Self-organization of river vegetation leads to emergent buffering of river flows and water levels

How do the growth forms of macrophytes affect the homogeneity of nearshore and open water areas?

Macrophytes with different growth forms exhibit diverse functional traits and ecological functions. In natural sub-deep lakes, there are often large differences in water quality between nearshore areas with macrophytes and open water areas. However, it remains unclear whether this phenomenon can be attributed to differences in plant growth forms. Therefore, we conducted continuous monitoring for four years, both before and after the implementation of an ecological restoration project, to explore whether the change in plant growth forms caused differences in water quality between the nearshore and open water areas. The results showed that implementing ecological restoration projects proved highly effective in improving the local environment, including water physicochemical properties and biological components, in the implementation area. First, the ecological restoration project greatly altered the plant community structure in the nearshore area before and after restoration. After restoration, there was a significant increase in the biomass and distribution area of noncanopy-forming plants (including erect and rosette-forming plants), while the opposite effect was observed for canopy-forming plants. Second, the transition of macrophyte community growth forms enhanced the stability of both macrophyte communities and water physicochemical parameters. Furthermore, the reduction in canopy-forming plants facilitated a more efficient water body exchange, resulting in greater homogeneity in water quality between the nearshore and open water areas. Overall, the presence of canopy-forming plants can hinder water body exchange due to large canopy formations on the water surface. In light of these findings, it is recommended that ecological restoration projects in natural lakes should consider the functional group composition of macrophytes.

Vegetation controls on channel network complexity in coastal wetlands

Channel networks are key to coastal wetland functioning and resilience under climate change. Vegetation affects sediment and hydrodynamics in many different ways, which calls for a coherent framework to explain how vegetation shapes channel network geometry and functioning. Here, we introduce an idealized model that shows how coastal wetland vegetation creates more complexly branching networks by increasing the ratio of channel incision versus topographic diffusion rates, thereby amplifying the channelization feedback that recursively incises finer-scale side-channels. This complexification trend qualitatively agrees with and provides an explanation for field data presented here as well as in earlier studies. Moreover, our model demonstrates that a stronger biogeomorphic feedback leads to higher and more densely vegetated marsh platforms and more extensive drainage networks. These findings may inspire future field research by raising the hypothesis that vegetation-induced self-organization enhances the storm surge buffering capacity of coastal wetlands and their resilience under sea-level rise.

Geomorphodynamics, evolution, and ecology of vertical roots

The roots of some coastal and wetland trees grow peculiar vertical protrusions, the function of which remains unclear. Here, using computational simulations based on first-principles fluid and sedimentation dynamics, we argue that the protrusions work together to create an elevated patch of sediment downstream of the tree, thereby creating its own fertile flood-protected breeding grounds for the seedlings. In our simulations, we vary the vertical root diameter, root spacing and total root area and show that there is an optimal vertical root spacing that depends on root thickness. Next, we quantify and discuss the cooperative effects between adjacent vertical root patches. Lastly, by varying vertical root spacing of a patch of trees, we estimate a maximal vegetation density for which vertical-root production has a beneficial geomorphological response. Our hypothesis suggests that vertical roots, such as the 'knee roots' of baldcypress trees, have an important role in shaping riparian geomorphology and community structure.