This data set includes groundwater chemistry values for aquifer water from a well in the uplands of the S2 catchment at the Marcell Experimental Forest (MEF) in Itasca County, Minnesota. Aquifer water has been collected about monthly since 2007 and sampling is ongoing.
Samples are measured for pH, specific conductivity, anions (chloride, sulfate), cations (calcium, magnesium, potassium, sodium, aluminum, manganese, strontium), silicon, nutrients (ammonium, nitrate, soluble reactive phosphorus, total nitrogen, total phosphorus), and total organic carbon. Stable isotopes of water (relative abundances of oxygen-18 and deuterium) have been measured on some samples.
The MEF is operated and maintained by the USDA Forest Service, Northern Research Station.
SITE DESCRIPTION:
The S2 catchment has a 6.5-ha deciduous upland forest and a natural, undrained 3.2 hectare peatland (raised-dome bog with a surrounding lag). The catchment has been used as a reference basin since 1960 for catchment and paired-catchment studies (Verry et al. 2011; Sebestyen et al. 2011).
The upland forest, dominated by aspen (Populus tremuloides), white birch (Betula papyrifera), red maple (Acer rubrum), and balsam fir (Abies balsamea, with some red oak (Quercus rubra), basswood (Tilia americana), and jack pine (Pinus banksiana). The upland forest was last harvested during the 1910s. In the uplands, a Warba sandy clay loam developed in glacial till atop deep (50 m) outwash sand deposits. The Warba soil series is a fine-loamy, mixed, superactive, frigid Haplic Glossudalfs; Alfisol (Nyberg 1987 )
The peatland has a black spruce (Picea mariana)-Sphagnum community with some tamarack (Larix laricinia) and ericaceous shrubs (primarily Rhododendron groenlandicum and Chamaedaphne calyculata).
The climate is continental with warm summers, cold winters, and an average air temperature since 1961 of 3.4 deg C (1961 to 2011, Sebestyen et al. 2011 ). Mean precipitation since 1961 is 78 cm. Most precipitation occurs as rainfall during summer and a winter snowpack accumulates from December to March or April when the snowpack melts.
LOCATIONS OF GROUNDWATER SAMPLING:
Aquifer groundwater is collected from a 14-m deep well. The location is named DW 202. The well is 3.2-cm internal-diameter galvanized metal pipe that was installed in a hole that was bored using a mobile drill rig. A drilling record documents a 3.4-m till layer at the surface, with 10.6 m of pipe in a sand outwash layer beneath the till layer. The bottom 1.2 to 1.8 m of the well is a sand point.
The well is loosely capped when not being sampled.
WATER SAMPLING:
The well was purged and sampled with a bailer. At the time of sampling, the bailer was used to remove water (3x the bailer volume) before the fourth bailer volume was used for sample collection.
Unfiltered groundwater was poured into a new, 250-mL low density polyethylene (LDPE) bottle for pH, specific conductivity, ion, and nutrient analyses. Starting during 2008, an aliquot of each sample was collected in a 16-mL scintillation vial with a Polyseal cap for liquid water isotope analysis (stored at room temperature). Scintillation vials for water isotope samples were completely filled, with no headspace or bubbles. For all samples collected during and after 2019, a separate 60-mL aliquot was saved in a new, 60-mL HDPE bottle solely for nutrient (nitrate, ammonium, total nitrogen, and total phosphorus analyses) analyses.
Sample bottles and vials were triple rinsed with sample water before filling. When collected, date/time of retrieval, sample location, and associated notes were recorded on field data sheets. A unique serial ID number was assigned to all aliquots of the same sample for tracking purposes in the laboratory and data reporting. Sample ID numbers are 6 digit integers. The samples IDs are not necessarily consecutive because water from other sites at the MEF are interspersed in the numbering series. Surface water samples were labelled as DW 202.
Samples were transported on ice in a cooler and frozen upon return to the Grand Rapids chemistry laboratory, where refrigerated (250-mL bottles), frozen (60-mL bottles for nutrient analysis), or stored at room temp (isotope vials) until analyzed.
ANALYTICAL METHODS:
Water samples were analyzed for pH, specific conductivity, and concentrations of cations, anions, nutrients, and total organic carbon at the Forestry Science Laboratory in Grand Rapids, Minnesota.
Unfiltered water was used for all laboratory analyses. The samples are likely to include colloids. If there was any fine particulates in samples, the particulates would have settled on the bottoms of bottles during storage and care would have been taken to decant water, not particulates, for analyses.
For each type of laboratory measurement, every tenth sample was run in duplicate followed by two reference standards. Analytical duplicates and the 10 preceding samples were acceptable for reporting when the relative error was less than 10 percent between duplicates.
Unless otherwise noted, autosamplers were used with instruments for analysis.
For anion, cation, nutrient, and TOC analyses, check and reference solutions were made in volumetric flasks with deionized water (18.0 megaohm/cm). When check standards differed by more than 5 percent from actual values, a batch of samples was reanalyzed. When a particular sample was higher in concentration than the highest calibration standard, that sample was diluted and re-run until within the range of the calibration standards. When check standards differed by more than 5 percent from actual values, a batch of samples was reanalyzed. When a particular sample was higher in concentration than the highest calibration standard, that sample was diluted and re-analyzed until within the range of the calibration standards.
pH: A Mettler Toledo (Columbus, OH) DL53 Autotitrator was used to measure pH according to Standard Method 4500-H+ B (APHA 2017). A four-point calibration was performed before each batch of 15 samples. A sodium carbonate reference was run after every ten samples. Samples were only analyzed if the reference values were accurate to within 10 percent and pH is reported to the nearest tenth of a decimal place. Samples for pH analysis typically were analyzed within days of collection. Although rare, samples sometimes were held for weeks to several months while awaiting maintenance on the analyzers.
Specific conductivity: Conductivity was measured on a Yellow Springs Instruments (YSI; Yellow Spring, Ohio) Model 3100 meter. A YSI 3403 probe (cell constant = 1.0/cm) was used until March 2017 and a YSI 3253 probe (cell constant = 1.0/cm) thereafter. The meters were calibrated with a 46.7 microSiemen/cm standard, and periodically checked with 23.8, 84.0, or 150 microSiemen/cm references. The manually loaded cell of the conductivity probe was twice rinsed and then conductivity was measured on the third poured aliquot. Samples, the standard, and reference standards were measured at room temperature and in a laboratory maintained at 21 degree C. Conductivity values were recorded on paper. Specific conductivity (conductivity at 25 degree C) was calculated from conductivity (at 21 degree C) when values were transferred to spreadsheets. Samples for conductivity measurement typically were analyzed within days of collection. Although rare, samples sometimes were held for weeks to several months while awaiting maintenance on the analyzers.
Anions: Anion (chloride and sulfate) concentrations were measured using suppressed conductivity and conductimetric detection on two different ion chromatographs: on a Dionex (Sunnyvale, CA) DX-500 for samples collected through 2012 and a Thermo Scientific Dionex ICS-2100 thereafter. Samples were injected through 20 micrometer filter caps and through an IonPac AG14 pre-column and AS14 column (DX500) and AG22 pre-column and AS22 column (ICS-2100). Standard Method 4110-C was used (APHA 2017). The ion chromatograph was typically operated every business day. Daily throughput of samples is lower than the rate at which samples are sometimes collected. For that reason, samples for anion measurement were sometimes analyzed within several days of collection, but oftentimes held for months to a year before analysis.
Cations and silicon: Cation (calcium, magnesium, potassium, sodium, aluminum, iron, manganese, and strontium) and silicon concentrations were analyzed by inductively coupled optical emission spectroscopy (ICP-OES). A Thermo Electron Corporation (Waltham, Massachusetts) Iris Intrepid ICP-OES was for all samples collected through 2015, and a Thermo Scientific (Waltham, Massachusetts) ICAP 7600 Duo for samples collected during and after 2016. Standard method 3120 was used (APHA 2017). Calcium, iron, magnesium, potassium, sodium were measured for all samples. Aluminum, manganese, silicon, and strontium analyses were added during 2009. While measured, we do not report iron concentration due to likely contamination from the metal of well. Samples for cation analyses were typically run one to four times a year in large batches of samples; analysis occurred within several days of collection for some samples to a year from collection for those that were held longest.
Nutrients:
Ammonium was measured according to the Lachat (Milwaukee, Wisconsin) QuikChem 10-107-06-1-F method on a Lachat (Hach Company, Loveland, Colorado) QuickChem 8500 starting with samples collected during 2019. Ammonium is reported as the amount of nitrogen in ammonium. The Lachat methods are equivalent to the automated phenate method to form indephenol blue for colorimetric analysis (Standard Method 4500-NH3 H; APHA 2017 ).
Nitrate+nitrate was measured according to Lachat QuikChem 10-107-04-1-B on a QuickChem 8500 starting with samples collected during 2019. Nitrate was reduced to nitrite using the automated cadmium reduction method and concentration was colorimetrically determined as the amount of nitrogen in the resulting nitrite (Standard Method 4500-NO3- F; APHA 2017). Though nitrite was not separately measured using this method, it has been rare in our experience to observe nitrite in MEF water samples. All samples were also analyzed by ion chromatography and nitrite peaks were not visible in sample chromatograms.
Total nitrogen (TN) concentrations were measured colorimetrically after in-line automated persulfate-ultraviolet oxidation to nitrate (Standard Method 4500-N B; APHA 2017). Concentrations were measured according to the Lachat QuikChem 10-107-04-1-P method on a Lachat QuickChem for samples collected before 2016 and Lachat QuikChem E10-107-04-3-D method on a Lachat QuickChem 8500 thereafter.
Soluble reactive phosphorus was measured according to the Lachat QuikChem 10-115-01-1-B method on a Lachat QuikChem 8000 for samples collected through 2012 and Lachat QuikChem 8500 thereafter. The Lachat methods are equivalent to the automated ascorbic acid reduction method (Standard Method 4500-P F; APHA 2017).
Total phosphorus (TP) concentrations were measured colorimetrically using automated persulfate-UV digestion and ascorbic acid reduction for colorimetric detection (Standard Method 4500-P; APHA 2017). Concentrations were measured according to the Lachat QuikChem 10-115-01-3-A method on a Lachat QuickChem 8000 for samples collected before 2016 and Lachat QuikChem E10-115-01-3-A method on a Lachat QuickChem 8500 thereafter. Total phosphorus concentration is almost always below the detection limit of 0.05 mg/L.
Samples for nitrogen and phosphorus chemistry were typically run once or twice a year in large batches of samples. Analysis occurred within several days of collection for some samples to a year from collection for those that were held longest.
Total organic carbon (TOC): Concentrations of TOC were measured by high-temperature combustion with infrared detection (Standard Method 5310-B, APHA 1995) on a Shimadzu TOC-V CPH with External Sparge Kit for samples collected through 2012. A Shimadzu (Columbia, Maryland) TOC-VCP was used for samples collected from 2013 onward. Concentrations were measured as total carbon minus inorganic carbon (TC-IC) before June 2010. If inorganic carbon (IC) was greater than 10 mg/L, which was oftentimes the case, then a sample was reanalyzed using the non-purgeable organic carbon (NPOC) method. After June 2010, all samples were analyzed using the NPOC method. Potassium hydrogen phthalate (KHP) was used for reference and check standards. TOC concentrations were highly erratic before November 2013 and we do not report any of those values.
Liquid water isotopes: The glass scintillation vials for water isotope measurement are stored in a sample archive and are available for eventual analysis. Some groundwater samples have been analyzed on Picarro, Inc (Santa Clara, California) L1102-i Water Isotope Analyzer at Oak Ridge National Laboratory (ORNL) or a Los Gatos Research (Mountain View, California) T-LWIA-45-EP liquid water isotope analyzer at the Grand Rapids chemistry laboratory. The samples analyzed at ORNL have these IDs: 219001, 219011, 219074, 219090, 219110, 219152, 219196, 219237, 219286, 219308, 220003, 220016, 220081, 220125, 220157, 220209, and 220252.
We report the relative abundance of deuterium (D) and oxygen-18 (O-18). The natural abundance of stable isotopes were measured using laser absorption spectroscopy (Lis et al. 2008). Bot laboratories used similar procedures; 6-7 injections of 0.5-1.2 uL sample were analyzed. Isotopic values were scaled relative to the Vienna Standard Mean Ocean Water (VSMOW)-Standard Light Antarctic Precipitation (SLAP) scale. A series of secondary standards were calibrated to VSMOW and SLAP. Machine raw data was then post-processed to account for machine drift and between-sample memory. Values for D and O-18 are reported in delta-notation (permil relative to VSMOW; Craig 1961 ).
REPORTED VALUES:
To document when a sample was collected, we include a laboratory ID, sample name, and date/time of collection. Sometimes chemistry values are assigned -9999 for individual solutes or for all analytes (i.e., pH, specific conductivity, solute concentrations, and water isotopes), which may have resulted from insufficient sample volume to complete all analyses, contamination that affected individual solutes or suites of analytes that were simultaneously measured on a single instrument for a particular sample, or contamination that affected all solutes for a particular sample. Samples pending analysis are also assigned -9999.
While iron concentration is measured, we do not report values due to likely contamination from the metal of well.
We do not report TOC concentration values prior to November 2013.
Concentrations of nitrate and ammonium are only reported onward from 2019 when aliquots were frozen for analysis. Values are reported as -9999 prior to preservation with freezing.
Data values below the detection limit are reported in the data file and are not flagged. Detection limits, as listed above, must be considered when using these data.
The method detection limits were:
- 0.01 mg chlorine/L,
- 0.02 mg sulfate/L,
- 0.05 mg calcium/L,
- 0.05 mg magnesium/L,
- 0.5 mg potassium/L,
- 0.1 mg sodium/L,
- 0.01 mg aluminum/L,
- 0.01 mg manganese/L,
- 0.05 mg silicon/L,
- 0.01 mg strontium/L,
- 0.01 mg nitrogen/L for ammonium,
- 0.002 mg nitrogen/L for nitrate+nitrite,
- 0.001 mg phosphorus/L for soluble reactive phosphorus,
- 0.05 mg nitrogen/L for total nitrogen,
- 0.05 mg phosphorus/L for total phosphorus,
- 0.5 mg carbon/L for TOC.
The analytical precision for water isotopes was:
- 0.5 permil for D and 0.1 permil for O-18 at ORNL,
- 1 permil for D and 0.25 permil for 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.
REFERENCES:
APHA. (2017). Standard methods for the examination of water and wastewater (23rd ed.). Washington, DC: American Public Health Association.
Craig, H. (1961). Isotopic variations in meteoric waters. Science, 133(3465), 1702-1703. https://doi.org/10.1126/science.133.3465.1702
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.
Nyberg, P. R. (1987). Soil survey of Itasca County, Minnesota. USDA Soil Conservation Service, St. Paul, MN.
Sebestyen, S. D., Dorrance, C., Olson, D. M., Verry, E. S., Kolka, R. K., Elling, A. E., and Kyllander, R. (2011). Long-term monitoring sites and trends at the Marcell Experimental Forest. In Kolka, R. K., Sebestyen, S. D., Verry, E. S., and Brooks, K. N. (Eds.), Peatland biogeochemistry and watershed hydrology at the Marcell Experimental Forest (pp. 15-71). Boca Raton, FL: CRC Press.
Verry, E. S., Brooks, K. N., Nichols, D. S., Ferris, D. R., and Sebestyen, S. D. (2011). Watershed hydrology. In Kolka, R. K., Sebestyen, S. D., Verry, E. S., and Brooks, K. N. (Eds.), Peatland biogeochemistry and watershed hydrology at the Marcell Experimental Forest (pp. 193-212). Boca Raton, FL: CRC Press.
