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Soil Respiration

This file contains measurements of soil respiration, soil temperature, and volumetric water content taken northwest and southwest of the EMS Tower at Harvard Forest, Petersham, MA. In general, each of the six sites is an average of six individual measurements. The data are followed by their standard errors. To the southwest, the far site (+/-225m) is well-drained, the mid (+/-100m) is moderately drained, and the near site (+/-20m) is poorly drained. To the northwest, the far site (+/-500m) is poorly drained, the mid (+/-375m) is moderately drained, and the near site (+/-100m) is well-drained. Mixed hardwoods are the dominant vegetation except for NWF, which is located in a swampy area, and NWM, which is located among hemlocks.

Flux measurements were discontinued at the Farm and Hardwood sites at the end of 1998. Sampling ended at the NWF swamp site in the Fall of 1999 due to beavers flooding the site. In 2001 we reduced our sampling sites to the SWF, SWM and NWN sites. In 2003 we re-added the NWM and NWF sites. In 2004 we added a site located to the north of the EMS tower, called the Charlton, and in 2005 we added the Montauk to the northeast of the EMS tower. These two new sites have 12 collars per site and hence fluxes are the average of 12 for these 2 sites.

Soil CO2 Flux (mg C m-2 h-1) is measured by placing a chamber over collars (that are left in place) in the soil. Air from the chamber headspace is pumped into an Infrared Gas Analyzer (LICOR 6252) at a rate of 0.5L/min for a 5 minute period. The change in headspace CO2 concentration is recorded every 12s for 4.5 minutes using an HP200LX palmtop. A linear regression on the change in headspace concentration over time, along with air temperature, atmospheric pressure and chamber surface area are used to convert these measurements to units of mg C m-2 hr-1.

Soil temperature (degrees Celsius) is taken using a 10cm probe inserted vertically from the surface. Volumetric water content is determined with 15 cm probes inserted vertically in the soil, also from the surface. It is calculated as cc H2O/ cc soil using the Harvard Forest equation. This method was discontinued in 2005. No soil moisture was collected at the Farm, Hardwood, Charlton and Montauk sites.

Wintertime fluxes. During the winter season snow covers our collars. During these periods fluxes are collected by placing the chamber on-top of the snow. This is only done when snow continuously covers the soil and is deep enough to ensure a seal with the chamber.

Variables

  1. Date = date (YYYY-MM-DD)
  2. JD = Julian date
  3. DOY = day of year
  4. Flux = CO2 flux (mg C m-2 h-1)
  5. SE= standard error (mg C m-2 h-1)
  6. SoilT = soil temperature at 10cm depth (deg C)
  7. VSM= volumetric soil moisture over the top 15cm of soil (g H2O/g soil)
  8. Time = time of sampling (HH:MM)
  9. Site = site name
  10. Drainage = drainage class

NA = data not available