Soil Spatial Variability Associated with Tidal Creek Meandering on a Salt Marsh.

Lateral migrations of tidal creek meandering create point bars by sedimentation and cutbank edges by erosion. We investigated the micro-scale spatial pattern of soil physical and chemical properties across topographic sequences such as point bar-transitional zone-marsh interior and cutbank edge-transitional zone-marsh interior on the Skallingen salt marsh, Denmark. Preliminary results indicated that soil bulk density was generally highest at sites adjacent or close to the tidal channels and gradually decreased toward inner marsh fields. Such a pattern corresponded well to that of soil texture beginning from sandy point bars/cutbank edges to marsh interiors with high silt and clay contents. This spatial gradient of texture is believed to represent the decreasing ability of flooded water from the creeks to transport grains with increasing size. Previous literature reported a very close, positive relationship between bulk density and the degree of percolation from salt marsh soils. Such a relationship implies that natural levees of point bar parts or cutbank edges may show a relatively fast drainage of inundated sea water due to high bulk density of their sandy substrate, resulting in less anoxic and saline conditions than inner marshes. This interpretation facilitates our understanding of the fine-scale zonation of vegetation across tidal creeks: Sites close to the creeks (except point bars) are dominated by late-successional species, whereas marsh interiors are characterized by early- to mid-successional states. Most information about the spatial pattern of soil properties and vegetation on salt marshes has been at broad spatial perspectives encompassing the elevational gradient from seaward to landward marsh fields. Based on our linkage between fine-scale edaphic/floristic zonation and tidal creek processes, we address a need for adopting flexible hierarchical approaches in managing salt marshes that take into consideration different eco-geomorphic processes operating across various spatial scales.