The Suffolk estuaries

The following papers were delivered at a Regional Conference organised by the Suffolk Naturalists' Society and the National Rivers Authority Anglian Region.

Water Wilderness The conference was held at Ipswich School Conference Centre, Henley Road, Ipswich, on Saturday, 27th October, 1990.

THE SUFFOLK ESTUARIES CHARLES BEARDALL

The Formation and History of the Suffolk Estuaries The majority of the Suffolk estuaries were formed approximately 6,000 to 7,000 years ago. Before this period Suffolk was connected to the continent by a land bridge and todays estuaries were river valleys. As the glaciers melted after the last ice age and the land mass sank, the sea level rose flooding the river valleys of the Blyth, Aide, Butley, Orwell and Stour with tidal waters.

Once inundated sediment settled out of the relatively calm waters creating extensive areas of intertidal mudflat. The Ore estuary is however much younger having been created by the formation of Orfordness, which has been extending south at approximately 15m per year for the last 700 to 800 years and deflecting the mouth of the Aide estuary. By the 1100's the Ness extended little further than Orford and has since extended a further five and a half miles south.

Since their formation the Suffolk estuaries remained largely unaltered for many centuries and covered vast areas of the coastal strip. When agricultural land became more valuable sea walls were built, originally on saltmarsh but latterly on mudflats. In Suffolk alone approximately 10,800 hectares of the intertidal zone has been claimed for agriculture leaving only Vfeth of the area of the original estuaries. The first record of sea walls built in Suffolk are those around Orford castle in the 1100's, some may however date back to Roman times. T h e majority were built in the 14 to 17th century. Saltmarsh was originally converted into coastal grazing marshes which soon developed into important wildlife habitats in their own right, however today the majority have been extensively drained, ploughed and farmed for cereal crops.

Important aspects of the Ecology of the Suffolk Estuaries Intertidal mudflats are one of the most biologically productive ecosystems on the planet, however the majority of this life is in the form of benthic invertebrates living in or on the mud. The most obvious indication of this wealth of life is the enormous flocks of waders and wildfowl that over-winter

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in Suffolk. Approximately 4% of the total UK population of waders overwinter in Suffolk, but probably three times this number use our estuaries as vital refuelling stations as they migrate from the arctic and sub-arctic breeding grounds to over-wintering grounds in Africa and the mediterranean shores. Suffolk is internationally important for five species of wader and wildfowl and nationally important for another eleven. Of particular note are the numbers of avocet that over-winter on the Alde/Ore/Butley complex (53% of the UK population) and black-tailed godwits on the Stour and Orwell. It is primarily on ornithological grounds that the majority of the Suffolk Estuaries have been designated as SSSI's.

The importance of our estuaries for waders and wildfowl is of course dependent on the composition and abundance of intertidal benthic invertebrates. In Suffolk these communities are dominated by molluscs (predominantly Baltic tellin, cockle, mussel, gapers and the mud-snail Hydrobia ulvae), crustacea (the shrimp-like Corophium volutator) and polychaete worms (mainly ragworm and lugworm). Studies by the Suffolk Wildlife Trust have revealed that on average each square metre of mudflat on the Orwell contains 0.6kg of invertebrates, with the most productive areas reaching 2.0kg. The total weight of invertebrates inhabiting the Orwell alone is estimated to be 4,250,000kg.

The Suffolk estuaries are not particularly well endowed with saltmarsh accounting for only 2.4% of the total area of this important habitat in the UK. Our saltings are particularly important however for a variety of saltmarsh plant communities, including a number of rare species, as well as for breeding waders. Saltmarsh erosion has been studied by the Suffolk Wildlife Trust in some detail and whilst some estuaries appear to contain a relatively stable area of this habitat over the last one and half centuries (for example the Deben) others have suffered severe losses (the area of saltmarsh on the Orwell today is one half of that shown on the tithe maps of the 1840's, the majority has been lost to port developments). Detailed studies on the Trimley and Shotley marshes reveal that these areas are experiencing 1 metre of erosion a year in some places. This not only represents a severe loss of important habitat but also has major implications for sea defences (saltmarshes can absorb a high proportion of the energy of a wave before it hits the sea wall).

Other estuarine habitats reviewed in the presentation included reedbeds, where there is a strong influence of freshwater, and shingle. Suffolk is particularly important for areas of vegetated shingle providing the habitat for many rare species of plant and breeding birds. Indeed Orfordness is the largest vegetated shingle spit in Europe and a National Nature Reserve.

Grazing marshes provide another important habitat linked to and derived from the Suffolk estuaries. Detailed surveys by the Trust have highlighted the importance of the few remaining traditionally managed grazing marshes in Suffolk. Over 65% of Suffolks coastal marshes have been lost to arable farming since 1953, and the majority of the remaining marshes are intensively farmed and hence of little use to wildlife. The few remaining areas are exceptionally important for breeding and over-wintering waders and wildfowl.

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Ecological impact of human activities on the Suffolk Estuaries Estuaries around the UK are under tremendous pressure and the Suffolk estuaries are no exception. The estuaries of Suffolk have, for many centuries, been of great importance to those living along the coast providing food, salt and other natural products as well as a means of communication and trade.

However, in the last hundred years these demands have dramatically increased in response to the needs of modern industry and transport and the development of a wide range of recreational pursuits.

The most obvious impact of any human activity on our estuaries is the direct development of the intertidal zone. The conversion of saltmarsh and mudflats into agricultural land may now have ceased, but the 20th century has brought new pressures in the form of demands for land for industry, marinas, ports and the tipping of refuse and flyash. At this very point in time 75 hectares of Fagbury mudflats and saltmarsh are being developed by the Felixstowe Dock and Railway Company, 14 hectares of mudflat are being infilled for the extension of the West-bank terminal of Ipswich Port and 100 hectares of Bathside Bay are being developed to extended Parkeston Quay and to build houses, marinas etc. at the mouth of the Stour. Many other smaller 'reclamation' schemes are also occurring (predominantly for the extension of marinas). Whilst the impact of any single small scheme may be considered by some to be negligible the collective impact over a wider time base will account for a substantial loss of the intertidal zone and its associated wildlife. It is hard to imagine how better these sites could be protected (i.e. as SSSI's, Special Protection Areas under the E C wild Birds Directive, proposed R A M S A R sites, Areas of Outstanding Natural Beauty and Heritage Coasts) and yet we still see the continual destruction of internationally recognised wildlife habitats.

The major ports of Felixstowe, Ipswich and Harwich not only bring with them the ceaseless hunger for more land but also many other pressures. Both the Orwell and the Stour are extensively dredged to accommodate some of the world's largest container vessels. Since 1947 four million cubic metres of mud have been dredged out of the Orwell alone, deepening and straightening the navigable channel and increasing the tidal volume by 56%. Such dramatic changes will have substantially altered the physical characteristics of the estuary and hence had a major impact on the associated plants and animals that are dependent on the estuarine environment. Small wonder the Orwell saltings and mudflats are suffering severe erosion.

Throughout history, estuaries have been used as the dustbin for a variety of waste products, both from industrial processes and domestic sources. As a result the upper reaches of the Orwell are the most polluted stretch of estuary in the Anglian Waters region. This however creates a small dilemma for conservationists. Some input of sewage will boost the productivity of the estuary providing extra food for invertebrates (the majority of which are detritivores) living within the mudflats. However beyond a critical level excessive input of sewage becomes polluting due to increased bacterial activity stripping the water of oxygen, the promotion of excessive algal growth smothering the mudflats and saltmarshes and the toxicity of am-

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monia, amongst other impacts. The upper reaches of the Orwell exhibit many of these problems.

The Orwell also suffers from other sources of pollution. Oil spills have regularly occurred over the last few years, often associated with oiled birds and dead invertebrates lying on the surface of the mudflats. The mudflats of the upper reaches of the Orwell are also heavily charged with mercury and copper illustrating the potential for estuaries to act as sinks for pollutants due to the adsorption properties of particles of silt which form the mudflats.

Tri-butyl tin (TBT), the active ingredient in anti-fouling paints used on boat hulls since the early 1970's, has now been banned from 'retail sale' due to its devastating effect on marine organisms. Many people, including yacht owners, may feel relieved by this ban, however TBT-based paints are still in use on boats above 25 metres. Felixstowe, Ipswich and Harwich are three of the largest container ports in Britain, frequented by some of the world's largest container vessels. The effects of TBT entering the water, or becoming fixed into the sediments, from these vessels is unknown and the cause of some concern.

It is not only commercial shipping that has increased. Since the early 1950's the popularity of both water and land based recreational pursuits has burgeoned. Yachting now dominates many of our estuaries in the summer (the Orwell alone has 3,000 leisure craft whilst the relatively small Deben has 2,000). The impact of this activity on wildlife is hard to monitor but unless controlled will undoubtedly increase. Perhaps of even more concern is the uncontrolled expansion of personalised water craft on our estuaries, and especially jet skis. These craft can penetrate previously undisturbed areas of our estuaries, including saltmarsh creeks, and if unrestricted will undoubtedly decimate the importance of our saltmarshes for breeding birds.

Sea angling too has become more popular and has led to a greater demand for bait. Bait-digging occurs on all of Suffolk's estuaries but is currently only of concern on the Orwell and Stour. Bait-digging has only a small impact on the species of invertebrate that are harvested, however there are many hidden impacts on other invertebrate species as well as disturbance to feeding waders.

Wildfowling is another traditional estuarine activity and up to the 1940's provided both income and a valuable supply of protein for the local population. It is now solely a recreational pursuit and is enjoyed by over 160,000 people nationally. An estimated one million wildfowl are shot annually through out the UK, 70 to 75% of which are mallard and the remainder teal and wigeon. Studies in the USA suggest that an additional 20 to 35% of those shot are wounded and die unretrieved. For wigeon the annual kill is thought to amount to 60,000 to 120,000. With a peak overwintering population of 224,000, the total number shot is therefore a significant percentage of the British population and conservationists are keen to see wildfowling clubs more carefully monitor the impact their activity is having on wildfowl populations.

Safeguarding the important species and communities that inhabit the Suffolk estuaries requires the conservation and sensitive management of the whole ecosystem. With so many demands brought on our estuaries, it is time

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that each user-group became more accountable for the wider environmental implications of their activities. This will require a greater commitment to protecting the environment than in the past (from industry, recreational users, adjacent land uses, local and national government etc.) and a less isolated approach to how we all use and abuse the environment.

The estuaries of Suffolk are one of our last remaining wildernesses providing a livelihood and enjoyment not only for local people but also many visitors. It is in everybody's interest that their natural integrity is conserved.

Dr. Charles Beardall, The Suffolk Wildlife Trust, Park Cottage, Saxmundham, Suffolk

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Plate 9: Water Wilderness Conference, October 1990. Speakers and organisers (left to right): Dr Brian Crook.

Dr Barrie Rickards, Dr Charles Beardall, Dr Peter Maitland, The Earl of Cranbrook, Howard Mendel, Juliet Hawkins, Dr Chris Spray and Steve Piotrowski. (p. 65).

(Photo: S. Dumican)