Abstract
Global climate change is expected to impact hydrodynamic conditions in stream ecosystems. There is limited understanding of how stream ecosystems interact and possibly adapt to novel hydrodynamic conditions. Combining mathematical modelling with field data, we demonstrate that bio-physical feedback between plant growth and flow redistribution triggers spatial self-organization of in-channel vegetation that buffers for changed hydrological conditions. The interplay of vegetation growth and hydrodynamics results in a spatial separation of the stream into densely vegetated, low-flow zones divided by unvegetated channels of higher flow velocities. This self-organization process decouples both local flow velocities and water levels from the forcing effect of changing stream discharge. Field data from two lowland, baseflow-dominated streams support model predictions and highlight two important stream-level emergent properties: vegetation controls flow conveyance in fast-flowing channels throughout the annual growth cycle, and this buffering of discharge variations maintains water depths and wetted habitat for the stream community. Our results provide important evidence of how plant-driven self-organization allows stream ecosystems to adapt to changing hydrological conditions, maintaining suitable hydrodynamic conditions to support high biodiversity.
Highlights
The importance of vegetation in affecting water and air flow and shaping physical landscapes has been widely recognized [1,2]
Combining mathematical modelling with field data, we demonstrate that bio-physical feedback between plant growth and flow redistribution triggers spatial self-organization of in-channel vegetation that buffers for changed hydrological conditions
Our results provide important evidence of how plant-driven self-organization allows stream ecosystems to adapt to changing hydrological conditions, maintaining suitable hydrodynamic conditions to support high biodiversity
Summary
The importance of vegetation in affecting water and air flow and shaping physical landscapes has been widely recognized [1,2]. Low-energy rivers, submerged and marginal aquatic vegetation imparts a resistance to water flow [12] that affects water velocities in the channel [13,14,15]. Aquatic vegetation typically grows as monospecific patches within streams [17] with a patterning caused by selforganization processes emerging from the divergence of water around vegetation patches [20] This interaction results in spatial patterns of patch alignment [21] that are important for species facilitation [22]. A model is developed that describes the interplay of plant growth and hydrodynamics within a spatially heterogeneous vegetated stream With this model, we explore how self-organization processes that emerge from this interaction create heterogeneity in plant biomass and water flow, and how this, in turn, affects stream hydrodynamic conditions. (c) 100 80 mixed vegetation (Bere Stream) dominant submergents (Frome Vauchurch) macrophyte cover (%)
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