Ewa Jabłońska

One of the largest peatland complexes in Europe is located in Polesie. The most intensive drainage of this area has taken place in the last 100 years. At the turn of the 1920s and 1930s, Professor Kulczyński’s team carried out extensive studies of the western part of Polesie. We digitised and attached the maps and species lists published by Kulczyński. The results of this research served as the starting point for analysing vegetation changes over the last 100 years. Our estimates showed that 28–42% of the original mire area has survived to the present day, while the rest has been converted into arable fields, intensively used meadows and peat mines. Most of the remaining mires are located in large complexes. The vegetation within the present poor fens and bogs retained most of its natural characteristics. We observed changes in vegetation within the preserved rich fens – taxa associated with low-productivity rich fens are disappearing, while species indicative of drying and increased habitat fertility are increasing. The degradation of the Polesie peatlands has not only led to a loss of biodiversity but also has contributed significantly to climate change. In the period 1965–2023, the drained peatlands of this area may have emitted between 0.33 and 0.74 Gt CO₂ eq.

Palsa mires constitute a zonal peatland type in the discontinuous permafrost region of the Northern Hemisphere. They typically consist of permafrost mounds and thermokarst ponds. Global warming has accelerated thawing of permafrost in palsa mounds and an increase in the area of thermokarst ponds in recent decades. Understanding long-term consequences of this process requires in-depth knowledge of the internal diversity of palsa mire vegetation types and their functions. Most studies so-far focused on the palsa mounds. Hereby, we focus on the thermokarst ponds, analysing their vegetation composition and habitat conditions from the top of a palsa plateau down to a fen without current palsa formation close to an adjacent river. We observed a distinct ecological gradient from Sphagnum-dominated ponds in the uppermost part of peat plateau to brown moss-dominated fen flarks at the riverside. This reflected well the poor – rich gradient typically recognised in mire vegetation, confirmed by our hydrochemical analyses. However, in contrast to the gradual shifts in species composition along typical mire zonation in temperate regions, palsa microtopography with mounds, rims, strings, and hollows, creates a sequence of mire basins forming a discrete gradient from base-poor to base-rich conditions, allowing different plant species to dominate these distinct locations.

A comparative phytosociological and habitat analysis of 84 pleustonic phytocoenoses in northern Poland was carried out in order to determine the scale of their floristic distinctiveness and to obtain an answer to the question whether and to what extent the floristic differentiation of pleustonic communities corresponds to the differentiation of their habitat conditions. Based on phytosociological studies, it was shown that the investigated phytocoenoses are not random groups of species, but well differentiated in terms of floristic composition and phytocoenotic structure by communities. It was shown that the studied phytocoenoses represent the following separate associations in phytosociological terms:Salvinio natantis-Spirodeletum polyrhizae, Lemno-Spirodeletum polyrhizae, Riccietum fluitantisandRicciocarpetum natantis.Hydrochemical studies showed that the floristic distinctiveness of these communities is largely confirmed by the differentiation of properties of the water habitat.Salvinio natantis-Spirodeletum polyrhizaeis characterised by the deepest waters (mainly 0.7–1.2 m), alkaline, of a low colour, rich in ions (Mg²⁺, Na⁺, Cl⁻) and therefore characterised by the highest electrolytic conductivity, poor in dissolved organic matter, NO₃⁻and total iron.Lemno-Spirodeletum polyrhizaeis characterised by medium deep waters (mainly 0.3–0.8 m), mostly alkaline, of a low colour, less rich in ions (Ca²⁺, Na⁺, Cl⁻) and relatively low in dissolved organic matter and NO₃⁻.Riccietum fluitantisis characterised by shallow waters (mainly 0.2–0.4 m), most often slightly acidic, of a quite high colour, low in cations and Cl⁻, and relatively rich in total iron, NO₃⁻, and dissolved organic matter.Ricciocarpetum natantisis characterised by the shallowest waters, (mainly < 0.3 m), most often acidic, of the highest colour, low in ions, and rich in total iron, dissolved silica, NO₃⁻and dissolved organic matter. By demonstrating habitat distinctiveness, the studied pleustonic communities may have significance as indicators of various types of aquatic environment.

The aim of this study was to understand the variation in traits relevant for desiccation avoidance among bryophyte species dominant in rich fens and to assess whether these traits explain the formation of a hummock-hollow gradient within peatlands. In samples of 10 species (Aulacomnium palustre, Calliergonella cuspidata, Climacium dendroides, Hamatocaulis vernicosus, Helodium blandowii, Marchantia polymorpha, Plagiomnium ellipticum, Sphagnum teres, S. warnstorfii, Tomentypnum nitens) collected in rich fens of NE Poland, we calculated: canopy bulk density of wet (CDW) and dry (CDD) colonies, maximum water content of bryophyte colonies (WC_max), desiccation rate (K), shoot area index (SAI), canopy dry mass per surface-projected area (CMA), and specific leaf area of a whole living bryophyte part (SLA). The hummock-forming frequency was quantified for each species in the field. Sphagna had the highest WC_max, SAI and CDW, T. nitens and C. dendroides had the lowest WC_max and SLA, P. ellipticum had the highest K, the lowest CMA and CDD. Hummock-forming frequency was positively correlated with CMA and generally negatively related to K, with exception of H. vernicosus showing a high water-retaining ability (low K) despite a hollow or lawn form of growth.

Nutrient availability determines vegetation patterns and ecological functioning of intact groundwater‐fed peatlands (fens). Bryophytes, commonly referred to as ‘brown mosses', dominate calcareous fens (rich fens), are an integral part of their unique biodiversity and contribute significantly to peat formation and carbon sequestration. Brown mosses are replaced by vascular plants as nutrient availability increases. The decline of brown mosses may either be due to their physiological intolerance of high nutrient levels or to them being outcompeted by vascular plants. We aimed to distinguish between these two hypotheses by investigating whether the ecological optima reflect the physiological optima of brown mosses. Eight brown moss species, common in calcareous fens of the northern hemisphere, were grown under a gradient of nitrogen and phosphorus availability. Biomass increment, chlorophyll content and biomass nutrient concentration were measured. All brown moss species studied achieved the highest growth rates and chlorophyll contents when grown under conditions of nitrogen and phosphorus concentrations higher than those where they occur naturally at the highest frequency. Two of the species showed no growth saturation even at the highest levels of nutrient availability, while the others appeared potassium‐limited at the highest N and P levels. Brown mosses dominate natural fens at the lower edge of their physiological optimum in terms of nutrient availability, i.e. their realized niche is much narrower than the fundamental one. Based on the literature, we argue that it is the competition for light with vascular plants which limits the occurrence of brown mosses in nutrient‐rich habitats and prevents them from occupying their entire fundamental niche.

The study documents a process of ice lenses persistence under hummocks during spring snowmelt in a rich fen in Poland. Air temperature, as well as the temperature under vascular plant litter, Hamatocaulis vernicosus mat, Tomentypnum nitens hummocks and Sphagnum teres hummocks, was measured from December to March using temperature data loggers. The Capital Asset Pricing Model was adapted to analyse relationships between air temperature and temperature under litter and mosses. Sphagnum teres best insulated the temperature of the upper peat layer from changing air temperatures and maintained frozen peat under its hummocks the longest (for about a month after the frost had stopped). Tomentypnum nitens insulated similarly effectively in winter, also maintaining the ice lenses under its hummocks, but less effectively in warmer spring, which may be due to differences in hummock structure between the two species. The observed phenomenon may soon disappear due to global warming, which may affect the fen functioning.

Fertiliser use in agriculture increases the non-point pollution of waters with nitrogen (N) and phosphorus (P). Wetland buffer zones (WBZs) are wetland ecosystems between agricultural lands and water bodies that protect surface waters from non-point source pollution. We assessed how vegetation harvesting within WBZs impacts their N and P removal efficiency, nutrient uptake by plants and their biomass quality. We surveyed vegetation of a spontaneously rewetted fen along a small river in Poland, and analysed plant biomass, its nutrient contents and nutrient-leaching potential and the water chemistry. Total N removal reached 34–92% and total P removal 17–63%. N removal was positively related to the initial N concentration, regardless of mowing status. We found a high N removal efficiency (92%) in the harvested site. Vegetation of mown sites differed from that of unmown sites by a higher water-leached carbon and P contents in the biomass. We found that vegetation harvesting may stimulate the overall N removal, but may increase potential biomass decomposability, which eases the recycling of plant-incorporated nutrients back to WBZ. Thus, mowing should always be followed by the removal of biomass. Neglecting already mown WBZs may temporarily lower their nutrient removal efficiency due to potentially faster decomposition of plant biomass.

Large-scale re-establishment of wetland buffer zones (WBZ) along rivers is regarded as an effective measure in order to reduce non-point source nitrogen (N) and phosphorus (P) pollution in agricultural catchments. We estimated efficiency and costs of a hypothetical establishment of WBZs along all watercourses in an agricultural landscape of the lower Narew River catchment (north-eastern Poland, 16,444 km², amounting to 5% of Poland) by upscaling results obtained in five sub-catchments (1087 km²). Two scenarios were analysed, with either rewetting selected wetland polygons that collect water from larger areas (polygonal WBZs) or reshaping and rewetting banks of rivers (linear WBZs), both considered in all ecologically suitable locations along rivers. Cost calculation included engineering works necessary in order to establish WBZs, costs of land purchase where relevant, and compensation costs of income forgone to farmers (needed only for polygonal WBZs). Polygonal WBZs were estimated in order to remove 11%–30% N and 14%–42% P load from the catchment, whereas linear WBZs were even higher with 33%–82% N and 41%–87% P. Upscaled costs of WBZ establishment for the study area were found to be 8.9 M EUR plus 26.4 M EUR per year (polygonal WBZ scenario) or 170.8 M EUR (linear WBZ scenario). The latter value compares to costs of building about 20 km of an express road. Implementation of buffer zones on a larger scale is thus a question of setting policy priorities rather than financial impossibility.