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Amazon forests capture high levels of atmospheric mercury pollution from artisanal gold mining

Citation

Gerson, Jacqueline et al. (2022), Amazon forests capture high levels of atmospheric mercury pollution from artisanal gold mining, Dryad, Dataset, https://doi.org/10.6078/D1DH6F

Abstract

AbstractMercury emissions from artisanal and small-scale gold mining throughout the Global South exceed coal combustion as the largest global source of mercury. We examined mercury deposition and storage in an area of the Peruvian Amazon heavily impacted by artisanal gold mining. Intact forests in the Peruvian Amazon near gold mining receive extremely high inputs of mercury and experience elevated total mercury and methylmercury in the atmosphere, canopy foliage, and soils. Here we show for the first time that an intact forest canopy near artisanal gold mining intercepts large amounts of particulate and gaseous mercury, at a rate proportional with total leaf area. We document substantial mercury accumulation in soils, biomass, and resident songbirds in some of the Amazon’s most protected and biodiverse areas, raising important questions about how mercury pollution may constrain modern and future conservation efforts in these tropical ecosystems.

Methods

All information regarding sampling sites is described in Gerson et al. (2020) and Gerson et al (In review). All data were collected from the Madre de Dios region of Peru. Specific site coordinates and descriptions are found in individual data files.

All methods for sample collection, laboratory analyses, and quality control assurance have been outlined fully in two publications: Gerson et al. (2020) and Gerson et al (In review). Briefly, we collected surface water, precipitation, throughfall, leaves, sediment, soil, and air samples from across the Madre de Dios region of Peru, in locations near and remote from ASGM. These data were collected to determine the fate and transport of Hg across the landscape. Samples were collected in 2018 and 2019. Data predominantly include total Hg and methyl Hg concentrations in surface water, precipitation, throughfall, leaves, sediment, soil, and air. Additional water and soil parameters were also measured to better characterize their chemistry. Coordinates for each site can be found in the csv files and maps can be found in Figures 1 and 2.

Below is the text on laboratory analysis and quality control in surface water and sediment samples, as reported in Gerson et al. (2020):

“All samples for Hg analysis were collected in July and August 2019 during the dry season (Figure 1). River samples were collected from the Madre de Dios River mainstem, upstream of a river confluence, downstream of a confluence, and from each tributary. One water sample was taken from near the water surface at each sampling point after the boat motor had been off for at least one minute. For oxbow lakes and mining ponds, one water sample was taken from the water surface. Water samples were collected using the clean hands-dirty hands protocol (EPA Method 1669) in new polyethylene terephthalate copolyester glycol (PETG) bottles and acidified to 0.4% with trace grade hydrochloric acid (HCl) within 24 hours of collection. Water samples were stored on ice in the field and then stored at 4°C until analysis. Note that all water samples are unfiltered, and all Hg values reported represent the concentration for the total water column. River sediment samples were collected underwater from the channel margins by compositing surficial sediment from at least five sampling points along a 30-meter transect using a shovel. These samples were taken during the dry season; during the wet season, the sampling locations are closer to the center of the channel since the width of the river increases by tens of meters. We therefore assume that the river sediment samples we collected are representative of well-mixed fluvial sediments. Oxbow lake and mining pond sediments were collected as channel margin sediment using a shovel (collected underwater as surficial sediment) and from three points in the center of the lake using an Eckman grab sampler. Sediment samples were collected using the clean hands-dirty hands protocol, double-bagged, frozen on dry ice in the field, and stored frozen until sample processing. Note that mining ponds were sampled in the La Pampa region, a watershed located adjacent to the Colorado watershed. La Pampa is an area that, until recently, contained widespread ASGM (Espejo et al. 2018). It has been under military control since February 2019 (Operacion Mercurio) making it a safe area for field sampling. Due to logistical and safety concerns stemming from a lack of police or military presence, it was not possible to sample mining ponds from the other actively mined watersheds examined in this study; however, mining practices in La Pampa are representative of those in the region.

Water samples for total suspended solids (TSS) were collected immediately after collecting water samples for Hg analysis. Water from just below the surface was pumped through a drill-operated pump with in-line glass fiber filter (pre-weighed), and the amount of water filtered was recorded. The filter was stored frozen until sample processing. A filter field blank was also taken and frozen for analysis.

Unfiltered water samples were analyzed for total Hg via oxidation with bromine chloride for a minimum of 24 hours, purge and trap, cold vapor atomic fluorescence spectroscopy (CVAFS), and gas chromatographic (GC) separation (EPA Method 1631, revision E) on a Tekran 2600 Automated Total Mercury Analyzer. Calibration and continuous calibration verification (CCV) were performed using Brooks Rand Instruments Total Mercury Standard (1.0 ng/L) and initial calibration verification (ICV) was performed using SPEX Centriprep Inductively Coupled Plasma Mass Spectrometry (ICP-MS) Multi-Element in Solution Standard 2A. Instrument detection limit was 0.5 ng/L. All standards had average recoveries within 10% of the accepted values. The field blank, digestion blanks, and analysis blanks were below detection limit (BDL).

After lyophilization for at least five days, sediment samples were analyzed for total Hg on a Milestone Direct Mercury Analyzer (DMA-80) via thermal decomposition, catalytic reduction, amalgamation, desorption, and atomic absorption spectroscopy (EPA Method 7473). Calibration of the DMA-80 was performed using Brooks Rand Instruments Total Mercury Standard (1.0 ng/L). CCV and matrix spike (MS) were performed using NIST standard reference material 1633c (coal fly ash, 1005 ng/g), and QCS was performed using NIST certified reference material 2709a (San Joaquin Soil, 1100 ng/g). Instrument detection limit was 0.5 ng Hg. All samples were run in duplicate, with values accepted when the relative percent difference between the two samples was within 10%. All standards and MS had average recoveries within 10% of the accepted values, and all blanks were BDL.

For MeHg, unfiltered water samples were extracted with trace grade sulfuric acid for a minimum of 24 hours (Munson et al. 2014). Samples were analyzed by aqueous ethylation with sodium tetraethylborate, purge and trap, CVAFS, GC, and ICP-MS on an Agilent 770 (EPA Method 1630) (Imura et al. 1971; Hintelmann and Evans 1997). Calibration and CCV were performed using Brooks Rand Instruments Methylmercury Standard (1 ng/L). Method detection limit was 1 pg. All standards had average recoveries within 13% of the accepted values, and all blanks were BDL.

For TSS, filters were placed in the oven at 105°C for 48 hours. Filters were then reweighed. TSS was defined as the difference in filter mass before and after filtration divided by the volume of water that passed through the filter. The filter field blank had a negligible difference in mass.”

In addition to the methods employed in Gerson et al. (2020), the following methods were also applied. In the field, we measured conductivity, temperature, and specific conductivity using a conductivity probe submerged near the surface of the water. We also measured pH of the water in the field. We collected additional filtered water samples for other chemical analyses with a 0.45 mm membrane filter. Samples for total organic carbon, total dissolved nitrogen, and trace elements were acidified in the field to 0.4% with hydrochloric. We stored all samples on ice or in the fridge when possible until return to the United States, and then stored samples at 4°C until analysis immediately upon return to the United States, within one month of sampling. We analyzed unacidified water samples for anions (chloride, nitrate, sulfate) and cations (calcium, magnesium, potassium, sodium) via ion chromatography (EPA Method 4110B) with a Dionex ICS 2000 ion chromatograph. All standards had recoveries within 10% of the accepted values, and all blanks were BDL. We analyzed acidified water samples for trace elements via inductively coupled plasma mass spectrometry with a Thermofisher X-Series II. We analyzed acidified samples for dissolved organic carbon and total dissolved nitrogen (USEPA Method 5310C) with a Shimadzu total organic carbon analyzer. Instrument calibration standards were prepared via serial dilution of certified water standard NIST1643f. All blanks were BDL. We also analyzed unacidified water samples for UVA in order to calculate SUVA on a spectrophotometer with a 254 nm wavelength (EPA Method 415.3 Rev. 1.1).

In the field, we also pumped water from just below the surface through a drill-operated pump with in-line glass fiber filter, and the amount of water filtered was recorded. The filter was wrapped in foil and stored frozen until sample processing. A filter field blank was also taken and frozen for analysis. In the lab, filters were digested with acetone and analyzed for chlorophyll on a TD-700 Fluorometer (EPA Method 445.0). The filter field blank was BDL.

Dried sediment samples were analyzed for carbon, hydrogen, and nitrogen (CHN) using a Perkin Elmer 2400 CHNS Analyzer and pH using a probe. Dried sediment samples were also digested in concentrated nitric acid for S, Se, and Mn analysis using USEPA Method 3050B. Samples were analyzed for Se and Mn with a Perkin Elmer Elan DRCII ICP-MS and S using a Perkin Elmer ICP-Optical Emission Spectrometer Model 8000. All standards had recoveries within 10% of the accepted values, and all blanks were BDL.

Below is the text on laboratory analysis and quality control for precipitation, throughfall, soil, leaf, and air samples, as reported in Gerson et al (In review).

“We established five sites along a 200-km reach of the Madre de Dios River. We chose sampling locations based on their proximity to intense ASGM activities, with approximately 50 km between each sampling site and accessible by the Madre de Dios River (Figure 2A). We selected two sites without any mining (Boca Manu and Chilive, approximately 100 km and 50 km from ASGM, respectively), hereafter referred to as “remote sites.” We selected three sites within the mining zone, hereafter referred to as “mining sites,” with two of the mining sites located in secondary growth forests near the towns of Boca Colorado and Laberinto and one mining site located in the intact old-growth forests of the Los Amigos Conservation Concession. Note that Hg-gold amalgam burning also occurs within this mining zone, at both Boca Colorado and Laberinto, and we refer to mining and amalgam burning collectively as “ASGM activity.” At each of the five sites, we installed deposition samplers both in clearings (deforested areas) and beneath the tree canopy (forested areas) in the 2018 dry season (July and August 2018) and 2018 wet season (December 2018 and January 2019) to collect wet deposition (n=3) and throughfall (n=4), respectively. Precipitation samples were collected over the course of four weeks in the dry season and two to three weeks in the wet season. In the second year of sampling during the dry season (July and August 2019), we installed collectors (n=4) at six additional forested plots at Los Amigos based on the high rates of deposition measured during the first year, for a total of seven forested plots and one deforested plot at Los Amigos. The distance between plots ranged from 0.1-2.5 km. We collected a GPS waypoint at each plot using a handheld Garmin GPS.

We deployed passive air samplers (PAS) at each of the five sites during the 2018 dry season for a two-month period (July to August 2018) and the 2018 wet season for one month (December 2018 to January 2019). One PAS sampler was deployed per site during the dry season, and PAS samplers were deployed in duplicate during the wet season. The PAS (developed by McLagan et al. 59) collects GEM by passive diffusion through a Radiello© diffusive barrier and sorption onto a sulfur-impregnated carbon sorbent (HGR-AC). The diffusion barrier of the PAS acts as a barrier to prevent the passage of gaseous organic Hg species; thus, only GEM is sorbed onto the carbon. 60 We attached PAS to posts approximately 1m above the ground using plastic cable ties. All samplers were sealed with parafilm or stored in double resealable plastic bags prior to and post deployment. We collected field blanks and trip blank PASs to assess contamination introduced during sampling storage in the field, storage in the laboratory, and during sample transport.

During the deployment periods at all five sampling sites, we placed three precipitation collectors for Hg analysis and two collectors for other chemical analyses in the deforested sites and four throughfall collectors for Hg analysis and two collectors for other chemical analyses in the forested sites. Collectors were placed within one meter of each other. Note that while we installed a consistent number of collectors at each site, during some collection periods we had a smaller sample size due to flooding of sites, human interference with collectors, and connection malfunction between the tubing and collector bottle. At each forested and each deforested site, one of the collectors for Hg analysis contained a 500 mL bottle, while the others contained a 250 mL bottle; all collectors for other chemical analyses contained a 250 mL bottle. These samples were stored cold until access to a freezer allowed them to be frozen, transported to the United States on ice, and stored frozen until analyzed. Collectors for Hg analysis consisted of a glass funnel connected to a new polyethylene terephthalate copolyester glycol (PETG) bottle via new styrene-ethylene-butadiene-styrene block polymer (C-Flex) tubing with a loop as a vapor lock. At the time of deployment, all 250 mL PETG bottles were acidified with 1 mL of trace metal grade hydrochloric acid (HCl), and all 500 mL PETG bottles were acidified with 2 mL of trace metal grade HCl. Collectors for other chemical analyses consisted of a plastic funnel connected to a polyethylene bottle via new C-Flex tubing with a loop as a vapor lock. Prior to deployment, all glass funnels, plastic funnels, and polyethylene bottles were acid washed. We collected samples using the clean hands-dirty hands protocol (EPA Method 1669), kept the samples as cold as possible until return to the United States, and then stored samples at 4°C until analysis. A previous study using this methodology has shown laboratory blanks below detection limit and standard spikes to have recoveries of 90-110%. 32

At each of the five sites, we collected foliage as canopy leaves, grab leaf samples, fresh litterfall, and bulk litter using clean hands-dirty hands protocol (EPA Method 1669). All samples were collected under a collection permit from SERFOR in Peru and imported to the United States under a USDA import permit. We collected canopy leaves from two tree species found at all sites: an emergent tree species (Ficus insipida) and a medium-sized tree (Inga feuilleei). We collected leaves from the canopy of the trees (n=3 for each species) using a Notch Big Shot slingshot in the 2018 dry season, 2018 wet season, and 2019 dry season. We collected grab leaf samples (n=1) by sampling leaves in each plot from tree branches less than two meters from the ground in the 2018 dry season, 2018 wet season, and 2019 dry season. In 2019, we also collected grab leaf samples (n=1) from the additional six forested plots at Los Amigos. We collected fresh litterfall (“bulk litter”) in plastic mesh-lined baskets (n=5) in the 2018 wet season at all five forested sites and the 2019 dry season at the Los Amigos plots (n=5). Note that while we installed a consistent number of baskets at each site, during some collection periods we had a smaller sample size due to flooding of sites and human interference with collectors. All litterfall baskets were placed within one meter of the precipitation collectors. We collected bulk litter as grab samples of litterfall on the ground in the 2018 dry season, 2018 wet season, and 2019 dry season. In the 2019 dry season, we also collected bulk litter in all Los Amigos plots. We cold stored all leaf samples until access to a freezer allowed them to be frozen, transported to the United States on ice, then stored frozen until processed.

We collected soil samples in triplicate (n=3) from all five sites (open and canopy) during all three seasonal campaigns and from the Los Amigos plots in the 2019 dry season. All soil samples were collected within one meter of the precipitation collectors. We collected soil samples as surficial soil (0-5 cm) using a soil corer. Additionally, in the 2018 dry season, we collected soil cores up to 45 cm in depth and divided them into five depth segments. At Laberinto, we were only able to collect one soil profile because the water table was close to the soil surface. We collected all samples using clean hands-dirty hands protocol (EPA Method 1669). We cold stored all soil samples until access to a freezer allowed them to be frozen, transported to the United States on ice, then stored frozen until processed.

We quantified total Hg concentrations of GEM collected by PAS by thermal desorption, amalgamation, and atomic absorption spectroscopy (USEPA Method 7473) using a Hydra C instrument (Teledyne, CV-AAS). We performed calibration of the CV-AAS using National Institute of Standards and Technology (NIST) standard reference material 3133 (Hg standard solution, 10.004 mg g-1), with a detection limit of 0.5 ng Hg. We performed continuous calibration verification (CCV) using NIST SRM 3133 and quality control standard (QCS) using NIST 1632e (bituminous coal, 135.1 mg g-1). We divided each sample into separate boats, placed it between two thin layers of sodium carbonate (Na2CO3) powder, and covered it with a thin layer of aluminum hydroxide (Al(OH)3) powder. 62 We measured the entire HGR-AC contents from each sample to remove any inhomogeneity in the distribution of Hg within the HGR-AC sorbent. Therefore, we calculated the Hg concentration for each sample based on the sum of total Hg measured for each boat and the entire HGR-AC sorbent contents in the PAS. Given that only one PAS sample was collected in the 2018 dry season from each site for concentration measurements, method quality control and assurance was carried out by bracketing samples with monitoring procedural blanks, internal standards, and matrix-matched standards. In the 2018 wet season, we measured PAS samples in duplicate. Values were deemed acceptable when the relative percent difference (RPD) measured for both CCV and matrix-matched standards were within 5% of the accepted values, and all procedural blanks were below detection limit (BDL). We blank-corrected measured total Hg in PAS using concentrations determined from field and trip blanks (0.81 ± 0.18 ng g-1, n=5). We calculated GEM concentrations using the total mass of blank-corrected sorbed Hg divided by the deployment time and sampling rate (volume of air stripped of gaseous Hg per unit of time; 0.135 m3 day-1) 59,63 adjusted for temperature and wind using average temperature and wind measurements for the Madre de Dios region as obtained from World Weather Online. 63 Reported standard error of measured GEM concentrations is based on the error of external standards ran before and after the samples.

We analyzed water samples for total Hg via oxidation with bromine chloride for a minimum of 24 hours, followed by stannous chloride reduction and analysis with purge and trap, cold vapor atomic fluorescence spectroscopy (CVAFS), and gas chromatographic (GC) separation (EPA Method 1631, revision E) on a Tekran 2600 Automated Total Mercury Analyzer. We performed CCV for the 2018 dry season samples using Ultra Scientific certified aqueous Hg standard (10 μg L-1) and initial calibration verification (ICV) using NIST certified reference material 1641D (mercury in water, 1.557 mg kg-1), with a detection limit of 0.02 ng L-1. For the 2018 wet season and 2019 dry season samples, we performed calibration and CCV using Brooks Rand Instruments Total Mercury Standard (1.0 ng L-1), and ICV using SPEX Centriprep Inductively Coupled Plasma Mass Spectrometry (ICP-MS) Multi-Element in Solution Standard 2A, with a detection limit of 0.5 ng L-1. All standards had recoveries within 15% of the accepted values. The field blank, digestion blanks, and analysis blanks were BDL.

We lyophilized soil and leaf samples for five days. We homogenized the samples and then analyzed them for total Hg on a Milestone Direct Mercury Analyzer (DMA-80) via thermal decomposition, catalytic reduction, amalgamation, desorption, and atomic absorption spectroscopy (EPA Method 7473). For the 2018 dry season samples, we performed calibration of the DMA-80 using NIST 1633c (coal fly ash, 1005 ng g-1) and Canadian National Research Council certified reference material MESS-3 (marine sediment, 91 ng g-1). We performed CCV and MS using NIST 1633c and QCS using MESS-3, with a detection limit of 0.2 ng Hg. For the 2018 wet season and 2019 dry season samples, we performed calibration of the DMA-80 using Brooks Rand Instruments Total Mercury Standard (1.0 ng L-1). We performed CCV and MS using NIST standard reference material 2709a (San Joaquin Soil, 1100 ng g-1) and QCS using DORM-4 (fish protein, 410 ng g-1), with a detection limit of 0.5 ng Hg. For all seasons, we analyzed all samples in duplicate and accepted values when the relative percent difference between the two samples was within 10%. All standards and matrix spikes had average recoveries within 10% of the accepted values, and all blanks were BDL. All reported concentrations are for dry mass.

We analyzed water samples from all three seasonal campaigns, leaf samples from the 2018 dry season, and soil samples from all three seasonal campaigns for MeHg. We extracted water samples with trace grade sulfuric acid for a minimum of 24 hours, 64 digested leaves with 2% potassium hydroxide in methanol at 55°C for a minimum of 48 hours, 65 and digested soils via microwave digestion with trace metal grade HNO3 acid. 66,67 We analyzed the 2018 dry season samples via aqueous ethylation with sodium tetraethylborate, purge and trap, and CVAFS on a Tekran 2500 spectrometer (EPA Method 1630). We performed calibration and CCV using Frontier Geosciences certified laboratory MeHg standards and QCS for sediment using ERM CC580, with a method detection limit of 0.2 ng L-1. We analyzed the 2019 dry season samples by aqueous ethylation with sodium tetraethylborate, purge and trap, CVAFS, GC, and ICP-MS on an Agilent 770 (EPA Method 1630). 68 We performed calibration and CCV using Brooks Rand Instruments Methylmercury Standard (1 ng L-1), with a method detection limit of 1 pg. For all seasons, all standards had recoveries within 15% of the accepted values, and all blanks were BDL.

We filtered water samples for other chemical analyses with a 0.45 mm membrane filter. We analyzed water samples for anions (chloride, nitrate, sulfate) and cations (calcium, magnesium, potassium, sodium) via ion chromatography (EPA Method 4110B) with a Dionex ICS 2000 ion chromatograph. All standards had recoveries within 10% of the accepted values, and all blanks were BDL. We analyzed water samples for trace elements via inductively coupled plasma mass spectrometry with a Thermofisher X-Series II. Instrument calibration standards were prepared via serial dilution of certified water standard NIST1643f. All blanks were BDL.”

In addition to the methods employed in Gerson et al (In review), the following methods were also applied. Dried soil samples were analyzed for CHN using a Perkin Elmer 2400 CHNS Analyzer and pH using a probe. Dried sediment samples were also digested in concentrated nitric acid for S, Se, and Mn analysis using USEPA Method 3050B. Samples were analyzed for Se and Mn with a Perkin Elmer Elan DRCII ICP-MS and S using a Perkin Elmer ICP-Optical Emission Spectrometer Model 8000. All standards had recoveries within 10% of the accepted values, and all blanks were BDL.

Usage Notes

Note that values of <DL imply that the value is below detection limit.

Table 1: Dataset identities

Data file name

Description

Size

(not including headers)

Aquatic.data.csv

Contains data for all surface water and sediment samples collected

136 kb

4 columns

4079 rows

Aquatic.data.coordinates.csv

Contains information on site type, latitude, and longitude for all surface water and sediment samples collected

2 kb

4 columns

54 rows

Deposition.csv

Contains data for all deposition samples collected

51 kb

6 columns

979 rows

Litter.and.foliage.csv

Contains data for all leaf samples collected

4 kb

5 columns

88 rows

Soil.csv

Contains data for all soil samples collected

22 kb

8 columns

365 rows

GEM. csv

Contains data for all atmospheric samples collected

0.5 kb

4 columns

15 rows

Terrestrial.coordinates. csv

Contains information on site type, latitude, and longitude for all terrestrial (deposition, leaf, soil, and atmospheric) samples collected

0.6 kb

4 columns

13 rows

 

Table 2: Aquatic.data.csv

Attribute

Definition

 

Site.ID

Identification used across aquatic data

 

Collection.date

Date sample was collected

 

Value

Measured value of given parameter

 

Parameter

Parameter analyzed in surface water or sediment

 

 

Value

 

 

Aluminum

 

 

Antimony

 

 

Arsenic

 

 

Barium

 

 

Beryllium

 

 

Boron

 

 

Bromide

 

 

Cadmium

 

 

Calcium

 

 

Chloride

 

 

Chlorophyll

 

 

Chromium

 

 

Cobalt

 

 

Conductivity

 

 

Copper

 

 

Dissolved.organic.carbon

 

 

Gold

 

 

Iron

 

 

Lead

 

 

Lithium

 

 

Magnesium

 

 

Manganese

 

 

Methylmercury

 

 

Molybdenum

 

 

Nickel

 

 

Nitrate

 

 

pH

 

 

Phosphate

 

 

Potassium

 

 

Rubidium

 

 

Sediment.carbon

 

 

Sediment.manganese

 

 

Sediment.nitrogen

 

 

Sediment.pH

 

 

Sediment.selenium

 

 

Sediment.sulfur

 

 

Sediment.total.mercury

 

 

Selenium

 

 

Silver

 

 

Sodium

 

 

Strontium

 

 

Sulfate

 

 

SUVA

 

 

Temperature

 

 

Thallium

 

 

Thorium

 

 

Total.dissolved.nitrogen

 

 

Total.mercury

 

 

Total.suspended.solids

 

 

Uranium

 

 

Vanadium

 

 

Zinc

 

Unit

Units parameter were measured in

 

 

Value

Definition

 

ug.L

Micrograms per liter

 

mg.L

Millgrams per liter

 

mgN.L

Milligrams nitrogen per liter

 

mgS.L

Milligrams sulfur per liter

 

uS.cm

Microsiemens per centimeter

 

NA

Unitless

 

percent

Percent

 

ug.g

Micrograms per gram

 

L.mg.m

Liters per milligram per meter

 

Degrees.C

Degrees Celsius

 

ng.L

Nanograms per liter

 

Table 3: Aquatic.data.coordinates.csv

Attribute

Definition

 

Site.ID

Identification used across aquatic data

 

Site.type

Classification of water body

 

 

Value

Definition

 

river.downstream

Sample taken from a river downstream of artisanal and small-scale gold mining activity

 

river.upstream

Sample taken from a river upstream of artisanal and small-scale gold mining activity

 

mining.pond

Sample taken from a mining pond near artisanal and small-scale gold mining

 

oxbow.lake.downstream

Sample taken from an oxbow lake downstream of artisanal and small-scale gold mining activity

 

oxbow.lake.upstream

Sample taken from an oxbow lake upstream of artisanal and small-scale gold mining activity

Latitude

Latitude in decimal degrees

 

Longitude

Longitude in decimal degrees

 

 

Table 4: Deposition.csv

Attribute

Definition

 

Site

Location where sampling occurred

 

Type

Type of sample collected

 

 

Value

Definition

 

Bulk.precipitation

Precipitation collected in a clearing

 

Throughfall

Precipitation collected under forest canopy

Date.collected

Date sample was collected

 

Concentration

Measured concentration of given parameter

 

Parameter

Parameter analyzed

 

 

Value

 

 

Aluminum

 

 

Antimony

 

 

Arsenic

 

 

Barium

 

 

Beryllium

 

 

Boron

 

 

Bromide

 

 

Cadmium

 

 

Calcium

 

 

Chloride

 

 

Chromium

 

 

Cobalt

 

 

Copper

 

 

Iron

 

 

Lead

 

 

Lithium

 

 

Magnesium

 

 

Manganese

 

 

Methylmercury

 

 

Molybdenum

 

 

Nickel

 

 

Nitrate

 

 

Potassium

 

 

Rubidium

 

 

Selenium

 

 

Silver

 

 

Sodium

 

 

Strontium

 

 

Sulfate

 

 

Thallium

 

 

Thorium

 

 

Total.mercury

 

 

Uranium

 

 

Vanadium

 

 

Zinc

 

Units

Units parameter was measured in

 

 

Value

Definition

 

ug.L

Micrograms per liter

 

mg.L

Millgrams per liter

 

mgN.L

Milligrams nitrogen per liter

 

mgS.L

Milligrams sulfur per liter

 

ng.L

Nanograms per liter

 

Table 5: Litter.and.foliage.csv

Attribute

Definition

 

Site

Location where sampling occurred

 

Year

Year that the sample was collected in

 

Season

Season that the sample was collected in

 

 

Value

Definition

 

wet.season

Sample collected during the wet season (December and January)

 

dry.season

Sample collected during the dry season (July and August)

Type

Type of sample collected

 

 

Value

Definition

 

bulk.litter

Sample collected by gathering litter from the forest floor in the plot

 

Ficus.insipida

Leaves collected from the canopy of ficus insipida using a slingshot

 

Inga.feuillei

Leaves collected from the canopy of inga feuillei using a slingshot

 

litter.basket

Sample collected from litter baskets suspended above the forest floor in the plot

 

leafgrab

Sample collected by gathering leaves within arms’ reach from trees within the plot

Total.mercury.ug.g

Concentration of total mercury in the sample in mg/g

 

 

Table 6: Soil.csv

Attribute

Definition

 

Site

Location where sampling occurred

 

Type

Type of sample collected

 

 

Value

Definition

 

forested

Site was located under a tree canopy

 

deforested

Site was located in a clearing

Depth.cm

Depth range that the soil sample was taken from in cm, with the soil surface representing 0 cm

 

Season

Season that the sample was collected in

 

 

wet.season

Sample collected during the wet season (December and January)

 

dry.season

Sample collected during the dry season (July and August)

Year

Year that the sample was collected in

 

Concentration

Measured concentration of given parameter

 

Parameter

Parameter analyzed

 

 

Value

 

 

Carbon

 

 

Manganese

 

 

Methylmercury

 

 

Nitrogen

 

 

pH

 

 

Selenium

 

 

Sulfur

 

 

Total.mercury

 

Units

Units analyte was measured in

 

 

Value

Definition

 

percent

Percent

 

ug.g

Micrograms per gram

 

ng.g

Nanograms per gram

 

NA

Unitless

 

Table 7: GEM.csv

Attribute

Definition

 

Site

Location where sampling occurred

 

GEM.ng.m3

Gaseous elemental mercury concentration in the sample in ng/m3

 

Season

Season that the sample was collected in

 

 

wet.season

Sample collected during the wet season (December and January)

 

dry.season

Sample collected during the dry season (July and August)

Year

Year that the sample was collected in

 

 

Table 8: Terrestrial.coordinates.csv

Attribute

Definition

 

Site.Number

Location where sampling occurred

 

Type

Classification of site type

 

 

forested

Site was located under a tree canopy

 

deforested

Site was located in a clearing

Latitude

Latitude in decimal degrees

 

Longitude

Longitude in decimal degrees

 

Funding

Duke University

Duke University Bass Connections

Geological Society of America

Josiah Charles Trent Memorial Foundation

Lewis and Clark Fund

National Science Foundation