Salinity as decisive factor for seedling establishment in coastal wetlands

Abstract

Climate change is threatening the existence of coastal wetlands around the globe. Recently, ecosystem services of these wetlands, such as coastal protection, shoreline stabilization and erosion control have gained attention. Coastal wetlands can provide an ecosystem based solution for sustainable coastal protection. By restoring or creating wetlands, not only coastal protection, but also the effects of global change, are decreased by erosion control and accumulation of sediments. Seedling establishment is a crucial step in creating or restoring wetlands. Without establishment there can be no vegetative growth. Although the effects of many abiotic factors on seedling establishment have been well studied, how the combination of several abiotic factors influences seedling establishment and the window of opportunity is still poorly understood. In addition, physical disturbances originating from sediment dynamics, such as erosion, and hydrodynamic disturbances, such as flow, are regarded as bottlenecks in seedling establishment. Abiotic factors influence the survival and growth of seedlings, and therefore also change their vulnerability for erosion and flow. The aim of this research was to investigate the effect of several abiotic factors, such as, inundation period, nutrient level and salinity, on the survival, growth and resistance against physical disturbances of seedlings, from the wetland species, Spartina anglica, Scirpus maritimus and Phragmites australis. Mesocosm experiments were used to analyze how different inundation periods, nutrient levels and salinities influence the survival and growth of seedlings, while flume experiments were used to determine the critical erosion depth (CED) of seedlings. This study illustrates that within a combination of different abiotic factors, in this case different inundation periods, nutrient levels and salinities, salinity plays a dominant role, as it reduces the survival, growth and critical erosion depth of seedlings of several wetland species. The creation or restoration of wetlands should build upon the knowledge of salinity as a main factor driving seedling establishment and possibly the window of opportunity.