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The Holocene influence on the future evolution of the Venice Lagoon tidal marshes
Full text linkThe resilience of marsh ecosystems to expected sea-level rise is determined by a complex interplay of organic and inorganic sedimentation dynamics. Marshes have formed over past centuries to millennia and consist of extremely reactive bodies with sediments that can experience high compaction. Here we provide a quantification of the degree to which the past history of a salt marsh can affect its long-term evolution. A dataset of elevation dynamics was established in the Venice Lagoon (Italy) and interpreted using a physics-based model of deposition and large consolidation of newly deposited material. We found that the fate of low-lying tidal landscapes over the next century of accelerating sea-level rise will be highly dependent on compaction of soft, recently deposited soils. Our results imply that a sedimentation rate twice the present rate will be needed to counterbalance the expected sea-level rise.Holocene compaction in the Venice Lagoon, Italy, highlights the importance of soil properties and deposition rate in predicting the evolution of tidal marshes, according to numerical model simulations calibrated with 20 years of observations
Bio-geomorphic patterns in tidal environments
Full text linkIn times of natural and anthropogenic climate change, tidal bio-geomorphic systems are most exposed to possibly irreversible transformations with far-reaching ecological and
socio-economic implications.
It is thus of critical importance to develop models for predicting the evolution of such systems under varying forcings and, if
present, their dynamically-accessible stable states.
The notion that freshwater and terrestrial ecosystems may switch
abruptly to alternative stable states as a result of feedbacks
between consumers and limiting resources is widely acknowledged. On the contrary, theoretical or observational proofs of the existence of alternative equilibrium states in intertidal ecosystems has until recently proven to be elusive.
This is due to a prevalent reductionist approach, which has until recently mostly produced either purely ecological or purely geomorphological models, while the coupled dynamics of landforms and biota in the intertidal zone has remained largely unexplored.
The presence and continued existence of tidal morphologies, and in particular of salt marshes, is intimately connected with biological activity, especially with the presence of halophytic vegetation. In fact, observations and models coupling geomorphological and biological processes indicate that vegetation crucially affects marsh equilibrium configurations through the production of organic soil, the capture of sediment, and the stabilization against erosion produced by wind waves. Often, different vegetation species live within very narrow
elevation intervals, associated with similarly narrow ranges of environmental pressures, thus leading to the emerge of the zonation phenomenon.
Here we present modeling analysis on the spatial distribution of geomorphological and vegetational spatial patterns in tidal landscapes arising as a result of two-way feedbacks between physical and biological processes.
We challenge the traditional interpretation of zonation as a one--way relation between dominant processes in the intertidal frame (i.e. competition vs. edaphic controls), which fails to capture the active role played by vegetation in engineering its own environment.
We use a point model of the coupled elevation-vegetation dynamics, which retains the description of the chief processes shaping these systems, to show how competing stable states are responsible for the formation of characteristic large-scale bio-geomorphic features in tidal landscapes worldwide.
Our analyses extended to a one-dimensional context allows us to explore the mechanism that leads to the formation of well-known, smaller-scale patterns associated with marsh vegetation species distributions.
We develop and present a model that for the first time incorporates species competition, species mutations, sediment transport and soil accretion in a spatially-extended setting, emphasizing that the formation of smaller-scale intertwined topographic and vegetation patterns are driven by bio-geomorphic feedbacks.
We finally analyze the robustness of large-scale and marsh-scale bio-geomorphic features to changes in the forcings, with implications for marsh ecosystem resilience to climate change and anthropogenic pressure
Biomorphological modeling of tidal landscapes: the role of physical and biological processes in determining equilibrium states and transient dynamics
No full textVegetation engineers marsh morphology through multiple competing stable states
No full textMarshes display impressive biogeomorphic features, such as
zonation, a mosaic of extensive vegetation patches of rather
uniform composition, exhibiting sharp transitions in the presence
of extremely small topographic gradients. Although generally
associated with the accretion processes necessary for
marshes to keep up with relative sea level rise, competing
environmental constraints, and ecologic controls, zonation is still
poorly understood in terms of the underlying biogeomorphic
mechanisms. Here we find, through observations and modeling
interpretation, that zonation is the result of coupled geomorphological–
biological dynamics and that it stems from the ability
of vegetation to actively engineer the landscape by tuning soil
elevation within preferential ranges of optimal adaptation. We
find multiple peaks in the frequency distribution of observed
topographic elevation and identify them as the signature of
biologic controls on geomorphodynamics through competing
stable states modulated by the interplay of inorganic and organic
deposition. Interestingly, the stable biogeomorphic equilibria
correspond to suboptimal rates of biomass production, a result
coherent with recent observations. The emerging biogeomorphic
structures may display varying degrees of robustness to
changes in the rate of sea level rise and sediment availability,
with implications for the overall resilience of marsh ecosystems
to climatic changes
Marsh morphological-biological patterns as ecologically-engineered multiple stable states
No full text
Evolution through mutation and selection of biological and morphological features in the intertidal zone
No full text
The secret gardener: vegetation and the emergence of biogeomorphic patterns in tidal environments
No full textThe presence and continued existence of tidal
morphologies, and in particular of salt marshes,
is intimately connected with biological activity,
especially with the presence of halophytic vegetation.
Here, we review recent contributions to tidal
biogeomorphology and identify the presence of
multiple competing stable states arising from a
two-way feedback between biomass productivity
and topographic elevation. Hence, through the
analysis of previous and new results on spatially
extended biogeomorphological systems, we show that
multiple stable states constitute a unifying framework
explaining emerging patterns in tidal environments
from the local to the system scale. Furthermore, in
contrast with traditional views we propose that biota
in tidal environments is not just passively adapting
to morphological features prescribed by sediment
transport, but rather it is ‘The Secret Gardener’,
fundamentally constructing the tidal landscape. The
proposed framework allows to identify the observable
signature of the biogeomorphic feedbacks underlying
tidal landscapes and to explore the response and
resilience of tidal biogeomorphic patterns to variations
in the forcings, such as the rate of relative sea level
ris
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