Agricultural modifications of hydrological flows create ecological surprises

doi:10.1016/j.tree.2007.11.011

Trends in Ecology & Evolution

Volume 23, Issue 4, April 2008, Pages 211-219

https://doi.org/10.1016/j.tree.2007.11.011 Get rights and content

Agricultural expansion and intensification have altered the quantity and quality of global water flows. Research suggests that these changes have increased the risk of catastrophic ecosystem regime shifts. We identify and review evidence for agriculture-related regime shifts in three parts of the hydrological cycle: interactions between agriculture and aquatic systems, agriculture and soil, and agriculture and the atmosphere. We describe the processes that shape these regime shifts and the scales at which they operate. As global demands for agriculture and water continue to grow, it is increasingly urgent for ecologists to develop new ways of anticipating, analyzing and managing nonlinear changes across scales in human-dominated landscapes.

Section snippets

Humans have modified the water cycle through agriculture

Human transformation of global water flows has dramatically impacted ecosystems and the services they generate. Through water withdrawals, land use and land cover changes, agriculture, which covers almost 40% of the terrestrial surface [1], is arguably the major way in which humans change water quantity and quality (Box 1). Water for irrigation accounts for 66% of societal water withdrawals, reducing water availability for downstream ecosystems [2]. Irrigation and deforestation for agriculture

Three parts of the hydrological cycle where agriculture can trigger regime shifts

The hydrological cycle can be seen as the ‘bloodstream of the biosphere’ [18], because runoff, groundwater and evapotranspiration move materials among different ecosystems and alter energy balances in landscapes. This paper examines how agricultural changes across the whole hydrological cycle can produce regime shifts. We classify agriculture–water regime shifts into three categories depending on where they occur in relation to the hydrological cycle (Figure 1). These categories are:

(i)
agriculture

There is large variation in the spatial scales and reversibility of regime shifts

The regime shifts we have identified as related to agricultural changes to water flows (Table 1) operate at a wide range of spatial scales and are reversible at different temporal scales (Figure 2). Agriculture–aquatic system regime shifts occur at the watershed to river basin scales but vary from years to millennia in their reversibility. For example, freshwater eutrophication is often irreversible, or only reversible after massive reductions of phosphorus inputs for decades or longer, owing

Agriculture interacts with other drives to produce water-related regime shifts

Regime shifts are triggered by the interaction of changes internally in a system and changes in external drivers (Box 2). In Table 1, we identify critical internal ‘slow variables’ that strongly influence the vulnerability of an ecosystem to regime shifts. Managing these slow variables to maintain resilience can thus be an important management strategy. We also identify the external drivers that can produce regime shifts, separating these into agricultural and nonagricultural drivers. In many

Enhancing resilience of agricultural landscapes

Hydrological alterations due to growing agricultural demands (Box 1) are likely to increase the risk of surprising regime shifts unless management practices are changed. The expected alterations can be reduced by improving the productivity of water in agriculture (Box 1), but enhancing resilience to the regime shifts discussed here requires active management of ecosystem processes across agricultural landscapes. Avoiding the discussed regime shifts is thus not only a question of improving

Conclusions and research challenges

There is strong evidence that agricultural modification of water flows can produce a variety of ecological regime shifts that operate across a range of spatial and temporal scales. In a world of growing demands for water, agricultural products and other ecosystem services, there will inevitably be ecological surprises. Preparing for these surprises is essential to maintain ecosystem services of importance for human well-being. Preparation requires understanding the forces that drive these

Acknowledgements

L.J.G.'s research was funded by the Swedish Research Council for the Environment, Agricultural Sciences and Spatial Planning (Formas), and G.D.P.'s work was funded by the Canada Research Chairs Program. We would also like to thank Elin Enfors, Frédéric Guichard, Navin Ramankutty and Maria Tengö for comments on the manuscript, and Tove Gordon and Robert Kautsky for help with figures.

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Trends in Ecology & Evolution

ReviewAgricultural modifications of hydrological flows create ecological surprises

Section snippets

Humans have modified the water cycle through agriculture

Three parts of the hydrological cycle where agriculture can trigger regime shifts

There is large variation in the spatial scales and reversibility of regime shifts

Agriculture interacts with other drives to produce water-related regime shifts

Enhancing resilience of agricultural landscapes

Conclusions and research challenges

Acknowledgements

Geomorphology

Geomorphology

J. Environ. Econ. Manag.

Trends Ecol. Evol.

Global consequences of land use

Science

Global impacts of conversions from natural to agricultural ecosystems on water resources: quantity versus quality

Water Resour. Res.

Human modification of global water vapor flows from the land surface

Proc. Natl. Acad. Sci. U. S. A.

Nitrogen cycles: past, present, and future

Biogeochemistry

Human impact on erodable phosphorus and eutrophication: a global perspective

Bioscience

Ecosystems and Human Well-Being: Synthesis

Water for Food, Water for Life: A Comprehensive Assessment of Water Management in Agriculture

Millennium ecosystem assessment: research needs

Science

Uncertainty and the management of multistate ecosystems: an apparently rational route to collapse

Ecology

Regime shifts, resilience, and biodiversity in ecosystem management

Ann. Rev. Ecol. Evol. Syst.

Cross-scale interactions, nonlinearities, and forecasting catastrophic events

Proc. Natl. Acad. Sci. U. S. A.

Nonlinearities, feedbacks and critical thresholds within the Earth's climate system

Clim. Change

Self-organized patchiness and catastrophic shifts in ecosystems

Science

Catastrophic shifts in ecosystems

Nature

Thresholds in ecological and social-ecological systems: a developing database

Ecol. Soc.

Synergy between small- and large-scale feedbacks of vegetation on the water cycle

Glob. Change Biol.

Water: the bloodstream of the biosphere

Philos. Trans. R. Soc. Lond. B Biol. Sci.

Regime Shifts in Lake Ecosystems: Pattern and Variation

Eutrophication of aquatic ecosystems: bistability and soil phosphorus

Proc. Natl. Acad. Sci. U. S. A.

Overview of hypoxia around the world

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How climate controls the flux of nitrogen by the Mississippi River and the development of hypoxia in the Gulf of Mexico

Limnol. Oceanogr.

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Hydrobiologia

River meander behaviour and instability: a framework for analysis

Trans. Inst. Brit. Geograph.

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Philos. Trans. R. Soc. Lond. B Biol. Sci.

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Bioscience

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Ecology

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Nature

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Nature

Assessing the ecological risk from secondary salinity: a framework addressing questions of scale and threshold responses

Austral. Ecol.

Review
Agricultural modifications of hydrological flows create ecological surprises