 65 54 3.18 2.71 75.4 0.100 0.109 109.0

BC3-091510-001F 76 64 4.72 4.17 73.5 0.485 0.571 0.601 0.419 123.9

BC3-091510-002F 72 61 3.80 3.29 74.4 0.548 0.636 116.1

BC3-091510-003F 67 56 3.93 3.16 72.8 0.816 0.774 94.9

BC3-091510-004F 68 57 3.69 3.12 74.8 0.551 0.580 105.3

BC3-091510-005F 69 57 3.32 2.91 74.8 0.646 0.605 93.7

BC3-091510-006F 63 53 2.60 2.31 71.2 0.363 0.390 107.4

BC3-091510-007F 63 52 2.62 2.15 76.0 0.704 0.056 7.9
51

Table 10. Wet weight concentrations of total mercury (HgT) and monomethyl mercury (MMeHg) in California roach (Hesperoleucus symmetricus) from 

sites in the Bear Creek Watershed, June and September 2010.—Continued

Sample code

Total length 

(mm)

Standard 

length (mm)

Fresh 

mass (g)

Sample 

mass (g)

% 

moisture

HgT 

(μg/g, ww)

Geometric 

mean HgT 

(μg/g)

MMeHg 

(μg/g, ww)

Geometric mean 

MMeHg (μg/g)

Collection siteCollection dateSample number % MMeHg

BC4-091510-001F 91 76 9.26 8.02 69.3 0.744 0.599 0.744 0.483 100.0

BC4-091510-003F 85 73 6.17 5.25 74.2 0.638 0.599 93.9

BC4-091510-004F 75 63 5.05 4.49 72.2 0.532 0.462 86.8

BC4-091510-005F 71 60 4.35 3.58 72.4 0.542 0.613 113.1

BC4-091510-006F 75 62 3.59 3.14 74.4 0.757 0.149 19.7

BC4-091510-007F 73 62 3.25 2.91 73.2 0.548 0.567 103.5

BC4-091510-009F 62 53 2.60 2.14 73.1 0.490 0.571 116.5

BC7-0091510-001F 54 45 1.99 1.63 73.7 1.030 0.999 0.704 0.769 68.3

BC7-0091510-002F 57 48 1.89 1.58 71.1 0.697 0.563 80.8

BC7-0091510-003F 55 45 1.62 1.37 74.3 0.743 0.750 100.9

BC7-0091510-004F 53 44 1.53 1.37 76.9 1.670 0.962 57.6

BC7-0091510-005F 54 44 1.56 1.29 74.9 1.030 0.877 85.1

BC7-0091510-007F 51 42 1.30 1.15 76.2 0.791 0.720 91.0

BC7-0091510-008F 51 42 1.23 1.00 72.7 1.370 0.880 64.2

BC8-091510-001F 112 95 15.12 13.24 74.4 1.410 0.807 1.350 0.733 95.7

BC8-091510-003F 95 80 10.83 9.28 72.5 1.110 1.130 101.8

BC8-091510-005F 86 71 7.35 6.15 73.4 1.110 1.200 108.1

BC8-091510-008F 74 63 5.70 4.59 75.8 0.566 0.309 54.6

BC8-091510-009F 76 64 5.13 4.35 72.2 0.686 0.775 113.0

BC8-091510-011F 67 55 3.64 3.12 72.9 0.532 0.476 89.5

BC8-091510-014F 69 55 3.21 2.68 76.2 0.620 0.544 87.7
52

Table 10. Wet weight concentrations of total mercury (HgT) and monomethyl mercury (MMeHg) in California roach (Hesperoleucus symmetricus) from 

sites in the Bear Creek Watershed, June and September 2010.—Continued

Sample code

Total length 

(mm)

Standard 

length (mm)

Fresh 

mass (g)

Sample 

mass (g)

% 

moisture

HgT 

(μg/g, ww)

Geometric 

mean HgT 

(μg/g)

MMeHg 

(μg/g, ww)

Geometric mean 

MMeHg (μg/g)

Collection siteCollection dateSample number % MMeHg

BC9-091510-002F 96 83 11.53 10.19 74.6 1.340 0.657 0.536 0.583 40.0

BC9-091510-005F 94 80 8.37 7.03 74.5 0.748 1.140 152.4

BC9-091510-006F 67 56 3.73 3.08 72.7 0.524 0.449 85.7

BC9-091510-007F 73 62 4.21 3.69 74.6 0.986 0.727 73.7

BC9-091510-009F 65 55 3.46 2.67 73.1 0.377 0.395 104.8

BC9-091510-011F 62 51 2.95 2.44 73.7 0.545 0.524 96.1

BC9-091510-012F 55 45 2.00 1.59 74.6 0.496 0.552 111.3

BC10-091510-001F 92 76 8.91 7.47 75.1 0.672 0.508 0.890 0.513 132.4

BC10-091510-002F 88 73 7.25 5.93 75.9 0.360 0.389 108.1

BC10-091510-003F 87 73 7.45 6.15 75.4 0.492 0.467 94.9

BC10-091510-004F 85 70 6.07 5.18 77.2 0.675 0.697 103.3

BC10-091510-005F 80 66 5.62 4.78 76.9 0.648 0.604 93.2

BC10-091510-006F 75 61 4.62 3.93 75.4 0.494 0.466 94.3

BC10-091510-007F 40 33 0.64 0.47 NA 0.339 0.296 87.3
53

Figure 1. Bear Creek Watershed with locations of mines, springs, and locations of samples sites for water, 

sediment, and biota. Locations of figures 3 and 4 are indicated on this figure.
54

Figure 2. Geological map and ore deposits and geothermal springs located in the Clear Lake volcanic field, including the Bear Creek watershed. 

Wilbur Springs and adjacent Hg and Au deposits and geothermal springs in the Sulphur Creek tributary are significant sources of Hg to Bear Creek.
55

Figure 3. Geology and Hg and Au deposits located in the Sulphur Creek tributary to Bear Creek. Geothermal 

springs adjacent to the ore deposits are actively depositing Hg and Au and are sources of Hg-enriched sediment to 

Bear Creek.
56

Figure 4. Location of the Rathburn and Petray Hg mines and tributaries 1–5 that drain the mine area and release 

Hg-enriched sediment into Bear Creek. Some saline cold springs along the Bear Fault release Hg into Bear Creek. 

Cold carbonate springs east of the Petray Mine have relatively low concentrations of Hg as does the saline Cain 

Spring located east of Bear Creek. Sample site 2 located upstream of the mine input and sample site 3 located 

downstream from the mine area are shown by red dots. 
57

Figure 5. View of sample site BC1 located under Brim Road bridge during low flow conditions sampling on September 16, 2010. Biota were not 

collected at this site in 2010.
58

Figure 6. View of sample site BC2 located at the bridge upstream from the Rathburn and Petray mines. Samples were collected under this bridge 

during low conditions during the September 16, 2010 sampling event. Biota were collected here on June 29 and September 15, 2010.
59

Figure 7. View of Bear Creek during low conditions on September 16, 2010 of sample site BC3 located downstream from the Rathburn and Petray 

mines. Biota were collected here on June 29 and September 15, 2010. 
60

Figure 8. View of Bear Creek at water/sediment site BC4 (left photo) during low conditions on September 16, 2010. The biota site BC4 (right 

photo), located about 800 m upstream of the water/sediment site, was sampled on June 29 and September 15, 2010. Both sites are downstream 

from the Rathburn and Petray mines and upstream from Sulphur Creek.
61

Figure 9. Water/sediment sample site BC5 located in Sulphur Creek where several hot spring vents occur in and adjacent to the creek. The white 

material is elemental sulfur, and the black sediment is fine grained iron sulfide that contains HgS, which is deposited from the thermal water. View is 

during low conditions on September 16, 2010. Note Teflon® tubing used to sample water from the creek.
62

Figure 10. Biota sites BC5 (left photo) and BC6 (right photo), sampled on June 29 and September 17, 2010. The water/sediment site BC5 was 420 

m downstream of biota site BC5. The water/sediment site BC6 coincided with biota site BC6. 
63

Figure 11. View of Bear Creek downstream during low conditions on September 16, 2010 at sample site BC7 located downstream from the 

confluence with Sulphur Creek. Biota were collected at this site on June 29 and September 15, 2010.
64

Figure 12. View of Bear Creek during low conditions on June 15, 2010 at the water/sediment sample site BC8 (left photo), located 300 m upstream 

from Highway 20 bridge crossing. The biota BC8 sample site (right photo) is located at the bridge and was sampled on June 15 and September 15, 

2010.
65

Figure 13. View of Bear Creek during low flow conditions on June 15, 2010 at water/sediment sample site BC9. Biota were sampled at a site about 

80 m downstream near the Thompson Canyon bridge on June 15 and September 15, 2010.
66

Figure 14. View of Bear Creek during low conditions on September 16, 2010 at sample site BC10 about 60 m upstream from confluence with 

Cache Creek. Exposures of bedded siltstone and shale of the Great Valley Sequence occur in the creek. Biota were also collected at this site and 

further upstream on June 15 and September 15, 2010.
67

Figure 15. Plot showing Mean daily flows in Cache Creek in cubic feet per second over a three-year period beginning in January 2009. Flows were 

measured at the USGS Gaging Station in Cache Creek, downstream of Bear Creek at the Rumsey Bridge.
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Figure 16. Logarithmic-scale plot showing concentrations of total mercury (HgT) in water collected from sample sites in Bear Creek watershed, 

Colusa County, California, moving downstream to the right on the x-axis. Low-flow sampling events are shown with red bars; high-flow sampling 

events are shown with blue bars.
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Figure 17. Logarithmic-scale plot showing concentrations of filtered mercury (HgF) in water collected from sample sites in Bear Creek watershed, 

Colusa County, California, moving downstream to the right on the x-axis. Low-flow sampling events are shown with red bars; high-flow sampling 

events are shown with blue bars.
70

Figure 18. Logarithmic-scale plot showing concentrations of MMeHg in water collected from sample sites in Bear Creek watershed, Colusa County, 

California, moving downstream to the right on the x-axis. Low-flow sampling events are shown with red bars; high-flow sampling events are shown 

with blue bars.
71

 

Figure 19. Map showing concentrations of Hg in sediment collected from Bear Creek and Sulphur Creek, Colusa 

County, California, in June 2010. The increase in Hg in Bear Creek sediment downstream from Sulphur Creek is 

about five times greater than the increase in Hg in sediment downstream from the Rathburn-Petray Input. 
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Figure 20. Map showing concentrations of Hg in sediment collected from Bear Creek and Sulphur Creek, Colusa 

County, California, in September 2010. The increase in Hg in sediment is significantly greater after the Sulphur 

Creek saline input enters Bear Creek than the increase associated with the mine input at sample site BC3.
73

 

Figure 21. Map showing MMeHg levels in sediments collected from Bear Creek and Sulphur Creek, Colusa 

County, California, in June 2010. Figure shows high rates of methylation occurring downstream from the mine, and 

further downstream in Bear Creek at sites BC8 and 9.
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Figure 22. Map showing MMeHg levels in sediments collected from Bear Creek and Sulphur Creek, Colusa 

County, California, in September 2010. Figure shows high rates of methylation at sample site BC4 downstream 

from the mine input, as well as at sample site BC9 in downstream Bear Creek.
75

 

Figure 23. Logarithmic-scale plot showing concentrations of Hg and MMeHg in sediment collected from sample sites in Bear Creek watershed, Colusa 

County, California, moving downstream to the right on the x-axis. Hg concentrations are shown by red bars, and MMeHg concentrations with blue bars.
76

 

Figure 24. Logarithmic scale plot showing concentrations of Chloride (blue bars), Sulfate (grey bars), and Filtered Mercury (red bars) moving downstream 

in Bear Creek and Sulphur Creek, Colusa County, California. Data was collected in June 2010 under moderate high-flow conditions.
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Figure 25. Logarithmic scale plot showing concentrations of Chloride (blue bars), Sulfate, (grey bars), and Filtered Mercury (red bars) moving downstream

in Bear Creek and Sulphur Creek, Colusa County, California. Data was collected in September 2010 under low-flow conditions.
78

 

Figure 26. Plot of isotopic composition of waters in Bear Creek and Sulphur Creek, Colusa County, California, which shows that the waters do not fall along 

the meteoric water line and are, thus, a mixture of connate water, thermal water, and meteoric water.
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Figure 27. Plot showing changes in groundwater input and HgT and HgF concentration in low-flow condition waters collected from Bear Creek, Colusa 

County, California. Percent groundwater was calculated using a two endmember system in which high-flow waters collected from upstream Bear Creek sites 

were treated as background meteoric water, and low-flow waters collected from Sulphur Creek were treated as pure saline groundwater. Thus, at any given 

point in Bear Creek, stream water is a variable mixture of each endmember. Plot shows a linear increase in saline groundwater influence moving 

downstream in Bear Creek. The input of saline, isotopically-heavy groundwater from Sulphur Creek is also associated with large increases in HgT and HgF. 

High concentrations of HgT and HgF in Sulphur Creek samples are shown at the top of the blue area.
80

 

 

 

Figure 28. Seasonal comparisons for damselfly and dragonfly larvae collected from Bear Creek during 

June and September 2010.
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Figure 29. Monomethyl mercury concentrations in three families of dragonflies collected from Bear Creek in September 2010.
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Figure 30. Adjusted mean HgT concentrations and 95% confidence limits by site and season for California Roach collected from the Bear Creek Watershed 

during 2010. Within season, sites with the same letter are not significantly different.
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Figure 31. Adjusted mean MMeHg concentrations and 95% confidence limits by site and season for California Roach collected from the Bear Creek 

Watershed during 2010. Within seasons, sites with the same letter are not significantly different.