Abstract
The advances and retreats of ice sheets during Pleistocene significantly changed high- and mid-latitude landscapes and hydrological systems, albeit differently, in North America and Europe. On the southern margin of the Last Glacial Maximum (LGM) in the Baltic Sea basin, a specific type of valley has developed between glacial margins and upland or mountain slopes. We studied new geological data (boreholes, electrical resistivity imaging (ERI) from this geomorphic setting in Northeast Poland to understand: (1) how the landscape and river network evolved to eventually produce peat mires during the Holocene, and (2) the nature of groundwater recharge to fens in the upper Biebrza Valley. We present the results on a geological cross-section with hydrogeological interpretation. We also discuss regional geomorphology. In addition, we present the LGM extent derived from a spatial distribution of Vistulian (Weichselian) terminal moraines. These end moraines are also interpreted as Saalian kames. Thus, we additionally present another method of LGM extent delineation from a physicogeographical division. We link the steep slopes of the studied valley walls (kame terrace fronts) with thermokarst erosion in the periglacial zone. We then document the hydrogeological window (DISCONTINUITY in the till layer over the confined aquifer), which enables the outflow of groundwater into the peat bog. Although minerotrophic fen mire development in the study area is likely to be sustained in the near future through sufficient groundwater supply, the projected capture of the Biebrza River by the Neman River will not allow for sustaining peatland development.
Highlights
In stark contrast to the Laurentide Ice Sheet in North America, the Fennoscandian Ice Sheet had to advance upslope its southern margin in response to the higher topography of Middle Europe [1,2,3,4](Figure 3A and Figure 3A)
The valleys collected an enormous volume of water from both southward-flowing glacial meltwater and northward streamflow from rivers in ice-free areas in southern Germany and Poland (Figure 3A and Figure 3A)
We present new geological data collected in an ice-marginal valley in the southeastern sector of the Fennoscandian Ice Sheet during the LGM to achieve the following: (1) understand the evolution of the hydrological system that resulted in the formation of a large and relatively homogeneous minerotrophic fen mire, and (2) determine the groundwater recharge of mires in one of the largest coherent protected areas of fens in Europe
Summary
The valleys collected an enormous volume of water from both southward-flowing glacial meltwater (emanating from parts of Lithuania, Latvia and Estonia, as well as southern Finland) and northward streamflow from rivers in ice-free areas (uplands and mountains) in southern Germany and Poland (Figure 3A and Figure 3A). This type of large valley trending parallel to the margin of an ice sheet is called “Urstromtal” in German and “pradolina” in Polish. The term has slightly different meanings in North America and New Zealand [5]
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