Variation Of Electric Conductivity And Concentration Of Nitrate At The Exit Of Maocun Subteranean Stream, Guilin

Karst water resources is very rich in southwest of China karst region. Subteranean is the major location for karst water'movement and deposition. It plays an important role in the living and development of local people.With the influence of human's activities(land use,the use of fertilizer,waste, exploitation of minerals et.al),The water quality of subteranean streams tends to get worsen than twenty years ago. Nitrate comtamination is the most popular pollutant in the world. Nitrogen fertilization have been popular in agriculture,with low rate of ultilization , over 30 percent of them were lossed. Agricultural fertilization has become the most important pollution sources in the comtamination of groundwater.It's well known that the karst region is a brittleness environment as the margin of desert. In karst region,the groundwater and surface water associate with each other closely. The nitrate comtamination of subteranean stream become more invisible, more complex ,lasting more time,and more difficult to deal with. The effection facts of nitrate comtamination become more complex. It is difficult to recover from the comtamination of nitrate. To inverstigate the water quality changing trend since 1980 and the reason of changing,it is needed to combine the inverstigation,the valuation and the harnesing of subteranean stream with the planning ,the arrange and the exploitation of land use.The karst water resource worth people pay more attention to its right use,preventing from being influenced by human activities. Hower ,less research about the influence of agricultural land use on karst water quality has been taken. Especialy lack of system research of the variation of nitrate. This research take Maocun subteranean stream watershed as research object. This paper has do some research on the variaton of the concentration of nitrate and electric conductivity.The study area is about 10.5 km².The maocun subteranean stream is about 5.1km . he study area's catchment area located at depression. The button of depression is agricultural landand its total area is about 0.45km². Karst water charactered with its dynamic variation (water quality and water quantity). Methods of automatic hydrochemical logging and in-situ titrating were used to study the hydrochemical characteristics of Maocun subteranean stream, Guangxi,SW of China. Storm pulse effect have been observed. Some parameters like rainfall, water level, electric conductivity, temperature and pH et.al were monitored. Through about two years of inverstigation, some conclusions can be obtained: 1.The water quality of Maocun subteranean stream has seasonal dynamical variation.Most of the time,the water quality is good,but in some season,with the influence of agricultural activities,the water quality can become worse.2.Based on the analysis of samples taken from 2003 to 2005, it is obviously that the concentration of K⁺,Na⁺,SO₄^2-,NO₃^-,Cl^- has the trend of increase. Comparison the water analysis result between 1980 and present, we found that twenty years'agricultural activities has important effect on the water quality of subteranean stream.The concentration of K⁺,Na⁺,SO₄^2-,Cl^- and NO₃^- increased obviously.3.Through the inverstigation of storm effect ,we found that at the state of discharge begin to increase ,the concentration of SO₄^2-,NO₃^-,Cl^- higher than before.Then the concentration increased with the increasing discharge.When the discharge get to the largest,the concentration of SO₄^2-,NO₃^-,Cl^- began to depress.4.With the ultilization of autoreadable monitoring instrument,we can obtain the hydrogeochemical variation of subteranean during the storm pulse. The variation of hydrogeochemical variations were controled at least by two key processes. One is the dilution of rain,the other is the interaction between water-rock-CO2。5.The yearly total discharge of the subteranean from Feb,2004 to Jan,2005 is about 7.9*10⁶m³/a. The yearly total loss of nitrate is about 4.8*10⁴kg/a. The loss of nitrate vary obviously with the seasonal agricultural activities and precipitation. The amount of yearly total losses of Ca²⁺,HCO₃^-,SO₄^2-,Cl^- are about 4.6*105kg/a, 1.56*106kg/a, 3.08*104kg/a, 3.2*10⁴kg/a respectively.The loss of NO₃^-, Ca²⁺, HCO₃^-, SO₄^2- and Cl^- were centralized from May to July.6.In order to prevent the pollution from excessive use of nitrogen fertilizer and the large amount of losses of fertilizer, measures should be taken to control the sources of pollution. Agricultral science knowledge should be applied to the Manuring of fertilizer so as to improve crop's absorbance in fertilizer.