Three-year variations of water, energy and CO2 fluxes of cropland and degraded grassland surfaces in a semi-arid area of Northeastern China

Abstract

Based on 3 years of the eddy covariance (EC) observations on degraded grassland and cropland surfaces in a semi-arid area of Tongyu (44 • 25 N, 122• 52 E, 184 m a.s.l.), Northeast China, seasonal and annual variations of water, energy and CO2 fluxes have been investigated. The soil moisture in the thin soil layer (at 0.05, 0.10 and 0.20 m) clearly indicates the pronounced annual wet-dry cycle; the annual cycle is divided into the wet (growing season) and dry seasons (non-growing season). During the growing season (from May to September), the sensible and latent heat fluxes showed a linear dependence on the global solar radiation. However, in the non-growing season, the latent heat flux was always less than 50 W m −2 , while the available energy was dissipated as sensible, rather than latent heat flux. During the growing season in 2003-05, the daily average sensible and latent heat fluxes were larger on the cropland surface than on the degraded grassland surface. The cropland ecosystem absorbed more CO2 than the degraded grassland ecosystem in the growing season in 2003-05. The total evapotranspiration on the cropland was more than the total precipitation, while the total evapotranspiration on the degraded grassland was almost the same as the total annual precipitation in the growing season. The soil moisture had a good correlation with the rainfall in the growing season. Precipitation in the growing season is an important factor on the water and carbon budget in the semi-arid area.Key words: water, energy and flux, semi-arid area, eddy covariance, seasonal and annual variation Citation: Liu, H. Z., G. Tu, C. B. Fu, and L. Q. Shi, 2008: Three-year variations of water, energy and fluxes of cropland and degraded grassland surfaces in a semi-arid area of northeastern China.

Estimation of Surface Heat Fluxes Over the Central Tibetan Plateau using the Maximum Entropy Production Model

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Net ecosystem productivity of temperate grasslands in northern China: An upscaling study

“…For the eddy covariance sites from the COSAS in the arid and semi-arid areas of China, a linear interpolation method was applied to fill small gaps (less than two hours) of missing or bad data and larger gaps were filled with values derived from mean diurnal ensemble values (Wang et al, 2010). More details on data treatments can be found in Liu et al (2008) and Wang et al (2010). The other six sites (ID 7-12 in Table 1) include steppe and meadow sites and their vegetation greenness varied among sites.…”

Energy balance and partitioning over a rotating rapeseed crop

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