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A novel 3-dimensional numerical model resolving dynamic interactions between environmental drivers and benthic fauna was applied to an idealized domain as analogous to typical tidal embayments. The aim is to derive insights into the role of benthic fauna in guiding long-term (decadal to centennial) coastal morphological evolution at a system scale. Three major functions by benthic fauna on sediment dynamics, namely bio-destabilization, bio-deposition and bio-stabilization, were incorporated. Results indicate that each of the three functions is able to guide a unique and profound long-term change of the embayment morphology. Bioturbation-induced sediment mixing and bio-destabilization may result in net sediment export out of the embayment, whilst bio-deposition and bio-stabilization tend to alter the embayment toward a net sediment import environment. Benthic fauna is able to modify large-scale hydro-morphology toward a state favorable for living. A combined effect of the three functions is not just a simple neutralization of the opposing impacts between sediment stabilization and destabilization. Rather, it leads to a unique response of the embayment morphology due to interactions between different benthic functional groups. Comparison with a real tidal embayment (Jade Bay from the Wadden Sea) justified a general validity of the model results in terms of statistics in both morphology and benthic fauna, and suggested an equal importance of interactions between benthic fauna and bed morphology and between different benthic functional groups in guiding morphological development of complex coastal systems.

Abstract. We present a test case of river plume spreading to evaluate numerical methods used in coastal ocean modeling. The main characteristics of the plume dynamics are predicted analytically, but are difficult to reproduce numerically because of numerical mixing present in the models. Our test case reveals the level of numerical mixing as well as the ability of models to reproduce nonlinear processes and frontal zone dynamics. We propose an analysis of simulated plume spreading which may be useful in more general studies of plume dynamics. The major result of our comparative study is that accuracy in reproducing the analytical solution depends less on the type of applied model architecture or numerical grid than it does on the type of advection scheme.

Coastal morphology refers to the morphology and morphological development of the coast in response to a combined influence of atmospheric, oceanic and anthropogenic forcing. Coastal morphology comprises a wide variety of landforms (exposed to air) and bedforms (submerged in water) manifested in a large spectrum of spatial scales (10−2–105 m scale) and shapes ranging from mildly sloping lower shoreface to steep cliffs, from small ripples to large river deltas. Coastal zones are cradles for life. About 40% of the global human population and 50% of marine life are living in low-lying coastal zones with elevation less than 10 m above the mean sea level. Coasts contain the highest biodiversity in the surface earth system yet are highly vulnerable to environmental stressors associated with human activities and climate change. Climate impacts coastal morphology in multiple ways, including ice cover/melting, precipitation, temperature, and wind. In response to a changing climate, adaptation of coastal morphology can be categorized into three basic states: erosional, stable, and accretionary. Each state may persist or iterate at any given part of a coast, even in the context of a persistently warming or cooling climate. Anthropogenic protection has been globally implemented to ease erosion and protect human property. However, it remains largely unknown whether the existing measures would be able to counteract the effects of climate change in the upcoming decades.