DOI: 10.6073/pasta/b4e73caff4d107190826777d8150f87e
title: Mercury in soil, vegetation, and organisms across Niwot Ridge, Saddle Catchment, and Green Lakes Valley, 2020 - 2023.

description: 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.