Description: Coastal morphodynamic and hydrodynamic processes impose a first-order control on biogeochemical cycling and distribution of benthic habitats. However, little is known on how biota in turn affect sediment transport, biogeochemical cycling and morphodynamics at a regional scale and long-term. Here we firstly present a mini-review of recent progress on numerical modeling of interactions between benthic biota, biogeochemical cycling and coastal morphodynamics. Special focus is laid on 1) the synergetic effects of dominant benthic functional groups on sedimentation process, and 2) the macrobenthic response to changing morphological, hydrodynamic and biogeochemical conditions. In a second part we present preliminary results from a case study area (Jade Bay, Wadden Sea) based on simulations using a coupled hydrodynamic-biogeochemical-morphodynamic model and comparison with biogeochemical and taxonomic field monitoring data. The aim is to understand benthic ecosystem functioning and to identify the main drivers of coastal ecosystem changes for better prediction of their future development.

Description: The current study provides a new test case for the coastal numerical solutions dedicated to the plume spreading in the estuary and on the shelf. The suggested estuary-shelf system represents a mixture between pronounced nonlinear flow dynamics with sharp frontal boundaries and linear dynamics and across-shore geostrophic balance. The major aspects of the plume dynamics are analytically predicted, but are difficult to reproduce numerically. The test case manifests the level of numerical diffusion, ability of the model to reproduce the nonlinear processes and frontal zone dynamics. Numerical solutions were obtained with three unstructured mesh models SCHISM, THETIS and FESOM-C. The current study also suggests the plume spreading analysis based on numerical results, which can be useful for any intercomparison studies with focus on the plume behavior.

Description: Benthic organisms and their bioturbation activities have a profound effect on a multitude of sediment properties. While many studies have already explored benthic impacts at small temporal and spatial scales, little is known on how the small-scale effects accumulate and interactively guide large-scale (km-scale) morphological evolution. Here we firstly summarize the most important processes of benthos affecting sediment stability and then explore existing biomorphodynamic modeling studies both at small- and large-scales. In general, microbenthos (body size 〈0.1 mm) mainly stabilizes sediments while meio- (0.1–1 mm) and macrobenthos (〉1 mm) may stabilize or destabilize sediments. Among all types of sediment, fine-grained fraction (silt and clay) is most sensitive to the impact of benthos. Benthic organisms have the capability to mediate sediment transport and sedimentation patterns beyond their habitats on the long-term and over a large-scale. However, so far, numerical models evaluating benthic impact are limited to explorative studies and have not reached a stage where they can be used for predictive modeling. The barriers hindering a further development of biomorphodynamic models include not only limited understanding of fundamental biological/bio-physical processes affecting morphological development and dynamic feedback loops among them but also a shortage of data for model calibration and confirmation of simulation results. On the other hand, thriving for higher model complexity does not necessarily lead to better performance. Before conducting biomorphodynamic modeling, researchers must figure out which questions can be answered in a meaningful sense with simulation results that can be compared with observations and which level of modeling complexity is sufficient for that purpose.