Effects of small-scale patterns of vegetation structure on suspended sediment concentration and sediment deposition in a salt marsh

Abstract

Salt marshes contribute to coastal protection by attenuating waves and reducing flow velocities. Nevertheless, coastal salt marshes are threatened by rising sea levels. In order to keep pace with rising sea levels, salt marshes need to grow vertically by sediment input. Although major processes contributing to sediment deposition in salt marshes are known, there is still a lack of understanding of the influence of canopy height and biomass on suspended sediment concentration and sediment deposition and on the spatial scale beyond which an influence of vegetation on sediment deposition comes into effect. Furthermore, vegetation can be heterogenous and little is known on the role of small-scale patterns of vegetation structure on suspended sediment concentration and sediment deposition. We investigated the effects of small-scale patterns of vegetation on suspended sediment concentration and sediment deposition in a field experiment with two vegetation types (i.e. Spartina anglica in the low marsh and Elymus athericus in the high marsh). Partial mowing of the vegetation resulted in a pattern of mown subplots and control subplots with a size of 4 m2 in various combinations adjacent to a creek. Based on the results, it can be concluded that on the spatial scale of 4 m2, there is no effect of the vegetation on water flow as the sediment deposition between mown and control subplots did not differ in both the high and the low marsh. Furthermore, a mown or a control subplot next to the creek had no influence on the sediment deposition on a mown or control subplot behind. In summary, based on the results of our study, it can be concluded that the presence of salt marsh vegetation not automatically leads to higher sediment deposition on vegetated patches compared to mown patches in both the low and high marsh.