Agriculture Land Use Impact On Ground Water Quality

Agriculture Land Use Impact On Ground Water Quality

Abstract:

Supported by RS and GIS, land use change from 1982 to 2004 was analyzed, and the impact of land use change on groundwater quality of Xiaojiang watershed, a typical karst agricultural region of Yunnan Province, Southwest China was assessed. The results indicate that: (1)The total land use converted during the past 22 years in the 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) There was a dynamic relation between the groundwater quality change and the land use change.The groundwater quality change is related to the non-point pollution of using fertilizer caused by the increasing of cultivated land and construction land, and the decreas of forestland and unused land. As forestland and unused land transformed into cultivated land, the pH value, and the concentration of NH4+,SO42-, NO3-, NO2-, and Cl- in groundwater increased, but the concentration of Ca2+ and HCO3- in groundwater declined.

Key words: Land use change; typical karst watershed; groundwater quality; Xiaojiang watershed; Yunnan Province

Introduction

Karst has been regarded as a fragile environment by environmental scientists. Because of karst system with a low capacity, it is difficult to restore once disturbed (Yuan 1988,1993). Changes in hydrological balances are not unique to karst regions, but karst regions are more sensitive than others (LeGrand 1984). Because there is often little or no soil or cover which means poor filtration, poor pre-purification, rapid infiltration, and that flow is turbulent and conduit dominated, high flow velocities allow transit times that may be too short for microorganisms to die off, particularly in shallow groundwater systems. Because large numbers of interconnected fissures mean that pollution inputs are possible from the surface almost anywhere, karst groundwater's particularly liable to contamination (Prohic 1989). Recent study has shown that land use change may give rise to a significant impact on karst groundwater quality. With forest clearance, the concentration of nitrate and chloride in the groundwater increase significantly (Kastrinos and White 1986; Mark 1998), and the expanding of cultivated land and developing intensive agriculture result in the increasing in the concentration of the nitrate, sulphate, phosphate and pesticides (Libra, et al. 1986,1987; Robert, et al, 1998; Molerio, et al 1998; Ramón et, al. 1998; Pertti et, al. 1999; Alice et, al. 1999; Andrzej 1999; Milde, et, al 1988; Zhang and Yuan 2004). Industrialisation and urbanization result in increasing concentrations of nitrate, sulphate, phosphate, and even causing bacteriological pollution (Howard 1989), organic contaminants (Barbee 1994; Fetter 1993; Barker 1996), and heavy metal contamination (André 1999; Jia and Yuan 2003).

In the present study we analyzed the land use change from 1982 to 2004, and assessed the effects of land use change on groundwater quality of the Xiaojiang watershed, a typical karst agricultural region of Yunnan Province, Southwest China.

The study area

The Xiaojiang watershed of Yunnan Province, Southwest China(Figure1), covers an area of about 1034 ...