Stable carbon and oxygen isotope studies are among the major proxies in investigations of recent and ancient freshwater environments. Mollusc shells are one the most frequently studied carbonates. In ...the present paper, stable carbon and oxygen isotope compositions of Dreissena polymorpha (Pallas) shells, regarded as the most aggressive freshwater invader worldwide, is compared with the stable isotope composition of ambient water. Macrophytes with modern D. polymorpha shells attached were sampled twice, in June and August 2011, from four transects established within the littoral of Lake Lednica (western Poland). The macrophytes were sampled between 0.5 and 7 m of depth at each site from the restricted area of the lake bottom. In order to avoid the influence of ontogeny on the results obtained the stable isotope compositions of shells of equal or nearly equal sizes within one population were compared. A significant spread was observed in the stable isotope signatures in the D. polymorpha shells, particularly in the δ¹³C values derived from one population. The spread in δ¹³C and δ¹⁸O values was observed in both juvenile and adult shells; however, it increased with age. It is suggested that stable isotope investigations of D. polymorpha shells should not be performed on single shells, as the isotope values will not be representative of the coeval individuals within population. While the shells of D. polymorpha were close to oxygen isotope equilibrium with the ambient water, they were characterised by a 1.5–2 ‰ depletion in ¹³C relative to δ¹³CDIC. Both the spread in δ¹³C values in the shells and the ¹³C depletion observed in the shells are interpreted as resulting from a strong metabolic influence on shell composition. Because the offset observed between dissolved inorganic carbon (DIC) and shells is relatively constant, the stable carbon isotope composition of D. polymorpha shells may reflect environmental conditions and thus may be used as a palaeolimnological proxy.
Major terrestrial vegetation shifts (MTVSs) resulting from either human activities or natural processes can exert substantial pressure on lakes mainly through impacts on catchment biogeochemical ...cycles and groundwater circulation. To better understand the links between terrestrial vegetation dynamics and lake ecosystem structure and functions over long temporal scales, in this study, we reconstructed the responses of shallow Lake Spore (N Poland) to major late-Holocene vegetation shifts. We combined newly acquired data from pollen and spores, Cladocera, TOC/N, δ13C, and δ15N analyses of bulk organic matter with the already published results from sediment dating and analyses of several biotic and geochemical proxies. Statistical analysis of the abundance data for all the major terrestrial pollen taxa and reconstruction of vegetation openness derived from the REVEALS model indicated five MTVSs, each followed by a change in the lake environment. Changes in Lake Spore trophic status at MTVS1 (~2.82 kyr BP) and MTVS2 (~2.17 kyr BP) were attributed to the reorganization of the catchment’s nutrient cycling associated with a decline (MTVS1) and subsequent regeneration (MTVS2) of deciduous tree stands in the area. A distinct drop in the CaCO3 content of the lake sediments that started at MTVS4 (~0.57 kyr BP) likely occurred due to the substantial depletion of the water calcium pool following an abrupt transition from a tree-dominated to an herb-dominated landscape. Our record also suggested slight lake acidification following a spread of
Pinus sylvestris
at MTVS1 (~2.82 kyr BP) and MTVS3 (~1.10 kyr BP) and a lake level rise concurrent with the sharp increase in landscape openness at MTVS4 (~0.57 kyr BP).
Despite the increasing interest in spring-fed fens’ sediments as a palaeoenvironmental archive, their potential as high-precision climatic records is rarely used to its full extent. Here, we present ...a detailed early to mid-Holocene record of environmental changes in the Turtul hanging spring-fed fen, northeastern Poland, to test whether the well preserved and accurately subsampled alternating peat and tufa sediments allow us to recognise short-duration local and regional climatic changes. Our reconstructions are based on a loss-on-ignition analysis of the sediment, carbon and oxygen stable isotope values of tufa, and biotic proxies: plant macrofossil and malacological analyses. A detailed environmental reconstruction was possible due to the combination of detailed sampling (1 cm intervals) and high sediment accumulation rates. The two sediment sequences collected from the fen revealed the congruent palaeoenvironmental history; however, the temporal shift associated with the distance of the coring site from the water outflow was also apparent, stressing the need for careful selection of the coring site in palaeoenvironmental research. Peat deposition at Turtul started at 10,300 cal yr BP; however, tufa precipitation did not begin before 9250 cal yr BP. During the most active tufa deposition, from 7850 to 6100 cal yr BP, a high sedimentation rate was observed (0.11–0.25 cm yr−1). We found several abrupt and short-duration declines in carbonate deposition corresponding to climatic fluctuations recorded in geological archives from the southeastern Baltic region. The carbonate drops at 8200–8130, 7900–7850, 7400–7300, 6600–6500, 5980–5870 and 5400 cal yr BP were associated with climate cooling or drying, whereas those at 10,200–9250, 8450–8340 and 6160–6100 cal yr BP can be attributed to drying with no cooling. We conclude that the evident sensitivity of the Turtul fen to climatic shifts that emerge from our high-resolution (one sample every 17 years on average) reconstruction complements the still rare high-resolution palaeoenvironmental records in the area.
Neolithic burials rich in grave goods, referred to as “princesses burials”, were excavated in the Kuyavia Lowland, central Poland, Central Europe. The most common elements of grave equipment recorded ...in these burials were ornaments composed of disc beads made of freshwater bivalve (
Unio
spp.) shells. Our study was aimed at determining the origin of the shells in question by analysing, for the first time, carbon and oxygen stable isotope compositions (δ
13
C and δ
18
O) of the beads and comparing the results with C and O isotope ratios in modern shells sampled in central Poland. In the research, the isotope values of modern shells were grouped into two data sets representing riverine and lacustrine endmembers.
Unio
spp. shells sampled from rivers were isotopically lighter (i.e. isotope values were more negative) compared with the shells collected from lakes. The range of δ
13
C and δ
18
O values in the beads was similar to the one observed in modern
Unio
spp. shells. However, the isotope values differed within and between the archaeological sites studied. In Krusza Zamkowa and Osłonki, two distinct isotopic groups of beads were recognised—riverine and lacustrine—suggesting changes in the shell source in time. The C and O isotope values of beads sampled from Brześć Kujawski indicated the lacustrine origin of the shells used for their production. Also, it was confirmed that shells used to produce one ornament were derived from a single source, and the choice of sources changed in time. Our research revealed that the selection of specific local sources of shells was important for the prehistoric communities under study, and it may be considered the evidence of the existence of a regional exchange network.
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•Multi-proxy long-term ecological studies are important tool to indicate peatland state.•Climate change and land cover in the catchment impact development of spring-fed fen.•Mollusc ...populations are sensitive to hydrological disturbances.•Restoring spring-fed ecosystems may also require catchment restoration.
The calcareous substrate of spring-fed fens makes them unique islands of biodiversity, hosting endangered, vulnerable, and protected vascular plants. Hence, spring-fed fens ecosystems require special conservation attention because many of them are destroyed (e.g. drained, forested) and it is extremely difficult or even impossible to restore the unique hydrogeological and geochemical conditions enabling their function. The long-term perspective of paleoecological studies allows indication of former wetland ecosystem states and provides understanding of their development over millennia. To examine the late Holocene dynamics of a calcareous spring-fed fen (Raganu Mire) ecosystem on the Baltic Sea coast (Latvia) in relation to environmental changes, substrate and human activity, we have undertaken high-resolution analyses of plant macrofossils, pollen, mollusc, stable carbon (δ13C) and oxygen (δ18O) isotopes combined with radiocarbon dating (AMS) in three coring locations. Our study revealed that peat deposits began accumulating ca. 7000 cal. yr BP and calcareous deposits (tufa) from 1450 cal. yr BP, coinciding with regional hydrological changes. Several fire events occurred between 4000 and 1600 cal. yr BP, which appeared to have had a limited effect on local vegetation. The most significant changes in the forest and peatland ecosystems were at 3200 cal. yr BP associated with a dry climate stage and high fire activity, and then between 1400 and 500 cal. yr BP potentially associated with temperature changes during the Medieval Climate Anomaly (MCA) and Little Ice Age. Hydrological disturbances in the peatland catchment from 1400 cal. yr BP were most likely strengthened by human activity (deforestation) in this region. The relationship between the development of this peatland and changes in its catchment area, such as land cover changes or fluctuations in groundwater levels, suggest that protection and restoration of spring-fed fen ecosystems should also include the surrounding catchment. The presence of calcareous sediments, as well as appropriate temperature and local hydrological conditions appear to be the most crucial factors controlling Cladium marisus populations in our site - currently at the eastern limit of its distribution in Europe.
We conducted year-round, monthly monitoring of the stable isotope composition of DIC and water in hypereutrophic Lake Kierskie, western Poland, along with isotope measures of calcite collected in ...sediment traps installed at 16 and 30 m water depth in the lake. Isotope data were supplemented by previously published data on physico-chemical variables in the lake water column. We sought to determine how carbon and oxygen isotopic disequilibria in calcite deposited in the lake’s laminated sediments vary seasonally, and what factors drive this variability. Deposition of calcite out of equilibrium with DIC and water was documented over the entire study period. For δ
18
O, the disequilibrium difference between successive months far exceeded the amplitude of the seasonal variability in the isotope composition of water. The biggest difference between the measured and calculated δ
13
C
calcite
and δ
18
O
calcite
values was observed during late autumn and winter sediment resuspension and redeposition (2.4‰ and 5.4‰, respectively). In the spring, δ
13
C
calcite
and δ
18
O
calcite
offsets from equilibria, 0.5‰ and 1.3‰, respectively, resulted from rapid precipitation of large calcite crystals. During summer, intense productivity and processes related to calcifying algae (“vital effects”) caused lower δ
13
C (0.5–1.8‰) and δ
18
O (2.8–2.9‰) in calcite. Differences between isotope values of calcite collected from the two water depths were small, and might have resulted from different settling velocities of small and large crystals, and/or preferential dissolution of smaller grains. We suggest that winter laminae should be excluded from isotope studies of varved sediments whenever possible, as they likely contain redeposited carbonate in which the isotope value is not indicative of conditions in the lake at the time of laminae formation. We also recommend supplementing isotope analysis of calcite in varved lake sediments with seasonally resolved analysis of carbonate content. It appears that major shifts in the proportion of carbonate deposited across seasons can cause notable changes in mean annual values of δ
18
O
calcite
and δ
13
C
calcite
, even if DIC and water isotopic compositions remain stable.
Accurate lake sediment-derived palaeoenvironmental reconstructions require in-depth knowledge on sediment record formation processes. In order to understand formation of laminated sediments in the ...eutrophic Lake Kierskie (western Poland) we conducted a year-round (November 2015–October 2016), monthly sediment trap study along with physico-chemical water properties, water transparency, hardness, alkalinity, nutrients and solute content, trophic state indices, and the phytoplankton assemblage monitoring. Sedimentation in Lake Kierskie primarily resulted from the activity of photosynthetic organisms. The maxima of biogenic silica accumulation were synchronous with the bloom of centric diatoms observed in March and April. These were followed by the most intensive precipitation of CaCO
3
noted between mid-April and mid-June, that corroborated with the domination of
Stephanodiscus hantzschii
and small flagellate forms acting as nucleation sites for crystal formation. At the same time shift from the diatom-dominated assemblages to the communities composed of chlorophytes, cryptophytes, and dinoflagellates, the groups with cellulose external covering, resulted in decreased proportion between SiO
2
and organic matter. CaCO
3
precipitation continued in the summer months, however its amount decreased simultaneously with a drop in
S. hantzschii
biomass. The significant overall flux of biogenically mediated materials from epilimnion was promoted by eutrophic towards hypertrophic conditions in Lake Kierskie revealed by the trophic state indices. Mixing of the water column in autumn triggered resuspension and redeposition of the previously deposited sediments resulting in the second, after the early spring, maximum sediment flux. Minima of sediment accumulation were observed during the winter water stratification when the smallest particles sedimented from suspension. The sediment flux to the lake bottom recorded by us in a 1-year, monthly sediment trap study matches a sequence of pale, whitish lamina deposited during spring and summer, followed by dark, grayish or black lamina deposited in the autumn and winter, observed in the macroscopic investigation of the short (0.5 m) core from Lake Kierskie. Preservation of distinct laminations in the dimictic Lake Kierskie is supported by anoxic hypolimnion developed under the high supply of organic matter from epilimnion of this highly eutrophic lake.
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 CaCO3 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 HCO3− and forming thick CaCO3 encrustations. Thus, this study was aimed at evaluating the CaCO3 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 CaCO3 per 1 m2 were investigated along three transects at three depths (1 m, 2 m and 3 m, with each sample area equal to 0·0625 m2) 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−2 and CaCO3 encrustations constituted from 59% to over 76% of the charophyte dry weight. Thus, the maximum and average values of carbonates precipitated by charophytes were 685·5 and 438 g m−2, 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−2 on average). As precipitated carbonates are ultimately stored in bottom deposits, the results highlight the significance of charophytes in lacustrine CaCO3 sedimentation.
Abstract This study identifies the relationships between the δ 13 C and δ 18 O signatures of extant charophyte carbonates (δ 13 C CARB and δ 18 O CARB ) and the δ 13 C of dissolved inorganic carbon ...and δ 18 O of water (δ 13 C DIC and δ 18 O WATER ), respectively, and the structure of charophyte beds and the physico‐chemical properties of the ambient water. Inter‐ and intra‐specific differences and lake‐related variability are assessed. Four morphologically different charophyte species ( Nitellopsis obtusa , Chara tomentosa , Chara rudis , Chara contraria ) were studied in four charophyte‐dominated lakes ( Chara ‐lakes) in Central Europe. A wide distribution of the species in calcium‐rich freshwater lakes, where they form extensive underwater beds and contribute to the deposition of calcareous sediments, makes the study representative of Chara ‐lakes. Charophytes and water above them were sampled monthly (June–September 2008) at permanent study sites. Additionally, three comparative macrophyte‐free pelagic sites were sampled in each lake. For all the charophytes studied, there was a greater variation in the δ 13 C and δ 18 O values of the encrustations than of the ambient and pelagic waters. Except for N . obtusa and C . tomentosa , the species differed significantly in the δ 13 C CARB values. The encrustations were enriched in 13 C compared to water DIC. Chara tomentosa encrustations were significantly depleted in 18 O compared to N . obtusa and C . contraria . In contrast to Chara species, N . obtusa encrustation was 18 O‐enriched compared to surrounding water. The largest isotope differences between carbonate encrustations and surrounding water were found for C . rudis . Considering the δ 13 C CARB versus δ 13 C DIC values, only slender species (i.e. N . obtusa and C . contraria ) precipitated encrustations close to isotopic equilibrium with water DIC. Based on theoretical δ 18 O CALCULATED and measured δ 18 O CARB values, only C. tomentosa precipitated encrustation in equilibrium with the δ 18 O WATER . Using redundancy analysis, the δ 13 C CARB values positively correlated with the δ 13 C DIC and δ 18 O WATER values and the percent volume of water inhabited by plants. The depth of sites, water mineralisation, alkalinity and fertility were inversely correlated with the δ 13 C CARB . The redundancy analysis revealed a clear division of samples into species and lakes; lakes were especially distinct. We postulate that the stable C and O isotope compositions of charophyte encrustations are lake‐ rather than species‐specific and that the isotopic signatures of charophyte carbonates are representative of the entire lake epilimnion, not just the vegetated littoral zone. Furthermore, the isotopic signal of bulk sediment can provide environmental information that is as useful as species‐specific isotope values.
Sediments of CaCO3-precipitating alkaline fens, comprising biotic and abiotic indicators of water table changes, are among the most reliable archives for obtaining palaeohydrological data. The study ...uses a semiquantitative method based on a combination of selected indicators (plant macrofossils, mollusc shells, degree of peat decomposition) to estimate the relative changes in the water table position at Lustūžkalns alkaline fen, Latvia, Eastern Baltic Region. The study also aims to determine the time frames of CaCO3 deposition at the fen using loss on ignition and carbon and oxygen stable isotope records. The chronology of the three sediment sequences studied is based on the AMS radiocarbon dating of terrestrial plant macrofossils. Although the reconstructed water table positions revealed differences between the cores, the major shift from the low water tables persisting since ca. 5000 cal yr BP to the prevailing high water stands at ca. 3000 cal yr BP was common to all the sequences. The major shift observed is consistent with a change from low to high water tables in peatlands in Latvia and at numerous fens and bogs across the Eastern Baltic Region, Fennoscandia and NW Europe. Concurrent with the increase in the water tables was the onset of CaCO3 precipitation on the Lustūžkalns fen surface, which began at ca. 3000 cal yr BP and accelerated from ca. 2500 cal yr BP. The Late Holocene CaCO3 precipitation at Lustūžkalns can be attributed to the change from warm and dry conditions during the Holocene Thermal Maximum (HTM) to cooler but humid during the Late Holocene. In contrast, in Central and Western Europe, the main period of freshwater carbonate precipitation occurred during the warm and humid HTM.
•Shift to high water tables in central Latvia was reconstructed after 3000 cal yr BP.•Rising water tables resulted in intensive CaCO3 precipitation at alkaline fen.•Late Holocene tufa deposition in central Latvia contrasts western and central Europe.•Differences in hydroclimate triggered the differences in CaCO3 precipitation timing.
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