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Humanity is facing an enormous challenge in managing water to secure adequate food production without undermining the life support systems on which society depends

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Simplified, there are three main ways to meet this water requirement: increasing water use on current agricultural lands through intensification of production (see chapters 8 on rainfed agriculture and 9 on irrigation), expanding agricultural lands, and increasing water productivity (see chapters 7 on water productivity and 15 on land).

  • ese options have vastly different implications for ecosystems and the services they

generate. Increased water use on agricultural lands through irrigation will reduce the avail- ability of blue water resources (surface water and groundwater), especially for downstream aquatic systems, and can contribute to waterscape alterations, for example, through the introduction of dams for irrigation. Increased green water flows (soil moisture generated from rainfall that infiltrates the soil) through higher consumptive water use in rainfed agriculture (as a result of increased crop productivity) will also reduce the availability of water downstream, although the extent to which this could occur varies [established but incomplete]. Expanding agricultural land can alter the water flow in the landscape, with impacts on terrestrial and aquatic ecosystems. Finally, while increased water productivity is intended to produce more food without using more water, it can lead to deterioration in water quality through increased use of agrochemicals.

Humanity is facing an enormous challenge in managing water to secure adequate food production without undermining the life support systems on which society depends—and in some instances while simultaneously rehabilitating or restoring those systems. Research on ecosystems has generally been separate from research on water in agriculture, leading to a seg- regated view of humans and food security on one side and nature conservation on the other. In this chapter we challenge this view by describing recent understanding of how all ecosystems support human well-being, including ensuring food security and redressing social inequities.

We focus on the links between ecosystems and management of water in agriculture. Water functions as the “bloodstream of the biosphere” (Falkenmark 2003). It is vital for the generation of many ecosystem services in both terrestrial and aquatic ecosystems and provides a link between ecosystems, including agroecosystems. As for agricultural produc- tion, we consider the importance of both blue and green water (see chapter 1 on setting the scene) for ecosystems, both those characterized by the presence of blue water, such as marsh- es, rivers, and lakes, and terrestrial ecosystems that depend on and modify green water.

We first assess the ecosystem effects of past water-related management in agriculture, highlighting some of the often unintentional tradeoffs between water for food production and water for other ecosystem services. We then outline response options for improving water management. We emphasize the need to intentionally deal with the unavoidable and often surprising tradeoffs that arise when making decisions to increase food production, noting that these are often embedded within complex social situations where different stakeholders have highly diverse interests, skills, and influence (see, for example, chapters 5 on policies and institutions, 15 on land, and 17 on river basins).

Agriculture and ecosystems While agricultural production is driven by human management (soil tillage, irrigation, nu- trient additions), it is still influenced by the same ecological processes that shape and drive nonagricultural ecosystems, particularly those that support biomass production and others

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