Land Cover Change And Fluctuation Of Lacustrine Water Quality In Okutama Lake
Susumu Ogawa* and Moe Moriyama**
Faculty of Geo-Environment Science, Rissho University
1700 Magechi, Kumagaya, Saitama, 360-0194 Japan
Phone: +81-48-539-1652 Facsimile: +81-48-539-1632
E-mail: *ogawa@ris.ac.jp; **moriMoe77@hotmail.com
Keywords: forest basins, lacustrine water, water quality, Landsat TM, land cover
Abstract Land cover change and fluctuation of lacustrine water quality in Okutama Lake were analyzed using two-date Landsat TM data. The relationship between its forest constitution and water quality was investigated. Most land cover was forest in this area. Forest was composed of evergreen and deciduous trees. Two long-term water quality trends were obtained: soil and sewer origins. The former origin might be derived from the change of forest constitution.
1. Introduction
Okutama located in the upper Tama River has been managed for stable flow rate and natural environment by protecting and planting forest. On the other hand, land use change with the management abandonment by aged landowners and the reduction policy of paddy fields affected directly on water quality in the river. The purpose of this study is to examine relationship between land cover change and lacustrine water quality from two-date Landsat TM and water quality data for 39 years in the Ogouchi Dam (Aoyama & Nishikawa, 1990; Kazama, Tada & Sawamoto, 1996; Yamada, Shimizu, Inoue & Tachibana, 1999; Kishimoto, Kakuchi, Somiya & Nakamura, 1999).
2. Materials And Method
2.1 Study Area and Data Used
Study area is located in the upper Tama River in Tokyo and Yamanashi prefectures as shown in Figure 1. For calculation of watershed area and watershed separation, digital elevation models '2,500' and '50m-mesh' by the Geological Survey Institute were used.
2.2 Land Cover Classification
Two-date satellite data were used for land cover classification and each area calculation. With most likelihood method, land cover classification was carried out for 1984 and 1997 as shown in Table 1.
2.3 Watershed Separation
The objective watershed was determined semi-automatically with GIS software from digital elevation models '50m-mesh' by the Geological Survey Institute.
2.4 Water Quality Analysis
Water quality items are water temperature, turbidity, pH, transparency, chlorophyll-a, total nitrogen, and total phosphorus, which were measured at the Ogouchi Dam (Waterworks Bureau, Tokyo Metropolitan Government, 1959-1997). They were analyzed to seasonal and annual changes each item. Moreover, they were calculated for correlation.
3 Results
3.1 Land Cover Change
Table 2 shows land cover classification in the forest of Okutama upper watershed. During the observation, the area of forest and urban increased, while agricultural field decreased as shown in Figure 2. Forest was composed of evergreen and deciduous ones. The latter increased more than the former. Figures 3 and 4 show long-term hydrological observation, which has almost constant trends each variable.
3.2 Water Quality Fluctuation
Figure 5 shows long-term fluctuation for turbidity, transparency, and chlorophyll-a. Transparency and chlorophyll-a increased, while turbidity decreased in trend. In seasonal water quality fluctuation, turbidity and total nitrogen decreased in summer, while chlorophyll-a increased in summer. However, sedimentation increased though turbidity decreased during this period as shown in Figure 6.
3.3 Water Quality Correlation
Table 3 shows correlation between water quality items. Turbidity correlates with total phosphorus positively, but with transparency, chlorophyll-a, and total nitrogen negatively. On the other hand, total nitrogen correlates with water temperature and pH negatively. Chlorophyll-a correlates with transparency, pH, and total inorganic nitrogen (Figure 7) positively. Moreover, sedimentation correlates with the square of flow rate as shown in Figure 8.
