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Functional trait composition of aquatic plants can serve to disentangle multiple interacting stressors in lowland streams

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Historically, close attention has been paid to negative impacts associated with nutrient loads to streams and rivers, but today hydromorphological alterations are considered increasingly implicated when lowland streams do not achieve good ecological status. Here, we explore if trait-abundance patterns of aquatic plants change along gradients in hydromorphological degradation and eutrophication in lowland stream sites located in Denmark. Specifically, we hypothesised that: i) changes in trait-abundance patterns occur along gradients in hydromorphological degradation and ii) trait-abundance patterns can serve to disentangle effects of eutrophication and hydromorphological degradation in lowland streams reflecting that the mechanisms behind changes differ. We used monitoring data from a total of 147 stream reaches with combined data on aquatic plant species abundance, catchment land use, hydromorphological alterations (i.e. planform, cross section, weed cutting) and water chemistry parameters. Traits related to life form, dispersal, reproduction and survival together with ecological preference values for nutrients and light (Ellenberg N and L) were allocated to 41 species representing 79% of the total species pool. We found clear evidence that habitat degradation (hydromorphological alterations and eutrophication) mediated selective changes in the trait-abundance patterns of the plant community. Specific traits could distinguish hydromorphological degradation (free-floating, surface; anchored floating leaves; anchored heterophylly) from eutrophication (free-floating, submerged; leaf area). We provide a conceptual framework for interpretation of how eutrophication and hydromorphological degradation interact and how this is reflected in trait-abundance patterns in aquatic plant communities in lowland streams. Our findings support the merit of trait-based approaches in biomonitoring as they shed light on mechanisms controlling structural changes under environmental stress. The ability to disentangle several stressors is particularly important in lowland stream environments where several stressors act in concert since the impact of the most important stressor can be targeted first, which is essential to improve the ecological status.
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Functional trait composition of aquatic plants can serve to disentangle
multiple interacting stressors in lowland streams
Annette Baattrup-Pedersen
a,
, Emma Göthe
a
,TennaRiis
b
, Matthew T. O'Hare
c
a
Department of Bioscience, Aarhus University, Vejlsøvej 25, P.O. Box 314, DK-8600 Silkeborg, Denmark
b
Department of Bioscience, Aarhus University, Ole Worms Allé 1, Building 1135, Room 217, DK-8000 Aarhus C, Denmark
c
Centre for Ecology and Hydrology, Bush Estate, Penicuik EH26 0QB, United Kingdom
HIGHLIGHTS
Functional trait composition of aquatic
plants can distinguish hydromorpholog-
ical degradation from eutrophication in
streams
A conceptual framework on how
eutrophication and hydromorphological
degradation interact on functional trait
composition
Weed cutting can set aside light as a
factor controlling trait-abundance pat-
tern in eutrophic lowland streams.
GRAPHICAL ABSTRACT
abstractarticle info
Article history:
Received 22 September 2015
Received in revised form 5 November 2015
Accepted 5 November 2015
Available online xxxx
Editor: D. Barcelo
Keywords:
Macrophyte
Weed cutting
Channelisation
Eutrophication
Habitat degradation
River
Historically, close attention has been paid to negative impacts associated with nutrient loads to streamsand riv-
ers, but today hydromorphological alterations are considered increasingly implicated when lowland streams do
not achieve good ecological status. Here, we explore if trait-abundance patterns of aquatic plants change along
gradients in hydromorphological degradation and eutrophication in lowland stream sites located in Denmark.
Specically, we hypothesised that: i) changes in trait-abundance patterns occur along gradients in
hydromorphologicaldegradation and ii) trait-abundancepatterns can serve to disentangle effects of eutrophica-
tion and hydromorphological degradation in lowland streams reecting that the mechanisms behind changes
differ. We used monitoring data from a total of 147 stream reaches with combined data on aquatic plant species
abundance, catchmentland use, hydromorphological alterations (i.e. planform, cross section, weed cutting) and
water chemistry parameters. Traitsrelated to life form, dispersal, reproduction and survival together with ecolog-
ical preference valuesfor nutrients and light (Ellenberg N and L) were allocated to41 species representing 79% of
the total species pool.We found clear evidence that habitat degradation (hydromorphologicalalterations and eu-
trophication) mediated selective changes in the trait-abundance patterns of the plant community. Specictraits
could distinguish hydromorphological degradation (free-oating, surface; anchored oating leaves; anchored
heterophylly) from eutrophication (free-oating, submerged; leaf area). We provide a conceptual framework
for interpretation of how eutrophication and hydromorphological degradation interact and how this is reected
Science of the Total Environment 543 (2016) 230238
Corresponding author.
E-mail address: abp@bios.au.dk (A. Baattrup-Pedersen).
http://dx.doi.org/10.1016/j.scitotenv.2015.11.027
0048-9697/© 2015 Elsevier B.V. All rights reserved.
Contents lists available at ScienceDirect
Science of the Total Environment
journal homepage: www.elsevier.com/locate/scitotenv
in trait-abundance patterns in aquatic plant communities in lowland streams. Our ndings support the merit of
trait-based approaches in biomonitoring as they shed light on mechanisms controlling structural changes under
environmental stress. The ability to disentangle several stressors is particularly important in lowland stream en-
vironments where several stressors act in concert sincethe impact of the most important stressor can betargeted
rst, which is essential to improve the ecological status.
© 2015 Elsevier B.V. All rights reserved.
1. Introduction
Today, anthropogenic pressures related to agriculture are one of the
main drivers of ecological deterioration of stream and river ecosystems,
primarily through emissions of nitrogen and phosphorous, increased
sediment load and hydromorphological alterations (Vörösmarty et al.,
2010). Historically, close attention has been paidto negative impacts as-
sociated with nutrient loads to streams and rivers, but today
hydromorphological alterations are considered increasingly implicated
when lowland streams do not achieve good ecological status (EEA,
2012). Even though the importance of hydromorphological degradation
is accepted as a major stressor, the ability to assess the level of
hydromorphological impact on the biological communities is limited
(e.g. Vaughan et al., 2009; Feld et al., 2014), and there is a clear need
for improving our conceptual understanding of the underlying response
mechanisms. One reason for the current limited knowledge could be
that the high level of spatial and temporal variability characterising
stream and river habitats makes it difcult to assess the hydromorpho-
logical impact at a scale relevant for the biological communities. At the
reach scale, the biota responds to local hydromorphological features
(i.e. the interaction between the ow of water and the channel form),
but, additionally, disturbances occurring at larger spatial scales (stream
network) (Poff, 1997) and even historical disturbances (Harding et al.,
1998) can mask the effect of local factors on species composition
(Poff, 1997; Kail and Wolter, 2013).
The majority of studies investigating the effects of hydromorpho-
logical degradation on biological communities have focused on species
richness and/or multivariate descriptors of species composition (e.g.
Hering et al., 2006; Dahm et al., 2013, but see also Feld et al., 2014,
Elosegi and Sabater, 2013, and references therein). However, the taxo-
nomic composition may differ between regions due to spatial con-
straints on community assemblies, making compositional approaches
vulnerable to scale-dependent processes. Functional community char-
acteristics have been suggested as an alternative or complement to
compositional characteristics. Because the same traits (responding to
similar environmental conditions) can be applied to most species in
the world, functional composition is thought to be less vulnerable to
scale-dependent processes (e.g. Dolédec et al., 2006; Friberg et al.,
2011) than taxonomic composition. Additionally, traits provide a
means to gain insight into the mechanisms mediating the response to
natural and anthropogenic drivers of change (Diaz et al., 2007; Moretti
and Legg, 2009).
Functional trait composition has recently proven useful to assess ef-
fects of eutrophication on aquatic plant communities in European low-
land streams (Baattrup-Pedersen et al., in press). Clear indications exist
that eutrophication promotes species that efciently capture light by
concentrating their photosynthetic active biomass near the water sur-
face and species that utilise light efciently. The mechanism behind
these changes was suggested to be intensied competition due to en-
hanced aquatic plant growth, biolm development and more turbid wa-
ters under nutrient-rich conditions. Here, we explore whether
functional trait composition of the aquatic plant community can be
used as a means to assess hydromorphological degradation as well. Cur-
rently, there is no comprehensive theory on how aquatic vegetation re-
sponds to hydromorphological degradation, but from ecological niche
theory we expect that signicant changes occur (Southwood, 1988).
As aquatic vegetation is known to exhibit preference for and adaptation
to substrates, current velocities and depths (Dawson et al., 1999;
Baattrup-Pedersen and Riis, 1999; Gurnell et al., 2010; Puijalon et al.,
2011), we expect that channelisation (e.g. deepened, widened and
straightened; Brookes and Gregory, 1983; Brookes, 1987; Mattingly
et al., 1993; Verdonschot and Nijboer, 2002; Landwehr and Rhoads,
2003) will restrict the niches available for aquatic plants. In particular
loss of poolrife sequences in channelised streams implies that the
habitats that predominate are generally deeper and ow velocities
higher and, at the same time, ow patterns, substrate conditions and
depth characteristics get more uniform (Baattrup-Pedersen and Riis,
1999; Rambaud et al., 2009). Consequently, channelisation likely affects
the presence and distribution of different plant life forms. For example,
the abundance of submerged species is likely to be higher in
channelised streams because these species may bend, thereby mitigat-
ing the increase in drag at higher velocities compared to emergent spe-
cies (Brewer and Parker, 1990; Schutten and Davy, 2000). Furthermore,
species that have their biomass distributed evenly in the water column
experience lower drag than species that have their biomass in high-
velocity areas near the surface (Bal et al., 2011).
Active maintenance of the channelised stream prole by dredging
and mechanical removal of the vegetation by cutting, as performed reg-
ularly in many lowland streams today (for instance Fox and Murphy,
1990; Kaenel and Uehlinger, 1999; Vereecken et al., 2006; Baattrup-
Pedersen et al., 2009; Wiegleb et al., 2014), may also affect the func-
tional traits composition of the aquatic plant community. Dredging is
a very dramatic form of disturbance that can remove all vegetation
and reset the community (Wade and Edwards, 1980; Wade, 1993). In
cases where the channel bed is only supercially scrapped,
overwintering propagules may be left in place, whereas a more
profound removal of the bottom sediments may affect also the
overwintering organs. In regularly dredged streams we may therefore
expect that traits related to species dispersal and establishment may
be of overriding importance for community composition. Effects of
weed cutting has particularly been studied in cases where single species
have been implicated in blocking channels (Dawson, 1989; Dawson,
1976; Pitlo and Dawson, 1990; Kern Hansen and Dawson, 1978),
whereas studies on the effects of cutting on community composition
are scarce and geographically restricted (Baattrup-Pedersen et al.,
2002; Baattrup-Pedersen et al., 2003; Baattrup-Pedersen and Riis,
2004). However, weed cutting can be compared to grazing and
expectedly has a similar selective pressure favouring species that re-
cover fast, i.e. those with intact growth meristems following cutting
(Baattrup-Pedersen et al., 2002; Wood et al., 2012).
To investigate how hydromorphological degradation and eutrophi-
cation affect plant trait composition we have examined how traits
related to morphology, dispersal, survival and the ecological prefer-
ences of thespecies vary along gradients in the impact of these stressors
in lowland streams in Denmark. Specically, we hypothesised that:
i) changes in trait-abundance patterns occur along gradients in
hydromorphological degradation and ii) trait-abundance patterns can
be used to identify the main stressor in lowland streams, for instance
high abundance of species that efciently capture or utilise light indi-
cates that the main stressor is related to eutrophication (see Baattrup-
Pedersen et al., in press), whereas these traits will be subordinate in
streams where the main stressor is related to hydromorphological deg-
radation, reecting that weed cutting improves light availability and
therefore the light climate in eutrophic streams.
231A. Baattrup-Pedersen et al. / Science of the Total Environment 543 (2016) 230238
2. Methods
2.1. Aquatic plants and environmental data
The data used were obtained from the Danish monitoring program
(20042007; NOVANA; Friberg et al., 2005). From a total of 147 stream
reaches on which we possessed combined data on aquatic plant cover-
age, catchment and buffer strip land use, hydromorphological alter-
ations (i.e. cross section, planform, weed cutting) and water chemistry
parameters. These 147 sites were all categorised as middle-sized
(types 2 and 3; Baattrup-Pedersen et al., 2004) with a catchment area
larger than 10 km
2
; they were distributed throughout Denmark and
covered existing gradients in alkalinity and catchment land use. Aquatic
plant data were collected following the protocol described in Pedersen
et al. (2007). In each stream reach, plant recordings were made in
July/August at maximum biomass. Recordings were made in approxi-
mately 150 plots (25 × 25 cm) placed side by side in cross-sectional
transects at a 100 m long stream reach. Depending on the width of the
stream, the number of transects varied from a minimum of 10 to 20 in
small streams. A cover score was allocated to each species present in
the plots using the following abundance scale: 1 = 15%, 2 = 625%,
3=2650%, 4 = 5175%, and 5 = 76100%. Species abundance at
each stream reach was then calculated as the sum of cover scores to
the maximum score sum (i.e. the number of plots multiplied by the
maximum score of ve; Pedersen et al., 2006).
The catchments upstream of the stream reaches and in a 50 m wide
buffer were delineated using the Analysis Tools in ESRI ArcGIS 9.2. Agri-
cultural land use wasthen determined from a national land coverraster
map (25 m grid) with 12 land cover classes (Nielsen et al., 2000) and
from mandatory annual reports on land use from all farmers to the Dan-
ish Ministry of Agriculture (DFFE, 2008). The latter source contains in-
formation on eld location and crop type. Only land cover polygons
classied as arable land were allocated to agriculture.
Hydromorphological features of the stream sites (i.e. cross section
and planform) were recorded at the time of the aquatic plant sampling,
whereas information on weed cutting practice was obtained from the
water authorities. Cross section was categorised as either natural or
channelised using prole characteristics (Table 1). Channelised cross
sections had a trapezoid form with similar depths across the channel
prole, whereas natural cross sections exhibited variability in depth
characteristics. Furthermore, contrary to natural cross sections,
channelised cross sectionswere deeply positioned compared to the sur-
rounding land. To assess sinuosity, stream shape was recorded in the
eld and data were gathered from aerial photos. The following catego-
ries were used: channelised planform, sinuous planform, straight (nat-
ural) planform and meandering planform (Table 1). Weed cutting was
categorised according to the extent of the cutting of the channel as ei-
ther Nhalf width, which included reaches cut from their full width to
half the width of the cross section, or net-half width, which included
reaches cut up to half their width, and none, which included stream
reaches that were left uncut. The number of stream sites within each
of the three categories is given in Table 1. Water chemistry data used
for the analyses were based on ve yearly samplings conducted within
5 years of the vegetation surveys. Since water chemistry has been rather
constant in Danish streams over the last years we nd this approach ap-
propriate (Wiberg-Larsen et al., 2013). The water samples were
analysed for phosphate (PO
4
P), nitrate (NO
3
N) and ammonium
(NH
4
N) in the laboratory according to European standards.
2.2. Description of traits
A total of 52 submerged and amphibious taxa were observed of
which we were able to allocate traits to 41 species representing 79% of
the total submerged and amphibious species pool. We covered traits
that we believe respond to eutrophication and hydromorphological
degradation (see Introduction). These encompassed morphological
traits including life forms and traits important for species dispersal, re-
production and survival. We also included ecological preference values
(Ellenberg N and L; Table 2). The Ellenberg indicator values (Ellenberg
et al., 1991) offer autecological information on the response of approx-
imately2000 species to a rangeof climatic and edaphic factorsin Central
Europe. EN and EL have recently proven useful in combination with
plant traits to identify the biological mechanism behind changes in
community composition in response to eutrophication (Baattrup-
Pedersen et al., in press). Trait data were extracted from the literature
and online databases (Willby et al., 2000;Table 2). The life forms (LF)
were divided into six categories: free-oating (surface and submerged),
anchored with oating and submerged leaves, and anchored amphibi-
ous species with homophyllus emergent leaves and heterophyllus
emergent leaves. Growth morphology was divided into three catego-
ries: single basal, single apical and multi-apical (Table 2). Plant morpho-
logical traits also included a morphology index building on the height
and lateral extension of the canopy and the leaf area of the species. Dis-
persal was characterised by four traits: the abilityto disperse by forming
extensive rootrhizome systems, the ability to reproduce by fragmenta-
tion, the number of seeds and the number of reproductive organs pro-
duced by the species. We also integrated traits related to survival in
terms of overwintering organs such as tubers, turions and rhizomes.
Table 1
Overviewof number of stream reaches categorised into hydromorphological groups.More
information on how the streams were categorised is given in the methods section.
Variable Category N %
Channel planform PL_Channelised 27 18.4
PL_Meandering 42 28.6
PL_Sinuous 55 37.4
PL_Straight, natural 23 15.6
Cross section CS_Channelised 52 35.4
CS_Natural 95 64.6
Weed cutting intensity Weed Nhalfwidth 68 46.3
Weed bhalfwidth 22 15.0
Weed_none 57 38.8
Table 2
The 18 functional traitsused in the present study to characterisethe plant species. The se-
lected traits give information on ecological preference (Ellenberg Light and Ellenberg Ni-
trogen), life form, mo rphology (merist em characteristics; leaf area; canopy
characteristics), dispersal (rootrhizome growth; fragmentation; seed production) and
survival (overwintering organs). See text for further explanation.
Short trait name Explanation Category
LE Ellenberg Light Ecological
preference
NE Ellenberg Nitrogen Ecological
preference
Frsr Free oating, surface Life form
Frsb Free oating, submerged Life form
Anle Anchored, oating leaves Life form
Ansule Anchored, submerged leaves Life form
Anemle Anchored, emergent leaves Life form
Anhete Anchored, heterophylly Life form
Meris.ma Meristem multiple apical growth point Morphology
Meris.sb Meristem single basal growth point Morphology
Meris.sa Meristem single apical growth point Morphology
Morph.ind Morphology index = (height + lateral
extension of the canopy) / 2
Morphology
Leaf.area Leaf area Morphology
Seeds Reproduction by seeds Dispersal
Rhizome Reproduction by rhizomes Dispersal
Frag Reproduction by fragmentation Dispersal
N.rep.org Number of reproductive organs per year and
individual
Dispersal
Overwintering.org Overwintering organs Survival
232 A. Baattrup-Pedersen et al. / Science of the Total Environment 543 (2016) 230238
The life form traits, and traits covering fragmentation, seeds,
overwintering organs and rhizomes, were based on presence/absence
of the attribute, with a score of 0 for absence, 1 for occasionally but
not generally present attributes and 2 for present attributes. The mor-
phology traits describing the meristem growth point type were based
on presence (1) or absence (0) of the attribute. The number of repro-
ductive organs was classied into low (b10), medium (10100), high
(1001000) and very high (N1000), with values ranging from 1 to 4
based on number per individual per year. Leaf area was classied ac-
cording to the leaf size categories with values ranging from 1 to 4,
representing small (b1cm
3
), medium (120 cm
3
), large (20
100 cm
3
) and very large (N100 cm
3
). The morphology index was also
classied into categories (2, 35, 67, 89 and 10) with values ranging
from 1 to 5. In some cases species were classied in-between two cate-
gories regarding the number of reproductive organs, leaf area and mor-
phology index (Willby et al., 2000). In these cases a classication code
in-between was allocated to the particular trait (i.e. 1.5, 2.5, 3.5 and 4.5).
2.3. Data analysis
The relationships between species abundance and trait variables
were examined using multivariate ordination techniques. Stream typol-
ogy did not signicantly explain variation in trait composition (RDA
ANOVA; p N0.05) and we therefore analysed sites from the two typolo-
gies together. We used RLQ and fourth-corner analyses to assess the co-
variation between environmental variables (hydromorphological and
nutrient variables) and traits. RLQ analysis is an extension of co-inertia
analysis that provides an overview of the multivariate associations by
searching for a combination of traits (Table Q) and environmental vari-
ables (Table R) with maximum covariance, which is weighted by the
abundance of the species in the plots (Table L) (Dolédec et al., 1996).
First, correspondence analysis (CA) was applied to Table L, principle
component analysis was applied to Table Q and Hill and Smith analysis
(Hill and Smith, 1976) was applied to Table R as it contained a mix of
qualitative (hydromorphological variables) and quantitative (water
chemistry variables) variables. RLQ analysis was then applied, combin-
ing the three separate ordinations and identifying the main associations
between Tables R and Q, linked by Table L. In the RLQ analysis, the site
scores in Table R constrain the site scores in Table L, and the species
scores in Table Q constrain the species scores in Table L. The axis that
maximises the covariance in Table L is then selected, resulting in a com-
promise between thebest joint combination of site scores by their envi-
ronmental characteristics, the best combination of species scores by
their trait attributes and the simultaneous ordination of sites and scores.
The overall signicance of the relationship between the environmental
variables (R) and species traits(Q) was assessed with a Monte Carlo test
with 999 permutations on total inertia of the RLQ analyses (Dolédec
et al., 1996).
We also performed a fourth-corner analysis that, similarly to RLQ,
computes a new matrix relating the environmental variables to biolog-
ical traits (Legendre et al., 1997). However, the fourth-corner method
provides an additional signicance test of all possible bivariate associa-
tions between single traits and environmental variables, which allows
for a more detailed and specic interpretation of trait-environment as-
sociations. We rst performed an analysis of variance statistic (i.e. the
global F-statistic) for the categorical environmental variables (cross sec-
tion, river planform and weed cutting) to test whether an overall trait-
environment association existed. In case of a signicant F, at least one
environmental category differed from the others in terms of species
traits. We then explored the bivariate relationships further. The statis-
tics of the fourth-corner method depend on the type of variables. In
case of two quantitative variables (i.e.when both the trait and the envi-
ronmental variable are quantitative), the Pearson productmoment
correlation (r) coefcient is used. However, in case of quantitative traits
and qualitative environmental variables, Legendre et al. (1997) sug-
gested the use of either homogeneity statistic (d) or Pearson product
moment correlation coefcient (r). We used the latter option (r) to ob-
tain both the strengthand direction (positive or negative) of association
between the environmental variables and traits. The signicance of r
and F was obtained by permuting simultaneously the rows of Tables R
and Q (999 runs) following the model proposed by Dolédec et al.
(1996). RLQ and fourth-corner analyses were all performed in R pack-
age ade4 (Dray and Dufour, 2007).
3. Results
The stream reaches were highly variable regarding total plantcover-
age, present agriculture close to the stream (50 m wide zone) and in the
catchment, and also in the concentration of major nutrients in the
stream water (Table 3). The distribution of plants in the streams was ex-
plained by linking the trait characteristics of the species to the environ-
mental conditions (Monte-Carlo test; p b0.001). The rst two axes of
the RLQ explained 52% and 22% of the total variance that links the envi-
ronmental characteristicsin Table R with species traits in Table Q (Fig.1;
Table 4). The rst RLQ axis differentiated channelised reaches from
more meandering reaches (straight natural; meandering) without cut-
tings (Fig. 1a), whereas the second axis differentiated reaches with a
channelised cross section and lower cutting intensity from reaches
with a natural cross section but more intensive cutting. The amounts
of nutrients in the stream water were related to both axis one and
two. Interestingly though, reaches with high levels of PO
4
P were differ-
entiated from those with high levels of NO
3
N(Fig. 1a). For the traits, the
rst RLQ axis differentiated survival (overwintering), productivity (EN)
and dispersal by rhizome growth from some of the specic life form
characteristics (heterophylly; anchored oating leaved) and dispersal
by fragmentation, whereas the second axis differentiated meristem
characteristics, i.e. apical and multi-apical meristem growth from basal
meristem growth (Fig. 1b). The differentiation of species according to
RLQaxesisshowninFig. 1c.
We found several signicant associations between environmental
variables and trait characteristics (Table 5). Generally, we found that
traits within each of the ve categories (ecological preference; life
form; morphology; dispersal; survival) were signicantly related to
one or more hydromorphological variables (planform, cross section
and weed cutting; Table 5). One of the life form traits (heterophylly)
and one trait related to survival (overwintering) responded to all
types of hydromorphological degradation (i.e. planform, cross section
and weed cutting) (Table 5).
Investigating the specic hydromorphological stressors, we found
signicant bivariate associations with several trait characteristics
(Fig. 2). In many instances, the relationships were similar regarding
planform and cross section. The ecological preference for light (LE),
the life form anchored emergent leaves and the life form anchored het-
erophylly were all negatively associated with channelisation, whereas
overwintering organs were positively associated with channelisation
(Fig. 2). Additionally, the morphology index and reproduction by rhi-
zome growth were positively associated with a channelised planform
but not with a channelised cross section. Anchored heterophylly was
negatively associated with weed cutting together with single and
multi-apical growth meristems, whereas both heterophylly and apical
Table 3
Key characteristics of the study reaches. Nutrient concentrations are based on ve yearly
samples. Percentages of agriculture were derived from GIS in the whole catchment and
in a 50 m wide zone from the stream channel.
Mean SE Min Max
Aquatic plant coverage (%) 32.7 1.7 0.7 84.1
NH
4
N (mg l
1
) 0.10 0.01 0.02 0.39
NO
3
N (mg l
1
) 3.42 0.17 0.04 8.48
PO
4
P (mg l
1
) 0.05 0.00 0.01 0.18
Agriculture buffer (%) 44.3 1.6 0.9 84.1
Agricultural catchment (%) 62.6 1.4 0.6 86.8
233A. Baattrup-Pedersen et al. / Science of the Total Environment 543 (2016) 230238
growth were positively associated with no cutting. In contrast, single
basal growth meristem was positively associated with weed cutting
but negatively with no cutting. NE and overwintering were also traits
negatively associated with no cutting.
Several traits were also signicantly related to the level of eutrophi-
cation (Fig. 2), but the response varied for the different types of nutri-
ents. The ecological preference for light (LE) decreased with increasing
levels of NH
4
N but increased with increasing levels of NO
3
N, whereas
no signicant relationship was found between LE and PO
4
P(Fig. 2). In-
stead, a signicant relationship was found between the ecological pref-
erence for nutrients (NE) and PO
4
P(Fig. 2). Several life form
characteristics were also related to the concentration of nutrients in
the stream water. For example, anchored species with submerged
leaves increased with increasing concentrations of NO
3
NandNH
4
N,
whereas anchored species with emergent leaves increased with
Fig. 1. Results of the rst two axes of RLQ analysis: (a)coefcients for the environmental variables, (b) coefcients forthe trait, (c) eigenvalues and scoresof species and (d) eigenvalues
with the rst two axes in black. The dvalues give thegrid size for scale comparison across thethree gures. Codes forvariables are given in Tables 1 and 2 and for species in Suppo rting
information Table S1.
Table 4
Summaryof the RLQ analysis: eigenvalues and percentage of totalco-inertia accounted for
by rst three RLQ axes, covariance refers to the covariance between the two new sets of
factorialscores projected onto the rst three RLQ axes (square root of eigenvalue); corre-
lation refers to the correlationbetween the two new setsof factorial scoresprojected onto
the rst three RLQ axes; cumulative inertia refers to the variance of each set of factorial
scores computed in the RLQ analysis, both for the environment and for the traits.
Axis 1 Axis 2
Eigenvalues 0.39 0.17
% of total co-inertia 52% 22%
Covariance 0.62 0.41
Correlation 0.33 0.21
Cumulative inertia (environment) 1.58 2.80
Cumulative inertia (traits) 2.25 5.26
234 A. Baattrup-Pedersen et al. / Science of the Total Environment 543 (2016) 230238
increasing concentrations of NO
3
NandPO
4
P, but declined with increas-
ing concentrations of NH
4
N(Fig. 3). We also found that several morpho-
logical traits (i.e. position of growth meristems and canopy
characteristics) were signicantly related to the concentration of nutri-
ents (Fig. 2). In particular, apical growth meristems were negatively as-
sociated with increasing levels of PO
4
P, whereas single basal growth
meristems were positively associated with increasing levels of PO
4
P
(Fig. 2). The overwintering capacity increased signicantlywith increas-
ing concentrations of PO
4
PandNH
4
N, but declined with increasing con-
centrations of NO
3
N(Fig. 2).
4. Discussion
We found a highly signicant relationship between aquatic plant
trait composition and important environmental stressors affecting low-
land stream habitats. This nding strongly indicates that habitat degra-
dation (hydromorphological alterations and eutrophication) mediates
selective changes in the mean functional trait composition of the
community. In accordance with our rst hypothesis, we found that
several life forms and growth characteristics were affected by
hydromorphological degradation. In particular, the trait heterophylly
responded in a consistent manner to our measures of hydromor-
phological degradation as the abundance of heterophyllous species
was negatively associated with a channelised planform, a channelised
cross section and intensive weed cutting. The consistency in the re-
sponse of this trait was also reected in positive associations between
heterophylly and a natural planform (meanderingor naturally straight),
a natural cross section and absence of weed cutting.
We suggest that the lower fraction of heterophyllous species in
channelised and weed cut stream reaches is related to less diverse and
less variable habitats, specically lack of appropriate depositional habi-
tats. Thus, heterophyllous species are particularly abundant in streams
with heterogeneous environmental conditions (Levins, 1963;
Bradshaw, 1965; Cook and Johnson, 1968), and heterophylly can be
seen as a means to maximise resource uptake by producing submerged
leaves under high ow velocities in winter and early spring and then
later on during summer as the sediment builds up and water depth de-
clines, by producing oating or aerial type leaves (Allsopp, 1965;
Sculthorpe, 1967). In natural sinuous and meandering streams, sedi-
ment is eroded along the outside of meander bends and deposited fur-
ther downstream on the inside of the bends where the shear stress is
lower (Pedersen et al., 2006), and depositional areas may build up dur-
ing summer as ow velocities decline. In channelised reaches, on the
other hand, habitatsare quite uniform regarding depth and velocity pat-
terns. Furthermore, dredging and weed cutting add to homogenise in-
stream habitat conditions by preventing deposition zones from devel-
oping fully through uvial geomorphological processes during low
ow in summer.
Other life form traits were also uniquely affected by hydromorpho-
logical degradation (free-oating surface, anchored oating leaves),
which may be due to differences in ow tolerances among life forms.
Today, the dependency between plant traits (e.g. morphology, exibil-
ity and size) and ow characteristics in streams (e.g. velocity, turbu-
lence and unidirectional versus oscillating ow) is poorly elucidated
(Sand-Jensen, 2003; Sand-Jensen, 2008; Bal et al., 2011). However, it
has been shown that with increasing velocities, plants with evenly dis-
tributed biomass along the water column will experience lower drag
values as they have less biomass in high-velocity areas near the surface
compared to species that concentrate their biomass near the surface
(Bal et al., 2011). For example, a species like Sparganium ssp. with linear
exible leaves is less susceptible to high water velocities compared to,
for instance, Potamogeton pectinatus that grows from multi-apical mer-
istems and concentrates its biomass in the upper waters (Sand-Jensen
et al., 1989). Therefore, the nding that free-oating species were neg-
atively associated with channelisation may reect the fact that this life
form is associated with low current velocity habitats, for example back-
waters that are rare in channelised streams, whereas the opposite holds
true for more natural reaches, especially so if no weed cutting takes
place.
The overwintering capacity (i.e. species with extensive formation of
vegetative propagules such as turbers, turions and rhizomes) also
responded to all types of hydromorphological degradation (channelised
planform, channelised cross section, high weed cutting intensity). A
common characteristic for vegetative propagules is that they remain
dormant during the coldest seasons (Sculthorpe, 1967). Species with
extensive formation of propagules may therefore better survive
unfavourable conditions during winter. Species with a high
Table 5
Pseudo F-statistics of the fourth-corner analysis for the categorical hydromorphological
variables (cross section, river shape and weed cutting).
Stat. Planform Cross section Weed cutting
Value Prob. Value Prob. Value Prob.
LE F 2.75 0.005 ⁎⁎ 4.06 0.014 0.59 0.377
NE F 1.11 0.162 0.85 0.24 2.42 0.032
Frsr F 0.94 0.233 0.66 0.291 0.52 0.438
Frsb F 0.45 0.54 1.29 0.158 0.38 0.51
Anle F 0.10 0.92 2.55 0.052 1.52 0.097
Ansule F 1.08 0.182 0.54 0.375 0.62 0.359
Anemle F 1.96 0.027 ⁎⁎ 9.10 0.002 ⁎⁎ 0.89 0.252
Anhete F 4.51 0.001 ⁎⁎⁎ 3.25 0.027 ⁎⁎ 7.14 0.002 ⁎⁎
Meris.ma F 1.34 0.091 3.30 0.024 ⁎⁎ 1.42 0.108
Meris.sb F 1.42 0.081 0.52 0.371 3.47 0.007 ⁎⁎
Meris.sa F 1.17 0.126 3.21 0.028 ⁎⁎ 3.32 0.005 ⁎⁎
Morph.ind F 1.11 0.158 0.41 0.424 1.45 0.092
Leaf.area F 0.17 0.851 1.27 0.169 0.13 0.81
Seeds F 0.53 0.45 1.26 0.172 1.01 0.196
Rhizome F 2.21 0.011 0.29 0.494 1.17 0.162
Frag F 2.91 0.006 ⁎⁎ 0.13 0.655 1.15 0.156
N.rep.org F 1.16 0.134 2.14 0.073 1.32 0.147
Overwintering.
org
F 6.12 0.002 ⁎⁎ 4.80 0.013 ⁎⁎ 9.64 0.001 ⁎⁎⁎
pb0.1.
pb0.05.
⁎⁎ pb0.01.
⁎⁎⁎ pb0.001.
Fig. 2. Results of the fourth-corner analysis. The table shows all possible bivariate associa-
tions between the environmental variables (hydromorphological categories and nutrient
variables) and aquatic plant traits. Signicant (p b0.05) positive associations are repre-
sented by blackcells and signicantnegative associations by greycells. Non-signicant as-
sociationsare white. Codesfor traits and environmental variables are explained in Tables1
and 2. Note that NO
3
N, PO
4
PandNH
4
N were all log transformed prior to analyses.
235A. Baattrup-Pedersen et al. / Science of the Total Environment 543 (2016) 230238
overwintering capacity in the present study were a highly diverse
group comprising several submerged species (e.g. Potamogeton spp.,
Myriophyllum spp., Ceratophyllum spp., Elodea canadensis), free-
oating species (e.g. Lemna spp., Spirodela polyrhiza,Utricularia spp.)
and species producing both submerged and emergent leaves (e.g.
Sparganium spp., Sagittaria sagittifolia,Myositis palustris). A majority of
the species were, however, submerged, reecting that propagules may
also be used for propagation and dispersal in streams (Sculthorpe,
1967).
The coupling between hydromorphological degradation and the
abundance of species witha high overwintering capacity can be associ-
ated with a generally higher resilience of the plant community in an-
thropogenically disturbed habitats. Additionally, weed cutting and
dredging may provide a competitive advantage for species with a high
overwintering capacity. Weed cutting may extend the growing season
by improving the amount of light that reaches the stream bottom
(Dawson,1976; Ham et al., 1981). Dawson (1976) observed that cutting
during summer increased the summer biomass the following year by
giving rise to a higher overwintering biomass from which re-growth
could take place. Propagule-forming species may have a particular ad-
vantage in these streams, especially in regions like Denmark with die-
back during winter. Furthermore, species producing overwintering or-
gans may also survive weed cuttings performed in late autumn since
overwintering propagules are likely to be left intact near the stream
bottom.
As expected, we found that traits associated with growth meristem
characteristics were inuenced by weed cutting (basal, single and
multi-apical growth meristems). A clear and consistent pattern was
found with higher abundance of species growing from basal meristems
in stream reaches with high weed cutting intensity and lower abun-
dance of these species in stream reaches without weed cutting. At the
same time, we found the opposite pattern for species growing from api-
cal meristems. Previous studies have shown that weed cutting canhave
a severe inuence on community structure (Baattrup-Pedersenand Riis,
1999; Baattrup-Pedersen et al., 2003, 2004; Pedersen et al., 2006), and
here we provide evidence that tolerance towards cutting can be con-
trolled by growth meristem characteristics. This nding seems intui-
tively logical since the position of the growth meristem determines
the potential for re-growth following cutting. That is, species with
basal meristems have an intact growth point after cutting and may
therefore start re-growth immediately after the intervention, whereas
species with apical growth meristems likely exhibit delayed re-growth.
Sparganium spp. has previously been identied as a species that is
highly tolerant to intensive weed cutting (Baattrup-Pedersen et al.,
2003). A likely reason is that the leaf-producing meristems are located
just above thestream bottom and therefore remain intact following cut-
ting. Additionally, this species also has extensive rhizomes that may
provide a competitive advantage in disturbed environments
(Baattrup-Pedersen et al., 2003; Wiegleb et al., 2014). Using continuous
multi-year data, Wiegleb et al. (2014) noticed an increase in Sparganium
emersum along with other rhizomatic species in response to increasing
anthropogenic disturbance in German rivers when combining both
hydromorphological stressors (e.g. cutting, dredging and construction
work) and stressors associated with water quality such as malfunction
of sewage plants and intensication of agricultural land use. Interest-
ingly, S. emersum is also widely distributed and abundant in the least-
disturbed lowland streams in Europe (Baattrup-Pedersen et al., 2008)
but still less abundant than in anthropogenically disturbed streams
(Riis et al., 2000; Baattrup-Pedersen et al., 2002; Pedersen et al., 2006;
Birk and Wilby, 2010; Steffen et al., 2013). The success of this species
in non-impacted streams may be linked to its low light compensation
point and low photosaturation level (Sand-Jensen et al., 1989), which
explains why it is often observed in the sub-layer in multi-layer com-
munities (Baattrup-Pedersen et al., 2002).
In accordance with our second hypothesis, we also found that some
traits could distinguish hydromorphological degradation (free-oating,
Fig. 3. A conceptual model integrating ndings obtained in this study on how hydromorphological degradation affects trait-abundance patterns in aquatic plant communities in lowland
streams with a recently published study on how eutrophication affects trait-abundance patterns in European lowland streams (Baattrup-Pedersenetal.,2015). Dotted arrow indicates
how weed cutting can interact with eutrophication in affecting trait-abundance patterns. Weed cutting improves light availability, implying that efcient light capture or utilisation are
set aside as traits of importance in eutrophic streams. Instead traits associated with high levels of productivity become important, such as preference for high nutrient levels (Ellenberg
N) and the ability to form dense standing crops with extensive lateral spread (Morphology index). Note that the overwintering capacity of the plant community was positively affected
by PO
4
PandNH
4
N but negatively affected by NO
3
N(notspecied in the gure).
236 A. Baattrup-Pedersen et al. / Science of the Total Environment 543 (2016) 230238
surface; anchored oating leaves; anchored heterophylly) from eutro-
phication (free-oating submerged; leaf area). We have summarised
our main ndings in Fig. 3 together with those found in a recently pub-
lished study on how eutrophication affects trait-abundance patterns of
aquatic plants in European lowland streams (Baattrup-Pedersen et al.,
in press). Together these results provide a conceptual framework for in-
terpretation of how multiple stressors interact and affect trait-
abundance patterns in lowland streams. Lowland streams that are
mainly affected by eutrophication have a high abundance of species
growing from apical meristems and species that can efciently utilise
light (Baattrup-Pedersen et al., in press), because species possessing
these traits have a competitive advantage due to light limitation under
eutrophic conditions. The apparently opposite response found here in
streams with high phosphate levels likely indicates that weed cutting
interacts with nutrient availability in affecting trait-abundancepatterns
as depictedin g. 3. Thus, as opposedto streams with high nitrate levels,
we found that high phosphate levels were positively associated with
weed cutting intensity and, consequently, streams with high phosphate
levels also experienced regular cuttings. Therefore, weed cutting proba-
bly sets aside light as a factor controlling species composition under
phosphate-rich conditions likely because plenty of light reach the
stream bottom following biomass removal, and at the same time shad-
ing from epiphytic algae becomes less important since it takes time be-
fore mats develop on the new leaves that develop after cutting. This
interpretation of our results also implies that the positive response ob-
served between phosphate levels in the stream water and the abun-
dance of species with basal growth meristems is without causality, but
merely reects that species growing from basal meristems dominate
in regularly cut reaches.
Interestingly, we also observed a direct and positive response of
traits associated with species productivity (NE and a high morphology
index; Birk et al., 2006; Dudley et al., 2013) and phosphate levels in
the stream water, indicating that phosphate played a direct role in
trait-abundance patterns as depicted in Fig. 3. Again, this nding may
highlight that constraints associated with low light availability in eutro-
phic streams (Hilton et al., 2006; Baattrup-Pedersen et al., in press)are
relieved if these streams are regularly cut. Biomass removal through
cutting improves the light climate and may enable productive species
that are inefcient in light capture or utilisation to compete successfully
provided that they are resilient towards weed cutting. According to
Grime (1988), this should be reected in an increase in the proportion
of species with an ecological preference for high nutrient levels (high
Ellenberg N) as well as an increase in tall species forming dense stand-
ing crops with extensive lateral spread as depicted in Fig. 3.
5. Conclusions
We found clear evidence that habitat degradation in the studied
lowland streams (hydromorphological alterations and eutrophication)
mediated selective changes in the functional trait composition of the
aquatic plant community. The abundance of heterophyllous species
showed a unique and negative response to hydromorphological degra-
dation (channelised planform, a channelised cross section and higher
weed cutting intensity), probably reecting that channelisation
and weed cutting both contribute to homogenise in-stream habitats,
leaving restricted space for deposition zones suitable forheterophyllous
species. We also found indications that eutrophication and
hydromorphological degradation interacted in their effects on the trait
composition of the community. We provide a conceptual framework
for interpretation of how eutrophication and hydromorphological deg-
radation interact on trait-abundance patterns (Fig. 3) that might be ap-
plicable for plant-dominated lowland streams in other regions as well.
We propose that weed cutting can set aside light as a factor controlling
species composition under nutrient-rich conditions in lowland streams
and that high productive species will increase in abundance. Our nd-
ings support the merit of trait-based approaches in biomonitoring as
these can throw light on mechanisms controlling structural changes
under environmental stress (Fig. 3;Baattrup-Pedersen et al., in press).
The ability to disentangle several stressors is particularly important in
lowland stream environments where several stressors are acting in con-
cert since it can enable managers to target the impact of the most im-
portant stressor rst, this being essential to improve the ecological
status.
Supplementary data to this article can be found online at http://dx.
doi.org/10.1016/j.scitotenv.2015.11.027.
Acknowledgement
The study was supported by the European Union 7th Framework
Project REFORM under contract no. 282656 and MARS under contract
no. 603378. We thank Anne Mette Poulsen for manuscript editing and
Tinna Christensen for gure layout.
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... Macrophyte communities are strongly influenced by river hydrology, reflecting both anthropogenic and natural disturbances, where these environmental factors have stronger effect on the trait composition than on the species composition of the community (Papastergiadou et al., 2016;Göthe et al., 2017;Baattrup-Pedersen et al., 2018;Bejarano et al., 2018). Due to the great potential that functional diversity and trait composition of macrophyte communities might have in bioindication of hydro-morphological disturbances in running water-bodies, and its potential importance in river management, there is a growing number of studies investigating the influence of these factors on the trait distribution and/or functional diversity of macrophyte communities (e.g., Baattrup-Pedersen et al., 2016;Göthe et al., 2017;Lukács et al., 2019;Manolaki et al., 2020;Paz et al., 2021;Stefanidis et al., 2021). However, there is still a lack of data on the effects that hydro-morphological disturbances have on the functional diversity and trait composition of macrophyte communities in a large, heavily modified river, such as Danube. ...
... Traits: Rooting at nodes, High below: above-ground biomass, Evergreen leaf, and Amphibius, had binary states (0 meaning the trait is absent, and 1 meaning the trait is present). States of other traits had values: 0 for absence, 1 for occasional but not general presence, and 2 for general presence of the trait state (Willby et al., 2000;Baattrup-Pedersen et al., 2016). ...
... Rhizomes provide clonal growth, which can theoretically lead to unlimited horizonal spreading of the population, competition avoidance, and exploitation and saving of resources (Klimešová, 2018;Manolaki et al., 2020). They also provide the lateral mobility and the capacity to survive unfavorable conditions (Baattrup-Pedersen et al., 2016). Since the surveyed side water-bodies dry up during the low water level, plants with rhizomes are fit to survive, and due to their capacity to reproduce by rhizomes, particularly when the water level is too high during the flowering periods, enable their populations to thrive. ...
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Macrophyte communities have major role in the functioning of freshwater ecosystems. However, there is gap in knowledge about how natural and anthropogenic hydro-morphological disturbances affect their functional diversity and trait structure, particularly in the temperate large rivers. In this study we investigated the effect of hydro-morphology on functional diversity and trait structure of macrophyte communities in the middle section of the Danube course. We collected macrophyte and environmental data from 947 sampling units in the main river channel and connected side waterbodies. We extracted data on 18 traits with 65 trait states and calculated seven functional diversity metrics and cumulative weighted means of trait states (CWMs). We applied redundancy analysis (RDA) to investigate the response of functional diversity metrics to the environmental variables, and Variation Partitioning to determine whether natural, or anthropogenic subset of hydro-morphological factors is more important predictor of functional diversity. To relate CWMs and environmental variables, we performed RLQ and fourth-corner analysis, followed by false discovery rate procedure. Hydro-morphological variables explained 36.7% of the variability in the functional diversity metrics. Combined effect of two subsets of environmental variables explained largest part of the variability in functional diversity metrics. Six associations between traits and environmental variables were found. We found that functional diversity metrics indicate prevailing ecological processes, from environmental to biotic filtering, along the natural-anthropogenic hydro-morphological gradient. We concluded that functional diversity metrics are potentially useful tools in the identification of the causes of ecological degradation, and could be applied in river bioassessments and management.
... Ali et al. (1999) were early adopters of functional (e.g., traitbased) models, and suggested that this approach has the potential to predict water P conditions to the same precision or better than the existing species assemblage-based methods (such as Holmes et al., 1999). Researchers continue to report encouraging results for trait-based modeling in ecological monitoring (Baattrup-Pedersen et al., 2016;Stefanidis and Papastergiadou, 2019). The universal adaptive strategy theory (derived from the competitive, stresstolerant, and ruderal [CSR] trigonal model; Grime, 2002;Grime and Pierce, 2012) predicts that plants with a competitive growth strategy have a greater advantage at low levels of disturbance. ...
... Although the use of growth form values should be validated using data from Europe where the indices originated, the data used here enable us to show that a general trophic index using a plant trait can indicate water trophy across a broad geographic scale. Using the patterns in community traits (versus taxonomy) has both predictive power and provides a mechanistic explanation because organism function (i.e., phenotypic expression), rather than species identity (a genotypic surrogate), has a direct relationship with water P concentrations, similar to the results found by Baattrup-Pedersen et al. (2016). Moreover, functional groupings of macrophytes have been shown to have less sampling variation, and thus greater statistical power for detecting changes, than taxonomy-based calculations (Beck et al., 2014). ...
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Premise: Aquatic macrophyte species abundance and nutrient affinity are used in metrics to assess the trophic condition of lakes and rivers. The development of these indices is often regional, with inter-regional comparisons being complicated by the lack of taxonomic overlap. Here, we use a traits-based approach to expand the geographic scope of existing metrics. Methods: We generalized European trophic affinity values using the response of plant growth form to the light-nutrient gradient, then applied these values to sites in Canada. We evaluated the method's performance against the measured total phosphorus concentration (TP). Results: Free-floating and emergent growth forms were associated with enriched waters (>0.2 mg/L TP), whereas rosette forms were associated with oligotrophic conditions (<0.05 mg/L TP). The responses were longitudinally consistent, and the site scores among indices were highly collinear. Growth form-based scores were more strongly correlated with TP than were species-based scores (0.42-0.56 versus 0.008-0.25). Discussion: We leveraged the ecological relationship between increased surface water nutrient enrichment and the dominance of particular aquatic plant growth forms to generalize aquatic plant trophic indices. We demonstrated an approach for adapting species-based indices to plant traits to facilitate a broader geographic application and simpler data collection, which could be used to develop an easily applied trait-based method of assessing water nutrient status.
... Therefore, more appropriate indicators such as functional traits (e.g., diatom profile guild) have been proposed and used to reflect the environmental changes. The functional trait has been shown to tackle a complex mixture of stressors, e.g., disentanglement of multiple interacting influential factors (Baattrup-Pedersen et al. 2016). ...
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It has been well documented that periphyton communities play a key role in primary productivity, nutrient cycling, and food web interactions. However, a worldwide overview of research on the key themes, current situation, and major trends within the field is lacking. In this study, we applied the machine learning technique (latent Dirichlet allocation, LDA) to analyze the abstracts of 6690 publications related to periphyton from 1991 to 2020 based on the Web of Science database. The relative frequency of classical and basic research on periphyton related to colonization, biomass, growth rate, and habitats has been clearly decreasing. The increasing trends of research on periphyton are embodied in the periphyton function in freshwater ecosystems (e.g., application as ecological indicators, function in the removal of nutrients, and application in paleolimnology), the research at macroscales (e.g., spatial–temporal variation, and functional and taxonomic diversity), and the anthropogenic themes (e.g., climate warming, response to multiple stressors, and land use type). The keyword and title analysis showed that the periphyton studies are concentrated mainly on diatom aspects, especially with respect to streams relative to lakes. The thematic space based on non-metric multidimensional scaling (NMDS) showed that the classical themes such as growth rate, colonization, and environmental factors (e.g., multiple stressors and climate warming) were most linked to other research themes. We proposed that future trends in the periphyton should focus on the function of periphyton in lakes and their response to multiple environmental pressures with the increasingly extensive eutrophication in lakes and the increasingly significant change in the climate.
... They have been widely used as bioindicators in freshwater habitats because certain species and communities are known to respond to environmental changes caused by anthropogenic perturbations such as eutrophication, acidification and hydromorphological alteration [2][3][4][5][6]. Several studies have investigated the role of anthropogenic disturbances in shaping the structure and functioning of macrophyte communities [7][8][9][10] revealing various and complex responses of diversity and community indices to gradients of hydromorphological features and nutrients. It is well known that numerous/multiple human activities such as agriculture, aquaculture, urban infrastructure and settlements, alterations in the hydromorphology and flow regime, significantly influence the abundance, structure and the extent of the macrophyte communities [11,12]. ...
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Aquatic macrophytes are one of the four biological quality elements (BQE) used for assessing the ecological status of inland waters according to the EU Water Framework Directive (WFD 2000/60). With this article, we present the methodological approach for the implementation of a WFD compliant macrophyte index to the riverine systems of Greece. In addition to the definition and harmonization of the ecological quality class boundaries, the results from the pilot application of the index and the ecological classification of the monitored river reaches are also presented. Aquatic plants and environmental parameters were sampled from 93 river reaches between 2012 and 2015. A multivariate analysis with optimal scaling (MVAOS) was conducted to define the main stressor gradient and to identify the least disturbed sites and the reference conditions that are required for the derivation of the ecological quality classes. The Macrophyte Biological Index IBMR for Greek rivers (IBMRGR) was calculated for all the sites and the boundaries for the five quality classes were derived according to the methodology proposed by the Mediterranean Geographic Intercalibration Group (MedGIG). The main findings showed that the hydromorphological modifications were the main environmental stressors that correlated strongly with the IBMRGR, whereas physicochemical stressors were of lesser importance. More specifically, the first principal component explained 51% of the total variance of the data, representing a moderately strong gradient of hydromorphological stress, whereas the second component explained 22.5%, representing a weaker gradient of physicochemical stress. In addition, the ecological assessment showed that almost 60% of the sites failed the WFD target of the “Good” ecological quality class, which agrees with classification assessments based on other BQEs for Greece and many Mediterranean countries. Overall, this work provides a first assessment of the ecological classification of Greek rivers with the BQE of aquatic macrophytes with significant implications for ecological monitoring and decision making within the frame of the WFD implementation.
... Conversely, plants in lower stress environments tend to be taller with longer life cycles(Kyle and Leishman, 2009;Stromberg and Merritt, 2016;McCoy-Sulentic et al., 2017). Factors such as nutrient loading(Baattrup-Pedersen et al., 2016;Lukacs et al., 2019), light conditions(Baattrup-Pedersen et al., 2015), carbon availability(Lukacs et al., 2019), and anthropogenic interference(Baattrup-Pedersen, Larsen and Riis, 2002;O'Briain, Shephard and Coghlan, 2017) ...
Thesis
The importance of vegetation within the fluvial domain is well established, influencing both flow and morphology, and has long been recognised as a key component of the river corridor. Despite this, adequately capturing the spatial and structural variability of vegetation for us to understand the eco-geomorphic feedbacks occurring at a range of scales remains a challenge. Currently, the focus of this research takes place at either the individual plant scale, looking into vegetation-flow interactions, or at larger scales, attempting to spatially discretise vegetation for bulk roughness metrics. Subsequently, hydrodynamic models are typically based around these bulk roughness values which exclude vegetation structure. The aim of this research is to attempt to bridge this gap and link the different scales of analysis to improve our understanding of eco-geomorphic interactions. This is achieved by: (1) Examining current remote sensing methods that may be used for fluvial research, (2) Developing a novel UAV based remote sensing system to collect plant scale data for reach scale analysis, (3) Extracting trait-based metrics for individual plants and upscaling these to reach scale extents, (4) Implementing these traits-based parameters in to a 2D hydrodynamic model. At present, the main trade offs in remote sensing centre around scale and resolution, whereby capturing larger areas reduces the detail of the phenomena being studied. Structure from Motion (SfM) photogrammetry has helped to bridge this gap yet fails to reconstruct topography in vegetated reaches and cannot resolve vegetation structure. These drawbacks have herein been overcome with the introduction of UAV based laser scanning techniques, capable of accurately capturing topography in vegetated reaches as well as resolving vegetation structure. This data can be used to extract traits-based vegetation metrics, identify individual guilds within a river corridor, and be scaled to spatially discretise vegetation structure at reach scales. Guilds are then evaluated against monitored morphological change to investigate eco-geomorphic feedbacks. These vegetation metrics and classifications are subsequently used to parameterise a 2D hydrodynamic model, showing the impact that vegetation discretisation methods have on model outputs. This research has developed methods for obtaining reach scale data on vegetation structure to better inform our understanding of eco-geomorphic feedbacks. The robustness and scalability of these methods presents future avenues of research, both within the fluvial domain and for other environmental research applications, where eco-geomorphic feedbacks have a major influence in shaping the Earth’s surface.
... The relationship between biotic and abiotic factors in natural streams is still too poorly understood (Erba et al. 2006) and it also affects knowledge about the effects of disturbance in regulated streams. Although historically eutrophication has been considered a major pressure on European rivers, hydromorphological degradation today plays a major role (Baattrup-Pedersen et al. 2015). About 150 small hydropower plants (HPP) are operating on Latvian rivers and hydromorphological alterations are one of the most significant pressures within water bodies. ...
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This study analyses the impact of small hydropower plants (HPP) on fish in three Latvian transboundary river basin districts. The MesoHABSIM habitat simulation model was applied to seven Latvian lowland rivers regulated by HPP, four of which belong to the salmonid river type and three to the cyprinid type. Daily stream flow time series for 1961–2018 were used for flow regime calculations in reference (unimpacted) and altered (impacted by HPP operation) flow conditions. Conditional habitat suitability model/criteria for fish were used to assess a potentially available habitat at different flow conditions. Brown trout (Salmo trutta) for salmonid rivers and chub (Squalius cephalus) for cyprinid rivers were selected as case examples to show habitat suitability for different stream types. The authors found significant differences in habitat availability for salmonid and cyprinid rivers, indicating that ecological flows must be calculated separately for fast- and slow-flowing rivers. This study is the first attempt in Latvia to set ecological flow values not only using hydrological calculations but also biological data as an indicator of ecological changes. HIGHLIGHTS A new approach for ecological flow calculations based on fish data and suggestions for a flow regime instead of one single flow value.; A better understanding of habitat differences between cyprinid and salmonid rivers.; Although a relatively small country, hydromorphological differences based on hydrological regions were found in Latvia.;
... Meanwhile, recent advances in environmental risk assessment studies have demonstrated that community-wide changes can be mechanistically related to a given stressor and can be determined with ecological diagnostic tools [18][19][20][21]. Several of these tools are based upon the foundational concept that combinations of morphological, physiological, and behavioral characteristics, as well as ecological preferences of species (i.e., species traits) in a given biological assemblage, can indicate how species interact with their environment and inform on various habitat characteristics, including anthropogenic pressures [22][23][24]. ...
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The ecological quality of freshwater ecosystems is endangered by various micropollutants released into the environment by human activities. The cumulative effects of these micropollutants can affect the fitness of organisms and populations and the functional diversity of stream ecosystems. In this study, we investigated the relationships between the joint toxicity of micropollutants and trait syndromes. A trait syndrome corresponds to a combination of traits that could occur together in communities due to the trait selection driven by exposure to these micropollutants. Our objectives were to (i) identify trait syndromes specific to diatom, macroinvertebrate, and fish assemblages and their responses to exposure, taking into account four micropollutant types (mineral micropollutants, pesticides, PAHs, and other organic micropollutants) and nine modes of action (only for pesticides), (ii) explore how these syndromes vary within and among the three biological compartments, (iii) investigate the trait categories driving the responses of syndromes to micropollutant exposure, and (iv) identify specific taxa, so-called paragons, which are highly representative of these syndromes. To achieve these objectives, we analyzed a dataset including the biological and physico-chemical results of 2007 sampling events from a large-scale monitoring survey routinely performed in French wadeable streams. We have identified five (diatoms), eight (macroinvertebrates), and eight (fishes) trait syndromes, either positively or negatively related to an increasing toxicity gradient of different clusters of micropollutant types or modes of action. Our analyses identified several key trait categories and sets of paragons, exhibiting good potential for highlighting exposure by specific micropollutant types and modes of action. Overall, trait syndromes might represent a novel and integrative bioassessment tool, driven by the diversity of trait-based responses to increasing gradients of micropollutant toxic cocktails.
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In this study, we aimed to identify the macrophyte pattern and diversity under exposure to substantial hydromorphological degradation in rivers, taking into account the water quality factor. The study was based on 190 small and medium lowland rivers in Poland that had experienced channel alterations. The number of taxa identified (153 species) was consistent with natural/seminatural rivers, and the average species richness for the survey site was 16. Nevertheless, nearly 25% of the survey sites were poor in species for which ten or fewer taxa were noted. The most common species were emergent Phalaris arundinacea; free-floating Lemna minor; heterophyllous Sparganium emersum; filamentous algae Cladophora sp.; and some amphibious species, including Agrostis stolonifera. The surveyed sites represented a wide diversity gradient, from sites poor in species and with low diversity based on relative abundance to highly diverse river sites in less transformed rivers. Our results revealed that macrophyte species were mostly determined by hydromorphological degradation, as well as other distinguished environmental factors, such as water trophy (e.g., Lemna gibba, Bidens tripartita, and Ceratophylum demersum) and channel dimensions (e.g., Nuphar lutea, Sagittaria sagittifolia, and Typha latiflolia).
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This paper synthesises insights and offers new quantitative analyses of data gathered during 40 years of stream research by Danish researchers and international associates. Lowland Danish streams mostly drain fertile cropland and contain high nutrient concentrations saturating maximum yield and growth rate of plants. Concentrations of carbon dioxide (CO2) are variable, although usually high, supporting a range of wetland and permanently submerged species. All terrestrial and most amphibious species are obligate CO2 users, while the majority of permanently submerged species can supplement their inorganic carbon demand with bicarbonate. In lake outlets, the average CO2 concentration was close to air saturation during summer, whereas sites with no lake influence were 9‐fold supersaturated. The 20% increase of atmospheric CO2 concentrations over the past 40 years has marginal influence on CO2 concentrations in the streams. In lake outlets with low CO2 concentrations, calculations on 33 stream species showed essentially no underwater photosynthesis by temporarily submerged terrestrial species, low rates by amphibious species, and high rates by permanently submerged bicarbonate users. Underwater photosynthetic rates increased at sites with high CO2 concentrations (no lake influence): they were lowest for terrestrial wetland species (mean 1.8 mg O2 g dry weight−1 hr−1), followed by homophyllous (3.0) and heterophyllous amphibious species (5.6), and highest among permanently submerged species (15.0). Terrestrial and amphibious species grew very slowly when CO2 levels were low, but rapidly in CO2 rich water, or when in contact with air above the water's surface. Decreasing CO2 concentrations from upstream to downstream caused lower photosynthesis rates of amphibious species, while photosynthesis by bicarbonate users was consistently high. The relative abundance of terrestrial and amphibious species decreased significantly as CO2 resources decline from upstream to downstream, while the abundance of permanently submerged species increased as streams progressed. However, plant abundance as a function of CO2 concentrations did not differ markedly among the plant groups. We conclude that photosynthesis and growth of species of different plant types under controlled experimental conditions resembling high in situ nutrient availability are closely related to inorganic carbon supplies, while their representation in plant assemblages is influenced by the spatially and temporally highly diverse ecological conditions from upstream to downstream in the mostly CO2‐rich lowland streams. Submerged terrestrial and amphibious species restricted to CO2 use for photosynthesis can partly escape the slow gas diffusion under water by growing in very CO2‐rich streams and having apical leaves in contact with air. Thus, strong restrictions on their growth and existence should be identified at sites where CO2 concentrations are consistently low and no air contact is possible, while co‐limitation by nutrients is likely to be marginal. Generally, rising atmospheric CO2 is irrelevant to photosynthesis of permanently submerged plants because of their ability to use bicarbonate and the high CO2 supersaturation in most stream sites. In contrast, photosynthesis and growth of amphibious and terrestrial plants under water are highly dependent on CO2 concentrations varying from close to air saturation in lake outlets to supersaturation in headwaters.
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Problems related to extensive macrophyte growth are widespread both in modified and man-made canals and streams, and in streams with natural morphology and rich vegetation. The weed cutting is a common management practice in order to reduce flood risk and enhance water conveyance. Although the short- and long-term impacts on the stream physical habitats and biota have been extensively studied, only little information exists on the effects of weed cutting on ecosystem metabolism, especially for larger rivers. This study aims to quantify effects of weed cutting on metabolic rates in a large lowland river in Denmark. We measured Gross Primary Production (GPP), Ecosystem Respiration (ER) and physical parameters (water depth, discharge, water velocity and reaeration rate) one week prior and 2–6 weeks after weed cutting in 2014 and 2020. Physical river conditions changed significantly after the removal of approximately 60% of macrophytic volume, and a significant reduction in water depth and increased water velocity was recorded. We found an immediate 38% and 61% reduction in GPP and 28% and 35% reduction in ER after weed cutting in 2014 and 2020 respectively. We also found that the metabolic rates did not recover to pre-weed cutting levels within 2–6 weeks after weed cutting. The higher decline in GPP compared to that in ER indicates that the heterotrophic contribution to ER was higher compared to the autotrophic contribution. Our results display that even in a large macrophyte-rich river, where only one-third of the channel is managed by weed cutting, GPP and ER can be reduced significantly. The cascade effects of metabolic rates alterations on ecosystem structure and functioning need to be considered in the future management plans, where higher plant biomass and increased flow is anticipated due to the ongoing climate change and thus, the demand for weed cutting might be intensified.
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Although the great majority of vascular plants are restricted to typical land habitats, a considerable number, the water plants or hydrophytes, attain their optimum development in various aquatic environments. Such hydrophytes are well characterised both morphologically and physiologically, and constitute a distinctive biological group, but taxonomically they are very heterogeneous, including several genera of pteridophytes and representatives from a wide range of angiosperm families. It is generally accepted that the various taxonomic groups of vascular hydrophytes have originated independently from typical land ancestors and that consequently the aquatic habit has been secondarily acquired.
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Previous studies investigating community-level relationships between plant functional trait characteristics and stream environmental characteristics remain scarce. Here, we used community-weighted means to identify how plant traits link to lowland stream typology and how agricultural intensity in the catchment affects trait composition. We analysed plant trait characteristics in 772 European lowland streams to test the following two hypotheses: i) trait characteristics differ between plant communities in small and medium-sized streams, reflecting adaptations to different habitat characteristics, and ii) trait characteristics vary with the intensity of agricultural land use in the stream catchment, mediated either directly by an increase in productive species or indirectly by an increase in species that efficiently intercept and utilize light. We found that the communities in small streams were characterized by a higher abundance of light-demanding species growing from single apical meristems, reproducing by seeds and rooted to the bottom with floating and/or heterophyllous leaves, whereas the community in medium-sized streams was characterized by a higher abundance of productive species growing from multi-apical and basal growth meristems forming large canopies. We also found indications that community trait characteristics were affected by eutrophication. We did not find enhanced abundance of productive species with an increasing proportion of agriculture in the catchments. Instead, we found an increase in the abundance of species growing from apical and multi-apical growth meristems as well as in the abundance of species tolerant of low light availability. The increase in the abundance of species possessing these traits likely reflects different strategies to obtain greater efficiency in light interception and utilization in nutrient-enriched environments. Synthesis and applications. Our findings challenge the general assumption of the EU Water Framework Directive (WFD) compliant assessment systems that plant community patterns in streams reflect the nutrient preference of the community. Instead light availability and the ability to improve interception and utilization appeared to be of key importance for community composition in agricultural lowland streams. We therefore suggest moving from existing approaches building on species-specific preference values for nutrients to determine the level of nutrient impairment to trait-based approaches that provide insight into the biological mechanisms underlying the changes. We recommend that existing systems are critically appraised in the context of the findings of this study. This article is protected by copyright. All rights reserved.
Article
Protecting the worlds freshwater resources requires diagnosing threats over a broad range of scales, from global to local. Here we present the first worldwide synthesis to jointly consider human and biodiversity perspectives on water security using a spatial framework that quantifies multiple stressors and accounts for downstream impacts. We find that nearly 80% of the worlds population is exposed to high levels of threat to water security. Massive investment in water technology enables rich nations to offset high stressor levels without remedying their underlying causes, whereas less wealthy nations remain vulnerable. A similar lack of precautionary investment jeopardizes biodiversity, with habitats associated with 65% of continental discharge classified as moderately to highly threatened. The cumulative threat framework offers a tool for prioritizing policy and management responses to this crisis, and underscores the necessity of limiting threats at their source instead of through costly remediation of symptoms in order to assure global water security for both humans and freshwater biodiversity.
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The River Susa is a small, nutrient-rich stream. Discharge was variable daily and seasonally due to low groundwater input. Above-ground development of submerged macrophytes was restricted to late May to November, when water velocity and depth were low. Dominant macrophytes were rooted Potamogeton pectinatus and Sparganium emersi, and unrooted Cladophora. Growth rates of macrophytes were linearly related to light availability when self-shading was accounted for. P. pectinatus grew rapidly in May-June, concentrated the biomass at the water-surface during July-August, then declined exponentially when the shoots became basally senescent. S. emersum had linear, flexible leaves that were continuously replaced from a basal meristem; it was less susceptible to high water velocities than P. pectinatus and the biomass declined later and at lower rates during autumn. Sparganium also regrew after cutting that left its meristem intact in the sediment. Cladophora developed a high biomass during sunny periods and subsequently disappeared at high discharges. The summer biomass of rooted macrophytes was greater in years with high summer discharge, whereas the biomass of Cladophora and of the epiphytic mnicrobial community was lower due to scouring. Submerged macrophytes played a key role in structure and functioning of the ecosystem. They reduced water velocities 2-4 fold during summer and promoted extensive organic sedimentation. The biomass of benthic diatoms declined parallel to increased macrophyte shading and sedimentation. Submerged macrophytes also formed a large substratum for macroinvertebrates and for a microbial community. -from Authors
Article
Labour-intensive cutting treatments in 2 of the 4 UK rivers removed most Ranunculus from the centres of the channels. In the Petteril (Cumbria) the cut in July was sufficiently late to prevent regrowth, but in the Windrush (Oxfordshire) a significant regrowth was evident 6 wk after the June cut. Diquat-alginate was very effective in removing Ranunculus from the shallow, swiftly flowing and moderately calcareous (60-80 mg l-1) Petteril and Mouse Water (a tributary of the Clyde). Due to large changes in the untreated macrophyte community of the Mouse Water, reductions in plant biomass and cover caused by the herbicide were significant in the Petteril only. Ranunculus was removed or damaged for considerable distances downstream of the point of herbicide application. Less susceptible species, such as filamentous algae and Potamogeton natans, showed herbicide damage only in treated areas. Maximum concentrations of diquat residues detected in these rivers exceeded 1.0 mg l-1 for at least 40 min. The herbicide appeared to be ineffective in the Windrush, but in the Coln (Gloucestershire) of similar size and calcium content, a large proportion of the predominant Ranunculus was removed. Differences in the plant species composition, lengths of river treated, and water turbidity may have led to the differences in the efficacy of the herbicide. Adsorption and inactivation of diquat ions by suspended clay particles may have been responsible for the low concentrations and short persistence of diquat in the Windrush. -from Authors
Article
The paper reviews current concepts that relate particular life-history strategies to habitat characteristics. The strategy selection system is described: through effects on the fitness of individual organisms in ecological time certain combinations of adaptations for survival and reproduction are selected. These combinations arise through trade-offs between different tactics. The author's hypothesis that the habitat provides the templet on which evolution forges characteristic life-history strategies is further explored and related to similar concepts proposed by others. It is shown that in general these formulations define habitat along two axes: one being the frequency of disturbances and the other the general level adversity or harshness. When these axes and the orientation of the figures are made to correspond, the predictions from the different approaches have many similarities. Although the habitat may be defined in terms of two abiotic axes, the scaling of these in time and space must be appropriate to the temporal (e.g. generation time) and spatial (e.g. trivial range) scales of the organism being considered. It is pointed out that the pattern of trade-offs will be constrained by the available genetic variability (a reflection of the organism's phylogenetic history) and there may be more than one stable strategy for a particular environment. The templet constrains the range of life-history strategies, but it does not impose uniformity. The extent of variation may correspond to the dichotomy between high risk and low risk strategies recently explored by Ellner.
Article
Intra- and interpopulation variability in heterophylly of Ranunculus flammula was analyzed by growing samples of several Oregon populations both in terrestrial and aquatic conditions. Leaf blade and petiole widths were measured and an index of heterophylly was computed from the ratio of terrestrial dimensions (blade width/petiole width) to aquatic dimensions (blade width/petiole width). Individuals which are most heterophyllous are associated with immature and most unpredictable environments. Disruptive selection acts on the populations to produce individuals specially adapted to persistently terrestrial or aquatic conditions. The terrestrial specialists have relatively little heterophylly but evidently more between individual variation in terrestrial blade width than the more heterophyllous generalists. The populations were tested for their adaptability (ecological amplitude) by reciprocal transplantation and subjecting them to long-term submergence and desiccation. In general, the most heterophyllous plants are the most adaptable. Leaf expansion in first generation hybrids and their parents is best explained by assuming existence of dominant inhibitor genes which prevent lateral laminar cell expansion at low temperatures. It is concluded that the most adaptable, heterophyllous genotypes are best adapted for pioneering in new biotopes. As succession proceeds microdifferentiation occurs within populations in response to disruptive selection on genes governing leaf morphology and heterophylly. It is argued that hybrids are more likely to be adapted to existence in ecotonal and unpredictable environments because of the developmental flexibility (adaptability) that heterozygosity affords, and that this thesis is not incompatible with the hypothesis of control of heterophylly by dominant inhibitor genes. Developmental flexibility may evolve rapidly through hybridization or slowly through the build-up of modifiers.