IJERD – International Journal of Environmental and Rural Development (2022) 13-1

Research article
erdCharacteristics of Ion Components of Clearwater Stream
Watershed in an Agricultural Area with MultivariateAnalysis
YURI YAMAZAKI*Tokyo University of Agriculture, Tokyo, Japan
Email: yy206792@nodai.ac.jp

TOSHIMI MUNEOKA
Obihiro University of Agriculture and Veterinary Medicine, Hokkaido, Japan

CHIE MATSUDA
Zukosha Co., Ltd., Hokkaido, Japan

MASATO KIMURA
Obihiro University of Agriculture and Veterinary Medicine, Hokkaido, JapanOSAMU TSUJI
Zukosha Co., Ltd. / Obihiro University of Agriculture and Veterinary Medicine, Hokkaido,JapanReceived 29 January 2022

Accepted 25 April 2022(*Corresponding Author)

Abstract Restoring the clear-stream environment that once existed in agricultural areas is
one of the major challenges for the development of sustainable agriculture. Therefore, we
analyzed the ionic components of the Rekifune and Satsunai River basins, which areregarded as clear-water basins in the Tokachi region of Hokkaido, using principal
component analysis and cluster analysis based on surveys conducted in June and September
2014. The results showed that most of the sampling points in the Rekifune and Satsunai
drainages were comparable to the average values of water quality assessed as clear-streams
in Japan. However, in the tributaries of the Rekifune River, since Cl- and Na+ increased
characteristically, the water quality was degraded by anthropogenic pollution sources suchas domestic wastewater. In the Satsunai River, the water quality of the downstream
tributaries was degraded due to agriculture. In addition, in one of the tributaries,
deterioration of water quality was observed only in September, and the water quality of themain river immediately after the inflow of this tributary was also affected. These results
indicate that the water quality in the two basins in the predominantly agricultural area isgenerally good. Still, it is necessary to identify the source of pollution in some areas andtake countermeasures.
Keywords river water quality, agricultural area, principal component analysis,cluster analysis

INTRODUCTION
Historically, rivers flowing through rural areas in Japan had clear water and were home to various
aquatic life. However, modern agricultural land-use changes and river alterations have resulted in
the disappearance of the 'clear water' environment in rural areas. This water pollution caused bymodern agriculture has become a global problem. We now understand the need to conserve intact
rivers in agricultural areas and restore altered river ecosystems to meet the global challenge ofmore sustainable agriculture.

Ⓒ ISERD124

IJERD – International Journal of Environmental and Rural Development (2022) 13-1

The term “clearwater stream” generally refers to uncontaminated rivers-however, no scientificdefinition in Japan. For example, the Japanese government publicizes river rankings based on water
quality measurements, particularly biochemical oxygen demand (BOD). Therefore, any riverranked highly in the river-ranking program is defined as a clearwater stream. Also, rivers selected
as “100 clearest streams in Japan” by the Ministry of the Environment are evaluated as clearwaterstreams.
The Tokachi region of Japan, which has an essential role in Japan’s food supply, has twoclearwater streams: the Rekifune and Satsunai rivers. Both had been ranked high in thegovernment's river-ranking program in prior years, and both had low BOD values. In aquestionnaire provided to Hokkaido residents to rank clearwater streams, the Rekifune Riverranked second, and the Satsunai River ranked 5th place (Shimatani et al., 1996). Therefore, it isclear that both rivers are recognized as being clearwater streams in Hokkaido. However, ever sincelarge-scale agriculture commenced in the watershed of the Rekifune and Satsunai drainage basins,
water pollution caused by these agricultural activities has become a concern. In 2008, for example,
water quality studies of the Rekifune and Satsunai rivers had shown elevated nitrogenconcentrations in river water caused by agricultural runoff (Yamazaki et al., 2017).
OBJECTIVE
This study evaluated ion components of river water and all water quality factors using multivariate
analysis in clear stream watersheds at a large agricultural area to develop guidelines for preserving
river environments.
MATERIALS AND METHODOLOGY
Study Sites
This investigation examined two clearwater stream drainages in the Tokachi region in eastern
Hokkaido, Japan: the Rekifune and Satsunai drainages. Both rivers supply irrigation and tap water
to the residents in the Tokachi region. Also, the Rekifune and Satsunai watersheds are
geographically adjacent to one another in their headwaters. The catchment areas are similar, andthe primary land use of the region is agriculture and forest.
The primary land use in the Satsunai drainage is agricultural cropland (30% of total area),
including wheat, potato, sugar beet, and beans. Both chemical and organic fertilizers (livestockmanure) are applied to croplands. In the Rekifune drainage, pasture and forage crops are produced,constituting 17% of the total land area.
Water Quality Investigation
We selected fourteen water quality sampling stations in the Rekifune drainage and 21 points in theSatsunai drainage; these stations were sampled once per month in June and September 2014 during
normal water levels; a total of 42 and 63 samples were collected from the Rekifune and Satsunai
River drainages respectively (Fig. 1). The sampling points were located on the main stems (StationsA-F on the Rekifune River and Stations 1-11 on the Satsunai River) and downstream along
tributaries (Stations G–N on the Rekifune River and Stations 12-21 on Satsunai River).
Electrical conductivity and water temperature were measured using a digital conductivity
meter (DKK TOA Corporation; 592896; Japan). We analyzed the following ion components ineach sample: Cl−, NO3−, NO2−, SO42−, Na+, K+, Ca2+, and Mg2+ using liquid chromatography.
Multivariate AalysisⒸ ISERD

125

IJERD – International Journal of Environmental and Rural Development (2022) 13-1

Fig. 1 Land use and sampling stations of the Rekifune and Satsunai River drainages
We used the R package (R Foundation for Statistical Computing; Ver. 3.0.3; Austria) for cluster
and principal component analyses. The ion components (Cl−, NO3−, SO42−, Na+, K+, Ca2+, andMg2+) were used as input variables. Cluster analysis and principal component analysis are bothtypes of multivariate techniques. We applied Ward’s method to the cluster analysis. Principalcomponent analysis (PCA) was derived using the “princomp” algorithm of the R package.
RESULTS AND DISCUSSION
Cluster Aalysis and Pincipal Cmponent Aalysis of the Rver Water Qality
Cluster and principal component analysis using correlation matrix were carried out for sevenvariables: ion concentrations (Cl−, NO3−, SO42−, Na+, K+, Ca2+, and Mg2+) at 35 sampling stations inthe Rekifune and Satsunai drainages. We compared water quality between the mean ion
concentration of river water and groundwater from “100 clearest streams in Japan” of 1985 and2008 (Yabuzaki et al., 2009) as a reference. These analyses were performed for the July andSeptember observations in the Rekifune and Sastunai drainages, respectively.
Table 1 shows the cluster analysis results and PCA score of PC1 and PC2 of the July and theSeptember observations, respectively. First, the “100 clearest streams in Japan” of 1985 and 2008
were classified as Cluster1 and Cluster2, respectively, in the July observation data. Also, twentyeight sampling stations (11 stations of the Rekifune and 17 stations in the Satsunai) were classifiedⒸ ISERD126

IJERD – International Journal of Environmental and Rural Development (2022) 13-1

into Cluster1 and Cluster2. Therefore, most of the main stems and the tributaries of the Rekifune
and the Satsunai drainages have the same level of water quality concentration as the “100 clearest
streams in Japan”. However, three tributaries of the Rekifune and four of Satsunai drainages,
classified as Cluster3 to Cluster5, show a different trend from the “100 clearest streams in Japan”.
Next, in the September observation data, the “100 clearest streams in Japan” of 1985 and 2008
were classified as Cluster1. Also, twenty-four sampling stations (11 stations of the Rekifune and 13stations in the Satsunai) were classified into Cluster1. The results of the Rekifune River were likethose of the July cluster analysis, while the Satsunai River showed a different trend. Particularly,
Stations 5 and 14 in the Satsunai River were classified as Cluster5.
Table 1 Results of cluster analysis and PCA score

Fig. 2 shows the eigenvector of PC1 and PC2, also Fig. 3 shows the results of the principal
component analysis, color-coded into clusters 1 to 5 as described above. The x-axis is the firstprincipal component (PC1), and the y-axis is the second principal component (PC2).
The cumulative contribution of the principal component analysis was 95% and 82% from thefirst to the second principal components in July and September observations, respectively,indicating that the characteristics of river water quality in the Rekifune and Satsunai Riverdrainages can be summarized by two principal components. The eigenvectors of the first andsecond principal components showed a similar trend in both July and September. First, theeigenvectors of PC1 were positive for all items. PC1 indicates the overall characteristics of theriver water quality, and the larger the positive value of PC1 is, the worse the river water quality is.
The eigenvectors of PC2 showed positive values for Cl−, Na+, and K+, and negative values for NO3−,SO42−, Ca2+, and Mg2+. The negative values of PC2 indicate that the components are contained infertilizer, so it can be inferred that when PC2 is large with negative values, the influence ofagriculture is significant. On the other hand, for the item with a positive PC2, the increase in Cl−,and Na+ concentrations in river water due to the inflow of domestic wastewater was reported in thesuburbs of urban areas (Taniguchi et al., 2004; Hirata et al., 1999), which may reflect
anthropogenic influences other than agriculture.
Cluster1 and Cluster2 in July, and Cluster1 in September, show the range of -1.9 to 0.8 forPC1 and the content of -0.6 to 0.5 for PC2. The main stems and most of the tributaries of theRekifune and Satsunai Rivers are comparable to those of the “100 clearest streams in Japan”.
On the other hand, the three sites in the tributaries of the Satsunai River, classified as Cluster3in July and Cluster2 in September, showed positively large values of PC1 and negative values ofPC2 in both July and September. The tributaries located in the lower reaches of the Satsunai RiverⒸ ISERD

127

IJERD – International Journal of Environmental and Rural Development (2022) 13-1

are affected by agriculture. Although the water quality is worse than “100 clearest streams inJapan”, it does not significantly affect the water quality of the main river of the Satsunai River.
In addition, Cluster4 in July and Cluster3 in September have a larger PC1 than the “100clearest streams in Japan”. Therefore, the water quality tends to deteriorate, although not as
markedly as the tributaries in the lower reaches of the Satsunai River.
One tributary station of the Rekifune River, classified as Cluster5 in July and Cluster4 in
September, showed large positive results for both PC1 and PC2. The water quality at station M ofthe Rekifune River is degraded by anthropogenic influences other than agricultural influences inthe period of July to September at least.
Finally, one station in the main stem of the Satsunai River and one station in a tributaryclassified as Cluster 5 in September were both classified as Cluster 1 in July, and the river water
quality in July was good. However, in September, PC1 became larger with positive values, and thewater quality deteriorated. On the other hand, PC2 is positive, ranging from 0.8 to 1.4. Therefore,
although it is not as pronounced as station M in the Rekifune River, it is considered that the river isaffected by anthropogenic factors other than agriculture only in September. Since station 5 of themain stem of the Satsunai River is just after the inflow of the tributary of station14, it is consideredthat there is a pollution source around station 14, which deteriorates the river water quality of themain stem around station5.

Fig. 2 Eigenvector of PC1 and PC2

Fig. 3 Relationships between PC1 and PC2Ⓒ ISERD

128

IJERD – International Journal of Environmental and Rural Development (2022) 13-1CONCLUSION
In this study, we investigated the water quality of the Rekifune and the Satsunai drainages, which
are in a large agricultural area and are regarded as clear streams. We compared them with the "100clearest streams in Japan" results using multivariate analysis. As a result, the water quality of bothrivers is comparable to that of the “100 clearest streams in Japan” and can be evaluated as a goodwater quality environment. However, the Rekifune River deteriorated at one station due toanthropogenic influences such as domestic wastewater. Furthermore, there is a concern about
pollution sources operating at different times in the Satsunai River. Although the effects of thesepollution sources have not had a significant impact on the main rivers of both the Rekifune and theSatsunai Rivers, it is necessary to identify these pollution sources and take measures to ensuresustainable conservation in the future.
ACKNOWLEDGEMENTS
This research was supported by JSPS KAKENHI, Grant Number 15J04743, 2015. We would liketo express my gratitude to the research assistance provided by the students, the Obihiro Universityof Agriculture and Veterinary Medicine.
REFERENCES
Hirata, T., Ii, H., Hasebe, M., Egusa, N., Sakamoto, Y., Kumekawa, T., Nishiyama, K., Sakai, N. and Iwasaki,H. 1999. The effect of land use upon river water chemistry -The Ishi River basin in Osaka Prefecture-.
Journal of Japan Society of Civil Engineering, 1999 (614), 97-107, Retrieved from DOI https://doi.org/10.2208/jscej.1999.614_97
Shimatani, Y., Denda, M., Mashita, K. and Koike, T. 1996. The study on the image of clear streams, Howdoes people evaluate the rivers. Environmental System Research, 24, 20-25, Retrieved from DOI
https://doi.org/10.2208/proer1988.24.20
Taniguchi, M., Ii, H., Hirata, T. and Ishizuka, M. 2004. Changes of substances derived from domestic sewage
in Yamatogawa River Basin. Proceedings of Hydraulic Engineering, 48, 1465-1470, Retrieved from DOI
https://doi.org/10.2208/prohe.48.1465
Yabuzaki, S. and Shimano, A. 2009. Characteristics of water quality in the selected 100 spots of clearlypreserved water of the Heisei Era in Japan. Journal of Groundwater Hydrology, 51 (2), 127-139,
Retrieved from DOI https://doi.org/10.5917/jagh.51.127
Yamazaki, Y., Muneoka, T., Okazawa, H., Kimura, M. and Tsuji, O. 2017. Evaluation of river water quality
with multivariate analysis in clear stream watersheds in agricultural area. Journal of Water andEnvironment Technology, 15 (3), 86-95, Retrieved from DOI https://doi.org/10.2965/jwet.16-040Ⓒ ISERD129