LATE GLA CIAL AND HO LO CENE MOL LUS CAN AS SEM BLAGES IN DE POS ITS FILL ING PALAEOLAKES IN NORTH ERN PO LAND
Late Gla cial and Ho lo cene car bon ate lac us trine de pos its de vel oped as lac us trine chalk and cal car e ousgyttja are fairlywide spread across north ern Po land. They form fill ings of palaeolakes which de vel oped dur ing the deglaciation. Thesefor ma tions are usu ally cov ered by peat. Rich and di ver si fied malacofauna has been found in the afore men tioned sed i -ments. The pro files from 154 sites de scribed and pub lished by var i ous au thors were sub jected to malacological anal y- sis. In the whole ma te rial, 18 mol lus can as sem blages were dis tin guished, rep re sent ing three types of hab i tats: terres-trial, of tem po rary wa ter bod ies, and of per ma nent wa ter bod ies. The com po si tion and struc ture of these as sem blagesal lowschar ac ter iz in g cli mate and dif fer en ti at ing hab i tatsThe . time-se quencesof malacological as sem blages pro vided pos si bil ity to de fine three types of malacological se quences. On the ba sis of these suc ces sions, a scheme of the lakewa ter bod ies evo lu tion dur ing Late Gla cial and in north ern Po land was elab o rated.
Late Gla cial and Ho lo
This study pro vides a veg e ta tion and cli mate his tory of an al pine wet land in the cen tre of China’s Qinghai–Ti betan Pla teau (QTP) over the last 14.8 ka. High res o lu tion cli mate prox ies in clude veg e ta tion (pol len), geo chem i cal (Ba, Rb, dC) and phys i cal (par ti cle size and mag netic sus cep ti bil ity) data; op ti cally stim u lated lu mi nes cence (OSL) and AMS ra dio car bon dat ing were used to re con struct the en vi ron men tal changes in the wet land eco sys tem. Based on phys i cal and geo chem i cal prox ies, the sucession di vided into five strati graphic units en com pass ing time in ter vals of 14.76–14.31, 14.31–13.17, 13.17–4.47, 4.47–0.51 and 0.51–0 ka. The av er age sed i men ta tion rate of all these units was 0.098 mm/a. The study showed that this eco sys tem was sen si tive to cli mate change.
Filling of a wetland (Seine estuary, France): natural eutrophication or anthropogenic process? A sedimentological and geochemical study of wetland organic sediments
For over a century the Seine estuary has been highly affected by human activities, resulting in a reduction of the surface of wetland habitat. Several ponds of the Vernier Marsh, one of the main wetlands of the estuary, are being filled in by sediment. The St. Aubin canal, the only inlet from the Seine to the wetland, has regularly been opened in summer to maintain a sufficiently high water level in the system. The purpose of this study was to identify the origin of filling: natural evolution of eutrophication or human intervention by the opening of the St. Aubin canal? Sediment cores were sampled at 19 stations randomly distributed in the ponds of the wetland. Granulometric, micro-granulometric and geochemical analyses (ignition loss, C/N/P, chemical fractionation of particulate phosphate) were performed on the top 10 cm of sediment. Moreover nutrient concentrations (ammonium and phosphate) were measured in the interstitial waters using diffusion samplers. The results revealed that sediments sampled from the north are weakly organic (ignition loss: 19%, 15% C, 0.9% N , 40% organic P of total P) whereas those sampled from the southern stations are highly organic (ignition loss: 50–93%, 35% C, 1% N: 59–81% organic P of total P). In summary, sediments accumulating in the north of the ecosystem mainly consist of minerogenic particles from the Seine transported by the St. Aubin canal and thus are a result of the human interference. Interestingly the accumulation of sediments in the southern part is the result of a natural evolution of eutrophication: a peat bog. These sediments are highly organic, enriched with organic particulate phosphate, specifically a humic-acid-bound-phosphorus, a refractory form of phosphorus.