104562723 diatoms as indicators of water pollution in rivers
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DIATOMS AS INDICATORS OF WATER
POLLUTION IN RIVERS
Contents:
Abstract.2
Introduction...3
Aims..6
Methods.7
Sites description.7
Map of sites...9
Field sampling..10
Digestion..10
Preparation of permanent slides...11
TDI calculation.12
Biodiversity calculation13
Statistics description.13
Results..14
Testing for normality17
Testing for correlation..18
Testing for significant differences24
Independent Pooled T-test25
Discussion.26
Reference..29Appendix...30
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Abstract:
Benthic diatoms are used for assessment of eutrophication of water systems, but their
relationship to water quality is not always definite. This study assessed the correlation
of TDI to some physico-chemical factors of rivers.
Diatoms were sampled from eight sites of four different water qualities assigned by
the EPA, based on the Q-scheme value. Each site was tested for Dissolved Oxygen
(mg/L), Temperature (C), Conductivity (S/cm) and pH. TDI for each site was
calculated and assessed for correlation to these physico-chemical factors and to
calculated biodiversity (Shannon Wiener index) of each site. No relationship of TDI
to any of the above was found.
More samples would have to be obtained from the sites over longer period in order to
be able to assign representative TDI values. It is also highly recommended to assess
other communities (macrophytes, invertebrates, grazers pressure) and physical
factors (type of sediment, light intensity, flow, etc.) and take holistic approach of the
assessment.
Keywords:
Diatoms, TDI, Trophic Diatom Index, Physico-chemical factors,
River Eutrophication.
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Introduction:
Diatoms or Bacillariophyceae are Class of Division Heterokontrophyta (brown
algae). They are unicellular representatives of brown algae which can form colonies,
but are mainly attached to substrate by stalks or glide on mud with aid of mucilage
they produce. Their presence can be seen as thin biofilm layer present on surfaces of
stones, macrophytes or other macroalgae.
They are cosmopolitan species inhabiting freshwater or marine environment
and can occur in terrestrial habitat also. Around 12,000 species is known of more than
250 genera, but there may be over 100,000 species in total. In freshwaters, around 80
genera of diatoms are known. In oceans, diatoms form major part of photosynthetic
phytoplankton and it is estimated that themselves, they contribute about 25 35 % of
the worlds productivity in terms of carbon fixation (Kelly, 2005).
Diatom body consists of protoplasma enclosed in a cell wall (frustule) made of
silica. This consists of two overlapping, interlocking halves epitheca and hypotheca,
joined together by girdle bands. Girdle holds the two valves together by cementing
organic substance (Kumar & Singh, 1979). Identification of diatoms relies almost
exclusively on frustules visible in light microscope.
Figure 1: Exploded pennate diatom:(Kelly,200)
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Valves are usually identical for one species. They vary between species in shape and
symmetry, as well as in the type of arrangement of pores, slits and other features of
the silica wall. These differences formed the basis of diatom identification (Kelly,
2005).
Diatoms are divided into two major groups depending on the shape of the cell.
Centric diatoms are circular and pennate diatoms are elongated in valve view.
Some diatoms have a raphe paired longitudinal slit system associated with
motility. Raphe secretes mucilage which aids in locomotion or can be used for
attachment of diatoms. Mucilage can be also secreted by rimoportula, a tube-like slit
found in most centric diatoms and some pennales.
Diatoms can be prostrate Cocconeis sp. lying on substrate
stalked -Achnanthidium sp. attached on stalk
arborescent Gomphonema sp. on branched stalks
These different growth forms lead to different assemblages depending upon
the type of substrate (e.g. stable rock is preferred by Achnanthidium sp. and
Gomphonema sp. and fine sediments are favoured by motile species ( Nitzschia sp.)).
Silica wall of diatoms is relatively insoluble, their remains can accumulate and
preserve in sediments of rivers and lakes. These fossil records in conjunction with
knowledge of diatoms ecological specificity have been used to infer lake or ocean
histories, in particular pH changes and nutrient status as well as climate change
(Kelly, 2005).
Scientists have noticed that certain diatom species thrive in certain environmentalconditions and reflect influence of physical and chemical factor of site. These
observations have been developed into indices used for routine water quality
monitoring. TDI (Trophic Diatom Index) was designed to monitor eutrophication in
rivers (Kelly, 2000).
Diatoms are being used in most EU Member States as cost-effective proxies for
phytobenthos one of the biological elements required by Water Framework
Directive from Member States to be included in ecological status assessment. Rapid
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To calculate TDI values of the sites to estimate the level of eutrophication.
To compare calculated TDI values to Q-scheme status of those sites
designated by EPA.
To assess difference between sites of poor/moderate status and good/excellentstatus.
To assess relationship between TDI and physico-chemical factors of the sites.
To estimate biodiversity of diatom populations in each site.
Methods:
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Diatom samples were obtained from following sites on following dates shown in
Figure 2:
Terryland 27
th
January 2010 Lough Kip River 27th January 2010
Grange - 10th February 2010
Abbert - 10th February 2010
Black - 12th March 2010
Ballycuirke 12th March 2010
Owenriff - 18th March 2010
Loughinch River - 18th March 2010
Sites description:
Terryland - Originates in Castlegar - Galway
Grid reference: M 31306 27263
EPA status: Poor (Q 2-3)
Water is derived mainly from calcareous material. Slower river, where sedimentation
can occur.
Its main part is in Galway city.
Lough Kip River - west of Lough Corrib, Co. Galway
Grid reference: M 22182 31250
EPA status: Good (Q 4) 2006, 2009 survey
High status (Q 4-5) from 1997 - 2003 surveysRiver flows from Lough Kip to Ballycuirke over acidic soil; relatively fast flowing
without sedimentation.
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Grange east of Lough Corrib, co. Galway
Grid reference: M 47654 47624
EPA status: Good (Q 4) - year 2000 onwards
Moderate (Q 3-4) measurement in 1997
Poor (Q 3) 1994
River is on calcareous, medium to high base soil. Farming is frequent in area.
Abbert east of Lough Corrib, co. Galway
Grid reference: M 55661 42846
EPA status: Good (Q4) from 2006 onwards
River flows over calcareous soil region; area highly farmed.
Black - east of Lough Corrib, co. Galway
Grid reference: M 25519 49076
EPA status: Moderate (Q3-4) 2003
Good (Q 4) 2000
Moderate (Q 3-4) 1989
River flows over calcareous stone and surrounding land is used for farming.
Ballycuirke sample was taken from river flowing from this lake, it is on west side of
Lough Corrib, co. Galway
Grid reference: M 22998 32557
EPA status: Mesotrophic Lake
Owenriff river on west side of Lough Corrib, co. Galway
Grid reference: M 11486 42604
EPA status: Good (Q 4) - 2006 and 2009 assessments
High status (Q 4-5) 2003, 2000
Moderate (Q 3-4) - 1997
River flowing from Glengowla area in Connemara through Oughterard, where the
sample was taken. River is fast flowing without much sedimentation. Quite large
number of freshwater mussels was noted at the site, implying good water quality.
Loughinch River west of Galway city
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Grid reference: M 18895 23997
EPA status: moderate (Q 3-4)
River flowing from Lough Inch over acidic soils into the sea near Furbogh town.
This water body was quite stagnant with plenty of sediment present.
Figure 2: Site map
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Field sampling:
Two samples were obtained from River Owenriff and Loughinch River. Other
samples were taken by other students as part of their fieldwork.
Five cobbles from across each river of about the same size were picked. Each was
gently swirled in the river to remove any macroinvertebrates and placed into white
tray with little of the river water and its top side was brushed with toothbrush until the
water was dark brown. Stone was returned to the river so as it was not picked again
for the sampling. This was repeated with other four cobbles. Water from the white
tray containing diatom samples was poured into plastic jar labelled accordingly.
Toothbrush was rinsed and cleaned against Wellingtons boots.
Physico chemical data were obtained. Dissolved oxygen using probe ORION
Model 810, pH was measured by Metter Toledo MP120 pH Meter together with
conductivity and temperature. On the return to lab, samples were preserved with few
drops of Lugols Iodine and stored in dark until needed.
Digestion:
Large pieces of material were removed from samples, jars shaken and
approximately 15 ml of the material were transferred into 30 ml centrifuge tube.
Calcareous material wasnt expected, but after previous experience, few drops of HCl
were added. Distilled water was added to bring the volume to 25ml. These were then
centrifuged until the material settled at the bottom of centrifuge tubes.
Supernatant was discarded into waste jar in fume hood and centrifuge tubes placed
into a rack submerged in cold water.
Concentrated sulphuric acid (5 ml) was added to each tube, then 2ml of saturated
solution of potassium permanganate were added and tubes were shaken gently to mix
the sample with chemicals.
Oxalic acid (10 ml) was added slowly to each sample, which caused effervescence. If
the mixture didnt become clear, 5 more ml were added.
After 10 minutes, all reactions in samples stopped and cooled down. Distilled
water was added to the neck of tubes and samples were centrifuged until they settled.
Supernatant was discarded into waste jar and material transferred into smaller test
tubes with distilled water. These were centrifuged until material settled and
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supernatant was discarded to waste jar. This was repeated until the sample reached
neutral pH.
As soon as the sample reached neutral pH, sample was transferred into clean, fully
labelled vial and stored.
Preparation of permanent slides - mounting:
Distilled water was added to the samples which were too concentrated until
slightly cloudy solutions were obtained.
Samples were shaken to obtain homogenous solution and few drops of one sample
were placed onto a glass cover slip with clean pipette. Cover slip was dried on low
heat on a hot plate.
A glass slide was labelled and placed onto heated hot plate placed in fume hood. One
drop of Naphrax was placed on the glass slide and cover slip placed onto it with the
side containing diatom film down. The slide was left on the hot plate until the
Naphrax stopped producing bubbles; cover slip was gently pressed onto slide, so as all
the left bubbles were pressed away and slide was taken off the hot plate and left in
fume hood to cool down.
Slide was then checked for the right diatom density under microscope.
This procedure was repeated for all samples.
Slides were examined and diatoms identified using identification key: Kelly, Martyn.
Identification of common benthic diatoms in rivers. 2000 AIDGAP, and Kelly M.G.,
Bennion H., Cox. E. J., Goldsmith B., Jamieson J., Juggins S., Mann D.G. + Telford
R.J. (2005). Common freshwater diatoms of Britain and Ireland: an interactive key.
Environment Agency, Bristol.
Slides were examined from right to left side with slide label being placed on the right
side. If the slide reached its end and 300 frustules count was not reached, slide moved
down one field view and counting continued from left to right.
TDI calculation:
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TDI index is based on the weighted average equation (Zelinka and Marvan 1961 cited
in Kelly, 2000):
where: aj = abundance (proportion) of valves of species
j in sample
sj = pollution sensitivity (optimum) of species
j in sample (values 1 5)
vj = indicator value (tolerance) of species j in
sample
Sensitivity scores: 1 = diatoms which favour very low nutrient concentrations
(sj) 2 = diatoms which favour low nutrient concentrations
3 = diatoms which favour intermediate nutrient concentrations
4 = diatoms which favour high concentrations of nutrients
5 = diatoms which favour very high nutrient concentrations
A few taxa have sensitivity values of zero. These include taxa relatively rare in
freshwaters and whose ecological preferences are not well defined (Lucid Diatom
Key).
This index calculates WMS (Weighed Mean Sensitivity) value, which is further used
in equation TDI = (WMS x 25) - 25 to calculate TDI.
TDI values range from 0- 100, with higher values indicating higher levels of nutrients
in the water system.
Biodiversity calculation:
12
=
== n
j
jj
n
j
jjj
va
vsa
index
1
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For estimation of biodiversity, Shannon Wiener index was used. Its formula is as
follows:
where: s = number of species
pi = relative abundance of species the
i-th species (calculated ni/N)
ni = no. of individuals of the i-th species
N = total number of individuals in the community
Statistical calculations:
All data were tested for normality, using Ryan-Joiner test for normality. If some data
were found not to be normal, they were log10-transformed and then worked on those.
Physico-chemical data, number of frustules and biodiversity data were tested for
correlation to TDI values using Correlation test in Minitab.
Poor and moderate status rivers data were joined and the same was done with good
and excellent rivers. These two groups were separately tested for normality with
Ryan-Joiner normality test. In order to test these two groups for significant difference
between them, they had to have proven equal variances and the independent pooled T-
test was then used.
Results:
13
i
s
i
i ppH log1
'
=
=
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Within the eight sites 93 taxa were recorded belonging to 37 genera. The
composition of species in each site was different from site to site, even though there
were species found to be common and abundant for some sites. The most abundant
species for each site and their percentages are noted in Table 1 below.
Table 1: Four most abundant species from each river and percentage in which they
appear in that river with TDI of each site.
River Site SpeciesPercentage(%) TDI value
Abbert
Amphora pediculus 35.5
85.6Navicula lanceolata 17.9
Amphora lybica 10.2
Cocconeis placentula 7.7
Ballycurike
Nitzschia dissipata 32.2
66.6Encyonema silesiacum 18.8Achnanthidium minutissimum 13.4
Fragilaria capucina 6.1
Black
Navicula lanceolata 30.7
86.5
Achnanthidium minutissimum 10.4
Gomphonema parvulum 9.3
Navicula molestiformis 9.3
Gomphonema olivaceum 9.1
Grange
Amphora pediculus 42.5
88.4Navicula lanceolata 15.8
Nitzschia dissipata 10.2
Cocconeis placentula 8.6
Lough KipRiver
Achnanthidium minutissimum 27.1
51.6Nitzschia dissipata 12.1
Achnanthes oblongella 8.8
Cocconeis placentula 5.9
Owenriff
Fragilaria capucina 36.6
49.6Gomphonema parvulum 11.6
Cymbella sp. 9.2
Achnanthidium minutissimum 8.2
LoughinchRiver
Achnanthidium minutissimum 47.5
41.5Sellaphora bacillum 10.6
Navicula oblonga 7.6
Rossithidium linearis 5.6
Terryland
Achnanthidium minutissimum 30
67.4Rhoicosphenia abbreviata 17.8
Gomphonema olivaceum 13.8
Navicula minima 7.4
Achnanthidium sp. was found on six sites and was also found in large proportions. In
Lough Kip River, it formed 27.1% of diatom community and in Loughinch River site,
it was found to take 47.5% of the community. Navicula sp. was found on five sites,
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being the most abundant in river Black with 30.7% (N. lanceolata) and 9.3%
(N.molestiformis). Cocconeis sp., Nitzschia sp and Gomphonema sp. were all found
on three sites all in relatively low numbers. Fragilaria sp. and Amphora sp. were
found on two sites only with Fragillaria sp. being the most abundant in river
Owenriff (36.6 %).Amphora sp. was the most abundant in River Grange (42.5 % of
species) and in River Abbert, two Amphora sp. were found - A. pediculus (35.5 %)
andA. lybica (10.2 %).
Table 2: Data collected for TDI analysis.
River SiteConducti
vity
(s/cm)
DO(mg O2
dm-3
)
pH TDIEPA
StatusNo.spp.
No. frustulesH'Identifi
ed
Non
- IDBallycuirke 194.0 9.60 7.73 66.6 poor 21 314 0 2.2
Terryland 653.0 6.35 7.07 67.4 poor 30 484 64 2.3
Abbert 648.0 11.50 7.75 85.6 moderate 19 352 45 2.1
Loughinch River 157.0 8.87 7.68 41.5 moderate 31 301 30 2.2
Grange 122.7 12.42 8.02 88.4 good 27 266 26 2.1
Lough Kip 148.6 11.40 6.83 51.6 good 31 306 73 2.7
Black 121.2 10.42 7.76 86.5 excellent 17 450 15 2.3
Owenriff 109.3 9.98 6.30 49.6 excellent 22 404 39 2.2
Conductivity (S/cm) had two outlier values in rivers Terryland and Abbert.
Conductivity is a measure of dissolved salts or dissolved ions in solution. It is
controlled by geology, watershed size and other sources of ions (e.g. pollution).
Therefore higher conductivity values ( > 500 S/cm) can indicate hard water, whilst
low conductivity values ( < 100 S/cm) can indicate soft water rivers.
DO (mg O2/dm3) was highest in rivers Grange, Abbert and Lough Kip.
The pH values were smallest at Owenriff (6.3) and Lough Kip River ( 6.83).
TDI values are mixed for different EPA status values, which were based on Q-scheme
system. Rivers described as excellent based on Q-scheme were found to have both
low and high TDI values. Same pattern can be seen in other sites of good and
moderate status. One site from each pair has much lower TDI value than the other site
of same Q-system status. Rivers Ballycuirke and Terryland are classified as poor
water quality sites and their TDI values are very close to each other of TDI 66.6 and
67.4 respectively.
TDI values around 60 are classified as moderately eutrophic and values around 80 are
fairly eutrophic (N Chathin 2008).
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Biodiversity indices of diatoms in each site were found to be quite high, 2.1 to 2.7
with the lowest value being of rivers Grange (2.1) and Abbert (2.1) and the highest of
Lough Kip River (2.7).
Figure 3: Graphical representation of collected data on different sites.
Physico-chemical factors and TDI of rive
0
100
200
300
400
500
600
700
Ballyqurike
Terryland
Abbert
Spiddal
Grange
Loughkip
Black
Owenriff
River site
Value
Conductivity (s/cm) DO (mg O2 dm-3) pH TDI No. spp.
Apart from two conductivity measurements outliers, it seems that when conductivity
is lower (sites Grange and Black), TDI values are higher and in raised conductivity
values (sites Loughinch River and Lough Kip River) the TDI is lower. These factorsdont appear to be in correlation with any other physico-chemical properties or
biodiversity.
All samples were tested for normality by performing Ryan-Joiner test for normality.
Conductivity data were found to be not normal, therefore had to be log- transformed.
All other data were found to be normal.
Testing for normality
H0: Data do not deviate from straight line (Data are normal).
HA: Data do deviate from straight line (Data are not normal).
Accept H0 if RJcrit< RJcalc. or if p-value >/=0.05 (p=0.05, n-2df); n=8
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Conductivity
RJ calc. = 0.819 p-value < 0.010
RJ crit. = 0.8804
RJ crit. > RJ calc. also p value < 0.05
Accept HA - Data are not normal.
Log-transformed conductivity
RJ calc. = 0.881 p-value = 0.028
RJ crit. = 0.8804
RJ crit. < RJ calc, also p value > 0.05
Accept H0- Log-transformed conductivity data are normal.
DO
RJ calc. = 0.965 p-value > 1.000
RJ crit. = 0.8804
RJ crit. < RJ calc, also p value > 0.05
Accept H0- DO data are normal.
pH
RJ calc. = 0.928 p-value > 1.000
RJ crit. = 0.8804
RJ crit. < RJ calc, also p value > 0.05
Accept H0- pH data are normal.
TDI
RJ calc. = 0.958 p-value > 1.000
RJ crit. = 0.8804
RJ crit. < RJ calc, also p value > 0.05
Accept H0- TDI data are normal.
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No. of Frustules
RJ calc. = 0.965 p-value > 1.000
RJ crit. = 0.8804
RJ crit. < RJ calc, also p value > 0.05
Accept H0- frustule count data are normal.
In calculation of biodiversity normality p-value was calculated 0.045 therefore less
than probability of 0.05, but after calculating critical RJ and calculated RJ it was
decided the data are normal also.
Correlation of separate physico-chemical data to TDI was tested both by generating
plots and by hypothesis testing.
Biodiversity
RJcalc. = 0.900
RJcrit. = 0.8804
RJcrit. < RJcalc. p - value > 0.045
Accept H0- Biodiversity data are normal.
Testing for correlation:
H0: There is no association between TDI and conductivity.
HA: There is association between TDI and conductivity.
rcritical at p=0.05; n-2 df
Decision: Accept H0 if rcalculated < rcritical also if p value > or = 0.05
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2.92.82.72.62.52.42.32.22.12.0
90
80
70
60
50
40
Figure 4: Exploration of correlation of TDI to conductivity (S/cm).
rcalculated = 0.247
pvalue = 0.556
rcritical = 0.707
n = 8
rcalculated < rcritical
Accept H0 there is no association between TDI and conductivity.
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131211109876
90
80
70
60
50
40
Figure 5: Exploration of correlation of TDI to DO (mg O2/L).
H0: There is no association between TDI and DO.
HA: There is association between TDI and DO.
rcalculated = 0.386
pvalue = 0.344
rcritical = 0.707
n = 8
rcalculated < rcritical
Accept H0 there is no association between TDI and DO.
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8.07.57.06.5
90
80
70
60
50
40
Figure 6: Exploration of correlation of TDI to pH.
H0: There is no association between TDI and pH.
HA: There is association between TDI and pH.
rcalculated = 0.618
pvalue = 0.102
rcritical = 0.707
n = 8
rcalculated < rcritical
Accept H0 there is no statistically significant association between TDI and pH.
From the plot, we could say that there is some positive correlation between TDI and
pH, even though it is not statistically significant correlation.
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500450400350300
90
80
70
60
50
40
Figure 7: Exploration of correlation of TDI to number of frustules counted.
H0: There is no association between TDI and No. of frustules counted.
HA: There is association between TDI and No. of frustules counted.
rcalculated = 0.122
pvalue = 0.773
rcritical = 0.707
n = 8
rcalculated < rcritical
Accept H0 there is no association between TDI and no. of frustules.
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2.72.62.52.42.32.22.1
90
80
70
60
50
40
Figure 8: Exploration of correlation of TDI to diversity (H).
H0: There is no association between TDI and diversity.
HA: There is association between TDI and diversity.
rcalculated = -0.395
pvalue = 0.333
rcritical = 0.707
n = 8
rcalculated < rcritical
Accept H0 there is no association between TDI and biodiversity.
There was no significant correlation found between any of the physical factors to TDI.
Number of frustules counted was found not to be significantly correlated to TDI
either. There is no statistically significant correlation of TDI to biodiversity.
The strongest relationship was found between TDI and pH. TDI and no. of frustules
had the smallest correlation. All relationships were positive except TDI against
biodiversity, which was quite strong, but negative.
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Test for significant difference between poor/moderate status rivers and good/excellent
status rivers:
Ryan-Joiner test for normality was performed with positive result. In order to assess
significance in difference between the sites, F-test for equal variances was also done
as follows:
Test for equal variances:
H0: There is no difference in group variances.
HA: There is difference in the two group variances.
Fcritical at p=0.05; (n1 - 1 df; n2 1 df)
Decision: Accept H0 if Fcalculated < Fcritical also if p value > or =0.05
Fcalculated = 1.38
pvalue = 0.796
Fcritical = 9.2766
n = 4
Fcalculated < Fcritical
Accept H0 there is no significant difference in variances between poor/moderate and
good/excellent rivers.
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Independent pooled T test:
Performed for two independent, random, small samples which are normal and their
variances are equal.
H0- there's no difference between the two samples of different water qualities.
HA - there's a difference between the two samples of different water qualities.
Accept H0 if t-calc < t-crit. (p = 0.05, n1+n2 -2df)
good/excellpoor/moderate
90
80
70
60
50
40
Figure 9: Boxplot to explore relationship and similarity of poor/moderate and
good/excellent rivers.
Estimate for difference: -3.8
95% CI for difference: (-38.0, 30.5)TValue = -0.27 p-Value = 0.798 DF = 6
CIs span 0 therefore there is no difference between the two sample means. Also p-
value > 0.05 also accept H0.
Therefore the TDI values for poor/moderate rivers are not significantly different from
good/excellent rivers TDI values.
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Discussion
During the diatom identification, ninety-three taxa belonging to thirty-three
genera were found. The most abundant species within all sites was Achnanthidium
minutissimum and the next most abundant were motileNavicula sp.
TDI calculated from sites at given dates were 66.6 for Ballycuirke river, 67.4 for
Terryland both being classified as poor status rivers. For Abbert and Loughinch rivers
both of moderate status, the TDIs were 85.6 and 41.5 respectively. Good status rivers
Grange and Lough Kip River had TDI 88.4 and 52.6 respectively and the excellent
rivers Black and Owenriff had TDIs calculated to be 86.5.and 49.6 respectively. TDI
values greatly vary between sites of the same water quality status based upon the Q-
scheme index.
Dissolved oxygen (mg O2/L) had highest values in rivers Grange, Lough Kip River
both being good status rivers and river Abbert, being classed as moderate water
quality site. Correlation of this factor to TDI wasnt proven in statistical testing.
Conductivity readings were also found not to be correlated to TDI and also included
two outlier data of higher values if compared to the rest (653 S/cm and 648 S/cm in
rivers Terryland and Abbert respectively). Figure 3 in results section suggests some
relationship between TDI and conductivity, e.g. when TDI is low, conductivity values
raise (Loughinch River and Lough Kip River) and the opposite when the TDI values
are higher, conductivity readings are lower (rivers Grange and Black). pH data were
found not to have statistically significant correlation to TDI, but after visual
exploration of the result (Figure 6) it seems that there is some positive relationship.
The pH correlation suggests possible correlation of pH to TDI, but the sample size is
too small to confirm this theory with statistical significance.
The differences in TDIs within the sites of same Q-value could have been
caused by myriads of factors which act upon any river community. These factors are
temperature, amount of light received, nature of substrate, nutrient availability
(nitrates and phosphates), competition for space, natural succession processes, grazing
pressure and hydromorphological regime (Kelly & Bennion, 2009). Assessments of
water quality based on Q-scheme system of TDI should also take these factors into an
account and assess the site as a whole. Q-scheme Index is based on macroinvertebrate
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communities, which may not react to physico-chemical changes as fast as diatoms. Q-
scheme Index is also assessing level of organic pollution of water body, not
eutrophication as TDI does. Taking only one sample for the water quality analysis
cant represent accurately the ecological status of the water system, because diatom
assemblages are dynamic. For example Achnanthidium minutissimum is usually the
dominant species during early succession, but as its resources become limiting in the
biofilm, longer stalked taxa such as Gomphonema acuminatum and loosely attached
and tangled taxa asFragilaria capucina (Kelly & King, 2009). Based on this pattern,
Rivers Lough Kip and Lough Inch river communities are quite new, river Black has
these two species abundant also, together with motile diatom Navicula sp. River
Owenriff has most abundant taxon Fragilaria capucina and Cymbella sp. is also
present, which suggests that this community is older than the previous rivers.
Also higher percentage of motile species indicates that factors other than water
quality, such as sedimentation, may be influencing the diatom assemblages (N
Chathin, 2008). Again many factors are affecting the community structure and
therefore the TDI value.
In statistical analyses, Q-scheme based poor/moderate and good/excellent sites didnt
show significant difference in TDI values because both high and low TDI values
occur in rivers assigned same Q-value; again more samples would be needed to
confirm this result.
There was no correlation of TDI of sampled sites to any of the physico-
chemical factors. Leira and Sabater (2004) study confirms this as follows: Chemical
analyses of water is a good indicator of the chemical quality of the aquatic systems,
but do not integrate ecological factors and dont necessarily reflect the ecological state
of the system.
Although not significant, there was some correlation found of TDI to pH. pH was
used in several analyses of sediment cores of diatom fossils. These were used as
estimation of previous conditions on Earth and ocean acidity. Based upon this, I
would agree with the association of pH to TDI values and diatom community
structure, and would suggest that bigger, more representative samples were taken in
future analyses. Samples should be taken repeatedly at same sites for two to three
years, with three samples spread over a year to obtain consistent data. I would also
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suggest that sampling of nutrients (phosphates and nitrates) are added to the analyses,
as they play an important role in phytoplankton growth and their biodiversity.
A holistic view on the assessment of communities in sites should be developed
rather than focusing on the biological elements separately (Kelly, Haig 2009), because
the stream ecosystem assemblages closely interact within.
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Reference:
Atazadeh I., Sharifi M., Kelly M.G. 2007Evaluation of the Trophic Diatom Index for assessing water
quality in River Gharasou, western Iran. Springer Science + Business Media B.V.
Kelly M., Bennion H., Burgess A., Ellis J., Juggins S., Gurthie R., Jamieason J., Adriaenssens V.,
Yallop M. 2009 Uncertainty in ecological status assessments of lakes and rivers using diatoms.
Springer Science + Business Media B.V.
Kelly M.G., Bennion H., Cox. E. J., Goldsmith B., Jamieson J., Juggins S., Mann D.G. + Telford R.J.
(2005). Common freshwater diatoms of Britain and Ireland: an interactive key. Environment Agency,
Bristol.
Kelly M. G., Haigh A., Colette J. & Zgrundo A. 2009. Effect of environmental improvements on the
diatoms of the River Axe, southern England.
Kelly M., King L., N Chathin B. 2009. The Conceptual Basis of Ecological-Status Assessments using
Diatoms. Biology and Environment: Proceedings of the Royal Irish Academy.
Kelly Martyn;Identification of common benthic diatoms in rivers. 2000, by AIDGAP
Kumar H.D. and Singh H. N.; 1979 A Textbook on Algae. Macmillan Tropical Biology Series;
Macmillan International College Editions.
Leira M., Sabater S. 2004Diatom assemblages distribution in catalan rivers, NE Spain, in relation to
chemical and physiographical factors. Elsevier Ltd.
N Chathin B. and Harrington T. J. 2008 Benthic Diatoms of the River Deel: Diversity and
Community Structure. Royal Irish Academy.
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Appendix:
Examples of diatoms present in sites sampled
Achnanthes oblongella Achnanthidium minutissimum
Amphora lybica Amphora pediculus
Cocconeis placentula Cymbella sp.
Encyonema silesiacum Fragilaria capucina
30
http://openwin%28%27kelly_fracaprad_1%27%2C%27800%27%2C%27308%27%2C%27fragilaria%20capucina%27%2C%27../images/Kelly_fracaprad_1.jpg','Phase%20contrast%20var.%20radians.%20%20Goodie%20Water,%20Scotland.','Image:%20M.G.%20Kelly%20Copyright:%20M.G.%20Kelly.');http://openwin%28%27000275b%27%2C%27482%27%2C%27306%27%2C%27encyonema%20silesiacum%27%2C%27../images/000275b.jpg','valve%20view%20brightfield%20','Image:%20M.%20Bayer%20Copyright:%20RBGE.');http://openwin%28%27uk000418%27%2C%27800%27%2C%27401%27%2C%27cymbella%20spp.%27%2C%27../images/uk000418.jpg','valve%20view%20brightfield%20Cymbella%20tumida','Image:%20D.G.%20Mann.');http://openwin%28%27000363b%27%2C%27430%27%2C%27269%27%2C%27cocconeis%20placentula%27%2C%27../images/000363B.jpg','Raphe%20valve%20view%20Brightfield%20','Image:%20M.%20Bayer%20Copyright:%20RBGE.');http://openwin%28%27000104b%27%2C%27346%27%2C%27237%27%2C%27amphora%20libyca%27%2C%27../images/000104b.jpg','valve%20view%20brightfield%20','Image:%20ADIAC%20Copyright:%20RBGE.'); -
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Gomphonema olivaceum Gomphonema parvulum
Navicula lanceolata Navicula minima
Navicula molestiformis Navicula oblonga
Nitzschia dissipata Rhoicosphenia abbreviata
Rossithidium sp. Sellaphora bacillum
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