In search of a hydrological explanation for vegetation changes along a fen gradient in the Biebrza Upper Basin (Poland)

The understanding of succession from rich fen to poorer fen types requires knowledge of changes in hydrology, water composition, peat chemistry and peat accumulation in the successional process. Water flow patterns, water levels and water chemistry, mineralisation rates and nutrient concentrations in above-ground vegetation were studied along a extreme-rich fen-moderate-rich fen gradient at Biebrza (Poland). The extreme-rich fen was a temporary groundwater discharge area, while in the moderate-rich fen groundwater flows laterally towards the river. The moderate-rich fen has a rainwater lens in spring and significant lower concentrations of calcium and higher concentrations of phosphate in the surface water. Mineralisation rates for N, P and K were higher in the moderate-rich fen. Phosphorus concentrations in plant material of the moderate-rich fen were higher than in the extreme-rich fen, but concentrations of N and K in plant material did not differ between both fen types. Water level dynamics and macro-remains of superficial peat deposits were similar in both fen types.We concluded that the differences observed in the moderate-rich and the extreme-rich fens were caused by subtile differences in the proportion of water sources at the peat surface (rainwater and calcareous groundwater, respectively). Development of an extreme-rich fen into a moderate-rich fen was ascribed to recent changes in river hydrology possibly associated with a change in management practices. The observed differences in P-availability between the fen types did not result in significantly different biomass. Moreover, biomass production in both fen types was primarily N-limited although P-availability was restricted too in the extreme-rich fen. Aulacomnium palustre, the dominant moss in the moderate-rich fen, might be favoured in competition because of its broad nutrient tolerance and its quick establishment after disturbance. It might outcompete low productive rich fen species which were shown to be N-limited in both fens. We present a conceptual model of successional pathways of rich fen vegetation in the Biebrza region.     

Patterns in vegetation, hydrology, and nutrient availability in an undisturbed river floodplain in Poland

In the undisturbed floodplain of the Biebrza river (N.E. Poland) wecompared vegetation composition, standing crop and the nutrients in standingcrop to site factors such as flood duration and inundation depth during springfloods, summer water levels and concentrations of chemical constituents inwaterand nutrient release rates from peat. Our analysis shows a number of clearspatial patterns of biotic and abiotic variables in the ca. 1 kmwide river marginal wetland. The distribution of vegetation types follows acertain pattern: Glycerietum maximae close to the river,followed by respectively Caricetum gracilis andCaricetum elatae and finally Calamagrostietumstrictae at the margin of the river plain. Species richnessincreasesand standing crop decreases from the river towards the margin. The elevation ofthe ground surface gently rises with increasing distance from the river; floodduration and flooding depths in spring decrease in the same direction.Groundwater tables in summer are less correlated to the elevation gradient buttend to be closer to the ground surface at the valley margin. These differencesalso lead to a higher amplitude close to the river and a fairly stable watertable far away from the river. Concentrations of major ions and ammoniumincrease towards the river. Nutrient release rates are also higher closer totheriver. Absence and presence of species and the variation in species compositionof the vegetation was explained best by flood variables; variables fromgroundwater explained much less of the variance. Variations in standing cropandnutrients in standing crop corresponded better to the rates of nutrient releasefrom the organic soil than to nutrient concentrations in the soil water. Weconcluded that river hydrology and nutrient release from the soil are clearlyrelated to vegetation composition, species richness and productivity of thevegetation.     

Methane emissions from fen,bog and swamp peatlands in Quebec

A static chamber technique was used weekly from spring thaw to winter freezing to measure methane emissions from 10 sites representing subarctic fens and temperate swamps and bogs. Rates of < 200 mg CH₄ m^–2 d^–1 were recorded in subarctic fens: within-site emissions were primarily controlled by the evolution of the peat thermal regime, though significant releases during spring thaw were recorded at some sites. Between subarctic fens, topography and water table elevation were important controls on methane emissions, with the general sequence: pool = horizontal fen> string. Emission rates from the 2 swamp sites were lower (< 20 mg CH₄ m^–2 d^–1 ), except during the spring thaw and when the sites were saturated. The low water table ( < 80 cm depth) in abnormally dry years reduced emission rates; rates were also low from a swamp site which had been drained and cleared of vegetation for horticulture. Methane emission rates were also low (< 5 mg CH₄ m^–2 d^–1) from 2 ombrotrophic bog sites. Laboratory measurements of rates of methane production under anaerobic conditions and methane consumption under aerobic conditions revealed that production rates were generally highest in the surface layers (0 to 2.5 cm depth); production was high in the fens and very low in the bogs. The swamp samples were able to produce methane under anaerobic conditions, but were also able to consume methane under aerobic conditions. Annual methane emission rates are estimated to be 1 to 10 g CH₄ m^–2 from the fens, 1 to 4 g CH4 m^–2 from the swamps and <0.2 g CH₄ m^–2 from the bogs and drained swamp.     

Flooding and groundwater dynamics in fens in eastern Poland

Abstract. Dynamics in hydrology and water chemistry in the Biebrza mires (Poland) were examined by means of a sampling survey that was repeated four times between 1987 and 1992. The dynamics in the vertical stratigraphy of water types in the peat profile are considerable from close to the mire surface to a depth of 50 cm. Water composition in the root zone correlated best with vegetation types during extremely dry or wet conditions. In the root zone of groundwater-fed rich fens with Caricetum limoso-diandrae and Calamagrostietum strictae vegetation, specific groundwater types evolve from the interaction of discharging groundwater from below the root zone and the temporal influence of precipitation and evapotranspiration. The Caricetum limoso-diandrae is fed by the continuous discharge of nutrient-poor, relatively mineral-rich water. The site conditions in the Calamagrostietum strictae are determined by occasional flooding and the presence of discharging mineral-poor groundwater in the lower part of the root zone. In the Caricetum limoso-diandrae and the Calamagrostietum strictae the maximum variations in water level were 56 and 86 cm, respectively. The composition of shallow groundwater of the Betuletum humilis/Caricetum rostratodiandrae fen is diluted most compared to other vegetation types by rainwater in wet periods. In periods of prolonged drought it has a water type that is affected by evapotranspiration and peat mineralisation. The water level varies by only 33 cm. In the Magnocaricion and Glycerietum maximae in the floodplain the water composition is determined by spring flooding of the river and the natural draw-down that occurs in the following summer. Here, maximum variations in water level were 108 and 117 cm, respectively.     

Soil and vegetation responses to hydrological manipulation in a partially drained polje fen in New Zealand

Anthropogenic drainage causes loss of natural character in herbaceous wetlands due to increased soil oxygen penetration. We related vegetation gradients in a New Zealand polje fen to long-term effects of drains by using hydrological, edaphic and vegetation data, and a before-after-control-impact (BACI) design to test responses to experimental drain closure. Soil profiles and continuous water level records revealed a site subject to frequent disturbance by intense but brief floods, followed by long drying periods during which areas close to drains experienced lower water tables and more variable water levels. Classification of vegetation data identified 12 groups along a moisture gradient, from dry areas dominated by pastoral alien species, to wet communities dominated by native wetland sedges. Lower total species diversity and native representation in pastoral communities were related to the high proportion of alien competitor and competitor-disturbance species, compared with the stress tolerator-dominated flora of other groups. Species–environment relationships revealed highly significant correlations with soil water content and aeration as measured by redox potential (E_H) and steel rod oxidation depth, as well as soil nutrient content and bulk density. Comparison of root anatomy confirmed greater development of flood-tolerant traits in native species than in pastoral aliens, and vegetation N:P ratios indicated that most communities were probably nitrogen-limited. Flooding rapidly re-established wetland hydrology in dried sites in the impact area, and lowered E_H and soil oxidation depth, but had no effect on N and P availability. Presence and cover of pastoral alien species decreased in these areas. This study supports the use of hydrological manipulation as a tool for reducing soil oxidation and thus the impact of alien plant species at restoration sites with minimal intervention, but suggests the need for detailed information on species flooding tolerances and hydrological preferences to underpin this approach.     

Hybridization in Epilobium (Onagraceae): the effect of clearance and re-establishment of fen carr

A population of hybridizing Epilobium in a clearing in fen carr was observed for two years. Traditional and statistical techniques were used to identify hybrids, of which there appeared to be three, involving three parents. The identified hybrids showed correlation in abundance with that of their parents and with the successional status of the vegetation. Even what purported to be a pure E. obscurum population showed characteristics of E. palustre , suggesting a hybrid swarm, but there was evidence that selection was gradually restoring the population to its presumed pre-clearance state.     

Spatial patterns in seed bank and vegetation of semi-natural mountain meadows

Soil seed bank composition and vegetative spatial patterns were studied in four mountain meadow communities in the Broto Valley (N. Spain), in order to analyse the differences that might exists between the two life forms. Soil and vegetation samples were taken at 1 m intervals from 10 m × 10 m quadrats in each meadow in one-year study. The spatial distribution of species was analysed along with the calculation of an autocorrelation coefficient which takes account of the relative position of samples: (Moran’s I). The results indicate that the abundance of the majority of the species in the seed bank and in the vegetation are randomly distributed, the percentage of species with a clumped distribution only exceeds 35% in the vegetation of one meadow and none of the taxa identified showed a uniform spatial organisation. The species that were distributed in the seed bank in a clumped pattern in more than one meadow were those of the pioneer species (Anagallis arvensis, Centaurium erythraea, Lamium purpureum and Stellaria media). All of these formed long-term persistent seed banks but were absent in the established vegetation in these meadows. According to the results, there exist not only differences between the spatial distribution of the species present in the same community, but also, that some species change their pattern of distribution according to the life form and to the grassland type in which they are found.     

Spatial and temporal patterns in the hydrogeochemistry of a poor fen in northern Wisconsin

We studied the factors causing spatial and temporal patterning of interstitial water chemistry in Crystal Bog, a 7 ha northern Wisconsin kettle-hole peatland. Over the course of the snow-free season Crystal Bog exhibited spatial and temporal patterns in chemistry, especially hydrogen-ion, dissolved organic carbon, and specific conductance. The peatland contains a 0.5 ha pond that has water more dilute than the interstitial water of the surrounding peatland. The direction of groundwater flow between the lake and the peatland was seasonally dependent. In the spring and early summer, flow was from the lake into the peatland, especially on the eastern side of the lake. This flow resulted in a plume of relatively dilute surface interstitial water in the peatland. In mid and late summer direction of groundwater flow was from the peatland into the lake and the dilute plume was reduced in areal extent. By fall the direction of water flow was again from the lake to the peatland.The spatial and temporal heterogeneity in water chemistry produced by the seasonal variation in the direction of horizontal water flow was substantial. Minimum and maximum observed concentrations of dissolved organic carbon (DOC) in the interstitial water of the peatland, for example, differed by more than a factor of three, and pH ranged between 3.8 and 5.0. Correlations of DOC with anion deficit and hydrogen ion concentration and experiments of photo-oxidation of water samples showed that organic acids were the primary cause of acidity in the peatland. Specific conductance was highly correlated with DOC, probably because of DOC's correlation with the very conductive hydrogen ion. In Crystal Bog it was possible to use the relatively simple measure of specific conductance to estimate the temporal and spatial distribution of the more difficult to determine DOC.     

Species richness, diversity and biomass production of desert annuals in an ungrazed Rhanterium epapposum community over three growth seasons in Kuwait

Two blocks, each consisting of twelve 0.25 m²permanent plots, were established in a community dominated by desert annuals inan area of Kuwait protected from grazing, and community attributes wereinvestigated over three growth seasons. A linear relationship was found betweenestimated desert annual cover and biomass production. Species frequency wasassessed by the number of 100 cm² subplots occupied byaspecies in a block (block incidence). Over the three seasons,vegetation features varied considerably. The first season (spring 1997) wascharacterised by very sparse vegetation cover, low vegetation block incidence(sum of individual block incidences of each species present in a block) and lowspecies richness. The second season (spring 1998) had high vegetation cover,relatively low vegetation block incidence, but high species richness. In thethird season (spring 2000), vegetation cover was very sparse (as in 1997), butboth blocks had the highest vegetation block incidence of the three years andspecies richness was moderately high, although individual plants were verysmall. The growth period was much shorter in the very productive andspecies-rich 1998 season than in 2000. Fluctuations in biomass and speciesincidence coincided with pronounced variation in key meteorological variables,in particular the onset of the first rains, the amount of rainfall during thegrowing season and its temporal distribution. Species composition, however,appears mainly to be determined by the amount and possibly the timing of thefirst rainfalls of the season to trigger germination. There was little evidenceto suggest that particularly favourable or unfavourable microsites existed inplots for more than one vegetation period, either for individual species or fordiversity in general. Despite substantial between-season fluctuations inincidence, the relative abundances of the more frequent species to each otherremained broadly similar over the three seasons, with Plantagoboissieri being the predominant species and accounting for thelargest proportion of biomass.     

Environmental drivers of subalpine and alpine fen vegetation in the Southern Rocky Mountains,Colorado, USA

Fens are widely distributed wetlands worldwide and provide vital habitat for plant and animal species in mountainous regions. Alpine fens are rare in the Rocky Mountains and concentrated in the San Juan Mountains where broad regions at high elevation have relatively level topography and suitable climate to favor peat accumulation. Studies of montane and boreal peatlands have identified water chemistry as a main driver of vegetation composition. This study investigated whether similar drivers of vegetation composition are important for alpine and subalpine fens in the San Juan Mountains of Colorado, USA. Water chemistry variables were most important in structuring subalpine and alpine fen vegetation. However, these variables explained considerably less variation in alpine than subalpine fen vegetation. In addition, lower variance of water chemistry in alpine fens did not lead to lower beta diversity of vegetation in alpine than in subalpine fens. Although alpine and subalpine fen vegetation supports similar beta diversity, key differences occur in the environmental drivers of their vegetation composition.     

The influence of environmental factors and management methods on the vegetation of mesic grasslands in a central European mountain range

We examined how environmental factors combined with the diverse ways of the extensive management of mesic mountain grasslands affect species composition and diversity in the Polish part of Central Sudetes Mts. Based on the data from 100 research plots altitude, organic matter content and exchangeable magnesium in the soil, as well as the maximum soil water capacity and amount of sand fraction significantly affected species composition. Among the management methods, a significant effect on the differentiation of species composition was observed following the cessation of usage and mowing. Mown meadows had the highest share of forbs in the biomass, whereas those abandoned ones were dominated by tall and expansive grasses, mainly Calamagrostis epigejos. The species richest grasslands occurred in areas with soils of high water capacity, containing high concentrations of calcium and low amounts of total nitrogen. No significant effect of management methods on the total number of species as well as on the number of forb species was observed. Mown pastures had the highest mean value of the Shannon–Wiener diversity index.     

Small-scale field mapping of lichen distribution in three dimensions with a computer-based position-tracking system

A trial was undertaken with an electromagnetic position-tracking (Tracker) system by mapping a small section of a lichen habitat near Cape Royds, Ross Island, Antarctica. This method facilitated the simultaneous collection of precise information about both the topography of the site and the distribution of lichen species. These data were used to produce accurate maps and three-dimensional reconstructions of the mapped area. The technique offers considerable savings in time over conventional methods used in plant and lichen surveys, and has potential to enhance the information collected from broader-scale transect surveys. Received: 6 January 1999 / Accepted: 23 January 1999     

Seasonal variation in CH4 emissions and production and oxidation potentials at microsites on an oligotrophic pine fen

 Temporal and spatial variation in CH₄ emissions was studied at hummock, Eriophorum lawn, flark and Carex lawn microsites in an oligotrophic pine fen over the growing season using a static chamber method, and CH₄ production and oxidation potentials in peat profiles from hummock and flark were determined in laboratory incubation experiments. Emissions were lowest in the hummocks, and decreased with increasing hummock height, while in the lawns and flarks they increased with increasing sedge cover. Statistical response functions with water table and peat temperature as independent variables were calculated in order to reconstruct seasonal CH₄ emissions by reference to the time series for peat temperature and water table specific to each microsite type. Mean CH₄ emissions in the whole area in the snow-free period of 1993, weighted in terms of the proportions of the microsites, were 1.7 mol CH₄ m^–2. Potential CH₄ production and oxidation rates were very low in the hummocks rising above the groundwater table, but were relatively similar when expressed per dry weight of peat both in the hummocks and flarks below the water table. The CH₄ production potential increased in autumn at both microsites and CH₄ oxidation potential seemed to decrease. The decrease in temperature in autumn certainly reduced in situ decomposition processes, possibly leaving unused substrates in the peat, which would explain the increase in CH₄ production potential. Received: 16 August 1996 / Accepted: 30 November 1996     

Sediment Fe:PO4 ratio as a diagnostic and prognostic tool for the restoration of macrophyte biodiversity in fen waters

1. Globally, freshwater wetlands, including fen waters, are suffering from biodiversity loss due to eutrophication, water shortage and toxic substances, and to mitigate these pressures numerous restoration projects have been launched. Water quality data are generally used to evaluate the chances of reestablishment of aquatic vegetation in fen waters and shallow peat lakes. Here we investigated whether sediment characteristics, which are less prone to fluctuate in time, would result in more reliable predictions. 2. To test if sediment characteristics can indeed be used not only for an easy and early diagnosis of nutrient availability and water quality changes in fen waters, but also for the prognosis of biodiversity response, we recorded the aquatic vegetation and collected surface water, sediment pore water and sediment samples in 145 fen waters in the Netherlands, Ireland and Poland. 3. Endangered macrophyte species were more closely related to surface water chemistry than common species in terms of occurrence and abundance. Sites featuring endangered species appeared to have significantly lower turbidity and pH, and lower concentrations of SO₄, PO₄, total phosphorus (TP) and NH₄ than other sites. 4. PO₄ and TP concentrations in the water layer increased markedly at PO₄ concentrations above 5–10 μmol L^?1 in the sediment pore water. High surface water PO₄ and TP concentrations appeared to be SO₄‐induced and only occurred below certain threshold values for pore water Fe:PO₄ (3.5 mol mol^?1) and total sediment Fe:P (10 mol mol^?1). 5. Interestingly, the occurrence of endangered species also correlated strongly with sediment and sediment pore water ratios; the number of endangered species increased markedly at pore water Fe:PO₄ ratios above 1 mol mol^?1, whereas their actual abundance had the greatest increase at ratios above 10 mol mol^?1. Additionally, endangered species seemed to be more sensitive to accumulation of potentially toxic substances such as sulphide and ammonium than non‐endangered species. 6. As an indicator of both biogeochemical processes and biodiversity, pore water Fe:PO₄ ratios could be a valuable diagnostic and prognostic tool for the restoration of water quality and biodiversity in fen waters, e.g. for selecting the most promising sites for restoration and for optimization of restoration measures.     

Characterization of dissolved organic carbon (DOC) in a dystrophic lake and an adjacent fen

Dissolved organic carbon (DOC), humicsubstances (HS), polysaccharides (PS) and lowmolecular weight acids (LMWA) werecharacterized in water from the dystrophicLake Große Fuchskuhle over a period ofseven months. In addition, porewater from anadjacent fen was investigated in order toobtain information about the DOC in thecatchment area. Size-exclusion-chromatographycombined with UV- and organic carbon(IR)-detection was used to quantify DOC andits fractions. The lake had previously beendivided into four separate sections by largesheets of plastic, and the DOC compositiondiffered markedly between the fourcompartments. Spatial variations in HS and PSconcentrations were greater than seasonalvariations. The high amounts of HS (up to58%) in the western sections of the lake,indicated influence by subsurface water fromthe fen, whereas the eastern sections weredominated by PS (up to 35%) of algal origin.These differences could be explained byhydrological conditions, indicating thatcompletely different catchment areasinfluenced the water chemistry in the separatecompartments. By characterizing the HS bytheir average molecular weight and theiraromaticity, three different groups of HScould be distinguished depending on theirorigin and fate. Microbial degradation of DOCand its fractions differed between two of thecompartments during incubation studies over aperiod of six weeks.     

Climate and vegetation structure determine plant diversity in Quercus ilex woodlands along an aridity and human-use gradient in Northern Algeria

We studied the influence of environmental factors relating to climate, soil and vegetation cover on total species richness, species richness of different life-forms and species composition of plant communities occurring in Quercus ilex woodlands, across a 450-km long transect in Northern Algeria constituting a gradient of aridity and human use. We sampled vegetation and collected environmental data in 81 10 m × 10 m plots in five zones representing the largest Q. ilex woodlands throughout the study area, analysing them within an a priori hypothesis framework with the use of Path Analysis. Changes in plant diversity were mainly influenced by environmental factors related to precipitation and temperature regimes, as well as by total plant cover. In particular, changes in species composition were determined by factors associated with the temperature regime through their influence on both woody and annual herbaceous plant richness, and by factors related to the precipitation regime through their influence on perennial herbaceous plant richness, likely due to the differential tolerances of these functional groups to cold and water stress. Our results emphasize the importance of differences in environmental adaptability of the most important life-forms with regard to explaining compositional change (beta diversity) along aridity gradients, and the mediator role of total plant cover in relation to the effects of soil conditions on plant diversity.     

Groundwater chemistry and vegetation of gradients from rich fen to poor fen in the Naardermeer (the Netherlands)

In the eastern part of the Naardermeer peatlands (the Netherlands) a regional calcium-rich groundwater flow discharges (here often called the seepage area), whereas in the western part infiltration takes place. The ecological consequence of this hydrological pattern is reflected by the pattern in reedland communities. In the seepage area, which is characterized by Thelypteris-reedlands including many rare and endangered species (Caricion davallianae, Calthion palustris), there is a complex gradient of water types. The lime potential in the peat soil is clearly influenced by the hydrological gradient. In the ombrotrophic (poor fen) part of the gradient (containing species of Caricion curto-nigrae) the lime potentials are low and the groundwater contains low amounts of dissolved ions. The rare and endangered species (Caricion davallianae) are restricted to a small area with high lime potentials which is nourished by regional calcium-rich groundwater. High lime potentials were also measured in eutrophic reedlands influenced by brackish groundwater. Several species which generally occur in wet meadows even show a preference for this brackish environment.In a part of the seepage area succession from rich fen to poor fen and Alnus wood has taken place over a period of 40 years. This development has been caused by the diminishing amount of fresh seepage due to a lowering of the water levels in the surrounding area.The characteristics of poikilotrophic zones (contact zones between water flows) are discussed in relation to their significance for the preservation of endangered marsh species.Abbreviations EC₂₅= Electrical conductivity measured at 25 °C