How to create a saltmarsh: understanding the roles of topography, redox and nutrient dynamics

Lawrence, Peter John (2018) How to create a saltmarsh: understanding the roles of topography, redox and nutrient dynamics. Doctoral thesis (PhD), Manchester Metropolitan University.

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Abstract

The restoration of saltmarsh is critical given the importance of the habitat and the degradation and losses it faces. However, success of saltmarsh restoration has been limited, particularly in replacing plant communities, despite like-for-like replacement being a legal requirement. Previous research found elevation in the tidal frame and sediment redox potential are important drivers of vegetation communities, and are different between restored and natural marshes. However, elevation and sediment redox potential together are insufficient to explain differences in plant communities. Topographic features are thought to alter redox potential-elevation relationships, though its role in plant communities is not currently known. Nutrient concentrations can also impact vegetation, however we lack evidence as to the typical concentrations in natural saltmarsh or restored sites, and how close these are to detrimental levels. This thesis explores these environmental properties in restored and natural saltmarshes, and how they may interact to drive plant communities. Results indicated that nutrients were highly variable both spatially and temporally. In contrast to expectations, there was a negligible effect of former land-use on surface soil development in a newly developing marsh. Instead of land-use, a combination of sedimentation and elevation appears to be the strongest predictor of nutrient properties, thus a better understanding of incoming sediment and elevation changes may lead to improved predictions of likely soil development. The results from nutrient analysis also indicated that globally saltmarshes are typically Phosphate enriched and thus the management of N input at natural saltmarshes should be avoided. Restored marshes have different topographic characteristics (flatter, wetter and more often concave). A lack of topography existed on both site and local scales, resulting in more homogenous plant communities (again at, sites and local-scales). Natural plant diversity was driven by elevation, local topography and redox, whereas on MR sites it was almost entirely driven by redox potential. The results show that more topographic manipulation is required to aid community convergence with natural diversity, and thus replicate natural conditions in restored saltmarshes.