Geochemical data supporting investigation of solute and particle cycling and fluxes from two tidal wetlands on the south shore of Cape Cod, Massachusetts, 2012-19 (ver. 2.0, October 2022)

Surface water sampling at Sage Lot Pond:
Surface water samples were collected from the mouth of a tidal creek (2012-2016) and marsh platform ponds (2016) at Sage Lot Pond for analysis of a suite of dissolved constituents and field water quality parameters. Much of the creek mouth sampling occurred over full-tidal cycle timeseries events at different points in the spring/neap cycle and season. The water intake manifold, which was deployed into the creek prior the start of each timeseries, consisted of a ~30 cm length of 13 cm diameter slotted polyvinylchloride pipe sheathed in a plastic mesh filter (~2mm mesh size) secured to a weighted crate. The inlet rested ~30 cm above creek bottom and was connected to a 12 volt 3 gallon per minute diaphragm pump with a length of polyvinylchloride tubing. During tidal timeseries, sample water was pumped to a nearby sampling station through 1 cm inner diameter rigid plastic Cole Parmer Bev-A-Line tubing. The sampling station was located adjacent to the creek mouth (2012 through 6/13/2013) or landward near the marsh/upland edge (7/10/2013 through 2016). The transit time of water to the sampling station, calculated based on measured volumetric flow rate, tubing length and inner diameter, was ~3 min for 2013-2016 and negligible for 2012. Discrete bottle samples were collected every 0.5 to 2 hours at the sampling site during the timeseries. The specifics of sample collection, preservation and analysis of the individual analytes are described below in separate process steps. In 2014-2016, field water quality parameters (temperature, specific conductance, salinity, pH and oxidation/reduction potential) were measured with a calibrated YSI ProPlus multiparameter sonde in a flow through cell. Details of instrument specifications including precision of individual parameters can be found at: https://www.ysi.com/proplus. The date and times (Coordinated Universal Time, UTC) corresponding to sampling mid-point for each set of samples and water quality parameters are reported in SurfaceWater_GeochemicalData_SageLotPond.csv. Sampling duration at each time point was, on average, ~15 minutes.
Additional discrete surface water sample sets and field water quality parameters were collected or measured outside of the full-tidal timeseries events in the tidal creek (2014-2016) and in marsh platform ponds (2016). In these cases, samples were collected with a weighted tygon tube (deployed at a height of ~30 cm above creek or pond bottom) and peristaltic pump and subsampled into individual vials. A short length of Cole-Parmer C-Flex silicone pump tubing was used with the peristaltic pump. The specifics of sample collection, preservation and analysis of the individual analytes are described below in separate process steps. Field water quality parameters (temperature, specific conductance, salinity, pH and oxidation/reduction potential) were measured with a calibrated YSI ProPlus multiparameter sonde in a flow through cell. Subsampling occurred adjacent to the creek mouth and ponds, therefore water transit time was negligible. The date and time (Coordinated Universal Time, UTC) corresponding to sampling mid-point for each set of samples and water quality parameters is reported in SurfaceWater_GeochemicalData_SageLotPond.csv. Sampling duration was, on average, ~10 -15 minutes. Five samples collected from marsh platform ponds in 2016 are identified as such with an additional descriptor appended to the sample ID, e.g. 'SLP2016-59-Pond'.
Much of the tidal creek data reported was concurrent with additional field water quality parameters, volumetric water discharge, and carbonate chemistry data published in Mann and others (2019), and Wang and others (2019, 2020).
This process took place over a range of time from 2012 to 2016. The process date below represents the most recent date.
The contact person is listed below for this process step and is the same for all subsequent process steps.
References cited:
Mann, A.G., O'Keefe Suttles, J.A., Gonneea, M.E., Brosnahan, S.M., Brooks, T.W., Wang, Z.A., Ganju, N.K., and Kroeger, K.D., 2019, Time-series of biogeochemical and flow data from a tidal salt-marsh creek, Sage Lot Pond, Waquoit Bay, Massachusetts (2012-2016): U.S. Geological Survey data release, https://doi.org/10.5066/P9STIROQ.
Wang, Z., Kroeger, K., Gonneea, M., 2019, Discrete bottle sample measurements for carbonate chemistry from samples collected in the Sage Lot Pond salt marsh tidal creek in Waquoit Bay, MA from 2012 to 2015: Biological and Chemical Oceanography Data Management Office (BCO-DMO). (Version 1) Version Date 2019-05-23, https://doi.org/10.1575/1912/bco-dmo.768577.1.
Wang, Z., Song, S., Gonneea, M., Kroeger, K., 2020, Discrete bottle sample measurements for carbonate chemistry, organic alkalinity and organic carbon from samples collected in Waquoit Bay and Vineyard Sound, MA in 2016: Biological and Chemical Oceanography Data Management Office (BCO-DMO). (Version 1) Version Date 2020-02-25, https://doi.org/10.1575/1912/bco-dmo.794163.1.

Porewater sampling:
Porewater samples were collected at multiple depths (9-245 centimeters below sediment surface) in profiles along transects extending across the marsh platform at Sage Lot Pond (2014-2019) and Great Pond (2014). Horizontal distance between the marsh/ upland edge depth profile and each subsequent profile along the transect was measured with a meter tape to an accuracy of ~2 meters. Additionally, location was measured with a handheld Garmin GPSMAP 76Cx using the WGS84 datum to an accuracy of 3 meters or less. In many cases porewater sample collections at Sage Lot Pond were concurrent with full-tidal timeseries surface water sampling at the creek mouth. Note that datapoints with Sample_ID including GW correspond to samples collected landward of the marsh/upland edge in a forested upland location.
Samples were collected with 0.6 cm inner diameter, 4 cm long screened interval stainless steel push-point sampling devices (https://www.mheproducts.com/). Samples were either collected into acid-cleaned 60 mL syringes through tygon tubing or with a peristaltic pump through a short length of Cole-Parmer C-Flex silicone pump tubing. Sampling depth is reported as the depth of the midpoint of the well screen below the sediment surface. Depth relative to the North American Vertical Datum of 1988 (NAVD 88) was calculated as the elevation of NAVD 88 at the surface minus the depth of the well screen below the surface. For samples collected during 2014-2016, field water quality parameters (temperature, specific conductance, salinity, dissolved oxygen, pH, oxidation/reduction potential) were measured with a calibrated YSI ProPlus multiparameter sonde in a flow-through cell. Details of instrument specifications including precision of individual parameters can be found at: https://www.ysi.com/proplus. For samples collected during 2018-2019, Salinity and pH were measured with a handheld refractometer and a calibrated Cole-Parmer P200 pH meter. Porewater was then subsampled into individual vials in the field for geochemical analysis of a suite of dissolved constituents. The specifics of sample collection, preservation and analysis of the individual analytes are described below in subsequent process steps.
This process took place over a range of time from 2014 to 2019. The process date below represents the most recent date.

Suspended particulate matter in surface water:
Surface water samples for analysis of suspended particulate matter were collected with a Van Dorn grab sampler or a peristaltic pump from the tidal creek (2012-2016) and marsh platform ponds (2016) at the Sage Lot Pond field site. Samples were collected ~30 cm above creek or pond bottom and transferred into 500 mL polyethylene bottles and stored at ~4 degrees Celsius until analysis. Samples were analyzed at the USGS in Woods Hole, MA for suspended sediment concentration (SSC) within 7 days of collection following the method described in APHA (2005). Samples were filtered through glass fiber filters, either 1.2 micron pore size (2012-2014), or 0.7 micron pore size (2015-2016). Average coefficient of variation in SSC among 10 pairs of field duplicate samples from the tidal creek, representing analytical precision plus environmental variability, was 9 percent. Additionally, three pairs of field duplicate samples were collected with the Van Dorn sampler and the peristaltic pump and analyzed for difference in means with a paired t-test. No significant difference in SSC was detected for the different sampling methods (NS, df=2).
A subset of the samples collected in 2012, 2013, and 2016 were HCl-treated in a fuming acid desiccator for ~5 hours to remove inorganic carbon and analyzed at the Marine Biological Laboratory (MBL) Stable Isotope Laboratory in Woods Hole, MA using a Europa 20-20 continuous-flow isotope ratio mass spectrometer interfaced with a Europa ANCA-SL elemental analyzer for total organic Carbon (C), total Nitrogen (N), d13C, and d15N. Isotopic C and N results are expressed relative to Vienna Peedee Belemnite (VPDB), and air, respectively. The analytical precision based on replicate analyses of isotopically homogeneous international standards is ~0.1 per mil for d13C, and d15N. Coefficient of variation is ~2 percent for total C and N. Particulate organic carbon (POC) and total particulate nitrogen (TPN) concentrations were calculated by dividing lab-reported total C and N by the water sample volume. No formal tests were conducted on the influence of filter pore size on SSC or particulate C or N. Five samples collected from marsh platform ponds in 2016 are identified as such with an additional descriptor appended to the sample ID, e.g. 'SLP2016-59-Pond'.
This process took place over a range of time from 2012 to 2016. The process date below represents the most recent date.
Reference cited:
APHA, 2005, Standard methods for the examination of water and waste water, 21st edn., American Public Health Association, Washington, DC, https://doi.org/10.2105/SMWW.2882.001.

Concentrations and stable isotopic ratios of dissolved organic carbon in porewater and surface water:
Samples for dissolved organic carbon (DOC) concentration, and delta 13C of DOC (d13C-DOC) were filtered through sample-rinsed 0.45 micron pore size polyethersulfone filters (2012-2014) or a PALL AcroPak 200 Capsule Filter (sterile 0.8/0.2 micron Supor hydrophilic polyethersulfone membrane; part number 12941) (2015-2016) into combusted borosilicate glass vials with acid-cleaned teflon-lined septa caps. Vials were pretreated with 20 percent hydrochloric acid (12 microliters per milliliter of sample) to decrease the pH of the sample to 2 or less, and samples were stored at 4 degrees Celsius until analysis. Samples were analyzed for DOC on an O.I. Analytical Aurora 1030C auto-analyzer by high temperature catalytic oxidation and nondispersive infrared detection (HTCO-NDIR). Concentrations are reported relative to potassium hydrogen phthalate (KHP) calibration standard.
A subset of the surface water and porewater samples were analyzed for d13C-DOC using a Thermo-Finnigan DELTAplus XL Isotope Ratio Mass Spectrometer interfaced to the Aurora 1030C following the method of Lalonde and others (2014). Stable carbon isotope ratios are reported in standard delta (d) notation relative to Vienna Pee Dee Belemnite (VPDB). Quality assurance included replicate analysis of natural reference materials, field samples and calibration standards. In a subset of the porewater samples, a solid white or brown precipitate formed in the sample vial during storage, or in many cases immediately after collection. Porewater samples were vigorously shaken in an attempt to re-dissolve the material, and needle depth on the 1030C auto-analyzer was set to an appropriate depth to avoid sampling precipitated solids. Analytical uncertainties in concentration and d13C were determined separately for creek and porewater based on replicate measurement of field samples from a single vial. Coefficient of variation in DOC concentration and d13C were 5 percent or less, and 2 percent or less for both creek and porewater respectively. No formal tests were conducted on the influence of precipitated solids in porewater samples on accuracy of DOC or d13C.
This process took place over a range of time from 2012 to 2019. The process date below represents the most recent date.
Reference cited:
Lalonde, K., Middlestead, P. and Gelinas, Y., 2014, Automation of 13C/12C ratio measurement for freshwater and seawater DOC using high temperature combustion: Limnology and Oceanography: Methods, 12(12), pp.816-829, https://doi.org/10.4319/lom.2014.12.816.

Stable isotopic ratio of dissolved inorganic carbon in porewater and surface water:
Samples for delta 13C of dissolved inorganic carbon (d13C-DIC) were collected from the tidal creek and from porewater profiles, unfiltered, and submitted to the University of California Stable Isotope Facility in Davis, CA (UC Davis SIF) for analysis. Samples were collected in 2012 and 2013 into pre-combusted borosilicate glass vials with teflon-lined butyl rubber septa screw caps. Vials were filled from the bottom, overflowed with >3 void volumes, capped immediately without headspace, and stored at 4 degrees Celsius until analysis. All subsequent samples (2014-2016) were collected into 12 mL glass exetainers with pierceable chlorobutyl septa-lined screw caps (Labco, High Wycombe, UK). Exetainers were prepared in the laboratory by adding 1 mL of 85 percent phosphoric acid; vials were capped, evacuated, then flushed with helium. Using a needle and syringe, unfiltered sample, either 2 or 3 mL for porewater or surface water, respectively, was added to the exetainer.
Samples were analyzed on a GasBench II system interfaced to a Delta V Plus isotope ratio mass spectrometer at the UC Davis SIF (https://stableisotopefacility.ucdavis.edu/dictracegas.html). Stable isotopic ratios are reported in standard delta notation relative to Vienna Pee Dee Belemnite (VPDB). Quality assurance included replicate analysis of natural reference materials and field samples. Reported long-term standard deviation in d13C and Limit of Quantification in DIC as CO2 are 150 nanomoles, and 0.1 per mil.
This process took place over a range of time from 2012 to 2016. The process date below represents the most recent date.

Dissolved methane and nitrous oxide gas in porewater and surface water:
Surface water samples from the tidal creek at Sage Lot Pond were collected during 2012 and 2013 for analysis of dissolved methane (CH4) and nitrous oxide (N2O) gas. Samples were collected, unfiltered, into 60 mL syringes fitted with a two-way stopcock free of headspace. After collection, 30 milliliters of high-purity Zero Air was drawn into the syringe, and the sample was manually shaken for 2 min to equilibrate dissolved gas concentrations in the liquid sample with that of the introduced headspace. Once the sample was equilibrated, the liquid sample was expelled from the syringe and the headspace gas was stored at 4 degrees Celsius until analysis, which was within 4 days of collection.
Porewater samples were collected in 2014 and 2015 into pre-evacuated 30 mL borosilicate glass serum bottles with butyl rubber stoppers and crimp caps for CH4 analysis. Bottles were pretreated with 100 microliters 8 Molar (M) KOH solution (7 microliters per milliliter of sample) prior to evacuation to increase the pH of the sample to 12 or greater (Magen and others, 2014). Using a needle and syringe, 15 mL of headspace-free unfiltered sample was added to the bottle through the rubber stopper in the field. Upon return to the lab, a known volume of high purity Zero Air was added to the bottles with a syringe and needle through the stopper to bring the bottles to atmospheric pressure at room temperature (~25 deg. Celsius). Samples were manually equilibrated for 2 min and stored at room temperature until analysis.
Headspace CH4 and N2O concentrations in creek samples were measured on a Shimadzu GC-2014 gas chromatograph equipped with a flame ionization detector (FID) and electron capture detector (ECD). Headspace CH4 concentration in porewater samples was measured on a Shimadzu GC-14B gas chromatograph equipped with an FID. Coefficient of variation based on replicate measurements of a single sample were 2 percent or less for both instruments. Solubility coefficients and dissolved concentrations for CH4 and N2O were calculated based on temperature and salinity at time of equilibration, sample to headspace volume ratio and GC-measured headspace concentrations (Wiesenburg and Guinasso, 1979; Weiss and Price, 1980).
This process took place over a range of time from 2012 to 2015. The process date below represents the most recent date.
References cited:
Magen, C., Lapham, L.L., Pohlman, J.W., Marshall, K., Bosman, S., Casso, M. and Chanton, J.P., 2014, A simple headspace equilibration method for measuring dissolved methane: Limnology and Oceanography: Methods, 12(9), pp.637-650, https://doi.org/10.4319/lom.2014.12.637.
Wiesenburg, D.A. and Guinasso Jr, N.L., 1979, Equilibrium solubilities of methane, carbon monoxide, and hydrogen in water and sea water: Journal of Chemical and Engineering Data, 24(4), pp.356-360.
Weiss, R.F. and Price, B.A., 1980, Nitrous oxide solubility in water and seawater: Marine Chemistry, 8(4), pp.347-359.

Nutrients in porewater and surface water:
Samples for analysis of nutrients nitrate, ammonium, phosphate, and total silica were filtered through a sample-rinsed 0.45 micron pore size polyethersulfone filters (2012-2014) or a PALL AcroPak 200 Capsule Filter (sterile 0.8/0.2 micron Supor hydrophilic polyethersulfone membrane; part number 12941) (2015-2016) into a sample-rinsed, acid-cleaned polyethylene vials. Samples for nitrate, ammonium, and phosphate were kept on ice in the field and then stored frozen until analysis. Samples for total silica were stored at 4 degrees Celsius until analysis.
Nitrate and ammonium were measured on a Unity Scientific SmartChem 200 autoanalyzer (2012-2013), or a Lachat Instruments QuickChem 8000 injection analyzer (2014-2016) using standard colorimetric techniques according to APHA (2005), method 4500-NH3-G, and method 4500-NO3-F. Nitrate (NO3-) and nitrite (NO2-) were not quantified separately and their sum is referred to as nitrate (NO3-) in this report. Phosphate was measured on a Lachat Instruments QuickChem 8000 following method 4500-P-F (APHA, 2005). Detection limit was 0.05 uM, and coefficient of variation was 5 percent or less for nitrate, ammonium, and phosphate.
Silicate was measured on a Lachat autoanalyzer (QuikChem Method 31-114-27-1-A) by the molybdenum blue colorimetric method at the Marine Biological Laboratory. We used sodium hexafluorosilicate (Na2SiF6) as the Si standard (Strickland and Parsons, 1968), and external standards (Hach) were always within 5 percent accuracy.
This process took place over a range of time from 2012 to 2016. The process date below represents the most recent date.
References cited:
APHA, 2005, Standard methods for the examination of water and waste water, 21st edn., American Public Health Association, Washington, DC, https://doi.org/10.2105/SMWW.2882.001.
Strickland, J. D. H., and R. T. Parson, 1972, A practical guide to seawater analysis: Bull. Fish. Res. Board Can 167, p. 95-98.

Total dissolved nitrogen in surface water:
Samples for total dissolved nitrogen (TDN) were filtered through a sample-rinsed 0.45 micron pore size polyethersulfone filter (2012-2014) or a PALL AcroPak 200 Capsule Filter (sterile 0.8/0.2 micron Supor hydrophilic polyethersulfone membrane; part number 12941) (2015-2016) into pre-combusted borosilicate glass vials with acid-cleaned teflon-lined septa caps. Vials were pretreated with 20% hydrochloric acid (12 microliters per milliliter of sample) to decrease the pH of the sample to 2 or less, and samples were stored at 4 degrees Celsius until analysis.
Samples were analyzed on an O.I. Analytical Aurora 1030C autoanalyzer by high temperature catalytic oxidation and chemiluminescence detection. Concentrations are reported relative to nicotinic acid calibration standards. Quality assurance included replicate analysis of natural reference materials, field samples and calibration standards. Coefficient of variation is 5 percent or less.
This process took place over a range of time from 2012 to 2016. The process date below represents the most recent date.

Dissolved inorganic carbon in porewater and surface water:
Samples for analysis of dissolved inorganic carbon (DIC) were collected into unevacuated 6 mL glass serum vials with butyl rubber septa and crimp caps. New vials were triple rinsed with distilled water and pre-combusted at 500 degrees Celsius, pre-used vials were HCl-cleaned and oven-dried. Using a needle and syringe, 3 mL of unfiltered sample water was added to the vial. Samples were stored on ice in the field and stored frozen until analysis.
DIC concentrations were determined with a Model 5015 UIC coulometer and quantified relative to a sea water certified reference material (https://www.ncei.noaa.gov/access/ocean-carbon-data-system/oceans/Dickson_CRM/batches.html). Samples were acidified with 20 percent phosphoric acid and purged with Ultra-high purity nitrogen, and the evolved carbon dioxide gas was delivered to the detector and quantified. Coefficient of variation was 4 percent.
This process took place over a range of time from 2014 to 2019. The process date below represents the most recent date.

Total alkalinity in porewater and surface water:
Samples for total alkalinity were collected into acid-cleaned 60 mL HDPE plastic syringes with a two-way stopcock unfiltered without headspace and stored at 4 degrees Celsius until analysis. Samples were analyzed on a Hiranuma Sangyo Aquacounter COM-300A Automatic Titrator following standard protocols within 7 days of collection. Quality assurance included replicate analysis of natural reference materials and field samples. Results were within the acceptable range of precision and accuracy. Coefficient of variation = 2 percent.
This process took place over a range of time from 2014 to 2016. The process date below represents the most recent date. **Subsequent to the original release of these data, version 2 of the dataset replaced 81 total alkalinity values (attribute TotalAlkalinity_ueqperL) with “removed” to indicate the removal of those values. This is further documented in the 16th process step “Summary of changes for version 2.0”.

Radium (Ra)isotopes in porewater and surface water:
Samples for Ra isotopes were collected in large plastic barrels (60 L) for surface water and cubitainers (2.0 to 23.1 L) for porewater. Surface water samples were then filtered through manganese oxide (MnO2) impregnated acrylic fibers (hereafter referred to as Mn fibers) at a flow rate of 0.2-0.8 L per minute to quantitatively sorb Ra onto the MnO2 (Moore and Reid, 1973). 100ml of bleach was added to porewater samples to oxidize the sulfide, which strips Mn from the Mn fibers. After 20 minutes of reaction, porewater was gravity filtered through Mn fibers at a flow rate of less than 0.5 L per minute.
Mn fibers were brought to the lab and rinsed with Ra-free water to remove salts, which interfere with counting (Sun and Torgersen, 1998), partially dried and placed in a delayed coincidence counter (RaDECC) to measure 223Ra and 224Ra 1-3 days after collection (Moore and Arnold, 1996). Additional counts were done at 11 to 17 days post sampling to improve 223Ra measurements and four weeks to correct for supported 224Ra. Mn fibers were combusted at 820 degrees Celsius for 16 hours, homogenized and capped with epoxy, prior to being placed within a well-type gamma spectrometer to measure 228Ra (via 228Ac at 911 keV) and 226Ra (via 214Pb at 351.9 keV) (Charette and others, 2001). All detectors were standardized using a 226Ra NIST-certified Standard Reference Material (#4967A) and a gravimetrically prepared ThNO3 powder, with thorium daughters (228Ra) in equilibrium, which was dissolved and calibrated via isotope dilution MC-ICP-MS with the 226Ra NIST standard. These solutions were sorbed to Mn fibers and prepared in the same manner as the samples. 223Ra, 224Ra and 228Ra activities were decay corrected to the time of collection. Signal to noise ratio for each sample was calculated for 226Ra and 228Ra in the APTEC software during analysis. Typical detection limit of 226Ra and 228Ra were 0.2 (porewater and groundwater) and 5 (surface water) dpm/100L. Coefficient of variation was 2 and 3 percent for 226Ra and 228Ra, respectively. Analysis of 223 and 224Ra via the RaDECC system results in uncertainties of 10 and 5 percent respectively, at the volumes and activities measured in these samples (Garcia-Solsona and others, 2008.
This process took place over a range of time from 2014 to 2019. The process date below represents the most recent date.
References cited:
Charette, M.A., Buesseler, K.O. and Andrews, J.E., 2001, Utility of radium isotopes for evaluating the input and transport of groundwater-derived nitrogen to a Cape Cod estuary: Limnology and Oceanography, 46(2): p. 465-470.
Garcia-Solsona, E., Garcia-Orellana, J., Masque, P., and Dulaiova, H., 2008, Uncertainties associated with 223Ra and 224Ra measurements in water via a Delayed Coincidence Counter (RaDeCC): Marine Chemistry 109, p. 198–219, https://doi.org/10.1016/j.marchem.2007.11.006.
Moore, W.S. and Reid, D.F., 1973, Extraction of Radium from Natural Waters Using Manganese-Impregnated Acrylic Fibers: Journal of Geophysical Research, 78(36): p. 8880-8886.
Moore, W.S. and Arnold, R., 1996, Measurement of Ra-223 and Ra-224 in coastal waters using a delayed coincidence counter: Journal of Geophysical Research-Oceans, 101(C1): p. 1321-1329.
Sun, Y., and T. Torgersen, 1998, Rapid and precise measurement method for adsorbed 224Ra on sediments: Marine Chemistry, v. 61, p. 163-171.

Trace elements in porewater and surface water:
Samples for trace elements analysis were filtered through a sample-rinsed PALL AcroPak 200 Capsule Filter (sterile 0.8/0.2 micron Supor hydrophilic polyethersulfone membrane; part number 12941) into acid cleaned polyethylene vials, spiked with 8 normal (N) Optima nitric acid to a pH of less than 2, and stored at room temperature until analysis.
Samples were diluted 20-fold with 5% Optima nitric acid and analyzed on a Thermo Fisher iCAP Qc at the Woods Hole Oceanographic Institution (WHOI) in Woods Hole, MA for manganese (Mn), iron (Fe), copper (Cu), strontium (Sr), barium (Ba), and uranium (U). Count rates were normalized to an internal indium (In) standard to account for drift and matrix interference of the solution. Water sample density was calculated based on field salinity and a typical lab temperature of 25 deg. Celsius following the method of Fofonoff and Millard (1983). Molar concentration was calculated as the product of lab-measured molal concentration and density. Quality assurance included replicate analysis of natural reference materials and field samples. Detection limits were determined as 3 times the standard deviation of the analytical blank. LOD = 0.01 uM for Mn, Fe, and Sr; and 0.01 nM 0.01 nM for Cu, Ba, and U. Coefficient of variation = 1, 12, 11, 5, 0.3, and 7 percent for Mn, Fe, Cu, Sr, Ba, and U, respectively.
Germanium (Ge) was measured by Inductively-Coupled Plasma Mass Spectrometry (ICP-MS) at Boston University, Boston, MA using methods adapted from Wada and others, 1979 and Kurtz and others, 2002. To prepare samples for analysis, we combined 5g of porewater or groundwater sample with 1g of 5.43 pmol/g Ge spike and acidified samples using concentrated nitric acid. Spiked and unspiked blanks (deionized water) and standards (laboratory-prepared samples of known Ge concentration) were interspersed throughout the unknown samples so that instrument error could be incorporated mathematically during analysis.
This process took place over a range of time from 2014 to 2016. The process date below represents the most recent date.
References cited:
Fofonoff, N.P., and R.C. Millard, 1983. Algorithms for computation of fundamental properties of seawater. UNESCO Technical Papers is Marine Science. No. 44. pp. 53.
Kurtz, A.C., Derry, L.A. and Chadwick, O.A., 2002. Germanium-silicon fractionation in the weathering environment. Geochimica et Cosmochimica Acta, 66(9), pp.1525-1537.
Wada, K., Takaoka, H., Inoue, N. and Kohra, K., 1979. Growth of Stacking Faults by Bardeen-Herring Mechanism in Czochralski Silicon. Japanese Journal of Applied Physics, 18(8), p.1629.

Autosal Salinity in porewater and surface water:
Samples for salinity analysis were collected unfiltered in 125 mL borosilicate glass bottles and measured with a Guideline Instruments Autosal Salinometer at the WHOI CTD Calibration Laboratory and referenced against NIST standards to a precision of 0.0001 practical salinity units (PSU, dimensionless).
This process took place over a range of time from 2014 to 2016. The process date below represents the most recent date.

Sulfide in porewater:
Sulfide sample vials were prepared in the laboratory prior to sample collection by adding 25 microliters of saturated zinc-acetate solution to a 12-milliliter glass exetainer with pierceable chlorobutyl septa-lined screw cap. The exetainer was evacuated after adding the zinc-acetate preservative. Using a needle and syringe, 8 milliliters of unfiltered sample water was added to the exetainer. Samples were stored at 4 degrees Celsius until analyzed.
Sulfide samples were analyzed spectrophotometrically following the methylene blue method (Cline, 1969; Reese and others, 2011) using a Thermo Scientific GENESYS 20 spectrophotometer (1 cm cell, 670 nanometer wavelength). The detection limit was determined as 2 times the concentration of the reagent blank (Reese et al. 2011) or LOD =1 uM. Quality assurance included replicate analysis of prepared standards and field samples. Average coefficient of variation of replicates for this sample set was less than 1 percent.
This process took place over a range of time from 2015 to 2016. The process date below represents the most recent date.
References cited:
Cline, J.D., 1969, Spectrophotometric determination of hydrogen sulfide in natural waters: Limnology and Oceanography, v. 14, p. 454-458.
Reese, B.K., Finneran, D.W., Mills, H.J., Zhu, M.X., and Morse, J.W., 2011, Examination and refinement of the determination of aqueous hydrogen sulfide by the methylene blue method: Aquatic Geochemistry, v. 17, p. 567-582.

Summary of changes for version 2.0:
81 porewater alkalinity measurements from 2014 were removed from column “TotalAlkalinity_ueqperL” (cells X2: X82 in Porewater_GeochemicalData_SageLotPond_GreatPond.csv) and replaced with “removed”. In 2014, 0.5 milliliters of saturated zinc acetate solution was added to porewater samples for preservation. Upon analysis of the porewater alkalinity data collected in 2014, 2015 and 2016, it was clear that 2014 samples were both outliers compared to 2015 and 2016 and had environmentally inconsistent dissolved inorganic carbon to alkalinity ratios. A test was conducted in 2022 whereby alkalinity was measured on frozen sample aliquots from 2014 (n=10) and it was determined that zinc acetate preservation greatly reduced the porewater alkalinity measured in 2014. Therefore, these values were removed from the dataset. Alkalinity samples collected in 2015 and 2016 were stored in the fridge and analyzed quickly, in alignment with recent recommendations for storage and analysis of alkalinity (Korfmacher and Musselman, 2007; Mos and others, 2021).
The minimum value for alkalinity measurements in porewater was updated in DataDictionary_SageLotPond_GreatPond.csv, and in the entity and attribute section. Metadata details including the edition, title, and other citation details were updated.
References cited:
Korfmacher, J.L., and Musselman, R.C., 2007, Evaluation of Storage and Filtration Protocols for Alpine/Subalpine Lake Water Quality Samples: Environmental Monitoring and Assessment, v. 131(1), p. 107–116, https://doi.org/10.1007/s10661-006-9460-x.
Mos, B., Holloway, C., Kelaher, B.P., Santos, I.R., and Dworjanyn, S.A., 2021, Alkalinity of diverse water samples can be altered by mercury preservation and borosilicate vial storage: Scientific Reports, v. 11(1), p. 1-11, https://doi.org/10.1038/s41598-021-89110-w.