EMS - Canopy-Atmosphere Exchange of Carbon, Water and Energy
HF004 Overview Data EML Archive- Investigators: Carol Barford, William Munger, Shawn Urbanski, Steven Wofsy
- Contact: William Munger
- Start date: 1990-01-01
- End date: ongoing
- Location: Prospect Hill Tract (Harvard Forest)
- Latitude: +42.537755
- Longitude: -72.171478
- Elevation: 340 meters
- Taxa:
- Keywords: carbon budget, CO2, eddy covariance, evapotranspiration, heat flux, humidity, momentum flux, net ecosystem exchange, temperature
- Abstract:
The tower-based CO2 measurements and key meteorological drivers are intended to examine how regional and ecosystem level processes in a mid-latitude forest contribute to global carbon cycling. Specifically, we endeavor to understand quantitatively 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 tower was installed 1989 and the resulting eddy-flux measurements constitute 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 climate anomalies on carbon fluxes for seasonal and annual time scales. For example, reduced soil frost allows greater respiration in the winter leading to lower C sequestration. Cumulative gross photosynthesis depends on when the canopy emerges in the spring. Warmer springtime temperatures lead to greater uptake of C. As the NEE record is extended and augmented by supporting ecological measurements, we can further identify longer-term effects of climate perturbations on carbon fluxes and further define the relationship between stand history and carbon sequestration. Climatic anomalies in one season or year may have a longer-term effect on the sequestration of carbon in subsequent seasons or years.
The flux and ecological measurements are coordinated with studies at other sites through the AmeriFlux network. By examining the relationships between carbon fluxes and the driving physical and biological variables across a range of sites we are enhancing understanding of the processes that control NEE.
- 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.
- Related datasets: HF066 HF069 HF102