EMS - Soil Respiration Along a Hydrological Gradient
HF068 Overview Data EML Archive- Investigators: Patrick Crill, Ruth Varner, Steven Wofsy
- Contact: Ruth Varner
- Start date: 2003-04-01
- End date: ongoing
- Location: Prospect Hill Tract (Harvard Forest)
- Latitude: +42.54
- Longitude: -72.17
- Elevation: 340 meters
- Taxa:
- Keywords: automated measurement, hydrologic drivers, soil respiration, spatio-temporal variation
- Abstract:
Soil respiration is an important component of the terrestrial carbon budget. Spatial variation of organic matter and plant cover induce temperature and moisture gradations that obscure direct response of soil respiration to radiative forcing. Separation of spatial patterns from microclimate and substrate availability is vital to predict the response to global change. We are measuring temporal and spatial patterns of soil CO2 flux across a hydrological gradient from wetland to upland soils.
A system of 8 automated opaque chambers were installed in 2003 along a hydrological gradient on the northeast margin of the "Beaver Swamp" north of the EMS tower (+42.537755,-72.171478). Two additional clear chambers were installed in the wetland in 2006. Each automated chamber closes for a measurement every four hours. The resulting semi-continuous data has been providing a high-temporal density characterization of soil flux during the growing season since 2003. Soil temperature and moisture were recorded in the litter, organic, and mineral soils during 2004 at three locations along the slope.
These structures will provide a database of soil respiration flux, temperature, and soil moisture with both high spatial and temporal resolution, across multiple cover types and ground water levels. The analysis will seek to determine the appropriate spatial scale of soil respiration measurement in eastern hardwood forests.
- Methods:
Chambers 1 through 8 consist of aluminum chambers (43.2 x 43.2 x 15.2 cm) that close over metal frames that extend 2 cm into the soil. The chambers are numbered by distance to upland, with 1 being the top of the slope and 8 closest to the wetland. The chambers are not aligned in a linear transect, but are spread throughout the hill slope. Chambers 9 and 10 are clear lexan chambers measuring net ecosystem exchange and are located in the wetland.
When a chamber is closed, air from the headspace is pumped to an infrared gas analyzer (LiCor 820) and the air is returned to the chamber to minimize pressure effects. The measurement system is controlled by a datalogger (Campbell Scientific CR10X) that opens and closes the chambers according to the measurement cycle. Linear regression of the change in CO2 mixing ratios (d ppmv/min) was converted to a flux rate (umol m-2 s-1). Soil temperature is measured by thermocouples (Omega Engineering Type-T) and soil water content is recorded using TDR probes (Decagon Devices ECH2O) inserted horizontally at the base of each soil horizon.
- Related datasets: HF004 HF006