Post-reclamation changes in estuarine mudflat sediments at Bothkennar, Grangemouth, Scotland

Abstract

AbstractThe Engineering & Physical Sciences Research Council research site at Bothkennar is located on former intertidal mudflats adjacent to the Forth estuary, which were reclaimed for agricultural use around the year 1784. A desiccated surface crust has developed in the 200 years following the reclamation, largely in response to the introduction of artificial drainage. Its formation has involved both compaction and material translocation, due to effective stress changes and to infiltration and geochemical alteration respectively. At first, new deposits accumulated in an artificial tidal lagoon and underwent autocompaction under saturated conditions. The subsequent introduction of field drains and cultivation then induced suction stresses due to evapotranspiration, leading to overconsolidation by around 150–200 kPa. These processes have also been associated with the development of an immature soil profile to a depth of around 0.7 m. The infiltration of fresh water has caused both desalination and the eluviation of clay particles. There is also a general rise in pH and fall in Eh with depth, which is associated with leaching and the downward translocation of DCB (dithionate-citrate-bicarbonate) soluble iron compounds. We conclude that the physical development of the crust was rapid and is now largely completed, whereas the chemical development is not yet completed and thus the soil profile remains immature.