Zhu Zhilin

Statistical analysis and comparative study of energy balance components estimated using micrometeorological techniques during HUBEX/IOP 1998/99

In order to study energy and water cycles in the Huaihe River Basin, micrometeorological measurements were carried out in Shouxian County, Anhui Province, during HUBEX/IOP (May to August 1998 and June to July 1999). The employed techniques included Bowen Ratio-Energy Balance (BREB) and Eddy Covariance (EC) methods. In this paper, the basic characteristics of the energy balance components in the district are analyzed. Furthermore, the results are compared with those from other regions of China. The main results are as follows: (1) There was a consistency between the available energy (Rn−G) and the sum of sensible (H) and latent (E) heat fluxes measured by the EC method (H+E)ec, but Ebr was slightly larger (about 10%) than Eec; (2) Most of the net radiation (Rn) was used to evaporate water from the surface. During HUBEX/IOP in 1998 and 1999, the mean daily amounts of Rn were 13.89 MJ m−2d−1 and 11.83 MJ m−2d−1, and the mean Bowen Ratios (β) were 0.14 (over ruderal) and 0.06 (over paddy) respectively; (3) The diurnal variation characteristic of β was larger and unsteady at sunrise and sunset, and smaller and steady during the rest of the daytime. Local advection appeared in the afternoon over paddy areas in 1999; (4) In comparison with the results from other regions of China, the mean β was the lowest (0.06) over paddy areas in the Huaihe River Basin and the highest (0.57) during June–August 1998 in Inner Mongolia grassland. The Bowen Ratio β is mainly related to the soil humidity.

Mechanism and bio‐environmental controls of ecosystem respiration in a cropland in the North China plains

Abstract CO2 flux was measured continuously using the eddy covariance technique in a wheat‐maize rotation system in the North China Plains from October 2002 to October 2006. The annual and seasonal variation of ecosystem respiration and the bio‐environmental controls on them were investigated. The results show that ecosystem respiration (Rec) in the cropland increased exponentially with soil temperature at 5 cm depth. The temperature sensitivity coefficient (Q10) for ecosystem respiration varied from 3.5 to 5.4 for wheat and from 2.4 to 4.5 for maize. In the wheat growing season, monthly average R0 (ecosystem respiration at 0°C) increased linearly with soil temperature and logarithmically with leaf area index (LAI). Monthly average Q10 decreased logarithmically with R 0. Residual R ec was significantly correlated with LAI. After considering LAI, the modified Q10 model could estimate R ec better than before. The simulation results show that annual ecosystem respiration in the wheat‐maize rotation system in the North China Plains was 1327, 1348, 1040 and 1171 gC m‐2 yr‐1 for the 4 years of the study. As a 4‐year average, seasonal mean ecosystem respiration in wheat (2.60 gC m‐2 day‐1) was much lower than in maize (6.09 gC m‐2 day‐1). However, integrated ecosystem respiration for the wheat growing season (566 gC m‐2) was slightly higher than that for maize (520 gC m‐2). These account for 46.4 and 42.6% of the annual values, respectively.