Modelling the effects of dynamic saltmarsh and microphytobenthos growth on the large-scale morphology of estuaries

Abstract:

Biostabilizing organisms, such as saltmarsh and microphytobenthos, can play a crucial role in shaping the morphology of estuaries and coasts by protecting the sediment from erosion. However, their impact on large-scale morphology, which highly depends on the feedback between spatio-temporal changes in their abundance and physical forcing, remains highly uncertain.

We studied the effect of seasonal growth and decay of biostabilizing organisms, in response to field calibrated physical forcings, on estuarine morphology over decadal timescales using a novel eco-morphodynamic model. The code includes temporal saltmarsh and microphytobenthos growth and aging as well as spatially varying vegetation fractions determined by mortality pressures. Growth representations are empirical and literature-based.

Novel natural patterns emerged in this model revealing that observed density gradients in vegetation are defined by the life-stages that increase vegetation resilience with age. The model revealed that the formation of seasonal and long term mud layering is governed by a ratio of flow velocity and hydroperiod altered by saltmarsh and microphytobenthos differently, showing that the type of biostabilizer determines the environmental conditions under which mud can settle and be preserved. Moreover, we investigate whether saltmarsh growth determines mud settling or whether mud settling is a prerequisite for saltmarsh establishment. The results show that eco-engineering effects define emerging saltmarsh patterns from a combination of a positive effect reducing flow velocities and a negative effect enhancing hydroperiod that enhances mud settling. Consequently, saltmarsh and mud patterns emerge from their bilateral interactions that hence strongly define morphological development in estuaries.