Geoscience Reference
In-Depth Information
2002). Typical helophytes include
Carex elata
,
Galium broterianum
,
Osmunda regalis
,
Myosotis
stolonifera
,
Viola palustris
and
Oenanthe crocata
(Costa
et al.,
1998); characteristic bryophytes
include
Platyhypnidium lusitanicum
,
Scapania
undulata
,
Fissidens polyphyllus
,
Fontinalis squamosa
,
Racomitrium aciculare
and
Racomitrium lamprocarpum
(Vieira
et al.,
2005), with macroalgae such as
Lemanea fluviatilis
,
Cladophora
spp. and the lichen
Dermatocarpon
1981). The value of this index usually ranges from
1 to 4 (Glime
et al
., 1981).
Environmental conditions were assessed locally
following a field protocol using the methods,
equipment and parameter classes presented in
Table 12.1 or taken from national Geographic
Information System data (Ag encia Portuguesa do
Ambiente, 2008).
luridum
which
is
also
typically
Data analysis
found.
In general, these fluvial ecosystems are in good
ecological condition and most are included within
Natura 2000
network of protected sites designated
under the European Habitats Directive (Council
of the European Communities, 1992). However,
human pressures do occur, most notably point and
diffuse sources of organic and nutrient pollution,
and alterations of natural flow regimes caused by
hydro-electric power generation.
Richness, cover abundance, taxon groups (von
Konrat
et al.,
2010) and diversity of bryophytes
were correlated with the environmental
parameters using Spearman correlation coefficients
(Rs) and analysed using the SPSS 15.0 software
package (SPSS, 2006). Bryophyte community types
were analysed with the dichotomous hierarchical
classification 'Two Way Indicator Species Analysis'
(TWINSPAN), a technique developed by Hill
(Gauch and Whittaker, 1981) using Community
Analysis Package 1.52 (Hederson and Seaby,
1999). Species abundance values were treated
throughout the classification process by the choice
of 'cut levels' (0, 2, 4, 6, 8) recommended when
using scales such as Domin (Causton, 1988),
to define up to five pseudo-differential species
in the dendrogram (McCune and Grace, 2002).
The contribution of each species for intra-group
similarity was calculated with SIMPER analysis
('Similarity Percentages - Species Contributions')
in the Community Analysis Package 1.52 for each
TWINSPAN group (Hederson and Seaby, 1999).
Distribution patterns of bryophyte communities
were investigated by indirect ordination
(Detrended Correspondence Analysis - DCA).
This was done by plotting the total variance
of floristic data and by projecting,
a posteriori
,
environmental parameters as co-variables in
ordination space without forcing ordination axes
to be distorted by the environmental gradients,
using the software program CANOCO 4.52 (ter
Braak and Smilauer, 2003). In addition, the first
four axes of DCA ordination were further analysed
using a weighted correlation matrix derived by
environmental variables and scaling axes of species
ordination.
Field sampling and data
collection
A total of 187 stream segments, each 100 m
long and located in 11 river catchments, were
surveyed between May 2003 and October 2008
(Figure 12.1). Macrophyte groups and the presence
of macro-algae, bryophyte, lichen and vascular
plant species were recorded as percentage cover
in each 100 m segment. Aquatic and semi-aquatic
bryophyte species found in the micro-habitats
of the stream bed and along the channel
margins were recorded and distinguished as either
liverworts (
Marchantiophyta
)ormosses(
Bryophyta
)
(von Konrat
et al.,
2010). Species percentage data
were converted to abundance-frequency values
of the Domin scale (Curral, 1987) to highlight
differences in cover of uncommon or rare species
and also to reduce the emphasis of dominant
species (Jager and Looman, 1995). The diversity
of bryophyte communities in each stream segment
was calculated using the Brillouin Index (HB
=
1/N(ln(N!)-
ln n
i
!)), where N
=
total cover of
bryophyte species in the segment, and n
i
=
cover
of species 'i' in the stream segment (Glime
et al
.,
