Landscape evolution in tidal embayments: Modeling the interplay of erosion, sedimentation, and vegetation dynamics

Abstract

[1] We propose an ecomorphodynamic model which conceptualizes the chief land-forming processes operating on the intertwined, long-term evolution of marsh platforms and embedded tidal networks. The rapid network incision (previously addressed by the authors) is decoupled from the geomorphological dynamics of intertidal areas, governed by sediment erosion and deposition and crucially affected by the presence of vegetation. This allows us to investigate the response of tidal morphologies to different scenarios of sediment supply, colonization by halophytes, and changing sea level. Different morphological evolutionary regimes are shown to depend on marsh ecology. Marsh accretion rates, enhanced by vegetation growth, and the related platform elevations tend to decrease with distance from the creek, measured along suitably defined flow paths. The negative feedback between surface elevation and its inorganic accretion rate is reinforced by the relation between plant productivity and soil elevation in Spartina-dominated marshes and counteracted by positive feedbacks in multispecies-vegetated marshes. When evolving under constant sea level, unvegetated and Spartina-dominated marshes asymptotically tend to mean high water level (MHWL), different from multiple vegetation species marshes, which can make the evolutionary transition to upland. Equilibrium configurations below MHWL can be reached under constant rates of sea level rise, depending on sediment supply and vegetation productivity. Our analyses on marine regressions and transgressions show that when the system is in a supply-limited regime, network retreat and expansion (associated with regressions and transgressions, respectively) tend to be cyclic. Conversely, in a transport-limited regime, network reexpansion following a regression tends to take on a new configuration, showing a hysteretic behavior.Citation: D'Alpaos, A., S. Lanzoni, M. Marani, and A. Rinaldo (2007), Landscape evolution in tidal embayments: Modeling the interplay of erosion, sedimentation, and vegetation dynamics,

Signatures of sea level changes on tidal geomorphology: Experiments on network incision and retreat

“…[7] The laboratory experiments presented herein support the description of network evolution and dynamics addressed by conceptual [e.g., Allen, 1997] and numerical models [D'Alpaos et al, 2007a;Kirwan and Murray, 2007], and deepen our understanding of the effects of cyclic changes triggered by RMSL variations. The latter in fact, cannot be observed directly in nature owing to the long timescales involved, and have only been addressed so far on the basis of numerical experiments [D'Alpaos et al, 2007a].…”

“…The latter in fact, cannot be observed directly in nature owing to the long timescales involved, and have only been addressed so far on the basis of numerical experiments [D'Alpaos et al, 2007a].…”

“…These studies showed that laboratory experiments can successfully model tidal network dynamics. Although tidal network response to RMSL changes has been addressed by conceptual [e.g., Allen, 1997] and numerical models [D'Alpaos et al, 2007a;Kirwan and Murray, 2007], the effects of cyclic variations in RMSL on the characteristics and structure of tidal networks remain poorly understood, and the possibility of detecting signatures of past conditions imprinted on the landscape justifies analyses of the type proposed herein.…”

The secret gardener: vegetation and the emergence of biogeomorphic patterns in tidal environments

“…At a smaller scale, zonation patterns, a mosaic of sharply bounded and nearly homogeneous vegetation patches, are widespread in marshes worldwide [8][9][10]. Indeed, many aspects of tidal biogeomorphodynamics and of the associated patterns have been seen to be tightly linked to interactions between biotic and abiotic processes [11][12][13][14][15][16][17][18].…”

Understanding and predicting wave erosion of marsh edges

“…Much attention has been devoted to the understanding and description of the processes which lead to observed equilibria in the vertical direction, or lack thereof, producing a rather comprehensive understanding of the controlling biological and physical processes [Allen, 1990;Morris et al, 2002;D'Alpaos et al, 2007;Kirwan and Murray, 2007;Marani et al, 2007;Mudd et al, 2009;Marani et al, 2010]. On the contrary, "lateral" evolution mechanisms have received comparatively much less attention, even though marsh degradation associated with edge erosion is arguably the chief mechanism by which marshes in coastal areas worldwide are being lost [Schwimmer, 2001;Gedan et al, 2009;van de Koppel et al, 2005;Mariotti and Fagherazzi, 2010].…”