Frank Lam 1/ . 1 .A„Drian De Kraker , Burghard Flemming', Han Lindeboonli, Han~'Jörg Streif
Total Page：16
File Type：pdf, Size：1020Kb
Climate and Human lnduced Impacts on the Coastal Zone of the Southern North Sea 1 2 3 Victor Smetacek* , Gerold v~~fer , Jürgen Alheit , Frank Lam_1/ . 1 .A„drian de Kraker , Burghard Flemming', Han Lindeboonli, Han~'jörg Streif. 6 9 Tjeerd van Weering , Hans von Storch 1Alfred-FVegener-Jnsritute.for Polar and ivfarine Research, Am Handelshafen 12. D-27570 Bremerhaven. Germanv :: Universi~v ofßremen. Departmenr of Geosciences~ Postfach 33 04 40. D-28334 Bremen. Germany 3Baltic Sea Research Institute, Seestra/ie 15. D-18119 VVi7rnemünde, Germanv 4University 14Amsterdam, Department qflluman Geograph); Nieuwe PrinsengraL~ht !30, NL-1018 VZ Amsterdam, The Netherfands 5Senckenbe1g Institute. Schleusenstraße. J9A. D-26382 fflilhelmshaven. Germany 6Nether!ands fnstitutefor Sea Research fNIOZj, PO. Box 59. NL-1790 AB Den Burg, The Netherlands ' Niedersächsisches Landesamt für Boder~(Orschung. Sti!leiveg 2, 30655 Hannover, Germany 8lnstitutefor Coastal Research, GKSS Research Center: Afax-Planck-Strasse !, D-21502 Geesthachr, Germany * corresponding author (e-mail).„ [email protected] Abstract: Ongoing changes in the morphology and ecology ofthe coastal zone and expected future scenarios \V-ith emphasis on the southem No1th Sea were discussed and research needs identified. The lmpact of sea level rise and the effects ofresultant dyking activity need tobe considered for the entire coastal zone as manipulation in one region can havc unexpected etfocts in neighbouring areas. The extent to which the ban·ier islands can be maintained in their present state has also to be c1itically assessed. Anthropogenie impacts on coastal ecosy::>tems can be direct (e.g. diking, fisheries) or subtle (pollutants). However, differentiating climate-induced from anthropogenic impacts is not always obvious. Long-term, integrnted data sets provide the best context for evaluating observations of individual phenomena. Maimenance of monitoring programmcs and introduction of new methodologies to extcnd coverage and detail is required for this purpose. The role ofpublic perception was discussed at length as coastal management is not as much management of nature as it is management of human activity. Hence it is essential that social scientists be involved to a greater extent in decision-making processes. lntroduction ti.m<lamentally alters the land-sea interface, hence also the coastal sea and its ecosystems. Until rc The coastal zone has been occupied by humans for cently coastal engineering was mainly concerned many millennia but it is only sincc about the l 6th with protecting the land from ravages of the sea but centmy that anthropogenic impact has become a experience gained so far has led to the realisation significant shaping force. Coastal plain environ that the entire coastal system needs to be treated as ments such as the southern coast of the North Sea a \Vhole, as modifications in one area can lead to arc most strongly irnpacted because dyke building unexpccted developments in adjoining regions. From \\TFER G. BERGER W. BEHRE K-E.. Jf\NSEN E !etis). 200::;, Climau.· D,,vef1Jpmen; und flisiorc· u/tltc Xur!h Aila111ic R,·aim. Sprin:;<:r-V<:rlag ßcrlin !kiddbcrg, pr 4~3-4::\li 474 Smcracek et al. Besidcs. the impact on marine ecosystems is in Bight are extended open tidal tlats an<l rounded to creasingly becoming a cause für concern. sickle-shaped sandy shoals (tvlellurn, Scharhörn, This rcport summarises the discussion thar \V('fC Trischcn. Tertius, and Blauort), which in pan are held by a multidisciplinary group at the Hansc mobile and epberneral struchJres. \Vissenschaftskolleg. The intention of the discus Additionally. rhe present-day moq1hology ofthe sions \\'as to asce1tain \Vhat has been learned so far coastal Jandscape is strongly intluenced by geo and wlm can be expected in the fut1ire. logical c!ements which were formed prior to the \Veichselian late glacial and Holocene sca-level Coasfüne, Islands and Sediments rise. Cores of Pliocene and Pleistocene sediments, surToumkd by Holocene coastal deposirs. crop out The southern North Sea is roughly triangular in on rhe islands of Sylt, Schleswig-Holstein, as well shape. From the Rhine delta the coastline stretchc:s as on Texel. in the Netherlands. Othcr structures in north-eastern to eastern directions as fär as rhe werc formed by the medieval storm surges which Elbe estuary where it turns north\vard along the destroyed extended areas of former coastal western coast of Schles,vig-Holstein and Jutland. marshlands and fönned huge tidal bays like the Denmark. A maximum vvater depth of the southern former Zuider Zee (nowadays fjsselmeer) and the North Sea of about 70 m is encountered on the Lauwcrs Zee in the Netherlands. Comparab!e north-\\'ötcm flank of the Dogger Bank: however, structures are the bay flats existing along the coast the depth is generally less than 45 m in the inner of Niedersachsen, Germany, Dollart and Jade Bay. part of the German Bight. Severc destruction of former coastal marshland The following tidal zones can bc distinguished which occurred along the westcrn coast of along the southem N0tth Sea coast. Low mesotides Schleswig-Holstein in the coursc of the storrn 'vith an amplitude between l and 2 m occur be surges of 1362 and 1634 AD created a special fon11 tv-:een the Rhine delta and tbe island ofTerschelling, of islands. the so-called Halligen. These rnarsh the Netherlands. High mesotides with an amplitude islands like Nordstrand, Pellwom1 and a group of of2 to 3 m occur eastward from Terschelling as far smaller islands consist of Holocene tidal t1at to as the island of Wangerooge. Low macrotides with brackisch sediments as weil as of peat. Special an amplitude of more than 3 m occur in the fonns of the Halligen arc Föhr and Amrum which innermost part of the German Bight (Siefert and have cores of outcropping Pleistocene sediments. Lassen 1985), between the tidal inlet of the Jade Additionally, Amrum is characterised by a spit-like Bay and the peninsula of Eiderstedt, Schleswig sandy beach. Holstein. reaching a maxirnum value of 4.2 m at Bremen on the Weser est1iary. The tidal amplitude Late Holocene Sea-Level Evolution decreases in a northerly direction to that character istic of high mesotides between Eiderstedt and Sylt, f irst cvidence für marine influences along the to that of Jow mesotides between Sylt and southern margin of the North Sea basin date at Blävands-Huk, and to that of microtides on the roughly 8000 years BP when the rising sea reached north ofNymindegab, Denmark. a level of about 25 m below the present and began The present tidal conditions are partly mirrored to intrude into the !ower valleys of Jocal rivers and by the coastal morphology. Continuous barrier streams drnining the more devated Pleistocene systems partly with lagoons (Ringk0bingt]ord and samt bodics (e.g. Hanisch l 980; Zagwijn 1986). Nissuml}ord) ex ist in the zone of small tidal ampli The posrglacia! sca-Jevel rise is documented in a tu<les along the western coasrs of the Nctherlands nurnber of sea-leve! curves reconstructed for dif and Denmark Elongatcd barrier islands (West Frie ferent sections of the coast. This is represented in sian and East Friesian islands) and sheltered tidal Fig. l by the rise of mean high-water lcvels which !1ars occur in the zone which is affected by tow to are more relevant för coastal processes (rnodified high mesotides. Characteristic for the macrotidal after Flemming and Davis 1994). Besides having conditions in the innermost pan of the German some fearures in cornmon, thc curves revcal quite Climate and Human [nduced lmpacts on the Coastal Zone - Group Report 475 distinct local trends. Thus, the curves rise more as much as 8.8 mm/year O\:er the next century. How steep!y up to about 6500 years BP (>110 mm/year), this would affect the evo1ution of mean high-water followed by a period of a more gradual rise {" 1.5 levels is unkno\1.-n, but a threefold increase in the mm/year) up to the onset of the "Little Ice Age „ in cunent rate would not appear unrealistic. the late i'v!iddle Ages. A distinct acceleration is Of interest in the context of this article are also again observed over the past 300 years or so, mean the deparrures in the trends of the individual curves. high-water levels currently ri.sing by as much as 2.5 Quite e\·idently. and irrespective of potential errors mm;year. This acceleration predates any anthropo in the individual reconstructions. the relative ver genic infiuence and has evidently been overlooked tical motions of the sea and the local land masses in recent disputes over human impacts on climate are not synchronised along the shoreline of the change. The current estimates of global warrning southern North Sea. even over distances as little as over the next century {up to 5 .8°C) recently re 100 km. This means that the effects ofsea-Jevel rise ported by the IPCC has led to a corresponding "vill have slightly different Impacts depending on upv;,·ard correction of the predicted acce!eration in the location along the coast. mean sea-kvel rise which is now estimated to reach Any acceleration in the rate of sea-level rise will also result in !arger tidal ranges. This is intirnated in the model illustrated in Fig. 2 (modified alter Flemming and Davis l 994; based on data reported 1O' Years Bafore Present in Franken t 987). The individual curves apply to 10 8 6 4 2 0 different locations along the coast and show simi lar temporal trends as the evolution of mean high \Vater levels (curve l: westenHnost Dutch Wadden Sea and northem-most Danish Wadden Sea; curve 2: north of Ameland, central Dutch Wadden Sea: curve 3: north of Spiekeroog, centra! East Frisian Wadden Sea, Germany).