IJERD – International Journal of Environmental and Rural Development (2013) 4-1

Research articleerd

I
The Difference of AgriculturalLand Use in Watersheds and7d the River Water Quality
Long Term Fluctuation onent

YURI YAMAZAKI

4Obihiro University of Agriculture and Veterinary
Medicine, Hokkaido, JapanTOSHIMI MUNEOKA*.
72

Obihiro University of Agriculture and Veterinary Medicine, Hokkaido, Japanw
Email: muneoka@obihiro.ac.jp
or
SACHIYO WAKOU
dIbaraki Prefectural Government, Ibaraki, Japans

MOTOKO SHIMURA
National Agriculture and Food Research Organization, Hiroshima, JapanKUNIHIKO YOSHINO
Faculty of Engineering, Information and Systems Division of Policy and Planning Sciences,
University of Tsukuba, Ibaraki, JapanOSAMU TSUJI
Obihiro University of Agriculture and Veterinary Medicine, Hokkaido, JapanTOSHIO TABUCHI
Former professor of the University of Tokyo, Tokyo, Japan
Received 15 December 2012

Accepted 30 January 2013(*Corresponding Author)

Abstract This study was conducted to determine the relationship between thecharacteristics of fluctuations in river water quality at the normal water level and theproportion of agricultural land in watersheds of Eastern Hokkaido that have different
agricultural land use, based on the 20 years observations. The investigations were carriedout during late August to early September in 1992, 2003 to 2006, and 2012 at 35
watersheds in two areas, and NO3-N, EC of river water and river discharge were measured.
The Tokachi area (24 watersheds) is located in the northwestern part of the Tokachi
General Subprefectural Bureau, the main land uses are upland and dairy farming. The
Nemuro area (11 watersheds) is located in the western part of the Nemuro SubprefecturalBureau, the main land use is large-scale dairy farming. In the 20 years since 1992, NO3-Nconcentration and EC have shown increasing tendency in some of the investigated riverwatersheds. The river water quality in some watersheds investigated in 2004, immediately
before the full implementation of “The Law on   Animal   Waste   Regulation”, greatly
differed from the observation results of several years before and after 2004. When the twoareas had the same proportion of agricultural land, the NO3-N concentration in the riverwater tended to be higher in Tokachi area than in Nemuro area. This is attributed to theproportion of upland fields, which require large inputs of chemical fertilizer in the Tokachiarea. EC, however, tended to be high in the Nemuro area, even for watersheds with similar
proportion of agricultural land. This suggests that the river water in the Nemuro area
contains many materials of geological origin, in addition to containing NO3−.
Keywords NO3-N concentration, EC value, agricultural land use, long-term fluctuationⒸ ISERD152

IJERD – International Journal of Environmental and Rural Development (2013) 4-1

INTRODUCTION
Large-scale farming under harsh climatic conditions has long prospered in Eastern Hokkaido,
whose natural environment differs from those of other Asian monsoons regions. In recent years,
water contamination including nitrate pollution of river water and groundwater has been pointedout (Tabuchi et al., 1995; Matsumoto and Tou, 2006).
In the Tokachi district, large-scale upland and dairy farming were established early years
before World War II. In the Kushiro and Nemuro districts, however, agricultural land has expanded
only   since   the   1960’s,   with the large-scale reclamation of wilderness to grassland. As the landdevelopment expands, the varieties of cultivated crops have been reduced and agricultural land use
has been unified for grassland. Several studies have conducted to determine the influence of thedrastic land use changes on the river water quality there  since  the  1990’s (Kuramochi et al., 1994;
Nagasawa et al., 1995; Inoue et al., 1999; Muneoka et al., 2001). In the Tokachi district, however,studies on agricultural land use and river water quality have only just begun (Okazawa et al., 2011;
Muneoka et al., 2012).
Tabuchi et al., (1995) conducted investigations of the river water quality at the normal waterlevel in watersheds of an extensive area of Eastern Hokkaido in the summer of 1992. They had
shown that there was a positive correlation between the nitrate nitrogen concentration in river waterand the extent of agricultural land use in each investigated area. Based on this study, the authors
have conducted investigations in the Tokachi and Nemuro areas during the same periods at normal
water level. There has been no similar research anywhere in which to weigh the river water quality
in two large areas with the different agricultural land use over a long period.
Thus, the objective of this study was to evaluate the impact from the different agricultural land
use of watersheds on the river water quality at the normal water level, based on a 20-year
observation.
METHODOLOGY
The outline of this study sites are shown in Fig. 1. The Tokachi area, which consists of 24
watersheds on the Tokachi River system and the Shikaribetsu River system (No. 1 to 24), is locatedin the northwestern part of the Tokachi General Subprefectural Bureau, and it is an area withupland and dairy farming. The Nemuro area, which consists of 11 watersheds on the Shibetsu Riversystem, the Tokotan River system and the Nishibetsu River system (A to K), is located in thewestern part of the Nemuro Subprefectural Bureau, and it is an area mainly of dairy farming. In
both of these areas, large-scale farming has been operated, and there have been no considerable
changes in agricultural land use in either area since 1985.
For the years 1981 to 2010, the annual mean air temperature and the yearly precipitation were5.9 ℃ and 840.7 mm at Komaba in the Tokachi area, and 5.4 ℃ and 1158.0 mm at Nakashibetsu in
the vicinity of the Nemuro area. Both areas have a relatively cold climate with less rainfall.
The investigation of the river water quality was conducted at the normal water level at 35
sampling points. Electric conductivity (EC) and water temperature were measured at sampling
points. And discharge was also measured on the rivers in small watersheds (varied between 22 and25 by year). The indices and the methods used for water quality analysis varied with each year,nitrate nitrogen (NO3-N) concentration and EC as indices in this study. The investigations werecarried out during late August to early September in 1992, 2003 to 2006, and 2012.
The GIS software application ArcGIS Desktop (Ver. 10, ESRI) was used for analyzing landuse  in  the  study  sites.  The  data  were  “rivers”,  ”watershed boundaries”  and “detailed land use mesh”
from digital national information that used to determine the proportion of agricultural land inwatersheds. The detailed land use mesh (100 m × 100 m) shows 11 types of land uses; however, weredefined the mesh into the three items of “agricultural  land”, “forest” and “other”. The proportionof agricultural land was determined for each watershed by overlaying the watershed map created
for the sampling points on the detailed land use mesh.

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IJERD – International Journal of Environmental and Rural Development (2013) 4-1

Sampling
River name
Point

NBridge nameArea
Land use ( %)(km2 ) Agricultural land Forest

Tokachi area

Hokkaido

Nemuro Area

Tokachi Area
Shibetsu River

Tokotan River

Shikaribesu River
Tokachi River

Nishibetsu River
Agricultural landForestOtherRiver
Sampling point12345678910111213
14
15
16
17
18
19
20
21
22
23
24

TokachiOojika632
PenkenaiPennai23
Penkenikorbetsu Penkenikorobetsu
48
Penkenikoro
Minamiiwamatsu
72
TokachiNakajima
1798
Shikaribetsu
Urimaku
217
Sikanosawa
Kikuchi5Kamihoronai
Kamihoronai
3
Shikaribetsu
Momiji256
Minami1sen
Nakashikakann2gou 13
Iketo
Minamisawa
9
Pankebibaushi Kousui
27
Urimaku( no bridge )9Poronai( no bridge )3
Urimaku
Mutsu
49
Penkeutorei
Honnmaki
3Pankeutorei( no name )5Pankeutorei
Komadome
17
Penkechin
Okuyama26
PonchinKamimaki
13Penkechin
Isami
63
Pankechin
Sinnei
10Pankechin
Taneuma
72
Shikaribetu
Kunimi
667

1022
21483
88
1372
95
90
1390
58
88
93
65
2275
4652
72
48

94
98
96
97
70
91
1312
81
172
766
732
11
625
49
18
33
32
1545

4
732
3
22
32
49
81
1054
73

71
81
57
91
72
64
46
1460
32
21

Nemuro area
A
B
C
D
E
F
G
H
I
JK

Kanjiushi
KenekaKenekaShibetsu
Shibetsu
Masu
Masu
TokotanNishibetsu
Nishibetsu
Pononnebetsu

Yourouushi
MinoriHakuyou
Nagori
Kamisibetu
Masukawa
KenebetsuHoutoku
Kousai
Nishisyunnbetsu
Akashi

1141825482
1028121914919Fig. 1 Outline of the Tokachi and Nemuro areas
RESULTS AND DISCUSSION
The characteristics of long-term fluctuations at the 35 locations in the two areas, which areindicated by using the NO3-N concentration and the EC of the river water as indices, are shown inFig. 2.
The NO3-N concentration in 1992 were <0.1 to 3.9 mg/L for Tokachi area and <0.1 to 2.0
mg/L for Nemuro area. In and after 2003, a tendency of year-on-year increase in the maximum
value of NO3-N concentration was observed for both areas. The maximum NO3-N concentration
was 7.2 mg/L in Tokachi area and 2.6 mg/L in Nemuro area.
The tendency of increase in NO3-N concentration was noticeable at four sampling points inTokachi area (No. 10, 11, 12 and 17) and at three sampling points in Nemuro area (G, H and K).
These seven points were distinctive that they were small watersheds of 5 to 28 km2 in area and they
had high proportions of agricultural land (49 to 95%). It is worth noting that the NO3-N
concentration showed drastic decreases in 2004 at six points (No. 7, 8, 14, 15, 23 and 24) inTokachi area and at three points (C, G and J) in Nemuro area, irrespective of the watershed size andthe proportion of agricultural land (Fig.2 (a), (b)).
The EC in the two areas in 1992 were 5.1 to 23.3 mS/m in Tokachi area and 5.8 to 18.6 mS/min Nemuro area. However, the maximum values of EC tended to show slight increases in both areasin the 20-year period. The maximum EC was 26.8 mS/m in Tokachi area and 20.4 mS/m inNemuro area for the period from 2003 to 2012. EC showed drastic increases at one point (No. 8) inTokachi area and at three points (D, E and G) in Nemuro area in 2004 (Fig.2 (c), (d)).
Based on these data, it can be assumed that the fluctuations in river water quality, which areindicated by the decrease in NO3-N and the increase in EC in 2004, reflect the changes in thebehavior of farmers, including the management of livestock manure, that resulted from the full
implementation of “The Law on  Animal  Waste  Regulation” in November 2004.

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8.0

24.0

2'3(b) Nemuro area(a) Tokachi area

3'
4NO3-N (mg/L)

NO3-N (mg/L)

6.0

4.0

2.0

4'

3.0

55'
66'

2.0

7
7'
88'
9

1.0

9'
10
10'

0.0

110.0
1992

2003

2004

2005

2006

2012

11'

1992

2003

2004

Investigated year

2005

2006

2012

Investigated year

1212'
1313'
14

Tendency of increase

14'

Drastic decreases in 2004

15
15'
1630.016'30.0(c) Tokachi area

1717'(d) Nemuro area

1818'

20.0

EC (mS/m)

EC (mS/m)1910.0

19'

20.0

2020'
2121'
2222'

10.0

2323'
2424'

0.00.0
1992

2003

2004

2005

2006

2012

1992

Investigated year

2003

2004

2005

2006

2012

Investigated year
Drastic increases in 2004

Fig. 2 Long-term fluctuation on the NO3-N concentration and the EC of the river waterin the Tokachi and Nemuro areas
Fig. 3 shows the regression lines and the results of calculation for the coefficients ofcorrelation r, which indicate the relationship between the NO3-N concentration of the river waterand the proportion of agricultural land and that between the EC of the river water and theproportion of agricultural land in watersheds at the two areas.
From the relationship between the NO3-N concentration (Y) and the proportion of agriculturalland (X) in the watershed is expressed as Y = a X. The slopes “a”,  which  indicates impact factor(IF) values, were 0.030 to 0.055 in Tokachi area and 0.020 to 0.031 in Nemuro area during theperiod. When two watersheds, one from the Tokachi area and the other from Nemuro area, that had
similar proportions of agricultural land were compared, the NO3-N concentration in the river water
tended to be higher in Tokachi area. In the Tokachi area, land use was for dairy farming and thefarming of various upland crops. In addition to livestock manure, the loading source includes
chemical fertilizers that were applied in large quantities to the upland fields. It is assumed that theuse of chemical fertilizers contributed to the higher concentration of nitrogen in river water.
From the relationship between the EC of the river water (Y) and the proportion of agriculturalland (X) in the watershed is expressed as Y = a` X + b`. The slopes “a`” were 0.102 to 0.150 inTokachi area and 0.119 to 0.149 in Nemuro area during the period. The intercepts “b`” of the areas
were 6.11 to 6.65 for Tokachi area and 6.81 to 8.78 for Nemuro area. As shown above, when thewatersheds in Tokachi area had the same proportion of agricultural land as that in the Nemuro area,Ⓒ ISERD155

IJERD – International Journal of Environmental and Rural Development (2013) 4-1

the EC of the river water tended to be higher in Nemuro area. It is assumed that the river water inthe Nemuro area contains considerable amount of dissolved ions derived from geologic material, inaddition to the nitrate ions (NO3-) from farmland.
When the coefficient of correlation r was examined by using NO3-N concentration as theindex, r for Tokachi area was 0.65※※ to 0.89※※, and r for the Nemuro area was 0.85※※ to 0.97※※.
When EC was used as the index, r for Tokachi area was 0.70※※ to 0.82※※ and r for Nemuro area
was 0.77※※to 0.89※※. As described above, r for Nemuro area was constantly higher during theperiod. A factor contributing to this result could be that the agricultural land in Nemuro area isunified into grassland, whereas the agricultural land uses in Tokachi area are more diverse.
30.0(a) NO3-N (2012)

6.0
4.0

EC (mS/m)

NO3-N (mg/L)

8.0

Y = 0.049 X
r = 0.84 ※※20.0(b) EC (2012)

Y = 0.134 X + 7.88
r = 0.86 ※※

10.0

2.0

Y = 0.132 X + 6.65
r = 0.75 ※※Y = 0.029 X
r = 0.97 ※※0.000.0020406080
100
Proportion of agricultural land (%)

20406080
100
Proportion of agricultural land (%)

Tokachi area
NO3-N (mg/L) [ Y = a X ]Investigatedyear

Nemuro area

EC (mS/m) [ Y = a` X + b` ]Tokachi areaar

Nemuro areaar

1992

0.031

0.88 ※※

0.020

0.85 ※※

0.111

6.29 0.76 ※※0.127

7.09 0.86 ※※

2003

0.036

0.84 ※※

0.022

0.96 ※※

0.102

6.39 0.70 ※※0.124

6.81 0.88 ※※

2004

0.030

0.65

※※

0.022

0.93

※※

0.133

6.63 0.77

※※

0.119

8.78 0.77 ※※

2005

0.051

0.89 ※※

0.024

0.95 ※※

0.150

6.11 0.80 ※※

0.132

7.73 0.84 ※※

2006

0.055

0.89 ※※

0.031

0.96 ※※

0.148

6.28 0.82 ※※0.149

6.85 0.89 ※※

2012

0.049

0.84 ※※

0.029

0.97 ※※

0.132

6.65 0.75 ※※

0.134

7.88 0.86 ※※ (a), (b)a`Tokachi areab`ra`

Nemuro areab`rN.B

significance of 1%※※

Fig. 3 Relationship between the NO3-N, the EC of the river water and the proportionof agricultural land in watersheds at the Tokachi and Nemuro areas
CONCLUSION
Fluctuations in river water quality at the normal water level were investigated during a period of 20years at 35 sampling points in two areas in Eastern Hokkaido, with a focus on the differences inagricultural land use between the watersheds. This study evaluated that, in the Tokachi area,upland-field-derived NO3-N constantly flowed into the rivers in high concentrations at the normalwater level. As a result of the long-term observation, the concentration of river water quality hasn’t  drastically decreased in spite of the full implementation of “The Law on  Animal  Waste  Regulation”
in November 2004. Toward improving the river water quality in extensive agricultural areas fromthe standpoint of conserving the water environment, it is necessary to evaluate and review themanagement of livestock manure by individual farms as well as examining the relative positions offarmland and rivers and the land in between these.
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IJERD – International Journal of Environmental and Rural Development (2013) 4-1

ACKNOWLEDGEMENTS
We would like to express my gratitude to the staffs, the University of Tokyo. The authors are also
grateful for the research assistance provided by the students, the University of Tokyo and Obihiro
University of Agriculture and Veterinary Medicine.
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