Search

We use a range of environmental variables to explore the possible drivers influencing the biota, especially the composition of aquatic invertebrates, during the Younger Dryas (YD) and Early Holocene (EH) in different river valley sites: a well-developed meandering river and the confluence zone of headwater streams. Using pollen, macrofossil, cladoceran, and chironomid as well as geochemical and lithological data as proxies for environmental factors (i.e., water depth and temperature), we attempt to show that these different sites display similar hydroclimatic signals (especially floods). The geochemical records in the studied valley are correlated with environmental factors, such as the evolution of the vegetation, the intensification phase of slope processes, and fluvial activities. Cladocerans and chironomids potentially play important roles in the recognition of flood episodes in the study sites, and any shift in their diversity and, especially, the co-occurrence of planktonic, sediment-associated cladocerans with rheophilic chironomids could be valuable indicators of floods and flow episodes. The variable changes in water levels at the sites reconstructed by the cladoceran-based water-depth model were positively associated with changes in lithophilic elements (K, Na, Al, Mg, and Ti), SiO 2(biog + ter) and Fe/Mn, and our estimates of the paleohydraulic parameters for the study sites are generally consistent with changes in the composition of aquatic invertebrates. The recorded YD floods appear to be synchronous, regardless of the size and the different geological and geomorphological settings of each part of the river catchment. Our investigation demonstrates that flood magnitude increases in the downstream direction along the valley. The common increases in the water level at all study sites from the Grabia River valley are significant from 12,400 to 12,200 and from 11,900 to 11,800 cal BP and are comparable with those from elsewhere in Poland and Europe. [ABSTRACT FROM AUTHOR]

Abstract: The developmental history, from the Oldest Dryas to the Late Holocene, of a paleolake and mire located in a river valley in Central Poland was studied using high-resolution records of pollen, macrofossils, Cladocera, sedimentology, and geochemistry from a 14 C dated sediment core. We inferred temperature and water level dynamics using cladocerans and palynological and geochemical methods were employed to investigate natural fluvial activity, particularly for these elements that are difficult to find through sedimentological methods. Our research demonstrates how climate fluctuation in the Late Glacial and Holocene periods influenced the development of a paleolake and mire in a small river valley and shows the importance of long-term research to establish hydroclimatic conditions in biogenic sediments. We propose that water level fluctuations were important in modifying biotic assemblages. The results of our multiproxy analysis clearly suggest that the main driver of changes in aquatic and terrestrial ecosystems, as well as in geomorphological processes in the valley, was climate: reconstructed temperatures generally follow the known trends, showing an increase at the beginning of the Bølling, Allerød, and Holocene and a decrease at the beginning of the Oldest and Younger Dryas. Similarly, periods of water level increase are synchronous with climatic changes. However, the local environmental forces were a significant factors affecting biotic diversity in the studied time span. Fish predation, macrophyte structure, pH, and calcium content partly influence the results of the cladoceran-based water depth reconstruction in particular. Interestingly, the cladoceran-inferred summer temperature reconstruction for Pawłowa appear realistic. Although the temperature trends can be considered reliable, our results indicate the important role of local factors which control the species composition of the subfossil assemblages. [ABSTRACT FROM AUTHOR]

The Ner River valley (central Poland) underwent substantial transformation during the Weichselian–Holocene transition as a result of fluvial processes and climate changes, resulting in the establishment of its present shape in the Holocene. A multiproxy study based on organic deposits from a palaeochannel fill (Lutomiersk–Koziówki) shows that after the channel was cut off during the late glacial termination, it became a shallow oxbow, fed by local springs. In the Boreal period, the oxbow lake was also fed by precipitation and became a telmatic environment overgrown by rush and swamp vegetation. Finally, it was covered by overbank deposits. The first flooding phase (9900–9600 cal. BP) was followed by the accumulation of overbank sediments (after 9500 cal. BP) and flooding increased after ca. 9300–9000 cal. BP. Pollen data provide information on the regional vegetation context for local and regional changes. In the Atlantic period, an increase in both summer and winter temperatures is inferred from the pollen data, corresponding to an expansion of thermophilous deciduous forests. While in general, flooding phases of the Early Holocene are poorly recognised in Eastern Europe, the Lutomiersk–Koziówki site may be considered as one of the reference points for this phenomenon in the region. [ABSTRACT FROM AUTHOR]

This paper presents a palaeoenvironmental reconstruction of the Wilczków fen (central Poland). The fen developed in an inactive valley at the onset of the Holocene (~11 ka BP) and peat accumulation lasted until 5.7 ka BP. Multi-proxy reconstructions were made on the basis of palaeobotanical, cladoceran, chironomid, beetle and geochemical analyses. A Kohonen self-organizing map ( SOM, unsupervised artificial neural network) of the biotic sequence distinguished four stages of fen history. Stage X1 (11.0-10.7 ka BP) was relatively wet and cool. Organic matter started to accumulate but the habitat conditions remained unstable. Moss, sedge and fern communities then developed. Sedimentary changes reveal an intensive groundwater supply at that time. Numerous and diverse chironomid and cladoceran subfossils indicate nearly permanent aquatic conditions. During stage Y1 (10.6-9.2 ka BP) conditions were dry and the upper peat layer desiccated. Cladocera nearly disappeared whereas chironomids were represented by semi-terrestrial and predatory (Tanypodinae) species. Conditions started to be more reducing. All the remaining samples belonged to the interweaving stages X2 and Y2. Stage Y2 (mostly 9.1-7.3 and 6.0-5.7 ka BP) was also dry but humidity increased towards the top. Oxidizing conditions occurred and the pH became more alkaline, favouring Cladium mariscus. The basin received mostly allochthonous matter input at that time. Stage X2 (mostly 6.8-6.1 ka BP) was humid and warm. The groundwater supply remained low but there was an increase in precipitation, changing local conditions to ombrotrophic. Species-rich chironomid and cladoceran communities were associated with temporary pools. Finally, conditions returned to those characteristic of stage Y2. The presented reconstruction documents long-term abiotic and biotic changes determined by water supply, including groundwater outflow, which have rarely been detected at a multi-proxy scale. We show that inactivated valley fens are sensitive to climate-driven hydrological fluctuations. Kohonen neural networks appear to be a promising method for analysing variability in multi-proxy data. [ABSTRACT FROM AUTHOR]