AVIS-IBIS

Birds of Indian Subcontinent

Spartina Salt Marshes in Southern England: IV. The Physiography of Poole Harbour, Dorset

Publication Type:Journal Article
Year of Publication:1964
Authors:Bird, ECF, Ranwell, DS
Journal:Journal of Ecology
Volume:52
Issue:2
Date Published:1964
ISBN Number:00220477
Keywords:Calidris, Calidris canutus, Scolopacidae
Abstract:The shape of Poole Harbour is due largely to a marine submergence that probably reached its maximum about 6000 years ago. Its branched configuration is typical of a valley system partly drowned by Recent marine submergence with the higher parts persisting as promontories and islands. Sand spits at the harbour entrance are thought to be derived partly from the erosion of Tertiary cliffs to the north, and partly from the floor of Studland Bay to the south of the harbour entrance where Bagshot Beds are believed to outcrop. Longshore drift and counter-drift are checked by tidal currents of up to 5 knots (2.6 m/sec) which maintain the harbour entrance. Shore-line forms and marsh development in Poole Harbour depend largely on exposure to wave action at high tide, cliffs occurring (with beaches associated locally) opposite regions of longest fetch, while marshlands are best developed on more sheltered sections of the shore. Before the marshlands developed, much of the harbour shore was cliffed, the steep bluff behind the marshlands being a degraded cliff with basal relics of sand and gravel beaches partly concealed by marsh soil and vegetation. Topography in the intertidal zone and below depends especially on currents developed in creeks and channels during the ebb. The pattern of tidal channels has remained much as it was since it was first surveyed 178 years ago, although minor changes have been recorded. The sources of sediment delivered to the harbour are discussed and evidence given that significant amounts are still being delivered to the upper reaches of the harbour by the rivers when in spate. The broad lagoon-like form of the harbour acts as a `settling tank' for sediment. The part played by Spartina as a physiographic agent is discussed and estimates of the depth of silt accumulated by this plant vary from 70 to 100 cm in different parts of the harbour. Approximately 2158 ac (873 ha) of Spartina marsh and about 620 ac (251 ha) of Phragmites marsh occur, together occupying about 36% of the intertidal zone. The development of Spartina marsh has probably passed its peak in the area and relatively little active spread is found. Erosion and `die-back' release silt which may be redeposited on areas where Spartina marsh is still actively developing.
URL:http://www.jstor.org/stable/2257602
Short Title:Journal of Ecology
Scratchpads developed and conceived by (alphabetical): Ed Baker, Katherine Bouton Alice Heaton Dimitris Koureas, Laurence Livermore, Dave Roberts, Simon Rycroft, Ben Scott, Vince Smith