Fen Mires Research Articles

Mire Development and Disappearance due to River Capture as Hydrogeological and Geomorphological Consequences of LGM Ice-Marginal Valley Evolution at the Vistula-Neman Watershed

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.

High N2O consumption potential of weakly disturbed fen mires with dissimilar denitrifier community structure

Peat soils can be strong sources of atmospheric nitrous oxide (N2O), but at the same time act as sinks for the greenhouse gas N2O. However, the role of N2O reduction to dinitrogen (N2) here is still not fully understood. In particular, this applies to pristine or weakly disturbed fen mires. These types of peatland ecosystems are characterised by anoxic soil conditions and special N dynamics restricted to ammonium (NH4+) turnover and very low nitrate (NO3−) availability. N2O and N2 fluxes from intact soil cores from three weakly disturbed fen mire types and two soil habitats (tussocks and hollows) were investigated using the helium (He) incubation approach. Ambient air in headspaces were first substituted with a He-O2 trace gas mixture to quantify N2O and N2 exchanges under prevailing soil oxygen (O2) conditions, and then with an anoxic He trace gas mixture (99.9% He) for establishing the maximum possible denitrification rate. Changing from the He-O2 mixture to a pure He trace gas mixture led to strong increase of N2 fluxes (up to 2916 μg N m−2 h−1) and negative N2O fluxes of up to −72 μg N m−2 h−1. Whilst small differences in N gas fluxes were found between all types of fen mires, an analysis of the denitrifier abundance based on nirK, nirS and nosZ genes indicated respectively more pronounced variation. The structure of denitrifier communities exhibited a strong plot specificity driven by water-filled pore space, soil organic matter and soil pH. This short-term He incubation experiment revealed that weakly disturbed fen mires act as considerable N2O sinks under anoxic conditions and improved our knowledge of the original N dynamics in this peatland ecosystem.

Conservation of disappearing cultural landscape\u2019s biodiversity: are people in Belarus willing to pay for wet grassland restoration?

Abandonment of traditional farming practices, such as hay-making and pasturing, has resulted in rapid loss of open wet grassland habitats in Europe. The globally threatened Aquatic Warbler (Acrocephalus paludicola L.) is a bird species that occurs almost exclusively in open fen mires, which have virtually disappeared in Western Europe, but still persist locally in Eastern Europe. Focusing on the world’s most important breeding site for Aquatic Warbler, the Zvaniec fen mire in Belarus, we estimated Belarusian citizens’ willingness-to-pay for adequate conservation management of this fen mire and its focal species the Aquatic Warbler. Results from a discrete choice experiment indicated that Belarusian citizens were willing to pay for appropriate conservation programmes of the Zvaniec fen mire. Scything and mechanical mowing were preferred compared to controlled burning, and especially over herbicide treatment of encroaching shrubs. Conservation management was preferred over legal protection of wetland areas without management. Respondents considered such passive conservation to be insufficient to maintain open fen mire habitat and gave a higher priority to active conservation management programmes. These preferences are consistent with evidence-based knowledge about what is effective conservation management for the Aquatic Warbler. Given the gradual disappearance of Europe’s traditional cultural landscapes, we discuss the challenge to fund the maintenance of this biocultural biodiversity legacy.

Water on the Fen Mire as a Problem in the Protection of Globally Threatened Species: Long-Term Changes in Aquatic Warbler Numbers

Water on the Fen Mire as a Problem in the Protection of Globally Threatened Species: Long-Term Changes in Aquatic Warbler Numbers

Comparative seed germination traits in bog and fen mire wetlands

Mires are continental wetlands of high scientific and conservation interest. Knowing the seed germination traits of mire species is essential for understanding their regeneration ecology and conducting active restoration policies. Here, a comparative study of seed germination traits was performed with 34 plant species from bog and fen communities, including many European indicators of these habitats. Freshly collected seeds were exposed to a laboratory germination experiment designed to characterize their response to (1) cold stratification and (2) simulated field temperatures. Germination strategy groups were interpreted according to these responses, and the relation between these groups and different mire types was discussed. Seeds of all tested species had physiological dormancy. Most of them showed conditional type 2 non-deep physiological dormancy: fresh seeds could germinate only at warm temperature, but attained the ability to germinate at colder temperature as they lost dormancy. Most mire species from bogs, poor fens and base-rich fens followed a warm germination strategy analogous to that of other wetland species. Species from this warm group responded to very warm temperatures which rarely occur in the field, and this was interpreted as a gap-detecting mechanism. In contrast, species from calcareous springs and flushes had a cold germination strategy, which would fit with the cold and stable soils where they occur. Finally, a group of species associated with the pioneer Rhynchosporion vegetation of bare peat areas had very low germination, suggesting an intermediate or deep seed dormancy and a long term seed bank.

Optimal habitat conditions for the globally threatened Aquatic Warbler Acrocephalus paludicola in eastern Poland and their implications for fen management

To identify optimal habitat for the Aquatic Warbler Acrocephalus paludicola, a flagship species of fen mires, we related numbers of singing males to habitat variables in all core breeding sites in eastern Poland. The density of male Aquatic Warblers increased with increasing ground cover by water and mosses and litter layer height, and was highest where vegetation was 60–90 cm tall. Male densities also increased with the biomass of arthropods > 10 mm length, estimated by sweep netting, and with the abundance of spiders, estimated by pan trapping. We suggest that habitat management should take into account species‐specific morphological adaptations, nest safety and arthropod productivity. Prevention of vegetation succession is a conservation priority for open fen mires. However, modern management practices to achieve this, especially mowing using tracked vehicles, should be evaluated and optimized to ensure that such practices do not adversely affect the long‐term development of moss cover and litter structure.

Understanding the Long Term Ecosystem Stability of a Fen Mire by Analyzing Subsurface Geology, Eco-Hydrology and Nutrient Stoichiometry – Case Study of the Rospuda Valley (NE Poland)

We explored the background of differences in long–term stability between two parts in an undisturbed mire system (Rospuda fen, NE Poland). We re-constructed the Holocene history of the mire and compared it with current vegetation, water level dynamics, water chemistry and nutrient availability in two basins: A, where the mire terrestrialised a deep gyttja–filled lake, and B, where peatland developed directly on fluvial sands. The current vegetation of sedge–moss fens was described in 10 releves from each basin, groundwater was sampled from piezometers and analysed for major ions, while its relative water level was recorded during three years. N and P content was measured in above ground vascular plant samples collected within the releves. Fens in basin A were stable in the past, whereas fens in basin B switched between open and wooded or reed–dominated phases. In basin B, where trees are more abundant, we found higher water fluctuations, occurrence of river floods and a higher N:P ratio than in basin A. Our interpretation follows that the subsurface geology of fen basin may govern mire stability by determining its hydrological–buffering capacity, which may affect N:P ratios. Our results suggest that P–limited fens are more vulnerable for changes in water level.

Model-Based Selection of Areas for the Restoration of Acrocephalus paludicola Habitats in NE Germany

The global Aquatic Warbler (Acrocephalus paludicola, Vieillot, 1817) population has suffered a major decline due to the large-scale destruction of its natural habitat (fen mires). The species is at risk of extinction, especially in NE Germany/NW Poland. In this study, we developed habitat suitability models based on satellite and environmental data to identify potential areas for habitat restoration on which further surveys and planning should be focused. To create a reliable model, we used all Aquatic Warbler presences in the study area since 1990 as well as additional potentially suitable habitats identified in the field. We combined the presence/absence regression tree algorithm Cubist with the presence-only algorithm Maxent since both commonly outperform other algorithms. To integrate the separate model results, we present a new way to create a metamodel using the initial model results as variables. Additionally, a histogram approach was applied to further reduce the final search area to the most promising sites. Accuracy increased when using both remote sensing and environmental data. It was highest for the integrated metamodel (Cohen's Kappa of 0.4, P<0.001). The final result of this study supports the selection of the most promising sites for Aquatic Warbler habitat restoration.

Effect of mowing on productivity in the endangered Aquatic Warbler Acrocephalus paludicola

SummaryThe Aquatic Warbler Acrocephalus paludicola is a globally threatened habitat specialist that breeds in open fens in Central and Eastern Europe. Because bush and reed encroachment threaten many suitable breeding areas, habitat management is necessary to maintain the open wetlands that Aquatic Warblers require for nesting. The effectiveness of mowing as habitat management has so far only been assessed by counting the number of singing males. To assess whether mowing also affected vital reproduction parameters, we analysed Aquatic Warbler productivity in the Biebrza National Park, Poland, on plots in four different successional stages after mowing. Our study showed that productivity was lowest in the first year after mowing, but increased to the highest levels in the second year after mowing. The productivity differences between areas at different stages after mowing resulted from differences in nest density, since we found little evidence for an effect of mowing on nest survival or the number of fledglings produced per successful nest. Nest survival was highly variable between years and varied mostly with nest age and nest initiation date. The density of singing males was positively correlated with both the nest density and the number of fledglings produced in an area, suggesting that this simple indicator could be used to rank the quality of Aquatic Warbler habitats. We recommend that in mesotrophic fen mires, such as the Biebrza valley, mowing as habitat management is applied less frequently than every second year.

Polish Wetlands and Marshland Birds: Looking for Undisturbed References

With the loss of natural wetlands in western Europe, conservationists involved in ‘restoration projects’ become increasingly interested in eastern Europe for reference. In Poland, for example, still some 5% of the country is covered by fen mires, raised peat bogs and other types of wetlands. Although not in a pristine state anymore, size and quality of these wetlands are still sufficient to guarantee high biodiversity and a buffer against stochastic events. If anything, these reserves show that size really matters, and also that any attempt at ‘restoration’ of a pristine state is doomed to failure.

Diet and fuelling of the globally threatened aquatic warbler at autumn migration stopover as compared with two congeners

AbstractThe effective conservation of aquatic warblerAcrocephalus paludicola, one of the most threatened western Palaearctic migratory passerines, requires good knowledge of its ecological needs at stopover sites. In particular, identifying its diet, which controls the accumulation of fat reserves during migration, facilitates the selection and management of adequately protected areas. Further key information includes the relationship between prey species abundance and habitats of aquatic warbler on stopover. We performed standardized mist netting in the Audierne marshes (western France) during 12 years, which resulted in the capture of 1200 aquatic warblers, and provided measurements for mass gain and the collection of faeces to infer the birds' diet. Invertebrate sampling was carried out in the three main Audierne marsh habitats (reed bed, fen mire and meadow). In order to go beyond prey digestibility bias, we also studied two closely relatedAcrocephalusspecies, present at migration stopover sites during the same period. We found that the diet composition of aquatic warbler observed at migration stopover sites is based on large‐sized prey (Odonata, Orthoptera, Lepidoptera). Like sedge warblers, aquatic warblers put on weight during migration stopovers (daily mass gain=0.38 g). This increase in weight suggests that the aquatic warblers might have adopted a strategy for long‐distance migration with few stopovers only. Owing to great differences in diet, conservation management for the threatened aquatic warbler at stopover sites should not rely on existing knowledge about sedge and reed warblers. Similarities in the diet of aquatic warbler between nesting areas and migration stopover areas and the relationship between habitat and prey abundance suggest that fen mires play an important role in the quality of the foraging habitat at stopover sites.

Breeding ecology of the Aquatic Warbler Acrocephalus paludicola on the Biebrza marshes, northeast Poland

Aquatic Warblers Acrocephalus paludicola were studied in a natural fen mire in the Biebrza River valley, the main breeding ground of the species in its entire distribution range. The number of males present and singing at the sample plot changed considerably during the breeding season. Individual identified colour‐ringed males sang with unchanged intensity throughout the breeding season. The period of daily singing activity differed from other species of Acrocephalus; males sang at dusk rather than at dawn. Males took no part in rearing nestlings but remained on territory and showed vigilance behaviour. The density of males in the breeding season ranged from 1.0 to 10.9 per 10 ha. The density of nesting females ranged from 1.3 to 15.7 per 10 ha. In the most suitable habitat females were more numerous than males. The distribution of females (nests) was clumped where potential food resources were higher. Nests were well hidden in places with deeper water between sedge tufts and an abundance of old dry sedge. Females feeding nestlings collected most food within a 5–60‐m radius (mean 31.7 m). The return rate of males was higher than that of females. The results suggest a mating system that is intermediate between facultative polygyny and promiscuity.

Seasonal changes in census efficiency of birds at marshes and fen mires in southern Sweden

Sixteen fens and marshes with areas between 10 and 285 ha was censused at least six times in the period 11 April to 10 June. The proportion of the number of resident species observed on a visit increased from the beginning of the census period up to the end of May. Thereafter it decreased. Variability in the census of the number of species was lowest in the end of May and the beginning of June. Throughout the seasons studied there were frequent visits of non‐resident species. The proportion of non‐resident, but not the proportion of resident species, observed on a visit, increased as the number of resident species at a locality increased.Census efficiencies per ten‐day periods are given for 14 species. Census efficiency of a species correlated positively with the body weight of the species. The highest census efficiency for most species occurred in the period 21 April to 31 May. It is suggested that if two visits are made in that period about 80% (S.D. = 9.8) of the resident species will be observed.