A significant portion of calcium carbonate is deposited in lake sediments as a result of biological processes related to the photosynthetic activity of phytoplankton in the pelagic realm and, in addition, macrophytes in the littoral zone. Lake Wigry, one of the largest lakes in Poland (north-east Poland), is characterized by: (i) carbonate sediments with a CaCO 3 content exceeding 80% within the littoral zone; and (ii) large areas of submerged vegetation dominated by charophytes (macroscopic green algae, Characeae family). It is claimed that charophytes are highly effective in utilizing HCO 3 À and forming thick CaCO 3 encrustations. Thus, this study was aimed at evaluating the CaCO 3 production by dense Chara stands overgrowing the lake bottom reaching a depth of 4 m. In late July 2009, the fresh and dry mass of plants, the percentage contribution of calcium carbonate and the production of CaCO 3 per 1 m 2 were investigated along three transects at three depths (1 m, 2 m and 3 m, with each sample area equal to 0Á0625 m 2 ) per transect. The composition and structure of phytoplankton and the physico-chemical properties of the water analysed in both the littoral and pelagic zones served as the environmental background and demonstrated moderately low fertility in the lake. The greatest dry plant mass exceeded 1000 g m À2 and CaCO 3 encrustations constituted from 59% to over 76% of the charophyte dry weight. Thus, the maximum and average values of carbonates precipitated by charophytes were 685Á5 and 438 g m À2 , respectively, which exceeded previously reported results. A correlation of carbonate production with the depth of Chara stands was detected, and intermediate depths offered the most favourable conditions for carbonate precipitation (589 g m À2 on average). As precipitated carbonates are ultimately stored in bottom deposits, the results highlight the significance of charophytes in lacustrine CaCO 3 sedimentation.

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This paper presents a comprehensive palaeoenvironmental data set from Lake Skrzynka, northern Poland. A sediment core from the lake was investigated to reconstruct Lateglacial and Holocene environmental changes in northern Poland using a combination of palynology and stable carbon and oxygen isotope studies of carbonates and sediment geochemistry. The undisturbed sedimentation in Lake Skrzynka continues from the Allerød to the present. Our data suggest the persistence of dead ice in the Lake Skrzynka basin up to the Allerød. The sedimentary record of the lake reflects a considerable difference between the Lateglacial/early Holocene and the middle/late Holocene in terms of environmental conditions. The Lateglacial was characterized by rapid environmental changes, while climatic conditions throughout the Holocene were relatively stable. The trophic state of the lake was strictly dependent on climatically controlled vegetation changes and erosion tendencies in the vicinity of Lake Skrzynka. During the Lateglacial and early Holocene, as a result of predominantly open plant communities and enhanced nutrient export from the watershed, Lake Skrzynka experienced an increased trophy. The stabilization of forest cover and reduced input of nutrients resulted in the establishment of oligotrophic conditions in the lake in the early Boreal. During the late Subatlantic, the lake became eutrophic as a result of human disturbance of the local hydrological balance. The postglacial history of Lake Skrzynka can be regarded as representative of small, alkaline, through‐flow lakes in temperate climates.

Apolinarska, K. and Hammarlund, D. 2009. Multi-component stable isotope records from Late Weichselian and early Holocene lake sediments at Imiol --ki, Poland: palaeoclimatic and methodological implications.ABSTRACT: Late Weichselian and early Holocene climatic and environmental changes are inferred from stable carbon and oxygen isotope records obtained on bulk and biogenic carbonates from the sediment sequence of Lake Lednica, western Poland. Along with sediment and pollen stratigraphic data, a wide range of carbonate components occurring in the sediments was analysed for d 13 C and d 18 O, including shells of several gastropod species and the bivalve genus Pisidium, carapaces of the ostracod subfamily Candoninae and oogonia of the aquatic macrophyte genus Chara. The development of catchment soils and the onset of authigenic carbonate production in response to the climatic amelioration during the Late Weichselian are clearly reflected by rising carbonate content, distinct isotopic shifts in bulk carbonates and decreasing d 13 C values of bulk organic matter in the sediments. The GI-1/GS-1 (the Bølling-Allerød Interstadial complex/Younger Dryas Stadial) and the GS-1/ Preboreal transitions are marked by significant shifts in d 18 O values of 2-3%, as well as by distinct changes in carbonate content, indicative of a decrease and a subsequent increase in mean annual temperature. Corresponding d 13 C records reflect primarily changes in aquatic productivity, with favourable conditions for phytoplankton and macrophytes during GI-1 and the Preboreal resulting in persistent 13 C enrichment. The Younger Dryas Stadial is characterised by depletions in 13 C and 18 O, with indications of a climatic tripartition. Consistent offsets in d 13 C and d 18 O between records obtained on specific carbonate components reflect vital effects in combination with seasonal characteristics and habitat preferences of the respective carbonate-precipitating biota. Largely parallel first-order variations in d 13 C and d 18 O of the different carbonate components demonstrate that individual isotope records may provide important palaeoclimatic information, although more detailed reconstructions can be obtained from multi-component analysis.

Stable isotope composition (d 13 C and d18 O) was analysed in mineral incrustation of Chara rudis and surrounding waters. This macroalga forms dense and extensive charophyte meadows and may significantly contribute to the calcium carbonate precipitation and deposition of marl lake sediments. The study aimed to find out if charophyte calcium carbonate was precipitated in an isotopic equilibrium with lake water and if the precipitation was related to the environmental conditions. Two apical internodes of 10 individuals of C. rudis were collected monthly between June and late October 2008 at three permanent study sites (1.0 m, 1.5 m and 2.0 m deep) in a small (15.1 ha) and shallow (mean depth: 4.3 m) mid-forest lake with extensively developed charophyte meadows (Lake Jasne, mid-Western Poland). Basic physical-chemical analyses were performed at each study site, and water samples for further laboratory determinations, including stable isotope analyses, were collected from the above searched C. rudis stands and, simultaneously, at three comparative sites in the macrophyte-free pelagial. The difference in d 13 C between incrustation and water from above C. rudis exceeded 2% V-PDB at each site. In the case of d 18 O, it exceeded 2% between July and September. Accordingly, it is postulated that calcium carbonate was not precipitated in an isotopic equilibrium with lake water. Incrustation was enriched in heavier carbon isotope, 13 C, and water was enriched in 18 O. d 13 C of incrustation and DIC were positively correlated, whereas negative relation 18 O of incrustation and water. Several dependencies were found with water chemistry above the plants. The content of mineral incrustation in Chara dry weight had negative influence on the d 18 O but not on the d 13 C. Community depth, structure and PVI had no effect. No significant differences appeared between isotope composition in the pelagic zone and Chara stands.