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Journal of Coastal Research 417-427 Charlottesville, Virginia Coastal Lagoons of East Anglia, U.K.! R.S.K. Barnes Department of Zoology University of Cambridge Cambridge CB2 3EJ United Kingdom ABSTRACT _ BARNES, R.S.K., 1987. Coastal Lagoons of East Anglia, U.K.Joumal of CoastalResearch, 3(4), 417 427. Charlottesville, ISSN 0749-0208. ~ ~"""".,. Twenty-six remaining coastal lagoons in East Anglia, U.K., fall into six distinct categories •• • on the basis of their origin, physiography, hydrography, and sedimentology, all six either ••• createdor heavily influenced by man: (1) pits orotherexcavationswi thin shingleformations in to whichwaterpercolates; (2) depressions remaining in reclaimedsaltmarshes in to which springs discharge water retained within adjacent sand dunes; (3) shallow pools floored by clay and filled by water issuing to landwards from out of longshore shingle ridges; (4) streamsorsmall rivers ponded back by low-lyingbarrier beaches; (5) short-circuitedformer estuaries; and (6) relict bodies ofbrackish water. From a world viewpoint, all but category (4) are aberrant in having neither any freshwater inflow (other than rainfall) nor any direct influx ofsea water; in common with other northern Atlantic lagoons, all are further atypical in being confined behind barriers composed largely ofshingle. Their rather limited macro faunas and macrofloras, however, are characteristically lagoonal, although there is a wide variation in species from lagoon to lagoon, even between geographically adjacent systems. The precise species found in any given lagoon appear largely to be the result ofstochiastic processes, there beingno correlationofbiotaswith physiographic category or environmen tal type, with the partial exception oflagoonal salinity. ADDITIONAL INDEX WORDS: Barrier beaches, brackish-water fauna, coas tal lagoons, East Anglin, l rK., peomorpholouy; reclamation, shingle ridge« INTRODUCTION although from a world viewpoint they are aberrant in being enclosed behind barriers of shingle instead Coastal lagoons are an important element in the of sand. This has resulted from two circumstances: world's coastal environment. All continents, except first, the prevalence of shingle as a coastal marine Europe, have between 10% and 20l}{, of their coas substratum in high latitude regions which have tlines in the form of barrier beaches, spits, or is been subjected to glacial action; and secondly, the lands enclosing lagoons to landwards (CROMWELL, large tidal ranges typical of the North Atlantic. 1971). Characteristically, the enclosing barriers are Large tidal ranges generate powerful tidal currents formed of sand and were constructed by wind and these are capable of destroying any incipient driven waves around the margins of microtidal seas, barriers of sand created by wave action. Large and typically the lagoons communicate with the masses of sea- bed shingle can be swept onshore by parent sea through open channels (BARNES, storm action, however, and shingle ridges can persist 1980). in the face of more vigorous water movements. Europe is unusual in having only 5% of its coas During the rise in sea level at the start of the tline formed by lagoonal habitats, and European present interglacial period, shingle masses were lagoons are common only around the shores of the moved landwards and dammed several small microtidal Baltic, Mediterranean, and Black Seas. drowned river valleys and estuaries (e.g., LITTLE et Nevertheless, lagoons do occur along the North aL, 1973). Where the enclosed region was subjec Atlantic seaboard and around the North Sea, ted to large throughputs of tidal or river water, this flux sufficed ( and still suffices) to prevent complete 1This work was supported with funds from the Nature Conservancy Council, under contract HF/3/11/37. 86012 received 24 March, isolation from the sea, and the shingle ridges here 1986; accepted in revision 23 June 1986. take the form of spits partially enclosing estuaries. 418 Barnes Where, however, the throughput of water was less mon in Essex, nor the drainage- dykes and borrow (usually because of a relatively small fres hwater input), ditches abundantly located immediately to land complete isolation was effected, with outflow from wards of the sea walls throughout East Anglia Phys the enclosed lagoon being only via percolation through iographically, these are in no sense lagoons, although the shingle barrier. Such lagoons rapidly evolved into they do contain a characteristically brackish-water coastal freshwater lakes, and most of the lagoons of biota (e.g. HOWES, 1939) and would repay survey the Atlantic coast of Europe are now in this state, and detailed investigation in respect of the occur sedimentation often having raised the bed of the one ranee of nationally rare brackish-water species. The time lagoon above the level of high water in the adja same applies to a numbel' of ornamental lakes, boat cent sea. Examples include Slapton Ley and (until ing ponds, and swimming pools (many of them ori 1826) Swanpool, in south-west England, and the ginating as lagoons) into which sea or estuarine E tang de Kergalan and E tang de Trunvel in Finis water is now pumped artificially. tere, Brittany. Where the freshwater input is negli Potential lagoons were identified from large gible and the bed of the lagoon is relatively low, scale Ordnance Survey maps, from aerial photo brackish water in the form of a mixture of sea water graphs in the collection of The Committee for and rain water which have both soaked into the shingle Aerial Photography in the University of Cam barrier can issue into the lagoonal basin through dis bridge, as a result of personal communications from crete springs orvia more diffuse discharges; here a the various officers of the Nature Conservancy more typical lagoonal habitat is maintained, as, for Council in East Anglia, and from the available example, the Etang de Nerizelec in Finistere and pu blished literature. A total of 40 coastal bodies of various small lagoons entirely enclosed within some water or sites where such bodies had been reported shingle-ridge systems, e.g. at Porlock in southwest England (BARNES, unpubl.). All such lagoons, how ever, are still further aberrant in lacking any direct I connection with the sea Only when the orientation of / 45 6-11 I' the coastline is such that the shingle barriertakes the / form of a spit rather than a barrier beach (a rare r / / ~- ..... occurrance in Atlantic Europe) does a more typical " lagoon result, with an entrance/exit channel near the tip of the enclosing spit, as seen in The Fleetin south west England. In Britain, shingle occurs at various points around the coast, besides in the southwest(RANDALL, 1977), and lagoons or lagoon-like systems are accordingly scattered along the British coastline. East Anglia, however, possesses a more marked concentration of such features than most areas outside Devon and Cornwall, and this paperpresents the results of a sur vey of these habitats from The Wash to the Thames Estuary, carried out under contract to the Nature 22-26 Conservancy Council as part of a larger survey of Britain's remaining coastal lagoons. For the pur ~ poses of the East Anglian survey, a lagoon was con 10km sidered to be a permanent coastal pond of saline or brackishwater, isolated or semi- isolatedfrom the sea but which nevertheless receives its salts from the sea as a result of natural causes. Artificial' scrapes' con structed within bird reserves for waders and wild fowl-for example those created by the Royal Society for the Protection of Birds atTitchwell (Norfolk) and at Minsmere and Havergate (Suffolk)-were not in Figure 1. Sketch-map of East Anglia, showing the location ofthe cluded within this survey; neither were the linear, 26 lagoons surveyed. sluiced, former tidal creeks ('fleets') which are com- Journal of Coastal Research, Vol. :~, No.4, 1987 Coastal Lagoons of East Anglia 419 to occur were visited in 1984 (Norfolk) and 1985 sheets on each site have been lodged with the (Suffolk and Essex), of which 26, all in a 200 km Nature Conservancy Council, Peterborough, U.K.: stretch of the Norfolk and Suffolk coastline (Figure this paper therefore concentrates on general fea 1 and Table 1), proved to fall within the definition of tures and presents an overview. a lagoon accepted above. The majority of the other 14 sites were once lagoons but have now RESULTS: THE NATURE OF ceased to be so as a result of man-made changes. THE LAGOONS Information on the topography, geomorphology, hydrology, salinity of the water, bottom sediments, The surviving lagoons of East Anglia fall into one and dominant macroscopic organisms (submerged or other of six distinct physiographic types. and emergent macroflora, and benthic and pelagic macrofauna) was recorded from each lagoon. It 1: Pits Located Within Shingle Formations should be stressed, however, that the survey was extensive, not intensive in nature, and that the These are often created in whole or part as a organisms recorded can in no sense be regarded as result of the extraction of shingle for construction complete species inventories. Individual data- purposes (Figure 2 and Table 1: lagoons 1, 12, 13, Table I. The coastal lruioons: 0/ r.:ast Anglin. Salinity British Area at time Freshwater Means of National water of visit input (other seawater ) Site Grid ref. (ha) ('J/u u than rainfall) input Pits located within shingle formations Snctfisham TF 649::W6- 64R:~:{:~ lR 17-20 percolation 12 NW Pool, The Denes TM 5:H')R42 1.5 .r.s percolation 1:3 NE Pool, The Denes TM 5:~6840 2 24 percolation and overtopping of barrier 14 S Pool, The Denes 'I'M 5:~68:n O.;~ :~O percolation and overtopping of harrier 22 'Lagoon 7', Shingle Street 'I'M :i744:~7 2.0 :31 percolation 2:~ 'Lagoon 6'. Shingle Street TM :37:~4;n 0.:3 :~O percolation 24 'Lagoon 4', Shingle Street TM :3724:~:J O.R :31 percolation 25 'Lagoon 1', Shingle Street TM :362419 0.8 :n percolation 26 .