Ref ID : 4608
Louis Beyens; [Paleoecologische en Paleoklimatologische Aspecten van de Holocene Ontwikkeling van de Antwerpse Noorderkempen] (Palaeoecological and palaeoclimatological aspects of the Holocene evolution of the Antwerpse Noorderkempen). Academie voor Wetenschappen,Letteren en Schone Kunsten van Belgie 46(2):16-56, 1984
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A number of Holocene sequences from the Mark basin (Belgian Campine) have been studied palynologically and, where possible, the diatom flora and the testate amoebae assemblages analyzed. In this article only the site Ipenrooi-ven is described, followed by a brief discussion of some of the climatic changes indicated. Holocene peatgrowth began round 10.230 B.P. The open park-landscape with Betula as dominant tree species was soon replaced by a rather dense Pinus-Betula wood. This evolution was interrupted twice by an unfavourable climatic oscillation. The first one, corresponding to the Piottino, could be dated around 9.660 B.P. and is characterized by a sudden decrease in Pinus in favour of Betula which again become dominant. The second one, which is coined the Mark-oscillation, occurred towards the end of the Preboreal. It did not have such a severe impact on the vegetation and was probably of a more oceanic nature. Pinus displays only as light decrease, but the most conspicuous feature in the pollen-diagram is the expansion of Gramineae. Renewed peatgrowth during Atlantic times in the bog at Ipenrooi and the flooding of the valleyfen at Wortel, as detected by diatomanalysis, are indicative of a more humid climate with the water-table rising to its Preboreal level. In this period, the bogsurface at Ipenrooi was only moderately humid or even dry during the summer, as demonstrated by a tyrphoxene thecamoeba association dominated by Hyalosphenia subflava and the presence of the aerophilous form of the diatom Pinnularia borealis. The high Tabellaria fenestrata percentages indicate the minerotrophic nature of the peatmoss. However the occurrence of zygospores suggests that the bog surface was under water in the spring. During the first part of the Subboreal the vegetation at Ipenrooi was still very similar to that of the Late-Atlantic. The testate amoebae associations, with Hyalosphenia subflava and Cyclopyxis eurystoma as dominant species indicate drier conditions during the Subboreal summers, except between +/-4.300 B.P. and 4.000 B.P. when an increase in Difflugia rubescens points to submerged conditions. In the pollendiagram a hiatus became evident due to peatcutting by medieval man around 785 A.D. The removal of the waterlogged peat left a depression filled with water. Potamogeton growing in this pool was colonized by the rhizopod Difflugia lobostoma and the diatom Tabellaria flocculosa. Lemna floated on the acid-oligotrophic water. In the following phase periodic oxygen shortage occurred in the developing Sphagnum bog, characterized by diatoms with a low oxygen demand, such as Pinnularia viridis and P. subcapitata var. hilseana. Once the mosses grew above the waterlevel, the oxygen balance was restored and a typical peatmoss flora with Frustulia rhomboides var. saxonica and Eunotia spp. occur, together with the Assulina species. Further changes in the rhizopod associations enable the recognition of a number of fluctuations in the moisture content. During the dry periods Calluna colonized the bog. With the aid of Calluna peaks the evolution of the testate amoeba fauna and lesser extent the diatoms, it was possible to construct a peatgrowth curve reflecting climatic fluctuations such as Medieval Climatic Optimum and the Little Ice Age. It would appear that Pinus did not disappear entirely but survived in some rare refugia. The afforestation of the moorland with this tree from the end of the 17th century on is clearly reflected in the pollendiagram. The diatom flora in the bog evolved into an association adapted to a highly acidic and oligotrophic environment, with Eunotia exigua forming almost monocultures. This is believed to be consequence of the acid rain phenomenon.