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ABSTRACT The water quality of six rivers in Hadano basin was investigated and its relationship with nonpoint sources of pollution was analyzed. This study was undertaken to spatially examine the present status of the river water quality of Hadano basin. Ground water circulation influenced both the water quality and quantity. In the downstream basins of Muro and Kuzuha Rivers, COD and TP were diluted by the ground water inflow. In Mizunashi River and the upstream of Kuzuha River, water infiltrated to the subsurface due to the higher permeability of the river bed. Chemical oxygen demand (COD), total phosphorus (TP) and total dissolved solids (TDS) showed good correlation with unsewered population and agriculture area. While total nitrogen (TN) had good correlation with atmospheric nitrogen (N) deposition loads. Multiple regression analysis between water quality pollution loads and influencing factors revealed that unsewered population had higher impact on the river water quality; nonetheless, agriculture also had some effects. For TN, atmospheric N deposition load was taking effect, implying that it plays a significant role on the water quality and cannot be denied for proper water quality management. Development of sewerage system could be considered as the decisive factor to maintain the river water quality in the Hadano basin.
Journal of Water and Environment Technology, Vol. 9, No.2, 2011 Address correspondence to Gaurav Shrestha, Graduate School of Environment and Information Sciences, Yokohama National University, Email: gaurav_shresth@hotmail.com Received September 16, 2010, Accepted February 2, 2011. - 141 - River Water Quality Analysis of Hadano Basin and its Relationship with Nonpoint Sources of Pollution Gaurav SHRESTHA*, Satoru SADOHARA*, Shigeki MASUNAGA*, Hiroaki KONDO**, Satoshi YOSHIDA*, Yuichi SATO* *Graduate School of Environment and Information Sciences, Yokohama National University, 79-7 Tokiwadai, Hodogaya-ku Yokohama 240-8501, Japan **Research Institute for Environmental Management Technology, National Institute of Advanced Industrial Science and Technology (AIST), 16-1 Onogawa, Tsukuba 305-8569, Japan ABSTRACT The water quality of six rivers in Hadano basin was investigated and its relationship with nonpoint sources of pollution was analyzed. This study was undertaken to spatially examine the present status of the river water quality of Hadano basin. Ground water circulation influenced both the water quality and quantity. In the downstream basins of Muro and Kuzuha Rivers, COD and TP were diluted by the ground water inflow. In Mizunashi River and the upstream of Kuzuha River, water infiltrated to the subsurface due to the higher permeability of the river bed. Chemical oxygen demand (COD), total phosphorus (TP) and total dissolved solids (TDS) showed good correlation with unsewered population and agriculture area. While total nitrogen (TN) had good correlation with atmospheric nitrogen (N) deposition loads. Multiple regression analysis between water quality pollution loads and influencing factors revealed that unsewered population had higher impact on the river water quality; nonetheless, agriculture also had some effects. For TN, atmospheric N deposition load was taking effect, implying that it plays a significant role on the water quality and cannot be denied for proper water quality management. Development of sewerage system could be considered as the decisive factor to maintain the river water quality in the Hadano basin. Keywords: atmospheric nitrogen, unsewered population, water quality INTRODUCTION Water is one of the most abundant elements found on Earth. It forms an essential component of the ecosystem and its services (Millennium Ecosystem Assessment, 2005). However, because of modernization and urbanization, there is an increasing and concurrent prevalence of problems in water environment. Degradation of vital water resources indicates the loss of natural systems and the services they provide (Carpenter et al., 1998). Japan has a long history of struggle with water environment conservation and it is still endeavoring to achieve conservation (Otsuka et al., 2009). The rapid urbanization of Japan over the last 50 years has caused changes in land use and lifestyle, which have affected the river water quality (Tabayashi and Yamamuro, 2009). UNESCO (2003) stated that in seven prefectures, including Tokyo, the amount of land used for building in 2000 had increased by 7.2% as compared to 1974, while agricultural land had reduced by the same percentage. Increase of nitrogen (N) and phosphorus (P) loads to rivers due to land use alteration has been the major sources of water pollution (Oki and Yasuoka, 2008). Remarkable water quality improvements have been observed over the recent years because of the reinforced regulations imposed on the industrial wastewater and the consequent development of sewerage systems. However, pollution loads from Journal of Water and Environment Technology, Vol. 9, No.2, 2011 - 142 - households and agricultural lands are still high (UNESCO, 2003). Besides, the coverage ratio of the sewerage system is still low in small and medium cities (Kohata and Mizuochi, 2007). Nonpoint source pollution such as runoff from unsewered developments and urban area runoff accompanied by agricultural runoff with higher amount of fertilizer, contribute to the significant amount of P and N to surface waters (Carpenter et al., 1998). In general, unsewered pollution is treated as a point source of pollution since it is caused by the domestic wastewater discharged from households. When wastewater generated from unsewered areas as a whole is considered, then it is taken as nonpoint source of pollution (Carpenter et al., 1998; Loague and Corwin, 2005). These pollutants generally exist in medium to low concentrations but their behavior cause them to be widely distributed in nature, making their sources difficult to identify and this can be the greatest threat to surface waters (Corwin et al., 1997; Verro et al., 2002; Li et al., 2004; Banadda et al., 2009). As the river basins in Japan are commonly characterized by rugged hilly terrains, rivers are steep and short so pollution loads discharging from catchments are basically generated from nonpoint sources, scattered over various land covers (Oki and Yasuoka, 2008). Analyzing the impact of nonpoint sources of pollution on water quality is difficult due mainly to the difficulty in their identification (Sharpley et al., 2001; Bahar et al., 2008). In the present era of urbanization, the effect of atmospheric N on water bodies cannot be neglected. Atmospheric N is one of the complicated nonpoint sources that can seriously affect the river water environment because it has been known that reactive N is now accumulating in the environment on all spatial scales; local, regional and global (Galloway et al., 2003). Recently, the deposition of atmospheric N has been gradually increasing in the forested areas like Tanzawa Mountains of Hadano City where Kaname and Mizunashi Rivers originate. It had been reported that the forested watersheds neighboring the Kanto District of Japan had the highest levels of nitrate export to streams (Fujimaki et al., 2008), indicating that the atmospheric N generated from the heavily urbanized Kanto region is presumably playing an important role in the N concentrations of river waters. Generally, urban areas have higher atmospheric N pollution caused by anthropogenic activities as a consequence of energy production. Hadano City is known for its abundant water resources including surface water, ground water and springs. However, there was a problem of water quality deterioration in the past and the problem still persists with the variation in pollution scale. Rivers in Hadano City are polluted due to the inflow of domestic wastewater, urban and agricultural runoffs (Fujino et al., 1997). Being a middle-sized city, Hadano City is comprised of various types of land cover. The core areas of the city are mostly urbanized, whereas rural areas with dense forest and agriculture are also present in uplands. Hadano City has been experiencing a gradual rate of urbanization with corresponding expansion of newly developed areas, whereas the development of sewerage system is still behind the pace of urbanization. With these perspectives, Hadano City as a research area is a spatial combination of different land uses such as developed and rural areas. Most of all, Hadano City with its abundant ground water and existing water circulation is a very complex system regarding water quantity and its influence on water quality. Subsurface infiltration of water and natural outflow of ground water (spring) are the salient features Journal of Water and Environment Technology, Vol. 9, No.2, 2011 - 143 - of this city. This study on the analysis of river water quality and its relationship with nonpoint sources of pollution including the complex ground water circulation and atmospheric N, that has not been elucidated yet, can be effectively employed for water quality management of Hadano basin as well as other watersheds, both with and without complex ground water circulation. Therefore, as a research area of this study, it is significant and it has socio-economic values in terms of water quality management. With the start of the sewerage system in 1978 and its progressive development, the river water quality in the Hadano basin became better with time. Nevertheless, in the areas where installation of sewerage system is still in progress and where it is not introduced, improvements in water quality have not been observed yet and it has been a big problem hereafter. Furthermore, the rapid rate of urbanization was also affecting the river water quality in Hadano (Fujino et al., 1997). Therefore, nonpoint sources of pollution such as non-development of sewerage system, urban area and agriculture, as well as atmospheric N deposition loads could be considered as determining factors of the water quality in this basin. Understanding the pollution scenario of the whole basin in a broader scale is necessary for the proper management of river water quality. With this in mind, this study was undertaken to spatially investigate the present status of the river water quality in Hadano basin and its relation with nonpoint sources of pollution. Up to now, river water quality had been monitored only at the downstream of rivers. This monitoring system could not comprehend in detail, the water quality condition of the whole river system. In addition, the study on the relationship of river water quality with sewerage system and land use has not been done yet in the Hadano basin. Thus, with a holistic approach, this study was carried out to spatially examine the water quality variation of each river at its upstream, midstream and downstream, including that of tributaries and service water canals. The inclusion of atmospheric N deposition load as one of the factors that influence water quality is completely new in this study and has not been considered before. METHODS Study Area and Rivers Hadano City lies in the western part of Kanagawa Prefecture with an area of 103.61 km 2 . In the north, Tanzawa mountain range is situated and Shibusawa Hill exists in the south. Six rivers of Hadano City (Muro, Mizunashi, Kuzuha, Kaname, Ohne and Shijuhase rivers) were studied. Mizunashi River is flowing at the central region and at its eastern part, Kuzuha and Kaname Rivers are flowing, forming an alluvial fan in the plains. Muro River is flowing along the Shibusawa faults at the southern part. Ohne River is flowing at the southeast part and Shijuhase River at the western region, flowing from north to south (Fig. 1). Muro, Mizunashi, Kuzuha and Kaname Rivers merge at the southern end, then flows as Kaname River. Kaname River, originating from Tanzawa mountains, is the longest river of Hadano City with the length of 21 km (Fujino et al., 1997). Monitoring Stations and Delineation of Drainage Basins Water quality monitoring stations were allocated at 32 locations (Table 1) along the Journal of Water and Environment Technology, Vol. 9, No.2, 2011 - 144 - main rivers, tributaries and service water canals. This was done depending upon the condition of sewerage system, land use pattern and local conditions. The monitoring stations were allotted at upstream, midstream and downstream sections of rivers as well as at the outlet of respective tributaries and service water canals inflowing to rivers. Drainage basins corresponding to each monitoring station were delineated (Fig. 2) with the help of ArcGIS’s Spatial Analyst tool for hydrologic analysis, using a Digital Elevation Model (DEM) (Maidment, 2002; Kawasaki, 2006). Drainage basins were delineated estimating that water within each basin drains to their respective monitoring stations. The prepared data were modified on the basis of the detailed rainwater Shijuhase Muro Mizunashi Kuzuha Kaname Kaname Ohne # # # # ## # # # # # # # # # # # # # # # # # # # # # ## # # # 32 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 2728 29 30 31 # Monitoring Station Drainage Basin Hadano Basin River Fig. 1 - Hadano Basin and its river system Fig. 2 - Locations of water quality monitoring stations Table 1 - Water quality monitoring stations and the corresponding river basins No. Monitoring Station River Basin No. Monitoring Station River Basin 1 Chimura Muro 17 Shimo-ochiai (Tributary) Kaname 2 Ishiuchiba Muro 18 Irifuna (Tributary) Kaname 3 Neshitabashi Muro 19 Kaguchi (Tributary) Kaname 4 Sakagawa (Tributary) Muro 20 Shinsaibashi Kaname 5 Yamanokami Mizunashi 21 Saigabun ( Service Water Canal) Kaname 6 Minasebashi Mizunashi 22 Neshita-yohsui ( Service Water Canal ) Kaname 7 Sakurabashi Mizunashi 23 Shimo-oduki ( Service Water Canal ) Kaname 8 Shintokiwabashi Mizunashi 24 Chuobashi Ohne 9 Sakurazawabashi Kuzuha 25 Minamiyanazawa (Tributary) Ohne 10 Shiyamabashi Kuzuha 26 Jakubozawa (Tributary) Ohne 11 Kobane Kuzuha 27 Sanadabashi Ohne 12 Kuzuhaohashi Kuzuha 28 Shingawa (Tributary) Ohne 13 Kusawabashi Kuzuha 29 Kenmin-mori Shijuhase 14 Minoge Kaname 30 Shobukobara Shijuhase 15 Kanamegawabashi Kaname 31 Kawachibashi Shijuhase 16 Ochiaibashi Kaname 32 Yanagawa (Tributary) Shijuhase Journal of Water and Environment Technology, Vol. 9, No.2, 2011 - 145 - drainage area map of Hadano City. Then, to verify the accuracy of data with respect to the real condition of the study site, they were checked by the concerned officers of Hadano City and the data were revised based on their advices. Accurate locations of the monitoring stations were digitally recorded by using Mobile GIS (ArcPad and GPS) (Fig. 2). Ochiaibashi monitoring station of Kaname River was situated before any rivers merged with it and Shinsaibashi monitoring station was located after Kuzuha, Mizunashi and Muro rivers along with its other tributaries merged with it. Water Sampling and Chemical Analysis At the allocated monitoring stations (Table 1), water samples were collected once every two months from May 2009 to March 2010. Water samples (1500 mL each) were collected manually at each station using polyethylene bottles (1000 mL and 500 mL). The pre-washed bottles were rinsed thrice with water samples on the site before sample collection. Water samples were stored in a cooler box and transported to the laboratory. Chemical oxygen demand (COD) concentration was determined by analyzing the oxygen demand by potassium permanganate at 100 o C (COD Mn ) (JIS K0102 17). Total nitrogen (TN) concentration was determined by ultraviolet absorption photometry (JIS K0102 45.2) and total phosphorus (TP) concentration was determined by potassium peroxydisulfate resolution method (JIS KO102 46.3.1). These analytical methods for the determination of COD, TN and TP concentrations were based on the testing methods for industrial wastewater, Japan Industrial Standard (JIS) KO102 published by Japanese Standards Association in 2009. Electrical conductivity (EC) was measured on-site using an EC meter (ES-51; Horiba, Tokyo). The EC meter was first calibrated using a standard solution of potassium chloride. A conversion factor was used to estimate total dissolved solids (TDS) (mg/L) from EC (µs/cm), which depends on the salts specifically present in the water. In this study, the conversion factor of 0.7 was considered (Walton, 1989). At the same time, river flow velocity was also measured with a flow velocity meter (CM-1BN; Toho Dentan, Tokyo) at each station. River flow was calculated by multiplying the river cross-sectional area by the flow velocity at various points along a transect across the rivers and tributaries. Sampling was always done in clear weather condition to prevent any abrupt changes in measurements, except in January which was influenced by an unpredicted rainfall. To avoid unsteady conditions, sampling was not conducted within 3 to 4 days after rainfall events. Sampling and measurements along each individual river were done continuously from upstream to downstream and at its tributary. Only after this that the sampling was done in other rivers. There were three working groups sampling in three different rivers at the same time to shorten the time lag as much as possible. The monitoring sequence was always in the order: Kaname, Kuzuha, Mizunashi and Muro rivers as they merge with one another. Then only Ohne and Shijuhase rivers were monitored. It took about five hours on the average to monitor six rivers in each monitoring day. Thus, the average time consumed for the monitoring of each river was almost about an hour a day. Data Collection and Preparation Data of areas where the sewerage system had been installed until 2009 were acquired from Hadano City as a sewerage system data in paper format. These data were digitally prepared in ArcGIS (Fig. 3). Population data were obtained from the national census Journal of Water and Environment Technology, Vol. 9, No.2, 2011 - 146 - data of Japan and the data of each drainage basin were prepared in GIS and were calculated based on area proportion (Fig. 4). Land use data of 2005 used in this study were acquired from Kanagawa Prefecture City Planning Basic Survey data. Land use data consisted of 14 categories (Fig. 5), which were recategorized into 4 categories: paddy field, cultivated land, forest and urban area. The river, water body and seashore were not considered. While recategorizing, open space, residence, park, business, industry, agriculture facility, road and railway were categorized as urban areas. Similarly, abandoned farm was merged with cultivated land. Paddy field and forest were used as it is (Table 2). Fig. 5 - Land use Data LandUse 2005 Openspace Residence Park Business Forest Industry River, waterbody Seashore Paddy field Cultivated land Abandoned farm Agriculture facility Road Railway Fig. 3 - Sewerage System Data Sewerage System Sewered Area Drainage Basin Hadano Basin Fig. 4 - Population Data Population 2009 (Person) 0 - 515 516 - 3287 3288 - 7588 7589 - 13699 13700 - 19755 Drainage Basin Hadano Basin Table 2 - Recategorization of Land use Land Use Category Recategorized Areas 1 Paddy field Paddy field 2 Cultivated land 3 Abandoned farm 4 Forest Forest 5 Openspace 6 Residence 7Park 8Business 9 Industry 10 Agriculture facility 11 Road 12 Railway 13 River, water body River, water body 14 Seas hore Seashore Cult ivated lan d Urban area Journal of Water and Environment Technology, Vol. 9, No.2, 2011 - 147 - Land use data of each drainage basin was extracted in GIS and the area of each land use type was calculated (Fig. 6).Building data with floor area were also acquired from Kanagawa Prefecture City Planning Basic Survey data. Then, unsewered population was calculated in GIS by overlaying layers of sewered areas, households with total floor areas and population data for each basin. On the basis of sewered areas and household data, households without connection to the sewerage system were distinguished first (Fig. 7). After that, unsewered population was calculated using unsewered household buildings and population data, based on area proportion (Fig. 8). Overlay of sewered area Sewered Area Minasebashi Basin Separation of unsewered households Unsewered Household Sewered Household Minasebashi Basin Overlay of sewered area and households Household Sewered Area Minasebashi Basin Fig. 6 - Land use proportion of each drainage basin Fig. 7 - Separation of unsewered households of Minasebashi basin of Mizunashi River Journal of Water and Environment Technology, Vol. 9, No.2, 2011 - 148 - Pollution Load of Individual Basin As river flows downstream, pollution from upstream basins are also carried to downstream basins. Thus, pollution observed at downstream basin also includes pollution loads from its upstream basin in addition to those contributed by the pollution sources within the basin. However, pollutants headed downstream get self-purified to some extent because of physical processes like dilution, diffusion and settling; chemical processes like oxidation, reduction and adsorption; and biological processes like decomposition and uptake by organisms. Fig. 9 shows the upstream Chimura, midstream Ishiuchiba and downstream Neshitabashi sub-basins of Muro River basin. Pollution loads at Chimura sub-basin include the loads of this basin only. While at Ishiuchiba sub-basin, pollution loads Unsewered Population (Person) 0 - 269 270 - 547 548 - 1036 1037 - 1964 1965 - 3417 Drainage Basin Hadano Basin Chimura Ishiuchiba Neshitabashi # Monitoring Station Chimura Ishiuchiba Neshitabashi River Fig. 8 - Unsewered population of each drainage basin Fig. 9 - Upstream, midstream and downstream basins of Muro River ▲ Journal of Water and Environment Technology, Vol. 9, No.2, 2011 - 149 - include those from upstream Chimura basin in addition to loads from this basin. Similarly, at downstream Neshitabashi sub-basin, pollution loads are also contributed by the upstream basins Chimura and Ishiuchiba, in addition to its own loads. In this study, as the water quality was monitored at the upstream, midstream and downstream sections of each river, analysis was done considering the water quality pollution load of individual basin (P n ) of each monitoring station, so that the pollution scenario and the related influencing factors of each individual basin could be analyzed in detail, reflecting its own characteristics. This was calculated through equation (ii) below by deducting the pollution loads observed at the upstream basins (Po n-1 ) multiplied by pollution remnant rate (Rr) after self purification from those observed at downstream ones (Po n ). The general equation for pollution load is given as 1000 QC P ………… (i) where P: pollution load (kg/day) C: concentration of water quality parameter (mg/L) Q: river flow (m 3 /day) while the pollution load of individual basin was calculated as (Yoshida and Yasui, 1992; Modified from Ministry of Construction, 1999) P n = Po n – Po n-1 × Rr ……… . (ii) where P n : pollution load of n th basin Po n : pollution load observed at the monitoring station of n th basin Po n-1 : pollution load observed at the upstream monitoring station of n th basin Rr: pollution remnant rate after self-purification The pollution remnant rate after self-purification was calculated as Rr = exp (-Kr • t) ………… . (iii) where Kr: self-purification coefficient (day -1 ) t: time for pollution to flow from upstream to downstream station (day) Meanwhile, t was calculated as L v t 86.4 …………… (iv) where L: river section length (km) v: river flow velocity (m/s) While calculating the pollution load of the individual basin, the influence of ground water circulation, such as infiltration and inflow of ground water were also taken into consideration on the basis of river flow survey. In the rivers with highly permeable geology, water easily infiltrates to the subsurface and as a result river flow is less and in some sections water does not flow at all. Consequently, pollution loads will not flow to Journal of Water and Environment Technology, Vol. 9, No.2, 2011 - 150 - downstream basins. In these cases, it was considered that upstream basins do not contribute to pollution in downstream basins. On the other hand, in the drainage basins that experience the influence of ground water inflow, river flow is higher than its upstream, thereby diluting the pollution. In these contexts, the dilution factor was calculated based on the monitored river flow and considered in the analysis for COD and TP. In case of TN, its inorganic form (NO 3 - ) gets easily transported to ground water so ground water can contribute to N concentrations in the river water. Likewise, it can also contribute to TDS concentrations. Therefore, dilution factor was not considered for TN and TDS. Detailed explanation is presented in the results and discussion section. Self-Purification Coefficient (Kr) With reference to the values of several rivers in Japan reported by Nagasawa and Teraguchi (1971), Yoshida and Yasui (1992), and MLIT (2003), self-purification coefficients (Kr) were selected from 0.5 to 2.5 with 0.5 interval, i.e. 0.5, 1, 1.5, 2 and 2.5. Pollution loads of individual basins (P n ) were calculated for each Kr at different time periods of monitoring, using equation (ii). Then, Kr was chosen by comparing the calculated pollution loads of individual basins with the pollution loads generated from nonpoint sources of pollution within the respective basins such as unsewered population and different land uses, which were calculated by using the unit loads of pollution reported by the Ministry of Construction, Sewerage and Wastewater Management Department (Ministry of Construction, 1999) (Table 3). Detailed explanation is presented in the results and discussion section. As there was no animal husbandry within the study area, its pollution loads were not taken into account. River Flow Survey Water of the Hadano basin, on its way from top of the alluvial fan to its center, infiltrates to the subsurface, flows as a ground water and springs out at the southern part or gets stored deep under the ground (Ichikawa, 1978; Hadano City, 2003). Hence, to comprehend this kind of complex water circulation and its impact on water quality and quantity, the river flow survey was carried out in February 2010, on the basis of the water temperature survey carried out in February 2009 (Shrestha et al ., 2009). The flow of each river was measured in detail from upstream to downstream at an interval of 200m to 300m. River flow velocity was measured with a flow velocity meter (CM-1BN; Toho Dentan, Japan) at each monitoring point. River flow was calculated by Table 3 - Unit loads of pollution Source: Ministry of Construction, 1999 COD TN TP Unsewered Population (g/capita/day) 17 3 0.9 Paddy Field (kg/ha/day) 0.565 0.113 0.011 Cultivated Land (kg/ha/day) 0.073 0.189 0.002 Urban Area (kg/ha/day) 0.293 0.044 0.005 Forest (kg/ha/day) 0.100 0.012 0.001 . Basin Fig. 4 - Population Data Population 20 09 (Person) 0 - 515 516 - 3287 3288 - 7588 75 89 - 13 699 13700 - 197 55 Drainage Basin Hadano Basin Table 2 - Recategorization. individual basin was calculated as (Yoshida and Yasui, 199 2; Modified from Ministry of Construction, 199 9) P n = Po n – Po n-1 × Rr ……… . (ii) where