花崗岩質 小規模 河川流域의 物質收支特性에 關한 硏究

Abstract

The purpose of this study is to clarify the nutrient flux and nutrient budget under the present climatic conditions. The study area is a small granitic catchment (3.62㎢) on the southeastern slope of Kwanak mountain in Anyang-shi, Kyingki-do. In this study area, stream water, ground water, and rain, fall water were weekly collected and the respective concentrations of twelve ions.( H+, Na+, K+, Ca2+, Mn, Fe, Mg2+, Al, Si, HCO3-, Cl-, and SO42-) were measured during one year (Oct.1990-Oct.1991) The result of the analysis are as follows;

Firstly, the water budget of study period was that 34.8% of the incoming water was evapotranspirated, 65.2% was flowed out as stream water, and the storage by soil water and ground water was 0.001%. The runoff ratios by season were: summer(79.2%)>spring(55.1%)>fall(16.6%)>winter(15.6%)

Secondly, the solutes concentraton of precipitation was greatly different in terms of seasons. Especially the precipitation during the winter and spring includes lots of surface origin materials from atmospheric pollution and yellow sand phenomena. But during the summer and fall, not only the concentration of solutes was much lower than that of winter and spring precipitations, but also the characteristics of solutes were different.

Thirdly, in general, the concentrations of the ions in drainage water were relatively constant although the discharge is varied greatly. The concentrations of pH, Al, Fe, HCO3 -and SO42- were partially correlated with the discharge. HCO3-had the negative correlation, the others had the positive correlations, But the concentrations of Na+,Ca2+,K+,Si and Cl- did not have correlation with the discharge. Such results came from the low-weathering rate of the granite rock, material influx from the atmosphere, and the hydrological characteristics of the research area.

Fourthly, the solutes of stream water are more greatly influenced by influx from atmosphere than by the chemical weathering of granite rock. Considering the dry impaction, the amount of input from the atmosphere accounted for about 61% of the amount of removal from the drainage basis.

Fifthly, in the aspect of nutrien t budget, it was possible to classify the influx-dominant period and efflux-dominant period. During the fall and winter period, the amount of influx from the atmosphere exceeded that of efflux by the streamwater except H+. But during the summer and spring, the amount of efflux was much greater than that of the influx. Especially the amount of efflux during the summer period accounts for net-output, so that the weathering of rock and the removal of nutrient are limited to the summer period under present clamatic condition (temperate monsoon climate).

Sixthly, Oversupplied ions into the drainage basin were H+, K+, Fe and Mn, but Na+, Mg2+, Ca2+, Si, Al, and HCO3- were removed from the basin by the stream. The surplus of K+ reflects that the vegetation is under agradation stage, and the nutrient cycle in the studying forest did not reach to the stable state. And it is presumed that the accumulation of K+ in the top soil is also related to the surplus of K+; Oversupplied Fe and Mn are accumulated in soil by forming iron-oxide and iron-hydroxide.

In opposite, the removal of Na+, Si, Al results from the chemical weathering of albite and biotite, and the amount of removal reflects the weathering rate of bedrock. But Ca2+ and Mg2+ are contaminated by the scatterd calareous structures.