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Monitoring and Management of Irrigation Water Quality in Japan
Yutaka Matsuno
Department of Environmental Management,
School of Agriculture, Kinki University
Japan, 2010-04-16

Abstract

This paper primarily discusses the water quality standard of Japan, the development of water quality monitoring program for irrigation and drainage water, the water quality management of agricultural drainage, and the case of Hachiro-Kata, Japan for water quality monitoring and management. Japan's Environmental Water Quality Standard for water pollutants was established to achieve and maintain the levels of water quality for the healthy environment of public waters. In 2007, the Ministry of Agriculture, Forestry, and Fisheries (MAFF) introduced guidelines for agricultural water quality monitoring. The guidelines contain water quality for crop production, the aquatic environment of irrigation and drainage canals and reservoirs, and concerns for sediment outflow from paddy fields. Physical interventions for water quality improvement are physical, chemical, and biological treatments; sediment removal; aeration, dilution and filtration; and change of canal alignment. Other management interventions include irrigation scheduling, land preparation, fertilizer and pesticide management, drainage control, and recycling of irrigation water. Hachiro-Kata located in Akita Prefecture exemplifies a case where water quality monitoring and management were well established. The program's activities were intended to attain sustainable development of agriculture and fisheries and improve the natural environment of the rural community. With these objectives, major activities implemented include use of less water for land preparation to reduce sediment flow to the lake; improved management of tidal gate and pumps to enhance the circulation of water within the lake; biological treatment of drainage water; establishment of protected zone for constructed wetland; modernization of sewage system and expansion of the sewage network; and cultivation of foreign fish species to remove nutrients in the lake and use it as organic fertilizer. In 2007, these activities resulted in reduced incidence of algal bloom in the lake and improved water quality. The participation of farmers and local communities in the program and the seminars and workshops for residents and school children contributed in the improvement of the lake environment.

Key words: environmental water quality standards, agricultural water quality, Japan

Introduction

Paddy rice is the major crop in monsoon Asia and is often perceived as the largest water consumer in basins. Since hydrological impact of paddy irrigation is significant in this region, the water quality of paddy irrigation and drainage becomes an important issue in water resources management in Asia amidst increasing concern for the environment.

Japan experienced rapid economic growth and industrialization since the early 1960s. Agricultural land in 2005 was approximately 4.7 million ha, more than half of which were paddy fields. The average land size of a farm household was approximately 1.8 ha. With urbanization and industrialization, the demand for domestic and industrial water has increased. However, the total requirement for agricultural water has not decreased in proportion to the reduced farmland area. The urban sprawl resulted in meeting the requirement for a certain volume of canal water flow to reach scattered paddy fields and a bigger unit of water requirement because of the increased multi-cropping patterns in agricultural lands. As such, the agricultural sector remains the largest water consumer (Matsuno et al. 2007). Consequently, because of this mixture of land uses in many peri-urban areas of Japan, domestic and industrial wastewater flows into irrigation and drainage canals affecting crop production and the environment in downstream water bodies.

Also, the importation of vast amounts of food stuff in the country makes the nutrient balance of Japan overloaded. This results in increased eutrophication in many stagnant water bodies. It was estimated that 1,090,000 tons of nitrogen and 117,000 tons of phosphorus were annually loaded into water bodies in Japan (Takeda 2001).

This paper describes: 1) the water quality standard of Japan; 2) the development of water quality monitoring program for irrigation and drainage water; 3) the water quality management of agricultural drainage; and 4) a case of Hachirou-Kata, Japan for water quality monitoring and management.

Water Quality Standard and Status of Water Quality in Japan

Environmental Water Quality Standard was established decades ago in Japan, and since then has been revised several times. Environmental Water Quality Standard for water pollutants aims to achieve and maintain the levels of water quality for the healthy environment of public waters. The standards have two major goals: protection of human health, and conservation of the environment. The first goal is supposed to be achieved by setting uniform national standards for all public waters. To meet the second goal, rivers, lakes, reservoirs, and coastal waters were classified according to water usage, and the standard values for each class were established (Ministry of the Environment 2008). The Japanese government has been implementing nationwide water quality-monitoring program in major water bodies to assess the state of water qualities with respect to the guidelines.

Fig. 1(1127) shows a time series of the rate of non-compliance with the water quality standards for human health. The rates for heavy metals were significantly reduced after the 1970s owing to strict enforcement of the regulation by the government and increased public concern for industrial pollution during the early stage of rapid economic growth.

Table 1(1263) shows an example of the Environmental Quality Standards for conservation of the environment, and Table 2(1481) shows the rate of compliance to the Environmental Quality Standards for the environmental conservation for fiscal year 2004.

As shown in Table 2(1481), half of lakes and reservoirs did not meet the standard concentrations, while almost 90% of river water quality was satisfied. This indicates the need for improving water quality of stagnant water bodies in Japan, and better understanding and management of material loadings in lakes and reservoir.

Characteristics of Agricultural Water Quality

Agricultural practices cause downstream water quality problems because of excessive application of pesticides, nitrogen leaching, phosphorus, and sediments that flow through the water system. However, changes in water quality with paddy rice production may be advantageous, depending on the quality of the incoming water, the irrigation and drainage system, and on fertilizer and pesticide management (Comprehensive Assessment of Water Management in Agriculture 2007). In some instances, a paddy field or artificial wetland may be constructed, such that water is purified if the incoming irrigation water contains high concentrations of nitrogen and phosphorus. Tabuchi (1998) reported that natural water purification occurred when the nitrogen concentration in the inflow was 2-3 mg/L or greater, and conversely, the nitrogen concentration in the flooded water increased when the concentration was lower than 2-3 mg/L. The flooding condition of a paddy field increases denitrification (Yamaoka et al. 2003) and the volcanic ash soil, which is the major soil in many paddy fields of Japan, readily absorbs phosphorus (Shiratani et al. 2003, Takeda and Fukushima 2004). The denitrification rate of paddy fields is reported to be between 0.02 and 0.8 g/m2 per day (Tabuchi 1998).

On the other hand, nitrate pollution of groundwater under paddy fields exceeded the 10 mg/L limit for safe drinking water only when highly fertilized vegetables were included in the cropping system in the Philippines (Bouman, Castañeda, and Bhuiyan 2002). Even though the input of water is less than that for paddy rice system, upland cropping systems have high risk of becoming sources of groundwater pollution because of the soil's aerobic condition, such that nitrogen readily penetrates into the soils in the form of nitrate. Also, chemical input to non-paddy land is normally much higher than that for paddy land. Table 3(1306) shows the fertilizer and pesticide inputs for various cultivation systems.

Development of Monitoring Program for Agricultural Water Quality

Any water quality monitoring program must have well-defined objectives and well-developed systems to achieve the objectives. Principal elements of the monitoring may be the following (UNEP/ WHO 1996):

  • Describing water resources and identifying actual and emerging problems of water pollution;
  • Formulating plans and setting priorities for water quality management;
  • Developing and implementing water quality management programs; and
  • Evaluating the effectiveness of management actions.

There are basically two main concerns for agricultural water quality: 1) quality of irrigation water going to agricultural land; and 2) quality of water draining out of agricultural land. The former may involve monitoring the quality of water sources and domestic and/industrial effluents coming into irrigation water, and the latter may involve monitoring the quality of downstream water bodies such as lakes and reservoirs.

For the establishment of water quality monitoring program, the following should be considered:

  • Parameters (including non-quality parameters);
  • Sampling points;
  • Sampling frequency and timing;
  • Method of analysis;
  • Transport;
  • Human resources;
  • Use and management of the data;
  • Quality assurance; and
  • Budget.

As an example of parameters for irrigation water quality monitoring, Table 4(1316) shows irrigation water quality guidelines for paddy rice system in Japan. It was formulated in 1969 and since then has not been officially revised. Heavy metals are, of course, concerns for the health of consumers. Nitrogen concentration is also of concern due to a potential of over nutrition that may result in productivity decline and falling down of rice straw before harvest. Professionals believe that the guideline value for nitrogen of 1 mg/L is not realistic. Most nitrogen concentrations in Japan's irrigation water exceed this value, and many believe that up to 3 mg/L is acceptable (Msawa 1999).

The Ministry of Agriculture, Forestry, and Fisheries (MAFF) of Japan recently introduced the guidelines for water quality monitoring (Tables 4 and 5). The guidelines contain the water quality for crop production as well as the aquatic environment of irrigation and drainage canals and reservoirs. In addition, there has been increased concern for sediments outflow from paddy fields through the drainage, especially during land preparation period.

Management Options for Water Quality Improvement

Developing the strategy for water quality improvement depends on the results of water quality monitoring. The options for intervention can be categorized as follows:

  • Physical intervention
  • Treatment (physical, chemical, biological), sediment removal, aeration, dilution, filtration, change of canal alignment; and
  • Management alternation
  • Irrigation scheduling, land preparation, fertilizer and pesticide management, drainage control, recycling of irrigation water.

Several options can be combined for effective intervention, and the selection depends on parameters concerned, target level of improvement, resource availability, and others. Normally, improvement through changes in agricultural management requires less cost, but needs strong commitment and cooperation of farmers and local community. The effectiveness of interventions should be evaluated and continuously monitored after introducing the intervention.

Hachiro-Kata As an Example

The case of Hachiro-Kata is one of the well-established water quality monitoring and management programs in Japan. Hachiro-Kata, located in the Akita Prefecture, was a brackish water lagoon of 22,024 ha that was reclaimed in 1966 to create 12,792 ha of agricultural land mainly for paddy rice production. The unreclaimed area of 4732 ha around the reclaimed land became a freshwater lake so-called Lake Hachiro. Fig. 2(1234) shows the map of Hachiro-Kata and water quality sampling points denoted by the dots.

Lake Hachiro is a freshwater lake. When the gate between the sea and lake was closed to prevent exchange of water, the lake water became stagnant. The water quality problem of the lake was apparent as blue-green algae bloom was observed in 1970s. In 2003, Lake Hachiro was listed as fifth worst lake in terms of water quality. As shown in Fig. 3(1256), around half of pollution sources originated from paddy field. In this regard, the water quality monitoring started as early as 1976. The present monitoring points include major rivers flowing to the lake (11 points, 4 or 12 samples/yr), main drainage canals in the reclaimed land (2 points, continuous automatic sampling), and lake water body (9 points, 10 or 12 samples/yr). Sediment of the lake is also collected for the analysis (3 points, 1 sample/yr). Monitoring parameters include nitrogen and phosphorus compounds, SS, transparency, BOD, COD, and others.

In addition to the monitoring program, the Akita Prefecture recently initiated a series of activities for the improvement of lake water quality in partnership with research organizations, universities, and local communities (Akita Prefecture 2008) ( Fig. 3(1256)). The activities aim to: 1) attain sustainable development of agriculture and fisheries; 2) improve the natural environment of rural community; and 3) protect and enhance biodiversity. The major activities include: 1) use of less water for land preparation to reduce the sediment flow to the lake; 2) improved management of tidal gate and pumps to enhance the circulation of water within the lake; 3) biological treatment of drainage water; 4) establishment of protected zone for constructed wetland; 5) modernization of sewage system and expansion of the sewage network; and 6) cultivation of foreign fish species for removal of nutrients from the lake and making use of those as organic fertilizer. In 2007, the positive impact of those activities became evident even though there still exist few occasions of algae bloom in the lake. An important approach is to encourage the participation of farmers and local communities. Seminars and workshops for residents and school children were held to increase their awareness on the importance of improving the lake environment.

Acknowledgment

The author would like to thank Mr. Fumuhiro Kawamura of the Akita Prefecture, Japan for providing valuable comments and information on the Hachito-kata water quality monitoring and management.

Reference

  • Akita Prefecture (2008): Homepage at http://www.pref.akita.lg.jp/ (accessed 1 Sep 2008)
  • UNEP/ WHO (1996) Water Quality Monitoring - A Practical Guide to the Design and Implementation of Freshwater Quality Studies and Monitoring Programmes (Ed. J. Bartram and R. Balance), United Nations Environment Programme and the World Health Organization. 348.
  • Bouman, B. A. M., A. Castañeda, and S.I. Bhuiyan (2002): "Nitrate and Pesticide Contamination of Groundwater under Rice-Based Cropping Systems: Evidence from the Philippines." Agriculture, Ecosystems and Environment 92 (2_3): 185_99.
  • Comprehensive Assessment of Water Management in Agriculture (2007): 14 Rice: feeding the billions. In Water for Food, Water for Life: A Comprehensive Assessment of Water Management in Agriculture. London: Earthscan, and Colombo: International Water Management Institute.
  • Matsuno, Y., N. Hatcho and S. Shindou (2007) Water Transfer from Agriculture to Urban Domestic Users: A Case Study of the Tone River Basin, Japan. Paddy Water Environment 5: 239-246
  • Matsuno, Y, K. Nakamura, T. Masumoto, H. Matsui, T. Kato, and Y. Sato (2006) Prospects for multifunctionality of paddy rice cultivation in Japan and other countries in monsoon Asia. Paddy Water Environment 4: 189_197.
  • Ministry of the Environment, Japan (2008) Environmental Quality Standards for Water Pollution, http://www.env.go.jp/en/water/ (accessed 1 Sep 2008).
  • Misawa, S. (1999) Water Quality in Irrigation and Drainage. Chapter 8. In Advanced Paddy Field Engineering. Shinzan-Sha Sci. &Tech, 135-148.
  • Shiratani E, Shiofuku T, Kubota T, Yoshinaga I, Hasebe H (2003) Estimation of nutrient elution and removal on sediment surface of clayey canal based on hydraulic model experiments. JARQ 36(4):195_200
  • Tabuchi T (1998) Science for clean water. Chapter V: Water cycle in watershed (Ed. Water quality environment committee). Jpn Soc Irrigat, Drain, Reclamat Eng 100_107, 115_118 (in Japanese)
  • Takeda I, Fukushima A (2004) Phosphorus removal in a paddy field watershed using a circular irrigation system and the role of iron compounds. Water Res 38:4065_4074
  • Takeda, I (2001) Fundamental Knowledge for Water and Water Quality Environment. Ohmsa: 198 (In Japanese)
  • Yamaoka M, ShinogiY, Abenney-Mickson S, Saito T (2003) Estimation of nitrate removal potential for upland soil. Trans Jpn Soc Irrigat, Drain, Reclamat Eng 225:43_53 (in Japanese)

Index of Images

Figure 1 Rates of Non-Compliance with the Water Quality Standards for the Protection of Human Health (Source: Ministry of the Environment, Japan).

Figure 1 Rates of Non-Compliance with the Water Quality Standards for the Protection of Human Health (Source: Ministry of the Environment, Japan).

Figure 2 Hachiro-Kata and Sampling Points (from Google Earth).

Figure 2 Hachiro-Kata and Sampling Points (from Google Earth).

Figure 3 Pollution Source in Lake Hachiro. Source: Akita Prefecture

Figure 3 Pollution Source in Lake Hachiro. Source: Akita Prefecture

Table 1 Environmental Quality Standards for Conservation of the Environment for Rivers

Table 1 Environmental Quality Standards for Conservation of the Environment for Rivers

Table 2 The Rate of Compliance with the Environmental Water Quality Standard in Year 2004

Table 2 The Rate of Compliance with the Environmental Water Quality Standard in Year 2004

Table 3 Fertilizer and Pesticide Inputs to Agricultural Land in Japan

Table 3 Fertilizer and Pesticide Inputs to Agricultural Land in Japan

Table 4 Irrigation Water Quality Standards for Paddy Rice in Japan

Table 4 Irrigation Water Quality Standards for Paddy Rice in Japan

Table 5 Parameter, Monitoring Location and Frequency of Agricultural Water Quality Monitoring (Maff Recommendation 2007)

Table 5 Parameter, Monitoring Location and Frequency of Agricultural Water Quality Monitoring (Maff Recommendation 2007)

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