Publication

Stability Analysis of Submerged Vegetation Patterns in Rivers

Giulio Calvani
2022
Journal paper
Abstract

Aquatic vegetation in fluvial systems is often characterized by spatial patterning of the plant patches. To investigate the conditions for the formation of vegetation patches, we explore the stability of a uniform flow over a non-erodible bed with a uniform vegetation cover of submerged plants. The flow model consists of the two-dimensional shallow water and continuity equations. The hydrodynamic equations are coupled firstly to the classic formulation for vegetation dynamics, and secondly to a modified version of the equation. The revised relationship for vegetation dynamics accounts for the influence of removal, transport, and resettlement of propagules on the growth rate of aquatic vegetation. Linear stability analysis of the eco-hydrodynamic problem is performed by enforcing the quasi-steady approximation. We obtain a dispersion relation disclosing the growth rate and the migration rate of the perturbations of vegetation density as a function of the wavenumber and the relevant flow and vegetation parameters. The present theory predicts the onset of vegetation patterns and includes an adequate wavelength selection mechanism. While uprooting initially reduces plant density, the analysis demonstrates that resettled propagules after removal are fundamental for further plant population increases and the development of vegetation patterns. The proposed framework is then validated against data available in the literature. Additionally, the presence of an upper threshold in terms of vegetation density, above which uniform vegetation cover is stable, might explain the absence of any spatial pattern and thus the extremely dense vegetation cover induced by climate change and invasive species in altered ecosystems.

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Related concepts (34)
Vegetation
Vegetation is an assemblage of plant species and the ground cover they provide. It is a general term, without specific reference to particular taxa, life forms, structure, spatial extent, or any other specific botanical or geographic characteristics. It is broader than the term flora which refers to species composition. Perhaps the closest synonym is plant community, but vegetation can, and often does, refer to a wider range of spatial scales than that term does, including scales as large as the global.
Aquatic ecosystem
An aquatic ecosystem is an ecosystem found in and around a body of water, in contrast to land-based terrestrial ecosystems. Aquatic ecosystems contain communities of organisms—aquatic life—that are dependent on each other and on their environment. The two main types of aquatic ecosystems are marine ecosystems and freshwater ecosystems. Freshwater ecosystems may be lentic (slow moving water, including pools, ponds, and lakes); lotic (faster moving water, for example streams and rivers); and wetlands (areas where the soil is saturated or inundated for at least part of the time).
Freshwater ecosystem
Freshwater ecosystems are a subset of Earth's aquatic ecosystems. They include lakes, ponds, rivers, streams, springs, bogs, and wetlands. They can be contrasted with marine ecosystems, which have a larger salt content. Freshwater habitats can be classified by different factors, including temperature, light penetration, nutrients, and vegetation. There are three basic types of freshwater ecosystems: Lentic (slow moving water, including pools, ponds, and lakes), lotic (faster moving water, for example streams and rivers) and wetlands (areas where the soil is saturated or inundated for at least part of the time).
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