Warunki funkcjonowania kopuł źródliskowych w południowej części Wzniesień Łódzkich
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CG_2012_3_4-47.pdf (3.37 MB)
Date
2012
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Polskie Towarzystwo Geograficzne
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Abstract
W regionie łódzkim, jednym z najzasobniejszych w źródła obszarów na Niżu Polskim, stwierdzono występowanie torfowo-martwicowych kopuł źródliskowych, utworzonych na wypływach ascensyjnych. Są one położone w okolicach wsi Wardzyń, w południowej części Wzniesień Łódzkich, poza głównymi strefami źródliskowymi regionu: Kotliną Szczercowską i północną krawędzią Wzniesień Łódzkich. Kopuły mają charakter eutroficzno-wapienny i znajdują się u podnóża Pagórków Romanowskich, stanowiących lokalną strefę kulminacyjną i jednocześnie wododział dorzecza Wisły i Odry. Współczesny stan hydrochemiczny wód poziomu międzymorenowego, który alimentuje źródła, nie pozwala na wytrącanie węglanu w obrębie kopuł, a nawet sprzyja ich ługowaniu. Skład chemiczny udokumentowanych osadów pozwolił na ocenę zmian sposobu zasilania badanego torfowiska oraz rekonstrukcję względnych rozmiarów denudacji mechanicznej i chemicznej w zlewni analizowanego ekosystemu.In the past, Central Poland was considered as an area where springs do not occur in abundance. Gradually collected results of regional hydrological studies, however, permit us to include the vicinity of Łódź to the group of areas with the highest representation of springs in the Polish Lowland. Two zones particularly stand out in this respect: the northern boundary of the Łódź Hills, and the Szczerców Basin. Otherwise, the occurrence of springs is largely confined to deeply indented river valleys. Although the modern Wolbórka River valley is not one of them, it includes a waterhead zone stretching from Tuszyn to the east to Wardzyń to the west. The exceptional character of the springs in Wardzyń involves peat formations elevated above the lower waterhead zone, developing two recognisable dome-like formations made of organic and tufa sediments. Such formations do not occur anywhere else in this thoroughly crenologically studied region. Therefore, they should be considered as the first documented case of the existence of such formations in Central Poland. Therefore, preliminary research has been conducted, aimed at an identification of conditions of development and modern functioning of spring-fed peat domes in the direct vicinity of Łódź, outside the currently known areas of occurrence of this type of peatlands. Works conducted so far covered hydrological, hydrochemical, geological, and geomorphological field research, including sampling of waters and rocks, further analysed in the laboratories of the Faculty of Geographical Sciences of the University of Łódź. The waterhead niche and the adjacent peat dome Wardzyń I were selected for analyses due to the constant, locally concentrated groundwater outflow present on its surface. Hydrochemical observations were carried out during one year, from March 2011 to March 2012. Five sites were selected for the study: two in the waterhead niche, directly on the outflows of groundwaters – one ascending and one descending, and three on the surface of the dome, in the direct vicinity of nonconcentrated groundwater outflows. The objective of the geological and geochemical analyses of the peat-tufa domes was to reconstruct the conditions of deposition of the sediments. The works included: mapping of the spring-fed domes, involving 100 corings by means of stick and 30 corings by means of a gouge auger. Two peat-tufa sediment cores were also taken by means of an Instorf corer; sampling in laboratory conditions; the cores were divided into sections with a length from 1 cm (at high lithofacial differentiation of sediments) to 2.5 cm (in the case of homogenous sediment). A total of 185 biogenic sediment samples were taken from the cores: 73 samples from the core from the Wardzyń I dome, and 112 samples from the core from the Wardzyń II dome; identification of basic components of biogenic sediments, i.e. organic matter (loss on ignition method in a muffle furnace at a temperature of 550oC), calcium carbonate (volumetric method by means of the Scheibler’s apparatus), terigenic and biogenic silica (sample dissolution in hydrochloric acid and potassium hydroxide), and reaction (potentiometric method – in distilled water). Changes in humidity conditions during peat sedention were determined based on the degree of decomposition according to the von Post scale (Tobolski 2000). Two types of decomposition process of autochthonous organic matter are distinguished: primary (related to peatlands with growing peat) and secondary (related to e.g. dehydration) (Drzymulska 2003). Additionally, in the Geochemical Laboratory of the Faulty of Earth Sciences of the University of Szczecin detailed geochemical analyses were performed for 93 samples from the profile Wardzyń II (i.e. identification of content of micro- and macroelements). Ash resulting from ignition, devoid of organic matter, was subject to wet dissolution in a microwave mineraliser by means of concentrated nitric acid, 10% hydrochloric acid, and perhydrol. In the resulting solution, elements helpful in palaeogeographical reconstruction were identified by the method of atomic absorption spectroscopy: Na, K, Ca, Mg, Fe, and Mn. The analysis of environmental change during the sediment deposition applied the content of calcium and potassium, and the following geochemical indices reflect the most important changes in contribution of selected elements: sediment carbonacity index – as the relation of the content of calcium carbonate to organic matter. The index constitutes a quantitative measure of lithological variability of sediments (Wojciechowski 2000), and reflects relative changes in the intensity of leaching of calcium carbonate from the ecosystem’s underground catchment, water eutrophication index – as the relation of the content of iron to calcium (Wojciechowski 2000, Bałaga et al. 2002, Betchel et al. 2007), indices of the type of mechanical and chemical denudation in the peatland catchment – as the relation of the content of sodium to potassium, and content of calcium to magnesium. The analysis of morphological and hydrographic location of the spring-fed peat domes in Wardzyń suggests their similarity to localities described in other parts of Poland. Tufa domes frequently occur on boggy valley floors, e.g. in the Topiel Stream valley in the catchment of the Parsęta River (Osadowski et al. 2009), as well as at the foot of the upstanding landforms and in the vicinity of an important watershed running through them (Ilnicki 2002). The objects discussed in the article represent the eutrophiccalcareous type, documented among others by Wołejko (2000) in the Pomerania region. The springs which contributed to the development of the peat domes in Wardzyń correspond with the conditions of functioning of groundwater outflows in the Łódź region in terms of hypsometric and morphological location, efficiency, and water mineralisation. The groundwaters of the intermorainic horizon, feeding the sources in Wardzyń, show the evidence of pollution – high contribution of non-carbonate hardness, abnormal concentrations of nitrate nitrogen, and an increased nitric nitrogen. This is reflected in changes recorded in the direct vicinity over at least the last 30 years, occurring in the deep parts of the aquifer drained by the springs. The oxygenation-reduction conditions occurring in the sediments of the peat domes result in the change of hydrochemical type of spring waters from hydrogen carbonate-sulfate-calcareous to hydrogen carbonatecalcareous. Waters penetrating the peat domes also show the denitrification process. The modern groundwaters penetrating the spring-fed bog remain in balance with calcite, and are in the state of non-saturation in relation to dolomite and siderite. Therefore, no possibility currently occurs of abiotic deposition of carbonate sediments within the analysed peat dome. The change in the SI index for dolomite and siderite resulting from filtration of groundwaters through organic-tufa sediments suggests selective leaching of Mg and Fe. The chemical composition of the documented peat and calcareous sediments permit us to distinguish periods with an increased allochthonous supply of mineral matter, and to reconstruct humidity conditions occurring in the vicinity of the waterhead niche. Deposition of the calcareous sediments constitutes a record of enhanced chemical denudation in the catchment. The moderate to strong degree of peat decomposition suggests growth of autochthonous organic matter in conditions of good oxygenation and an increased mechanical denudation of the vicinity of the niche.
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Ziułkiewicz M., Okupny D., Forysiak J., Fortuniak A., 2012, Warunki funkcjonowania kopuł źródliskowych w południowej części Wzniesień Łódzkich, Czasopismo Geograficzne, 83(3): 175–196.