Biogeochemical heterogeneity in the salt marsh pools of the north Norfolk coast

This thesis presents a study of pools found on the salt marshes of the north Norfolk coast, whose sediments have previously been observed to be extremely geochemically heterogeneous on small spatial scales. The work tests the hypothesis that the larger geomorphic features of the marsh exert a spatial control on the local pool geochemistry. The primary effects are on the surface inputs of fluids and sediments to the pools, which in turn alter the balance of subsurface early-diagenetic reactions and lead to the geochemical differences that are observed. This work comprises three parts. The first is a GIS study of the characteristics of pools across a large section of the marsh, which concluded that the creek network exerts a primary control over both the number of pools and their individual areas. A study over a smaller area of the marsh also indicates a control from the creeks on the geochemical nature of each pool. In the second part, two heterogeneous pools are analysed in detail for changes in their composition with depth, in particular with respect to sedimentary carbon-iron-sulfur cycling. It is found that the observed pool geochemistry is a function of the balance between sedimentary oxidation and reduction processes, and these processes are postulated to be controlled by the ratio of organic to mineral matter delivered to the pool surface. In the final part, initial work towards creating a computational model of the creek-pool system is presented. The results are considered in the context of carbon storage and processing within intertidal sediments, and in particular within coastal pools. It is postulated that the marsh drainage networks, and therefore the number, area and geochemistry of pools, may change with future climate change and anthropogenic marsh use. The capability of coastal marshes to capture and store atmospheric carbon may then be altered.