표선수계 토양의 규산 침출 특성

Abstract

This study was carried out to find out the cause of high silicate (SiO2) content which is contained in bottled Jeju volcanic groundwater. The soils used in this experiment were collected from 4 series of volcanic ash soil, 1 series of non-volcanic ash soil in Pyosun watershed and 5 series of forest soil in mainland of Korea. The whole soils collected were analyzed for chemical properties and silicate content by soil depth. The average contents of organic matter were largest as 24.20% in Pyeongdea series, and Pyosun watershed soils were 2∼10 times higher than mainland soils. In addition, the average available phosphorus content was low as 11.31 mg kg-1 for the Pyosun watershed soils, compared to 32.12 mg kg-1 for the mainland soils. In the whole series, soil pH had tendency to increase with soil depth and the average exchangeable cation contents were in the order of Ca ＞ Mg ＞ K ＞ Na. The stronger the characteristics of volcanic ash soil, the lower the total SiO2 content in the soil. The average total SiO2 content in Pyeongdea, Nogsan, and Namweon series of black volcanic ash soil was 33.2%, and Ora and the total SiO2 content of Ido series was 45.2% on average. On the contrary, the total SiO2 content of mainland soils was 64.03% on average which was larger than Pyosun watershed soils. In Pyeongdea, Nogsan and Ora series, the total SiO2 content of lowestsoil was larger than topsoil. The extractable SiO2 content was analyzed using 4 different methods such as water, 1 N sodium acetate buffer (pH 4.0), citric acid 1% and 0.5 N HCl extraction. Extractable SiO2 content was lowest using the water extraction but the result was similar regardless of soil series. In 1 N NaOAc extraction the contents of Pyosun watershed soils were 2∼11 times higher than mainland soils. The contents of Pyosun watershed soils were also higher than mainland soils by 1% citric acid and 0.5N HCl extraction. Nogsan series was largest, 0.5 N HCl extractable SiO2 content as 23,414.4 mg kg-1. By soil depth black volcanic ash soils tended to increase extractable SiO2 content with soil depth except water extraction. The content of soil extractable SiO2 in 4 different extractions was in the order of 0.5 N HCl > 1% citric acid > 1 N NaOAc > water. Pyosun watershed soils had low content of total SiO2, but large content of extractable SiO2. However, mainland soils had large content of total SiO2, but low content of extractable SiO2. The sum of extractable SiO2 content in Pyosun watershed soils was 15,435.0 mg kg-1 on average, which was 7.9 times larger than mainland soils. By soil depth the content of organic matters decreased when extractable SiO2 content increased in black volcanic ash soils. In the volcanic ash soil of Jeju island, most of the active Al complex with humus (organic matter), forming stabilized Al-humus complexes by rapid weathering. Allophane is formed by combination of dissolved Si and uncomplexed Al available in soil solution. The residual Si which is unable to form allophane remains in the volcanic ash soil, moves downward. Therefore, the content of organic matters content and extractable SiO2 content are inversely related by soil depth. In conclusion, the cause of larger silicate content in Jeju volcanic groundwater is to be derived from extractable silicate weakly bound to soil by genesis of volcanic ash soil, not parent material and rock.