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Recovery of target bryophytes in floating rich fens after 25 yr of inundation by base-rich surface water with lower nutrient contents

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QuestionWhat are the changes in mineral-rich fens (H7410A) after 25 yr of improved surface water quality in a national park?LocationStobbenribben floating-fen complex in National Park Weerribben-Wieden, the Netherlands.Methods Bryophyte species composition, peak above-ground biomass and vascular plant nutrients, as well as electrical conductivity of various layers in the peat were measured between 1988 and 2013.ResultsThe eutrophic moss Calliergonella cuspidata clearly decreased in aerial extent over the 25-yr study, especially near the ditch supplying base-rich surface water to the fen. In contrast, the characteristic rich fen species Scorpidium scorpioides expanded locally near the ditch. In the rich fen zone, peak above-ground biomass decreased from ca. 1000 to 250 g·m−2. Also, foliar N:P ratios in vascular plant tissues increased from 16 to more than 22 g·g−1, which clearly point to lower P availability over time. Improved surface water quality probably also promoted persistence of rich fen habitats in a different way. A large part of the rich fen peatland in 1988 changed into Sphagnum peatland by 2013, probably due to the reduction of base-rich water from below the floating root mat. This mat had become ca. 35 cm thicker in the past 50 yr. However, in areas closer to the ditch, rich fen species persisted, due to inundation with base-rich water during high water periods. Base-rich water probably no longer comes to the surface through the floating root mat, but more likely from the ditch.Conclusions Water quality improvement can be important in the long-term re-establishment of target fen species. Also, local inundation can be helpful if regional groundwater access becomes limited. In the national park, rich fens are more threatened than Sphagnum peatlands. This study suggests that the rich fen stage can be maintained, and succession towards Sphagnum peatland prevented, with occasional inundation with high pH, nutrient-poor water.
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Applied Vegetation Science
&&
(2015)
Recovery of target bryophytes in floating rich fens after
25 yr of inundation by base-rich surface water with
lower nutrient contents
A.M. Kooijman, C. Cusell, I.S. Mettrop & L.P.M. Lamers
Keywords
Bryophytes; Eutrophication; H7140A
(Transition mires in the European Habitat
directive); Hydrology;Nature conservation;
Phosphorus; Restoration; Succession
Nomenclature
Van Tooren & Sparrius (2007)
Received 26 February 2015
Accepted 17 June 2015
Co-ordinating Editor: Beth Middleton
Kooijman, A.M. (corresponding author,
a.m.kooijman@uva.nl)
1
,
Cusell, C. (c.cusell@witteveenbos.nl)
1,2,3
,
Mettrop, I.S. (i.mettrop@uva.nl)
1,2
,
Lamers, L.P.M. (l.lamers@science.ru.nl)
2
1
Institute for Biodiversity and Ecosystem
Dynamics, University of Amsterdam, Science
Park, PO box 94062, 1090 GB Amsterdam, the
Netherlands;
2
Department of Aquatic Ecology &
Environmental Biology, Institute for Water and
Wetland Research, Radboud University
Nijmegen, NL-6525 Nijmegen, The
Netherlands;
3
Witteveen+Bos, PO Box 233, 7400 AE
Deventer, the Netherlands
Abstract
Question: What are the changes in mineral-rich fens (H7410A) after 25 yr of
improved surface water quality in a national park?
Location: Stobbenribben floating-fen complex in National Park Weerribben-
Wieden, the Netherlands.
Methods: Bryophyte species composition, peak above-ground biomass and vas-
cular plant nutrients, as well as electrical conductivity of various layers in the
peat were measured between 1988 and 2013.
Results: The eutrophic moss Calliergonella cuspidata clearly decreased in aerial
extent over the 25-yr study, especially near the ditch supplying base-rich surface
water to the fen. In contrast, the characteristic rich fen species Scorpidium scorpi-
oides expanded locally near the ditch. In the rich fen zone, peak above-ground
biomass decreased from ca. 1000 to 250 gm
2
. Also, foliar N:P ratios in vascular
plant tissues increased from 16 to more than 22 gg
1
, which clearly point to
lower P availability over time. Improved surface water quality probably also pro-
moted persistence of rich fen habitats in a different way. A large part of the rich
fen peatland in 1988 changed into Sphagnum peatland by 2013, probably due to
the reduction of base-rich water from below the floating root mat. This mat had
become ca. 35 cm thicker in the past 50 yr. However, in areascloser to the ditch,
rich fen species persisted, due to inundation with base-rich water during high
water periods. Base-rich water probably no longer comes to the surface through
the floating root mat, but more likely from the ditch.
Conclusions: Water quality improvement can be important in the long-term
re-establishment of target fen species. Also, local inundation can be helpful if
regional groundwater access becomes limited. In the national park, rich fens are
more threatened than Sphagnum peatlands. This study suggests that the rich fen
stage can be maintained, and succession towards Sphagnum peatland prevented,
with occasional inundation with high pH, nutrient-poor water.
Introduction
Mineral-rich fens are threatened in Europe by acidification
and eutrophication (Kooijman 1992; Gunnarson et al.
2000; Heino et al. 2005; Juutinen 2011; Lamers et al.
2015), and are protected by the EU Habitat directive (Euro-
pean Union 1992). Mineral-rich fens have become very
rare, and well-developed fens with Scorpidium spp. may
cover less than 10 ha in the Netherlands (Cusell et al.
2013a). Mineral-rich fens are characterized by high plant
diversity, including EU habitat directive species such as
Liparis loeselii, and many brown moss species (Sj
ors 1950;
Succow & Jeschke 1986; Hallingb
ack & Hodgetts 2000; Vitt
& Wieder 2009). Bryophytes are not only important in
terms of biomass dominance, but also good indicators of
environmental conditions, because they have no roots and
are only one cell layer thick (Proctor 1982). In fact, the
bryophyte layer is a sensitive indicator of environmental
change in rich fen ecosystems (Sj
ors 1950; Gorham et al.
1987).
Many rich fens are threatened by acidification (e.g.
Clapham 1940; Koerselman et al. 1990; Van Wirdum
1
Applied Vegetation Science
Doi: 10.1111/avsc.12197©2015 The Authors. Applied Vegetation Science published by John Wiley & Sons Ltd
on behalf of International Association for Vegetation Science.
This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and
distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.
1991; Van Diggelen et al. 1996; Soudzilovskaia et al. 2010;
Lamers et al. 2015). To maintain sufficient acid neutraliza-
tion capacity and ensure survival of rich fen species, input
of calcium and bicarbonate-rich water is needed (Hajek &
Adamec 2009; Soudzilovskaia et al. 2010). When access of
base-rich water to the fen surface is reduced, rich fen
mosses are replaced by Sphagnum species, and these mosses
actively acidify these wetlands (Clymo 1963; Kooijman &
Paulissen 2006). In many industrialized countries, high
atmospheric deposition also contributes to acidification
(De Haan et al. 2008). This process may result in approxi-
mately 1.5 times higher amounts of buffer components
needed to sustain a suitable pH (Kooijman 2012). How-
ever, in many fens, supply of base-rich water has become
limited. Groundwater input has been reduced in many
areas, due to extraction for drinking water and agriculture
(Schot & Molenaar 1992; Van Loon 2010).
Many rich fens are also threatened by eutrophication,
which is a problem in densely populated countries with
intensive agriculture (Lamers et al. 2015). Many rich fens
are P-limited (Wassen et al. 2005). Eutrophication gener-
ally leads to an increase in biomass production and
changes in plant species composition, especially in the
bryophyte layer. In many rich fens, characteristic brown-
moss species such as Scorpidium scorpioides and S. cossoni
have been replaced by more eutrophic species, such as Cal-
liergonella cuspidata (Kooijman 1992, 1993). In the 1980s,
even the most biodiverse rich fens of the Netherlands con-
tained moss species of more eutrophic habitats (Verhoeven
et al. 1988; Van Wirdum 1991). Meanwhile, measures
have been taken to improve water quality and decrease
eutrophication in many wetland nature reserves, espe-
cially eutrophication with P (Lamers et al. 2015). In Weer-
ribben-Wieden National Park, such measures included
wastewater treatment and redirection of regional and local
water flows, to reduce input of nutrients to natural sys-
tems. Although concentrations of total P did not change
between 1982 and 2000, phosphate concentrations in the
main channels decreased from 12to0.51.0 lmolL
1
(Cusell et al. 2013a).
The goal of this study was to evaluate 25 yr of changes
in bryophyte species composition, nutrient availability
and base status in response to water quality improvement,
in one of the largest and best-preserved rich fen com-
plexes in the Netherlands. Rich fen studies over such peri-
ods are becoming more common (Van Diggelen et al.
1996, 2015; Gunnarson et al. 2000; Juutinen 2011), but
are not always conducted by the same researcher, and
only address environmental changes in e.g. base status
and nutrient availability, to a limited extent. In our study,
we compared detailed surveys of the bryophyte layer in
5m95 m grid cells in one of the fens, undertaken by
the first author in 1988 and 2013. To analyse changes in
nutrient status, peak above-ground biomass and vascular
plant nutrient concentrations were measured in the rich
fen zone in 1984, 1990, 2005, 2010, 2011 and 2012.
Changes in base status in various peat layers were studied
in various years using measurements of electrical conduc-
tivity as a proxy.
Methods
Study area
The Stobbenribben fens are located in Weerribben-Wieden
National Park (eastern Netherlands), in one of the largest
wetland areas in NW Europe (Fig. 1). The climate is tem-
perate-humid, with 800 mm rainfall, evenly distributed
over the year. The national park is surrounded by low-
lying agricultural polders; during wet periods, water is
pumped from these polders into the park to ensure
constant water levels in the agricultural areas. Inside the
park, water levels are also maintained more or less
constant through water control structures, but are allowed
to fluctuate 10 cm between 0.83 and 0.73 m below mean
sea level (Cusell et al. 2013a).
The Stobbenribben consists of a few adjacent rectangu-
lar ponds of ca. 2040 m width and 200 m length, cre-
ated by cutting the Carex peat around AD 1900 (Van
Wirdum 1991). Depth of the ponds to the Pleistocene
sandy underlayer is ca. 2.53.0 m. Kuiper & Kuiper
(1958) mentioned the site as a good example of floating
fens, with many characteristic rich fen species, such as
S. scorpioides and the EU Habitat directive species Liparis
loeselii. The fens are annually mown with small machines
to prevent establishment of shrubs and trees (Cusell et al.
2013a).
Hydrology of the fen complex was studied in 1970
1980s by Van Wirdum (1991). To the southeast, this fen
complex borders an agricultural polder, which was
drained in the 1950s and is several meters lower than
the fens themselves (Fig. 1). As a result of their relative
elevation, the fens are subject to downward water move-
ment (infiltration) of ca. 12myr
1
. The water loss is
far larger than the precipitation surplus, and compen-
sated by lateral inflow of surface water from a ditch at
the NE side of the fens. This water flows beneath and
through the floating root mat. Towards the SW end, the
fens are hydrologically isolated with peat ridges, and
base-rich ditch water becomes increasingly mixed
with rain-water. As a result, the fens generally show a
vegetation gradient from brown moss communities with
S. scorpioides closer to the ditch to Sphagnum-dominated
vegetation in the more isolated parts of the fen (Van
Wirdum 1991).
In the 1980s, base-rich (ditch) water, needed to sustain
the rich fen vegetation, was probably mainly supplied to
Applied Vegetation Science
2Doi: 10.1111/avsc.12197 ©2015 The Authors. Applied Vegetation Science published by John Wiley & Sons Ltd
on behalf of InternationalAssociation for Vegetation Science.
Bryophyte recovery in floating fens over 25 yr A.M. Kooijman et al.
the fen surface from below the floating root mat, through
gaps in the young layer of bryophyte vegetation (Van Wir-
dum 1991). However, occasional flooding with ditch water
after heavy rain was reported, especially in areas close to
the ditch (Bergmans 1975; Van Wirdum 1991; Kooijman
1993). The chemical composition of ditch water varies
between seasons and years, depending on the amount of
rain and input of water pumped in from the surrounding
agricultural polders. Water moving out of the polders usu-
ally has relatively high calcium and bicarbonate content
(Cusell et al. 2014a). However, polder water is also rich in
nutrients, especially P.
Various measures have been applied to improve water
quality since the 1970s. The major surface water inlet of
the national park has been shifted from relatively
eutrophic rivers to the much cleaner Lake Vollenhoven.
Also, water purification facilities have been constructed,
and P input from urban areas has decreased (Cusell et al.
2013a). Local measures to improve water quality and
increase supply of base-rich ditch water were taken in
1992 (Schouwenberg & Van Wirdum 1997). The flow of
water to the ditch in the Stobbenribben fen complex was
redirected, leading to a longer pathway for nutrient
removal. Also, within this project, the local ditch at the NE
side of the fen complex was cleaned and enlarged.
Survey of the bryophyte layer
In one of the fens (Fen A), a detailed survey of the bryo-
phyte layer was conducted in Oct 1988. The fen was
divided in 200 grid cells of 5 m 95m,in40rowsofve
grid cells each. Unfortunately, in the last rows close to the
ditch, six grid cells with unmown reed swamp, dominated
by C. cuspidata, were inaccessible and thus not studied. In
each grid cell, all bryophyte species present were noted;
the total number of bryophyte species was 47. Bryophyte
nomenclature is according to Van Tooren & Sparrius
(2007). Cover values were adapted from Tansley (1946)
and estimated on a scale from 15 (rare, frequent, com-
mon, co-dominant and dominant, respectively). The sur-
vey of the bryophyte layer was repeated in May 2013,
within all 200 grid cells.
Peak above-ground biomass and foliar N:P ratios in
vascular plants
Living vascular plant biomass growing above the fen sur-
face was measured in the rich fen zone at 2550 m from
the ditch in Jul in 1984, 1990, 2005, 2010, 2011 and 2012.
The number of replicates varied between sampling years
from three in 1984, to three to five in later years. In 1984,
Low-lying
agricultural
polder outside
NP
Stobbenribben
fen A
Large canal
with polder
water
Isolated far end
of the fens
N
Brownmoss
vegetation
Sphagnum
vegetation
Ditch with
base-rich water
Fig. 1. Location of the Stobbenribben Fen complex in National Park (NP) Weerribben-Wieden. The dark brown colours in the fen complex indicate rich fen
(brownmoss) vegetation dominated by Scorpidium scorpioides, the lighter areas are Sphagnum peatland dominated by S. palustre. The length of the fens
is 200 m.
3
Applied Vegetation Science
Doi: 10.1111/avsc.12197©2015 The Authors. Applied Vegetation Science published by John Wiley & Sons Ltd
on behalf of International Association for Vegetation Science.
A.M. Kooijman et al. Bryophyte recovery in floating fensover 25 yr
the three replicates consisted of ten different subplots of
20 m 920 cm (Verhoeven et al. 1988). In later years,
above-ground living phanerogam biomass was collected in
plots of 25 cm 925 cm. Samples were collected, dried
and weighed. After weighing, samples were ground and
used for analysis of foliar N and P. In 19841990, N and P
content were determined with a method using H
2
SO
4
destruction with salicylic acid, and in 20052012 with a
CNS analyser and microwave destruction with HNO
3
(Westerman 1990) followed by element concentration
analysis with ICP-OES (Optima 3000 XL, PerkinElmer,
Waltham, MA, US). Foliar N:P ratios were calculated as
gg
1
. Foliar N:P ratios are a well-established proxy to esti-
mate whether N or P could be a limiting factor (Koersel-
man & Meuleman 1996; G
usewell 2004; Cusell et al.
2014a). N:P ratios of 1416 indicate more or less balanced
conditions, while values above 20 clearly suggest P limita-
tion (Koerselman & Meuleman 1996; G
usewell 2004). For
2010, however, P content was negligible so that these
ratios were not analysed.
Surface EC values
Electrical conductivity (EC) values in the peat are related
to calcium and bicarbonate concentrations in the water
(Van Wirdum 1991; Cusell et al. 2014b), so that EC values
may be used as a proxy for base status. EC values also help
to determine the origin of base-rich water. EC at 25 °Cand
surface pH were measured during the bryophyte survey in
Nov 1988, with a field meter at the fen surface near the
centre of each 5 m 95 m grid cell.
The EC measurements were repeated four times under
various hydrological conditions, three of them character-
ized by high inundation of the rich fen zone (Jul 2012,
May 2013 and Oct 2014), and one by low inundation
throughout the fen (Nov 2012). Redox sensors in the rich
fen zone showed low redox potentials during measure-
ments with high water, and high values during low water
(see Appendix A in Mettrop et al. 2014).
Electrical conductivity depth profiles
The EC depth profiles are very suitable to track the flow of
water in and below the floating root mat (Van Wirdum
1991), and may help to determine the origin of the base-
rich water. EC depth profiles were measured with a metal
stick of 2 m with EC and temperature sensors in the top,
which was pushed through the peat for measurements at
different depths (Van Wirdum 1991). EC measurements
were automatically corrected for temperature, standard-
ized at 25 °C, and transformed to standard values in
lScm
1
. EC depth profiles were measured to 100 cm
depth, which is in the zone of open water below the float-
ing root mat. Surface EC values could often not be
measured with the stick, and were measured with a field
EC meter.
The EC depth profiles were measured along transects in
the centre of the fen in Jun 1973 (Touber 1973) and in Jun
1990, Jul 2012, May 2013 and Oct 2014. EC depth profiles
were also measured in Nov 2012, but in only in the half of
the fen closest to the ditch; the plots in this case included
all 5 m 95 m grid cells as well as all wet hollows not in
the centre of the grid cells.
In 1973, unfortunately, only five EC depth profiles were
available, partly because parts of the floating fen were
inaccessible (Touber 1973; Bergmans 1975). In 1990 and
20122014, each transect consisted of 1628 measurement
points, divided over the entire length of the fen. For com-
parison, the fen was divided in ten zones of 20-m length,
and mean EC values for each zone were calculated.
In Jun 1973, the EC depth profiles started at 10-cm
depth, and in Jun 1990 at 20-cm depth. Also, in Jun 1990,
EC was measured every 20- rather than 10-cm intervals.
In 20122014, however, EC depth profiles were measured
from 0100-cm depth, at intervals of 10 cm. In addition to
the actual EC values, the data were used to calculate a
rough proxy for the relative contribution of ditch water.
Statistical analyses
For most statistical analyses, the fen was divided into four
zones of 50-m length, which more or less followed the
zonation patterns of the fen in 1988. Differences in the
number of grid cells containing particular bryophyte spe-
cies between 1988 and 2013 were tested with Pearson’s
chi-squared tests, with 1988 values as the expected fre-
quency (Mason et al. 1994). Differences were considered
significant with P-values below 0.05.
Since the original biomass data of 1984 could not be
retrieved, peak living above-ground phanerogam biomass
and foliar N:P ratios were assessed using only the mean
values and SD (Verhoeven et al. 1988). It was thus not
possible to test differences between measurement periods
directly with GLM. Instead, the changes over time were
tested with linear regression analysis, with year and mean
value per sampling period as input values.
Differences in surface EC values were tested with two-
factor GLM, with fen zone and measurement series (time)
as independent factors using SAS (Cody & Smith 1987).
Differences between individual mean values were post-hoc
tested with LSMeans tests. In zone 3, the zone at 100
150 m from the ditch, rich fen species still occurred in
1988, but became dominated by Sphagnum in 2013. In this
zone, surface EC values were generally lower than in other
zones, which masked potential differences between 1988
and 20122014 in the two-factor GLM. To further test such
Applied Vegetation Science
4Doi: 10.1111/avsc.12197 ©2015 The Authors. Applied Vegetation Science published by John Wiley & Sons Ltd
on behalf of InternationalAssociation for Vegetation Science.
Bryophyte recovery in floating fens over 25 yr A.M. Kooijman et al.
differences, a one-factor GLM was applied for this fen zone
separately, with time as independent factor.
Differences in EC depth profiles were tested for the three
periods with complete profiles and inundation in the rich
fen zone: Jul 2012, May 2013 and Oct 2014. Three-factor
GLM were used, with the 50-m fen zones, time and depth
as independent factors. Each factor turned out to be highly
significant, as well as some of their interactions. However,
general patterns with depth and fen zone were the same in
all periods, as shown by the insignificant interactions
between time 9depth and time 9zone. For a more gen-
eral analysis of EC differences with depth and between fen
zones, data from different periods were combined. Poten-
tial differences were tested with two-factor GLM, with fen
zone and depth as independent factors, and post-hoc
LSMeans tests. For the sake of clarity, this analysis was also
done for each fen zone separately.
In June 1973 and June 1990, EC depth profiles were
unfortunately incomplete, which made a direct compar-
ison with the values of 20122014 impossible. For a rough
estimate, five 20-m fen zones were selected for which data
were available for 1973, 1990, 2012, 2013 and 2014 at 0
20, 2040, 120140, 160180 and 180200 m from the
ditch. The data of 20122014 were combined to one mean
value per fen zone per depth, to give the present situation
equal weight to 1973 and 1990. We used the 20- and 40-
cm depth measurements, partly because EC values in 1990
were only measured every 20 cm, but also because
changes in water transport from below the root mat to the
fen surface could be better detected in the upper layers,
especially because inflow patterns below the floating root
mat seemed more or less the same. Differences in EC val-
ues were tested with three-factor GLM, with time, depth
and fen zone as independent factors.
Results
Vegetation changes between 1988 and 2013
In 1988, the moss layer of the Stobbenribben Fen consisted
of a mosaic of rich fen hollows interspersed with poor fen
hummocks (Fig. 2). The fen had a zonation pattern char-
acterized by dominant bryophyte vegetation near the ditch
including eutrophic species such as C. cuspidata,Brachythe-
cium rutabulum and Calliergon cordifolium (Table 1). By
2013, these eutrophic bryophytes had decreased, with
C. cuspidata dominant only in a small zone directly adjacent
to the ditch. B. rutabulum and C. cordifolium also decreased.
In 1988, a large part of the fen, up to 100-m distance
from the ditch, was dominated by the mesotrophic rich fen
species Scorpidium scorpioides. Other rich fen bryophytes
were also present, such as Campylium stellatum,Fissidens
adianthoides and Calliergon giganteum. In 2013, the rich fen
species more or less completely disappeared from the
central part of the fen. However, S. scorpioides increased
closer to the ditch, and partly replaced the eutrophic C. cus-
pidata. The rich fen species C. stellatum also disappeared
from the central fen, but increased near the ditch, albeit in
lower numbers.
In 1988, the central part of the fen, the area of 50
150 m from the ditch, was dominated by the intermediate
fen species Sphagnum subnitens, together with S. contortum.
By 2013, both of these species were replaced by the poor
fen species S. palustre, which by then dominated almost
70% of the area. Other poor-fen species also increased,
such as S. magellanicum,S. capillifolium and Polytrichum
commune.
Decrease in biomass production and P availability over
the past 25 yr
The decrease in eutrophic bryophytes after 1988 was
accompanied by a decrease in above-ground vascular plant
biomass production (Table 2). In 1984, peak standing crop
amounted to more than 1000 gm
2
in the rich fen zone
dominated by S. scorpioides and C. cuspidata. In 1990, values
in this area had decreased to ca. 500 gm
2
, and further
decreased to ca. 250 gm
2
in the last few years. Value of
foliar N:P ratios increased. In 1984, foliar N:P ratios were
about 16, but gradually increased over time to above 22.
Electrical conductivity values at the fen surface
In July 2012 (high-water period), water levels in the
national park ranged around the maximum for several
weeks, due to a prolonged wet period, and the rich fen
zone was completely inundated, with water levels of 3
12 cm above the surface. At the time of these measure-
ments, an open connection existed between the surface
water of the ditch and the fen, over a length of ca. 10 m. In
Nov 2012 (low-water period), water levels had gradually
dropped after Sept to the minimum. Water levels in the
ditch and fen were also low and the surface water in the
ditch and fen was not connected. In May 2013 (high-water
period), measurements were conducted 2 wk after the first
rise to maximum water levels since Sept 2012, which
lasted for about 1 wk. Water levels in ditch and fen were
still relatively high, and the open connection between
ditch and fen was ca. 0.5-m wide. In Oct 2014 (high-water
period), measurements were conducted 10 d after the first
rise to maximum water levels after a dry period of 2 mo.
During the measurements, the rich fen zone was still par-
tially inundated and anoxic, but the open connection
between ditch water and fen surface was not more than a
few cm. Mean EC of the ditch was 517 lScm
1
in Jul
2012, 353 lScm
1
in Nov 2012, 627 lScm
1
in May
2014 and 572 lScm
1
in Oct 2014.
5
Applied Vegetation Science
Doi: 10.1111/avsc.12197©2015 The Authors. Applied Vegetation Science published by John Wiley & Sons Ltd
on behalf of International Association for Vegetation Science.
A.M. Kooijman et al. Bryophyte recovery in floating fensover 25 yr
In general, EC values at the fen surface decreased from
the ditch to the more isolated end of the fen (Fig. 3,
Table 3). High EC values above 400 lScm
1
were mostly
present near the ditch in zone 1, where rich fen vegetation
prevailed. However, temporal and spatial variation was
rather large. In Nov 1988 and Jul 2012, EC values above
Calliergonella cuspidata 1988
5322 233222232222112223234444334455
3 222111 11 122111 2111112222344455
3 231 1 1 111111 1 122233334555
3 22431 11 11 111121222333354555
32233321211 12 1 31111122323334445
Calliergonella cuspidata 2013
51111 1 1 1 12122344455
31112222 111254
21221 153
21 1 21 252
3 1112121 112 1 115
Scorpidium scorpioides 1988
1224453444445444544321
2221222223242234445445555255441
23212221 111234432442354554541
224333321 112122344322454345322
3433212112121 1 1 43322225544311
Scorpidium scorpioides 2013
12 122555555555554453
11 2454545555555452
12 3555555552
1121 3545555552
255422221 122111245555555
Sphagnum subnitens 1988
2132455333334344 123222 2231 11
122333332344424443242 2211 232 11
2 1 22222344555434545544541321211
13333343354555555554455532432 121
2 332223224455555455445545552113
Sphagnum subnitens 2013
11 1 111 11 1212 12 21 1 3 11
2 121 11 2 3112 1 2221
1 1223122
1 1 12 1 1 121123322 22
1 11221 2 12111122312 1
Sphagnum palustre 1988
244444432144222 1132 1 1 31311
34544433533322112245211 11321
234432424435534222352
234433353313432 122221 1 12
132143345355432221132 11 1 1
Sphagnum palustre 2013
34444555454555555555455 2214233
444445435455555555555555533132 334321
55544554555555555555555555555414
3554455555555555555555555555552321 2
223445555555555555555555554554221
Z4 Z3 Z2 Z1
Fig. 2. Comparison of selected bryophyte species within the Stobbenribben Fen in 1988 and 2013 in 200 5 m 95 m grid cells. The ditch, which supplies
base-rich water to the grid cells, is represented toward the right of the figure. Z1 =zone 1, 050 m from the ditch at the right of the figure; Z2 =zone 2,
50100 m from the ditch; Z3 =zone 3, 100150 m from the ditch and Z4 =zone 4, 150200 m from the ditch. 1 =rare (light grey); 2 =frequent (light
grey); 3 =common (grey); 4 =co-dominant (dark grey) and 5 =dominant (dark grey).
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Bryophyte recovery in floating fens over 25 yr A.M. Kooijman et al.
400 lScm
1
were relatively common in zone 1, but in
Nov 2012, when water levels had been low for several
months, lower values prevailed. In contrast, in May 2013
and Oct 2014, when the rich fen zone became inundated
after a prolonged dry period, high EC values also occurred
in zone 2. In May 2013, 82% of the grid cells with S. scorpi-
oides had EC values above 400 lScm
1
.
While temporal variation was rather large, there were
no indications that the distribution of base-rich water near
the ditch drastically changed between 1988 and 2012
2014. Near the ditch, the 1988 values actually fell within
the range of values for 20122014, although we had only
one set of measurements in 1988 and do not know
whether EC values were high or low for that period. Also,
in both periods, high EC values were only found near the
ditch. However, in the central part of the fen, base status
of the fen surface water probably fell. In 1988, many sur-
face EC values ranged between 100300 lScm
1
,and
values below 100 lScm
1
were measured in only 9% of
the grid cells. These relatively high values point to at least
some contact with base-rich water. In 20122014, how-
ever, EC values below 100 lScm
1
were very common.
Also, in S. palustre vegetation, EC could often not be mea-
sured, due to lack of surface water. In the overall statistical
analysis, differences in zone 3 between 1988 and 2012
2013 were not significant, due to much higher EC values
in zone 1. However, when zone 3 was analysed sepa-
rately, 1988 showed significantly higher values than all
other years. These results suggest that contact of the peat
surface with base-rich water is no longer common, and
has actually diminished compared to the situation in
1988.
Table 1. Presence (in percentage) of characteristic bryophyte species in the Stobbenribben in 1988 and 2013, in total or in particular fen zones of 50-m
length, starting from the ditch at the NE side of the fen. Z1 =zone 1, 050 m from the ditch; Z2 =zone 2, 50100 m from the ditch; Z3 =zone 3, 100
150 m from the ditch and Z4 =zone 4, 150200 m from the ditch.
Bryophyte Species 1988 2013
Total Z1 Z2 Z3 Z4 Total Z1 Z2 Z3 Z4
Eutrophic Rich Fen Species
Calliergonella cuspidata 78 25 21 15 12 32* 18* 5* 1* 10
Sphagnum squarrosum 68 11 21 24 12 1* 0* 1* 0* 0*
Brachythecium rutabulum 21 11 1 1 8 4* 4* 0 0 0*
Calliergoncordifolium 12 21281* 1 0 0*0*
Rhytidiadelphus squarrosus 9 30063* 2 0 0 1*
Plagiomnium affine s.l. 8 4 1 0 4 6 2 0 0 1*
Drepanocladus aduncus 7 71001* 1*0 0 0
Mesotrophic Rich Fen Species
Sphagnum subnitens 76 16 23 25 14 41* 12 17 1* 11
Campylium stellatum 72 16 24 21 11 46* 21 15* 0* 10
Scorpidium scorpioides 71 17 24 21 9 44* 22 16* 0* 7
Sphagnum contortum 64 7 21 22 15 23* 3* 6 2 12
Bryum pseudotriquetrum 50 14 14 15 8 42 24* 9* 0* 10
Fissidens adianthoides 39 18 16 4 3 14* 11* 3* 0* 1
Calliergongiganteum 23 10 3 7 4 15* 8 3 0* 4
Poor Fen Species
Polytrichum commune 63 5 12 23 24 72 5 18* 25 25
Sphagnum palustre 62 7 7 24 25 83* 12 22* 25 25
Sphagnum fallax 58 7 4 24 43 69* 10 21* 22 16*
Aulacomnium palustre 40 4 3 18 15 22* 4 0* 5* 13
Sphagnum papillosum 17 0 0 6 11 19 0 0 5 14
Sphagnum capillifolium 5 0 0 2 4 20* 1 5* 12* 3
Sphagnum magellanicum 1000111*00210*
*Significant increase or decrease in number of grid cells between 1988 and 2013in total or in a particular fen zone (chi-square tests; P<0.05).
Table 2. Peak above-ground living vascular plant biomass and foliar N:P
ratios in July in Stobbenribben in the rich fen zone with S. scorpioides,
close to the ditch. Values are mean and SD in parentheses. The decrease
in phanerogam biomass and increase in N:P ratio with time was significant
for both factors (R
2
=0.79 and 0.90, respectively).
Year Vascular Plant Biomass (gm
2
) Foliar N:P Ratio (gg
1
)
1984 1123 (241) 16.0 (1.8)
1990 512 (73) 19.1 (3.1)
2005 212 (136) 22.4 (2.2)
2010 187 (110)
2011 229 (96) 23.7 (1.5)
2012 287 (74) 22.1 (1.1)
7
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A.M. Kooijman et al. Bryophyte recovery in floating fensover 25 yr
Electrical conductivity depth profiles
In 1973 and 1990, the EC depth profiles did not include
the depths 60120 cm (Fig. 4). Also, it is not clear whether
the values were relatively low or high during these time
periods. Nevertheless, they can be used to trace inflow pat-
terns of base-rich water from the ditch. The basic inflow
patterns below the floating fen have probably not changed
Table 3. Mean pH and EC values (lScm
1
) and SD at the fen surface in different measurement periods and different fen zones, starting from the ditch at
the NE side. Zone 14 are each progressively 50 m more distant from the ditch, with zone 1 050 m from the ditch. Different letters indicate significant dif-
ferences between fen zones and/or times (P<0.05).
Zone 1: 050 m from Ditch Zone 2: 50100 m from Ditch Zone 3: 100150 m from Ditch Zone 4: 150200 m from Ditch
pH
Nov 1988 6.2 (0.3)
c
6.1 (0.4)
c
5.0 (1.0)
b
4.7 (0.7)
a
EC
Nov 1988 342 (109)
c
177 (100)
ab
140 (50)
a
171 (41)
a
July 2012 396 (85)
c
184 (122)
ab
43 (-)
a
123 (48)
a
Nov 2012 264 (100)
b
95 (44)
a
-118(37)
a
May 2013 555 (59)
d
369 (224)
c
71 (33)
a
263 (176)
b
Oct 2014 530 (66)
d
226 (224)
ab
107 (19)
a
166 (75)
a
Z4 Z3 Z2 Z1
November 1988
220 200 200 240 175 192 242 215 267 154 122 178 280 260 271 254 386 414 203 165 435 312 224 235 412 482 432 227 297 335 304 nd
255 140 160 175 160 145 128 226 165 149 329 155 145 131 164 118 134 131 148 126 137 116 171 158 197 100 162 113 163 132 141 102 170 130 228 345 422 425 415 nd
140 210 160 130 120 194 162 138 181 123 164 117 123 128 159 122 74 185 121 154 89 108 121 104 126 117 165 182 111 503 123 199 151 422 324 410 411 432 451 nd
120 230 210 155 135 183 125 155 130 146 171 170 92 98 150 84 82 147 123 86 102 98 82 126 155 123 200 175 101 367 413 367 386 427 390 418 416 364 396 nd
290 205 225 210 160 150 171 98 136 168 107 129 116 102 93 148 107 87 98 73 73 64 87 119 179 151 108 140 111 227 268 424 450 431 423 389 421 431 nd nd
July 2012
114 73 65 63 51 43 41 48 228 272 309 282 306 295 303 302 297 337 359 356 374 387 395 429 392 390
78 301 302 265 360 326 335 432 381 390 781 477 378 416 397 392 392 426
66 91 73 125 435 441 522 447 437 440 442 456 419 416
95 50 66 69 71 61 152 350 216 350 520 437 380 452 417 411 397
188 182 175 163 171 161 157 154 116 83 61 61 88 78 60 204 297 275 227 258 348 306 353 384 430 nd
November 2012
120 90 52 76 119 119 135 92 134 232 170 270 293 304 238 278 389 299 362 320 346
54 68 79 119 138 140 189 217 160 227 182 256 278 43 54 61 373 371
52 71 65 85 51 102 61 69 127 260 189 279 458 233 153 314 285 337 95
92 71 82 52 83 57 112 64 63 92 274 109 256 475 270 332 297 291 454 166
94 186 124 60 57 50 50 107 81 86 68 77 92 141 284 290 170 292 221 324 288 117 345
May 2013
385 370 342 258 204 110 64 90 92 73 62 60 67 119 525 534 523 561 518 470 578 605 445 694 603 564 480 620 572 514 563 504 550 524
270 201 213 74 107 46 65 228 90 74 55 48 51 41 333 383 355 627 512 738 689 698 644 595 544 643 525 439 578 531 521 576 606 608
250 49 66 74 131 36 63 129 74 72 52 83 100 57 85 55 172 102 65 73 228 354 303 88 690 544 664 661 517 567 447 535 533 605 627
341 556 545 57 58 92 76 45 53 43 43 60 67 51 57 69 70 70 80 87 101 113 104 333 325 209 693 650 654 544 483 586 504 522 532 561 511
467 510 504 531 533 494 282 281 169 109 33 64 63 91 49 63 48 137 45 52 47 116 123 276 399 288 412 663 336 532 699 488 444 608 499 576 513 535 542 555
October 2014
321 304 290 272 215 187 122 100 192 152 88 107 132 102 134 92 102 101 90 134 216 285 305 388 378 450 474 487 493 535 558 540 540 574 566 569 585 594 580 490
345 138 194 198 111 105 120 103 106 109 143 115 105 99 105 107 118 153 135 99 300 200 440 221 419 528 514 477 530 514 451 570 555 574 602 586
298 99 100 99 93 120 87 110 63 91 96 92 108 115 155 102 110 108 82 102 106 81 115 239 120 124 329 488 508 511 537 567 563 561 565 605 430
188 114 135 92 112 86 104 103 115 121 84 163 129 104 93 129 81 96 113 108 96 244 109 150 166 140 200 285 408 468 527 510 540 551 588 563 575 555
208 280 261 162 154 151 121 123 121 141 81 88 126 110 91 109 99 81 108 105 116 109 109 147 148 185 168 167 191 336 269 321 469 475 525 525 554 595 605 562
Fig. 3. EC values (lScm
1
)atthefensurfaceinthe2005 m 95 m grid cells in the Stobbenribben Fen in Nov 1988, Jul 2012, Nov 2012 and May 2013.
Z1 =zone 1, 050 m from the ditch; Z2 =zone 2, 50100 m from the ditch; Z3 =zone 3, 100150 m from the ditch and Z4 =zone 4, 150200 m from
the ditch. If no values are given, EC could not be measured due to lack of surface water.Grid cells are classified as very low (white; EC <100 lScm
1
), low
(light grey; 100300 lScm
1
), intermediate (grey; 300400 lScm
1
)andhigh(darkgrey;>400 lScm
1
). July 2012 was a period with high rainfall and
high water table, Nov 2012 a period with low rainfall and low water table, and in May 2013 water table had increased after heavy rain to maximum levels
for the first time since autumn 2012. EC values in the ditch were 517 lScm
1
for July 2012, 353 lScm
1
for Nov 2012, 627 lScm
1
for May 2013, and
572 lScm
1
for Oct 2014.
Applied Vegetation Science
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on behalf of InternationalAssociation for Vegetation Science.
Bryophyte recovery in floating fens over 25 yr A.M. Kooijman et al.
since 1991 (Van Wirdum 1991). Inflow below the root mat
mayseemhigherin1973thanin20122014, but that may
be due to relatively high EC values in the ditch. In terms of
ditch water contribution, values at 100-cm depth were ca.
5156% in the zone furthest from the ditch in Jun 1973
and 4552% in Oct 2014.
180–200 160–180 140–160 120–140 100–120 80–100 60–80 40–60 20–40 0–20 m
June 1973
0 ndndndndndndndndndnd
10 168 210 234 576 480
20 152 159 288 459 636
30 243 189 459 597 606
40 312 264 405 513 588
50 261 339 324 675 678
60 384 351 498 696 675
70 399 407 543 663 582
80 416 417 501 603 597
90 432 456 492 513 606
100 408 450 543 465 537
June 1990
0 ndndndndndndndndndnd
20 161 101 146 142 82 228 219 223 468 371
40 161 132 171 165 122 246 251 291 473 406
60 219 263 254 258 203 333 395 437 467 462
80 223 292 284 351 288 371 374 435 447 459
100 228 309 315 358 374 374 346 418 454 420
July 2012
0 66 66 208 374 426
10 32 50 47 66 57 48 66 213 393 444
20 82 54 67 97 58 48 97 225 339 366
30 58 70 77 116 59 53 116 214 359 346
40 62 92 87 131 69 52 131 232 376 404
50 55 169 108 212 79 70 212 232 400 396
60 118 194 134 250 139 101 250 294 418 438
70 127 233 183 252 191 171 252 289 395 473
80 155 244 187 367 281 266 367 376 442 491
90 166 289 258 452 325 398 452 393 507 517
100 189 377 321 448 320 436 448 432 501 488
May 2013
0 94497780548580573 530 529
10 73 40 77 65 50 45 65 477 325 298
20 88 42 87 77 55 36 77 439 337 274
30 53 47 116 125 54 34 125 384 337 341
40 57 48 130 154 101 53 154 340 295 364
50 79 94 131 237 139 110 237 294 299 326
60 108 103 146 233 245 136 233 326 322 353
70 129 130 202 294 283 216 294 358 327 359
80 138 146 185 265 260 258 265 366 321 407
90 167 198 227 305 242 274 305 339 362 445
100 132 205 237 305 246 251 305 351 350 421
October 2014
0 98 115 105 92 109 105 368 511 553
10 95 69 74 82 64 64 82 307 358 350
20 77 57 74 66 49 48 66 302 339 341
30 76 57 103 78 74 57 78 303 337 390
40 76 66 151 101 85 75 101 353 340 357
50 123 117 184 168 180 102 168 406 376 395
60 149 197 217 326 336 138 326 377 351 405
70 165 283 292 382 356 269 382 428 417 427
80 227 337 314 439 407 384 439 438 447 469
90 223 328 327 489 388 433 489 449 416 464
100 257 300 331 468 395 415 468 463 455 448
Fig. 4. EC values (lScm
1
) at the surface and at different depths (cm) in the floating root mat, in different parts of a transect through the centre of the
Stobbenribben Fen. Distances are given in meters from the ditch, which is positioned to the right of the plots in the figure. Grid cells are classified as very
low (white; EC <100 lScm
1
), low (light grey; 100300 lScm
1
), intermediate (grey; 300400 lScm
1
) and high (dark grey; >400 lScm
1
). In June
1973, EC depth profiles were only measured in five parts of thefen, partly because the central part was inaccessible, and not at the surface. In July 1990, EC
values were only measured at every 20-cm depth and not at the surface. In July 2012, May 2014 and Oct 2014, the rich fen zone was inundated. (Mean) EC
values in the ditch were 800 lScm
1
for 1973, 516 lScm
1
for 1990, 517 lScm
1
for 2012, 627 lScm
1
for 2013, and 572 lScm
1
for 2014.
9
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on behalf of International Association for Vegetation Science.
A.M. Kooijman et al. Bryophyte recovery in floating fensover 25 yr
In the upper layers of the floating root mat, the water
was probably more base-rich in 1973 than in 20122014
(Fig. 5). At 2040-cm depth, EC values were significantly
higher in zones closer rather than farther from the ditch,
but also significantly higher in the overall fen in 1973 and
1990 than in 20122014. Differences were also significant
when expressed as percentage ditch water. In 20122014,
EC values at 2040-cm depth were always lower than in
1973 and 1990.
The EC values were examined to determine the source
of the water at the fen surface. In zone 1, closest to the
ditch, EC values were significantly higher at the fen surface
than at 10-, 20- or 30-cm depth during the three flooded
surveys (Jul 2012, May 2013 and Oct 2014) during inun-
dation of the rich fen zone (Table 4). At the surface, the
average contribution of ditch water amounted to 83%, but
this sharply decreased to 6360% at 1030-cm depth.
Below the floating root mat, around 90100-cm depth,
values increased again to 77% ditch water due to open
contact with the ditch. In both May 2013 and Oct 2014,
however, EC values at the fen surface were even higher
than below the floating root mat.
Discussion
Water quality improvement and long-term conservation
of protected area vegetation
In protected wetland areas, water quality improvement is
a key aspect of maintenance and restoration of aquatic and
semi-terrestrial ecosystems (Naiman et al. 1999; Nienhuis
& Gulati 2002; Lamers et al. 2015). Ecosystems such as the
Everglades in the USA and the Rhine River in NW Europe
have been severely polluted from urban and agricultural
sources, so that attention must be paid to water quality
improvement as part of the restoration process (Rudnick
et al. 1999; Nienhuis et al. 2002). In many countries,
legislation such as the Clean Water Act in the USA and
the Water Framework Directive in the EU has been
m from ditch
180–200 160–180 120–140 20–40 0–20
Depth
June 1973 20 cm 152 159 288 459 636
40 cm 312 264 405 513 588
June 1990 20 cm 161 101 142 468 371
40 cm 161 132 165 473 406
2012–2014 20 cm 82 51 54 338 327
40 cm 65 69 85 337 375
Fig. 5. Comparison of EC values at 20- and 40-cm depth in five different 20-m fen zones in 1973, 1990 and average in 20122014. Distances are given in
meters from the ditch at the right in the figure. Grid cells are classified as very low (white; EC <100 lScm
1
), low (light grey; 100300 lScm
1
),
intermediate (grey; 300400 lScm
1
) and high (dark grey; >400 lScm
1
). Differences were not significant between depths, but highly significant
(P<0.0001) between fen zones and years. EC values in the ditch were 800 lScm
1
for 1973, 516 lScm
1
for 1990 and average 572 lScm
1
for 2012
2014.
Table 4. EC values, given as percentage ditch water, and SD at different depths in different fen zones, starting fromthe ditch at the NE side of the fen. Mea-
surements of July 2012, May 2013 and Oct 2014, when the rich fen zone was inundated, were combined. Different letters indicate significant differences
within a particular fen zone between particular depths (i.e. within a column; P<0.05).
Zone 1: 050 m from Ditch Zone 2: 50100 m from Ditch Zone 3: 100150 m from Ditch Zone 4: 150200 m from Ditch
n23 14 13 13
EC 0 cm 83 (12)
c
22 (17)
ab
16 (4)
ab
15 (5)
ab
EC 10 cm 63 (13)
a
16 (12)
a
10 (2)
a
11 (4)
a
EC 20 cm 60 (10)
a
16 (12)
a
9(2)
a
13 (3)
a
EC 30 cm 60 (10)
a
21 (13)
ab
10 (4)
a
13 (5)
ab
EC 40 cm 62 (12)
a
27 (17)
b
12 (4)
ab
16 (9)
ab
EC 50 cm 65 (14)
a
36 (15)
b
20 (9)
b
21 (10)
b
EC 60 cm 67 (14)
a
48 (16)
c
31 (16)
c
28 (10)
bc
EC 70 cm 69 (14)
ab
56 (15)
cd
42 (14)
d
36 (15)
c
EC 80 cm 75 (15)
b
64 (15)
cd
53 (15)
e
41 (15)
cd
EC 90 cm 77 (16)
b
72 (16)
d
61 (15)
ef
44 (14)
d
EC 100 cm 77 (14)
bc
72 (15)
d
63 (16)
f
48 (19)
d
Applied Vegetation Science
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on behalf of InternationalAssociation for Vegetation Science.
Bryophyte recovery in floating fens over 25 yr A.M. Kooijman et al.
implemented recently (Naiman et al. 1999; European
Union 2000). In many areas, vegetative recovery is still lag-
ging, but some ecosystems have shown signs of renewed
vitality after reduction of water pollution (Makarewics &
Bertram 1991; Nienhuis et al. 2002). In small lakes,
improvement of water quality may lead to restoration of
functional attributes such as healthy macrophyte vegeta-
tion, including re-establishment of Chara species (Bootsma
et al. 1999). In our rich fen study, a vegetation shift over
25 yr towards the original vegetation type indicates that
some functional attributes can also be regained by reduc-
ing water pollution. In particular, low availability of P is a
desirable state for rich fens (Wassen et al. 2005). The
decrease in plant productivity and increase in foliar N:P
ratios of vascular species to values above 22 indeed shows
that P has become a limiting factor over time in our study
fen (Koerselman & Meuleman 1996; G
usewell 2004). The
idea that Stobbenribben Fen is currently P-limited is fur-
ther supported by the results of fertilization experiments in
the fen complex, which show that vascular plant biomass
increases with application of P, but not with N (Cusell
et al. 2014a).
Long-term hydrological, water quality and vegetation
changes with peat mat development
Despite the improvement in surface water quality in the
national park and rich fen area, a portion of the rich fen
turned into Sphagnum-dominated peatland. Rich fen vege-
tation is generally replaced by Sphagnum spp. when the
peat mass is exposed to less base-rich water (Clapham
1940; Clymo 1963; Soudzilovskaia et al. 2010), although
this process could be altered by high atmospheric deposi-
tion of acidic precipitation (Berendse et al. 2001; Limpens
et al. 2003; Kooijman 2012). Over time, peat layers grow
thicker, and the surface becomes more isolated, blocking
access of base-rich water from below the mat. A palaeoeco-
logical reconstruction of the succession in zone 2 of our
study fen suggests that the peat layer has become 35-cm
thicker in ca. 50 yr (A.H. Fabers, B. van Geel and A.M.
Kooijman, unpubl. data). Such a layer may effectively
reduce the flow of base-rich water from below the floating
root mat to the fen surface, as suggested from the decrease
in EC values in the upper part of the fen over the past dec-
ades. Weak spots in the root mat could still provide access
to base-rich water, but a detailed survey of EC depth pro-
files in all hollows in Nov 2012 suggests that the mat no
longer allows base-rich water to rise to the surface.
Despite on-going succession, rich fen bryophytes are
locally expanding in the Stobbenribben. In the SE fen of
the Stobbenribben complex, rich fen bryophytes even
increased from ca. 60% to 90% (1973 vs 2012: Van Wir-
dum 1991 and this study, respectively), while Sphagnum
communities decreased from ca. 40% to less than 10%
(1973 vs 2012: Van Wirdum 1991 and this study, respec-
tively). Currently, the SE fen is largely occupied by dark
brown Scorpidium vegetation (Fig. 1). While it is clear that
rich fen vegetation persists in regularly inundated areas, a
debate has started as to whether this situation is due to the
general raising of the water table inside the fen, which has
open connections with the ditch below the floating root
mat, or superficial flooding with ditch water. Although
occasional flooding of the Stobbenribben has been
reported (Bergmans 1975; Van Wirdum 1991; Kooijman
1993), this flooding was expected to play a minor role in
floating fens, which move up and down with the water
table. In the past, the fen surface was probably primarily
fed by base-rich water from below the floating root mat
(Van Wirdum 1991). At present, however, this contact has
probably become more restricted. Instead, superficial
flooding may play a more important role. This idea is sup-
ported by EC values, which were higher at the fen surface
than inside the floating root mat after flooding. In May
2013, EC values at the fen surface were even higher than
below the floating root mat, which suggests that inflow of
base-rich water from the ditch to the area below the root
mat only began recently, so that high EC values did not
extend further than 20 m from the ditch. At the fen sur-
face, however, high EC values were found up to 60 m
from the ditch, which supports the idea that the origin of
the water is the ditch. Open connections with the adjacent
ditch were indeed observed when the rich fen zone was
clearly inundated. Due to downward water movement
from the fen to the low-lying adjacent agricultural polders,
water tables inside the fens are generally lower than in the
ditch (Van Wirdum 1991), which at least allows inflow of
water from the ditch into the fen. Other aspects of water
dynamics in the system are still uncertain, for instance,
how much of the flood water comes from the ditch, the
relationship of EC values to reduction processes (Cusell
et al. 2013b), and the route of base-rich water over the
surface of the mat during flooding. Nevertheless, it is likely
that the current source of the water in the fen is the ditch,
which has recently improved in water quality.
Concluding remarks
This study shows that floating rich fens can be restored,
even in industrialized countries with a high amount of
human pressure, such as the Netherlands. One of the key
factors is the gradual improvement of water quality over
the past 25 yr, which resulted in a four-fold decrease in
above-ground biomass production, a clear increase in P
limitation, and replacement of eutrophic bryophytes such
as C. cuspidata by the mesotrophic species S. scorpioides.The
other key factors in the re-emergence of rich fen species
11
Applied Vegetation Science
Doi: 10.1111/avsc.12197©2015 The Authors. Applied Vegetation Science published by John Wiley & Sons Ltd
on behalf of International Association for Vegetation Science.
A.M. Kooijman et al. Bryophyte recovery in floating fensover 25 yr
may be high water levels and temporary inundation of the
fens with base-rich surface water from the ditch, especially
after improvement in water quality. Our results clearly
indicate that rich fen vegetation can persist, despite on-
going succession, when the fen surface is occasionally
inundated with mineral-rich but nutrient-poor water.
Acknowledgements
We thank Geert van Wirdum and his students Wim Berg-
mans and Luc Touber for their pioneering work in De
Stobbenribben. Bas van Dalen, Geert Kooijman and Nicko
Straathof helped with field equipment and interpretation
of the data, and Kees van Vliet was an important modera-
tor during discussions. Some of the measurements were
conducted by Maarten Bresjer and Henk Pieter Sterk. This
study was financially supported by the Dutch organization
of Scientific Research (NWO), the Dutch Ministry of Econ-
omy (OBN), the Province of Overijssel and the Waterboard
Reest en Wieden.
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Applied Vegetation Science
Doi: 10.1111/avsc.12197©2015 The Authors. Applied Vegetation Science published by John Wiley & Sons Ltd
on behalf of International Association for Vegetation Science.
A.M. Kooijman et al. Bryophyte recovery in floating fensover 25 yr
... Unfortunately, machinery mowing or mulching is frequently used instead of traditional hand mowing. Currently, many revitalization programs have sought to reverse undesired rich fen succession through restoration measures such as hydrological interventions including artificial flooding or pond excavation (Kooijman et al. 2016;Verhoeven and Bobbink 2001;Verhoeven et al. 2017), rebound mowing and grazing or other disturbances , or even by removing moss, sod, shrub or topsoil (Beltman, Van den Broek, and Bloemen 1995;Sundberg 2012;Emsens et al. 2015;Veeken and Wassen 2020;Singh et al. 2021). ...
... Beltman et al. (1995Beltman et al. ( , 1996 found that removing living Sphagnum plants is a successful restoration measure only if the initial pH is high and calcium levels are restored. Paulissen et al. (2004), Kooijman & Paulissen (2006), Vicherová et al. (2015), and Hájek et al. (2015) reported that the enhanced availability of phosphorus, ammonium, or potassium supports succession from brown moss rich fens to Sphagnum-dominated depauperated fens, and even prevent the successful restoration of rich fen stages (Kooijman et al. 2016;Kreyling et al. 2021). ...
... Even if patches suitable for brown mosses were created, acidicole species such as Aulacomnium palustre, Warnstorfia fluitans, and Apopellia epiphylla may colonize them instead of their rich fen counterparts if the alkalinity is low (Bootsma et al. 2002). However, in some restoration projects on Western European rich fens, alkalinity has been increased by inundation with mineral-rich but nutrient-poor water (Kooijman et al. 2016) or temporarily by liming . ...
Article
An undesired succession of rich fens leads to the formation of dense Sphagnum carpets that outcompete brown mosses and some vascular plants, resulting in biodiversity loss in fen habitats of high conservation importance. Small‐scale Sphagnum removal is a rarely implemented conservational measure, whose success may depend on soil alkalinity and fertility (i.e., nutrient availability). Therefore, characterizing the effects of pH and fertility levels would potentially allow for the development of better Sphagnum removal strategies. Two experiments were conducted across 24 rich fens of different alkalinity and fertility located in an area of approximately 32,000 km2 spanning from the Bohemian Massif to the Western Carpathians (Europe). We hypothesized that high alkalinity and low fertility support the restoration of rich fen vegetation after Sphagnum removal. Our study focused on four different Sphagnum groups. In Experiment 1, the treatment plots remained unfenced. In Experiment 2, the treatment plots were fenced off and target brown mosses were transplanted from the surroundings to overcome dispersal limitations. A repeated measures design was used, with vegetation composition recorded over a 5‐year period. High alkalinity rather than fertility facilitated species richness and the appearance of target brown mosses. High alkalinity generally hindered Sphagnum recovery, while high fertility supported the recurrence of S. teres and S. recurvum agg. Under high pH conditions, enhanced fertility further correlated with the spread of non‐sphagnaceous generalist bryophytes of low conservation value. Despite sustaining a significant overall reduction, all Sphagnum taxa began to recover throughout the experiment, albeit less obviously in fens with S. warnstorfii. Sphagnum removal may reverse biodiversity loss and allow for the restoration of brown mosses in rich fens where Sphagnum cover had increased due to slight eutrophication, acidification, or a decrease in the water table. In alkaline and nutrient‐poor conditions (e.g., S. warnstorfii fens), the effect is evident and long‐lasting and the intervention may not be extensive. In fens dominated by S. teres or S. recurvum agg., repeated or large‐scale removal may be needed if high nutrient availability (potassium, phosphorus) or low alkalinity supports Sphagnum recolonization. Treatment plots with S. subgenus Sphagnum exhibited the least promising brown‐moss restoration prospects.
... This water has high base richness and very low phosphate and sulfate concentrations. It has been possible to determine the quantity of supply water needed to ensure a high base richness of the fen areas while still adding only a minimal amount of phosphate and sulfate (Kooijman et al. 2016). In addition, experimental research of the functional traits of plants establishing floating mats in fen ponds has facilitated the choice of target species (van Zuidam et al. 2019). ...
... These shifts occurred too early in the succession of the fen vegetation and further threatened the persistence of the speciesrich mid-succession communities. Attempts to mitigate the acidifying effects on the nitrogen deposition have included short-term summer flooding of the fen system , removal of a thin layer of top soil (Lamers et al. 2002, Fig. 22) as well as long-term superficial flushing of the floating mat with base-rich and nutrient-poor water (Kooijman et al. 2016). These measures have resulted in favorable responses of the fen vegetation. ...
Chapter
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Wetlands are being degraded and destroyed at a faster rate than any other ecosystem on earth. Many key functions and values that wetlands provide have already been lost. Since the Ramsar Convention on Wetlands, the crucial benefits of wetland restoration and creation have been recognized by an increasing number of countries around the world. The goal of this chapter is to illuminate the ecological restoration and conservation strategies for marshes and peatlands using case studies. General principles and guidelines based on experience under different settings can offer a useful starting point for new restoration projects. We summarize eight key principles applied to different stages of a restoration project, from early planning to post-implementation monitoring that can be used widely. These principles focus on scientific and technical issues, but as in all environmental management activities, the importance of community perspectives and values should not be overlooked. We present an in-depth look at four different wetland restoration case studies. We acknowledge that every restoration project is unique and that there is no “cookbook” for restoring wetlands. Even so, these case studies provide a general outline regarding the historical causes of wetland degradation, the goal-setting required for successful restoration, and the details involved in significant wetland restoration efforts across different sites. In addition, the valuable lessons and challenges faced by the Chinese government in response to these case studies will be discussed.
... However, the MLTT is often unsuitable in areas where the remnant peat is non-existent (Daly et al., 2012;Price et al., 2010), contaminated and/or the degraded peatland is located in a basin where seasonal flooding is likely (Wilhelm et al., 2015). An alternative peatland restoration method, known as peat-block restoration technique, also referred to as an acrotelm transplant or wet harvesting, involves the transfer of extracted peat blocks (usually the upper few decimeters) from a donor peatland and directly placing them on the degraded peat surface (Cagampan and Waddington, 2008a), flooded peat surface (Tomassen et al., 2003;Kooijman et al., 2016) or on a constructed landscape (Daly et al., 2012). The thickness of the peat block reduces the likelihood of surface moss flooding (Wilhelm et al., 2015) and attenuates the upwelling of contaminants from underlying peat/sediment (Price et al., 2010), whilst allowing surface moss growth and CO 2 sequestration (Cagampan and Waddington, 2008b;Wilhelm et al., 2015). ...
Article
Northern peatlands are an important global climate regulator storing approximately one-third of the global carbon pool, however the degradation of these ecosystems from land-use change can switch peatlands to persistent and long-term sources of atmospheric carbon dioxide. Active restoration is often required to return degraded peatlands to a net carbon sink. The peat-block restoration technique, where intact peat blocks are extracted from a donor peatland and transferred to restore peatlands where the remnant peat is non-existent, contaminated, and/or undergoes seasonal flooding is increasingly being adopted as a peatland restoration technique given the carbon sequestration that can occur immediately post-restoration. However, donor peat blocks often need to be temporarily stockpiled during the restoration process due to logistical constraints. The dewatering of the peat blocks during this stockpiling period may alter hydrophysical peat properties that sustain critical peatland ecohydrological functionality and ultimately affect peatland restoration success. Yet, the hydrophysical evolution of stockpiled peat blocks remains unknown. Here, we examine how peat block stockpiling time (3, 7, 11, and 14 months and a reference site) impacts peat hydrophysical properties and sphagnum moss photosynthesis, both of which are critical for peatland restoration success. Stockpiling peat differentially impacted the hydrophysical properties between the shallower and deeper peats, where little to no impact from stockpiling was observed in the shallower peats, regardless of stockpiling time. Rather, as stockpiling time increased, there was a marked decrease in macroporosity (pores >75 μm) and mobile porosity (drainable porosity at approximately −100 hpa) at depths below 20 cm but the water conducting matrix porosity (defined as mobile porosity minus macroporosity) was not significantly different than the reference samples. However, stockpiling created inhospitable conditions for sphagnum mosses., as chlorophyll fluorescence ratio was below 0.3, indicating little to no photosynthesis of the stockpiled peat during summertime drought conditions. Taken together, we suggest limiting stockpiling time as much as possible would be advantageous for using the stockpiled peat blocks for the peat-block restoration technique or other restoration efforts, such as floating mat creation.
... For instance, the inflow of calcareous and Fe 2? -rich water into fens facilitates the precipitation of dissolved phosphorus rendering it less available for plants (Griffioen et al. 2013;van der Grift et al. 2016). Low availability of phosphorus seems to be particularly beneficial for rich fen species (Kooijman et al. 2016;Wassen et al. 2005). Inflow of acidic rainwater or accumulation of rainwater affects plant composition both directly (via H ? toxicity) and indirectly (by influencing the availability of nutrients) (Lamers et al. 2015). ...
Article
Full-text available
Restoration of rich fens is commonly attempted through local-scale measures, such as removal of sod or blockage of ditches. However, regional-scale restoration measures, that aim to re-establish the original hydrology in which rich fens developed, might have a more long-lasting effect. We investigated the effect of local- and regional-scale restoration measures on a vulnerable rich fen in the Naardermeer nature reserve in the Netherlands. We compared water quality and vegetation composition of the fen before and after the restoration measures, almost 30 years apart. Overall rich fen species increased and although this indicates the desired increased supply of fresh mineral-rich groundwater to the fen, continued succession towards poor fen vegetation has not been prevented in the entire fen. Despite sod layer removal, we observed an increase in a Polytrichum-dominated vegetation in patches that are primarily fed by rainwater. Our findings confirm results from a previous study which showed that brackish palaeo-groundwater is still contributing substantially to the water balance of the fen, especially in periods of precipitation deficit. We conclude that the local- and regional-scale restoration measures have been successful in increasing the abundance of rich fen species in parts of the fen. However, considering the pressures of climate change and high atmospheric N-deposition on the fen, it is uncertain whether rich fen species can be sustained in quite nutrient-poor conditions in the future. Therefore, there is a need for continued management that keeps the nutrient-poor and mineral-rich conditions of the fen intact.
... Nonetheless, relatively high and stable water levels are a general prerequisite, and prolonged deep desiccation may directly cause death or limited fen species performance (Manukjanova et al., 2014). Also, prolonged water table drawdown can indirectly limit survival of fen species: concomitant oxidation reactions lead to H + production, acidification and base cation leaching (Lamers et al., 1998;Van Haesebroeck et al., 1997), and this often induces a shift from rich fen species towards fen meadow species or Sphagnum dominance (Kooijman et al., 2016;Soudzilovskaia et al., 2010). However, since our study sites had been successfully rewetted in the past, groundwater levels were within the range for small sedge and brown moss communities (Goebel, 1996), and pore water pH (> 6), HCO 3 − (> 2 mmol L −1 ) and Ca (> 1 mmol L −1 ) concentrations were sufficiently high (Table 1). ...
Article
Many endangered plant species remain absent in rewetted, previously drained fens. We performed a 3-year introduction experiment with endangered fen species (9 Carex- and 6 bryophyte species) in 4 hydrologically restored fens to investigate which factors hamper establishment and survival. Carex species were introduced as adults and seedlings, mosses as gametophytes. Introductions were done on (initially) bare soil, which allowed us to exclude excessive competition for light during the first year. First year survival of the transplants was high in all fens (mean survival = 96%), indicating that there were no direct abiotic constraints on establishment. However, survival analysis revealed that a decrease in relative light intensity (RLI) at the soil surface during consecutive years (indicating an increase in biotic competition for light) drove high mortality rates in most species. As a result, overall final survival was lowest in the two most productive (low light) fens (mean survival = 38%), while most transplants persisted in the two less productive (high light) fens (mean survival = 79%). Taller and faster-growing Carex species were able to outgrow light limitation near the soil surface, and thus had a higher overall survivability than smaller and slower-growing species. Light limitation also drove the loss of 5 out of 6 bryophyte species. We conclude that both dispersal limitation and asymmetric competition for light may explain the lack and loss of small and endangered plant species in rewetted fens. A minimum empirical threshold of c. 30% relative light intensity near the soil surface is required for successful introduction.
... First, high and stable water levels are essential, and prolonged deep drainage may directly cause death or limited performance of vulnerable species (Manukjanova, Stechova & Kucera 2014). Also, prolonged drainage can indirectly limit survival of fen species: concomitant oxidation reactions lead to H + production, acidification and base cation leaching (Van Haesebroeck et al. 1997;Lamers, Van Roozendaal & Roelofs 1998), and this often induces a shift from rich fen species towards Sphagnum domination (Soudzilovskaia et al. 2010;Kooijman et al. 2016). However, since our study sites had been successfully rewetted in the past, groundwater levels were within the range for small sedge and brown moss communities (Goebel 1996), and pore water pH (> 6), HCO3 -(> 2 mmol L -1 ) and Ca (> 1 mmol L -1 ) concentrations were sufficiently high (Table S6.1 in Supporting information). ...
Article
Full-text available
Aim To further unravel P availability in mineral-rich fens, and test whether high Fe in the soil would lead to low P availability to the vegetation. Methods Mesotrophic fens were selected over gradients in Ca and Fe in central Sweden and the Netherlands, to study characteristics of vegetation, pore water and peat soil, including inorganic and organic forms of P, Fe and Al. Results Soil Fe was more important than region or soil Ca, and P availability to the vegetation increased from Fe-poor to Fe-rich fens. Contrary to expectations, precipitation of iron phosphates played a minor role in Fe-rich fens. Fe-rich fens were P-rich for three reasons: (1) high P sorption capacity, (2) relatively weak sorption to Fe-OM complexes and (3) high amounts of sorbed organic P, which probably consists of labile P. Also, nonmycorrhizal wetland plants probably especially take up weakly sorbed (organic) P. However, high P did not lead to high biomass or low plant diversity. Fe-rich fens were limited by other nutrients, and high P may help protect the vegetation against Fe-toxicity. Conclusions Fe-poor fens are P-poor, irrespective of Ca, and Fe-rich fens P-rich even under mesotrophic conditions. However, high P itself does not endanger Fe-rich fens.
Article
Terrestrialization stages of mire vegetation are important to Dutch nature conservancy because of high biodiversity, particularly of base-rich fens. In recent turbaries, terrestrialization has however not shown development of such a stage, while existing rich fens show accelerated development towards species-poor Sphagnum-dominated vegetation, due to acidification and lack of base-rich water input. We apply the analysis of microfossils and macroremains in two peat cores in order to get a better understanding of terrestrialization in the past, and thus provide information on actual vegetation successions, which is directly relevant to nature conservation.
Article
Full-text available
As sensitive indicators of environmental change, many bryophytes are particularly threatened by the degradation of habitats. A long term re-sampling study of bryophyte flora was conducted in springs in southeast Finland, in which the species occupancy and abundance, as well as the degree of human disturbance, of 60 springs were reinvestigated after a period of 50 years. A significant decrease was observed in the spring specialist species' occupancy and abundance, and bryophytes of spring-fed rich fens were found to have become regionally even rarer and locally less abundant than other spring specialists. The negative reaction of least concern (LC) species raises concern regarding the future of even common spring and rich fen bryophytes. The increase of human disturbance was found to poorly explain the observed negative changes and it was inferred that they are mainly caused by the almost total destruction of springs with rich fen characteristics. Thus, the protection of groundwater influenced rich fens independent of their degree of human disturbance is essential to the future of many specialized spring bryophytes.
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This work presents the state of the art of aquatic and semi-aquatic ecological restoration projects in The Netherlands. Starting from the conceptual basis of restoration ecology, the successes and failures of hundreds of restoration projects are described. Numerous successful projects are mentioned. In general ecological restoration endeavours greatly benefit from the progressive experience achieved in the course of the years. Failures mainly occur through insufficient application of physical, chemical or ecological principles. Spontaneous colonization by plants and animals, following habitat reconstruction, is preferred. However, sometimes the re-introduction of keystone species (e.g. eelgrass, salmon, beaver) is necessary in case the potential habitats are isolated or fragmented, or if a seed bank is lacking, thus not allowing viable populations to develop. Re-introducing traditional management techniques (e.g. mowing without fertilization, low intensity grazing) is important to rehabilitate the semi-natural and cultural landscapes that are so characteristic for The Netherlands.
Article
Introduction Peatlands are unbalanced ecosystems where plant production exceeds decomposition of organic material. As a result, considerable quantities of organic material, or peat, accumulate over long periods of time: millennia. This organic material is composed primarily of plant fragments remaining after partial decomposition of the plants that at one time lived on the surface of the peatland. Decomposition occurs through the action of micro-organisms that have the ability to utilize dead plant components as sources of carbon for respiration (Thormann & Bayley 1997) in both the upper, aerobic peat column (the acrotelm) and the lower, anaerobic peat (the catotelm) (Ingram 1978, Clymo 1984, Wieder et al. 1990, Kuhry & Vitt 1996). Labile cell contents, cellulose, and hemicellulose are more readily available sources of carbon than recalcitrant fractions that contain lignin-like compounds, with these latter compounds being concentrated in peat by decomposition (Williams et al. 1998, Turetsky et al. 2000). The vascular plant-dominated, tree, shrub, and herb layers produce less biomass (Campbell et al. 2000) and decompose more readily than the bryophyte-dominated ground layer (Moore 1989). Surfaces of northern peatlands are almost always completely covered by a continuous mat of moss (National Wetlands Working Group 1988, Vitt 1990), and the large amount of biomass contained in this layer is composed of cell wall material that decomposes slowly. This slow decomposition, coupled with water-saturated, anaerobic conditions in the peat, cool climate, and a cool moist growing season conducive to bryophyte growth, allows organic matter to accumulate over large areas.