地域学研究第 28 号 2015 図 1. ファーン川流域の概要と水質調査地点 Figure 1. Topography and distribution of check points for water quality in the Fang river basin. 32

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1 m 3 km JVC km 1914 km m 1/5001/

2 地域学研究第 28 号 2015 図 1. ファーン川流域の概要と水質調査地点 Figure 1. Topography and distribution of check points for water quality in the Fang river basin. 32

2.1 : 250,000 Geological mapfederal Institute for Geosciences and Natural Resources, Germany, 1976. Figure 2.

3 2.1 : 250,000 Geological mapfederal Institute for Geosciences and Natural Resources, Germany, Figure 2. Geological map of the Fang river basin. Compiled from Federal Institute for Geosciences and Natural Resources, Germany,

4 m 2000 m McQuistan 2004 Cl, NO 2, Ca, Br, NO 3, SO 4 TOA-DKK IA-200 IA-300HCO 3 Hardness CaMg2009 Hardness of watermg LCamg L 2.5 Mgmg L mm Tanaka et al mm EC ph TOA-DKK WM-22EPEC, ph COD Li, Na, NH 4, K, Mg, CaPO 4, F, 3 1 3a EC 57mS/m 40mS/m 2009 EC Ca 2 Mg 2 EC 34

5 Point # Name Lat. Lon. 1. Table 1. Results of water quality in the Fang river basin Distance km Date Temp. C ph EC COD TH ms/mmg/l mg/l Mae Fang Luang /12/ Huai Pong /12/ Ngaen Ngum /12/ Ai /8/ t1 Sai Khao Huai Sai /8/ Ban Ai Dam /8/ Si Dong Yen /8/ Huai Phai /12/ t2 Tha Nam Mae Thalop /8/ San Sai /12/ t3 Pong Nam Ron Nam Mae Chai /8/ Tha Mai Liam /8/ Point # Li Na NH 4 K Mg 2 Ca 2 PO 4 3 F Cl NO 2 unit: mg/l t t t Br NO 3 SO 4 2 HCO 3 Point # Li Na NH 4 K Mg 2 Ca 2 PO 4 3 F Cl NO 2 unit: meq/l t t t Br NO 3 SO 4 2 HCO 3 EC Ca 2 Mg 2 35 Ca 2 Mg a limestone area

6 Figure 3.Change of water quality along main stream of the Fang river. EC EC 3at1, t2, t3 EC

7 5. 4.Ai Figure 4. Agricultural Dam at Ban Ai (point, main stream of the Fang river. 20 km Ca 2 Mg 2 EC 33 km 40 km 40 km EC Ca 2 Mg 2 3 b 37 3bCa 2 Mg Na Cl Na/Cl 5 3,, 2t1, t2na/cl1 : 1 Na 5Na Cl NaCl Na Na/Cl Na Cl NO 3 6.

8 Figure 5.Relationship between sodium and chloride concentrations in the Fang river basin EC 20 km EC EC 33 km EC 38 EC Na/Cl 5 NaCl EC

9 NGO Link JVC NGO 29 ppjvc pp : pp 2014 Braun, E. V., and Hahn, L. eds Geological Map of Northern Thailand 1 : , Sheet 2 (Chiang Rai), Federal Institute for Geosciences and Natural Resources, Germany. McQuistan, C RRA Report on Mae Gok Watershed in Chiang Mai and Chiang Rai Provinces. 33 pp, Regional Environmental Technical Assistance 5771, Poverty Reduction & Environmental Management in Remote Greater Mekong Subregion Watersheds Project (Phase I). inland-waters-rra-report-on-mae-gok-watershedin-chiang-mai-and-chiang-rai-provinces.pdf (last accessed 10 Jan 2015) Tanaka, Y., YANAGIBA, S., and Satoh, T Geographical data book of the Fang River Basin pp, Department of Geography and Institute for Applied Geography, Komazawa University. 39

10 Surface Water Quality and its Formation Processes in the Fang River Basin, Northern Thailand Yasushi TANAKA*, Masahiro TAKAGI*, Tetsuo SATOH*, Survey Participants of Northern Thai Seminar, Komazawa University** We measured the surface water quality in the basin of the Fang River, which is one of the upper tributaries of the Mekong River in northern Thailand, and discussed its formation processes from the viewpoints of geology, current landuse and human impacts. The water quality along the main stream of the Fang River changes as follows: 1) At the farthest upstream segment (ca km from the headwaters area near Doi Wiang Pha), the river is a clear stream containing few dissolved ions. 2) In the segment from ca. 20 km to agricultural Dam point (ca. 33 km), hard water which includes rich calcium and magnesium ions flows into the main stream of the Fang River, bringing about the effect of limestone. Paleozoic limestone is widely overlaid on the left (west) side of the upstream of Fang River, and it is found that this is one of the keys to understanding the formation process of water quality in the watershed. The hard water has an effect on Electrical Conductivity (EC) as the value of EC suddenly grows in this segment. But this does not mean that the water is polluted. 3) At the agricultural Dam point, most of the main stream water is diverted, and therefore it resets the water quality of the main stream except the rainy season. 4) Between the downstream of the Dam point and Huai Phai point (ca. 40 km), almost all main stream water is formed by the runoff water from the neighboring limestone areas. As a result, EC and Total Hardness (TH) indicate the maximum value in this segment. 5) At the downstream from the ca. 40 km point, the main stream water is diluted by tributary flows that do not run through limestone areas. Therefore EC and TH values decrease as far as Tha Mai Liam point (ca. 100 km). Next, we examined human impacts on the water quality by use of relationship between sodium and chlorine ion concentrations. We detected a weak human signal between Ai point (ca. 32 km) and Tha Mai Liam point (ca. 100 km). But since its absolute values are not so large compared with ordinary river water quality of urban/suburban area, we estimated it will not have a bad influence on human life. * Department of Geography, Komazawa University ** Northern Thai Seminar, Komazawa University (Satsuki YANAGIBA, Shihori TOYOKURA, Mifuka ISHIKAWA, Tomoko KIYOTA, Masahiro ISEKI) 40

地域学研究 第 28 号 2015 図 1. ファーン川流域の概要と水質調査地点 Figure 1. Topography and distribution of check points for water quality in the Fang river basin. 32

地域学研究第 28 号 2015 図 1. ファーン川流域の概要と水質調査地点 Figure 1. Topography and distribution of check points for water quality in the Fang river basin. 32