IJERD – International Journal of Environmental and Rural Development (2018) 9-1

Research article
erd

Nonpoint Source Water Pollution in Rural Areas in theUpper Ayase River Basin of Saitama Prefecture in JapanKINGSHUK ROY*
College of Bioresource Sciences, Nihon University, Kanagawa, Japan
Email: roy.kingshuk@nihon-u.ac.jp
Received 27 February 2018

Accepted 10 May 2018(*Corresponding Author)

Abstract Nonpoint source pollution of water is an important environmental issue in Japan.
In this study, water samples were collected from 12 selected sites and 4 different periods at
the upper stretch of the Ayase River Basin located in Saitatma prefecture, and analyzed.
The results revealed that the water in the study area was in eutrophic condition and theextent of pollution varied in different ranges depending on the sites’ ambient conditions.
Moreover, the growing to harvesting period of crops (mainly mid-September to lateOctober) showed peak-values for nitrogen/phosphorus levels in water samples. The study
recommends that either a strict policy needs to be incorporated or much more care should
be taken to control pollution from agricultural runoffs.
Keywords water quality, nonpoint source pollution, agricultural water, Ayase River Basin

INTRODUCTION
While agriculture is the single largest user of global freshwater resources, surface water quality
detriment in agricultural watersheds is a major environmental concern in many parts of the world.
In Japan, efforts over the recent decades to address point source pollution from industrial andmunicipal sources have greatly improved the water quality. However, problems related to nonpoint
sources of pollution, e.g. agricultural sources still remain to be solved (Inoue, 2003; Roy, 2007,
Takeda et al., 2009). Depending on the land uses and management practices, different types ofnutrients, pesticides, fecal coliforms and sediments from agricultural activities are acknowledged
to be among the main causes of these problems (Kawashima, 1996; Takeuchi et at., 2005; Matsuno
et al., 2007; Kawamura and Ebise, 2014).
The Ayase River, which flows through the Saitama prefecture and Tokyo’s metropolitan city,
has been ranked as one of the country’s most polluted rivers while domestic and industrial effluenceswere detected as the prime causes for its pollution. The central government (Ministry of Land,
Infrastructure and Transport; MLIT) with the cooperation of local authorities/communities adopted
different measures to stop the inflows of domestic and industrial wastewater into the rivers which
resulted in the satisfactory recovery of the water quality in the Ayase River (MLIT, 2015). Also thegovernment policy (adopted in 1987) facilitated to control such point source pollution activities.
However, for nonpoint sources, although some monitoring guidelines and activities have beenlaunched in recent years by the central government and local authorities, there is no establishednational regulation/act or policy to stop the pollution caused mainly from agricultural effluents.
Therefore, individual consciousness and activities of farmers remain as the most dominating factors
to maintain the water quality in the public water bodies such as lakes, ponds, and rivers of a locality
in Japan. It is noted here that the amount of nitrogen/phosphorus input and pesticides per hectare of
agricultural lands in Japan is remarkably high compared to other developed countries in the world(Parris, 2011). Therefore, even the central government and the local authorities maintain the water
quality of the public waterbodies, such as sampling and monitoring works in the Ayase River are
carried out periodically by the respective bureaus; it could be difficult to determine the short-periodic(daily and weekly) load from every individual farmland and settlement to the river. However, toreduce the non-point source pollution, it is important to regular monitor the water quality at a microlevel in public waterbodies that reside next to agricultural settlements.
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This study focuses on the upper reach of the Ayase River Basin, which lies in the Saitama
prefecture and is a highly-dense and famous agricultural suburb. Along with other tributaries of the
Ayase River in the upper basin, the Minumadai irrigation canal, excavated in 1728, functions as
the trunk waterway to irrigate more than 12,000 hectares of farmland (Shibata, 1985). In short, theupper Ayase River Basin is a rural suburb characterized by a dense intermixtures of farmlands andfarmers’ residences, and this study analyzed the spatial (site-specific) and temporal (seasonal)
status of water quality linked to agricultural activities in the area. Accordingly, water samples fromthe mainstream and tributaries of the Ayase River as well as primary, secondary, and tertiary
canals of the Minumadai irrigation canal were collected periodically as the water passed throughdifferent agricultural settlements, and analyzed.
The objective of this study is to evaluate the spatial and temporal variations in the water
quality of the streams and canals in the upper Ayase River Basin as well as to identify different
variation patterns associated with either seasonal variations or pollution sources in the area.
METHODOLOGY
Study Area and Sampling
The length of the Ayase River is 47.6 km with a total basin area of 176 km2. In fact, agricultural
effluent is the main water source of the Ayase River, and the basin is characterized by a level toundulating topography. Average annual precipitation in the vicinity swings from 1100 to 1800 mm.
While most of the lands in the upper basin (present study area) are occupied mainly with paddy
fields, uplands, and farmers’ residences, the middle and the lower basins are full of residences,office-buildings and small- to medium-sized factories. The sampling sites were selected based on
preliminary surveys and information collected from the local government authorities. As seen in
Fig. 1, the study area (in the upper Ayase River Basin) overlaps the borders of three neighborwards, namely the Minuma ward, Midori ward, and Iwaki ward, all of which incorporate
agricultural fields with numerous surface inlets and outlets of the Ayase River and its tributaries aswell as the Minumadai irrigation canal and its diversions. Also in the study area, the lower reach of
the Fukasaku River joins the upstream of the Ayase River from the north (Fig. 1). Sampling of
surface water from these waterways was carried out from July 2014 to December 2014. The
average monthly precipitation was 143 mm in July, 100.5 mm in August, 71 mm in September,
300.5 mm in October, 74 mm in November and 45.5 mm in December (Japan Meteorological
Agency). Within this period, water samples were collected in daytime from 12 locations(waterways) at 4 different intervals: July 23 (1st sampling); September 19 (2nd sampling); October
26 (3rd sampling): and December 3 (4th sampling) in 2014. While the 1st sampling coveredseeding, sowing, and transplanting activities of paddy and upland crops and was labeled the“summer-irrigation” period, the 2nd sampling represented the peak-time of growing and fertilizer
use and was labeled the “fall-growth” period. Also, the 3rd sampling time was labeled the “fallharvest” period, and the 4th sampling time was labeled the “winter-fallow” period.
Samples of surface water were collected in polyethylene bottles, brought back to thelaboratory, and preserved and processed for major physico-chemical analyses while in-situ
measurements were carried out for several parameters. Specifically, the position of each samplingsite was recorded with a Global Positioning System receiver (Poke-Navi Map 21EX; Empex
Instruments Inc., Japan), the Dissolved Oxygen (DO: mg L-1) was measured at each site by using a
portable DO meter (YK-22DO; Lutron Co. Ltd.), and air and water temperatures (°C) were
measured by using a mercury thermometer (0-100°C). Table 1 summarizes the sampling details of
the survey.
Measurement and Analysis
The pH and Electrical Conductivity (EC: mS cm-1) of the water samples were measured with a pH
meter (Twin pH B-212; Horiba, Japan) and an EC meter (B-173; Horiba, Japan), respectively. TheⒸ ISERD

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Chemical Oxygen Demand (COD) of the water samples was measured by using a compact COD
analyzer (TNP-10 coupled with a TNP-HT heater; TOA-DKK Co., Japan). Moreover, theconcentrations of the major water-polluting ions (NO3⁻ , NO2⁻ , NH4+, PO4⁻ , SO42⁻ , Cl⁻ , Na+,
K+, Mg2+, and Ca2+) were measured with the ion-chromatography method (833 Basic IC plus ionchromatograph, 863 Compact Autosampler; Metrohm).

Fig. 1 Study area (the upper Ayase River Basin) showing the sampling sites ofagricultural water
Table 1 Detail of survey showing sampling period and positions in different sites of thestudy area, 2014
Sampling
location

Characteristics of the sampling site

Sampling position
LatitudeLongitude

1

Water intake point of the MIC*

2

MIC* water discharge outlet to the Ayase River

35° 41' 18.78" N
35° 56' 5.27" N

139° 45' 24.37" E
139° 40' 55.62" E

3

Joining point of the Fukasaku River35° 56' 23.03" N

139° 40' 47.49" E4
5Upper reach of the Ayase River/OSG* irrigation canal

35° 56' 30.89" N

139° 40' 56.13" E

OSG* drainage canal outlet

35° 56' 57.20" N

139° 41' 34.15" E

6Drainage outlet of OSG and others to the Ayase River **35° 55' 47.20" N

139° 41' 31.44" E

7

Drainage outlet to the Ayase River (mainly uplands)

35° 55' 32.24" N

139° 41' 57.06" E

8Drainage outlet to the Ayase River (near a factory)

35° 55' 11.7" N

139° 42' 1.42" E

9OSG* drainage canal final outlet

35° 55' 10.4" N

139° 41' 58.89" E

10Drainage outlet to the Ayase River (paddy fields)

35° 54' 55.5" N

139° 42' 8.15" E

11Lower reach of the Ayase River35° 54' 59.42" N

139° 42' 6.75" E

12Discharges mixed from locations (sampling sites) 10 and 11

35° 54' 42.89" N

139° 42' 22.54" E

Notes: * MIC indicates the Minumadai Irrigation Canal, and OSG the Ohashi Sluice Gate.
** In this sampling site, discharges from other outlets mixed with the discharges from the Ohashi Sluice Gatedrainage canal.

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RESULTS AND DISCUSSION
Spatio-temporal Variation in Water Quality

30

8.5

25

8

20

7.5

0.9
0.8

15

7

10

6.5

5

6

0.7
EC (mS cm-1 )pH

Water temperature (℃)

The average values of the parameters measured at the 12 selected sampling sites in the upper Ayase
River Basin are summarized in Fig. 2 (2.1 to 2.15). The temperature of water samples in all themeasured periods showed no extreme variation from the average value at the time of collection,
which decreased with the seasonal ambient temperature. However, the pH value at sites 1, 4, and 9(Fig. 2.2 and Table 1) showed little variation (alkaline) in the fall-growth and fall-harvest periods.
For EC, sampling site 7 (upland outlet; Fig. 2.3) particularly showed larger values (26 to 81 mS cm-1)
in all sampling periods while sampling site 1 (Minumadai Irrigation Canal: MIC intake) showed
extreme temporal fluctuation compared to the other sites (0.18 to 73 mS cm-1). Fig. 2.4 shows thatthe DO values in the sites increased gradually from the summer-irrigation to winter-fallow period.
Since DO is inversely dependent on temperature, the tendency is natural. With different ranges ofspatio-temporal fluctuations, the water in most of the sampled sites showed increased DO levels.
The samplings were carried out in daytime and under eutrophic conditions; DO greatly increases
during the day, but is greatly reduced after dark. The tendency of elevated COD (above 10 mg L-1)
at several sites, particularly at site 7 (upland outlet) and site 8 (factory outlet) in the fall-harvest
period, site 10 (paddy field outlet) and site 11 (lower reach of the Ayase) in the summer- irrigation
period indicated the water bodies had suffered some kind of deterioration due to the discharges of
effluents (see Fig. 2.5). Figs. 2.6, 2.7 and 2.8 show the forms of nitrogen (NO3⁻ , NO2⁻ , andNH4+)-effects to the water quality, all of which were caused by runoffs from fertilized lands.

0.6
0.5
0.4
0.3
0.2
0.1

Summerirrigation

Fallgrowth

Fallharvest

Winterfallow

Summerirrigation

Sampling period

Fallgrowth

Fallharvest

0

Winterfallow

Summerirrigation

Sampling period

Fallgrowth

Fallharvest

Winterfallow

Sampling period

Summerirrigation

Fallgrowth

Fallharvest

Sampling period

Winterfallow

20
18
16
14
12
10
8
6
4
2
0

Summerirrigation

3
Concentration (mg L-1 )

15
14
13
12
11
10
9
8
7
6
5

Concentration (mg L-1 )Concentration (mg L-1 )Fig. 2.1 Periodic variation in Fig. 2.2 Periodic variation in Fig. 2.3 Periodic variation intemperature
pH
EC

Fallgrowth

Fallharvest

Sampling period

Winterfallow

2.5
2
1.5
1
0.5
0

Summerirrigation

Fallgrowth

Fallharvest

Winterfallow

Sampling period

Fig. 2.4 Periodic variation in Fig. 2.5 Periodic variation in Fig. 2.6 Periodic variation in
DO
COD
NO3⁻

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0.18

8

0.17

0.3
0.25
0.2
0.15
0.1
0.05

Summerirrigation

7
6
5
4
3
2
1

Fallgrowth

Fallharvest

0

Winterfallow

Summerirrigation

Sampling period

Fallgrowth

Fallharvest

Winterfallow

50
45
40
35
30
25
20
15
10
5
0

Summerirrigation

Sampling period

0.12
0.11

Summerirrigation

Fallgrowth

Fallharvest

8
6
4
2

Winterfallow

50
45
40
35
30
25
20
15
10
5
0

Summerirrigation

Winterfallow

Sampling period

Fig. 2.13 Periodic variation in
K+

70
60

12
10
8
6
4
2
Fallgrowth

Fallharvest

Winterfallow

Fallgrowth

Fallharvest

Winterfallow

Fig. 2.12 Periodic variation inNa+

14

Summerirrigation

Fallharvest

Sampling period

160FallgrowthFig. 2.9 Periodic variation in
PO4⁻

Concentration (mg L-1 )Concentration (mg L-1 )Concentration (mg L-1 )10

Fall-growth Fall-harvest

0.13

Sampling period

12

Summerirrigation

0.14

Sampling period

Fig. 2.10 Periodic variation in Fig. 2.11 Periodic variation in
SO42⁻
Cl⁻

0

0.15

0.1

Winterfallow

Fig. 2.8 Periodic variation in
NH4+

Concentration (mg L-1 )Concentration (mg L-1 )Summerirrigation

0.16

Sampling period

Fig. 2.7 Periodic variation in
NO2⁻
100
90
80
70
60
50
40
30
20
10
0

Fall-growth Fall-harvest

Concentration (mg L-1 )0

Concentration (mg L-1 )

0.4
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Concentration (mg L-1 )Concentration (mg L-1 )IJERD – International Journal of Environmental and Rural Development (2018) 9-1

Winterfallow

50
40
30
20
10
0

Summerirrigation

Fallgrowth

Fallharvest

Winterfallow

Sampling period

Sampling period

Fig. 2.14 Periodic variation in
Mg2+

Fig. 2.15 Periodic variation in
Ca2+

Fig. 2 (2.1 to 2.15) Periodic variation in physico-chemical parameters of water at 12 selected
sampling locations(sites) in the upper reach of the Ayase River Basin in
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Among these items, nitrates (NO3⁻ ), which have an attraction for soil particles, dissolve inwater more readily than phosphates (PO4⁻ ) and are a better indicator of possible non-point
pollution of water while the oxidized/temporary ammonium (NH4+) and nitrite (NO2⁻ ) forms are
considerably more toxic. All sites except 4, 7, and 9 showed elevated amounts of nitrates in water
throughout the samplings (Fig. 2.6). In addition, the fall-growth season showed elevated amountsof nitrites in water samples at site 5 (Ohashi Sluice Gate: OSG outlet) and site 6 (outlet of OSG andothers) while site 7 (upland outlet) showed elevated amounts of ammonium. Fig. 2.9 shows thetraceable amount of orthophosphate (the detection limit of phosphate is 0.1 mg L-1 of the ionchromatograph used in the measurement) produced by runoffs at sites 3, 4, 6, 11 and 12 from thesummer-irrigation to fall-harvest period. Fig. 2.10 presents the distribution of sulfate (SO42⁻ ) at
different sites where site 7 (upland outlet) and site 8 (factory outlet) showed elevated amounts inthe fall-harvest and winter-fallow periods. Sulfate is an inorganic anionic substance that forms salts
with sodium, potassium, magnesium and other cations. Both sites 7 and 9 along with site 5 (OSG
outlet) showed elevated amounts of cations (Na+, K+, Mg2+, and Ca2+) between the fall-growth andwinter-fallow periods (see Fig. 2.12 to 2.15). Increases in chloride (Cl⁻ ) loads from the summerirrigation period to the fall growth period (Fig. 2.11) might be related to variety of factors such as
fertilizers and agricultural chemicals in irrigation water used in different fields. In particular, site 5(OSG outlet) showed elevated amount of chloride during the fall-growth period.
Analysis from the Existing Water Quality Standard Perspective
The sampling sites included multiple inflows and outflows of the Ayase River, and some of these
inflows and outflows were used as irrigation water sources. Lately, the irrigated water has beendischarged to the mainstream directly or through other diversion canals. In Japan, since there is no
regulatory act such as the Total Maximum Daily Load (TMDL) in USA, the status of agricultural
water quality in the studied area can only be judged from the country’s existing standards for
irrigation water quality in paddy fields (MAFF, 2009). On that basis, pH values at sites 1, 4 and 9
in different sampling periods exceeded the recommended limit (6.0 to 7.5). Regarding EC, thevalues in most of the sites exceeded the limit (below 0.3 mS cm-1) from the fall-growth to winterfallow period. DO with a spatio-temporal average value of 10.4 mg L-1 was much higher than theprescribed limit (above 5 mg L-1), and COD values in several sites and periods exceeded therecommended value (below 6 m L-1). For paddy field water, the recommended amount for total
nitrogen (T-N) is less than 1 mg L-1; however, only the nitrate-part in most of the samples exceeded
the limit. The measured values clearly indicated that the water flowing through the canals andstreams in the study area were oversupplied with nutrients, which is called eutrophication.
At the same time, the country has a strict regulation for the environmental water quality in ariver, and therefore, the water quality in a river is usually judged based on the country’s
environmental standard (MOE, 2015). Both standards share some common items such as pH, EC,
DO, COD, T-N and several heavy metal constituents (As, Zn and Cu). However, the latter standard
is stricter and is similar to other global standards of developed countries. For example, in Japan,
public waterbodies such as lakes, ponds, and rivers are classified into several groups, and thehealth-hazard parameters (Cd, Pb, As, PCBs, Hg etc.) are monitored regularly by responsible
authorities. However, the status of agricultural water is dependent completely upon the farmers’
personal attitudes and practices. Since many agricultural canals are directly or indirectly connectedwith public rivers, keeping the agricultural waterbodies healthy is a prerequisite of maintaining theenvironmental health of rivers and seas.
CONCLUSION
The upper reach of the Ayase River Basin is a typical agriculture-dominated suburb and the Ayase
River itself is an agricultural effluent-based stream. In this study, multiple sites were selected on
major waterways for more complete characterization and to allow examination of possible impacts
related to various land use practices. Results of this study reveal that, in general, mainstream waterⒸ ISERD

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quality (the Ayase River) as well as the discharge canals (upper stretch of the Ayase basin) is
linked to the ambient land-use practices, and agricultural land flushes more water-polluting agents
into the canals and streams between the growing and harvesting seasons, which is early September
to late October in the study area.
The control of water pollution from agriculture clearly needs to occur within broader
integrated water resource management frameworks that ensure linked land water use together withre-use management. In addition, sustained regulation and water quality monitoring activities at all
scales are essential. The findings of this paper provides baseline information and existing status ofa rural suburb with agriculture-derived water-pollution, which could be valuable to the design offuture participatory (individual and community-based) and policy-making strategies to stop
nonpoint source pollution in waterbodies.
ACKNOWLEDGEMENTS
The author wishes to thank Naoki Shimamura and Kento Hara, two graduates from the author’s lab
at Nihon University for their support in carrying out the samplings and analyses. Dr. Sadao
Nagasaka, an associate professor of Nihon University assisted in ion-chromatography analysis. The
author also acknowledges the anonymous referees of the journal for their valuable comments andsuggestions.
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