IJERD – International Journal of Environmental and Rural Development (2014) 5-1

Research article
erd

Evaluation of the Ion Components for the Estimation ofTotal Nitrogen Concentration in River Water based on
Electrical Conductivity
YURI YAMAZAKI
Obihiro University of Agriculture and Veterinary Medicine, Hokkaido, JapanTOSHIMI MUNEOKA*
Obihiro University of Agriculture and Veterinary Medicine, Hokkaido, Japan
Email: muneoka@obihiro.ac.jp

SACHIYO WAKOU
Department of Agriculture, Forestry & Fishery, Ibaraki Prefectural Government, Ibaraki,
Japan

MASATO KIMURA
Obihiro University of Agriculture and Veterinary Medicine, Hokkaido, JapanOSAMU TSUJI
Obihiro University of Agriculture and Veterinary Medicine, Hokkaido, Japan
Received 30 October 2013

Accepted 1 March 2014(*Corresponding Author)

Abstract It is generally known that the nitrogen concentration in river water is higher inagricultural areas. However, measurement of the nitrogen concentration is time- and costintensive. This study estimated total nitrogen (T-N) concentration based on electricalconductivity (EC) in river water at two agricultural watersheds area which are the Tokachi
area, the main land uses are upland and daily farming and the Nemuro area, the main land
use is daily farming. The ion components in river water were also considered. The
investigation was carried out from August to early September in 2003 to 2006 and in 2012,and T-N concentration, EC and ionic components in river water were measured. In the twoareas, there was a positive correlation between T-N concentration and EC in the riverwater. From this result, T-N concentration was able to be estimated from EC. However,the slope of the regression line differed between the two areas. It is causally related to theeffect of the ionic components, because there was a very strong correlation between theconcentrations of cationic and anionic components in river water and the EC. In theTokachi area, SO42- and NO3- account for a high percentage of the anionic components.
These derive from fertilizer, which correlates positively with T-N concentration. In theNemuro area, Na+ accounts for a high percentage of the cationic components. In
comparison with sea salt, the Na+ concentration is higher than Cl- concentration. In
addition, there was no correlation between Na+ and T-N concentration. In the Nemuro area,
the outflow of ion component of geological origin affects EC. In light of the above, T-N
concentration was able to be estimated based on EC; however, it is necessary to consider
the difference in the concentrations of water quality components for each region.
Keywords T-N concentration, EC, cationic components, anionic components

INTRODUCTION
Large-scale farming has long prospered in Eastern Hokkaido, whose natural environment differsfrom those of other Asian monsoon regions. In recent years, water contamination, including nitratepollution of river water and groundwater, has been pointed out there (Tabuchi et al., 1995;
Matsumoto and Tou, 2006).
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The authors investigated the long-term river water quality in the Tokachi area and the Nemuroarea, where the agricultural land use is mutually different. It was shown that the trend of nitrogenconcentration in the river water differed between the two areas because of their mutually different
agricultural land use (Yamazaki et al., 2013, Muneoka et al., 2013).
The nitrogen concentration in river water is usually measured by ion chromatography andspectrophotometry, which are time- and cost- intensive. In contrast, electrical conductivity can bemeasured relatively easily in the field.
This study estimated the total nitrogen (T-N) concentration based on the electricalconductivity (EC) of the river water. EC had been used to estimate the T-N concentration inirrigation water (Tomita et al., 2008). However there are not many examples of applying themethod to river water.
In this study, we examined whether the T-N concentration could be estimated from EC values.
To do this, based on the results of water quality investigations (2003 - 2012) in the Tokachi area
and in the Nemuro area of Eastern Hokkaido, the relationship between T-N concentration and EC
was expressed by using a linear regression. In addition, we considered the impact of the ioniccomponents in river water on the coefficients of the regression line.
METHODOLOGY
The study sites are outlined in Fig. 1. The Tokachi area, which consists of 24 watersheds in theTokachi river system and the Shikaribetsu river system (No. 1 to 24), is in the northwestern partwithin jurisdiction of the Tokachi General Subprefectural Bureau. It is an area of upland and dairyfarming. The Nemuro area, which consists of 11 watersheds in the Shibetsu river system, theTokotan river system and the Nishibetsu river system (A to K), is in the western within jurisdictionof the Nemuro Subprefectural Bureau. It is an area mainly of dairy farming. In both of these areas,large-scale farming has been pursued, and there have been no considerable changes in agriculturalland use in either area since 1985.

Fig. 1 Outline of the Tokachi and Nemuro areasⒸ ISERD

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For the years 1981 to 2010, the annual mean air temperature and the yearly precipitation were
5.9 ˚C and 840.7 mm at Komaba in the Tokachi area, and 5.4 ˚C and 1158.0 mm at Nakashibetsu in
the vicinity of the Nemuro area. Both areas have a relatively cold climate with less rainfall thanother agricultural areas in Japan.
The investigation of the river water quality was conducted at the normal water level at 35
sampling points. EC and water temperature were measured using a digital conductivity meter atsampling points. Discharge was also measured on the rivers in small watersheds (varying between
22 and 25 by year). The investigations were carried out from late August to early September in2003 to 2006, and in 2012. River water samples were analyzed for T-N concentration with
spectrophotometer using the cadmium reduction method and chromotropic acid method.
In addition, in late August 2005, ion components of river water were analyzed. These
components were Cl-, NO3-, NO2-, SO42-, HCO3-, CO3-, PO43-, NH4+, Na+, K+, Ca2+ and Mg2+. They
were analyzed by liquid chromatography.
RESULTS AND DISCUSSION
The results of the relationship between T-N concentration and EC in river water for each year in
two areas are shown in Fig. 2. The graph is an example of the results for 2012 (Fig. 2(a)).
Since there was a positive correlation between T-N concentration and EC in river water
through the study period in the two areas, it was possible to estimate the T-N concentration fromthe EC of the river water in these agricultural watersheds. The slope and intercept of the regression
line were virtually constant throughout the study period in the Nemuro area. In the Tokachi area,
the slope and intercept of the regression line were increased from 2005. After the full
implementation of “The Law on Animal Waste Regulation” in 2004, significant increases in nitrate
nitrogen concentration in river water from some sampling points in the Tokachi aera wereconfirmed (Yamazaki et al., 2013). The increasing trend of the slope and intercept since 2005 is
considered to reflect the changes in the behavior of farmers.
The slope of the regression line is small in the Nemuro area through the study period
comparing the two areas. This indicates that the increase in the EC due to change in the T-Nconcentration in the Nemuro area is higher than in the Tokachi area.
The coefficients of the regression line for estimating the T-N concentration from the EC inboth areas were different. As reasons for the differences, the influence of the ionic components
other than inorganic nitrogen can be considered. Therefore, cationic and anionic components inriver water were analyzed.
In the two areas, there was a very strong correlation between the cations and anions in theriver water and the EC (Fig. 3). The percentages of the cationic and anionic components in riverwater are shown in Fig. 4(a), (b) and Fig. 5(a), (b).
10.0

* 2012

Investigatedyear

T-N (mg/L)

8.0

2003

6.0
4.0

2.0
0.0
0

102030Tokachi area (Y = a X + b )Nemuro area (Y = a X + b )

abr

abr

0.24

⁃0.96

0.85 ※※

0.17

⁃1.00

0.87 ※※

0.17

⁃1.19

0.79 ※※

2004

0.24

⁃1.25

0.80 ※※

2005

0.38

⁃1.920.87 ※※

0.17

⁃0.97

0.83 ※※

2006

0.37

⁃1.65

0.92 ※※

0.19

⁃1.02

0.85 ※※

2012

0.32

⁃1.60

0.87 ※※

0.19⁃1.130.82 ※※Tokachi area

Nemuro area※※significnace of 1%

EC (mS/m)Fig. 2 Relationship between T-N concentration and EC in river waterⒸ ISERD

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N.B.

*

(a) Total cation concentration120

Total anion concentration (mg/L)

Total cation concentration (mg/L)

IJERD – International Journal of Environmental and Rural Development (2014) 5-180400010203060(b) Total anion concentration
coefficient of correlation rTokachi40

Nemuro(a)0.99 ※※ 1.0(b)0.99 ※※※※

0.99 ※※※※

significnace of 1%

20

Tokachi area
Nemuro area

001020EC (mS/m)

EC (mS/m)30

Fig. 3 Relationship between ionic components and EC in river water
Ca2+ and HCO3- are the main ionic components in the river water. The trend of the percentageof the ionic components differed between the two areas. The percentage of SO42- and NO3- werehigher in Tokachi area (Fig. 4(a), (b)). These components correlated positively with T-Nconcentration. They are derived from the outflow of fertilizer component. The runoffs of SO42- andNO3- were increased, because upland farming has been practiced on a large scale in the Tokachiarea. In the Nemuro area, the percentage of Na+ is comparable with the percentage of Ca2+ (Fig.
5(a), (b)). In general, most of the Na+ and Cl- are supplied from sea salt, and the ratio of Na+concentration to Cl- concentration in sea salt is 1:1.16. However, in comparison with sea salt, Na+concentration is higher than Cl- concentration in the Nemuro area. In addition, the Na+ in theNemuro area had no correlation with T-N concentration. From the above results, why the slope ofthe regression line of T-N concentration and EC in the Nemuro area is smaller than in the Tokachi
area, because the outflow of ionic components derived from the geological features of each arearather than agricultural origin affect the EC.

Fig. 4 Percentages of the ionic components in river water in Tokachi area

Fig. 5 Percentages of the ionic components in river water in Nemuro area
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CONCLUSION
The relationship between T-N concentration and EC was examined for two areas of eastern
Hokkaido with mutually different agricultural land use. Since there was a positive correlation, T-N
concentration in river water was able to be estimated from EC, and comparing the slope of theregression line, it is different in two areas. When the ion components of river water are compared
between the two areas, the percentages of SO42- and NO3- in the fertilizer component are higher inthe Tokachi area. In the Nemuro area, the outflow of ion components of geological origin affects
EC. From the above consideration, T-N concentration was able to be estimated based on EC;
however, it is necessary to consider the difference in the water quality components of each region.
ACKNOWLEDGEMENTS
We would like to express my gratitude to the research assistance provided by the students, theObihiro University of Agriculture and Veterinary Medicine.
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