Basic HTML Version
International Journal of Marine Science 2013, Vol.3, No.41, 333-343
http://ijms.sophiapublisher.com
339
Table 2 Mean squares and their significance values derived from ANOVA of total cell abundance, the abundances of Cyanophyceae,
Bacillariophyceae and Chlorophyceae (Log
10
(n+1) transformed), taxonomic richness and Shannon-Wiener index, among treatments,
at each sampling time. * =
p
<0.05; ** =
p
<0.01; *** =
p
<0.001. Bolded LSD results are shown where treatments are significantly different
Time interval df
Sources of
variation
Total cell
Cyanophyceae Bacillariophyceae Chlorophyceaea Taxonomic
richness
Shannon-Weiner
Index
0
2
6
Treatment
Residual
0.003ns
0.006
0.011ns
0.009
0.033ns
0.075
0.002ns
0.009
1.00ns
18.00
0.01ns
0.001
30 mins
2
6
Treatment
Residual
0.012ns
0.104
0.205***
C,CM>IM
0.005
4.104***
IM>CM>C
0.124
0.204*
C,CM>IM
0.032
58.11**
IM>CM>C
15.0
0.010ns
0.006
3 hrs
2
6
Treatment
Residual
0.007ns
0.42
0.002ns
0.038
6.904***
IM>CM>C
0.038
0.021ns
0.066
218.11***
IM>CM,C
23.33
0.003*
IM,CM>C
0.002
1 day
2
6
Treatment
Residual
0.099ns
0.053
0.190ns
0.057
3.166*
CM>IM,C
0.203
0.027ns
0.061
41.33**
IM,CM>C
3.56
0.003*
IM,CM>C
0.000
2 days
2
6
Treatment
Residual
0.024**
IM>CM,C
0.002
0.044**
IM>CM,C
0.002
1.288ns
0.482
0.019ns
0.007
10.33ns
9.22
0.002ns
0.006
3 days
2
6
Treatment
Residual
0.025*
IM,CM>C
0.003
0.065**
IM>CM,C
0.005
0.644ns
0.443
0.007ns
0.007
32.33**
IM,CM>C
2.22
0.004ns
0.005
4 days
2
6
Treatment
Residual
0.107***
IM>CM,C
0.003
0.153**
IM>CM,C
0.008
0.254ns
0.866
0.047*
IM>CM,C
0.009
30.00**
IM>CM>C
2.58
0.001ns
0.002
5 days
2
6
Treatment
Residual
0.063***
IM>CM>C
0.002
0.117**
IM>CM,C
0.006
1.138ns
0.604
0.024*
IM,CM>C
0.004
49.00*
IM>CM,C
9.67
0.001ns
0.001
Cyanophyceae, Dinophyceae, Cryptophyceae,
Chrysophyceae and Euglenophyceae.
The highest mean taxonomic richness (32 genera) was
observed in samples from IMs 2 hrs following
sediment disturbance (Figure 4e). This was largely
due to the temporary appearance of benthic diatoms as
a result of gyttja injection into overlying water.
One-way ANOVAs detected significant differences in
taxonomic richness on most of the sampling occasions,
with the LSD tests confirming that IMs were
significant greater in taxonomic richness than control
treatments. Although the number of taxa observed was
often higher in the IMs than the control treatments, the
Shannon-Wiener Index indicated a significant
difference only in samples collected 2 hours following
gyttja mixing (Table 2, Figure 4e).
3.3 Phytoplankton assemblages
Dominant taxa within treatments at each sampling
time are shown in Table 3 and include cyanophytes
(largely
Coelasphaerium
and
Merismopedia
) and
green microalgae (mostly
Gloeocystis
and
Coelastrum
).
Cyanophytes were numerically dominant in all
treatment groups, during the entire experiment.
Patterns in phytoplankton assemblages are depicted in
the series of nMDS plots in Figure 5. They show
stress levels below 0.10 and thus are reasonable
representations of the relationships between assemblages
in different treatments for each time sampled. On all
sampling occasions after IM gyttja disturbance, the
treatments yielded significantly different phytoplankton
assemblages (p<0.05). The impact of mixing was
clearly evident 30 min after mixing; at this time,
samples included suspended benthic diatoms.
SIMPER results for samples collected 30 min and 2
hours after mixing show that the taxa contributing
most to the differences between control sites and IMs
were the diatom genera
Nitzschia, Navicula, Melosira,
Pinnularia
and
Cocconeis
(Table 4), all of which are
known to include benthic species. The ordination plots
of phytoplankton assemblages on Days 2-5 showed