Krystyna Szeroczyńska

High-resolution lacustrine record of the late glacial/holocene transition in central Europe

Abstract In this paper we present the high-resolution record of proxy climatic data in central Europe during the final stages of the last deglaciation, derived from the annually laminated sediments of Lake Gościaz (central Poland). The isotopic, palynological and other microfossil data confirm sudden changes of climate at the onset and termination of the Younger Dryas (completed within 150 and 70 years, respectively), in close agreement with the previous estimates derived from the polar ice cores and marine sediments. In the upper YD some amelioration of climate took place already about 600 years before the main YD/Preboreal transition. Counting of annual varves in the lake sediments allows a direct estimate of the duration of the Younger sDryas in central Europe; it lasted approximately 1640 years, substantially longer than suggested by previous estimates derived from laminated lake sediments and glacial varves, but agreeing with the radiocarbon calibration data obtained for Barbados corals. The calendar ages of the boundaries of the YD, 12,920 and 11,280 cal BP, are tentatively set.

Anthropogenic changes in the sediment composition of Lake Gości& aogon;ż (central Poland), during the last 330 yrs*

According to historical sources, the development of settlement around Lake Gości& aogon;ż during the last 330 yrs was intense at two time periods: the second half of the 1700s, and from ca. 1880 until 1944. The small farms were then abandoned, following which the lake surroundings were planted with forest trees. The presented study of human influence on the lake ecosystem and surrounding vegetation has been based on analyses of general sediment composition and its chemistry, pollen, Cyanobacteria, Chlorophyceae, Rotatoria, Cladocera, and a preliminary diatom survey. The history of human impact has been divided into four phases: 1. Phase of small local hamlets (before ca. 1770): The human impact was rather moderate then, but the cultivation of Canabis sativa, Secale cereale and later of Fagopyrum is evidenced from that time. 2. Phase of ‘Hollandii’ settlement (ca. 1770-1863). Its influence is indicated first by the recession of deciduous wood (Corylus, Carpinus) stands, which triggered drastic drop of calcium in sediments. The development of rural economy in the area, including, an extension of agriculture (Secale and other cereals, crucifers, potatoes), and animal breeding based partly on grazing in the forest, is evidenced only after 1820. 3. Phase of German colonization (1863-1944): In the early periods (before 1910) the pollen spectra do not document any essential change in the type of farming, however, a serious disturbance of the lake ecosystem and sediment chemistry is evidenced by the blooms of Araphidinae diatoms and Tetraedron minimum, a maximum frequency of Bosmina longirostris, disturbances of the regular spring blooms of Chrysophyceae, appearance of vivianite, distinct maxima of organic matter, potassium, and iron concentration in sediments and an increase of the sedimentation rate. An intensification of agricultural activities commenced around 1910; woods, including also pinewoods, were then heavily devastated, and farming extended on poor soils, what was symptomatic for the general poverty of population. Coincidently in the lake, Centriceae showed blooms, Araphidinae diatoms and Tetraedron minimum developed, and the content of potassium, iron and phosphorus increased substantially, indicating altogether rising eutrophication. 4. Phase of restoration of the natural landscape (after 1945): The farm degradation from ca. 1944 is very weakly expressed in pollen data, which show a substantial fall of farming indicators from 1953/6 only, when the whole area was used for forest plantation. It was accompanied by a certainly spontaneous development of Betula and Alnus woods, this process progressing till recent time. The gradual extinction of farming activity near Lake Gościąż was accompanied by abrupt changes in the lake ecosystem, expressed by the restored blooms of Chrysophyceae expansion of planktonic Cladocera, rapid decline of phosphorus and extinction of vivianite from sediments. As documented by the drop of Cu/Zn ratio, lake hypolimnion has been weakly oxidized since 1949, what was probably responsible for the drop of Fe and Mn content in sediments. Increasing strength of overturns affected preservation of laminae in sediments, which almost completely disappeared after 1966.

Human impact on lakes recorded in the remains of Cladocera (Crustacea)

Abstract Subfossil Cladocera analysis allows discussion of the influence of human activity on the lake environments from Neolithic times up to the present. Three lakes were chosen for the analysis: two in northern Poland and the third on Cres Island, Adriatic Sea (Croatia). During the Holocene the species composition and the specimen abundance often changed, resulting mainly from climate changes, and also from human activity. This phenomenon is recognized on the diagrams of absolute abundance and percentage ratio of specimens of the pelagic species to the littoral ones. The data from Cladocera analysis were compared with the abundance of some plants reflecting human activity. A large degree of correlation was noted between the increased presence of these plants and the occurrence of the Cladocera species preferring more trophic water. Some phases of increased lake eutrophication were distinguished on the basis of Cladocera species preferring nutrient rich water. According to the comparative palynological and archaeological studies, these phases are correlated with the periods of settler groups’ activity beginning in Neolithic times. The most distinct changes in the species composition of Cladocera have been noted in the lake sediment from the Medieval Period. They were brought on by the agricultural revolution, which has lasted uninterruptedly up to now. It was observed that the intensity of the expressed abundance of index species in sediments is dependent on the size (area and depth) of the lake. The smaller the lake is, the greater is the change in species composition of zooplankton. The smaller water bodies react faster to an excessive supply of eutrophic compounds, and therefore the change is more clearly evident in the sediment record. Considerable secondary influence of these changes on the species composition of plankton was noted in the large lakes: Lednickie Lake (Poland) and Vrana Lake (Adriatic).

Changes in macrophytic flora and planktonic organisms in Lake Ostrowite, Poland, as a response to climatic and trophic fluctuations:

This article presents some selected results of palaeoecological analysis based on subfossil pollen and Cladocera in a core of deep-water sediments. It was drilled in the SW part of Lake Ostrowite in National Park Bory Tucholskie, Poland. The core contains fine-detritus gyttja with no calcium carbonate. Nine local pollen assemblage zones show the stages of vegetation succession around the lake from the Younger Dryas through the Holocene up to the present time. Local pollen assemblage zones and seven phases in the development of Cladocera permit ecological reconstruction and description of local changes in the lake itself. Changes of trophic status are based on the quality and quantity of Cladocera species and the curve of Pediastrum. Human activity around Ostrowite is discussed in relation to the changes in regional plant cover and the trophic state of the lake.

The development history of Wigry Lake as shown by subfossil cladocera

The Development History of Wigry Lake as Shown by Subfossil Cladocera Environmental changes in Wigry Lake during the Late Glacial and Holocene were studied on the basis of subfossil Cladocera analysis. Cladocera are present in a long core WZS/03 (Słupiańska Bay), and a surface sediments. The sediment contains remains of twenty-seven species belonging to 5 families. Species composition of plankton and the variability in the frequency of specimens of Cladocera made possible to distinguish five phases of their development, which well correlated with palynological phases. The correlation proves that the biological development of Wigry Lake was determined mainly by climatic changes. During the history of the lake, planktonic forms were dominant and represented by Bosminidae. It indicates that the lake was (excluding the initial part) deep and oligo- or mesotrophic. The mesotrophic state has been noted during the Atlantic chronozone and temporary. Taking into consideration the size and the depth as well as the rare human population around the lake it can be stated that the trophy rise was the result of the warm climate. It is also possible that during the last few decades the natural and anthropogenic factors could add. Probably mild winters, warm and long summers, increased tourists number were partly responsible for changes of water state.

Abrupt Changes in Bosmina (Cladocera, Crustacea) Assemblages During the History of the Ostrowite Lake (Northern Poland)

During the 10000-year history of the Ostrowite Lake, there have been several episodes of change in dominance amongst species of the genus Bosmina. The dominants were alternately B.longirostris and Eubosmina spp. Amongst the subgenus Eubosmina, two species prevailed in different periods:Bosmina coregoni and Bosmina reflexa. The first species, Bosmina coregoni, is characterized by long antennae and short carapace mucrones, while the second one, Bosmina reflexa, by short antennae and very long mucrones. Bosmina reflexa was dominant at the beginning of the lakes history (Preboreal, 10000--9000 BP) and during the early Subboreal Period (5000–3500 BP). Only a small number of remains of Bosmina longispina(Eubosmina spp.) were present along the entire profile. Such strong changes in the domination of Bosmina species were observed for the first time in the sediments of Polish lakes. A similar transition from one species to another has been described in a few German lakes and was linked to climate changes. However, the changes in the Ostrowite Lake do not correlate with climate changes, but most probably, with changes in the lakes trophic level. This is suggested by the simultaneous increase of Bosmina reflexa and a good indicator of eutrophy, Bosmina longirostris.

Impact of prehistoric settlements on the Cladocera in the sediments of Lakes Suszek, Bł\cedowo, and Skrzetuszewskie

An analysis of Cladocera has been made on sediments from the three Polish lakes Suszek, Bl\cedowo, and Skrzetuszewskie. The analysed sediments are gyttja from the Subboreal and Subatlantic periods, during which the lakes were subject variously to eutrophication. The eutrophication process has been analysed from the frequency of Cladocera, particularly the index species, and has been correlated with climatic and settlement changes. It was found that in Suszek lake, in which no significant human activity had taken place (palynologically documented), the eutrophication must have been slow and gradual. On the contrary, in the two remaining lakes, in which the human influence was more intense, the eutrophication process underwent intensive changes and coincided somewhat with settlement fluctuations.

Possibilities for Reconstructing Radiocarbon Level Changes During the Late Glacial by Using a Laminated Sequence of Lake

Laminated sediments of Gościąz Lake can be used as an independent source of material for calibrating the radiocarbon time scale. The varve chronology is based on three long cores from the deepest part of the lake, with one additional core from the second deepest part. From pollen and Cladocera spectra and stable isotope and chemical content sequences, we have determined the Allerod(AL)/Younger Dryas(YD) and Younger Dryas/Preboreal(PB) boundaries in the three long cores with relatively good accuracy, and have tentatively defined the AL/YD boundary in the fourth core. The Younger Dryas period contains at least 1520 varves, with 980 varves in fragments well replicated in all four cores. The duration of the Younger Dryas as recorded in sediments of Gościąz Lake corresponds well to the duration derived from 230Th/234U and 14C dates on Barbados corals, but disagrees with estimates from Soppensee, Lake Holzmaar and Swedish varves. Two AMS dates of terrestrial macrofossils from the PB and YD periods seem to fit both the data obtained for Swiss lake sediments and Barbados corals.

Climate-related changes during the Late Glacial and early Holocene in northern Poland, as derived from the sediments of Lake Sierzywk

Reconstruction of past climate change and ecosystem response is important to correctly assess the impacts of global warming. In this study, we provide a paleoenvironmental record of in-lake and catchment changes in northern Poland during the Late Glacial and early Holocene using various biotic proxies (pollen, macrofossils and Cladocera) preserved in the lake sedimentary record. Chronology was derived from palynological correlation with a well-dated pollen sequence from nearby-lying Lake Ostrowite and some well-dated events of vegetation history in Central Europe. Pollen analysis provided information on regional climate change affecting vegetation dynamics, whereas macrofossils supplied substantial information on the response of local flora and fauna to climatic, geomorphological and limnological changes. Data were supplemented by analysis of Cladocera remains, which are of special importance because of their quick response to changes in trophic conditions and climate (especially temperature). The bottom of the sediment core reflects an initial stage of the lake formed during the late Alleröd. The Younger Dryas cooling apparently resulted in forest recession and presence of cold tolerant Cladocera species. Due to amelioration of climate at the end of the Younger Dryas and melting of ice, the lake deepened. The beginning of the Holocene was characterised by forest shrinkage and induced clear changes in local flora and fauna communities. The regional vegetation development deduced from the lake’s core is generally consistent with the vegetation history of central Europe. Due to the location of the site near the seashore (oceanic climate and western wind), signals of warming came earlier than inland and in eastern Poland.

Varve microfacies and varve preservation record of climate change and human impact for the last 6000 years at Lake Tiefer See (NE Germany)

The Holocene sediment record of Lake Tiefer See exhibits striking alternations between well-varved and non-varved intervals. Here, we present a high-resolution multi-proxy record for the past ~6000 years and discuss possible causes for the observed sediment variability. This approach comprises microfacies, geochemical and microfossil analyses and a multiple dating concept including varve counting, tephrochronology and radiocarbon dating. Four periods of predominantly well-varved sediment were identified at 6000–3950, 3100–2850 and 2100–750 cal. a BP and AD 1924–present. Except of sub-recent varve formation, these periods are considered to reflect reduced lake circulation and consequently, stronger anoxic bottom water conditions. In contrast, intercalated intervals of poor varve preservation or even extensively mixed non-varved sediments indicate strengthened lake circulation. Sub-recent varve formation since AD 1924 is, in addition to natural forcing, influenced by enhanced lake productivity due to modern anthropogenic eutrophication. The general increase in periods of intensified lake circulation in Lake Tiefer See since ~4000 cal. a BP presumably is caused by gradual changes in the northern hemisphere orbital forcing, leading to cooler and windier conditions in Central Europe. Superimposed decadal- to centennial-scale variability of the lake circulation regime is likely the result of additional human-induced changes of the catchment vegetation. The coincidence of major non-varved periods at Lake Tiefer See and intervals of bioturbated sediments in the Baltic Sea implies a broader regional significance of our findings.