Jiang Yong-jun

Groundwater quality and land use change in a typical karst agricultural region： a case study of Xiaojiang watershed, Yunnan

Taking the typical karst agricultural region, Xiaojiang watershed in Luxi of Yunnan Province as a research unit, utilizing the groundwater quality data in 1982 and 2004, the aerial photos in 1982 and TM images in 2004, supported by the GIS, we probe into the law and the reason of its space-time change of the groundwater quality over the past 22 years in the paper. The results show: (1) There were obvious temporal and spatial changes of groundwater quality during the past 22 years. (2) Concentrations of NH4+, SO42−, NO3−, NO2−, Cl− and the pH value, total hardness, total alkalinity increased significantly, in which NH4+, NO3−, and NO2− of groundwater exceeded the drinking water standards as a result of non-point pollution caused by the expansion of cultivated land and mass use of the fertilizer and pesticide. (3) Oppositely, Ca2+ and HCO3− showed an obvious decline trend due to forest reduction and degradation and stony desertification. Meantime, there was a dynamic relation between the groundwater quality change and the land use change.

The impact of land use on soil properties in a karst agricultural region of Southwest China: a case study of Xiaojiang watershed, Yunnan

Supported by RS and GIS, the land use change from 1982 to 2003 were analyzed and the impacts of land use changes on pH value, organic matter, total N, total P, total K, available N, available P, and available K in soil of Xiaojiang watershed, a typical karst agricultural region of Yunnan Province, Southwest China were assessed. The following aspects are concluded. (1) The total land use converted during the past 20 years in Xiaojiang watershed covers an area of 610.12 km2, of which 134.29 km2 of forestland was converted into cultivated land, and 210 km2 of unused land was converted into cultivated land. (2) The rapid growth of population and the economic development were the main driving forces of land use change. (3) With the change in land use, the soil properties have been changed significantly. The pH, organic matter, total N, total P, total K, available N, available P and available K in soil in 1982 were 6.3, 38.02 g kg−1, 1.86 g kg−1, 1.63 g kg−1, 10.94 g kg−1, 114.42 g kg−1, 11.65 mg kg−1 and 64.69 mg kg−1g, respectively; and those in 2003 were 6.73, 25.26 g kg−1, 1.41 g kg−1, 0.99 g kg−1, 12.6 g kg−1, 113.43 mg kg−1, 11.11 mg kg−1 and 151.59 mg kg−1, respectively. Pared samples t-test of the tested indices of soil properties indicate that those indices have changed significantly during the last 20 years. But the soil properties changed differently, due to the differences in land use change. (4) Also, with the change in land use and management measures of soil, the modifications in soil properties which developed from carbonate rocks were more sensitive than those in the soil developed from sandstone.