Agriculture, water, and ecosystems: avoiding the costs of going too far
or gone through regime shifts leading to a collapse of ecosystem services, making the costs of restoration (if possible at all) very high. ese losses have adverse effects on livelihoods and economic production [well established]. ere is ongoing debate whether the positive outcomes in terms of increased upstream production of food outweigh the negative consequences for people dependent on downstream ecosystem services. While most cost-benefit studies show that the costs of the losses have been higher than the gains, other scientists argue that these studies have many weaknesses (Balmford and others 2002).
Although agriculture, especially water management in agriculture, is a major driver behind the loss of downstream ecosystem services [well established], there are competing explanations for the manner and importance of individual processes and events and the ultimate role of agriculture as a triggering force for degradation is in many situations un- known. Dams, overfishing, urban water withdrawals, and natural and anthropogenic cli- mate variation can contribute to cumulative and synergistic effects, reduced resilience, and increased degradation of downstream ecosystems (photo 6.4). Uncertainty is often high when it comes to the exact location or timing of the response of downstream ecosystems to upstream water alterations. is does not mean that we can ignore the role of agriculture. But we need to address the problems as complex and interacting, and to consider a systems perspective for analyzing multiple drivers of change.
e next two sections offer examples of how water-related management in agriculture
has changed the capacity of downstream ecosystems to generate ecosystem services and a brief discussion of the consequences of some of these changes.
Water quantity and waterscape alterations. Increased cultivation in recent decades has resulted in increased diversion of freshwater, with some 70% of water now being used for agriculture and reaching as high as 85%–90% in parts of Africa, Asia, and the Middle
Photo 6.4 Dams provide many benets for people, but also affect ecosystems by changing the hydrology and fragmenting rivers
Longterm trend analysis of 145 major world rivers indicates that discharge has declined in onefifth of cases
Photo by C. Max Finlayson