Coastal wetlands, such as tidal flats and marshes, provide crucial ecosystem functions including biodiversity and flood protection of densely populated coastlines. Channel networks dissecting these landscapes govern the tidal transport of water, sediment and organisms, thus laying the foundations of wetland functioning. My thesis is aimed at unraveling the spatial structure of channelized wetlands, which ranges from simple to highly complex, and the influence of landscape complexity on ecosystem functioning. I developed mathematical models for channel network formation and conducted laboratory experiments and field measurements. I found that simple, spatially regular channel patterns emerge from self-organization, i.e. large-scale structuring due to small-scale feedbacks between hydrodynamics, sediment dynamics and vegetation. I showed that simple wetland patterns are modern analogues for fossil ecosystems dating back to the Precambrian, implying that self-organization may have shaped landscapes throughout Earth’s geological history. Furthermore, I found that complex, multi-scale channel patterns can emerge from the same self-organization process. The strength of the underlying biogeomorphic feedback controls the degree of network complexity. Finally, I showed that such feedbacks can even be driven by primitive organisms such as algae and can induce tipping points between alternative stable states with strongly contrasting wetland properties. My thesis results are practically relevant, illustrating how spatial complexity affects wetland resilience to flooding and how wetland restoration efforts could be optimized, ultimately contributing to nature-based coastal flood defense. Moreover, my findings are of fundamental importance, unifying spatially simple and complex patterns in the present and geological past in a single self-organization framework. |
