Malacofauna of the Holsteinian lake de pos its at Hrud II ( East ern Po land ) and its palaeo eco logi

Mol lusc-bear ing de pos its at Hrud II (East ern Po land) ac cu mu lated in the west ern part of a palaeolake of Holsteinian age (MIS 11). The fau nal as sem blage is typ i cal of fresh wa ter en vi ron ments and pre sum ably rep re sents a part of the inter gla cial cli ma tic op ti mum (Carpinus–Abies Zone). On the ba sis of its var ied com po si tion, the evo lu tion of the wa ter body is de scribed. Re in ter pre ta tion of the data from the east ern part of the lake (Hrud I) and com bin ing of the re sults from both sites en able a wider palaeo eco logi cal re con struc tion. Fluc tu a tions in lake level, wa ter dy nam ics and changes in the aquatic veg e ta tion are in ferred from quan ti ta tive re la tions be tween se lected molluscs, es pe cially Lithoglyphus jahni, Valvata piscinalis and Bithynia tentaculata, which pre vail in the de pos its in ves ti gated. A pre dom i nance of Valvata piscinalis in di cates a rise in wa ter level, whereas the com mu ni ties with abun dant Bithynia opercula are typ i cal of a more shal low lake with rich reed fields. Ame lio ra tion of the trophic con di tions be tween the pre-op ti mal and op ti mal part of the Holsteinian Inter gla cial can also be recognized.