Fluxes of Molecular Hydrogen (H2) at Harvard Forest EMS Tower 2010-2012

doi:10.6073/pasta/132513a992c9f3e554ae4012175e5b0a Fluxes of Molecular Hydrogen (H2) at Harvard Forest EMS Tower 2010-2012 Laura Meredith https://orcid.org/0000-0003-4244-4366 Steven Wofsy https://orcid.org/0000-0002-3133-2089 Ronald Prinn Roisin Commane https://orcid.org/0000-0003-1373-1550 Researcher William Munger https://orcid.org/0000-0002-1042-8452 Researcher Jim Tang https://orcid.org/0000-0003-2498-9012 Researcher 2023 English

Molecular hydrogen (H2) is an atmospheric trace gas with a large microbe-mediated soil sink, yet cycling of this compound throughout ecosystems is poorly understood. Measurements of the sources and sinks of H2 in various ecosystems are sparse, resulting in large uncertainties in the global H2 budget. Constraining the H2 cycle is critical to understanding its role in atmospheric chemistry and climate. We measured H2 fluxes at high frequency in a temperate mixed deciduous forest for 15 months using a tower-based flux-gradient approach to determine both the soil-atmosphere and the net ecosystem flux of H2. The data presented here along with other data available at Harvard Forest can be used for efforts to model the H2 soil sink.

atmospheric deposition biogeochemistry gas flux hydrogen snow wind direction wind speed LTER controlled vocabulary inorganic nutrients LTER core area Harvard Forest HFR LTER USA HFR default

This dataset is released to the public under Creative Commons CC0 1.0 (No Rights Reserved). Please keep the dataset creators informed of any plans to use the dataset. Consultation with the original investigators is strongly encouraged. Publications and data products that make use of the dataset should include proper acknowledgement.

Creative Commons Zero v1.0 Universal https://spdx.org/licenses/CC0-1.0.html CC0-1.0 https://harvardforest.fas.harvard.edu/exist/apps/datasets/showData.html?id=hf288 Prospect Hill Tract (Harvard Forest). Coordinates based on WGS84 datum. -72.171478 -72.171478 +42.537755 +42.537755 340 340 meter 2010 2012 complete Information Manager Harvard Forest

324 North Main Street Petersham MA 01366 USA

(978) 724-3302 hf-im@lists.fas.harvard.edu Harvard Forest

324 North Main Street Petersham MA 01366 USA

(978) 724-3302 (978) 724-3595 https://harvardforest.fas.harvard.edu

H2, CO2, H2O mole fractions and gradients Between December 2010 and March 2012, mole fractions of H2, CO2, and H2O were measured year-round at high frequency from gas inlets installed at heights above the ground of 24 m and 28 m (EMS tower above the forest canopy) and 0.5 m and 3.5 m (small tower below the canopy and over undisturbed soil 14 m to the west). H2 was measured with a gas chromatograph (Agilent, 6890, Santa Clara, CA) equipped with a pulsed discharge helium ionization detector (Valco, D-3, Houston, TX) and CO2 and H2O with non-dispersive, infrared gas analyzers (LI-COR, 6262, Lincoln, NE). Mole fractions were measured to high precision (0.06-0.11% for H2, 0.025-0.043% for CO2, and 0.04-0.05% for H2O) and were calibrated against H2 and CO2 standards traceable to National Oceanic and Atmospheric Administration (NOAA) Earth System Research Laboratory Global Monitoring Division (ESRL/GMD) primary standard scales. We used well-mixed integrating volumes to smooth out temporal fluctuations in mole fractions occurring at a higher frequency than our ability to measure their vertical gradients. Routine null bias tests were used test that no bias existed (offsets in measured mole fractions) between gas inlets. Here, we report mole fractions measurements of H2, CO2, and H2O at the following tower inlet heights and the resulting vertical mole fraction gradients d[H2]/dz. Mole fractions: H2 (parts per billion; ppb; 1e-9; nmol mol-1). CO2 (parts per million; ppm; 1e-6; umol mol-1). H2O (parts per thousand; ppth; 1e-3; mmol mol-1). Inlet heights: 28 m (above forest canopy, EMS tower). 24 m (above forest canopy, EMS tower). 3.5 m (below forest canopy, small tower 14 m to west of EMS tower, undisturbed soil). 0.5 m (below forest canopy, small tower 14 m to west of EMS tower, undisturbed soil). Mole fraction gradients: dH2dz_26 m (H2_28m – H2_24 m)/(28 m – 24 m) [units: ppb m-1]. dH2dz_10 m (H2_24m – H2_3.5 m)/(24 m – 3.5 m) [units: ppb m-1]. dH2dz_2 m (H2_3.5m – H2_0.5 m)/(3.5 m – 0.5 m) [units: ppb m-1].

H2 gradient fluxes H2 fluxes were determined by the flux-gradient method, which assumes a proportional relationship between trace gas fluxes, F, and their vertical (z) concentration gradients (d[H2]/dz) scaled by the rate of turbulent exchange or eddy diffusivity, k: F = -kd[H2]/dz. Briefly, we used two flux-gradient approaches to infer k by 1) similarity to the flux and gradient of other trace gases (Modified Bowen Ratio) or 2) parameterization of the eddy diffusivity (k parameterization). For the Modified Bowen Ratio (1) we used mole fraction gradients of CO2 or H2O and the following independent flux measurements: eddy covariance CO2 and H2O flux measurements made above the forest canopy at a height of 29 m (HF001) or automated soil chamber CO2 respiration rates from a site approximately 0.6 km south of the EMS tower with similar soils and vegetation (HF284). We parameterized K (2) from the friction velocity and and heat flux from the sonic anemometer. Here, we present H2 fluxes calculated by the following methods and filtered as described below: H2 fluxes: FH2_26 m [units: nmol m-2 s-1] -- Method 1: Modified Bowen Ratio using eddy covariance CO2 flux and CO2 gradient, gap-filled with Modified Bowen Ratio using eddy covariance H2O flux and H2O gradient. Above canopy 26 m gradients used from June-November; whole canopy 10 m gradients used in other months when above canopy H2 gradient was exceedingly small. FH2_2 m [units: nmol m-2 s-1] -- Method 1: Modified Bowen Ratio using CO2 soil respiration flux and 2 m CO2 gradient, gap-filled Method 2: K parameterization using sonic anemometer at 2 m. FH2_2 m represents soil-atmosphere fluxes; little to no sub-canopy vegetation was present in the footprint of below-canopy measurements. FH2_26m represents net ecosystem Negative values of the H2 flux indicates trace gas uptake by the soil, ecosystem, or aboveground components from the atmosphere, while positive fluxes indicate emissions to the atmosphere. In addition to the flux, we also calculate the concentration-independent uptake rate of H2 to account for differences in ambient H2 that can influence first-order uptake rates: H2 deposition velocity, vd = -Fs⁄[H2]; cm s-1 Data were filtered to eliminate the following from calculated fluxes: small gradients in the denominator (less than 0.1 times the standard deviation of the gradient measurement), periods with more than 0.3 mm of rain per 30 min, poorly developed turbulence (friction velocity, u* less than 0.07 m s-1 and u* less than 0.17 m s-1, below and above canopy, respectively), and unrealistic large values of the implied turbulent transfer coefficients, k (|k |≤0.1 m2 s-1 and |k|≤30 m2 s-1, below and above canopy, respectively). We did not filter based on the wind sector because we found no interference from the tower and instrument shed to the east (45 to 180 degrees).

Snow depth and porosity Snow depth (SD) was determined from the number of stripes visible on five painted graduated snow stakes (PVC with alternating vertical red and white stripes of 5 cm height) distributed within the field of vision of the subcanopy webcam mounted on the EMS tower that takes images every 30 minutes during daylight hours (HF158). The snowpack water content (snow water equivalent, SWE) was continuously measured in a nearby forest stand (HF155). Snow porosity (percent air-filled space) was determined from SWE and SD as (1- SD/SWE)x100% and represents an average bulk porosity of the snow profile.

Below canopy sonic anemometer A sonic anemometer was installed on a small tower at a height of 2 m above the ground over undisturbed soil 14 m to the west of the main EMS tower (3D sonic anemometer (CSAT3, Campbell Scientific Inc. (CSI), Logan, Utah). Small tower was in the field of view of the EMS subcanopy PhenoCam (HF158-02). Data were collected from the sonic at less than 1Hz frequency and are averaged into 30-min intervals here.

Harvard Forest Long-Term Ecological Research Harvard Forest

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(978) 724-3302 (978) 724-3595 https://harvardforest.fas.harvard.edu https://ror.org/059cpzx98 pointOfContact The Harvard Forest Long-Term Ecological Research (LTER) program examines ecological dynamics in the New England region resulting from natural disturbances, environmental change, and human impacts. National Science Foundation LTER grants: DEB-8811764, DEB-9411975, DEB-0080592, DEB-0620443, DEB-1237491, DEB-1832210. hf288-01-h2-data.csv H2, CO2, H2O mole fractions and gradients; H2 fluxes hf288-01-h2-data.csv 6352991 eab7e6383dab2064122ae7c02a096f55 1 \r\n column , https://harvardforest.fas.harvard.edu/data/p28/hf288/hf288-01-h2-data.csv gmt matlab serial datenum; days since January 0, 0000; greenwich mean time number 0.0001 real NA missing value est matlab serial datenum; days since January 0, 0000; eastern standard time number 0.0001 real NA missing value year year YYYY 1 year NA missing value doy day of year nominalDay 0.0000001 real NA missing value datetime date and time YYYY-MM-DDThh:mm 1 minute NA missing value h2.28m H2 mole fraction at 28 m (ppb) dimensionless 0.0000001 real NA missing value h2.24m H2 mole fraction at 24 m (ppb) dimensionless 0.0000001 real NA missing value h2.3.5m H2 mole fraction at 3.5 m (ppb) dimensionless 0.0000001 real NA missing value h2.0.5m H2 mole fraction at 0.5 m (ppb) dimensionless 0.0000001 real NA missing value d.h2dz.26m H2 gradient between 28 and 24 m (ppb m-1) dimensionless 0.000000001 real NA missing value d.h2dz.10m H2 gradient between 24 and 3.5 m (ppb m-1) dimensionless 0.000000001 real NA missing value d.h2dz.2m H2 gradient between 3.5 and 0.5 m (ppb m-1) dimensionless 0.000000001 real NA missing value co2.28m CO2 mole fraction at 28 m (ppm) dimensionless 0.0000001 real NA missing value co2.24m CO2 mole fraction at 24 m (ppm) dimensionless 0.0000001 real NA missing value co2.3.5m CO2 mole fraction at 3.5 m (ppm) dimensionless 0.0000001 real NA missing value co2.0.5m CO2 mole fraction at 0.5 m (ppm) dimensionless 0.0000001 real NA missing value dco2dz.26m CO2 gradient between 28 and 24 m (ppm m-1) dimensionless 0.000000001 real NA missing value d.co2dz.10m CO2 gradient between 24 and 3.5 m (ppm m-1) dimensionless 0.000000001 real NA missing value d.co2dz.2m CO2 gradient between 3.5 and 0.5 m (ppm m-1) dimensionless 0.000000001 real NA missing value h2o.28m H2O mole fraction at 28 m (ppth) dimensionless 0.000000001 real NA missing value h2o.24m H2O mole fraction at 24 m (ppth) dimensionless 0.000000001 real NA missing value h2o.3.5m H2O mole fraction at 3.5 m (ppth) dimensionless 0.000000001 real NA missing value h2o.0.5m H2O mole fraction at 0.5 m (ppth) dimensionless 0.000000001 real NA missing value d.h2odz.26m H2O gradient between 28 and 24 m (ppth m-1) dimensionless 0.000000001 real NA missing value d.h2odz.10m H2O gradient between 24 and 3.5 m (ppth m-1) dimensionless 0.000000001 real NA missing value d.h2odz.2m H2O gradient between 3.5 and 0.5 m (ppth m-1) dimensionless 0.000000001 real NA missing value f.h2.26m H2 flux at 26 m; H2 net ecosystem flux nanomolePerMeterSquaredPerSecond 0.000000001 real NA missing value f.h2.2m H2 flux at 2 m; H2 soil-atmosphere flux nanomolePerMeterSquaredPerSecond 0.000000001 real NA missing value vd.h2.2m H2 deposition velocity; concentration-independent soil-atmosphere flux centimeterPerSecond 0.000000001 real NA missing value 22177 hf288-02-snow-data.csv snow depth and bulk porosity hf288-02-snow-data.csv 1441279 0b9c6c95f5896a3a49f532df6d02aa70 1 \r\n column , https://harvardforest.fas.harvard.edu/data/p28/hf288/hf288-02-snow-data.csv gmt matlab serial datenum; days since January 0, 0000; greenwich mean time number 0.0001 real NA missing value est matlab serial datenum; days since January 0, 0000; eastern standard time number 0.0001 real NA missing value year year YYYY 1 year NA missing value doy day of year nominalDay 0.0000001 real NA missing value datetime date and time YYYY-MM-DDThh:mm 1 minute NA missing value snow.depth snow depth centimeter 0.00000001 real NA missing value snow.porosity snow porosity (1-bulk density) dimensionless 0.000000001 real NA missing value 22177 hf288-03-sonic-data.csv below canopy sonic anemometer hf288-03-sonic-data.csv 2164175 f79c61a13f8e0b77bc7db74cbac110c0 1 \r\n column , https://harvardforest.fas.harvard.edu/data/p28/hf288/hf288-03-sonic-data.csv gmt matlab serial datenum; days since January 0, 0000; greenwich mean time number 0.0001 real NA missing value est matlab serial datenum; days since January 0, 0000; eastern standard time number 0.0001 real NA missing value year year YYYY 1 year NA missing value doy day of year nominalDay 0.0000001 real NA missing value datetime date and time YYYY-MM-DDThh:mm 1 minute NA missing value ustar.2m friction velocity at 2 m height metersPerSecond 0.000000001 real NA missing value wspd.2m wind speed at 2 m height metersPerSecond 0.000000001 real NA missing value wdir.2m wind direction at 2m height degree 0.0000001 real NA missing value t.2m sonic temperature at 2m height celsius 0.000000001 real NA missing value 22177