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内容記述 |
We have conducted an investigation into the water quality of the basin of the Naka river. Our findings are summarized as follows. (1) In the mainstream of the Naka, the pH value is 7.0～8.0. In the upper reaches, it is 7.2～7.4; in the middle reaches, 7.4～8.0; in the lower reaches, it is 7.2. In the tributaries, it is 6.8～8.0. In the middle reaches, however, it is constantly 7.4～7.6 between the Matsuba river (Yashio bridge: No.42) and the ogawa river (Ogawa bridge: No. 12). (2) The electric conductivity of the mainstream is 82.6～173μ℧/cm. In the upper reaches, it shows the high value because of Itamuro hot springs. In the middle reaches, it is constantly between 150 and 160μ℧/cm. In the lower reaches, five branches except Shinmachi bridge (No.3) across the Sakura river show more than 200μ℧/cm. Generally, in the upper reaches and the branches in the lower reaches, the electric conductivity shows the high values, but in the middle reaches, it shows the low values. (3) In the mainstream, the content of Cl^- is between 8 and 80ppm. In the most points of observation, it is 30ppm or below. The high values are seen in Kozume bridge (No. 32, 70ppm), and Wakaayu big bridge (No.28, 80ppm) and chitose bridge (No.4, 44ppm). In the tributaries, it is between 8 and 84ppm. In the most places of observation, it is less than 30ppm. It is more than 40ppm in the five points, including Takano bridge (No. 36, 84ppm) and Taisho bridge (No.47, 52ppm). Generally, it is high value in the upper stream. It slightly gets lower in the middle stream and rises again in the lower stream. (4) In the main course, the content of Ca^<2+> is 2.0～11.5ppm. In the branhes, it is 5.5～34.5ppm. (5) In the mainstream, the content of Mg^<2+> is 1.3～3.7ppm. In the tributaries, it is 1.3～3.7ppm. (6) In the mainstream, the NH_4-N content is 0.13～0.16ppm. It is just about a fixed amount for the most part. The content of NH_4-N in the tributary streams is 0.13～0.2ppm. (7) In the mainstream, the PO_4^<3-> content is 0.07～0.18ppm. It is 0.14ppm at Shomei bridge (No.37), 0.5ppm at Kunida bridge (No.5), 0.15ppm at Katsuta bridge, and 0.16ppm at Chitose bridge (No.4). These points are surrounded by rice paddies and fields. In the branches, it is 0.03～0.27ppm. (8) The dissolved oxygen (DO) of the mainstream is 8.0～12.4ppm. In the upper stream, it is 8.4～9.6ppm. It gets lower in densely populated areas downstream. DO of the branches is 7.2～14.9ppm. Generally, in the thinly populated areas, it shows high values, but it gets lower in the heavily populated areas. (9) The load of Cl^- is 1.0～629.0 g/sec. The high figures are found in Johoji bridge across the Hoki river (No.44: 629.0 g/sec), Okada bridge across the Arakawa river (No.20: 295.5 g/sec), Kinomata bridge across the Kinomata river (No.35: 171.2 g/sec), Shin-Hayato bridge across the Hayato river (No.1: 169.1 g/sec), and Shinozawa bridge across the Egawa river (No.24: 161.0 g/sec). (10) The load of Na^<2+> is 0.1～687.4 g/sec. The high values are seen at Johoji bridge over the Hoki river (No.44: 687.4 g/sec), Okada bridge over the Arakawa river (No.20: 295.5 g/sec), Shin-Hayato bridge over the Hayato river (No.1: 172.1 g/sec) and Kinomata bridge over the Kinomata river (No.35: 52.7 g/sec). (11) The load of NH_4-N and PO_4^<3-> are 0.002～6.29 g/sec and 0.06～4.49 g/sec, respectively. The each value of the research ponts is as follows. Johoji bridge across the Hoki river (No.44), 6.29 g/sec, 4.49 g/sec: Okada bridge across the Arakawa river (No.20), 2.59 g/sec, 2.22 g/sec: Shinozawa bridge across the Egawa river (No.24), 1.28 g/sec, 0.64 g/sec. (12) The middle streams of the Hoki river and the arakawa river show the high values of the load because these rivers flow through the areas of holiday homes, rice paddies and fields, and because the rivers show high flow rates. |
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