C. Bischoff¹, M. Paul^1*

¹

Leibniz University Hannover, Ludwig Franzius Institute of Hydraulic, Estuarine and Coastal Engineering, Germany

^* Corresponding author: paul@lufi.uni-hannover.de

Introduction

In the Wadden Sea area, brushwood groynes are used in the dike foreshore to reduce hydrodynamic energy, enhance sediment deposition, and support salt marsh development.  Despite centuries of use, the biogeomorphological effects of these interventions are still not fully understood. Salt marsh plants have species-specific growth niches within the hydrodynamic domain. Their trait variation leads to distinct interaction with hydrodynamic conditions, which results in varying plant-induced sediment accumulation patterns. It is hypothesised that these patterns are also affected by the groyne’s life and maintenance cycle which exhibits a natural decay followed by a reconstruction of the groyne.

Objective and Methods

This study examines vegetation and sediment dynamics on the island of Pellworm in the German Wadden Sea, where salt marshes have been shaped by anthropogenic activities, including groyne construction and dredging, over the past 70 years. Data on surface elevation changes, vegetation development and sediment characteristics have been collected over one year prior and after groyne reconstruction.

Results

Key findings confirm that sediment dynamics are influenced by the brushwood groyne reconstruction. Furthermore, salt marsh zonation within the groyne field followed not only a landward, but also a sheltered-to-exposed dike parallel gradient in sediment and vegetation patterns, likely resulting from groyne-induced hydrodynamic conditions. Thus, there appear to be both long and short term effects of brushwood groynes on biogeomorphic feedbacks in managed salt marshes, which provides valuable insights for ecosystem-based coastal protection.