Livestock grazing reduces sediment deposition and accretion rates on a highly anthropogenically altered marsh island in the Wadden Sea

Autor: Dennis Schulze, Stefanie Nolte, Kai Jensen
Rok vydání: 2021
Předmět:
Zdroj: Estuarine, Coastal and Shelf Science. 251:107191
ISSN: 0272-7714
Popis: Coastal salt marshes and their provided ecosystem services are threatened by rising sea levels all over the world. In the Northern Wadden Sea region, a sea-level rise of 4 mm y−1 was recorded for recent years. Identifying and understanding factors that affect sediment deposition and determine vertical accretion of salt marshes is crucial for the management of these ecosystems. Even though major processes contributing to sedimentation and accretion have already been identified, the influence of reduced canopy heights due to livestock grazing is still debated. On a highly anthropogenically altered marsh island in the Wadden Sea, sediment deposition, accretion and suspended sediment concentration was analyzed on grazed and adjacent ungrazed plots both at the marsh edge and at the marsh interior. Due to a low seawall (a so-called ‘summer dike’), flooding frequency on the island is reduced and flooding mainly takes place during storm surges. After five flooding events within a year, mean sediment deposition and accretion were found to be up to seven times higher on ungrazed plots compared to grazed plots, but only at the marsh edges. This result was not explained by the overmarsh suspended sediment concentration (SSC), which was found to be twice as high on grazed plots compared to ungrazed plots. It is concluded that grazing has a negative effect on sediment deposition and accretion on Wadden Sea marsh islands and areas with similar conditions (e.g. presence of a summer dike) by reducing the sediment trapping capacity of those marshes. Overall, vertical marsh accretion ranged from 0.11 ± 0.09 mm y−1 on a grazed plot at the marsh edge to 1.12 ± 0.71 mm y−1 on an ungrazed plot at the marsh edge. By increasing the discrepancy between accretion and sea-level rise, livestock grazing can lead to higher inundation levels and in turn to increased hydrodynamic forces acting on these anthropogenically altered marshes. Highlights • Accretion rates on a Wadden Sea marsh island cannot keep pace with rising sea level. • Ungrazed plots showed significantly higher sediment deposition and accretion rates. • Suspended sediment concentration was higher under grazing treatment. • Natural marsh vegetation is thought to have a considerable sediment trapping effect. • Accretion rates can be improved by abandonment of grazing.
Databáze: OpenAIRE
Externí odkaz: