|Microtopography in intertidal saltmarshes: The influence of elevated sediment on drainage and plant species growth
Bachmann, M. (2020). Microtopography in intertidal saltmarshes: The influence of elevated sediment on drainage and plant species growth. MSc Thesis. NIOZ Royal Netherlands Institute for Sea Research: Yerseke. 59 pp.
Background and Aims: Saltmarshes function as natural coastal protection barriers. They improve the resilience of coastal areas facing the increasing threat of sea level rise. These ecosystems are progressively vanishing due to anthropogenic exploitation and climate change. Restoration approaches for saltmarshes have shown to be rarely successful, the mechanisms leading to a thriving establishment of salt marsh specific plants are fractionally understood. Previous scientific studies indicate that microtopographic heterogeneity is an important factor in the facilitation of saltmarsh vegetation development and consequently preservation of these vital ecosystems. The following work focuses on the effect of microtopographic elevations on sediment drainage and plant growth.Methods: A field campaign was conducted in already established saltmarshes in which the drainage of vegetated tussocks and surrounding bare mudflat was investigated. Additionally, two mesocosm experiments were conducted. The first experiment was set-up to study if the results of the field campaign could be replicated (flat and raised sediment) in a controlled environment allowing further research with plant seedling recruits. The second experiment consisted of four different plant species typical for intertidal saltmarshes in the Netherlands, which were grown on either raised or flat sediment to investigate the effect of microtopography on plant growth rates.Key Results: This study shows that elevated microtopographic areas experience drainage of sediment, whereas the mudflats do not show evidence of drainage. Similar results for raised sediment drainage and undraining flat sediment are found in the mesocosm experiment. Contrary to expectations, plant growth rates did not increase in the elevated treatment but were overall higher in the flat sediment treatment. The outcome of the results is likely due to some minor errors in experiment design, which could easily be avoided in further experiments.Conclusions: This study shows the presence of drainage found in elevated microtopographic sediment. The drainage allows fresh oxygen enriched seawater to enter the sediment, likely boosting growth of saltmarsh plants. The understanding of this mechanism can be useful for future approaches of saltmarsh restoration, improving the probability of successful facilitation.