4.1.1. Relevee clustering

  The results of the clusterings were expressed in dendrograms. The clustering starts from the level of the individual relevees. On the vertical axis of the dendrogram the degree of similarity between clusters can be read. When comparing, the 'octave' and the 'binary' dendrograms showed resemblance above a certain level of branching. This level  appeared  to  be  the  level  above  which  the  information  was  useful  for  this investigation. Finally, 12 clusters  were  distinguished  (fig.  2),  corresponding  with  the results of the hierarchic binary clustering and each representing a certain combination of species (table 8, 9 ). A survey of the desmid relevees can be seen in table 13.

  Clustering  (octave)  with  RELOCATE  showed  most  agreement  with  the  hierarchic octave clustering, which was to be expected, as the scale used and the method of calculation of the similarities was the same (Ward's method). In fact the results of these three methods of clustering affirm each other. None is perfect, but they complete each other. Together they make it possible to distinguish the final clusters.

4.1.2. Species clustering

  The binary clustering of the species gave best interpretable results. For example, all (known) oligotraphent species were put together, whereas in the 'octave dendrogram' they could be found all over the dendrogram. In the survey of the clustered species (table 8), the species sequence is best reflecting the sequence of the binary clustering, although some modifications are made.

4.1.3. Macrophyte relevee clustering

  The resulting dendrograms of the clusterings of the vegetation relevees were hard to interprate, not matching at all the algal dendrograms. A probable reason for this is the species poorness of the vegetation types (cf. Buys 1986).


  For  the  results  of  the  chemical  analyses  I  refer  to  table 10.  The  results  of  the statistical analyses can be seen in the tables 4 and 5. In general it can be said that we deal  with  typical  oceanic  bogs,  as  can  be  seen  by  the  relatively  high  Cl- and Na+‑contents. The NaCl content can be compared with that of the oceanic bogs of the British isles (Moore & Bellamy  1974).  Also  pH  and  conductivity  of  the  oligotrophic waters of the area investigated, show higher values  than  those  of  continental  bogs (cf. Sjörs, 1950b and Persson, 1962). The chemical analyses of the sampling sites will be discussed further on, in combination with the clusters.


  Additional information  about  the  sampling  site,  such  as  visible  presence  of  iron, presence of waterflow etc. is noted in table 12 and will be discussed in combination with the clusters.


4.4.1. General

  As stated before, I finally decided, on the basis of the several clustering results, to class the algal relevees into 12 ecologically relevant clusters (assemblies). Each cluster represents a  certain  combination  of  algal  species,  differing  from  other  clusters.  This difference in species composition can be correlated with ecological conditions.

  In the clusters I distinguish 'constant species' ,i.e. species occurring in 40% or more of the samples belonging to a cluster. The threshold of 40% is arbitrary, in this case I follow Coesel  (1981).  An  overview  of  these  constant  species  is  given  in  table  8.  When discussing the clusters, species mentioned are constant species, if not, this is indicated. 'Unique species' are constant species limited to one cluster.   The mutual relationships of the clusters are visible in the dendrogram (fig.2). The 12 clusters have been put into 5 groups. Group 1, 2 and 5 form the left branch of the dendrogram. In general these groups consist of clusters relatively poor in species (see table 8). When comparing with the other branch, this left branch is associated with (for desmids) more extreme environments with nutrient poorness, high pH and high nutrient contents or drought. The  other  branch,  consisting  of  the  groups  C  and  D, represents clusters rich in species, combined with ecologically more optimal conditions for desmids. The sequence of the clusters in fig.2 is so that the most resembling clusters are put next to each other. An exception to this are the clusters 5‑A and 5‑B. Because of their low number of species the clustering program puts them in the left branch of the dendrogram. However, their species composition is more in agreement with cluster 4‑C, which they should join in the sequence 4-B > 4‑C > 5‑A > 5‑B. Below I will discuss the groups, and the clusters belonging to them, in the sequence just mentioned. Samples token in different substrates of a sampling site appeared, in most  cases,  to group in the same cluster (cf. Peterfi, 1974).

  Linked to the clusters are macrophytic vegetation and chemical analyses. A survey of the macrophytic vegetation can be seen in table 6 (vegetation types), table 7 (most important macrophytes) and table 11 (vegetation of the sampling sites). The 'chemical analyses of the clusters' is shown in table  4  and  5,  the  chemical  analyses  of  the sampling sites can be seen in table 10. When studying the chemistry especially the following  parameters  are  discriminating  the  desmid  assemblies;  pH,  conductivity, alkality, chloride and the cations of calcium, magnesium, sodium and potassium. Sulfate is just of interest in discriminating the higher trophic levels. The iron ions and the anions of phosphorus and nitrogen seem to be indifferent with respect to the clusters distinguished.  In  the  following  text  only  statistically  significant  parameters  will  be mentioned (table 5). When using the term Ca2+ ‑content or any other ionic content, the average  ionic‑content  of  that  group  or  cluster  is  meant.  When  pH‑values  and conductivities of clusters or groups are mentioned, also the average values are meant.

4.4.2. Group 1


  This  group  comprises  the  clusters  1‑A,  1‑B  and  1‑C.  These  clusters  represent  the habitats with the lowest trophic states. pH, conductivities and ionic contents show the lowest values in this group. Dominant vegetations are the Sphagnum majus‑S. lindbergii community and the Gymnocolea‑Carex limosa community. These oligotrophic vegetation types are poor in species. Sphagnum majus and Drepanocladus schulzei are restricted to group 1. The clusters are poor in desmid species. Species that are common in other groups, lack here: Euastrum ansatum ,E. elegans, E. pectinatum and Cosmarium difficile.

The clusters

Chemical analyses.

  There are hardly differences in the chemistry of the clusters 1‑A, 1‑B and 1‑C. The SO42- ‑ and N.NO3‑contents of cluster 1‑B are higher than those of cluster 1‑C, but with low significance. pH‑ values, conductivities, alkalinity and Cl-  , Ca2+ , Mg2+ , Na+  and K+  ‑contents are low in all clusters.


  The vegetation of the clusters 1‑A and 1‑B is roughly the same. Most sampling sites are representatives of the Sphagnum majus‑ S. lindbergii ‑ and the Gymnocolia‑ Carex limosa community, both representing oligotrophic wet hollow and pool vegetation. The first community occurs as floating mats in smaller deep pools or as carpets on the wettest  sites.  The  second  community  develops  in  wet  hollows  or  mudflats  with  a strongly fluctuating waterlevel. In both clusters Sphagnum tenellum , S.compactum and Scirpus cespitosus  occur.  These  species  prefer  relatively  dry  sites  (Eurola,  Hicks  & Kaakinen,  1984).  Compared  to  cluster  1‑A,  the  vegetation  of  1‑B  indicates  wetter conditions, as the Cyperaceae (flark indicating species) are present more frequently in 1‑B. In addition to the clusters 1‑A and 1‑B, Menyanthes trifoliata  ,  a  wet  growing species, occurs in cluster 1‑C. The vegetation of this cluster represents mossless pool or lake vegetations or belongs to the Sphagnum majusS. lindbergii community. Mossless lake vegetations occur on exposed sites like the shores of lakes.

  As indicated by the vegetation, the moisture of the sampling sites belonging to theclusters seems to be an important discriminating factor. The moisture, in this case linked with the volume of the waterbody, will be of importance, as larger waterbodies have more  ecological  niches  (planktonic  species),  a  better  nutrient  supply  (Tolonen  & Hosiaisluoma 1978) and are less sensitive to drought (Eurola, Hicks & Kaakinen, 1984). Indeed, cluster 1‑A comprises a number of shallow moss‑grown pools of a few square metres, cluster 1‑B comprises also shallow pools but often with a considerably larger surface , and 1‑C represents even larger pools, small lakes in fact, which are generally deeper (see table 12). In cluster 1‑A and 1‑B also atmophytic conditions will occur due to emergent Sphagnum plants and/or a fluctuating waterlevel.


‑ Cluster 1‑A contains just 12 constant species (see table 8). Species characterized by    cell extremities (planktonic species) are absent. Cosmarium obliquum just occurs in    the clusters 1‑A and  1‑B.  This  species  indicates  atmophytic  conditions  (Krieger  &    Gerloff,  1969  and  Symoens,  1957).  Unique  species  do  not  occur  here,  it  can  be    considered as a reduction flora of 1‑B and 1‑C.

 ‑ Cluster 1‑B contains 17 constant species. Cosmarium exiguum, Netrium oblongum and   Tetmemorus brebissonii just occur in this cluster. Within group 1 Staurastrum simonyi    and Tetmemorus laevis just occur in cluster 1‑B. Staurastrum avicula, though not a    constant species, is present more often in 1‑B than in any of the other clusters.

 ‑ Cluster 1‑C contains 23 constant species. Cosmarium sphaeroideum, C. nymannianum,   Euastrum insulare v . silesiacum , Staurastrum cingulum and Arthrodesmus octocornis    just  occur  in  1‑C.  Closterium  tumidum  and  Spondylosium  pulchellum  show  a    preference for this cluster but are not constant species. More species with extensions    are occurring here: Xanthidium armatum, X.smithii, Staurastrum cingulum , indicating    an environment with deeper water. Also  larger  and  flattened  forms  (sensitive  to    drought)  like  Cosmarium  nymannianumMicrasterias  truncata  and  Euastrum    ampullaceum occur in this environment.

4.4.3. Group 2

  Chemistry, vegetation and desmid species composition indicate an intermediate position of group 2 between the oligotrophic group 1 and the mesotrophic groups.


  As can be seen in the dendrogram (fig.2), the species composition of group 2 is closely related to that of group 1. When looking at the chemical analyses (table 4) the clusters of these groups show a lower pH and conductivity and lower Cl , Mg2+ ‑ and Na+   ‑contents  than  all  other  clusters.  Likewise  the  vegetation,  where  Sphagnum lindbergii is a dominant species, indicates low trophic levels. In the desmid species composition this level is reflected in the absence of species that are common in the other  'richer'  groups,  like  Cosmarium  difficile  v.constrictum,   C.quadratum,   C. margaritiferum, Closterium calosporum, Eastrum bidentatum. Two species are confined to group 1 and group 2: Actinotaenium silvae‑nigrae and Staurodesmus incus .

  When comparing with group 1, group 2 (cluster 2‑A) appears to be much sricher in desmid‑species,  many  of  which  do  not  occur  in  group  1.  The  oligo‑mesotrophic Drepanocladus procerusSphagnum lindbergii community, lacking in group 1, is the most important type of macrophytic vegetation. There are also macrophytic relations with the mesotrophic groups 3 and 4. Group 2 takes an intermediate position between these oligotrophic and mesotrophic groups.

Chemical analyses

When looking at the chemical analyses (table 4, 5) the clusters of the groups 1 and 2 show a lower pH and conductivity and a lower Cl , Mg2+ ‑ and Na+  ‑content than all other clusters. The trophic status of group 2 is higher than that of group 1, reflected by a higher pH and Ca2+  content.


  Sphagnum lindbergii is a representative of the oligotrophic environment and shows a preference for the groups 1 and 2 (table 7). Carex lasiocarpa , C.livida and Drepanocladus procerus have a mesotrophic preference and can be found in group  2  and  in  the mesotrophic groups. Interesting is the occurrence of Sphagnum annulatum which is almost confined to group 2. The vegetation of most sampling sites belongs to the Drepanocladus procerusSphagnum lindbergii community, which is described as oligo‑mesotrophic wet flark vegetation and shows a preference for this group. The variation within this community can be explained partly by a gradient along the trophic level. Sphagnum annulatum dominates the lower trophic levels.


  When comparing with group 1, group 2 (cluster 2‑A) appears to be much richer in desmid‑species, many of which do not occur in group 1 and are in common with mesotrophic  clusters.  There  are  35  constant  species.  Representatives  of  oligotrophic environments   are:   Euastrum   ampullaceumm,   Xanthidium   smithiii,   Actinotaenium silvae‑nigraee, Micrasterias truncataa, Staurodesmus incus.  Mesotrophic  species:  Euastrum ansatum, E.elegans, E.pectinatum, Tetmemorus granulatus, Cosmarium difficilee, C.blyttiii, C.pseudopyramidatum  and  many  more.  Some  species  are  confined  to  this  group: Staurastrum brachiatum, Euastrum cuneatum and Sphaerozosma granulatum. Closterium nilssonii is a non‑constant species with a strong preference for this group

4.4.4. Group 3


  Together with group 4, this group forms the right branch of the dendrogram, which is  characterized  by  oligo‑meso  to  meso‑eutrophic  conditions,  desmid‑species  richness, higher pH‑values and ionic contents, and a different vegetation. As a group on the whole, the chemistry of group 3 indicates a lower trophic status than group 4 (compare pH‑values, Mg2+  ‑, Na+  ‑ and K+ ‑contents). However there is a large overlap, due to the variation among the clusters within each group. Still the chemical analyses of each separate cluster in group 3 differs from that of each cluster in group 4. The overlap between the groups is caused by cluster 3‑C, which will be discussed below.   Allmost all sampling sites of group 3 represent vegetations of (very) shallow waters. The water table is instable (moving), due to swamp influence as is indicated by the vegetation:  the  Calliergon  sarmentosumDrepanocladus  purpurascens  community,  the Sphagnum  subsecundumDrepanocladus  purpurascens  community  and  the  Carex chordorrhiza community are the prevailing vegetation types. Also a (periodically) strong water  run‑off  (indicated  by  the  Juncus  alpinus  community)  can  be  responsible  for instability.  Characteristic  'shallow‑water  species'  are  for  example  Cinclidium  stigium, Andromeda  polifolia  ,  Carex  livida  and  Drosera  anglica.  'Swampy  species'  are Drepanocladus  purpurascensComarum   palustre,   Calliergon sarmentosum,   Carex chordorrhiza and Equisetum fluviatile.

  Most constant desmid‑species of group 3 are  also  present  in  group  4.  Closterium calosporum  ,  Cosmarium  tinctum  ,  C.  subundulatum Euastrum  bidentatum  and Staurastrum teliferum occur in (and are almost confined to) all clusters of these groups. The clusters of group 3 have no species in common that are not present in group 4. Like  with  the  chemical  analyses  it  is  necessary  to  consider  each  cluster  apart.  A common feature is that the desmid composition of each cluster of group 3 combines a (different) part of the constant species of group 4. A number of desmid species are limited to one or two clusters of group 3.

The clusters

Chemical analyses.

  Cluster  3‑A  and  3‑B   do  not  differ  significantly.  Cluster  3‑C  shows  higher conductivities  and  Ca2+   ‑  and  Na+   ‑contents  than  both  clusters.  Remarkable  is  the presence of a relatively high content of iron in cluster 3‑C. The chemistry of 3‑C causes the overlap of this group with group 4. Cluster 3‑C shows a higher Cl  and Fe‑ content than this group.


  Many species occur in all clusters of this group. Carex livida, Andromeda polifolia, Drosera anglica, Comarum  palustre Scorpidium  scorpioidesDrepanocladus  revolvens, D.purpurascens and Calliergon sarmentosum are often present together in many of the relevees of the clusters. This combination does not occur in the clusters of the other groups. As mentioned above, it is typical for shallow mesotrophic ( and meso‑eutrophic ) swampy waters. Like the chemical analyses, the vegetations of cluster 3‑A and 3‑B show no striking differences. The different 'swampy vegetation types' occur in  both clusters. Scirpus  caespitosus  occurs  more  frequent  in  cluster  3‑A,  whereas  Pedicularis palustris is present more frequently in 3‑B. Most samples of cluster 3‑C are token in the Carex  chordorrhiza  community  .  Campylium  stellatumCalliergon  richardsonii  and Sphagnum teres just occur in 3‑C (the latter two are entirely confined to this cluster).


 ‑ Cluster 3‑A: 30 constant species. This cluster shows the lowest  degree  of  trophy    within this group. The oligotrophic Cosmarium amoenum and C. sphagnicolum occur   here,  while  mesotrophic  species  like  Closterium  cynthia  ,  C.gracilePenium cylindrusCosmarium  pyramidatum  and  C.punctulatum  lack.  C.  laeve  var.    messikommeri  and  Staurastrum  punctulatum  are  limited  to  this  cluster.  Typical mesotrophic species like Micrasterias thomasiana, M. rotata, Cosmarium rectangulare var. croasdaleae, C.perforatum and C. tuddalense do not occur in this cluster

 ‑  Cluster  3‑B:  47  constant  species.  The  mesotrophic  species  mentioned  above  are    present here. Species limited to this cluster: Cosmarium globosum , Euastrum binale    v. binale and E. insulare. Closterium intermedium and Micrasterias thomasiana just    occur in cluster 3‑B and 3‑C.

 ‑ Cluster 3‑C: 58 constant species. A lot of species are present as constant species just    in this cluster: Micrasterias rotata, Closterium  incurvumC.rostratumC.angustatum,    C.venus, Cosmarium tuddalense, C.perforatum and Staurastrum trapezicum and more.    There are clear relations to the meso‑eu trophic clusters 5‑A and 5‑B. Species in    common  are:  Closterium  parvulum,  Cosmarium  conspersum  and  C.ochthodes.  The    absence  of  the  more  oligotrophic  Actinotaenium  cucurbita  and  Cosmarium    subtumidum is also a feature in common with these clusters.

  One might consider cluster 3‑C to be artificial, as many samples of 3‑C are token near each other (see below), reflected in a homogeneous vegetation  throughout  the cluster and the presence of many 'unique' species. However, vegetation as well as the desmid composition of the clusters 3‑A and 3‑B is closely related to that of 3-C. As the samples of these clusters are token on many different sites, this seems to me  an  argument  to  consider  cluster  3‑C  as  a  natural  one,  although perhaps somewhat too pronounced in this case.

  Near 'Skogvollvatnet', a lake in  the  SW‑corner  of  the  investigated  area,  a  small transect was made (the samples 1 to 12), between the 'richer' looking shore of the lake (sample 1) and the edge of an oligotrophic part of the mire (sample 12). In the tables 10, 11, 12 and 13 the data of the samples of the transect are shown. All samples of the transect appeared to group into the clusters of group 3 : respectively 2 in cluster 3‑A, 2 in 3‑B and 7 in 3‑C. The samples of cluster 3‑A were token near the oligotrophic mire, the samples of 3‑C near the lake, and the samples of 3‑B in between. Though not striking, an increase of pH‑value, conductivity, alkality and calcium‑contents along the transect is visible. Other ionic contents show no change along the transect. Apart from sample  nr.  12,  the  vegetation  of  all  samples  belongs  to  the  Carex  chordorrhiza community.

4.4.5. Group 4


  This group is most related to group 3. Group 4 represents the macrophytic vegetation of the flark pools. Much species that occur in group 3 are common here too, but the 'swampy species' lack here. Phragmites australis is much more common. The dominant types of vegetation represent sites that are permanently wet.   It's probable that the stability of the environment is the most important discriminating factor between the two groups: a constant presence of a water body with a sufficiently large volume in group 4, vs. a changing water table in group 3, which may cause periods  of  drought  and  fluctuating  nutrient  contents.  The  habitats  belonging  to  the clusters of group 4 are permanently wet, whether caused by the relative deepness of the water body (cluster 4‑A, 4‑ B, 4‑C) or by the stability of the water level in the shallow  waters  (also  in  4‑B).  The  chemical  analyses  indicates  oligo‑meso‑  to meso‑eutrophic conditions, but the individual clusters differ considerably.   In addition to the species mentioned in the former group, the desmid composition of  group 4 is characterized by the occurrence (in all clusters) of Euastrum pulchellum, Cosmarium   humile,   C.rectangulare   var.   croasdaleae,   Staurastrum lapponicum, S.tetracerum, and Pleurotaenium ehrenbergi . Some species are limited to the clusters of this  group:  Staurastrum  bicorne Euastrum  verrucosum  and  the  non‑constant  species Micraterias  pinnatifidaEuastrum  gemmatumCosmarium depressum  and  Desmidium  swartzii..

The clusters

Chemical analyses

The state of trophy increases in the sequence 4‑A > 4‑B > 4‑C. Conductivity, pH and Ca2+ ‑, Mg2+  ‑, Na+  ‑ and K+ ‑contents increase in this sequence.

 ‑ Cluster 4‑A shows the lowest pH‑values, conductivities, Ca2+ ‑ and Mg2+  ‑contents. Its    chemistry is quite similar to the poor mesotrophic clusters 3‑A and 3‑B, but pH is    higher and Ca2+‑ content lower (!).

 ‑ Cluster 4‑B Conductivities, Ca2+  ‑ and Mg2+  ‑contents are higher than in 4‑A. These    parameters as well as others like pH and SOO24  ‑, Ca2+  ‑, Na+  ‑ and K+ ‑contents are    lower than in cluster 4‑C.

 ‑ Cluster 4‑C is the cluster with the highest trophic status in this group. All chemical    parameters just mentioned show higher values than in cluster 4‑A and 4‑B.


 ‑Cluster 4‑A concerns shore vegetation of larger (>500m2) and deeper (>20cm) flark   pools. Often Phragmites australis is present, accompanied by Sphagnum platyphyllum   and/or S.annulatum . These mosses may also occur in absence of Phragmites . A   number of these pools is part of a series of flarks, separated by small strips of land.   Seepage of waters connects these pools. Seepage is indicated by Carex lasiocarpa ,   which is present on most sampling sites. The occurrence on some sampling sites of   Sphagnum annulatum and S. platyphyllum points to the relationship with cluster 2‑A.   Cluster  2‑A  is  dominated  by  the  Drepanocladus  procerusSphagnum  lindberghii community  which  also  occurs  in  cluster  4‑A.  However,  communities  indicating   'richer' conditions are dominant in this cluster ( Sphagnum platyphyllumScorpidium   community,  Scorpidium -community  and  Carex  oederi  -community).  Other  species   regularly occurring are Menyanthes trifoliata, Eriophorum angustifolium, Carex limosa,   C.livida, Drepanocladus revolvens and Scorpidium scorpioides .

 ‑Cluster 4‑B. Shore vegetation of large flark pools, as in cluster 4‑A, but with a higher    degree of trophy. 'Richer' conditions are indicated by the occurrence of Calliergon    trifarium  and  Carex  panicea  ,  while  Sphagnum  ‑species  are  absent.  Scorpidium    scorpioides  occurs  more  frequently  than  in  cluster  4‑A.  Other  common  species:    Menyanthes trifoliata, Carex limosa, C.lasiocarpa, and Eriophorum angustifolium. Less    frequent  are  Drosera  anglicaDrepanocladus  procerusD.  revolvens  and  Carex    rostrata, The Scorpidium scorpioides community occurs as the most frequent one. Part    of the vegetation of cluster 4‑B is resembling that of group 3, but the  'swampy    species' lack.

 ‑Cluster  4‑C.  Also  shore  vegetations  of  larger  and  deeper  waters,  with  'richer'    conditions  than  in  cluster  4‑B,  indicated  by  the  occurence  of  Utricularia  minor,    Calliergon giganteum, Chara spec. and Carex diandra. These species indicate calcium    richness.  Often  Drepanocladus  purpurascens  and  Comarum  palustre  are  present,    indicating  some  swamp  influence.  Other  species  of  importance  are  Menyanthes    trifoliata, Phragmites australis, Carex lasiocarpa, C.limosa,  Eriophorum  angustifolium,    Scirpus cespitosus, Scorpidium scorpioides and Calliergon trifarium. The Scorpidium    community and the CharaCalliergon community are dominating.


 ‑Cluster  4‑A.  55  constant  species.  As  in  the  macrophytic  vegetation  the  desmid    composition shows relations with the oligo‑ mesotrophic cluster 2‑A, and even with    the  oligotrophic  clusters  of  group  1.  Species  in  common  are  Xanthidium  smithii,    Tetmemorus  brebissonii  var.   minor,   Pleurotaenium   minutum,   E.pseudoboldtii,    E.humerosumE.denticulatumMicrasterias  truncata  and  Staurastrum  margaritaceum   However the degree of trophy of cluster 4‑A is distinctly higher than that of 2‑A    (and group 1),  indicated  by,  for  example,  the  occurrence  of  Closterium  cynthia,    C.gracile, Cosmarium tinctum and Pleurotaenium rectum. A lot  of  unique  species    occur  in  cluster  4‑A:  Pleurotaenium  baculoides,  Docidium  undulatumClosterium    navicula Euastrum  coeseliiE.inerme,  Cosmarium  contractum  var.  ellipsoideum,    C.quadrifarium and Staurastrum arachne . 9 out of 12 recordings of Pleurotaenium    baculoides and 9 out of 10 recordings of Euastrum inerme appeared to belong to    cluster 4‑A.

 ‑Cluster 4‑B. 52 constant species. The oligotrophic species of cluster 4‑A do not occur    in this cluster. Typical mesotrophic to meso‑eutrophic species, which lack in cluster    4‑A  are  Cosmarium  quadratum  C.  crenatum C.  granatum  ,  C.  difficile  var.    constrictum . The most striking difference with cluster 4‑A is the absence (of course)    of the unique species of 4‑A. Euastrum verrucosum is, as constant species, limited to    this cluster. Cosmarium capitulum var. groenlandicum, Staurastrum disputatum and S. subcruciatum are restricted to cluster 4‑B and 4‑C. Their occurence is not frequent    enough to be constant species. When comparing the species composition with group   3, cluster 4‑B is most related to cluster 3‑B, which shows the same degree of trophy.

 ‑Cluster 4‑C. 30 constant species. The meso‑eutrophic status is reflected in the absence    of species present in all lower degrees of trophy, like Cylindrocystis brebissonii ,    Tetmemorus laevis and Bambusina brebissonii . Mesotrophic species like Closterium    juncidum,   C.   cynthia,   Tetmemorus   granulatus,   Cosmarium   blyttii   and   C.    pseudopyramidatum do not occur. This property is shared with group 5. Probably the    high Ca2+  ‑ and K+ ‑contents (or factors correlated with these cations) are responsible    for the absence of these species. There are some unique species: Cosmarium regnelli    var.  minimum  ,  Staurastrum  bicorne,  S.  boreale  and  S.  furcigerumCosmarium    impressulum and C. portianum occur as constant species just in the calcium‑rich    clusters 4‑C and 3‑C.

4.4.6. Group 5


 This group consists of two clusters, cluster 5‑A and 5‑B. These clusters are poor in species. The species poorness is caused by extreme conditions, mainly high(er) ionic contents, eventually combined with drought. The pH often shows values above 6. The clusters differ in macrophytic vegetation. Cluster 5‑B concerns spring vegetations, while cluster 5‑A consists mainly of different types of 'rich' flark vegetation. In cluster 5‑B a constant supply of high concentrations of ions is the most important stress factor, while the  most  important  factor  in  cluster  5‑A  is  formed  by  less  extreme  ionic  contents combined with drought. Characteristic in the desmid composition is, besides the absence of many mesotrophic species, the presence in both clusters of Cosmarium anceps and C.speciosum var. biforme. Cluster 5‑A is much richer in species than cluster 5‑B, which in fact is a strongly impoverished version of 5‑A.

The clusters

Chemical analyses

 ‑Cluster 5‑A. The chemistry of this cluster is almost the same as in cluster 4‑C. The    NaCl content in cluster 4‑C is somewhat higher. pH values vary between 6 and 7,    conductivity may vary, values between 30 and 125  S occur. Likewise the Ca2+     ‑content shows values between 1 and 20 mg/l, but most values are above 4 mg/l. In    combination with a high Ca2+  ‑content, high SOO24  ‑ contents may occur.

 ‑ Cluster 5‑B. Most pH‑values > 6.6, conductivities > 58, up to 550  S . A Ca2+  content    > 10 mg/l,  also  the  Mg2+   ‑content  often  shows  high  values.  Due  to  the  spring    influence, most chemical parameters will show constant (high) values. Conductivity,    Cll  , P.PO24  and Mg2+  ‑contents show higher values than cluster 5‑A.


 ‑Cluster  5‑A.The  vegetations  of  this  cluster  are  often  dominated  by  mosses  like    Campylium stellatum, Drepanocladus revolvens, Scorpidium scorpioides and, in one    case, Calliergon giganteum. In  shallow  waters  Andromeda  polifolia  is  a  common    species, likewise Betula nana  and  Calliergon  trifarium  .  Other  species  are  Carex    chordorrhiiza, C. panicea, C. limosa, Eriophorum angustifolium, Scirpus cespitosus and    Pedicularis palustris . Different types of meso‑ to meso‑eutrophic communities occur.

 ‑Cluster  5‑B.  The  Philonotis  community  is  the  most  important  vegetation  type.  It    represents spring vegetations. Cratoneuron species, as well as Philonotis fontana and    Bryum pseudotriquetrum dominate the moss‑layer, and also Drepanocladus revolvens    , Campylium stellatum and Riccardia spec. occur frequently. The graminoid and herb    layers  are  heterogeneous.  The  samples  of  two  sampling  sites  (139,  156)  with  a    different  kind  of  vegetation  (resp.  Carex  chordorrhiza  community  and  Calliergon    sarmentosumDrepanocladus purpurascens community) are put into this cluster. With    the other samples of this cluster, they share the desmid‑ species poorness.


 ‑Cluster 5‑A. 25 constant species. Species that occurred in most mesotrophic clusters    and especially in cluster 4‑C, which has practically the same chemistry, lack in this    cluster: Cosmarium subtumidum (which also lacks in cluster 3‑C),  C.  tinctumC.    subundulatum,  Euastrum  elegans,  and  Closterium  calosporum  .  Some  species  are    shared only with cluster 3‑C: Closterium parvulum, Cosmarium conspersum and C. ochthodes. Like in this cluster, in cluster 3‑C there is also a periodical 'drought stress',    under  meso‑eotrophic  conditions.  Unique  species  are  Euastrum  crassicole  var.    dentiferum, Cosmarium cosmarioides, C.  pokornyanumC. annulatum  var.  elegans    and C. tetragonum .

 ‑  Cluster  5‑B.  6  constant  species.  They  are  Cosmarium  ancepsC.  hammeri  var.   homalodermum, C. holmiense var. integrum, C.  ochthodes,  C. quadratum,  and  C.   speciosum var. biforme.