Impact of changes in water management on hydrology and environment: A case study in North China
Introduction
Irrigated agriculture is important for ensuring food security. It provides 40% of the food produced worldwide from only 17% of the total cultivated land (Sundquist, 2007). The World Food Summit in 1996 estimated that 60% of the extra food required to sustain the world in the future must come from irrigated agriculture (FAO, 1996). It has been an essential component of all the strategies proposed to increase food supply (FAO, 1996, Liu et al., 2015, Mukherji et al., 2009).
However, activities involved in irrigation projects such as the construction and operation of irrigation projects and irrigated agriculture management practices affect the environment in various ways (Stockle, 2001). Common impacts of such activities include changes in hydrology, agricultural pollution, soil quality degradation, biological and ecological changes, human health issues, and social-economic impacts (Dougherty and Hall, 1995, Fernandez-Cirelli et al., 2009).
Among these, soil salinization and non-point-source agricultural pollution are the most critical problems. On average, 20% of the world’s irrigated land is affected by salts (Ghassemi et al., 1995), which not only reduce crop productivity but also causes other soil degradation phenomena such as soil dispersion, increased soil erosion, and engineering problems (Metternicht and Zinck, 2003). Leaching and drainage are often used to prevent salinization or to reclaim salinized soil, resulting in the transfer of dissolved salts to groundwater and surface water. In addition, various chemicals from fertilizers, pesticides, and other additives used in crop production are transferred through drainage, which cause non-point-source pollution if not disposed of in a planned manner. Agriculture is estimated to be the leading source of water pollution in many countries (EPA, 2002, Zhang et al., 2004). In China, agricultural pollutants accounted for 47.8% of the total chemical oxygen demand (COD) loads and 31.7% of the NH3-N loads for water bodies in 2012 (MEP, 2013). These impacts not only result in eutrophication of surface waters, poor downstream water quality, loss of biodiversity, and other types of degeneration in the ecological environment, but also threaten the continuation of irrigation and the sustainability of civilization (Khan et al., 2006, MacDonald et al., 2011, Postel, 1999).
Previous studies conclude that it is possible to meet the food security and sustainability challenges, if considerable changes in agricultural resources and landscape management are made (Foley et al., 2011, Mueller et al., 2012, Tilman et al., 2011). Improving irrigation performance was found to be the best management strategy to decrease off-site N pollution while maintaining or, in some cases, increasing crop yields in three Mediterranean watersheds (Cavero et al., 2012). Approaches including water-saving irrigation, controlled drainage, the use of bioreactors, water and fertilizer management, ecological drainage canals, and wetlands, have been proven to be effective in controlling non-point-source pollution from paddies in South China (Peng et al., 2013, Wang et al., 2013). Wasteland can be used to receive the excess salt from neighboring irrigated areas to control soil salinity in arid regions (Khouri, 1998, Konukcu et al., 2006, Wu et al., 2009). Tactics such as precision agriculture, drip irrigation, and wetland restoration have been developed and deployed (Foleyet al., 2011). However, their effective and sustainable deployment requires numerous and long-term verifications since the agroecosystem’s response time is often considerably delayed and spatio-temporally heterogeneous.
The Hetao Irrigation District (HID) is the third largest irrigation district in China. It is irrigated using water from the Yellow River and has existed for ∼2000 years. Over the past 60 years, the HID has experienced considerable innovation and the area is now equipped with a relatively complete irrigation and drainage system. Consequently, the agricultural productivity in the HID has markedly improved, which has had a significant impact on the hydrology and eco-environment of the region. The objective of this study is to examine the responses of the hydrology and environment of the HID to changes in water management in the region. The study also aims to explore reasonable water management strategies for achieving certain goals regarding food production and environmental protection in the HID and similar irrigation projects.
Section snippets
Study area
The HID is located in the Inner Mongolia Autonomous Region in North China (Fig. 1), at latitudes of 40°19′ to 41°18′ and longitudes of 160°20′ to 190°19. It covers a total area of 1,100,000 ha including 570,000 ha of agricultural land irrigated by water from the Yellow River.
According to climate data (1956–2015) released by the local meteorological bureau, the annual potential evaporation in the HID is as high as 2200 mm (measured using a 20-cm standard pan), and the average annual rainfall is
Materials and methods
Long-term (1954–2012) historical data regarding the quantity and quality of irrigation and drainage water in the HID were collected from the HID Administration and used to calculate the residual salt inside the system through the general water and salt balance performed at the district level. The groundwater table depth and salinity data (1966–2013) from more than 200 monitoring wells were collected and water-quality contouring maps for different years were created using Surfer 12 Software.
Agricultural water management
With the development of the irrigation and drainage system in the HID, the irrigated area expanded from 235,940 ha in 1954 to 580,666 ha in 2012. Simultaneously, the amount of inlet irrigation water increased correspondingly before 1991 and then significantly decreased from 5.7 billion m3 to 4.0 billion m3 (Fig. 2). The major reasons for this change are the water scarcity in the Yellow River basin and the implementation of a water allocation plan that necessitated changes in water management.
Soil salinization control and water management
Soil salinization is a frequent environmental problem caused by improper irrigation, which reduces the sustainability of irrigation. Effective leaching and drainage are important for soil salinity control because they enable not only the draining of salt introduced by irrigation but also the reduction of salt introduced through evaporation by lowering the groundwater table.
In the HID, the evolution of the soil salinity is strongly linked to the groundwater table, as stated earlier. However, it
Conclusions
The HID was considered as an example to study the responses of hydrology and the environment to changes in water management. Long-term data concerning irrigation, drainage, soil salinity, groundwater, and the environment of Wuliangsuhai Lake were collected and their relationships were analyzed. Their evolution histories show that agricultural water management could have extensive impacts on the hydrology and the environment, which is governed by a complex relationship. A comprehensive
Acknowledgements
The authors are grateful for financial support from the National Natural Science Foundation of China (Project No. 51790532, 41330854), the National key research and development program (Project No. 2017YFC0403304, 2016YFC0501304, 2016YFA0601501), the Opening Foundation of Key Laboratory of Water-Sediment Sciences and Water Disaster Prevention of Hunan Province (No. 2017SS02) and the Inner Mongolia Science and Technology Major Project.
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