When Does Vegetation Establish on Gravel Bars? Observations and Modeling in the Alpine Rhine River

Caponi, Francesco; Koch, Aurélie; Bertoldi, Walter; Vetsch, David; Siviglia, Annunziato

doi:10.3389/fenvs.2019.00124

Cited by 29 publications

(42 citation statements)

References 60 publications

(112 reference statements)

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“…In this study, we provide a quantitative insight and a modelling framework to investigate the effect of above and below-ground plant traits and their feedbacks on gravel bar ecomorphodynamics. Despite a point-to-point comparison with observations was not in our scopes, our model results agree, on a qualitative level, with recent field observations in the Alpine Rhine river in Switzerland 38 . Results on steady bars showed a gradual increase in vegetation cover on bars, especially after flood 6.…”

Section: Discussionsupporting

confidence: 69%

“…1c) and migrating bars ( Fig. 1d) compared well with the ones measured along the Alpine Rhine river 37,38 . The topography obtained in this way was then used as initial condition to perform model runs including vegetation.…”

Section: Numerical Simulationssupporting

confidence: 78%

“…flood 3) were able to completely remove pioneer vegetation by uprooting and reset the system to bare riverbed conditions. The tested flood frequencies did not allow plant traits to develop enough for slowing bar migration, which is key for establishment success of plants in alternating bar configurations 38,40 . On the contrary, vegetation was able to colonise more stable (steady) bars, to an extent that depended on the vegetation type.…”

Section: Discussionmentioning

confidence: 95%

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A model study of the combined effect of above and below ground plant traits on the ecomorphodynamics of gravel bars

Caponi

Vetsch

Siviglia

2020

Sci Rep

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Both above- and below-ground plant traits are known to modulate feedbacks between vegetation and river morphodynamic processes. However, how they collectively influence vegetation establishment on gravel bars remains less clear. Here we develop a numerical model that couples above- and below-ground vegetation dynamics with hydromorphological processes. The model dynamically links plant growth rate to water table fluctuations and includes plant mortality by uprooting and burial. We considered a realistic hydrological regime and used the model to simulate the coevolution of alternate gravel bars and vegetation that displays trade-offs in investment of above- and below-ground biomass. We found that a balanced plant growth above- and below-ground facilitates vegetation to establish on steady, stable bars, because it allows plants to develop traits that maximise growth performance during low flow periods and thus survival during floods. Regardless of the growth strategy, vegetation could not establish on migrating bars because of large plant loss by uprooting during floods. These findings add on previous studies suggesting that morphodynamic processes play a key role on determining plant trait distributions and highlight the importance of including the dynamics of both above- and below-ground plant traits for predicting shifts between bare and vegetated states in river bars.

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Section: Discussionsupporting

confidence: 69%

Section: Numerical Simulationssupporting

confidence: 78%

Section: Discussionmentioning

confidence: 95%

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A model study of the combined effect of above and below ground plant traits on the ecomorphodynamics of gravel bars

Caponi

Vetsch

Siviglia

2020

Sci Rep

Self Cite

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“…Currently, vegetated bars slowly evolve during floods, mostly through lateral erosion of bar heads (Jourdain, 2017a). Recently, Caponi et al (2019) developed a model based on the windows of opportunity concept to investigate the minimum duration of time needed for vegetation establishment on (bare) gravel bar in a reach of the Alpine Rhine river. A general description of the morphodynamics of alternate bars with vegetation in a wide range of configurations is still lacking.…”

Section: Introductionmentioning

confidence: 99%

Morphodynamics of alternate bars in the presence of riparian vegetation

Jourdain

Claude

Tassi

et al. 2020

Earth Surf Processes Landf

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Alpine gravel‐bed rivers are dynamic systems that have been subjected to many anthropic alterations in the past centuries. Riparian vegetation development on previously bare sediment bedforms has been a common adjustment, raising important management issues in terms of flood risks and biodiversity. Many of these rivers are also channelized, and as a result present a pattern of alternate bars. Considering recent advances in numerical biomorphodynamic modeling, this study aims at exploring numerically the morphodynamics of alternate bars in the presence of riparian vegetation. To this end, a dynamic vegetation module has been implemented on top of an existing morphodynamic model, accounting for ecological processes of seed dispersal, seedling recruitment, growth, and mortality. Numerical simulations have been performed on a simplified reach of a gravel‐bed river with free migrating alternate bars at initial state. In this work 96 scenarios have been simulated, each representing 50 years of channel evolution, with different flood regimes characterized by various peak discharges and flood durations. Yearly peak discharge variability is explicitly modeled in 48 scenarios. Model outcomes present two possible equilibrium biomorphodynamic behaviors: stationary vegetated bars, or free migrating bars in the case of frequent vegetation removal during floods. This binary behavior holds true when the stochasticity of annual peak discharges is represented, and for a wide range of parameter values included in vegetation dynamic modeling. Transient mobility of vegetated bars is observed in specific configurations where large sediment deposits deflect the flow field, eroding bar heads. Modeled bar wavelengths are in the range of values predicted for free bars by linear bar theory, and remain far from the theoretical values of hybrid, steady bars. The shift from unvegetated migrating bars to steady vegetated bars seems to show that in these simulations vegetation constitutes a hydraulic forcing, leading to a shift from free bars to forced bars, with a final configuration largely inherited from the initial state. © 2019 John Wiley & Sons, Ltd.

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“…Substrate erosion is another cause of vegetation loss that can lead to changes in the indices, however on a longer time-scale. The erosion and deposition of substrate influence vegetation growth on the floodplains [99]. Change in resources availability can also lead to changes in the floodplain vegetation.…”

Section: Limitations Of Satellite Imagerymentioning

confidence: 99%

Characterizing Flood Impact on Swiss Floodplains Using Interannual Time Series of Satellite Imagery

Milani

Kneubühler

Tonolla

et al. 2020

IEEE J. Sel. Top. Appl. Earth Observations Remote Sensing

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Pressure on the biodiversity of ecosystems along many rivers is growing continuously due to the increasing number of hydropower facilities regulating downstream flow and sediment regimes. Despite a thorough understanding of the shortterm processes and interactions at this hydro-biosphere interface, long-term analyses of the impacts on floodplain dynamics are lacking. We used inter-annual Landsat 4, 5, 7 and 8 time series to analyze the effects of hydrological events on floodplain vegetation in four mountainous floodplains in the Swiss Alps. Using a spectral mixture analysis approach, we demonstrate that the floodplain vegetation dynamics of mountainous rivers can be recovered at a spatial resolution of 30 meters. Our results suggest that interactions between floods and floodplain vegetation are complex and not exclusively related to flood magnitude. Of the four reaches analyzed, only data gathered along the submountainous reach with a quasi-natural flow regime show a clear link between remotely sensed vegetation indices and floods. In addition, our 29-year time series shows a continuous upward trend in vegetation indices along the floodplains, strongest in the reaches affected by hydropower facilities. The approach presented in this study can be easily replicated in other mountain ranges by providing available flow data to verify the impact of hydropower on floodplain vegetation dynamics.

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When Does Vegetation Establish on Gravel Bars? Observations and Modeling in the Alpine Rhine River

Cited by 29 publications

References 60 publications

A model study of the combined effect of above and below ground plant traits on the ecomorphodynamics of gravel bars

A model study of the combined effect of above and below ground plant traits on the ecomorphodynamics of gravel bars

Morphodynamics of alternate bars in the presence of riparian vegetation

Characterizing Flood Impact on Swiss Floodplains Using Interannual Time Series of Satellite Imagery

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