| dc.description.abstract | Salt marshes play an important role in carbon sequestration, habitat provision to marine life and coastal protection, but are degrading because of land use and climate change. Ecosystem engineers such as salt marsh vegetation, modify their environment by capturing sediment and reducing water flow to create a suitable habitat. Recent advances in ecological restoration used biodegradable structures produced of biopolymers to mimic these e ects. However, their biodegradability is understudied and the e ect of spatial arrangement of structures on sediment stabilization is unknown.
This study focused on the biodegradation of restoration structures made of PHA(polyhydroxyalkanoate), PLA (polylactic acid) and PBS (polybutylene succinate) biopolymers. The five-month experiment took place on the Dutch salt marsh the Dortsman, located in Zeeland, the Netherlands. To quantify biodegradation, we measured mechanical strength and material thickness. Additionally, we investigated the e ect of structure shape (rectangular and hexagonal) and spatial arrangement on the sediment stabilization of the restoration structures. To quantify sediment stabilization we measured the sediment profile and sediment motility. The results were analysed after two months on a structure-scale and spatial arrangement-scale.
PHA restoration structures showed a large decrease in strength, while the PLA and PBS structures showed an increase in strength after three months, likely due to processes such as crosslinking. We found a larger decrease in strength and cracking of the samples on the bottom sheet of PHA restoration structures, which indicates biodegradation by soil microorganisms. Additionally, PHA restoration structures assessed under lab conditions had degraded to the point where no samples
could be taken. Hexagonal and rectangular restoration structures perform equal at trapping sediment on a structure-scale, but at a spatial arrangement-scale hexagonal restoration structures retained more sediment. Mean relative sediment height inside the structures was 0.3 ± 0.2 cm higher than the control plots after two months. At a structure-scale we found the highest mean relative sediment height in a spatial arrangement based on salt marsh vegetation using rectangular restoration structures. However, on a spatial arrangement scale, we did not find any differences between spatial arrangements. Sediment motility indicated lower erosion in plots with hexagonal restoration structures.
This study found that PHA restoration structures biodegraded quickly, highlighting the need for further research to determine if PHA is suitable for salt marsh restoration, since restoration takes multiple years. Additionally, hexagonal structures retain more sediment than rectangular structures and experience less erosion, but long-term monitoring is needed to confirm their higher effectiveness and optimize spatial arrangement for improved restoration outcomes. | |
