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Vegetation gradients in fishpond mires in relation to seasonal fluctuations in environmental factors



The composition of the vegetation of fishpond mires in the Třeboň Basin (Czech Republic) was studed in relation to temporal fluctuations in certain environmental factors. The water-table depth, water pH and electrical conductivity at 49 permanent plots were measured at approximately three-week intervals from March to October 2003. Minimum, maximum, mean, median and variation in the above-mentioned environmental factors were correlated with vegetation composition. The most important environmental factors explaining the variation in vegetation were mean pH and maximum water-table level. Median conductivity increased with increase in waterlogging and eutrophication. Some seasonal trends in the dynamics of these parameters were observed. The lowest conductivity was in spring, increased continuously throughout summer and peaked in autumn. In contrast, water level decreased in summer, when evapotranspiration was greatest, and rose in autumn after heavy rainfall. The pH increased from March to June, then was stable and decreased at the end of summer. Seasonal trends were generally identical in all vegetation types. The fluctuations in the environmental factors were so considerable that they may influence the reliability of vegetation environmental analyses.
Vegetation gradients in fishpond mires in relation to seasonal fluctuations
in environmental factors
Sezónní kolísání faktorů prostředí a jejich souvislost s gradientem vegetace na rybničních rašeliništích
Jana N a v r á tilová1& Josef N a vr á t i l 2
1Masaryk University, Faculty of Science, Department of Botany, Kotlářská 2, CZ-611 37
Brno, Czech Republic, and Department of Plant Ecology, Institute of Botany, Academy of
Sciences, Dukelská 135, CZ-379 82 Třeboň, Czech Republic, e-mail:;
2University of South Bohemia, Faculty of Agriculture, Vančurova 2904, CZ-390 01 Tábor,
Czech Republic,
Navrátilová J. & Navrátil J. (2005): Vegetation gradients in fishpond mires in relation to seasonal
fluctuations in environmental factors. – Preslia, Praha, 77: 405–418.
The composition of the vegetation of fishpond mires in the Třeboň Basin (Czech Republic) was
studied in relation to temporal fluctuations in certain environmental factors. The water-table depth,
water pH and electrical conductivity at 49 permanent plots were measured at approximately three-
week intervals from March to October 2003. Minimum, maximum, mean, median and variation in
the above-mentioned environmental factors were correlated with vegetation composition. The most
important environmentalfactors explaining the variation in vegetation were mean pH and maximum
water-table level. Median conductivity increased with increase in waterlogging and eutrophication.
Some seasonal trends in the dynamics of these parameters were observed. The lowest conductivity
was in spring, increased continuously throughout summer and peaked in autumn. In contrast, water
level decreased in summer, when evapotranspiration was greatest, and rose in autumn after heavy
rainfall. The pH increased from March to June, then was stable and decreased at the end of summer.
Seasonal trends were generally identical in all vegetation types. The fluctuations in the environmen-
tal factors were so considerable that they may influence the reliability of vegetation environmental
K e y w o r d s : Central Europe, electrical conductivity, fen, fluctuation, mire vegetation, water pH,
water table
Water-table fluctuations and water quality are of fundamental importance for mire vegeta-
tion (Bragazza 1997, de Mars etal. 1997, Asada 2002, Tahvanainen et al. 2002, Hájková&
Hájek 2004). Water pH and electrical conductivity are the most easily measured parame-
ters of water chemistry (Hájek & Hekera 2004). There are many studies of environmental
factors and vegetation types in mountain and boreal mires (e.g. Malmer 1986, Gerdol
1995, Bragazza & Gerdol 1999, Wheeler & Proctor 2000, Økland et al. 2001, Hájek et al.
2002, Johnson & Steingraeber 2003). In contrast, data on vegetation-environment rela-
tionships are not available for Central-European lowland poor fens at fishpond margins,
which have a specific water regime and whose chemical conditions are closely connected
to the intensively managed fishpond ecosystem.
The mires around the fishponds in the Třeboň basin provide a good opportunity to fill
this gap in mire ecology. The ponds were developed from the thirteenth century onwards
from previously swampy lowlands. The littoral ecosystems of old fishponds contain reeds,
Preslia, Praha, 77: 405–418, 2005 405
tall sedges and fen vegetation. The hydrological conditions in these mires are probably
more determined by man than climatic and geological factors like those in mountain or bo-
real mires. These mires are not purely natural, they were formed and are still influenced by
man. Water-table depth in fens, for example, depends on the water regime in the adjacent
fishpond, which is regulated by water gates. Numerous studies indicate that the distribu-
tion of vegetation in mires depends not only on the mean depth of the water table but also
on its fluctuation (Malmer 1962, Dierschke 1969, Rybníček 1974, Asada 2002).
It has been suggested that water-table fluctuations affect root aeration and the mineral nu-
trition of plants (Ingram 1967). Analyses of seasonal variation in water chemistry during the
growing season, using comparably sampled data sets are important for assessing the sea-
sonal availability of nutrients in surface water (Tahvanainen et al. 2003). Most of the studies
of seasonal variation in mire hydrological conditions have concentrated on ombrogenous
bogs (Damman 1988, Bragazza 1993, Proctor 1994, Bragazza et al. 1998). Little is known
about fluctuating environmental factors in minerogenous fens (Malmer 1962, Proctor 1995,
Vitt et al. 1995, Hájková et al. 2004). It is very difficult to say to what extent the seasonal pat-
terns found in other mires apply to climatically and geologically different regions and to
those with different human impact. Hájek & Hekera (2004) report that major water chemis-
try variables connected with base saturation are stable and thus do not affect the reliability of
vegetation-environment analyses in spring-fed fens. The extrapolation of their results to
lowland fishpond mires is not, however, possible due to the completely different hydrologi-
cal regime and nutrient sources in fishpond mires. The study of seasonal fluctuation in major
ecological factors in mires located around fishponds is therefore needed to provide a more
detailed insight into the role of seasonal fluctuations in Central-European mires in general.
Although the fishpond mire vegetation has been studied extensively with respect to hydrol-
ogy, there are few studies on seasonal variation (Přibáň & Jeník 2002).
The aim of our study was to characterize the vegetation of fishpond edges and reveal
the seasonal patterns in major environmental factors in relation to vegetation gradients in
fishpond mires.
Materials and methods
Study site
The study site is situated within the Protected landscape area, the Třeboň Basin, in the
south of the Czech Republic. Six localities, fishpond Kukla (48°57'20'' N, 14°53'23'' E),
Příbrazský fishpond (49°02'15'' N, 14°56'14'' E), fishpond Staré jezero (48°58'43'' N,
14°53'52'' E), fishpond Starý Vdovec (49°02'22'' N, 14°50'12'' E), fishpond Velká
Lásenice (49°03'11'' N, 14°57'44'' E) and fishpond Vizír (48°57'43'' N, 14°53'19'' E) were
chosen for recording temporal variations in water level and water chemistry in fens. The
climate is temperate with a mean annual temperature of 7.8 °C, in the coldest month (Janu-
ary) of –2.2°C, and in the warmest month (July) of 17.7°C, and an average annual rainfall
of 627 mm (station Třeboň).
Most of the Třeboň basin is dominated by siliceous deposits with a low concentration
of electrolytes in the soil, and as a consequence poor fens are the most common type of
mires. Fens around the fishponds are characterized by peat deposits of various thickness
(from 10 cm to a few meters) on top of sandy deposits.
406 Preslia 77: 405–418, 2005
Vegetation data
In order to monitor fluctuations of environmental factors in subcontinental minerotrophic
fens, 49 permanent plots were established at the six localities. The distribution of plots was
intentionally not random. The plots were selected to represent all main mire vegetation
types in the study area (as in Podani 1994, Somodi & Botta-Dukát 2004). Species compo-
sition was recorded during the summer of 2003 at each locality in 1 m2plots. The cover of
both vascular plants and bryophytes was recorded using the nine-grade van der Maarel
scale (1979). The height of the vegetation cover was measured and used as an indirect ap-
proximation of the productivity of the vegetation. Plant names are those used by Kubát et
al. (2002), mosses by Kučera & Váňa (2003); the nomenclature of syntaxa follows
Moravec et al. (1995).
Environmental factors
The water-table depth was measured manually in PVC tubes perforated throughout their
length. Water pH and electrical conductivity were measured in situ using portable instru-
ments (PH 114 CM 113, Snail Instruments, Czech Republic). At each of the 49 plots, all of
the above mentioned factors were measured at approximately 20-day intervals from
March to October 2003. This period corresponds to the growing season in Central Europe,
when the water regime has the greatest influence on peat vegetation. The depth of peat was
recorded at each sampling plot using a soil probe.
Data processing
Three related multivariate statistical techniques were used to analyse the data: two-way indi-
cator species analysis (TWINSPAN), detrended correspondence analysis (DCA) and canon-
ical correspondence analysis (CCA). Each approach provides a somewhat different view of
the structure of the data and when employed together these techniques can be used to com-
plement, supplement, and evaluate other analyses (Økland 1996, Lepš & Šmilauer 2003).
Vegetation data from all stations were subjected to two-way indicator species analysis
(TWINSPAN, Hill 1979) to classify the plots into groups of communities. Pseudospecies
cut levels were set at 0, 5 and 25 to suit the dataset composed of percent frequency. Differ-
ences in species number in the different strata were evaluated using the Kruskal-Wallis test.
Gradient analysis was performed using DCA and CCA algorithms of the CANOCO 4.5
package (ter Braak & Šmilauer 2002). The percent frequency of the species was log-trans-
formed and rare species were downweighted. The parameters obtained from consecutive
measurements may have different significance in explaining vegetation gradients. There-
fore, five statistical parameters (mean, median, minimum, maximum and standard devia-
tion) obtained from consecutive measurement of each environmental factor, as well as the
thickness of the peat layer, were used in ordinations.
The vegetation data set was subjected first to DCA, in order to assess the overall varia-
tion patterns in species composition. Ordination site scores were correlated to environ-
mental factors using Pearson’s correlation coefficient. All environmental variables were
plotted onto DCA ordination diagrams as supplementary environmental data for better
ecological interpretation of the axes.
Navrátilová & Navrátil: Vegetation gradients in fishpond mires 407
Subsequently CCA was used to further examine the species-environmental relation-
ships. Sixteen environmental variables in total were subjected to forward selection (ter
Braak & Šmilauer 2002, Lepš & Šmilauer 2003) in order to determine the variables that
best account for the species distribution. The marginal and conditional effects of each of
these explanatory variables on species composition was then tested. The effect of the first
canonical axis was tested by a permutation test (499 permutations were always used). To
test the statistical significance of the second and next canonical axis partial CCA was cal-
culated in which the first axis (or next ones) is partialled out by the covariable. Signifi-
cance was again tested by permutation tests for the first canonical axis.
The seasonal trends in environmental factors and the differences in the factors among
the communities (pH and conductivity also measured in open water) were investigated by
Repeated measurements ANOVA. Data transformation was not required because the data
were normally distributed and homogeneity of variance was assumed.
Fen communities
The vegetation was classified by the third division of TWINSPAN into seven groups (Table 1).
Each community is named according to the dominant or diagnostic species. The “Utricularia
fen” (Type 1) occurs as an initial successional stage on permanently flooded sandy deposits.
Syntaxonomically, this community belongs to the alliance Sphagno-Utricularion characteris-
tically dominated by Utricularia intermedia. The shores of Utrichlaria pools are often occu-
pied by a “Rhynchospora alba community” (Type 2) (alliance Rhynchosporion albae). It oc-
curs on sandy deposits with some peat. The dominant species are Rhynchospora alba,Juncus
bulbosus and Sphagnum denticulatum. Fens dominated by tall sedges such as Carex
lasiocarpa and C. rostrata are referred to as “tall sedge communities” (Type 3) of the
Magnocarition elatae alliance. They are found in the littoral zone of mesotrophic water. The
soil is fen peat. One type of fen with a low electrolyte concentration but higher pH than poor
fens was found in the study area. This “medium-rich fen” vegetation (Type 4) belongs to the
alliance Eriophorion gracilis. Species growing there are more or less confined to rich fens:
Hamatocaulis vernicosus, Sphagnum subsecundum and S. contortum. They grow together
with all the common poor fen species. Such fens develop in stands saturated with mineral-rich
groundwater. Species such as Carex elata and C. lasiocarpa grow together with some of the
above-mentioned poor-fen and intermediate-fen species. The next three TWINSPAN columns
represent poor fen vegetation belonging to the alliance Sphagno recurvi-Caricion canescentis.
It is the most common mire vegetation in the Třeboň basin. Among the bryophytes, Sphagnum
species play a principal role. This group was further divided into three subtypes. The first rep-
resents an intermediate type with raised-bog vegetation (Type 5). The hummock species
Calluna vulgaris and Oxycoccus palustris are present here. In addition, some of the species
typical for pond margins are always present, e.g. Phragmites australis. The species composi-
tion of the “typical poor fen” vegetation (Type 6) is quite uniform. Species such as Carex
rostrata,Eriophorum angustifolium, Sphagnum papilosum or S. fallax often dominate.The
last type (Type 7) is poor fen vegetation associated with willow cars and other wet habitats,
which have an impact on species composition. The peat is slightly mineralized, as indicated by
species such as Polytrichum commune.
408 Preslia 77: 405–418, 2005
Table 1. – Synoptic table of vegetation types obtainedby TWINSPAN classification. The species percentage fre-
quencies (constancies) are shown. Species are sorted according to the decreasing value in the phi coefficient. Di-
agnostic species for particular columns have a phi > 0.20 and are highlighted by frames. Vegetation type:
Sphagno-Utricularion (1), Rhynchosporion albae (2), Magnocaricion elatae (3), Eriophorion gracilis (4),
Sphagno recurvi-Caricion canescentis (5, 6, 7).
Vegetation type 1234567
Number of relevés 55596154
Juncus bulbosus 40 40 . . 17 7 .
Utricularia intermedia 40.80....
Carex lasiocarpa 80 . 100 89 33 13 75
Pinus sylvestris juv. . 80 . 11 67 73 .
Rhynchospora alba 20 40 . . 50 13 .
Epilobium palustre ..80....
Typha latifolia ..40....
Carex acuta ..40....
Galium palustre 20.6044...
Viola palustris . . 40 11 . . 25
Agrostis canina 20 60 80 44 17 20 50
Lysimachia thyrsiflora . 206056 . 20 .
Lysimachia vulgaris . 208089332775
Lythrum salicaria . . 40 56 . . 25
Potentilla palustris 20 . 40 100 . 20 25
Peucedanum palustre . . 40 89 . 7 50
Salix cinerea juv. ...44...
Equisetum fluviatile ...44..25
Carex elata . 204056 . 7 25
Carex canescens . 2040781747 .
Carex nigra . 20204417 7 25
Calamagrostis canescens ...33.1325
Utricularia minor 20 20 . 22 . . .
Carex rostrata . . 60 56 33 33 50
Calluna vulgaris ....17..
Drosera rotundifolia 2020 . 67836025
Phragmites australis 20 . . 11 33 20 .
Oxycoccus palustris . 20 . 33 50 60 50
Hydrocotyle vulgaris .....13.
Molinia caerulea 20 20 20 . 50 47 25
Juncus filiformis ......25
Eriophorum angustifolium 100 100 100 89 83 93 .
Utricularia ochroleuca 20 20 . . . 7 .
Lycopus europaeus 20..11...
Frangula alnus juv. . . . 11 17 . .
Sphagnum denticulatum . 100 . . 33 20 .
Calliergonella cuspidata ..4022...
Sphagnum inundatum . . 40 11 . . 25
Calliergon stramineum . 2080671713100
Sphagnum flexuosum 20.4011. .50
Sphagnum subsecundum ...56...
Warnstorfia exannulata . 204078 . 7 .
Aneura pinguis ...33...
Lophocolea bidentata ...33...
Sphagnum fimbriatum ...33..50
Sphagnum palustre 20 . 20 . 100 7 100
Aulacomnium palustre . . 20 33 50 13 25
Navrátilová & Navrátil: Vegetation gradients in fishpond mires 409
Sphagnum papillosum .....
53 .
Sphagnum fallax 20 40 20 11 50 80 .
Polytrichum strictum .....27.
Sphagnum affine .....13.
Polytrichum commune . 20 . 22 33 47 75
Species present in only one column: E1: Potentilla erecta 3: 20, Utricularia australis 3: 20, Scutellaria
galericulata 3: 20, Cirsium palustre 3: 20, Cardamine amara 4: 11, Eriophorum vaginatum 6: 7, Drosera
intermedia 6: 7, Vaccinium vitis-idaea 6: 7, Betula pubescens juv. 4: 11, Salix aurita juv. 4: 11. E0: Sphagnum
platyphyllum 4: 11, Chiloscyphus polyanthos 4: 11, Drepanocladus aduncus 4: 11, Brachythecium rivulare 4: 11,
Sphagnum magellanicum 4: 11, Hamatocaulis vernicosus 4: 11, Sphagnum contortum 4: 11, Sphagnum obtusum
4: 11, Plagiothecium denticulatum 4: 11, Sphagnum rubellum 6: 7.
410 Preslia 77: 405–418, 2005
-1 4
-1 4
peat depth
height E1
sp. richness
axis 2
Fig. 1. – Ordination diagram of vegetation samples based on DCA with passive environmental variables. WME =
mean water-table depth, WMD = median water-table depth, WMI = minimum water-table depth, WMA = maxi-
mum water-table depth, WSD = standard deviation of water-table depth, PME = mean water pH, PMD = median
water pH, PMI = minimum water pH, PMA = maximum water pH, PSD = standard deviation of water pH, CME =
mean electrical conductivity, CMD = median electrical conductivity, CMI = minimum electrical conductivity, CMA
= maximum electrical conductivity, CSD = standard deviation of electrical conductivity, peat depth = thickness of
peat layer, height E1 = height of herb layer, E0 = cover of moss layer, E1 = cover of herb layer, sp. richness = species
richness. Vegetation types: =Utricularia fen, =Rhynchospora alba community, = tall sedges, =medium-
rich fen, =Sphagnum palustre poor fen, =Sphagnum fallax poor fen, =Polytrichum commune poor fen.
The Kruskal-Wallis test showed significant differences (P < 0.001) in the mean species
numbers among communities. The medium-rich fens are different from species-poor
communities like: Utricularia fens, the Rhynchospora alba community and Sphagnum
fallax poor fen.
Gradient analysis
The first two DCA axes are nearly equal inlength (Fig. 1) and explain about 20% of the to-
tal species variability. They also correlate well with environmental data (r1st ax. = 0.918; r2nd
ax. = 0.868). The first ordination axis is correlated significantly (P < 0.01) with mean pH,
with species richness, height of the vegetation and herb layer cover. The second ordination
axis is significantly correlated with variables related to the water regime, mainly maxi-
mum water level, and percent cover of mosses, and less markedly with mean and maxi-
mum electrical conductivity. Thickness of peat layer correlate significantly with both axes,
decreasing with increasing water-table depth and increasing with increasing pH. It is nega-
tively correlated with conductivity (Table 2).
Four canonical axes of CCA with all environmental variables were significant
(P < 0.01), explaining about 26% (first two about 17%) of the total variability in the spe-
cies data. Species-environmental correlation is similar to that in unconstrained ordination
(r1st ax. = 0.892, r2nd ax. = 0.900). The pH parameters and thickness of peat layer were gov-
erned by both the first and second canonical axes, while conductivity and water parame-
ters were governed by the second canonical axis.
Using the forward selection in CCA the four most important variables were selected:
thickness of peat layer, maximum water level, mean pH and median conductivity (Fig. 2).
They explain about 20% of the total variability in species data and a considerable part
(59%) of the variance in the species-environment relations.
Temporal fluctuations in environmental factors
There were marked seasonal fluctuations in water-table depth, water pH and water electri-
cal conductivity in the fishpond fens studied (Fig. 3). In general, seasonal trends were sim-
ilar for all vegetation types. In particular, water level decreased in summer, when
evapotranspiration was greatest, and rose again in autumn after rainfall. The pH increased
from March to June, then was stable and then decreased at the end of summer. Electrical
conductivity was low in spring, then increased continuously throughout summer and
peaked in autumn.
Comparison of environmental factors among communities
Means and standard error of measured environmental parameters in the different vegetation
types are shown in Table 3. Repeated measured ANOVA was significant for both, within-sub-
ject effect (seasonal fluctuation) and also between-subject effect (TWINSPAN clusters) in the
case of all measured factors. According to Tukey unequal N HSD post hoc test, significant dif-
ferences (P < 0.05) were found in pH between open pond water and all fens. Vegetation with
Rhynchospora alba differs in conductivity from medium-rich vegetation and poor fen vegeta-
tion with Sphagnum fallax, which have the lowest conductivity. There were no significant dif-
ferences among vegetation types in water regime according to the Tukey unequal N HSD test.
Navrátilová & Navrátil: Vegetation gradients in fishpond mires 411
Table 2. – Correlation coefficients between environmental variables and DCA ordination scores of the sample
plots along the first and the second axes. ** P < 0.01, * P < 0.05, ns – not significant.
Variable Axis 1 Axis 2
Mean water pH (PME) –0.40** ns
Median water pH (PMD) –0.36*ns
Minimum water pH (PMI) –0.30*ns
Maximum water pH (PMA) –0.35*–0.32*
Mean electrical conductivity (CME) ns –0.45**
Median electrical conductivity (CMD) ns –0.32*
Maximum electrical conductivity (CMA) ns –0.41**
Standard deviation of electrical conductivity(CSD) ns –0.36*
Mean water-table depth (WME) ns –0.63**
Median water-table depth (WMD) ns –0.50**
Minimum water-table depth (WMI) ns –0.54**
Maximum water-table depth (WMA) ns –0.68**
Peat depth –0.38** 0.53**
Height of herb layer –0.40** –0.32*
Species richness –0.62** 0.32*
Cover of herb layer (E1) –0.37** ns
Cover of moss layer (E0) ns 0.66**
412 Preslia 77: 405–418, 2005
-1.5 2.0
-1.5 1.5
peat depth
axis 2
Fig. 2. – The samples-environmental variables biplot based on CCA. WMA = maximum water-table depth, PME
= mean water pH, CMD = median water eletrical conductivity, peat depth = thickness of peat layer. For vegetation
types symbols see Fig. 1.
Navrátilová & Navrátil: Vegetation gradients in fishpond mires 413
Water-table depth
Water pH
Electrical conductivity
(µS/cm )
Fig. 3. – Temporal fluctuation in selected environmental variables. Vertical bars denote 0.95 confidence interval.
Measurements were carried out from March to October 2003 at approximately three-week intervals.
Table 3. – Mean values (±standard error, SE) of water characteristics in the different vegetation types. Repeated
measures ANOVA test revealed significant differences (P < 0.05) among vegetations types for the selected water
variables. Means with the same letter do not differ significantly (Tukey HSD multiple comparison test, P > 0.05).
Vegetation type pH Electrical conductivity
(μS/cm) Water-table depth
Mean SE Mean SE Mean SE
Utricularia fen 5.48a 0.15 118.7ab 12.4 –6.7a 5.9
Rhynchospora alba community 5.00a 0.13 125.5a 11.1 –15.2a 5.9
Tall sedges 5.36a 0.13 94.6ab 11.1 –14.3a 5.9
Medium-rich fen 5.34a 0.10 65.1b 8.8 –25.9a 4.6
Sphagnum fallax poor fen 5.28a 0.15 85.9ab 12.4 –28.9a 5.4
Sphagnum palustre poor fen 4.94a 0.09 71.1b 7.5 –28.6a 3.4
Polytrichum commune poor fen 5.14a 0.21 57.5ab 17.5 –33.0a 6.6
Open pond water 8.29b 0.29 155.2ab 24.8
The role of environmental conditions in plant species composition
The present analysis permitted the identification of the main environmental gradients affecting
the plant species composition of fishpond mires. The first two DCA axes are nearly equal in
length suggesting that the whole dataset is governed by two mains gradients. The first axis cor-
responds to an acidity-alkalinity gradient (from medium-rich fens to poor fens). Accordingly,
pH of surface water was significantly connected with this vegetation gradient. Along the sec-
ond ordination axis, the vegetation of flooded fens was separated from that of the other com-
munities, especially the drier ones (bog-fen-marsh gradient), so the second ordination axis cor-
responds to a water-table depth gradient. The correlation between samples and environmental
variables in CCA is similar to that in unconstrained ordination. This suggests that the selected
environmental variables are responsible for the variation in species composition.
Correlation between vegetation and environmental parameters permitted further clari-
fication of the influence of the environmental factors on vegetation differentiation. The
presence of tall sedge vegetation correlated with high water level, high pH and high elec-
trical conductivity. This vegetation was also the tallest, indicating a higher nutrient avail-
ability in tall sedge communities typically located in the littoral of meso- (eu-) trophic
ponds. In contrast to this, the moss cover increases in poor fen vegetation, as indicated by
the presence of Sphagnum species. The vegetation with the highest species richness occurs
in stands with the highest water pH, quite low electrical conductivity, and little
eutrophication due to man. In this habitat the fluctuation in environmental factors is also
very low. In contrast to this, pH, conductivity and water level fluctuate more in poor fen
vegetation. A very similar result was obtained for Carpathian fens, where water level fluc-
tuation, as well as seasonal variability in water chemistry, were larger in poor than in rich
fen microhabitats (Hájková et al. 2004). The species richness is generally lower in poor
than in rich fens (e.g. Hájková & Hájek 2003) due to the larger species pool of calcicole
species in Central-Europe (Chytrý et al. 2003). Our results suggest another explanation for
this difference in species richness – a pauperization of regional poor-fen flora due to
marked fluctuations in water level, which causes extinction of some obligate fen species
not adapted to changing water level. A periodical flooding by nutrient-rich pond water
seems to be a major factor affecting the occurrence of rare species in poor fens.
414 Preslia 77: 405–418, 2005
Seasonal variation in selected environmental factors
Fluctuation in the environmental variables measured is very conspicuous in fishpond
mires. For example, difference in water level from March to August is about 45 cm, differ-
ence in pH between spring, autumn and summer is about 1 pH unit, and conductivity dou-
bled from March to October. The fluctuation in time is, in some cases, bigger than the dif-
ferences among communities. The fluctuation in environmental factors is due to fluctua-
tions in water level related to evapotranspiration and precipitation. The evapotranspiration
is high in summer and as precipitation in summer 2003 were extremely low, the water level
fell. It is more difficult to explain the fluctuation in pH. Many different factors influence
the complex acid-base balance in mire waters, including hydrology, bedrock, soil quality,
weathering rate, nutrient uptake by plants, cation and anion exchange, decomposition, re-
dox reactions and atmospheric deposition (Shotyk 1988). The cation exchange by Sphag-
num is an important primary source of acidity in many cases (Clymo 1987, Vitt 2000). The
low pH at the beginning and end of the vegetation season may have been caused by Sphag-
num activity. The activity of Sphagnum species has a large impact on the organic acidity of
mire water (Tahvanainen et al. 2002). Sphagnum species, which are not noticeably limited
by low temperatures, acidify mire water mainly in spring and autumn, when they are not
limited by herb layer.
The significant autumnal increase in conductivity might be explained by decreasing
water level (Baumann 1996, Hájková et al. 2004). However, in the fishpond mires studied
the conductivity continued to increase even after the autumnal rains caused the water level
to rise. The water in fishponds mires accumulates after rains in contrast to spring fens
where the rainfall run off is accelerated and the ions are eluted. The dry and hot climate as-
sociated with the water table decrease in summer 2003 probably caused a higher biologi-
cal activity in the peat resulting in the release of chemical elements into the interstitial wa-
ter, which became more mobile after heavy rainfall and influenced conductivity in the
sampling device (Mörnsjö 1969)
In conclusion, the vegetation of fishpond mires is particularly affected by the chemical
and hydrological water conditions. These conditions are not static, but fluctuate markedly
during the growing season and have a significant role in affecting vegetation types.
Conservation note
The intensive fish-production (fertilizing, fish feeding) together with inputs from the
catchment area (agriculture, pollution and nutrient inputs) has caused the eutrophication
of the fishponds (Pechar et al. 2002) over the last 30 years. One of the wide spread meth-
ods used in current fish farming is to retain an extremely high water table in the ponds.
However, optimal hydrology for fens may not be optimal for fish breeding (Lamers et al.
2002). The nutrients in the eutrophic pond water enrich the fen areas, which are usually
distant from the pond edges. Only the vegetation of Utricularia fens, tall-sedge fens and
Sphagnum fallax poor fens can survive in stands influenced by eutrophic pond water.
These vegetation types are more resistant to overgrowing by plant species confined to
euthrophicated stands. The influence of pond water often causes tall sedges and shrubs to
invade low-sedge poor fen vegetation and accelerates the succession towards more pro-
ductive vegetation types.
Navrátilová & Navrátil: Vegetation gradients in fishpond mires 415
We thank Michal Hájek and two anonymous reviewers for many helpful comments, and Tony Dixon and Dana
Truffer Moudra for language revision. The research was supported by grant projects nos. FRVS 553/2004,GACR
524/05/H536, MSM 0021622416 and AV0Z 6005016.
Na vybraných rybničních rašeliništích Třeboňské pánve (ČR) bylo studováno složení vegetace ve vztahu k sezón-
nímu kolísání faktorů prostředí. Od března do října byla v třítýdenních intervalech prováděna měření výšky vodní
hladiny, pH a konduktivity na 49 trvalých plochách. Se složením vegetace byly následně korelovány minimum,
maximum, průměr, medián a odchylka od průměru měřených faktorů. Nejdůležitějšími faktory vysvětlujícími va-
riabilitu vegetace byly: průměr pH (koreluje signifikantně s 1. osou DCA), a maximální výška hladiny vody (ko-
reluje signifikantně s 2. osou DCA). Medián konduktivity koreloval s oběma osami a zvyšoval se s rostoucím
stupněm zamokření a současně vzrůstající eutrofizací stanovišť. V kolísání sledovaných parametrů byly zjištěny
určité sezónní trendy. Nejnižší konduktivita byla na jaře a zvyšovala se postupně během léta, s maximem na pod-
zim. Voda naproti tomu klesala během léta, kdy byla zvýšená evapotranspirace a začala růst až na podzim po vy-
datnějších deštích. Hodnota pH se zvyšovala od března do června, od konce léta pak klesala na počáteční hodnoty.
Tyto sezónní trendy byly u všech vegetačních typů podobné. Kolísání měřených faktorů prostředí bylo tak
výrazné, že by mohlo ovlivnit spolehlivost vegetačně-stanovištních analýz.
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Received 4 November 2004
Revision received 13 June 2005
Accepted 15 August 2005
418 Preslia 77: 405–418, 2005
... 5.5-6) and with low to medium concentrations of mineral N (NH 4 + ) and P (soluble phosphate). Oxygen concentration in these waters is usually reduced while that of free CO 2 is very high (Melzer, 1976;Pietsch, 1977;Dierssen and Dierssen, 1984;Schäfer-Guignier, 1994;Hofmann, 2001;Adamec and Lev, 2002;Kosiba, 2004;Navrátil, 2005a, Navrátilová andNavrátil, 2005b;Adamec, 2007a, Adamec, 2010a, Adamec, 2010b. About 240 species of the Utricularia L. genus have recently been recognized worldwide and around 60 species are aquatic or distinctly amphibious; others are terrestrial or epiphytic (Guisande et al., 2007;Adamec, 2018a;Jobson et al., 2018;Silva et al., 2018). ...
... UI usually grows in free water depths of 0−30 cm (up to 1 m; Melzer, 1976) but may also grow terrestrially, above > 5 cm of an organic, loose sediment (peat; see Fig. 5). Seasonal water level fluctuations of 10−30 cm are common at the sites (e.g., Schäfer-Guignier, 1994;Navrátilová and Navrátil, 2005a). However, greater fluctuations might be deleterious for the plants affixed to the bottom growing in dark water due to shortage of light. ...
... However, unlike UI, they also grow at 1-3 (5!) m depth (Melzer, 1976). Typical habitats of UO and US are usually dominated by Sphagnum spp., Utricularia minor, U. australis, Juncus bulbosus, Lemna minor, Drosera intermedia, Carex rostrata, Rhynchospora alba and Drepanocladus fluitans (Casper, 1974;Pietsch, 1977;Kleinsteuber, 1996;Hofmann, 2001;Navrátilová and Navrátil, 2005a;Adamec, 2007a;Fleischmann and Schlauer, 2014). UO and US occur most often as a diagnostic species within the plant association Sphagno-Utricularietum ochroleuci (or Sphagno-Utricularietum stygiae) of the alliance Sphagno-Utricularion and also within the Rhynchosporion albae. ...
Utricularia intermedia Hayne, U. ochroleuca R.W. Hartm., U. stygia Thor and U. bremii Heer ex Kölliker (Lentibulariaceae, Lamiales) are the four rarest and critically endangered European Utricularia (bladderwort) species from the generic section Utricularia. They are aquatic, submerged or amphibious carnivorous plants with suction traps which grow in very shallow, standing dystrophic (humic) waters such as pools in peat bogs and fens (also pools after peat or fen extraction), shores of peaty lakes and fishponds; U. bremii also grows in pools in old shallow sand-pits. These Utricularia species with boreal circumpolar distribution (except for U. bremii) are still commonly growing in northern parts of Europe (Scandinavia, Karelia) but their recent distribution in Central Europe is scarce to very rare following a marked population decline over the last 120 years. All species have very thin linear shoots with short narrow to filamentous leaves bearing carnivorous traps (bladders, utricles) 1-5 mm large. The first three species form distinctly dimorphic shoots differentiated into pale carnivorous ones bearing most or all traps, and green photosynthetic shoots with only a few (or without) traps, while the last species usually forms non-differentiated (monomorphic) or slightly differentiated shoots. The plants exhibit a marked physiological polarity along their linear shoots with rapid apical shoot growth. Their very high relative growth rate is in harmony with the record-high net photosynthetic rate of their photosynthetic shoots. Flowering of these species is common under favourable conditions and is stimulated by high temperatures but only U. intermedia sets seeds; the other species are sterile due to pollen malformation. Some molecular-taxonomic studies indicate that U. ochroleuca and U. stygia might be hybrids between U. intermedia and U. minor. All species propagate mainly vegetatively by regular branching and reach high relative growth rates under favourable conditions. All species form spherical dormant winter buds (turions). Suction traps actively form negative pressures of ca. -0.22 to -0.25 bar. The traps are physiologically very active organs with intensive metabolism: as a result of the presence of abundant glands inside the traps, which secrete digestive enzymes and absorb nutrients from captured prey carcasses (quadrifid glands) or take part in pumping water out of the traps and producing negative pressure (bifid glands), their aerobic respiration rate is ca. 2-3 times higher (per unit biomass) than that of leaves. Although oxygen concentrations inside reset traps are (almost) zero, traps are inhabited by many microscopic organisms (bacteria, euglens, algae, ciliates, rotifers, fungi). These commensal communities create a functional food web and in traps with captured macroscopic prey, they act as digestive mutualists and facilite prey digestion. Traps secrete a great amount of organic substances (sugars, organic acids, aminoacids) to support these commensals (‘gardening’). Yet the nutritional role of commensals in prey-free traps is still unclear. Quadrifid glands can also serve in the reliable determination of three species. Ecological requirements of U. intermedia, U. ochroleuca and U. stygia are very similar and include very shallow dystrophic waters (0-30 cm deep) with highly variable levels of dystrophy, common mild water level fluctuations, oligo-mesotrophic to slighly eutrophic waters, optimal pH values from 5.5-7.0 but always high free-CO2 concentrations of 0.8-1.5 mM. Limited data indicate that U. bremii is partly a stenotopic species preferring only slightly acidic to neutral (pH 6-7), very soft to slightly hard, oligo-mesotrophic waters. Yet it can grow well both in strongly dystrophic and clear waters, in peat bogs as well as sand-pits over peaty soil and clayish sand. Long-term, very low water levels in combination with habitat eutrophication, whatever the reason, leading to peat bog and fen infilling, are the most common and unfavourable ecological threads at the most sites of the four rare Utricularia species. However, ecological consequences of high-water level at the sites can be ambiguous for the populations: it reduces the strongly competitive cyperoid and graminoid species but can speed up site eutrophication. All four species are considered (critically) threatened in European countries and are usually under official species protection or their sites are protected. Regeneration of infilled fens or peat bogs and creation of shallow fen pools and canals in these mires, combined with (re)-introductions of these species have shown to be a very successful and efficient measure to protect the natural populations for many decades. Old shallow sand-pit pools have become outstanding substitution habitats for the protection of U. bremii.
... According to some authors [20,21] on the basis of pH none of the investigated objects gradient is associated with DCA axis 1. The fluctuations of pH and conductivity was inconsistent with temporal fluctuations found for other type of semi-natural mires in the vicinity of fishpond [22], however, in our study for anthropogenic mires there is medium correlation between pH and conductivity (rs=-0.64, p<001) what is common pattern observed in other studies. ...
... p<001) what is common pattern observed in other studies. In study by [22] conductivity was the lowest in spring and pH increased from March to June, then was stable and decreased at the end of summer and peaked at autumn. In our study peak was in spring. ...
... It is known that the water-table fluctuations condition both the root aeration and the mineral availability in aquatic ecosystems [61,62]. It has been reported that the reed die-back generally affects aquatic stands [63,64]. ...
... Consequently, factors responsible for biotic structure are easier to elucidate than in most other ecosystems (Økland 1992). Descriptions of the strong relationship between vegetation and environmental gradients, especially the level of the water table and peat-nutrient concentrations, are available for boreal peatlands (e.g., Malmer 1962, Damman 1986, Økland 1990, Jeglum & He 1995, Nordbakken 1996, bogs in the S Alps (Gerdol 1995, Bragazza & Gerdol 1999) and some Central European bogs and peat fens (Neuhäusl 1972, Dierssen & Dierssen 1984, Navrátilová & Navrátil 2005, Grootjans et al. 2006, Navrátilová et al. 2006. However, there is no detailed information for Central European pine bogs on changes in environmental gradients and vegetation with altitude. ...
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Vegetation analyses (phytosociological relevés) of 20 peat bogs arranged along an altitudinal gradient in the southern part of the Czech Republic, Central Europe, revealed relationships between vegetation and environmental gradients. Six of the peat bogs were investigated in detail. The bogs were dominated by Pinus rotundata, a species endemic to Central Europe, and its hybridogenous populations with P. mugo (the hybrid is called P. xpseudopumilio), with increasing proportions of the latter at higher altitudes. Data were processed using indirect (DCA) and direct (CCA) gradient analyses. Environmental variables (depth of the water table, mean and minimum temperatures, precipitation, pH, conductivity, NH4 and PO4 concentrations, total P, but not total N nor NO3 concentration), as well as biotic characteristics of the sites, such as species composition, and growth form of the dominant pines, were closely correlated with altitude. Woody species, herbs and bryophytes responded to the altitude similarly. Results also indicated the unique characteristics of each bog.
... Our findings also indicated the importance of Kjeldahl nitrogen in determining the occurrence of plant associations. Similar studies from Central Europe were reported from oligotrophic lakes and fens (Hájková et al. 2004, Navrátilová and Navrátil 2005, K³osowski 2006). ...
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We tested the relationship between water chemical variables and macrophyte vegetation in an oxbow-lake of the Upper-Tisza, Hungary. There were 42 relevés in random plots of 2 m by 2 m and 20 chemical variables (Ca, Fe, Hydrogencarbonate, K, carbonate, Kjeldahl-nitrogen, chloride, COD(Cr), Mg, m-alkalinity, Mn, Na, NH 4, NO 2, NO 3, dissolved orthophosphate-P, total phosphorus, pH, sulphate and conductivity) and a biological one (chlorophyll a) were measured. Detrended canonical correspondence analysis was used to explore the species-vegetation-water chemical variables relationship. Our results revealed that there were pronounced differences both in the vegetation and the chemical variables among the different kinds of vegetation patches. According to the DCCA, Trapetum natantis, Glycerietum maximae, Ceratophyllo-Nymphaeetum albae and Typhetum angustifoliae associations could be separated based on the relevés and environmental variables. Kjeldahl nitrogen and carbonate were found to be the most important variables. Our results suggest that water chemical variables had strong influence on vegetation development. The groups of relevés identified by the DCCA were coherent with classical phytosociological categories.
Sedge-moss fens are declining and are being replaced by more productive ecosystems in agricultural landscapes as a result of changes in the way how the landscape is used by society. We aim to identify commonalities between changes in vegetation species composition and changes in properties of groundwater on fens. Most similar resurvey studies use non-permanent or semi-permanent plots, while medium-term studies from fixed permanent plots are scarce. We studied fifteen years of change in vegetation composition within thirty permanent 4 × 4 m plots established in 2004 on fifteen sedge-moss fens in the eutrophicated landscape of the Třeboň Basin (Czech Republic, Central Europe). Complete species composition and abundance data, covers of the moss, herb and shrub layers, the mean and maximum height of the herb layer, and water chemistry and water level data were collected in 2004 and 2019 by the same person, and potential changes between 2004 and 2019 were tested. We found a significant compositional change between the two periods within poor and moderately rich fens, with an increasing abundance of woody plants, tall sedges, tall grasses and some fast-growing Sphagnum mosses. The same changes were observed on flooded and rich fens but were insignificant. Increasing ammonium concentrations in initially relatively ammonium-poor fens, a generally decreasing ratio between ammonium and nitrates, and declining water levels accounted significantly for the observed changes in composition. Species richness generally increased because of an increase in matrix-derived non-fen species whereas specialist species decreased in cover. Although massive environmental and compositional changes occurred before 2004, they continued between 2004 and 2019. Intensification of conservation management or reduction of pond farming is therefore needed.
Questions On‐going rapid loss of fen biodiversity in Central Europe is well known, but rigorous testing of this is complicated. We compared historical and present‐day vegetation plot records from a cultural landscape rich in fishponds, where recent eutrophication and water table manipulations threaten the unique fen diversity. We assess species composition change over the last 50 yr. Location Třeboň Basin, Czech Republic. Methods First, we revisited historical vegetation plots to collect present‐day data and then identified the most similar present‐day record (the present‐day counterpart ) because no permanent plots were available. Second, we inferred water level, pH and conductivity (a proxy of mineral richness) using a training set of present‐day field measurements, and calculated Ellenberg indicator values. Then we applied modified TWINSPAN classification, CCA , PERMANOVA , PERMDISP and RMANOVA in order to test changes in the species composition, β‐diversity and environmental conditions between the historical records and their present‐day counterparts . Results Fen vegetation has persisted on half of the sites. Out of four vegetation types, poor fens and especially flooded fens were over‐represented in the present‐day subset, while rich fens and quaking fens were under‐represented. Overall species composition differed between historical plots and their present‐day counterparts , even within individual vegetation types. Historical rich fens showed significantly higher β‐diversity than their present‐day counterparts , which predominantly represent flooded fens. Inferred water level and its fluctuation, Ellenberg moisture and nutrient values have increased, while inferred pH , conductivity and Ellenberg light value have decreased. Conclusions The historically wide array of fen vegetation has turned into a homogeneous and floristically depauperate set of acidic yet productive flooded fens with a high water level. Rich and quaking fens that were both low in nutrient availability and had a stable water level near the moss layer experienced a large and substantial reduction and have become rare in the landscape. Eutrophication combined with a lack of management has resulted in fen species persisting only in flooded fens. However, fluctuating water levels and high nutrient availability in flooded fens favour productive Sphagnum fens over the other vegetation types, and, importantly, do not support some endangered fen species.
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Changes of vegetation between 1984 and 2004 were studied in Ruda Natural Reserve. Two different methods usually used for monitoring vegetation changes were used - (i) repeating vegetation sampling and (ii) comparing vegetation maps using GIS. The results of both methods show succesional changes to more dense vegetation types. All indicate accelerated succession from open fen vegetation to the forest vegetation. Generally the fen vegetation became less spread and more isolated and pauperised and became more uniform. Comparison of increasing and decreasing species suggest a trend towards more acid-tolerant, nutrient-tolerant and shadow tolerant species. The difference between two used methods is in scale. The first method gives more detailed information about species composition, but it can miss changes in spatial composition of vegetation. In this case the second method is useful.
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Hamatocaulis vernicosus, a rare moss species, was monitored in 33 fens in the Czech Republic for five to six years. Population size, vitality and trends of population development were recorded. Water chemistry, water level fluctuation, vegetation type and cover, as well as mowing regime were assessed and the effect of these potential predictors on the species populations was examined. Populations of H. vernicosus were affected mainly by the density of vascular plants, the species thrived best in habitats with sparse herb and abundant “brown moss” cover. Other important factors included water table fluctuation and water concentration of iron. Populations were more vital and prospered better in sites with a stable water table and more iron-rich conditions. Dependence of population parameters on other measured characteristics of water chemistry was not detected.
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The second version of the checklist and Red List of bryophytes of the Czech Republic is provided. Generally accepted infraspecific taxa have been incorporated into the checklist for the first time. With respect to the Red List, IUCN criteria version 3.1 has been adopted for evaluation of taxa, and the criteria used for listing in the respective categories are listed under each red-listed taxon. Taxa without recent localities and those where extinction has not been proven are listed as a subset of DD taxa. Little known and rare non-threatened taxa with incomplete knowledge of distribution which are worthy of further investigation are listed on the so-called attention list. In total, 849 species plus 5 subspecies and 19 varieties have been accepted. 23 other historically reported species and one variety were evaluated as doubtful with respect to unproven but possible occurrence in the territory, and 6 other species with proven occurrence require taxonomic clarification. 43 taxa have been excluded from our flora compared to the last checklist version. 48.6 % of evaluated taxa have been listed in either of the Red List categories (EX (RE), CR, EN, VU, LR or DD), which is comparable to other industrialized regions of Central Europe.
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Mixed mires, widely distributed in the boreal zone, occur only rarely in the Carpathians. The fine-scale pattern of moss species composition and species richness in the mixed mire Havraník in the Muránska planina Mts was studied using 9 transects stretching from mineral-rich pools to high, ombrotrophic hummocks. The height above water level, pH, conductivity and redox potential were measured in all of 79 sample plots (78.5 cm2). A complete exchange of species composition was recorded along the ca 3-meter transects. The sequence of cryptogamous species was as follows (Chara, Drepanocladus cossonii) < (Bryum pseudotriquetrum, Campylium stellatum, Tomenthypnum nitens) < (Sphagnum teres, S. subnitens, Aulacomnium palustre) < (Sphagnum flexuosum, S. fallax, S. capillifolium s.s.) < (Sphagnum rubellum, Polytrichum strictum, Absconditella sphagnorum). The first DCA axis reflects this long gradient and is closely connected to the height above water level and pH, which strongly decreases from more than 7 in small pools to 3-4 on high hummocks. A well-developed poor-rich mire gradient exists on this single site through Sphagnum-directed succession. The moss species occupying the extremes of the water level gradient (pools and high hummocks) exhibit the lowest niche breadths for pH, whereas the highest niche breadths are found in moss lawn and midhummock species. The highest species richness was found in the moderately alkaline lawns, between 10 and 30 cm above water level. This small-scale pattern of species richness found in the studied mixed mire seems to correspond with that found on a landscape scale. We also detected a distinctly bimodal distribution in pH data, about 4 in hummocks and 6-7 in the lower-positioned rich fen. Our results indicate that this mixed mire ecosystem, which developed in the Carpathians on a small area, functions in the same way as those occurring in the boreal zone over large areas.
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Species richness and above-ground biomass of vascular plants and bryophytes of poor acidic fens (the Sphagno recurvi-Caricion canescentis alliance), rich Sphagnum fens (the Caricion fuscae and Sphagno warnstorfii-Tomenthypnion alliances) and calcareous spring fens (the Caricion davallianae alliance including tufa-forming spring fens) were studied. The study area was in the western parts of the Outer Carpathians in the border region of the Czech and Slovak Republics. The numbers of species were recorded in plots ranging from 0.00196 to 16 m2 and correlated with chemical factors and above-ground biomass. The chemical properties of springwater (mainly pH, conductivity, Ca2+, Mg2+) were the main factors influencing the species richness of vascular plants. Tufa-forming calcareous fen communities (Carici flavae-Cratoneuretum) had the highest species richness of vascular plants. In contrast, the highest species richness of bryophytes occurred at pH-neutral sites, in peat forming calcareous fen communities (Valeriano-Caricetum flavae) and in those with Sphagnum warnstorfii and S. teres. Bryophyte species richness of small plots was correlated with the iron concentration in the springwater. The differences in species richness of calcareous fens were related to the mowing regime. Litter mass had a negative effect on the species richness of vascular plants. Mosses responded to high amounts of litter or vascular plant biomass by a significant decrease in biomass. Two types of Sphagnum fens: (a) strongly dominated by Sphagnum flexuosum or S. palustre (rich in phosphates) and (b) polydominant (poor in phosphates), were also compared. In the former, the slope of the regression for the dependence of bryophyte species richness on plot size was less steep.
A simple model was established for calculating theoretical concentrations of cations in bog water, taking into account the effect of potential evapotranspiration. The actual concentrations of cations in bog water were then compared with the theoretical ones and this allowed to define different seasonal patterns of cation concentrations. Sodium accumulated in bog water with respect to precipitation, to an extent far exceeding the enrichment due to evaporation. A possible explanation of this resides in a surface enrichment owing to capillary flow. Potassium, and to a lesser extent magnesium, accumulated in spring and autumn but were actively removed by plants in summer. Calcium was removed outside the growing season by cation exchange on peat. -from Author
Temporal variation in fen water chemistry was studied in the Western Carpathian flysch zone (Czech Republic and Slovakia). Ten sites representing particular spring-fen types (tufa-forming fens, rich fens, spring-fen meadows, rich Sphagnum-fens, poor Sphagnum-fens) were studied. Water chemistry was determined three times a year (spring, summer, autumn) for 3 years. Water pH and conductivity were the most stable of the measured variables. Na+, K+, Ca2+ and SO42- were also relatively stable. In contrast, N-NO3-, Cl-, Fe, PO43- and redox-potential temporally varied. These fluctuating, unstable variables explained very little or insignificant amounts of the variation in plant species data in our study area, possibly because of their instability. Further, seasonal variation in physical-chemical properties of the water confounded associations with vegetation types when data from different 1seasons was used. The significance of the differences among vegetation types (between-subject effect in RM ANOVA) distinctly changed among seasons for temperature and Si, N-NO3 and Cl- concentrations and to a slight degree, for Fe, Mg and water redox-potential. The differences in Ca, Na and SO42- concentrations, pH and conductivity were highly significant in all three seasons. The first axis of the PCA of the chemical variables reflects the gradient from mineral-poor to mineral-rich fens in all the analyses, i.e. spring, summer and autumn. The separation of the sites along this axis is clearest in the ordination of the autumnal data. Major vegetation types were separated in PCA even when data from all three seasons were pooled. There is no major-nutrient that is characteristic of meadow-species rich and more productive fen habitats, even when repeated water samples are analyzed.
Peat-accumulating wetlands occupy 2–3% of the Earth’s land surface. Sphagnum, an important constituent of much of the peatland vegetation, is responsible for initiating acid conditions in ombrotrophic bogs and, because it decays disproportionately slowly, becomes over-represented in peat. Several features of Sphagnum physiology are important: (1) the plant produces polyuronic acids which, by cation exchange, release H+ into the bog watery (2) it is sensitive to the combination of high pH and high Ca2+ concentration together, though not to each separately; (3) it is sensitive to even moderate concentrations of o-phosphate, NO3− and NH4+; and (4) it is sensitive to moderate concentrations of HSO3−. Cation exchange may be an important source of acidity in some bogs but is probably less important generally than was once thought. The role of coloured organic acids as primary sources of acid is not clear. Acid rain sensu stricto has not been shown to affect Sphagnum, but atmospheric pollution in the wide sense is responsible for its disappearance from badly polluted areas of the southern Pennines. Since the last glaciation, peatlands have been a ‘sink’ for atmospheric carbon, but some bogs in Europe, at least, are becoming less effective as they approach the natural limit to their growth. Death of their vegetation, where it occurs, and mining of peat both contribute to increasing atmospheric CO2 concentration, the extent of which can only be guessed. Nor do we know how peatlands would respond to increased concentrations of CO2 in the atmosphere.