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Experimental floods cause ecosystem regime shift in a regulated river.
Christopher T Robinson1, Urs Uehlinger
1Department of Aquatic Ecology, EAWAG, 8600 Duebendorf, Switzerland. robinson@eawag.ch
Summary
Sequential experimental floods in a regulated river caused an ecosystem regime shift over three years, altering macroinvertebrate communities and reducing organic matter. Later floods showed less impact, indicating increased ecosystem resilience.
Area of Science:
- River ecology
- Ecosystem dynamics
- Environmental flow management
Background:
- River regulation by reservoirs alters natural flow regimes, impacting ecological integrity.
- Experimental floods are used globally to restore ecological conditions in regulated rivers.
- Sequential large-scale disturbances offer insights into ecosystem regime shifts.
Purpose of the Study:
- To evaluate the long-term effects of sequential experimental floods on a regulated river ecosystem.
- To test the hypothesis that cumulative floods induce an ecosystem regime shift.
Main Methods:
- Conducted 15 experimental floods over eight years on a regulated river.
- Monitored physicochemistry, organic matter (particulate and in-transport), and benthic communities (moss, periphyton, macroinvertebrates).
- Analyzed temporal changes using coefficients of variation and Kendall's W concordance test.
Main Results:
- Floods reduced particulate organic carbon and phosphorus, eliminated moss, and maintained low periphyton and benthic organic matter after three years.
- Macroinvertebrate richness and biomass decreased after year one; density decreased after year three, with reduced individual mass.
- Ecosystem showed initial nonequilibrium (increased variability) for three years, followed by decreased variability, indicating a more resilient state to subsequent floods.
Conclusions:
- Sequential floods induced a significant ecosystem regime shift, unfolding over three years.
- The macroinvertebrate community structure changed, becoming more resilient to flood disturbances.
- Long-term ecological recovery and further shifts are anticipated with continued colonization.
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