Taking into account the diversity of sedimentary and sedentary environments in which alkaline fens develop, it is necessary to consider substrates of different origin. These are underwater sediments (gyttjas), peats (mainly of fen and tran-sitional types) and spring water precipitates. A separate issue – presented in the next subsection – is the classification of soils formed from these substrates as a result of their spontaneous or human-induced transformations.
The most frequently used classification of gyttja is based primarily on the analysis of the percentage of the main components such as calcium carbonate, organic matter and clay parts (Markowski 1980). In addition to this approach, To-bolski (2000) also discusses other ways of identification and description of aquatic sediments, in particular the Troels-Smith method. It provides, among others, a description of the tested soils in accordance with the international code system.
The so-called genetic classification of peat (Tołpa et al. 1967) has been used for more than 50 years. Details of this classification system are presented in text-books on peat science (e.g., Tobolski 2000, Ilnicki 2002). An extensive range of different types and kinds of peat has been identified in the profiles of alkaline fens. However, from the point of view of the relationship of these formations with peat-forming plant communities of typical alkaline fens, the most important are sedge-moss, (brown) moss, and (tall) sedge peats. This does not exclude the oc-currence of other peat types and kinds in peat profiles, which reflects the diverse origins and multiple paths of development of the current alkaline fens. Table 1 presents a part of the classification system (Tołpa et al. 1967) covering the types and species of peat most often recognized in the profiles of alkaline fens.
Moss peats, which reflect the early, mesotrophic stages of fens development, deserve special attention. They were characterized in Poland as a result of M.
Jasnowski’s pioneer work (1959). The distinction of moss peat by definition means that it contains more than 60% of the remnants of a specific brown moss species (Bryales). Moss peat mainly consist of moss species that are considered glacial relics (Szafran 1948, Czubiński 1950). Based on their dominance in the peat, Jasnowski (1959) distinguished 7 kinds of moss peat named after the moss species forming them: Drepanocladus sendtneri, Calliergon giganteum, Calliergon trifarium ( =Pseudocalliergon trifarium), Scorpidium scorpioides, Camptothecium nitens (=Tomentypnum nitens), Meesea (=Meesia) and Paludella squarrosa. These peats are very often used as traces of the initial developmental stages of mires of lake origin, especially those situated in landscapes with a higher abundance of calcium compounds. These are usually not very thick layers; they are rather quickly replaced by other types of peat, and reflect subsequent succession stag-es within the terrstag-estrializing procstag-ess in mstag-esotrophic and eutrophic water bodistag-es (cf., Kowalewski 2014).
Photo 13: Moss peat with a low degree of decomposition (about 30%) and a characteristic light brown color – Bagno Stawek nature reserve
(photo by K. Barańska).
Photo 14: Very poorly decomposed moss peat (about 20–30%) with macroscopically identifiable bryophytes of the genera Drepanocladus and Pseudocalliergon
– Jezioro Ciche nature reserve (photo by R. Stańko).
Table 1. Genetic relationship between peat-forming plant communities and peat units most commonly found in the profiles of alkaline fens. The original naming of syntaxa has been maintained. Based on Tołpa et al. (1967) according to Tobol-ski (2000), modified.
Since the introduction of the genetic classification of peat both in the range of identified peat types and in the systematics of peat-forming plant communities, numerous significant modifications have been introduced. Also, various propos-als for additions and changes have been submitted (see: Tobolski 2000, Drzymul-ska 2018). Nevertheless, the genetic classification and the Polish Standard PN-85/G-02500 developed based on it, constitute the only coherent and widely used system of identification and naming of peat components of alkaline fens.
In addition to well characterised peat types alkaline fens may contain peats, that can not be part of the genetic classification system. This is a case of amor-phous peat often found in surface layer of fens. Such material has been described inconsistently in peat profiles, for instance as a “humopeat”, a mineralized
super-Fig. 15. Selected elements of alkaline fen stratigraphy (photo by D. Horabik).
I. Bukowskie Bagno reserve. A: moss sedge peat B: moss – sedge peat
II. Fen near Mielęcin (Drawa Forest). A: sedge-moss peat with a small amount of alder wood, passing into a sedge peat B: sedge peat with alder wood and Menyanthes seeds, C: sedge peat (Magnocaricion) with a small amount of willow wood – strongly hydrated;
III. Fen near Mielęcin (Drawa Forest). A: fine-grain organic gyttja with a small amount of sedge.
Photo 15: Vertical exposure of the calcareous peat, Slitere, Latvia (photo by A. Szafnagel-Wołejko).
ficial layer (Polish “wierzchnica”) or as strongly decomposed peat. We prefer the term strongly decomposed peat.
In the neighboring countries, peat deposits with a high calcium carbonate content are also distinguished, for example, in Germany as “Kalktorf”- Calcare-ous peat – (Succow & Jeschke 1986).
Photo 16: Calcareous tufa formed on the surface of the spring mire in the Magura National Park (photo by D. Horabik).
Photo 17: Calcareous tufa precipitation around Equisetum variegatum.
Močiar Reserve in Slovakia (photo by A. Szafnagel-Wołejko).
Dobrowolski (2011) attempted to sort the nomenclature related to carbonate spring deposits. According to this author, autogenous calcareous sediments pre-cipitated from flowing fresh water include calcareous tufa (light, highly porous carbonate sediments, undiagenized or poorly diagenized, formed in the vicinity of springs supplied with groundwater with CO2 originating from percolating rain water (meteogene), travertines (hard, highly diagenized, carbonate deposits building large calcareous terraces and/or barriers in streams with high flow dynamics), and sinters (hard, concise and non-porous calcite coatings precipitated mainly in thermogenic conditions).
Alternating peat layers and mineral precipitations are called peat-sinter mites (Dobrowolski 2011). Full stratigraphic profiles of peatlands with rhyth-mites, other types of sinters, peats, gyttjas and mineral sediments are an inter-esting subject of numerous paleoecological studies in Poland (Dobrowolski et al.
2002, Lamentowicz et al. 2013, Apolinarska & Gałka 2017, Osadowski et al. 2018, Pietruczuk et al. 2018) as well as neighboring countries (Hájková et al. 2012, Jam-richova et al. 2018, Šolcová et al. 2018). These studies, in addition to reconstructing the history of ecosystem development, relate to the transformations of vegetation, changes in ecological and climatic conditions, and the history of human influence.
Studies on the chemism of peatland formations allow for the reconstruction of the history of landscape development (Borówka et al. 2015).
Photo 18: Layered rhythmite from the “Wierzchołek” alkaline fen, near Złotów (photo by R. Stańko).
Fig. 16. Calcareous sediments – drilling in a mountain flush fen in the Magura National Park. A: sedge peat, decomposition 4, B: amorphous calcareous tufa
(photo by D. Horabik).