INTERaction of Fish, plAnts, Carbon & sEdiment: Management and ecosystem functions of Wadden Sea salt marshes - INTERFACE
Salt marshes form the interface between terrestrial and marine ecosystems and connect them via complex abiotic and biotic interactions. They are formed by the interplay of physical factors such as tidal currents and biological factors such as vegetation. Regular inundations bring suspended sediment to shallow, intertidal areas and this sediment settles if current velocity is low enough, thereby increasing marsh elevation. Once the marsh surface elevation is high enough, marsh vegetation can establish and in turn increases sediment deposition.
On most mainland marshes in the Wadden Sea region, sedimentation has been facilitated by the establishment of sedimentation fields with brushwood groynes. Furthermore, marsh development was sped up by artificial drainage ditches. Thus, most mainland marshes have a long history of human influence through these drainage ditches as well as through grazing with livestock. Most mainland salt marshes in Germany can be found in the Wadden Sea National Parks, where the central management goal is to allow natural dynamics to take place. However, even 25 years after maintenance of drainage ditches has been given up, natural dynamics and resulting structures do not resemble salt marshes free of human influence.
Salt marshes provide a wide range of ecosystem services, including coastal protection, biodiversity, carbon (C) sequestration and habitat for fish. These ecosystem services are most likely influenced by management, namely the type and effectiveness of the drainage system and livestock grazing. Effects of livestock grazing on salt marshes have been extensively studied in the past, especially with respect e.g. species richness in plants and birds, and - to a lesser extent - also sediment dynamics. In contrast, effects of the drainage system properties were hardly taken into account, even though they probably play a crucial role for many of these aspects. In addition, knowledge about C-sequestration and dynamics, which increase in importance in times of global change, and about the role of marshes as fish habitat are largely missing. Therefore, we investigate the effects of the drainage system and grazing on hydrology, plant species richness and sediment dynamics (part A), C-sequestration (part B) and C-dynamics (part C), and the habitat quality of the marsh as a growth environment for fish (part D). Finally, we want to integrate the results of all project parts and, in close cooperation with the National Park administrations, aim to give management recommendations for a sustainable salt-marsh management.