Ilaria Cunico

River ecosystem dynamics are governed by non-linear complex feedback loops among vegetation, flow, and sediment transport. Because of its non-linear dynamical nature, complexity, characterized by critical transitions, tipping points and strong dependence on initial conditions, can emerge from the model that describes such interactions. Due to this complexity, river ecosystem equilibrium and dynamics are still not totally well quantified. Understanding how river ecosystem dynamics work can help us preserve biodiversity, prevent irreversible anthropogenic modifications, enhance the hydraulic safety, and implement efficient restoration projects.

Therefore, we numerically investigate eco-morphodynamics complexity to quantify river ecosystem equilibrium and dynamics.

We conduct numerical simulations using a spatial deterministic model (1D) that captures the main feedbacks between hydro-morphodynamics and vegetation dynamics. We consider a straight channel with a vegetated patch that is periodically perturbed by growth-disturbance cycles. Vegetation growth occurs between two consecutive floods, and it may be uprooted during flood events. In our analysis, we vary the ratio “R” between flood intensity (disturbance) and vegetation dynamics (resistance).

Model results demonstrate that by modifying “R” the system can exhibit (i) a stable equilibrium or multi-equilibria (ii) periodic oscillations or (iii) chaotic behaviour. When the system shows multi-equilibria or chaotic behaviour it has a strong dependence on initial conditions and thus, small differences can matter. We also demonstrate how in our model critical transitions and tipping points are smoothed by space. Furthermore, chaotic behaviour limits the predictability of the river ecosystem to only a few flood events. Thus, by modifying the parameter “R” (e.g. through anthropogenic pressure) the system can switch from a predictable stable state to multi-stability or to unpredictable chaotic behaviour (or vice versa).