386
Land-Ocean Systems in the Siberian Arctic: Dynamics and History
Diversity
Diversity is a measure of the organizational level of a biocoenosis. The commonly used
diversity indices - number of species (S), Shannon-Weaver index (H'), and the related
evenness value (E) - have been calculated for the recorded diatom assemblages (Figure 6).
Since the taxonomical diversity of a biostratigraphic sample is a function of the counting sum,
this parameter is included as well. Lower counting sums than the recommended 400 to 500
valves (Battarbee, 1980) are derived from samples with low diatom concentrations and
probably result in some extreme values in the diversity indices.
The most common diversity index is the number of species per sample S (see Figure 6). The
maximum number is reached in DAZ-8 with a total of 91 species. Planktonic taxa contribute a
maximum of 23 species (DAZ-4). The minimum of 10 planktonic species was found in the
DAZ-l and 9. An assemblage with 36 species (Smin) was recorded from a sample at 4.72 m
(DAZ-5), along with the lowest diatom concentrations in the sequence and strong indications of
dissolution. Since it is difficult to determine the real number of species, the commonly used
diversity index according to Shannon and Weaver (1949) H' has been calculated as follows:
H'=-i=lI,s (pi*log pi)
(1)
where s is the total number of species, and pi is the relative abundance of species i. H'
measures the relative proportions of the single species to each other. It tends to increase as more
species occur in similar proportions. In contrast to other diversity indices, the Shannon-Weaver
index is sensitive to rare species (Kohmann and Schmedtje, 1986) which is considered to be
advantageous in the species-rich assemblage recorded from the Lama Lake sequence.
According to the calculated H' values the diatom assemblages in the Lama Lake sequence
reached their greatest diversity value H'max=3.72 in DAZ-l and DAZ-2 and a second
maximum H'=3.69 in DAZ-7. The diversity was lowest in a sample from 4.12 m sediment
depth (H'min=2.54, low DAZ-6).
In addition, the evenness E of the distribution of individuals with respect to species has been
calculated as follows:
E=H'lHmax=H'/log s
(2)
Highest evenness values approximating are reached when all individuals are evenly
distributed with respect to species. Consequently, E is a measure for the deviation of the given
diversity of the assemblage from the optimum (Kohmann and Schmedtje, 1986).
The highest evenness values were calculated for samples at 4.72 m (Emax=0.895) and 4.62
m (E=0.863) sediment depth in the lower part of DAZ-5. High values ranging from 0.76 to
0.87 were calculated for DAZ-l and 2. They were similarly high in DAZ-8 and 9. Lowest
evenness (E=0.616) was reached in the sample at 4.12 m sediment depth, which showed the
lowest diversity as well.
Life farm
It is generally considered difficult to subdivide periphytic taxa in sediment assemblages into
detailed life form groups, since few taxa show exclusive preferences. A general distinction
between planktonic and periphytic diatom taxa, however, can usually be made (Battarbee,
1986).
Some taxa often found in plankton can also occur in the periphyton (e.g. Tabellaria
flacculasa, Cyclatella acellata). The small chain-forming Fragilaria species (such as F.
pinnata and F. canstruens) are found attached only passively to the substrate and can thus
Land-Ocean Systems in the Siberian Arctic: Dynamics and History
Diversity
Diversity is a measure of the organizational level of a biocoenosis. The commonly used
diversity indices - number of species (S), Shannon-Weaver index (H'), and the related
evenness value (E) - have been calculated for the recorded diatom assemblages (Figure 6).
Since the taxonomical diversity of a biostratigraphic sample is a function of the counting sum,
this parameter is included as well. Lower counting sums than the recommended 400 to 500
valves (Battarbee, 1980) are derived from samples with low diatom concentrations and
probably result in some extreme values in the diversity indices.
The most common diversity index is the number of species per sample S (see Figure 6). The
maximum number is reached in DAZ-8 with a total of 91 species. Planktonic taxa contribute a
maximum of 23 species (DAZ-4). The minimum of 10 planktonic species was found in the
DAZ-l and 9. An assemblage with 36 species (Smin) was recorded from a sample at 4.72 m
(DAZ-5), along with the lowest diatom concentrations in the sequence and strong indications of
dissolution. Since it is difficult to determine the real number of species, the commonly used
diversity index according to Shannon and Weaver (1949) H' has been calculated as follows:
H'=-i=lI,s (pi*log pi)
(1)
where s is the total number of species, and pi is the relative abundance of species i. H'
measures the relative proportions of the single species to each other. It tends to increase as more
species occur in similar proportions. In contrast to other diversity indices, the Shannon-Weaver
index is sensitive to rare species (Kohmann and Schmedtje, 1986) which is considered to be
advantageous in the species-rich assemblage recorded from the Lama Lake sequence.
According to the calculated H' values the diatom assemblages in the Lama Lake sequence
reached their greatest diversity value H'max=3.72 in DAZ-l and DAZ-2 and a second
maximum H'=3.69 in DAZ-7. The diversity was lowest in a sample from 4.12 m sediment
depth (H'min=2.54, low DAZ-6).
In addition, the evenness E of the distribution of individuals with respect to species has been
calculated as follows:
E=H'lHmax=H'/log s
(2)
Highest evenness values approximating are reached when all individuals are evenly
distributed with respect to species. Consequently, E is a measure for the deviation of the given
diversity of the assemblage from the optimum (Kohmann and Schmedtje, 1986).
The highest evenness values were calculated for samples at 4.72 m (Emax=0.895) and 4.62
m (E=0.863) sediment depth in the lower part of DAZ-5. High values ranging from 0.76 to
0.87 were calculated for DAZ-l and 2. They were similarly high in DAZ-8 and 9. Lowest
evenness (E=0.616) was reached in the sample at 4.12 m sediment depth, which showed the
lowest diversity as well.
Life farm
It is generally considered difficult to subdivide periphytic taxa in sediment assemblages into
detailed life form groups, since few taxa show exclusive preferences. A general distinction
between planktonic and periphytic diatom taxa, however, can usually be made (Battarbee,
1986).
Some taxa often found in plankton can also occur in the periphyton (e.g. Tabellaria
flacculasa, Cyclatella acellata). The small chain-forming Fragilaria species (such as F.
pinnata and F. canstruens) are found attached only passively to the substrate and can thus