Location

 The eddy tower is sited on a northern meadow managed by the Songnen Grassland Ecology Field Station of the Northeast Normal University (NENU), in Changling, Jilin Province, China (123°300 E, 44°350 N, 171 m a s l) .This site was representative of a temperate meadow steppe.

Climatic

 The area had a temperate, semi-arid continental monsoonal climate, characterized as cold and dry springs and warm and wet summers. The mean annual temperature was 4.9 °C, with the maximum and minimum temperatures 39 °C and -33 °C, respectively. The frost-free period was about 130–165 days, and precipitation varied greatly within and between years. Annual long-term average rainfall was about 400 mm, 80% of which fell between June and August. The annual pan evaporation was as high as 1200–1600 mm, approximately 3–4 times the mean annual precipitation.

Vegetation and soil

 This site was representative of a temperate meadow steppe, Perennial grasses are the community dominants, in which Leymus chinensis (=Aneurolepidium chinensis) and Phragmitis communis indicate local climax communities. The Leymus chinensis production is 80-90% in total grassland biomass, and widely distributed, the vegetation total cover is more than 80%. Leymus chinensis dominant in the community, its density may reached 917/m², population biomass account for more than 95% of the entire aboveground biomass, soil type is alkali-saline soil, pH=9.6,organic matter content is about 2%.

Observation system

 An open-path EC flux measurement tower was deployed in 2007 for a long-term monitoring to evaluate the meteorological factors, and turbulent fluxes of CO₂, water vapor and energy at the study site. A 3-D ultrasonic anemometer (CSAT3, Campbell Scientific Inc. CSI, USA) and a CO₂/H₂O infrared gas analyzer (LI-7500, LI-COR Inc., USA) were mounted 2 m above the ground. Fluxes were calculated as the mean covariance of vertical wind speed fluctuation and the scalar fluctuation of interest. All raw data were sampled at 10 Hz and stored on a CR3000 data logger (CSI). The EC tower was installed in May 2007. Net radiation (Rn) was measured by using a four-component net radiometer (CNR-1, Kipp & Zonen, Netherlands) 2 m above the ground. Photosynthetically active radiation (PAR) and precipitation (P) were measured at a height of 6 m above the ground using a quantum sensor (LI190SB, LI-COR) and a tipping-bucket rain gauge (TE525MM, CSI), respectively. Air temperature and relative humidity (RH) were measured at three levels at the heights of 2, 4 and 6 m (HMP45C, CSI). Soil temperature profiles were measured at depths of 0.05 m, 0.10 m and 0.30 m by thermistors (107-L, CSI). Soil heat flux (HFT) was measured at a depth of 0.05 m using soil heat plates in three separate locations (HFT-3, CSI), and soil water content (SWC) was measured at a depth of 0.10 m by time-domain reflectometry probe (CS616, CSI), which was buried horizontally in the soil. Soil water potential (SWP) were estimated using watermark probes (257-L, CSI) at depths of 0.10 and 0.30 m. All micrometeorological data were recorded and averaged or summed over a 30 minute interval by another CR3000 data logger。

Principal Investigator

Jixun Guo

E-mail: gjixun@nenu.edu.cn