«Colophon Publishers Common Wadden Sea Secretariat (CWSS), Wilhelmshaven, Germany; Trilateral Monitoring and Assessment Group (TMAG); Trilateral ...»
Schuchardt, B., Schirmer, M., Janssen, G., Nehring, S. & Leuchs, H.
(1999): Estuaries and Brackish Waters.
– In: De Jong, F., Bakker, J.F., van Berkel, C.J.M., Dankers, N.M.J.A.,
Dahl, K., Gätje, C., Marencic, H. & Potel, P. (eds.), Wadden Sea Quality
Status Report. Common Wadden Sea Secretariat Wilhelmshaven,
Wadden Sea Ecosystem No. 9: 175-186
Common Wadden Sea Secretariat (CWSS), Wilhelmshaven, Germany;
Trilateral Monitoring and Assessment Group (TMAG);
Trilateral Quality Status Report Group (QSR Group).
Editors Folkert de Jong, Common Wadden Sea Secretariat (CWSS). Virchowstrasse 1, D - 26382 Wilhelmshaven, Germany;
Joop F. Bakker, Rijksinstituut voor Kust en Zee (RIKZ). Postbus 207, NL - 9750 AE Haren, The Netherlands;
Cees J. M. van Berkel, Ministerie van Landbouw, Natuurbeheer en Visserij (LNV), Dir. Noord, Postbus 30032, NL - 9700 RM Groningen, The Netherlands;
Karsten Dahl, Danmarks Miljøundersøgelser (DMU), Frederiksborgvej 399, DK - 4000 Roskilde, Denmark;
Norbert M.J.A. Dankers, IBN-DLO, Postbus 167, NL - 1790 AD Den Burg/Texel, The Netherlands;
Christiane Gätje, Landesamt für den Nationalpark Schleswig-Holsteinisches Wattenmeer, Schloßgarten 1, D - 25832 Tönning, Germany;
Harald Marencic, Common Wadden Sea Secretariat (CWSS), Virchowstrasse 1, D - 26382 Wilhelmshaven, Germany;
Petra Potel, Nationalparkverwaltung Niedersächsisches Wattenmeer, Virchowstrasse 1, D - 26382 Wilhelmshaven, Germany.
Cover illustration and graphic support Gerold Lüerßen Language support Wladimir Polanski Marijke Polanski Lay-out and print Druckerei Plakativ D-26209 Kirchhatten Paper Cyclus - 100% Recycling-Papier Number of copies Published ISSN 0946-896X To be cited as De Jong, F., Bakker, J.F., van Berkel, C.J.M., Dankers, N.M.J.A., Dahl, K., Gätje, C., Marencic, H. and Potel, P.
1999 Wadden Sea Quality Status Report. Wadden Sea Ecosystem No. 9. Common Wadden Sea Secretariat, Trilateral Monitoring and Assessment Group, Quality Status Report Group. Wilhelmshaven, Germany.
Wadden Sea QSR 1999
(Scholle and Schuchardt, 1997). However, motile of some importance as well as a number of mabenthic species (mostly crustacea) are of some rine species. Analyzing the existing data sets, a importance (Haesloop, 1990; Arntz et al., 1992). long-term data set compiled by Kolbe (1995b) is In the Eider estuary, the salinity gradient has of special interest. Data on infauna from the natubeen strongly altered (see above) resulting in a ral brackish water zone near Bremerhaven over reduction of the length of the brackish reach and 20 years show that strong variability of species a steepening of the salinity gradient. Marine spe- diversity and abundance is a typical feature of cies such as Nereis diversicolor, Arenicola marina estuarine communities, making it very difficult to and Cerastoderma edule have retreated down- differentiate between natural dynamics and stream (Fock and Heydemann, 1995) and the manmade changes (analyzing estuarine communumber of genuine brackish species is low nity data).
(Michaelis et al., 1992). However, recent surveys In the freshwater and the oligohaline reaches (Fock, 1996) have documented the occurrence of of the Ems estuary, species number, biomass and further brackish water species (Tubificoides he- densities are lower than in the mesohaline reaches terochaetus, Paranais frici, P. botniensis). Quanti- (IBL, 1994). Species most present in the tidal freshtatively, the low salinity region is characterized water reach are Limnodrilus hoffmeisteri and other by Marenzelleria spp. (Viridis/wireni complex), tubifids as well as Gammarus zaddachi. Species Heteromastus filiformis and Macoma balthica. composition in the oligohaline reaches is similar, Although the former situation of the macro- whereas in the mesohaline reach brackish species zoobenthos in the Elbe estuary is well documented, like Marenzelleria spp., Tubifex costatus, Bathyrecent published data are scattered. Stony em- poreia pilosa and some marine species are imporbankments have been sampled by Gaumert and tant. However, there is some evidence that reduced Spieker (1995) showing higher densities and di- habitat diversity and dredging have reduced the versity in the low salinity region (dominated by number of species (Dittmer, 1981; Rhode, 1982;
Balanus improvisus) than in the tidal freshwater IBL, 1994). Arntz et al. (1992) have described the reach (dominated by Dreissena polymorpha and quantitative importance of motile macrofauna Gammarus zaddachi). According to Nehring and species such as Paramysis kervillei and Neomysis Leuchs (1996), the low salinity region is charac- integer. However, recently, a decline of diversity terized by Marenzelleria spp., Boccardiella redeki and abundance, probably due to dredging activiand Neomysis integer. Riedel-Lorje et al. (1995) ties and anoxia, has become obvious (IBL, 1997).
and Krieg (1996) have described some upstream Comparison of recent data with older ones from extension of brackish water species such as Bathy- the beginning of the century, reveals a strong reporeia pilosa and Corophium volutator and con- duction of species number in the innermost Weser cluded that there has been an upstream move- estuary, which is mainly the result of morphologiment of the brackish water zone, perhaps as a cal changes, whereas in the middle reaches, result of engineering works in the estuary. How- changes are less significant (Haesloop and Schuever, this item is still open to scientific discus- chardt, 1995). It can be assumed that this is a sion. general tendency in the estuaries under considIn the Weser estuary, the situation is well docu- eration (for the Elbe see BfG, 1994). However, due mented by the results of, e.g. Haesloop (1990), to the intrusion of a number of ”new” species (neoKolbe (1995b) and Gosselck and Prena (1996). Due zoa), these losses have partly been compensated to elevated conductivity (resulting from potassium (see Nehring and Leuchs, 1999). These alien spemining upstream) in the tidal freshwater reach, cies seem to have become integrated into the food the benthic fauna is dominated by several brack- web without out-competing other species (in esish and marine crustaceans, most of them invad- tuarine sediment dumping areas Marenzelleria ing in large numbers from the natural brackish spp. becomes one of the dominant forms; Leuchs region in spring and summer. Among them, et al., 1996).
Gammarus zaddachi, Corophium lacustre, NeomyFish sis integer, Palaemon longirostris and Crangon Fish is relatively well documented as well, due to crangon are of particular importance (Haesloop its great commercial importance in historical and Schuchardt, 1995) as well as Balanus improtimes. This importance has been reduced strongly, visus and Marenzelleria spp. (Nehring and Leuchs, both due to a decrease or extinction of some fish 1996). In the natural brackish reach, further spespecies of commercial interest and changes in the cies such as Balanus improvisus, G. salinus, brackbehavior of consumers (Schuchardt et al., 1985;
ish oligochaetes like Peloscolex heterochaetus and Möller, 1989). However, in general, the estuaries Tubifex costatus as well as some polychaetes are
estuary, deepening and canalization for shipping tendencies existing, a further deterioration due purposes is most significant and has altered the to further deepening of the inner and outer estuestuary greatly. aries and active habitat restoration (Gaumert, Taking the actual situation into account, this 1995; Schuchardt, 1997).
ranking must be changed considerably. The eco- We will give a short summary of the most imlogical status of the inner Ems estuary must be portant or advanced schemes:
classified as heavily stressed regarding water qual- Ems estuary: irregular dredging of the inner ity, sediment budget, morphology and aquatic estuary (Papenburg to Pogum) from 6.8 m to 7.3 fauna, whereas the water quality parameters in m below high water for the transfer of ships from the Elbe and Weser estuaries have been improved. the Papenburg ship yard to Emden; extension of Data for the Varde Å are hardly available; thus, the Emden port; building of a storm-surge-barit cannot be evaluated in detail in the present rier.
paper. However, the Varde Å can be described as Weser estuary: Weser Tunnel at Dedesdorf; inmostly natural in terms of hydrographic and mor- dustrial district on the Luneplate; extension of phological structure, although the marshes have Nordenham and Brake harbors; extension of the also been strongly altered due to agricultural pur- container terminal in Bremerhaven (CT IIIa and poses. IV); filling of harbor basins in Bremen; canalizing Since some improvements of water quality have and dredging of the river Hunte (km 0 - 21); deep
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