Tidal marsh sedimentation and resilience to environmental change: Exploratory modelling of tidal, sea-level and sediment supply forcing in predominantly allochthonous systems

The existence and function of tidally dominated and predominantly allochthonous marshes are ultimately contingent upon the operation of hydrodynamic and sedimentary processes within constraints imposed by the available accommodation space and sediment supply. This paper re-interprets published data relating to contemporary vertical marsh growth and sea-level rise in the context of the conceptual model relating elevation, sedimentation, sea-level rise, sediment supply and tidal range. This analysis is supported by numerical mass balance modelling of the equivalent parameter space and of the sensitivity of marsh hydroperiod and sedimentation to sea-level and sediment supply forcing. The effect of autocompaction on the translation of sedimentation into elevation change is also considered. Parameter space modelling provides a framework for the interpretation of field data and affords indicative insights into marsh resilience to change. It is argued that the assessment of marsh response to external environmental forcing should be based not on empirical comparisons of sedimentation versus sea-level rise but on the estimation of sediment supply, and the efficiency with which this is depleted by deposition, as metrics of marsh resilience. This implies a shift towards more intensive process studies aimed at elucidating more fully the linkages between tidal marshes and adjacent estuarine and coastal systems. Model results also indicate significant variability in marsh sedimentation associated with 18.6 yr tidal modulation and meteorological processes at short-term scales. Such variability further complicates the interpretation of sedimentation or elevation change data obtained from monitoring programmes of short duration. Longer-term monitoring is of value, however, as a means of identifying important mechanisms of climate and sediment supply forcing that may contribute to the formation and maintenance of marsh sedimentary sequences. (c) 2006 Elsevier BY. All rights reserved.