Er-Si Kang

Water balance change for a re-vegetated xerophyte shrub area

Abstract Abstract Water balances for a re-vegetated xerophyte shrub (Caragana korshinskii) area were compared to that of a bare surface area by using auto-weighing type lysimeters during the 1990–1995 growing seasons at the southeast Tengger Desert, Shapotou, China. The six-year experiment displayed how major daily water balance components might vary for a bare and a re-vegetated sand dune area. Evapotranspiration from the C. korshinskii lysimeter represented a major part of the water balance. The average annual ET/P ratios varied between 69 and 142%. No seepage was observed for the vegetated lysimeter. For the bare lysimeter, on the other hand, 48 mm or 27% of observed rainfall per year occurred as seepage. These results suggest that re-vegetating large sandy areas with xerophytic shrubs could reduce soil water storage by transpiration. Also, the experimental results indicate that re-vegetating large sandy areas could significantly change groundwater recharge conditions. However, from a viewpoint of desert ecosystem reconstruction, it appears that natural rainfall can sustain xerophytic shrubs such as C. korshinskii which would reduce erosion loss of sand. However, re-vegetation has to be balanced with recharge/groundwater needs of local populations.

Analysis of Water Resources Supply and Demand and Security of Water Resources Development in Irrigation Regions of the Middle Reaches of the Heihe River Basin, Northwest China

Based on the data for meteorology, hydrology, soil, planting, vegetation, and socio-economic development of the irrigation region in the middle reaches of the Heihe River basin, Northwest China, the model of balance of water supply and demand in the region was established, and the security of water resource was assessed, from which the results that the effects of unified management of water resources in the Heihe River basin between Gansu Province and Inner Mongolia on regional hydrology are significant with a decrease in water supply diverted from Heihe River and an increase in groundwater extracted. In addition, it was found that the groundwater level has been steadily decreasing due to over pumping and decrease in recharges. In present year (2003), the volume of potential groundwater in the irrigation districts is far small because of the groundwater overdraft; even in the particular regions, there is no availability of groundwater resources for use. By 2003, water supply is not sufficient to meet the water demand in the different irrigation districts, the sustainable development and utilization of water resources are not secured, and the water supply crisis occurs in Pingchuan irrigation district. Achieving water security for the sustainable development of society, agriculture, economy, industry, and livelihoods while maintaining or improving the abilities of the management and planning of water resources, determining of the reasonable percentage between water supply and groundwater utilization and water saving in agricultural irrigation are taken into account. If this does not occur, it is feared that the present performance of water development and planning may further aggravate the problem of scarcities of water resources and further damage the fragile ecological system.

Analysing the forcing mechanisms for net primary productivity changes in the Heihe River Basin, north-west China

Most of the inland river basins in north‐west China have experienced ecosystem degradation and even desertification in the last few decades. As a case study, we estimated the net primary productivity (NPP) of the Heihe river basin and analysed its difference between 2002 and 1998 by using the C‐Fix, a Monteith type parametric NPP model. The data used include the normalized difference vegetation index (NDVI) derived from the 1‐km SPOT/VEGETATION sensor and other environmental records. By obtaining the spatiotemporal patterns of NPP change as well as land use changes from higher resolution imagery in the basin, we identified its forcing factors in terms of climate change and human activities. We suggest that a decline in rainfall over the five years was one reason for NPP decrease in the basin. Other factors, such as irrational reclamation upstream and intensive development of irrigated farmland in the midstream play more important roles. They reinforce water competition between artificial and natural ecosystems over the whole basin. It is also found that human activities can produce very different NPP changes in a short time in mountainous regions. The NPP decreased in the east Qilian Mountains due to farmland reclamation and overgrazing but increased in the west, according to the ecosystem preserve project.

Evapotranspiration of Artemisia ordosica vegetation in stabilized arid desert dune in Shapotou, China

More than 40 years of revegetation using mainly Artemisia ordosica, Hedysarum scoparium, and Caragana korshinskii at Shapotou Desert Experimental Research Station near Lanzhou has established a dwarf-shrub and herbaceous cover on the stabilized sand dunes. The evapotranspiration (ET) of the xerophyte dwarf-shrub A. ordosica plant vegetation was measured by the autoweighing lysimeter method during the growing seasons from 1990 to 1995, and 2002 on the southeast edge of the Tengger Desert at Shapotou, China. The study showed that the average ET rates were 0.88 mm d−1, and they varied from 0.6 mm d−1 to 1.31 mm d−1 during the 7-year experimental period from 1990 to 1995, and 2002. The ratios of ET/Precipitation (P) varied from 69.8% to 120.9% with an average of 90.9%. The higher ET/P value in 1991 was associated with the properties of intra year distribution of rainfall events, and resulted in soil moisture depletion. The correlation between the accumulative P and the accumulative ET was quite high. For the years 1990, 1993, and 1995, the relationship between the accumulative ET and the accumulative P had a closed linear relationship, resulting from the higher intensity of monthly P exceeding 40% of the overall P during the growing season. Whatever the variation in the monthly P, statistics showed that the relationship between the accumulative P and ET could be expressed as an equation, ET = 0.8003 P+5.8914, with a correlation coefficient of R 2 = 0.9035. Results suggest that in areas similar to Shapotou it is practical to establish an artificial protection belt using xerophytic shrubs.

Carbon Dioxide Exchange in an Irrigated Agricultural Field within an Oasis, Northwest China

AbstractContinuous eddy covariance measurements of CO2, water vapor, and heat fluxes were obtained from a maize field within an oasis in northwest China from 1 May 2008 to 30 April 2009. The experimental setup used was shown to provide reliable flux estimates on the basis of cross-checks made using various quality tests of the flux data. Results show that the highest half-hourly CO2 fluxes (Fc) were −55.7 and 6.9 μmol m−2 s−1 during the growing and nongrowing seasons, respectively. The daily net ecosystem exchange of carbon (NEE) ranged from −14.7 to 2.2 g C m−2 day−1 during the growing season; however, the daily NEE fell to between 0.2 and 2.1 g C m−2 day−1 during the nongrowing season. The annual NEE calculated by integrating flux measurements and filling in missing and spurious data was about −487.9 g C m−2. The total NEE during the growing season (−692.9 g C m−2) and the annual NEE were in the middle of the range, when compared with results obtained for maize fields in different studies and regions, w...