Estimation of Annual Total Nitrogen Load to lake from Basin with Remote Sensing
Kazuo Oki* , Yoshifumi Yasuoka** and Minour Inamura*
*Gunma University, Department of Electric and Electronic Engineering,
Tennin-machi, 1-5-1 Kiryuu-shi, Gunmea 376-8515 Japan
Tel: +81-277-30-1784,Fax : +81-277-50-1780,
E-mail : oki@rs.el.gunma-u.ac.jp
**University of Tokyo, Institute of Tokyo, Institute of industrial Science,
Roppongi 7-21-1, Minato-ku, Tokyo 106-8558 Japan
Tel : +81-3-3402-6231, Fax : +81-3-3479-2762,
E-mail : yyasuoka@cc.iis.u-tokyo.ac.jp
Abstract
In this study, a new method with remote sensing is proposed to evaluate total nitrogen load to la lake basin areas through rivers. In the method, following two parameters were evaluated from land cover distribution in the lake basin produced from LANDSAT MSS data and the nitrogen concentration measured at each river mouth to the lake;
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Basic units of total nitrogen load from different land cover categories
- Influent annual total nitrogen load to the lake.
A nitrogen load model which relates total nitrogen load with land cover condition was investigated and two parameters were estimated with an optimize method. The estimated result shows good agreement with the ground observation data.
1. Introduction
Land cover changes around lakes have caused serious environmental degradation in water areas. For example, the increase of nutrient load such as nitrogen and phosphorus to the lake due to land cover change in surrounding areas has been one of the major cause of water pollution or eutrophication. Monitoring influent nutrient load from the lake basin to the lake through rivers is now crucial in the management of lake environment. However, monitoring material flow from basin areas to lakes rivers is not easy because it requires spatial and temporal measurement tools for land cover distribution in lake basin areas and water qualities, and because it requires models relating them. Here, nitrogen is selected as a nutrient, and the model between land cover conditions and nitrogen load from the river basin areas is investigated.
Several methods have been proposed for the estimation of influent annual total nitrogen load to rivers and lakes based on the ground survey [e.g. Ibaraki Prefecture 1983]. Most of the conventional methods estimate influent annual total nitrogen load based on the sum of a basic unit of total influent load from each land cover category multiplied by each category area in the basin, and these methods could be applied only for the small basin areas because monitoring land cover conditions in a large extent of areas was not easy. Furthermore, the estimated values in these method usually differ much depending on the estimation methods, sites and seasons.
In this study, a remote sensing method was investigated to monitor land cover condition and changes in lake basin, and to analyze the relation between land cover and total amount of nutrient loaded to the lake through rivers. Lake Kasumigaura was selected as a test site.
2. Characteristic of Lake Kasumigaura Basin
2.1 Lake Kasumigaura and its Basin
Lake Kasumigaura is second largest lake in Japan with the water area of 220 square kilometers (Km
2) and with the lake basin area of 2,135 Km
2 . The lake is not so deep and the average water depth is about 4 meters (m) with the range of 0 - 7 m. the dominant land use category in the basin is agriculture including rice paddy, orchard, and it should be also noted that the hog raising (pig farming) is famous in the area which is a big point source of nitrogen load to the lake. For these thirty years urbanization and industrialization had been rapid along the railway, and the population has been increasing in the area.
Lake Kasumigaura is typical eutrophic lake and during summer season it is polluted by massive growth of blue green algae. It is mainly caused by influent nutrient such as nitrogen and phosphorus from the lake basin to the lake through rivers. These nutrient are consumed ion different ways for different purpose, and the nutrient load from land to river basins differs significantly among different land cover categories. The objective of the study is to estimate the nitrogen load to the lake from individual land cover categories.
Fig.1 Lake Kasumigaura and its basin area.
2.2 Definition of Lake Basin and River Basin Area with DEM
In order to investigate the quantitative relation between the land cover condition in each river basin and the influent nitrogen, first, the lake basin area and the river basin area are defined using DEM in order to evaluate relation between influent nutrient lad and land cover type in the lake basin. The procedure to delineate the basin areas are as follows.
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Calculation of slope
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Search for non-sloe point
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Decision of individual river basins.
Here ARC/INFO was used for a part of the procedure. Figure 2 shows the delineated basin area for each river pouring into the Lake Kasumigaura.
Fig.2 River basin of Lake Kasumigaura.
