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Harvard Forest Data Archive

HF148

Soil Respiration at Harvard Forest HEM and LPH Towers 1996-2007

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Data

Overview

  • Lead: Julian Hadley
  • Investigators:
  • Contact: Emery Boose
  • Start date: 1996
  • End date: 2007
  • Status: completed
  • Location: Prospect Hill Tract (Harvard Forest)
  • Latitude: +42.539 to +42.542
  • Longitude: -72.185 to -72.180
  • Elevation: 355 to 380 meter
  • Taxa:
  • Release date: 2009
  • Revisions:
  • EML file: knb-lter-hfr.148.12
  • DOI: digital object identifier
  • Related links:
  • Study type: long-term measurement
  • Research topic: soil carbon and nitrogen dynamics
  • LTER core area: inorganic nutrients
  • Keywords: decomposition, microbes, roots, soil respiration, soil temperature
  • Abstract:

    Soil respiration, including both CO2 produced during decomposition of organic matter in soil and surface litter, and CO2 produced during respiration of living roots, is a major component of forest-atmosphere carbon exchange, typically comprising 60 to 80% of whole-forest respiration. Soil respiration data can explain a major part of a forest ecosystem’s response to changing climate, and help in evaluating the accuracy of nighttime eddy flux data as estimates of whole-ecosystem respiration measurements. Soil respiration in the footprint areas of the Harvard Forest Hemlock and Little Prospect Hill eddy flux towers has shown generally similar responses to soil temperature and precipitation as soil respiration near the EMS flux tower (see data set HF006), but also some differences. Soil respiration at the Hemlock tower site has been lower than at the other tower sites during very wet summer weather, but higher during dry summer periods. Average estimated annual total soil respiration has been close to the same for all three tower footprint areas, however. There has been some evidence of lower soil respiration in the parts of the Little Prospect Hill tower footprint with lowest soil moisture (those with a high slope position, 100 m from the tower), as compared with other sites during very dry summer periods, but such periods have been very rare during the period of data collection. Soil respiration measured near the Little Prospect Hill tower in summer has also been higher than ecosystem respiration as estimated from nighttime carbon flux measured by an eddy covariance system. This indicates that during some nighttime periods, CO2 is being removed from the volume of air below the eddy flux system by a route other than through the top of the forest canopy near the flux tower, possibly by downslope advection, even under conditions when it initially appeared that atmospheric turbulence was high enough to prevent removal of CO2 by these other mechanisms.

  • Methods:

    Soil respiration was measured with a LI-6200 photosynthesis system (Licor, Inc., Lincoln, NE, USA), with an end-cap for 10-inch (25.4 cm) diameter pipe attached to the LI-6200 system. Chambers were formed by placing the end-cap on top of a 10 cm-long section of the pipe (a “soil collar”) placed on the soil surface. Soil collars were then pulled firmly against the soil surface using wires attached to eyebolts at three points equidistant around the collar circumference. The wires were secured to pairs of 10-inch galvanized steel spikes, each inserted at a 45 degree angle to the horizontal so that the two spikes formed an X that resisted any upward pull. Objects that would create gaps between the collar and the soil surface (e.g., twigs) were removed, but the litter layer was left intact and no cut was made in the litter layer or soil surface. Soil collars were moved each spring to avoid any long-term effect of the collar on the soil beneath or around it. During each soil respiration measurement, soil temperature at 10 cm depth within a few cm of the soil collar perimeter was measured using a hand-held thermocouple thermometer.

    It was noted that during measurements, the rate of increase in CO2 concentration in the LI-6200’s analyzer increased during the first several minutes, and then usually declined, with the rate of decline in the rate of CO2 increase varying substantially. This decline could be caused by at least two factors: (a) A decrease in the gradient in CO2 concentration between the soil pore volume and the interior of the chamber, as CO2 increased in the chamber and (b) leaks in the chamber or the tubing connecting the chamber it to the analyzer. Since the chambers were not inserted into the soil, but only pulled securely against the surface, the potential for such leaks was higher with this method than others in which the rim of the chamber is inserted into the soil. As a result the following procedure was used to correct for any decline in the rate of CO2 increase as measured by the analyzer: After an initial period of 4.5 minutes when no data was collected, the LI-6200 system calculated the soil respiration rate for 12 successive 15-second intervals, each separated by about 5 seconds. A regression of these 12 individual 15-second respiration estimates against the average CO2 concentration during each respiration estimate was used to predict a soil respiration rate at approximately the ambient CO2 concentration about 10 cm above the soil surface. This was measured at every fourth collar sampled, and was typically close to 400 ppm in summer and 380 to 390 ppm in winter.

    Collars were installed near the Harvard Hemlock eddy flux tower in summer 1996 at randomly selected distances between 25 and 50 m on twelve transects at 30 deg increments of compass bearing, originating at a canopy access tower at the site. In 2001, these collars were relocated to locations at randomly chosen points within 5 m of plot centers 50, 100, 150 and 200 m from the tower along transects at 195, 225 and 255 deg compass bearings. This change was made in order to place all of the soil respiration measurements within the region of hemlock forest that was measured by an eddy covariance system installed on the Hemlock tower beginning in October 2000. Soil respiration was not measured near the Hemlock tower in 2002 or 2003 because no eddy flux measurements were made from the Hemlock tower in these years, and effort was focused on Little Prospect Hill.

    Circular plots were established in spring 2002 near the Little Prospect Hill flux tower, at distances of approximately 100, 200, and 300 m along transects with compass bearings of 195 to 330 deg in 15 degree increments, to place them within the dominant SW and NW wind directions. A soil collar was placed at a randomly selected distance in a randomly selected direction, within 5 m of each plot center. In 2003, the range of compass bearings for locating the circular plots and soil collars was changed to 225 to 345 deg. This change was made after analysis of data from the flux tower showed that valid measurements could not be made when wind was blowing at compass bearings of about 90 to 215 deg, apparently because air flow patterns in the lee of Little Prospect Hill when wind is from a generally east to southward direction do not fit the airflow requirements for valid application of the eddy covariance technique, and result in spurious ecosystem respiration estimates (see Hadley et al. 2008).

    For more details see: Hadley, J.L., P.S. Kuzeja, M.J. Daley, N.G. Phillips, S. Singh and T. Mulcahy. 2008. Water use and carbon exchange of eastern hemlock (Tsuga canadensis L.) and deciduous forests in the northeastern U.S.: Implications for ecosystem-level effects of the hemlock woolly adelgid. Tree Physiology 28: 615-627.

  • Use:

    This dataset is released to the public under Creative Commons license CC BY (Attribution). Please keep the designated contact person informed of any plans to use the dataset. Consultation or collaboration with the original investigators is strongly encouraged. Publications and data products that make use of the dataset must include proper acknowledgement.

  • Citation:

    Hadley J. 2009. Soil Respiration at Harvard Forest HEM and LPH Towers 1996-2007. Harvard Forest Data Archive: HF148.

Detailed Metadata

hf148-01: Hemlock soil respiration

  1. year: year
  2. month: month
  3. day: day
  4. date: date
  5. doy: day of year (unit: nominalDay )
  6. time: time
  7. distance: distance from Hemlock tower (unit: meter / missing value: NA)
  8. transect: compass direction from Hemlock tower from geographic north (unit: degree / missing value: NA)
  9. collar: collar number or identifier
  10. collar.height: collar height (unit: meter / missing value: NA)
  11. soilt: soil temperature at 10 cm depth (unit: celsius / missing value: NA)
  12. co2flux: soil CO2 flux (unit: micromolePerMeterSquaredPerSecond / missing value: NA)
  13. notes: notes

hf148-02: Little Prospect Hill soil respiration

  1. datetime: date and time
  2. year: year
  3. month: month
  4. day: day
  5. date: date
  6. doy: day of year (unit: nominalDay )
  7. time: time
  8. distance: distance from LPH tower (unit: meter / missing value: NA)
  9. transect: compass direction from LPH tower from geographic north (unit: degree / missing value: NA)
  10. collar.height: collar height (unit: meter / missing value: NA)
  11. soilt: soil temperature at 10 cm depth (unit: celsius / missing value: NA)
  12. co2flux: soil CO2 flux (unit: micromolePerMeterSquaredPerSecond / missing value: NA)