This data set reports stable isotopic composition (the natural abundance of oxygen-18/oxygen-16 and deuterium/hydrogen relative to international reference standards) of waters from the Marcell Experimental Forest (MEF) in Itasca County, Minnesota. The data come from sites in catchments instrumented for hydrologic and environmental monitoring named S1, S2, S3, S4, S5, and S6. In addition, several lakes in the MEF and surrounding area have been sampled. All samples have been analyzed using laser absorption spectroscopy.
Starting during 2008, an aliquot of every water sample collected at the MEF has been archived for water isotope analysis. Only a subset of the samples has been analyzed, mostly from the S1 and S2 catchments. There are fewer water isotope values for samples from S3, S4, S5, S6, and the lake sites. We describe the broader sample collection effort (i.e., frequency and duration of sampling) even though this data set sometimes only includes brief portions of the entire period over which samples were collected. More water isotope values will be added as time and resources allow the archived samples to be analyzed.
The MEF is operated and maintained by the USDA Forest Service, Northern Research Station.
Most samples from the S1 bog were collected as part of the SPRUCE (Spruce and Peatland Responses Under Climatic and Environmental Change) experiment. The SPRUCE experiment is a multi-year cooperative project among scientists of the Oak Ridge National Laboratory operated by UT-Battelle, LLC and the USDA Forest Service, Northern Research Station, with funding from the US Department of Energy, Biological and Environmental Research Program. SPRUCE sample collection and analyses started prior to initiation of the warming experiment, during December of 2013 and will continue for the duration of the experiment (expected to end during 2025).
SITE DESCRIPTION:
The 1,140 ha Marcell Experimental Forest includes seven research catchments and additional research sites that are dispersed across two land areas, the North and South Units. The S1, S2, S3, S6, and S7 research catchments, along with the South Meteorological station (South MET) and Bog Lake peatland, are located on the South Unit. The S4 and S5 catchments are located on the North Unit. The overall landscape has peatlands and lakes interspersed among mineral-soil uplands. The overstory trees on uplands at the MEF are predominately aspen (Populus tremuloides, P. grandidentata, and P. balsamea), paper birch (Betula papyrifera), red maple (Acer saccharum), balsam fir (Abies balsamea), white pine (Pinus strobus), red pine (Pinus resinosa), and jack pine (Pinus banksiana).
The climate is continental with warm summers, cold winters, and an average air temperature since 1961 of 3.6 deg C (1961 to 2019, Sebestyen et al. 2021c). Mean precipitation since 1961 is 787 mm. Most precipitation occurs as rainfall during summer and a winter snowpack accumulates from December to March or April when the snowpack melts.
The S1, S2, S4, S5, and S6 catchments each have a central peatland with a raised-dome ombrotrophic bog surrounded by a lagg (intermediate peatland area between the bog and the surrounding mineral soil uplands). The catchments range in size from 9 to 53 hectare and the peatlands range in size from 2 to 8 hectare. The bogs have black spruce (Picea mariana) and tamarack (Larix laricina) with a dense understory of peat moss (Sphagnum spp.), ericaceous shrubs, and haircap moss (Polytrichum sp.). The ericaceous shrubs include Labrador tea (Rhododendron groenlandicum) and leatherleaf (Chamaedaphne calyculata) with some bog laurel (Kalmia polifolia) and blueberry (Vaccinium angustifolium). The laggs have richer plant communities. In addition to the bog species, laggs include speckled alder (Alnus incana), paper birch (Betula papyrifera), various Carex species, cotton grass (Eriophorum spissum) and many other species.
The S1 bog is also the site of the SPRUCE experiment, and there are 10 experimental plots: 5 warmed plots (+0, +2.25, +4.5, +6.75, +9 degrees C) at ambient atmospheric carbon dioxide concentration, and the same 5 temperature levels with carbon dioxide elevated to about 900 ppm. Below-ground warming began during June 2014, aboveground warming was initiated during 2015, and elevated carbon dioxide starting during 2016. Sampling of waters occurs inside these chambers, and at other sites within the S1 catchment (e.g., precipitation, aquifer groundwater, bog and lagg porewaters, bog runoff, and stream water).
The S2 catchment has a 6.5-hectare (ha) deciduous uplands forest dominated by aspen (Populus tremuloides) and white birch (Betula papyrifera). The S2 catchment is a reference basin for paired catchment studies at the MEF (Sebestyen et al. 2011). The S6 catchment has a 6.9-ha coniferous uplands forest. The S6 uplands forest has had conifer cover since 1983, after a 100% clearcut of the deciduous upland forest and planting of white spruce (Picea glauca) and red pine (Pinus resinosa; Sebestyen et al. 2011). Both catchments have upland mineral soils that developed in surficial glacial tills on deep (50 meters) outwash sand deposits. The bog in S2 is 3.2 ha in size and the bog in S6 is 1.9 ha. Some sampling sites in the S2 and S6 catchments include N or S in names to distinguish between locations on the north (N) or south (S) side of the peatland (e.g., S2S SUB for the subsurface stormflow plot to the south of the S2 peatland).
The S3 catchment has a central, 19-ha, rich fen surrounded by mineral-soil uplands. The peatland is covered with trees and shrubs including black spruce (Picea mariana), tamarack (Larix laricinia), willow (Salix sp.), speckled alder (Alnus incana).
SAMPLE COLLECTION METHODS
At the time of collection, date/time of retrieval, sample location, and associated notes were recorded on field data sheets. Glass scintillation vials for water isotope samples were completely filled, avoiding headspace or bubbles. A unique serial identification (Lab ID) number was assigned to all aliquots of the same sample for tracking purposes in the laboratory and data reporting. Samples for the SPRUCE experiment have a 5 digit integer as an ID, starting with 80,000 (the 80 to 90 ID series). Samples from elsewhere on the MEF have a 6 digit integer as an ID in various number series depending on the year and purpose (routine long-term monitoring or specific project) of sampling.
Regardless of water type, unfiltered water was stored at room temperature in 16-mL glass scintillation vial with a Polyseal cap for liquid water isotope analysis.
Additional aliquots of each sample were collected for other chemistry analyses, some of which are published (Griffiths and Sebestyen, 2016a, b; Sebestyen et al., 2020a, b, c, 2021a, b)
Precipitation sampling:
Precipitation was collected year round on an event-basis from one collector located in an upland clearing at the South meteorological (S2 MET) station in the S2 research catchment and three individual collectors (B1, B2, B3) located at the end of three boardwalks that are used to access the S1 bog and SPRUCE plots. Samples from S2 are named S2 MET precip. Samples from the three collectors in S1 were either individually analyzed (named B#- precip) or composited (named S1 precip), depending on the total volume of water available relative to the amount (at least 150 mL) needed to complete a suite of chemistry and isotopic measurements. More details on precipitation sampling are provided in Sebestyen et al. (2020). Precipitation sample analysis begins with those collected in January 2010 in S2, and August 2016 in S1.
Funnel/bottle collectors were used to collect rainfall and buckets were used to collect snowfall. When rainfall was expected, typically from March or April through October or November, a 20.3 cm (8 inch) diameter high density polyethylene (HDPE) funnel was used. Rainfall drained from funnels through reinforced clear vinyl tubing into a 2-L HDPE wide-mouth, graduated collection bottle. A narrow (0.95 cm) adaptor was used to connect tubing to a bottle cap. The narrow adaptor relative to the wide (approx. 5 cm), flat bottle cap reduces evaporative loss from a collection bottle.
Funnel/bottle collectors were not used for snowfall or mixed precipitation (i.e., some combination of rain, sleet, hail, ice, or snow). Instead, a large cylindrical HDPE container (bucket with outside diameter = 30.5 cm, height = 22.9 cm, capacity = 15 L) was placed in a bracket mounted on a post. No frozen precipitation samples were collected at S2 MET before autumn/winter of 2010.
The precipitation collectors were exposed to both wet and dry deposition (i.e., bulk precipitation). Precipitation was collected on an event-basis, rather than a fixed interval, to minimize exposure of samples to evaporation, sunlight, excessive heat, or freezing. Precipitation samples are cumulative composites of precipitation since the last collection.
The time between sample collection and retrieval was intended to be as minimal as possible, with sampling typically within 12 to 24 h of the end of a precipitation event. Precipitation events that ended after business hours, during weekends (Friday afternoon through Monday morning), or holidays were typically collected the next business day between 7 AM and 4 PM. The date/time reflects when the sample was retrieved, not when the precipitation event occurred or ended.
Snowpack sampling:
Snowpack core samples were collected from the S2 catchment. Snow was collected every two weeks to monthly from 2009 to 2015, and every two weeks from 2018 to 2020. Snow was occasionally collected in a forest clearing at the S2 MET station (S2S MET snow) and under the forest canopy on a north-facing upland hillslope (S2S snow), and in the lagg (S2S lagg).
To obtain these samples a PVC pipe was rinsed with snow and then driven into the snow until the ground surface was reached. Snow was then excavated from around the pipe and a plastic bag placed underneath to catch the snow as the PVC pipe was lifted. Excess air was removed from the plastic bags, they were then stored in a refrigerator to melt. Liquid water samples were then transferred to 16-mL glass scintillation vials.
Aquifer groundwater sampling:
Groundwater was sampled from the aquifer in the deep sandy outwash (~50 m deep above bedrock). Wells ranged in depth from 3.4 m to 14 m. The wells are located at upland locations with a single well (DW 202) at the S2 MET station and 4 wells (DW 101, DW 102, DW 105, and DW 106) located in the uplands surrounding the S1 bog. Monthly sampling of the S2 well (202) began in 2010, and the S1 wells (101, 102, 105, and 106) began in 2013. Wells in the S1 catchment were not sampled during freezing conditions. A bailer was used for sampling, with the first three volumes discarded before collecting the subsequent bailer volumes for isotopic analyses. Samples analyzed begins with those collected in January 2010 for S2 and August 2016 for S1.
Lake (Open-water sampling) sampling:
Several lakes near the bogs of the MEF were sampled beginning in August 2020. A 500-mL dipper (CXBA00, Global Water Instrumentation, Phoenix, Arizona) was rinsed three times with lake water. Then a sample was dipped from about 10-cm depth below the surface. The sample was poured into a glass scintillation vial. When a lake was frozen, a hole was augured through the ice, ice shards were dipped from the hole, and water was then sampled with the dipper.
Bog and lagg surface and pore water sampling:
Surface and pore waters have been collected from the S1 (since 2010) and S2 (since 2009) bogs and laggs.
Surface waters were occasionally collected before piezometers were installed for porewater sampling. Surface waters were only collected during periods when there was standing water in hollows of either the laggs or bogs.
Unfiltered surface water was dipped with a ladle and poured into a sample vial (see open-water sampling method). The dipper was used after about April 2010, though mostly for samples collected weekly from shallow excavations at the S2 lagg pool and S2N lagg sites. The dipper has occasionally been used for weekly sampling during periods when piezometers were frozen during snowmelt and there was standing water at a sampler. At those times, surface water was collected adjacent to a piezometer.
Samples were pumped from two different depth types of piezometers (near-surface or nested depths). Piezometers were made from 5-cm (2 inch) internal-diameter (ID) PVC pipe with a 10-cm slotted section. Piezometers were pushed or hammered into peat. Porewaters were never collected during freezing conditions, typically from November to March or April.
All water in a piezometer was evacuated immediately before to a day prior to sampling. A manual bellows pump (various Guzzler 400 series pumps, The Bosworth Co., East Providence, Rhode Island) was used to purge piezometers. Then, a peristaltic pump (Cole Parmer, Vernon Hills, Illinois, Masterflex PSF/CRS easy-load pump head mounted to a Dewalt, Townson, Maryland, portable drill) was used to sample piezometers. At least 3 volumes of the tubing volume (or 5-20 s of pumping) were purged prior to filling bottles to clean tubing between samples. Flexible pump tubing was rinsed before and after sampling with 18.0 megaohm deionized water.
Near-surface piezometers: There are many piezometers intended for sampling of near-surface waters (about 5-10 cm below hollow surfaces). A screened section (a hacksaw slot every 1 cm over a 10-cm interval) of a piezometer was glued to a 30-cm unscreened section of PVC on each end. A cap was glued to the bottom of each piezometer. The top of the screened interval was placed at about 5 to 10 cm below a hollow surface. Piezometers were pushed or hammered into the peat, deeply anchored to prevent toppling in the unconsolidated and saturated surficial peat, and prevent frost heaving during winter. Accordingly, each piezometer had at about 45 cm of pipe below the peat surface (about 5 cm of the top unscreened PVC, the 10 cm PVC screen and the full 30 cm of the bottom unscreened interval). The additional belowground pipe stabilized the piezometer and served as a reservoir to accumulate and hold water. The tops of piezometers were loosely capped when not being sampled and the piezometers were vented with an ~1-mm (1/8 inch) hole, immediately below the cap.
Nineteen near-surface (5- to 10-cm depth) samplers were located in the southern portion of the peatland along wooden boardwalks that were installed prior to the SPRUCE experiment for pre-experimental and baseline monitoring. Most of those piezometers were along three different transects that spanned the lagg into the bog. In S1, the site names are: EM1 shallow well, test and then a one- or two-digit number (e.g., Test 2), or N and then a two digit number (e.g., N13). The samplers named Test # are dispersed in bog, though all along boardwalks. The samplers named N## are along transects that span the lagg to the edge of the bog.
In the S2 peatland, lagg waters have been collected as surface water and porewater since 2009. Sampling of bog waters with piezometers was added during 2010. Surface water or porewater have been collected every week at four sites (5- to 10-cm depths), every other week at one site (5- to 10-cm depth), and occasionally during synoptic surveys at up to 40 sites (5- to 10-cm depths). The synoptic surveys included lagg waters from around the entire perimeter of the peatland, and six different transects that spanned the lagg into the bog. Piezometers around the perimeter and along transects have names that start with KF and then a one- or two-digit number for each site (e.g., KF45). Porewaters were collected from excavations in the peat (S2 lagg pool or S2N lagg pool sites; see open-water method) or pumping water from piezometers.
Nested piezometers: Some piezometers are nested for depth-specific sampling from the surface to as deep as 3 m. These piezometers had machine-cut 0.25-mm slots every 1 cm over the 10-cm screened intervals. Sectional pipe with polytetrafluoroethylene (PTFE) O-rings on male threads at connection points were then taped with PTFE before threading pieces together to the required length of pipe for each piezometer.
In each piezometer nest, the top of the screened interval was placed at 0, 30, 50, 100 cm below the hollow surface. About 1 m of each piezometer rises above the surface. A threaded well point was secured (joint was PTFE taped) to the bottom of each piezometer. Each nested piezometer had at least 1.5-m of pipe below the peat surface, such that the 0-cm depth piezometers, for example, had about 140 cm of pipe beneath the screen that served as a reservoir to accumulate and hold water. Piezometers were separated by no more than 10 to 15 cm between any adjacent pair of piezometers within a nest. After purging, 0- to 50-cm depth samplers usually refilled within minutes. Deeper samplers sometimes required one day to refill with enough water for sampling.
In S1, seventeen SPRUCE plots have nests of piezometers and these piezometers have been sampled since 2014. Each nest had 0-, 30-, 50-, 100-, 200-, and 300-cm depth piezometers. The piezometer nests in S1 are named as either TEST and a one- or two- digit number, or for the SPRUCE plot where located (2, 4-11, 13, 16-17, 19-21). The depth for these piezometers is provided in a DEPTH column in the CSV file with the data.
Bog runoff (lateral outflow):
A subsurface corral-outflow system has been designed and constructed to measure water flow and allow the collection of water samples from the outflow of each experimental enclosure within the SPRUCE project. Each SPRUCE enclosure has a subsurface barrier to preclude the inflow of surrounding bog water into the footprints of experimental enclosures. Shallow, lateral drains in the corral maintain passive, natural drainage of surface water and near-surface water (0 to about 30 cm) from enclosures into a sump basin that is used to measure outflow volume and for the collection of water samples. The system is described in detail by Sebestyen and Griffiths (2016).
Lateral outflow from SPRUCE enclosures was collected in two ways: as weekly flow-weighted composite samples from autosamplers or as grab samples during weeks that runoff occurred. An autosampler was used to collect an aliquot after each increment of outflow, typically every 75 L (named #-sampler). Samples were refrigerated inside an autosampler until retrieval. However, during winter, auto sampling is disabled when air temperatures are less than 10 degrees Celsius. When auto sampling is disabled, more than 75 L of water may have accumulated between samples. A grab sample was pumped using a peristaltic pump from the outflow pipes (named as #-outflow). Samples of runoff analyzed begin with those collected in August 2016.
Stream water:
Streams were sampled by placing a vial in the stream of water that flowed over a v-notch weir. In the case of S1, the open-water sampling technique was used. Water was collected throughout the year, whenever unfrozen. The S1 and S2 streams were sampled more frequently, beginning in March 2010 in S1 and July 2008 in S2. The other catchment outlets are sampled less frequently, and samples analyzed beginning with those collected in December 2018 in S3, December 2019 in S4 and S5, and April 2008 in S6.
Upland soil water:
Soil water from upland mineral soil was collected in the S2 catchment using two different devices: zero-tension lysimeters and piezometers. Sampling of soil water began in November 2009.
Piezometers: There are one or two piezometers in upland soil at the end of each of the six lagg to bog transects of piezometers (previously described). The samplers (KF7, KF7A, KF13, KF19, KF27, KF33, KF39) were sampled during 2010. The piezometers are identical in design to those described for near-surface lagg and bog porewater sampling. A hole was augered for each sampler and the hole was backfilled around the piezometer with native soil during installation.
Soil lysimeters: Soil water samples pumped from a zero-tension lysimeter. Soil water drains into a reservoir from four separate lysimeter pans. One lysimeter is at each of three hillslope positions: low-, mid- and up-slope locations on both north and south facing hillslopes. Samples are typically retrieved within 1 to 2 d of the end of precipitation or snowmelt runoff. Samples are either named for the S2S or S2N hillslope, with the hillslope position (LO, MI, or UP) and the abbreviation LYS for lysimeter. For example, S2S LO LYS for the low hillslope position on the S2S (north-facing, south side) hillslope in the S2 catchment.
Overland flow and subsurface stormflow (upland runoff):
Upland runoff waters were collected on an event-basis. Upland runoff included both overland flow (named Site#-SURF) and subsurface stormflow (named Site#-SUB) from runoff collection plots on north- and south-facing hillslopes in both the S2 and S6 catchments. The S2N and S6N runoff plots are located on the north side of each bog (south-facing slopes) and the S2S and S6S runoff plots are located on the south side of each bog (north-facing slopes).
Overland runoff from hillslopes: Saturated flow through the forest floor and above the sandy loam layer occurs usually when soils are frozen and sometimes during intense rainfall events. Downslope runoff is routed into a surface collection pan that drains through PVC to a 5-L pail that overflows to a large (700 L) collection tank. From 2008 to 2013, an autosampler was used to collect incremental samples as triggered by rising water level in the large tank (only S2S location). Samples were typically retrieved within 12 to 24 h of the end of precipitation or snowmelt runoff. See Sebestyen et al. (2020a), Timmons et al. (1977), and Verry and Timmons (1982). Samples analyzed begin with those collected in April 2008 from the S2S location, and March 2010 from the S2N location.
Lateral, subsurface stormflow through a sandy loam layer overlying a loamy clay is routed into a trench that drains through PVC to a 5-L pail that overflows to a large (700 L) collection tank. From 2008 to 2013, an autosampler was used to collect incremental samples as triggered by rising water level in the large tank (only S2S location). Samples were typically retrieved within 12 to 24 h of the end of precipitation or snowmelt runoff. See Sebestyen et al. (2020), Timmons et al. (1977), and Verry and Timmons (1982). Samples analyzed begin with those collected in March 2009 S2S location, March 2010 from the S2N location, and October 2019 in the S6N/S6S locations.
ANALYTICAL METHODS:
Water isotope samples were analyzed at various laboratories. Some samples that were collected from 2008 to 2010 were analyzed at the Center for the Environment Analytical Laboratory at Plymouth State University (New Hampshire, USA). Some samples that were collected from 2010 to 2012 were analyzed at the Integrated Watershed Hydrology and Biogeochemistry Research Facility at the University of Toronto (Ontario, Canada). Some samples (collected during 2009 and 2010) were analyzed at the Biometeorology Lab at University of Minnesota, Twin Cities (Minnesota, USA). A few samples that were collected during 2011 were analyzed at the Stable Isotope Facility at the University of California, Davis (California, USA). These four laboratories used the same instrument, a Los Gatos Research (Mountain View, California) DLT-100. Many samples that were collected from 2010 to 2013 were analyzed at the Ecosystem Laboratory at Oak Ridge National Laboratory (Tennessee, USA) using a Picarro Inc (Santa Clara, California) L1102-i instrument. Analysis for the ongoing project will be at USDA US Forest Service, Grand Rapids (Minnesota, USA) using a Los Gatos Research (Mountain View, California) T-LWIA-45-EP.
All water isotope samples were analyzed using laser absorption spectroscopy (Lis et al. 2008) and each laboratory used similar procedures. Unfiltered waters were injected 6 to 9 times with 0.5 to 1.2 microliter per sample. Isotopic values were scaled relative to the Vienna Standard Mean Ocean Water (VSMOW)-Standard Light Antarctic Precipitation (SLAP) scale. Each laboratory used secondary standards that were calibrated to VSMOW and SLAP. Machine raw data were post-processed to account for machine drift and between-sample memory (Wasseenar et al., 2014).
REPORTED VALUES:
To document when and where a sample was collected, we include a laboratory ID, site, sample name, depth (when applicable), and date/time of collection. Values for D and O-18 are reported in delta-notation in permil (parts per thousand; also written as per mille or per mil) relative to VSMOW (Craig 1961).
The analytical precision for water isotopes was:
0.8 permil for delta-D and 0.1 permil for delta-O-18 at Plymouth State University,
2 permil for delta-D and 0.25 permil for delta-O-18 at the University of California,
1 permil for delta-D and 0.25 permil for delta-O-18 at the University of Minnesota,
0.8 permil for delta-D and 0.25 permil for delta-O-18 at the University of Toronto,
0.5 permil for delta-D and 0.1 permil for delta-O-18 at Oak Ridge National Laboratory
0.5 permil for delta-D and 0.1 permil for delta-O-18 at the Grand Rapids Forestry Sciences Laboratory.
MARCELL EXPERIMENTAL FOREST sites and data collection are described in further detail in:
Sebestyen, S.D., C. Dorrance, D.M. Olson, E.S. Verry, R.K. Kolka, A.E. Elling, and R. Kyllander (2011). Chapter 2: Long-Term Monitoring Sites and Trends at the Marcell Experimental Forest. In Randall K. Kolka, Stephen D. Sebestyen, Elon S. Verry, and Kenneth N. Brooks (Ed.). Peatland Biogeochemistry and Watershed Hydrology at the Marcell Experimental Forest (pp 15-71). CRC Press, Boca Raton, FL. https://www.fs.usda.gov/treesearch/pubs/37979.
The SPRUCE Project Website (http://mnspruce.ornl.gov/) has project plans and additional information.
REFERENCES:
Craig, H. (1961). Isotopic variations in meteoric waters. Science, 133(3465), 1702-1703. https://doi:10.1126/science.133.3465.1702
Griffiths, N. A., and Sebestyen, S. D. (2016a). SPRUCE porewater chemistry data for experimental plots beginning in 2013. Oak Ridge National Laboratory, TES SFA, and U.S. Department of Energy. Oak Ridge, TN. Retrieved from: https://doi.org/10.3334/CDIAC/spruce.028.
Griffiths, N. A., and Sebestyen, S. D. (2016b). SPRUCE S1 bog porewater, groundwater, and stream chemistry data: 2011-2013. Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, and U.S. Department of Energy. Oak Ridge, TN. Retrieved from: https://doi.org/10.3334/CDIAC/spruce.018.
Lis, G., Wassenaar, L. I., and Hendry, M. J. (2007). High-precision laser spectroscopy D/H and 18O/16O measurements of microliter natural water samples. Analytical Chemistry, 80(1), 287-293. https://doi.org/10.1021/ac701716q
Sebestyen, S. D., Funke, M. M., Cotner, J., Larson, J. T., and Aspelin, N. A. (2020a). Water chemistry data for studies of the biodegradability of dissolved organic matter in peatland catchments at the Marcell Experimental Forest: 2009-2011, 2nd edition. Forest Service Research Data Archive. Fort Collins, CO. Retrieved from: https://doi.org/10.2737/RDS-2017-0067-2
Sebestyen, S. D., and Griffiths, N. A. (2016). SPRUCE enclosure corral and sump system: Description, operation, and calibration. Oak Ridge National Laboratory, Climate Change Science Institute, and U.S. Department of Energy. Oak Ridge, TN. Retrieved from: http://doi.org/10.3334/CDIAC/spruce.030
Sebestyen, S. D., Lany, N. K., Aspelin, N. A., Oleheiser, K. C., and Larson, J. T. (2021a). Marcell Experimental Forest monthly aquifer groundwater chemistry at the S2 catchment, 2007 - ongoing. USDA Forest Service. Environmental Data Initiative. Retrieved from: https://doi.org/10.6073/pasta/73f3053d71454f2b935c12bb8f0b6412.
Sebestyen, S. D., Lany, N. K., Larson, J. L., Aspelin, N. A., Oleheiser, K. C., and Nelson, D. K. (2021b). Marcell Experimental Forest porewater chemistry at the S2 catchment, 2009 - ongoing. USDA Forest Service. Environmental Data Initiative. Retrieved from: https://doi.org/10.6073/pasta/645ea2442f549a42bdd58e28ad58e3fe.
Sebestyen, S. D., Lany, N. K., Roman, D. T., Burdick, J. M., Kyllander, R. L., Verry, E. S., and Kolka, R. K. (2021c). Hydrological and meteorological data from research catchments at the Marcell Experimental Forest. Hydrological Processes. https://doi.org/10.1002/hyp.14092
Sebestyen, S. D., Oleheiser, K. C., Larson, J. L., Aspelin, N. A., Stelling, J. M., Griffiths, N. A., and Lany, N. K. (2020b). Marcell Experimental Forest event-based precipitation chemistry, 2008 - ongoing ver 1. USDA Forest Service. Environmental Data Initiative. Retrieved from: https://doi.org/10.6073/pasta/5b8eb3a9b7a572dd56186f0e6b59daf2
Timmons, D. R., Verry, E. S., Burwell, R. E., and Holt, R. F. (1977). Nutrient transport in surface runoff and interflow from an aspen-birch forest. Journal of Environmental Quality, 6(2), 188-192.
Verry, E. S., and Timmons, D. R. (1982). Waterborne nutrient flow through an upland-peatland watershed in Minnesota. Ecology, 63(5), 1456-1467. https://doi.org/10.2307/1938872
Wassenaar, L. I., et al. (2014). Approaches for achieving long-term accuracy and precision of delta18O and delta2H for waters analyzed using laser absorption spectrometers. Environ Sci Technol 48(2): 1123-1131. https://doi.org/10.1021/es403354n
