This data set includes the chemistry of peatland surface and pore waters collected at the S3 peatland at the Marcell Experimental Forest (MEF) in Itasca County, Minnesota. Porewaters at four depths (0 to 1 m depths) have been collected about monthly from three different nest of piezometers since 2013, though never when samplers were frozen (typically November to May).
Samples are measured for pH, specific conductivity, anions (chloride, sulfate), cations (calcium, magnesium, potassium, sodium, aluminum, iron, manganese, strontium), silicon, nutrients (ammonium, nitrate, soluble reactive phosphorus, total nitrogen, total phosphorus), and total organic carbon.
The S3 peatland is located in the long-term S3 research catchment where water level, soil temperature, meteorology, snow depth, and snow water equivalents have been monitored, with some measurements beginning as early as 1960.
The MEF is operated and maintained by the USDA Forest Service, Northern Research Station.
SITE DESCRIPTION:
The S3 pealtand is a 19-ha, rich fen. The peatland is covered with trees and shrubs including: black spruce (Picea mariana), tamarack (Larix laricinia), willow (Salix sp.), speckled alder (Alnus incana). The trees and shrubs on the fen were clearcut during the 1972-1973 winter. The following summer, the slash was burned across 86% of the surface area. Black spruce and white cedar (Thuja occidentalis) seeds were sown in the burned areas. Little to no cedar remains. The surrounding uplands have aspen (Populus tremuloides, P. balsamea, and P. grandidentata), birch (Betula papyrifera), red pine (Pinus resinosa), and jack pine (Pinus banksiana) forest cover. The S3 catchment is 72.0 ha.
The depth distribution of peat has not been surveyed, but in the area where porewaters were sampled, the peat is about 1-m deep. The peat, Mooselake and Lupton series organic soil (Euic, frigid Typic Haplohemists; Nyberg 1987 ) has accumulated in the last 10,000 y since Wisconsin glaciation (Verry & Janssens 2011 ). The peat has hummock and hollow microtropography. Hummocks are uneven, elevated areas that rise various heights, up to about 30 cm, above the adjacent hollows, which have a relatively uniform elevation within a localized area. The piezometers, used to sample porewater, were all placed in hollows.
The adjacent uplands have loamy sand soil textures formed in a glacial outwash plain: Eagleview/Menahga complex, and Menagha loamy sand soils (Nyberg 1987). The Eagleview soil (Mixed, frigid Lamellic Udipsamments) generally covers 60 percent of the soil complex and the Menahga soil covers about 25 percent, with 15 percent coverage in other soils. The Menagha soil is an Entisol; mixed, frigid, Typic Udipsamment.
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.
Water in the peatland originates from precipitation and subsurface exchange with a surrounding aquifer in a glacial outwash sand that blankets the entire area to a depth of about 50 m. The peatland water table fluctuates from about 0.10 m above the surface to 0.20 m below (Sebestyen et al. 2011).
LOCATIONS OF WATER SAMPLING:
Three nests of piezometers were installed in the S3 fen during August 2013 and first sampled during October 2013. Two piezometer nests, S3-1 (southmost) and S3-2 are located along a south-north boardwalk that has been used to access a rain gage (3-2) in the S3 fen from the south end of the peatland. Nest S3-2 is about 15 m north of S3-1. The third piezometer nest, S3-3 (northmost), is along a separate boardwalk that extends from the west margin with the upland about 6 m in to the peatland. Nest S3-3 is about 77 m west of north from S3-2.
The boardwalks allow access, prevent peat compaction, and eliminate trampling of the peat near and around the piezometers during installation and sampling. Piezometers were made from 5-cm (2 inch) internal-diameter (ID) PVC pipe. Piezometers were screened (a hacksaw slot every 1 cm) over 10-cm intervals. A cap was secured (friction fit) to the bottom of each piezometer. In each piezometer nest, the top of the screened interval was placed at 0, 30, 50, and 100 cm below the hollow surface. Piezometers were pushed or hammered into peat. Piezometers placed in peat need to be deeply anchored to prevent toppling in unconsolidated, saturated peat and frost heaving during winter. For those reasons, each piezometer had about 1 m of pipe below the peat surface, such that the 0 cm depth piezometers, for example, had about 0.9 m of pipe beneath the screen that served as a reservoir to hold water. Piezometers were aligned along the boardwalk, with no more than 10 to 15 cm between any adjacent pair of piezometers within a nest.
Piezometers were developed by scrubbing with a bottle brush, then pumped of all water over successive days until no particles were observed in the evacuated water. In subsequent years, if particular piezometers yielded peat particles when pumped, that piezometer would have been similarly re-developed.
A piece of 0.6-cm (1/4 inch) ID PVC tubing, reaching to the bottom, was placed inside each piezometer. That 0.6-cm PVC remained inside a particular sampler and was attached via a flexible silicone hose to a portable, manual bellows pump (various Guzzler 400 series pumps, The Bosworth Co., East Providence, Rhode Island) for purging or a peristaltic pump (Cole Parmer, Vernon Hills, Illinois, Masterflex PSF/CRS easy-load pump head mounted to a Dewalt, Townson, Maryland portable drill) for sample collection.
Piezometers were capped when not being sampled and vented with an approx 1 mm (1/8 inch) hole, immediately below the cap.
WATER SAMPLING:
All water in a piezometer was evacuated immediately before to a day prior to sampling. Samplers usually refilled within minutes. 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. Unfiltered pore water was pumped directly in to a 250-ml LDPE bottle.
An aliquot of every sample was collected in a 16-mL glass 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, 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. Porewaters were labelled by piezometer nest (S3-1, S2-2, or S3-3) and the corresponding depth as a three character integer for a depth in cm (i.e., 000, 030, 050, 100, and 185 or 200). For example, the sample from the 0 cm depth at S3-1 was labeled S3-1-000.
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), or stored at room temp (isotope vials) until analyzed.
ANALYTICAL METHODS:
Water samples were analyzed for pH, specific conductivity, and concentrations of cations, silicon, anions, nutrients, and total organic carbon at the Forestry Science Laboratory in Grand Rapids, Minnesota.
Unfiltered water was used for all laboratory analyses. It is important to keep in mind that porewater and surface waters in peatlands are free of inorganic particulates due to flowpaths through peat and slow transit times due to low hydraulic gradients that allow for deposition of particulates. For that reason, we have considered our unfiltered water samples of peatland porewaters to be dissolved. The samples are likely to include colloids, but no inorganic particulates and rarely peat particles.
For each type of laboratory measurement, every tenth sample was analyzed 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% 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.
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 a Thermo Scientific Dionex ICS-2100. Samples were injected through 20 micrometer filter caps and through an IonPac AG22 pre-column and AS22 column. 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. 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). Through 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). Concentrations were measured according to the Lachat QuikChem 10-107-04-1-P method on a Lachat QuickChem 8000 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 8500. 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.
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 (Columbia, Maryland) TOC-VCP using the non-purgeable organic carbon (NPOC) method. Potassium hydrogen phthalate (KHP) was used for reference and check standards. Samples typically were analyzed within days of collection. Although rare, samples sometimes were held for weeks to several months while awaiting maintenance on the analyzer.
Liquid water isotopes: The glass scintillation vials for water isotope measurement are stored in a sample archive and are available for eventual analysis on a Los Gatos Research (Mountain View, California) T-LWIA-45-EP liquid water isotope analyzer at the Grand Rapids chemistry laboratory.
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, and solute concentrations), 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.
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,
- 0.05 mg iron/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,
- mg carbon/L for TOC.
Water isotopes values will be added to this data publication in subsequent versions as samples are analyzed.
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.
DATA USED BY:
Griffiths, N. A., Sebestyen, S. D., and Oleheiser, K. C. (2019). Variation in peatland porewater chemistry over time and space along a bog to fen gradient. Science of The Total Environment, 697, 134152. https://doi.org/10.1016/j.scitotenv.2019.134152
REFERENCES:
Nyberg, P. R. (1987), Soil survey of Itasca County, Minnesota, 197 pp, USDA Soil Conservation Service.
Verry, E. S., and Janssens, J. (2011), Geology, vegetation, and hydrology of the S2 bog at the MEF: 12,000 years in northern Minnesota, in Peatland biogeochemistry and watershed hydrology at the Marcell Experimental Forest, edited by Kolka, R. K., et al., pp. 93-134, CRC Press, Boca Raton, FL.
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 Peatland biogeochemistry and watershed hydrology at the Marcell Experimental Forest, edited by Kolka, R. K., et al., pp. 15-71, CRC Press, Boca Raton, FL. https://doi.org/10.1201/b10708-3
