Abstract: Soil properties and their influence on the ecohydrology of salt marshes

John Hazelden and Laurence A. Boorman
L A B Coastal, Holywell, St. Ives, Cambridgeshire, PE27 4TQ, United Kingdom
E-mail:
johnh@labcoastal.co.uk
laurieb@labcoastal.co.uk

Salt marshes are largely controlled by the water regime they experience. This includes both salt water inputs at the seaward end and freshwater inputs from the land. All of the freshwater inputs except direct rainfall pass through, or over, the soil. This short presentation considers the role of soil and some of the ways in which its properties affect these inputs.

Freshwater inputs can come from rivers and streams, land drains and ditches draining directly into the marsh, and from aquifers and seepage zones (springs) around the edges and beneath the marsh surface. All these have the potential to bring nutrients and pollutants into the marsh. The soil controls the paths by, and the speed with, which this water reaches the marsh, and so influences the quality of this water.

Economic pressures on some wetlands have resulted in changes of land use, for example to extensive summer grazing and to more intensive agriculture. Where this has occurred, alterations to the soil water regime are commonly reflected in changes to soil properties. Not all these changes are reversible. Changes to soil physical properties have the most influence on ecohydrology, particularly the ‘ripening’ of soils and the consequent increase in bulk density. Where there are substantial peat layers, shrinkage and oxidation can substantially lower the land surface. Some important chemical changes occur also; where there are sulphides in the subsoil, land use changes with drainage and consequent better aeration can result in the formation of ‘acid sulphate soils’. It is important to consider these factors where attempts are made to restore wetlands to their ‘natural’ state.

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