Mercury in soil, vegetation, and organisms across Niwot Ridge, Saddle Catchment, and Green Lakes Valley, 2020 - 2023.

This dataset includes soil, vegetation, water, atmospheric
deposition, litterfall, incubation, and organism data from the Niwot
Ridge, Saddle Catchment, and Green Lakes Valley collected during
2020 and 2021 to investigate the storage, transformation, and
mobilization of mercury in the Colorado Rocky Mountains.

During Summer 2020, we collected soil cores (10cm x 3cm) across
vegetation plant functional groups in wet meadows, moist meadows,
dry meadows, krummholz, subalpine forest, shrub areas, as well as at
the inlet and outlet of the Green Lakes in Green Lakes Valley. At
each of these sites, we collected leaves from forbs, graminoids, and
shrubs, as well as litter (and moss if present). For organisms, we
sampled pika hairs from nine different pika trapped on the West
Knoll, in addition to caddisfly pupae found in wet meadows in the
Saddle Catchment. We analyzed hairs from weasel specimens at the CU
Boulder Natural History Museum that were trapped either on, or near,
Niwot Ridge. Finally, we analyzed dust samples collected by Dr. Ruth
Heindel in 2018 and 2019 on Niwot Ridge. We analyzed soil samples
for organic matter; pH; water content; percent carbon, nitrogen, and
sulfur; stable carbon, nitrogen, and sulfur isotopes; total mercury;
and methylmercury. We analyzed vegetation samples for percent
carbon, nitrogen, and sulfur; stable carbon, nitrogen, and sulfur
isotopes; total mercury; and methylmercury. We analyzed organism and
dust samples for total mercury and methylmercury.

During Spring 2021, we collected composite snow cores from 4 sites
in the Saddle region and 3 sites in the subalpine forest. We
measured snow depth and density to calculate snow water equivalent
and then analyzed these samples for sulfate, nitrate, chloride,
dissolved organic carbon, dissolved organic nitrogen, total mercury,
and methylmercury concentrations.

During Summer 2021, we collected soil cores (10cm x 3cm) every other
week from June through September from a solifluction lobe, alpine
wet meadow, shrubby riparian zone, alpine dry meadow, and subalpine
wetland inlet and outlet that we analyzed for the same constituents
as for the Summer 2020 soil samples. We also sampled the overlying
water from the six sites (when standing water was present) which we
measured for dissolved oxygen, conductivity, pH, temperature, total
dissolved solids, and nitrate in situ using a YSI probe, as well as
analyzed for sulfate, nitrate, chloride, dissolved organic carbon,
dissolved organic nitrogen, total mercury, and methylmercury
concentrations. We also collected weekly surface grab samples from
the Saddle Stream and Como Creek June – September which we measured
for the same constituents as the overlying water samples. For the
organism sampling, we collected grasshoppers and caddisfly pupae
from the Saddle region of Niwot Ridge, as well as fish from Green
Lakes 1-3 and Lake Albion in the Green Lakes Valley. We collected a
composite wet atmospheric deposition sample in collaboration with
the National Atmospheric Deposition Network and a composite dry
atmospheric deposition sample in collaboration with Dr Janice
Brahney from the Saddle region at Niwot Ridge which we analyzed for
total mercury and methylmercury concentrations.

In addition to the above sampling, we also collected soils and
vegetation from along an elevation gradient in Boulder County during
Summers 2021 and 2022 that included Niwot Ridge as the alpine
location and C1 as the subalpine location, as well as Montane
(Gordon Gulch), Foothills (Betasso), and Plains (Boulder Open
Space). We collected 4 replicate soil cores (10cm x 3cm) at each
site which we analyzed for organic matter; water content; percent
carbon, nitrogen, and sulfur; total mercury; and methylmercury. At
each of these sites, we also collected leaves from forbs,
graminoids, shrubs, deciduous, and coniferous species which we
analyzed for percent carbon, nitrogen, and sulfur, as well as total
mercury.

During Summer 2022, we collected litterfall samples from the along
the same Boulder County elevation gradient. Four replicate samples
were collected monthly in 0.44m^2 laundry baskets strapped to trees
from June – October. Litterfall samples were dried, weighed, and
analyzed for total mercury concentrations.

We conducted an incubation experiment during Summer 2022 with soils
from alpine solifluction lobes, subalpine wetlands, and alpine dry
meadow regions. Samples were spiked with inorganic mercury isotope
201 and mercury methylation rates were calculated based on the
production of excess methylmercury 201. Base mercury methylation
rates were determined with both pore water and precipitation spiking
solutions, as well as for sulfate additions (50, 100, and 200 uM)
for the subalpine wetland soils.