IJERD – International Journal of Environmental and Rural Development (2016) 7-1

Research article
erdCharacteristics of the River Water Quality Under Base FlowCondition in the Tokachi River Basin, JapanYURI YAMAZAKIThe United Graduate School of Agricultural Sciences, Iwate University, Iwate, JapanTOSHIMI MUNEOKA*
Obihiro University of Agriculture and Veterinary Medicine, Hokkaido, Japan
Email: muneoka@obihiro.ac.jp

HIROMU OKAZAWA
Faculty of Regional Environmental Science, Tokyo University of Agriculture, Tokyo

MASATO KIMURA
Obihiro University of Agriculture and Veterinary Medicine, Hokkaido, JapanOSAMU TSUJI
Obihiro University of Agriculture and Veterinary Medicine, Hokkaido, Japan
Received 15 November 2015

Accepted 11 April 2016(*Corresponding Author)

Abstract The Tokachi River basin has an important role as a food base of Japan. It is one of thesignificant challenges that achieve a good balance between a food production and water quality
conservation for the sustainable agriculture in this basin. Here, we carried out the river water
monitoring in the Tokachi River basin and evaluated the river water quality under base flow
condition. 37 sampling points in the main stream and the tributaries were monitored in late June,late August or early September, and late October 2007 to 2011. Five-year mean values andstandard deviation of pH, BOD, SS and EC were evaluated. The water quality of the TokachiRiver showed variations at each investigation period. However, there were no change trends ofseasons or years. The mean pH values of the Tokachi River basin were the range of 7.1-7.5.
The river water quality was neutrality and stable at each sampling point. The mean BOD
showed comparatively low values in the Tokachi River basin (0.9-1.8 mg/L). However, theBOD values increased gradually with the main stream flow. The mean SS values were less than
25 mg/L at all sampling points. Also, the SS values tended to increase basically with the mainstream flow. The mean EC values increased from upstream to downstream of the main stream(6.8-12.4 mg/L). Also, the EC values in 13 of 20 sampling points of the tributaries were higher
than the main stream values (5.0-22.2 mg/L). There were significant correlations between theEC values and the proportion of the agricultural land or forest land. From these results, it wasconsidered that the dissolved matter in the river water increased with a high proportion ofagricultural land in the Tokachi River basin.
Keywords river water quality, base flow condition, the Tokachi River basin

INTRODUCTION
One of the most important challenges that the world is facing today is the development of a sustainable
food system. The world population is expected to reach 9.1 billion people by 2050, and hence, we haveto double the current food production to accommodate the world food demand. Japan has a lower selfsufficiency rate than the United States and EU and depends on food from overseas for domesticⒸ ISERD154

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consumption. The Tokachi River basin in the eastern part of Hokkaido, Japan, is a large area ofcropland and dairy farming and is focused on as a food base of Japan. However, there are large
challenges with not only increasing the crop production such as improving the cultivation method, crop
breed and management of water resources but also reducing the environmental load from agriculturalland. For example, hydrosphere pollution caused by agricultural activities has been widely reported(Parris, 2011). Increasing nutrient runoff from agricultural land causes eutrophication of lakes,
ecosystem collapse and landscape deterioration. In the Tokachi River basin, increasing nitrogenconcentrations in the river water and a positive correlation between agricultural land and nitrogenconcentrations in the river water have been reported (Okazawa et al., 2011; Muneoka et al., 2013;
Yamazaki et al., 2013). Also, the water pollution in the agricultural area is considered to be caused bymaterials other than nutrient salts, such as pesticides, minerals, bacteria and metals. Until now, there
was no report of water quality evaluation by indicators other than nitrogen and phosphorus in theTokachi River basin.
Here, we report the result of a 5 year observation of pH, biological oxygen demand (BOD),
suspended solids (SS) and electrical conductivity (EC) measurements of the river water and evaluate
the current status of river water quality in the Tokachi River basin to improvement of water quality
with a goal of sustainable food system.
METHODOLOGYThis study was conducted in the Tokachi River basin located in the eastern part of Hokkaido, Japan(142.68–144.02°N, 42.55–43.65°E, 0–2,077 m altitude) (Fig.1 and Table 1). The basin has a total areaof 9,010 km2 and a total stream length of 156 km. The Tokachi River basin is characterized as a warm
summer continental climate type (Dfb) according to the Köppen–Geiger climate classification with anannual mean air temperature of 6.8°C and an annual precipitation of 887.8 mm/y; measurements wereperformed at Obihiro city from 1981 to 2010. The soil types in the Tokachi River basin are volcanic
soil, lowland soil, upland soil and peat soil. In particular, volcanic soil (andosols) is widely distributedin this basin. The main land uses in this river basin are agriculture and forests, with 60 % of theagricultural land used as cropland and the remaining 40 % used as pasture. Both chemical fertilizers
and livestock manure are applied to the agricultural land.
The river water quality was monitored at 37 sampling points located on the main stream (nos. 1–17) and each tributary (A–T) of the Tokachi River basin in June, either August or September andOctober from 2007 to 2011 under base flow conditions. Water samples were analysed for pH, BOD,SS and EC.
RESULTS AND DISCUSSION
Mean pH, BOD, SS and EC Values and the Standard Deviations in the Tokachi River Basin
Figure 2 shows the mean values and standard deviations of the pH, BOD, SS and EC measurements ofthe main stream and the tributaries in the Tokachi River basin. The pH values of the main stream andthe tributaries ranged from 7.2 to 7.3 and 7.1 to 7.5, respectively, indicating that the pH values in theTokachi River basin were neutral and stable. The standard deviations of the pH values were small andstable.
The mean BOD values of the main stream ranged from 1.1 to 1.8 mg/L and gradually increased
from upstream to downstream. The mean BOD values of the tributaries ranged from 0.9 to 1.8 mg/L
and were comparable with the values from the main stream. Since there were some variations in theBOD values by each observation year and season, the BOD in the Tokachi River basin ranged from 0.5
to 3.0 mg/L.
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IJERD – International Journal of Environmental and Rural Development (2016) 7-1Fig. 1 Locations and land uses in the Tokachi River basin
The mean SS values of the main stream ranged from
4.2 to 18 mg/L. Although the values fluctuated at eachsampling point, there was an increasing trend fromupstream to downstream. The SS values of the main stream
fluctuated by observation year and season, resulting incomparatively high standard deviations. On the other hand,
the mean SS values of the tributaries ranged from 1.1 to 20
mg/L, and except 2 sampling points, the mean SS values
were ≤10 mg/L. The standard deviations of 16 of the 20
sampling points were small, and the SS values of thetributaries were stable at these sampling points.
The mean EC values of the main stream ranged from
6.8 to 12 mS/m and increased from upstream to downstream.
The mean EC values of the tributaries ranged from 5.0 to 22
mS/m. The tributaries located in the upstream area had
lower EC values than the main stream; however, thetributaries located in the downstream area had EC values ofapproximately 20 mS/m. There were different trends in theEC values according to the location of the tributaries. The
standard deviations of the EC values were small and stable.
From these results, the river water quality in theTokahi River basin was at neutrality and stable with a pH
value of approximately 7, and there were small variations
between observation periods. However, the BOD, SS andEC values showed an increasing trend from upstream todownstream. In particular, the EC values of each sampling
point of the tributaries had a different trend according to theupstream area or the downstream area. Based on theseresults, the river water quality in the Tokachi River basin
was considered to have been affected by land use andanthropogenic impacts in the watershed.

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Table 1 Watershed and land use
information in sampling pointIJERD – International Journal of Environmental and Rural Development (2016) 7-1

Fig.2 Results of water quality in the main stream (a), (c), (e) and (g); that of tributaries (b), (d),(f) and (h); mean pH values (a) and (b); mean BOD values (c) and (d); mean SS values (e)and (f); mean EC values (g) and (h).

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Correlation Coefficients Between the River Water
Quality and the Land Use in the Watershed

Table 2 Correlation coefficeints
between the river water
quality and the land
uses in the TokachiRiver basin

We further examined the relationships between the riverwater quality and the proportion of land uses (agriculturalland, forest land and other land use). Table 2 shows thecorrelation coefficients of the relationships between themean pH, BOD, SS and EC values obtained from theTokahi River basin (i.e. the main stream and the tributaries),
and the proportion of the agricultural land, forest land andother land use (such as urban areas) at each sampling point.
The EC values had a significant correlation with theproportion of agricultural land and forest land (p < 0.01),
where the EC values of the river water tended to be higher
with a higher proportion of agricultural land and tended to
be lower with higher proportions of forest land. In general, the EC of river water is correlated with
dissolved materials such as ionic components in river water (de Sousa et al., 2014; Pawlowicz, 2015).
The results indicated that the dissolved materials in the river water might have increased with theintensity of agricultural land use in the watershed because the fertilizer components, livestock manureand cropland soil runoff into the river easily in an agricultural watershed.
The mean BOD and SS values of the Tokachi River basin had no correlation with the proportionof land uses. However, the BOD and SS values in the river water tended to increase with higher
contents of dissolved materials and nutrients in the river water.
CONCLUSION
In this study, the river water quality in the Tokachi River basin, which is the most important area for
agriculture in Japan, was determined to have deteriorated due to agricultural activity in the watershed.
At the main stream, the BOD, SS and EC values tended to increase from upstream to downstream, with
the EC values of the tributaries particularly showing higher concentrations in the downstream area.
Since the EC values of the river water had a positive correlation with the proportion of agricultural land,
the increase in dissolved materials in the river water was attributed to the presence of agriculturalactivities in the Tokachi River basin.
ACKNOWLEDGEMENTS
This research was supported by JSPS KAKENHI, Grant Number 15J04743, 2015.We would like toexpress our gratitude for the research assistance provided by the students and the Obihiro University ofAgriculture and Veterinary Medicine.
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