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Flow regime alteration degrades ecological networks in riparian ecosystems

Nature Ecology & Evolution volume 2, pages 86–93 (2018)Cite this article

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Abstract

Riverine ecosystems are governed by patterns of temporal variation in river flows. This dynamism will change due to climate change and the near-ubiquitous human control of river flows globally, which may have severe effects on species distributions and interactions. We employed a combination of population modelling and network theory to explore the consequences of possible flow regime futures on riparian plant communities, including scenarios of increased drought, flooding and flow homogenization (removal of flow variability). We found that even slight modifications to the historic natural flow regime had significant consequences for the structure of riparian plant networks. Networks of emergent interactions between plant guilds were most connected at the natural flow regime and became simplified with increasing flow alteration. The most influential component of flow alteration was flood reduction, with drought and flow homogenization both having greater simplifying community-wide consequences than increased flooding. These findings suggest that maintaining floods under future climates will be needed to overcome the negative long-term consequences of flow modification on riverine ecosystems.

The fundamental human demand for fresh water has resulted in the dramatic transformation of rivers throughout the world1. Dams, diversions and numerous other forms of infrastructure have enabled water flows to be controlled for human use, resulting in the dampening or elimination of flooding and other ecologically important aspects of flow regimes2,3 (see Table 1 for the definition of the natural flow regime). Such effects threaten riparian ecosystems4,5 and compromise many functions and services supported by these ecosystems, including the regulation of thermal regimes and water quality, flood attenuation, contribution of carbon to aquatic food webs, and the provision of wood and physical habitat structure along the terrestrial–aquatic interface6. These stressors to riparian ecosystems are exacerbated by climate change, which threatens to increase flow intermittency7 and modify species distributions and interactions via drought intensification in many regions globally8,9. What has emerged is a clear need for robust forecasting of how riparian ecosystems will respond to changing flooding and drought conditions over long timescales10.

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Fig. 1: Conceptual diagram outlining the workflow used in the analysis, from data collection to projection.
Fig. 2: Examination of riparian plant networks across a spectrum of possible flow regime futures.
Fig. 3: Summary metrics of full ecological networks spanning the spectrum of flow extremes from extreme drought to flood.
Fig. 4: Degree (number of links connected to the node) of each network node in relation to flow state.

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Acknowledgements

We thank N. L. Poff, A. Ruhi and members of the OSU Integrative Biology journal club for comments on earlier versions of the manuscript. Dinosaur National Monument and the US Bureau of Reclamation supported the research that led to the vital rate data. Funding was provided in part by the US Department of Defense (SERDP RC-2511) and the US Department of Agriculture Forest Service.

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Authors and Affiliations

  1. Department of Integrative Biology, Oregon State University, Corvallis, OR, 97331, USA

    Jonathan D. Tonkin & David A. Lytle

  2. Watershed, Fisheries, Wildlife, Air and Rare Plants Staff and the National Stream and Aquatic Ecology Center, U.S.D.A. Forest Service, Fort Collins, CO, 80526, USA

    David. M. Merritt & Lindsay V. Reynolds

  3. School of Aquatic and Fishery Sciences, University of Washington, Seattle, WA, 98195, USA

    Julian D. Olden

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  1. Jonathan D. Tonkin
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Contributions

J.D.T. and D.A.L. designed the study, developed the model and ran analyses; D.A.L. and D.M.M. compiled vital rate information; J.D.T. wrote the first draft of the manuscript in close collaboration with D.A.L., and all authors contributed substantially to writing in subsequent drafts.

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Correspondence to Jonathan D. Tonkin.

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Tonkin, J.D., Merritt, D.M., Olden, J.D. et al. Flow regime alteration degrades ecological networks in riparian ecosystems. Nat Ecol Evol 2, 86–93 (2018). https://doi.org/10.1038/s41559-017-0379-0

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