The Solent: an Estuarine System in Flux

The Solent:an estuarinesystem in flux

Colin Tubbs

Reprinted,by agreement with the editors, from the Shorelinesfeature in BTO NewsNo. 167 (March-April1990)

The modernSolent on the south-coastof Englandarose from the invasionof an ancientriver system by the sea following The sediments accumulated in the estuaries and harbours theend of thelast Ice Age. The mainstream formerly flowed mainlycomprise fine silts and organic matter - the mudsin the eastwardsthrough what is nowPoole Harbour, across the harboursare amongthe soffestI haveencountered and are bedof BournemouthBay and along the bedof the present mostlyonly negotiable with mud pattens. Saltmarshes, Solentwaterway, before turning south to an ancientcoastline probablyof medievalor possiblyearlier date, occur locally, southof the Isleof Wight(Figure 1). Risingsea leveldrowned thoughthey are nowreceding through erosion at the terminal thisriver and the lower parts of itstributaries, giving rise to the cliffs.From the 1870sthe invasivecord grass Spartina spread numerousestuaries and harbours of todayalong the south widelyon mid-levelmudflats, but these Spartina marshes are coastof Hampshire(extending just into West Sussex) and the nowin a degeneratephase and over large areas the plat- northshore of the Isleof Wight(Figure 2). formsof accretedmud are currentlyslumping back to somethingthought to approximateto the pre- Spartina SALTMARSH AND SEDIMENTS profile.

The largestof the harbours,those of Portsmouth,Langstone andChichester, derive from the drowningof a densenetwork RISING SEA LEVELS of streamsfollowed by a lateralexpansion through wave attackat highwater which in placeshas produced cliffs 2m or The processesinvolved are beyondmy scope here, but an morehigh, cut into a glacialterrace. The threeharbours of the implicationfor shorebirds isthat the potential feeding area northeastSolent are essentiallya single biological system, hasincreased. This increase, however, isin part balanced by comprisingconnected and extensive intertidal basins drained a progressivenarrowing of theintertidal zone during this at lowwater by systems of channelsand creeks which centurythrough processes which probably derive from sea probablyreflect the early postglacial drainage pattern. level rise. We need to remind ourselves that sea level has beenrising relatively rapidly since around the mid-19th Rgure1. The ancientSolent River systems in relationto the modernday Centuryirrespective of any20th Century greenhouse effect. coastline. Today,of 9,060 ha of intertidalsediment in the Solent,6,191 ha are mudflats,729 ha are sandflats,430 ha are ancient saltmarshesand 1,71 0 ha are Spartinamarshes, of which 650 ha arein an advancedstate of degeneration.There are extensivebeds of thesea grass Zostera and there is abun- dantgreen algae, mainly associated with sewage effluent dischargesinto estuaries. The Solentis a warm,nutrient-rich muddysystem in which there is abundantorganic debris and veryhigh densities of mud-flatinvertebrates.

Thebiological wealth of thesystem is reflectedin the large numbersand high densities of wadersand wildfowl which feedin the intertidalzone. Over the five year period 1983-84 to 1987-88,the average winter peak populations ofwaders

21 Figure2. Themain estuaries within the modern day Solent complex. leisuretime and disposable income.

Thisall representsa snapshotin time.A yearago, and X,__• p PO Ismouth Langstone •O•. I'• Harbour Harbour. doubtlessa year hence,there was, and will be, a different catalogueof threatsof equallength. Between 1930 and 1980, 11.5%of the intertidalarea of theSolent was destroyed by Lymlnglon • •t••'• "•' PorlsmoulhJ - • L Harbour.. land-claimand development. Were all the presentthreats to achievefruition, I guess they would remove another 1% - not, /e Newlown Medina •Harbour /Yar Bay youmay say, disastrous, but nonetheless another step in the processof attrition.Interestingly, we havenow reached the stagewhere the first applications are beingmade to fillin marinasin order to buildhouses, because houses pay better thanboats - the marinasin the first place having received planningpermission mainly on the grounds of an over-riding demandfor berthsin the Solent!If thistrend continues, then, andwildfowl were respectively103,000 and 40,000,repre- presumably,it will in turnexacerbate the demandfor more sentingabout 20 birdsper ha of mudand sandflat. This boatberths and hence add another turn in thespiral demands densitywould appear to be higherthan in othermajor UK made on the Solent. estuarinesystems. Among the Solent's component estuaries, Chichesterand Langstone Harbours support the highest Probablythe most far-reaching recent threat to theSolent numbersof winteringbirds, each ranking among the top15 wasthe CEGB'sproposal to builda 2500 kvcoal-fired power UK estuariesfor their total wader populations (Table 1). statonnext to theexisting oil fired station on the shore IndividualSolent estuaries support internationally important betweenFawley and Calshot Spit. Coal, and the limestone for concentrationsof Ringed Plover, Grey Plover, Dunlin, Black- a flue-gasdesulphurisation plant, would arrive by sea at a tailedGodwit, Bar-tailed Godwit, Redshank, Brent Geese, portconstructed over the saltmarshes and mudflats. Huge Wigeon,Teal andShelduck, and nationally important num- quantitiesof wasteswould be exportedthe same way or via a bersof Sanderling,Curlew and Turnstone. Langstone and newrail link. We - theconsortium of opposition,led by the ChichesterHarbours are alreadydesignated for conservation Countyand District-Councils- were still grappling with the underthe RamsarConvention and as a SpecialProtection ecologicalconsequences of marine and atmospheric pollution Area under the EEC Birds Directive. The remainder of the andwith the multitude of effectsderiving from the sheer scale Solentalso qualifies for both designations, and the Nature of the mega-station,when the Boardwithdrew in the shadow ConservancyCouncil propose to seekdesignation by the of privatisationearly in 1989.Yet, I am notoptimistic enough Secretaryof Stateonce the necessarypreliminary consulta- to assumethat the threat has been disposed of forever. tions have been carried out.

Table1. Averagepeak winter totals for waders wintering on Solent estuaries, Internationaldesignations deter but do notpreclude threats. 1983-84-1987-88. About1.1 millionpeople live within 15 kmof theSolent. It has 32,000yacht berths and moorings - the largest recreational fleetin theworld- and it hastwo major ports and the massive Estuary Waders Essorefinery at Fawleyon SouthamptonWater. It sharesin the biologicalmalaise of south-eastEngland - overabundant ChichesterHarbour 39,487 capitalavailable for investmentin up-marketwaterside LangstoneHarbour 38,811 housing,marinas, leisure centres and the claim of newland SouthamptonWater 10,858 fromthe tide. As I write,the catalogue of threatsto the PortsmouthHarbour 9,018 shorelineand intertidal of theSolent includes 11 proposed NW Solent 6,509 marinas,one large scale land-claim and part flooding of a 103 Beaulieu 4,316 acrestidal inlet, the canalisation ofthe Lymington estuary to Newtown 2,154 accommodatelarger ferries to the Isleof Wight,and a BradingHarbour 1,185 multiplicityof demands for pontoons, slipways, and shore Medina 782 facilitiesfor the amazing array of recreationalpursuits which Yar 553 we seemto haveinvented to mopup the abundanceof Wootton 538

22 MORE COUNTS NEEDED

I do notmean this article to be a catalogueof woes.We - I usethe termto embracethe NatureConservancy Council, Hampshireand Isle of WightNaturalists' Trust, RSPB and communityconservation bodies- have notlost a public 'inquirywhere the conservation ofthe intertidal orshoreline wasat stakesince the 1960s.It was notonly that different attitudesprevailed in the 1960sand before. More importantly, we simplydid not have the data- norto be brutal,the exper- tiseof presentation- that we nowpossess. Much of thatdata derivesfrom the British Trust for Ornithology based Birds of EstuariesEnquiry and the Wildfowl and Wetlands Trust based National Wildfowl Counts. Much else besides hascontributed tothe cases wehave presented atsucces- sivepublic inquiries, but without the counts I suspect we wouldhave been lost many times. I doubtif I needlabour the pointexcept to saydo pleasekeep counting and we will , continueto fight.