Ecohydrology of dune wetlands

Biodiversity is declining at an unprecedented rate, which will have significant impact on human health and well-being. Dune slacks are low-lying seasonal wetland habitats within coastal sand dunes. They are rich in biodiversity and expected to be sensitive to environmental changes due to complex interactions between hydrology and plant community compositions. However, there has been a lack of research in UK dune slacks exploring these interactions. Therefore, this thesis examines the relationship between plant communities and the underlying hydrological and environmental controls across UK dune slacks.

In Chapter 2 (methods chapter), I summarise the data collection, processing and groundwater modelling undertaken across 41 dune slacks in 12 coastal sand dunes systems, which underpin Chapter 3 and 5. I also summarise the data collection, processing and groundwater modelling undertaken across six dune slacks in one coastal sand dune system in north west England, which underpin Chapter 4. The outputs from this research are important for management, as they provide invaluable information on the plant communities present and the long-term hydrological regime of key UK sand dune systems.

In Chapter 3, I investigated plant community responses to environmental and hydrological drivers across spatial scales (coastal sand dune site, dune slack and plot) and taxonomic resolutions (species and genus) in UK dune slacks. Findings from this investigation show that ‘local’ environmental factors such as water table depth are important in shaping plant communities. Additionally, the response of genus data was similar to species data, therefore in the search for biodiversity short cuts genus data may be used.

In Chapter 4, I investigated species-specific responses and plant community responses to fine-scale hydrological variability in a coastal sand dune system in north west England (Ainsdale Sand Dunes). I found that hydrology is an important driver in dune slack communities between dune slacks. However, not all plant communities within a dune slack are structured by fine-scale hydrological variation, demonstrating the complexity of plant composition patterns. In addition to successional processes, topographic variation within slacks appears to impact plant community composition and diversity. Therefore, to maximise habitat space for many species, topographically varied dune slacks need to be created.

In Chapter 5, I explored how environmental drivers affect the relationship between a commonly used ecological indicator (Ellenberg moisture - F) and water table depth across UK dune slacks. Findings from this investigation demonstrate that Ellenberg F is a powerful biological indicator of soil hydrology in an ecological context, but other factors can alter this relationship. From a practical perspective these findings help us to understand which abiotic and biotic factors modify the relationship between Ellenberg F and hydrological regime, which aids interpretation of Ellenberg F-values at a sand dune site level.

The results presented here improve our understanding of the underlying hydrological and environmental control of UK dune slack plant communities. Additionally, this research provides a basis for future ecological and hydrological dune slack studies within the UK.