Full Paper Journal of Agricultural Meteorology 73 (1): 31-44, 2017 Quantitative Evaluation of Spatial Distribution of Nitrogen Loading in the Citarum River Basin, Indonesia Koshi YOSHIDA a , † , Kenji TANAKA a , Keigo NODA b , Koki HOMMA c Masayasu MAKI d, Chiharu HONGO e, Hiroaki SHIRAKAWA f and Kazuo OKI b a Faculty of Agriculture, Ibaraki University, 3-21-1 Chuo, Ami-machi, Ibaraki, 300-0393, Japan b Institute of Industrial Science, The University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo, 153-8505, Japan c Faculty of Agriculture, Tohoku University, 1-1 Amimiya, Aoba-ku, Sendai, Miyagi, 981-8555, Japan d Faculty of Engineering, Tohoku Institute of Technology, 35-1 Kasumi, Yagiyama, Sendai, Miyagi, 982-8577, Japan e Center for Environmental Remote Sensing, Chiba University, 1-33 Yayoi, Inage-ku, Chiba, 263-8522, Japan f Faculty of Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, 464-8603, JAPAN Abstract Human population growth has led to increases in energy and food production, use of fertilizers, and wastewater flows. Enhanced availability of nitrogen is a cause of eutrophication of rivers, lakes, and estuaries worldwide. In this study, Cita- rum River Basin, West Java, Indonesia was selected as a target area, supplying 80% of domestic water to Jakarta Metrop- olis. Meteorological and hydrological data from 1996 to 2009, and spatial data such as topography, land use, soil proper- ties were collected for model simulation. Conceptual nitrogen balance model, which has three nitrogen pools, was devel- oped and combined with rainfall runoff model. Proposed model was applied to the Citarum River Basin and simulated river discharge and nitrogen load in 1 km×1 km resolution to check the model applicability. By using the model, spatial distribution of nitrogen loading in whole basin level was estimated and histograms of nitrogen load from different land use also evaluated. The results provide a first insight into the magnitude and the spatial distribution of nitrogen loading in Citarum River Basin. Key words: Diffuse pollution, Land use, Nitrogen runoff, Point sources, West Java. basin, sediment accumulation and eutrophication have become 1. Introduction serious issues in downstream reservoirs due to inflows of During the past century, human activities have changed rapidly. wastewater from urban areas and fertilizer components from hilly Most importantly, human population growth has led to increases upland fields into the river (Hart et al., 2002). Eutrophic nutrients in energy and food production, use of fertilizer, and wastewater flow into the closed waterbodies from many kind of sources such flows (Pieterse et al., 2003). Nitrogen plays an important role in as point sources and non-point sources. It is important to identify controlling the trophic status of surface waters. Increased nitrogen the spatial distribution of nutrient effluent in basin wide level for loading from anthropogenic activity (agriculture, wastewater establishing the best practice to maximize the efficiency of coun- disposal, and atmospheric emissions) has resulted in widespread termeasures. However, few scientific researchers were conducted enrichment of nitrogen in surface waters and associated problems about spatial distribution of pollutant sources, because observed of eutrophication linked to excessive accumulation of algal bio- water quality data was limited and only available along the main mass, toxic algal blooms, and dissolved oxygen deple- stream. Therefore, the purpose of this study was quantitative eval- tion(Grizzetti. et al., 2005). If surface water withdrawal were uation of spatial distribution of nitrogen loading in Citarum River directly affected by water quality degradation, domestic water basin. Hydrological based nitrogen load assessment model was intake could be cut off for sanitary reasons. Therefore, evaluation proposed as a useful tool to evaluate the magnitude of spatial nu- of nitrogen polluted level in whole basin is important to discuss trient effluent. river environmental management under the impacts of intensified 2. Study Area human activities. The Citarum River is largest river in West Java, Indonesia (Fig. Having a length of 350 km and catchment area of 6,600 km2, 1). The Citarum River Basin is a region known for its highly pal- the Citarum River is the largest river in West Java (Fig. 1). An- atable rice and the most important basin in West Java, supplying nual mean precipitation varies from 1,600 to 2,800 mm/year, and water for Bandung and Jakarta City, with 80% of domestic water 70% of the annual precipitation falls during the rainy season from in Jakarta being withdrawn from this basin (Loebis and Syamman November to March. Bandung city is located along the upstream 1993; Fares 2003). As the population and economic growth in this reach of the Citarum River. The river has three large dams: the Saguling dam in the upstream reach, Cirata dam in the middle Received; August 21, 2015. reach, and Jatiluhur dam in the downstream reach. Table 1 lists Accepted; July 26, 2016. the characteristics of the Saguling, Cirata, and Jatiluhur reservoirs. †Corresponding Author: [email protected] The Citarum River is the most important river in West Java. It DOI: 10.2480/agrmet.D-15-00020 supplies water for the cities of Bandung and Jakarta, with 80% of - 31 - Journal of Agricultural Meteorology 73 (1), 2017 Jakarta River Watershed Analyzed area Reservoir Bojongsoang Jatiluhur WWTP Cirata Cianjur Saguling Cihea Bandung Nanjung km Fig. 1. Citarum river basin. Table 1. Characteristics of the three reservoirs in the Citarum River basin. Characteristics Saguling Reservoir Cirata Reservoir Jatiluhur Reservoir Catchment area (km2） 2283 4061 4500 Dam height (m) 99 125 96 Volume (M m3) 603 1927 2448 Purpose Electricity Electricity Multiple/irrigation Surface area(ha) 4869 6200 8200 Effective volume(M m3) 598.4 784.9 1869 Annual inflow(km3) 2.59 4.5 5.6 Installed capacity(turbins×MW) 700(4×175) 1000(8×125) 180(6×30) the domestic water in Jakarta being withdrawn downstream of the The land uses in the Citarum River Basin are paddy (35%), up- Jatiluhur dam (Loebis and Syamman 1993; Fares 2003). The land crop (25%), forest (23%), urban (12%), water (2%), and problem of water quality degradation in the Citarum River has others (3%). Figure 2 shows a land use map of the upper Jatiluhur increased from year to year due to increasing pollutant loads, par- dam basin in 2000. In this study, only the area upstream of Jati- ticularly those from the Bandung region located in the upper areas luhur dam was analyzed. The elevation of the downstream area is of the river basin when released without treatment. Therefore, it is quite flat, so a suitable river line could not be extracted from GIS important issue to evaluate the magnitude and the spatial distribu- analysis in the downstream area. However, this analytical bounda- tion of pollution load quantitatively in this basin (Abery, 2005; ry is sufficiently satisfied to evaluate the water resources or water ADB, 2007). However, water quality data is limited and most of quality for the downstream or Jakarta metropolis water supply. monitoring stations are located in mainstream of Citarum River so For the model run, historical observation data and spatial infor- that it is difficult to evaluate the spatial distribution of nutrient mation were collected, as shown Table 2. The available data were loading. quite limited, especially long-term water quality data were ob- - 32 - K. Yoshida et al.：Quantitative Evaluation of Spatial Distribution of Nitrogen Loading in the Citarum River Basin km Fig. 2. Land use of the upper Jatiluhur area. Table 2. Summary of data used for model simulation. Data (frequency) Description Sources Period Bandung station (including air temperature, relative humidity, sun- Meteorological data BMKG 1996-2009 shine duration, windspeed, rainfall) (daily) Cirata station (rainfall only) PT PJB 1996-2005 River discharge at Nanjung station (5 km upstream from Saguling Hydrological data RCWR 1996-2009 dam) (daily) Cirata station (Inflow to Reservoir) PT PJB 1996-2009 Water quality data Jatiluhur station (Inflow to Reservoir) PT PJB 2007-2009 Total nitrogen concentration at Nanjung station (5 km upstream (every 6 month before 2007) RCWR 1996-2009 from Saguling dam) (every 2 month after 2007) Cirata station PT PJB 2007-2009 Water Storage in Rservoir Jatiluhur station PT PJB 2007-2009 (daily) Cirata station PT PJB 1996-2009 Topograpy DEM(digital elevation map) (2000) PUB Land use Digital landuse map (2000) PUB Soil Clay content FAO Digital soil map of the world (2007) FAO Population density Population census (2010) BPS Notes: BMKG: Badan Meteorologi, Klimatologi, dan Geofisika in Bandung, RCWR: Research Center for Water Resources in Bandung PT PJB: PT Pembangkitan Jawa-Bali, Cirata, PUB: Ministry of Public Works in Bandung, FAO: Food and Agriculture Organization BPS: Badan Pusat Statistik served only at the Nanjung station (Fig. 1). Meteorological data data and distribution of population density data were available collected at the Bandung station were used to calculate evapotran- only in 2010(shown in Fig. 4); therefore, population in the upper spiration rate by the Penman-Monteith equation. Citarum River Basin was estimated by using the population in- Figure 3 shows the statistical population increase in West Java crease ratio of West Java Province and the pattern of population Province and the estimated population increase in the upper Cita- density distribution in 2010 was applied to the entire analysis rum River Basin from 1996 until 2010. In this study, population period. - 33 - Journal of Agricultural Meteorology 73 (1), 2017 Fig. 3. Population change in West Jawa and estimated upper Citarum population (1996–2010). Population density (persons/km2) 0 - 200 200 - 400 400 - 600 600 - 800 800 - 1,000 1,000 - 1,300 1,300 - 1,600 1,600 - 2,000 2,000 - 2,500 2,500 - 3,200 3,200 - 4,000 4,000 - 5,000 5,000 - 18,000 18,000 - 28,000 28,000 - 55,000 km Fig.