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Harvard Forest Research Project 2022

  • Title: HF EMS flux-tower measurements
  • Principal investigator: J. William Munger (jwmunger@seas.harvard.edu)
  • Institution: Harvard University
  • Primary contact: J. William Munger (jwmunger@seas.harvard.edu)
  • Team members: John Budney; Timothy Whitby
  • Abstract:

    The measurements of carbon dioxide (CO2), water (H2O), temperature and wind, along with key meteorological conditions will help to quantitatively understand how and why forested ecosystems take up or release carbon, on time scales from hours to decades, and to elucidate responses to climate changes and management interventions. The observations of whole-ecosystem metabolism contribute to evaluating carbon, water and energy budgets at stand-level to regional scales. These measurements are part of a larger set of coordinated observations that also help to quantify the role of forests as sources of trace gases and the role of forests in cleansing the atmosphere.
    The tower at the Harvard Forest Environmental Measurements Site (HFEMS) was installed in 1989 and the flux measurements from this tower are the longest running record of the net-ecosystem carbon exchange in a North American Forest. The resulting long-term record of Net Ecosystem Exchange (NEE) has shown the effects of weather anomalies on carbon fluxes for seasonal and annual time scales.
    The forest surrounding the tower is accumulating biomass and contributing to the terrestrial sink for carbon that currently is reducing the growth atmospheric CO2. The atmospheric carbon fluxes provide a top-down look at forest growth and are complemented by ground measurements of vegetation and litter at large and small plots where we can identify which components in the forest are gaining and losing carbon. The combination of short term carbon and water exchange fluxes observed at the tower with long-term changes in biomass and species composition observed at permanent plots provides a very powerful constraint to develop and evaluate ecosystem process models.

    Because of its rural location downwind of major east-coast urban areas, but away from nearby pollution sources the Harvard Forest site is an important observatory for tracking regional air quality. In addition to the carbon flux measurements at HFEMS, we measure ozone and nitrogen oxide to quantify potential air pollutant impacts on the forest and asses the role of the forest in removing these pollutants from the atmosphere. Several measurement campaigns have focused on emissions of volatile hydrocarbons such as isoprene from the vegetation. These compounds are an important precursor for atmospheric chemical reactions.

    # Methods:

    Vertical and horizontal wind speeds and sonic temperature are determined using an ATI Sonic Anemometer mounted at 29m. Wind speed and direction and momentum and sensible heat fluxes are computed from the anemometer data. Fast-response CO2-H2O are determined by closed-path IR-Absorbance analyzer. Vertical fluxes are computed on 30-min intervals. Concentration profiles of CO2 are determined by closed-path IR absorbance analyzer sampling from inlets at 30,24,18,12,6, 3,1,0.05m. Calibrated using a pair of absolute standards that bracket the range of ambient concentration. Air temperatures are measured using 30kW thermistors and relative humidity is measured using thin-film capacitor sensors mounted in aspirated radiation shields at 30,22,12,6,3m. Soil temperatures at the litter-soil interface and 20cm 50cm depth are measured with 30kW thermistors. Photosynthetically active photon flux density is determined by Quantum sensors at 29 and 12m. Net radiation is measured using a net radiation sensor.

    Continuous collection of canopy and sub-canopy camera images started in May 2008. The images provide quantitative measure of canopy status, and in the subcanopy of the snow extent and depth.
    Ongoing trace-gas measurements include Carbon Monoxide, Ozone, and total Nitrogen oxides

    In addition, the EMS site serves as a focal point for other research activities and groups.