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CHAPTER 6: SEASONALITY OF BENTHIC DIATOM
COMMUNITY IN INTERCONNECTED URBAN
WETLANDS OF BANGALORE, PENINSULAR INDIA
6.1 Introduction 72
6.2 Study area 74
6.3 Methods 76
6.3.1 Water sampling 76
6.3.2 Diatom sample analysis 76
6.3.3 Data Analysis 76
6.4 Results 77
6.4.1 Diatom distribution 81
6.5 Discussion 86
6.6 Conclusion 89
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6.1 Introduction
Inland aquatic ecosystems are vulnerable due to either natural events like seasonal,
volcanic, landslides, soil erosion or human induced activities like landuse changes,
dumping of pollutants, etc. Seasonal or temporal changes occur due to the variations in
meteorological conditions that alter aquatic environment; manipulating water
temperature, salinity, ionic concentrations, habitat availability, sedimentation and
nutrients- in short time interval (Surge and Lohmann, 2002). This perturbs metabolic
activities of aquatic life including primary producers, macroinvertebrates and
amphibians (Rosenzweig et al., 2007). Understanding the adaptability of primary
producers to changing environment provide insights to their evolutionary behavior,
community formation, species ecological preferences and their role in the ecosystem as
bioindicators (Adrian et al., 2009). Chemical variables of water though reflect seasonal
variations; they do not reveal its impact on biological organisms, which is necessary to
understand ecological integrity of an ecosystem (Karr et al., 2000).
Assessing ecological integrity through biological organisms is a cost effective
alternative for assessing substrate availability, light, and water flow along with chemical
variables (Leira and Sabarter, 2005). Among algae, diatoms adapt quickly to short term
seasonal changes owing to their species specific narrow to wide range of ecological
preferences that has evolved over millions of years (Malkin et al., 2009). This feature
helps in exploring physical and chemical factors in combination with human induced
anthropogenic disturbances that governs diatom assemblages (Walsh and Wepener,
2009; Chessman and Townsend, 2010). Diatom studies across time and space, would
aid in the sustainable and integrated water resources management through which the
human impacts and natural seasonal shifts can be conceptually differentiated.
In tropical India, seasonal dynamics of phytoplankton and periphytic diatoms have
been investigated from the Himalayan streams (Rout and Gaur, 1994), streams of
Western Ghats (Karthick et al., in press), freshwater ponds of West Bengal (Choudhury
and Pal, 2008), Majalgaon reservoir (Ingole et al., 2010) and in a tropical monsoonal
estuary (Pednekar et al., 2011). Detailed ecological studies of diatom communities were
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73
investigated in rivers and streams of Himalayas (Jüttner et al., 2011); Western Ghats
(Karthick et al., 2011); Jaipur (Pareek et al., 2011) and wetlands of Coimbatore
(Alakananda et al., 2011). However, studies on diatom communities in urban
ecosystems focusing on seasonal variations and the influence of human impacts are
less studied. Seasonal changes alter species composition; favouring particular species
dominating at a specific time of the year. Human disturbances alter the nutrient and
ion concentrations, which allow the domination of pollution tolerant species and
disappearance of native species. Tropical shallow wetlands of Peninsular India undergo
two stages across a year, first being limited water summer seasons with elevated
nutrients levels and secondly, water rich monsoon seasons which decrease nutrient
loads leading to oligotrophic environment (Wang et al., 2005). Most of wetlands in
urban pockets in many developing nations receive untreated domestic sewages and
industrial effluents, changing drastically the nutrients, ions and metal concentrations.
Impacts of such contaminants on diatom distribution are laregely unexplored.
Bangalore city once known as ‘Lake City’ had numerous wetlands, meeting the
domestic and irrigation requirements of the region. However, the rapid unplanned
urbanisation, leading to the large-scale landuse changes has affected the wetlands
ecosystems qualitatively and quantitatively. Most of Bangalore wetlands receives
untreated sewage and has attained eutrophic status. Lakshman Rao committee report
(1986) lists the overall status of existing lakes and recommended measures to
implement effectively the Ramsar principals of wetland’s restoration and management
plans. Research during the last two decades on Bangalore wetlands explored spatio-
temporal dynamics, water quality, nutrient dyanamics, ecosystems service and
community participation in lake conservations (Ramachandra and Kumar, 2008;
Chanakya et al., 2008; Ramachandra et al., 2011).
The current work focuses on the seasonal patterns on species distribution particularly
for lower organisms. Diverse spatiotemporal factors have decisive role on water quality
and hence in structuring species ecology. The aim of the current work is to investigate
(i) the variation in physical and chemical factors across selected wetlands of Bangalore,
(ii) the influence of water quality on diatom distribution in interconnected wetlands.
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For this investigation, water quality and diatom distribution across habitats were
studied closely in four wetlands for a one whole seasonal cycle in Bangalore Urban and
Rural districts of Southern India.
6.2 Study area
Figure 9. Map showing the Bangalore wetlands with four study wetlands highlighted.
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Bangalore located at 12° 39' N & 13° 18' N and 77° 22' E & 77° 52' E occupies an area
of 900 sq.km (under Bruhat Bengaluru Mahanagara Palike (BBMP), February 2010;
http://bbmp.gov.in) with an elevation of 920 m. Bangalore has dry tropical climate
with annual rainfall of 859.6 mm and soil types are red loamy and laterite soil which
divides Bangalore into rocky upland, plateau and flat topped hills forming slope at
south and south east, and pediplains along western parts (http://cgwb.gov.in). Kempe
Gowda, the founder of Bangalore constructed several tanks to meet the domestic
water requirement locally during 16th century due to lack of perennial water sources.
The late 19th century gave rise to industrialization and thus conversions of major
watershed areas into residential and commercial areas and lead to decrease in lakes by
79% (Ramachandra et al., 2012) and most of them are contniously sewage fed and has
attained eutrophic status (enrichment of nutrients).
Field investigations were carried out during November 2009 to December 2010
(November to February – winter and northeast monsoon; March to June – dry
summer season; July - pre-southwest monsoon; August and September - Southwest
monsoon, October and early November - onset of Northeast Monsoon). September
was the wettest month with mean rainfall of 194.8 mm (Indian Meterological
Department) in the year 2010. Present study deals with water quality and diatom
communities of four wetlands of Bangalore region selected based on the water quality,
urban/rural gradient, and population density in the catchment area (Figure 9).
Amongst four, Yellamallappa chetty (110 ha) and Varthur (166.87 ha) are located in
Bangalore urban district and drained by one of the densely populated area of Bangalore
metropolitan (Mahadevapura zone with population of 5, 19,663). Yellamallappa chetty
is contaminated with industrial waste and agricultural runoff and Varthur is heavily
polluted with domestic sewage, macrophyte growth and severe sludge deposition
(Mahapatra et al., 2011). Vaderahalli (55ha) (also known as Chudahalli reservoir) and
Valley school (18 ha) are located in Bangalore Rural district with less human
population (< 1 lakh) and more of plantation and forest in catchment area. Water from
Vaderahalli is used for irrigation and recreation purposes and Valley school is located
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in the school premises for school gardening usage and water for this wetland get
drained from forested area of Banneraghatta National Park, Bangalore.
6.3 Methods
6.3.1 Water sampling
Water samples were collected at 10 to 30 cm below water surface and stored in
disinfected plastic bottles for laboratory analysis. No preservatives were added as the
samples were immediately transported to the laboratory and refrigerated for
subsequent analysis. Water physical and chemical factors such as water temperature
(WT), pH, turbidity (TUR), salinity (SAL), electrical conductivity (EC), total dissolved
solids (TDS) and dissolved oxygen (DO) were assessed onsite using portable electrode
probe. Laboratory analysis includes total alkalinity (ALK), biological oxygen demand
(BOD), chemical oxygen demand (COD), total hardness (TH), calcium hardness
(CaH), Magnesium hardness (MgH), Potassium (K), Sodium (Na), nitrates (N),
inorganic phosphates (P) and chlorides (CHL) were followed using the standard
methods in American Public Health Association (APHA, 2005).
6.3.2 Diatom sample analysis
Diatoms were collected simultaneously with water samples (December 2009 –
November 2010) from habitats such as submerged plants, stones and sediments.
Cleaning and enumeration of samples was carried out following laboratory procedure
(Karthick et al., 2010). Samples were cleaned following Hot HCl and KMnO4 method
and slides were prepared using Naphrax® as the mounting medium. Relative
abundance of each taxon was determined after counting at least 400 valves in each
sample using light microscope model Olympus BX51 equipped with JENOPTIC
mircophotographic system. Diatoms were identified using Taylor et al., (2007a) and
Krammer and Lange-Bertalot, (1986-1991).
6.3.3 Data Analysis
Species composition or percentage turnover (T) was calculated to indicate community
persistence. T was calculated as T=[(G + L)/(S1 + S2)] * 100, where G and L are the
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77
taxa gained and lost between months respectively, and S1 and S2 are the taxa present in
successive sampling months (Soininen and Eloranta, 2004; Karthick et al., in press).
Later, one way ANOVA with F test for unequal variances was used to assess whether
species turnover across polluted and unpolluted sites were significantly different.
Temporal variations in diatom assemblages across sites were analyzed by NMDS using
PAST version 2.19 (Hammer et al., 2001), which is well suited for data that are non-
normal or are arbitrary or discontinuous and for ecological data containing numerous
zero values (McCune and Grace, 2002).
6.4 Results
Mean physical and chemical variables of each wetland for the study duration are listed
in Table 1. Alkaline pH was recorded at Yellamallappa chetty inlet (9.4 in May),
Yellamallappa chetty outlet (9.14 in July) and Valley school sampling sites while slightly
neutral range at Vaderahalli region. Electrical conductivity, being high at
Yallamallappachetty (YL) (1632 µScm-1 at YLI; 1804 µScm-1) and Varthur wetland
(1254 µScm-1 and 1238 µScm-1 at VRI and VRO respectively) were distinct from
Vaderahalli (VDI, 607 µScm-1; VDO, 608 µScm-1) and Valley school (VLI 1254 µScm-1;
VLO 933.8 µScm-1) which represented low conductivity and less sewage connectivity
with wetland. Total dissolved solids also revealed similar trends as that of conductivity.
In addition, turbidity was twice the permissible limits (Bureau of Indian standards (BIS)
for inland surface waters at Varthur and Yellamallappachetty than other two studied
wetlands (Table 10). Subsequent to EC, BOD and COD values also showed a similar
pattern in lake water quality analysis where BOD-COD was recorded to be high at
YLI, YLO, VRI and VRO and less than 30 mgL-1 at VD and VL wetlands. Nitrates
and phosphates ranged high at Yellamallappa chetty with an average of 0.33 and 1.8
ppm at YLI; 0.41 and 1.6 ppm at YLO while lowest at Vaderahalli (0.12 ppm of N and
0.81 ppm of P) followed by west part of Valley school wetland (0.28 ppm N and 0.36
ppm of P). Chlorides were high at YL and VR, beyond permissible limit, which were
relatively comparable with VD and VL. Alkalinity was found to be within BIS range
(<600 mgL-1), with an exception at VRF during November. All water quality variables
showed a marked difference between wetlands situated in the city region than located
SEASONALITY OF BENTHIC DIATAOMS
78
at sparsely populated peri-urban regions. Wetland with elevated conductivity defines
the inflow of untreated domestic sewage into the wetland. However a low value of
conductivity and dissolved solids was recorded at sampling sites of Yellamallappa
chetty and Varthur during monsoon season, reasoning dilution up to 30% because of
rain water.
Figure 10 and 11 illustrates the variation in main chemical parameters across seasons. An
increased pH value was observed in pre-monsoon, followed by post monsoon and
monsoon in all wetlands. Higher electric conductivity values indicate water contamination
at Varthur and Yallamallappa chetty; however Vaderahalli showed low range across
seasons. Dissolved oxygen being low at Varthur and Yallamallappa chetty inlet than outlet
sites is due to macrophytes infestation hindering the algal photosynthetic activity.
Phosphates ranged from 0.5-3.5 ppm with a high degree of deviation in monsoon months
due to the sustained flow of surface runoff from cultivation fields. Although nitrates
showed similar values across wetlands, Vaderahalli outlet ranged to a high value of 4 ppm
in monsoon due to non point source or runoff from the nearby horticulture gardens.
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Table 10. Mean and standard deviation of physical and chemical analysis of water samples
from study wetlands (refer section 6.3.1).
Site codes
YLI YLO VRI VRO VLI VLO VDI VDO
pH 8.71± 0.79
8.18 ± 0.55
7.73 ± 0.4
7.93 ± 0.52
8.95 ± 0.49
8.44 ± 0.43
9.01 ± 0.7
8.54 ± 0.26
TUR 62 ± 15.62
47.21 ± 17.28
72.22 ± 19.5
74.14 ± 25.86
21.23 ± 4.49
14.81 ± 8.11
16 ± 9.32
10.44 ± 5.4
ALK 542 ± 101.6
326.07 ± 83.78
379.55 ± 52.24
406.61 ± 53.45
309.6 ± 6.13
297.91± 86.6
293.3 ± 6.6
267.6 ± 41
EC (µScm-1)
1348 ± 203
1337.8 ± 67.13
934.44± 61.19
1037± 108.47
920.2 ± 4.71
710.2 ± 99.9
520± 64.6
550.5 ± 43.9
TDS (ppm)
1010 ± 6.88
971.73 ± 53.95
708.02± 37.98
770.5 ± 75.35
667.5 ± 62.2
579.2 ± 67.7
375± 59.6
400.1 ± 62
SAL (ppm)
710 ± 10.74
637.58 ± 97
509 ± 81.21
514.5 ± 77.39
491.7 ± 92.8
466.5 ± 41.1
249.9 ± 42
234.7 ± 21.5
DO (mgL-1)
0.89 ± 1.21
4.89 ± 5.09
0.53 ± 0.55
2.31 ± 2.6
8.92 ± 2.4
7.46 ± 1.33
4.8 ± 4.89
7.04 ± 1.67
BOD (mgL-1)
45.19 ± 22
49.43 ± 37.73
59.54 ± 17.37
41.29 ± 13.7
27.8 ± 16.6
17.99 ± 8.46
8.47 ± 6
7.8 ± 5.44
COD (mgL-1)
108.4 ± 32.5
123.99 ± 75.38
158.5 ± 80.6
129.45 ± 42.6
65.2 ± 31.3
42.36 ± 19.3
27.2 ±10
22.18 ± 7.68
TDS (mgL-1)
383.8 ± 71.5
296.98 ± 41.89
259 ± 33.71
221.6 ± 77.23
225.3 ± 54.4
219.2 ± 9.19
159.6 ± 27
162.8 ± 36.7
CaH (mgL-1)
346.9 ± 72
187.3 ± 74.04
154.23 ± 34.6
168.4 ± 83.82
214.9 ± 45.7
181.3 ± 46.9
130± 31
89.3 ± 35.54
CHL (mgL-1)
285.1 ± 68.5
259.67 ± 83.18
294.2 ± 206.03
219.8 ± 111.42
207.5 ± 133.29
139.7 ± 42.24
151.9 ± 71
117.1 ± 50
N
(mgL-1)
0.33 ± 0.21
0.41 ± 0.21
0.19 ± 0.12
0.18 ± 0.13
0.212 ± 0.3
0.07 ± 0.0489
0.34 ± 0.7
0.5± 0.78
P
(mgL-1)
1.8 ± 0.5
1.6 ± 1.07
1.15 ± 0.87
1.27 ± 1.06
0.13 ± 0.07
0.33 ± 0.41
0.1 ± 0.05
0.135 ± 0.08
SEASONALITY OF BENTHIC DIATAOMS
80
Figure 10. Bar graph showing variation in water quality variables viz., a. pH, b. water
temperature and c. electric conductivity, at all sampling sites across seasons. Color code,
blue-premonsoon, red- monsoon and green- post monsoon.
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Figure 11. Bar graph showing variation in water quality variables viz., a. Phosphates,
b.Nitrates and c. Chlorides, at all sampling sites across seasons. Color code, blue-
premonsoon, red- monsoon and green- post monsoon.
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6.4.1 Diatom distribution
165 species belonging to 41 genera were recorded during the current study. The taxa
that occurred with >10% relative abundance (RA) noticed at least in one sampling site
were considered for further analysis. Common and dominant taxa were Achnanthidium
sp. (ACHD), Craticula ambigua (Ehrenberg) Mann (CAMB), Craticula accomoda (Hustedt)
Mann (CACC), Gomphonema parvulum Kutzing (GPAR), Gomphonema sp. (GOMP),
Nitzschia palea (Kutzg) W.Smith (NPAL), Nitzschia umbonata (Ehrenberg) Lange-
Bertalot (NUMB), Cyclotella meneghiniana Kutzing (CMEN), Cymbella sp. (CYMB) and
Fragilaria sp. (FRAG) in the order of decreasing % relative abundance. Diatoms
dominated at high saprobic conditions were CAMB, CACC, GPAR, CMEN, NPAL
and NUMB at Yellamallappachetty and Varthur wetlands. Diatom composition at
Valley school was characteristic of ACHD, Caloneis bacillum (Grunow) Cl. (CBAC),
Gyrosigma attenuatum (Kützing) Cleve (GATT), Gyrosigma parkeri (Horrison) Elomore
(GPRK), Rophalodia gibba (Ehr.) O. Müller var. gibba (RGIB) at inlet while ACHD,
CYMB, Navicula subrhynchocephala Hustedt (NSUB) and RGIB at outlet station.
Vaderahalli, unlike former wetlands had different community structure with ACHD,
CYMB, Cymbella kappi (Cholnoky) Cholnoky (CKAP), Fragilaria biceps (Kützing) Lange-
Bertalot (FBCP), FRAG, GPAR and Nitzschia taylorii (NTYL) at inlet and
Achnanthidium sp., Amphora veneta Kützing (AVEN), Cymbella sp., Fragialria nanana
Lange-Bertalot (FNAN), FBCP, FRAG, Gomphonema gracile Ehernberg (GGRA) and
RGIB at outlet sampling site.
Among all, five most abundant taxa (>30% ra) such as NPAL, CMEN, ACHD and
CYMB were analyzed to investigate whether seasonal patterns or anthropogenic
activities influence on formation of diatom community structure. Figure 12 illustrates
monthly variations observed in the distribution of species. Nitzschia palea (NPAL) did
not reflect any seasonal pattern but abundantly found across all months. Cyclotella
meneghiniana (CMEN) being eutrophilic taxa, showed a high percent relative abundance
in dry seasons (May-June) but was found to be in less numbers in monsoon months
where low nutrient concentrations were recorded in waters due to dilution factor.
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Achnanthidium (ACHD) and Cymbella (CYMB) showed a clear pattern of seasonal
variation with prolific growth in monsoon months (low nutrients level) while replaced
by CMEN in dry months. Figure 13 explains the site wise (spatial) distributions of
dominate diatoms, justifying anthropogenic activity and its influence on wetland’s
diatom flora. Hypereutrophic affectionate diatoms such as NPAL and CMEN were
inhabited at Varthur and Yellammallappa chetty wetlands with more than 40% and
30% RA respectively. These two wetlands are characteristic of heavy pollution in terms
of BOD, COD and conductivity, which receive surrounding domestic sewage
contaminated water and is evident at inflow region. Whereas, ACHD (>20%) and
CYMB (>10%) occupied and dominanted Valley school and Vaderahalli, which are
oligotrophic-mesotrophic in nature. Though eutrophic condition favors the growth of
saprobic taxa like members of genus Nitzschia, the abundant growth of Achnanthidium
and Cymbella also indicated prolific growth at mesotrophic- oligotrophic conditions as
observed in this study.
Variation in species turnover (T) showed clear difference between polluted and
unpolluted sites and were comparable to water chemistry (Figure 14). The percent (%)
turnover ranged from 0-76 % and 0- 77.7% at Yellamallappa chetty and Varthur sites,
while Valley school represented 28.5- 80.4% of species turnover. The highest turnover
of 90.44% was observed at Vaderahalli in July month, which specified that the change
in the diatom composition might be due to variation in seasonal pattern. This was
followed by vaderahalli outlet (VDO) with 88.2% in April and 84% in December. One-
way ANOVA showed significant difference in the % turnover among sites i.e., polluted
YL and VR vs. unpolluted VY and VD (F = 3.587; p = 0.02). The species turnover
was less than 70% in YL and VR while it accounted for more than 75% at VY and VD
(in at least > 6 months). Duration of presence of taxa across 12 months was analysed
through persistent analysis (Figure 15). % Relative abundance (% RA) of taxa, which
continued to be abundantly existent across 12 months was found to be more than
60%. The higher % RA was reflective of species autecology i.e, availability of favored
habitat for prolific growth of particular taxa. Although few species showed 40% RA,
the persistency did not exceed more than 6 months and was replaced with dominant
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84
species, which shows clear evidence of effect of physical and chemical factors on
diatoms distribution. Yellamallappa chetty and Varthur wetlands with heavy pollution
loads (see Table 10), showed persistence and abundant growth of CMEN and NPAL
for more than 6 months. Wetlands at Vaderahalli and Valley school, comparatively less
polluted revealed low species persistency because of evenly distribution across seasons.
Figure 12. Month wise (Temporal) distributional pattern among dominant
diatom taxa across sampling sites
SEASONALITY OF BENTHIC DIATAOMS
85
Figure 13. Site wise (spatial) distributional pattern among dominant diatoms across
months.
Figure 14. Box plot of percentage of turnover at eight sites over 12 months. Turnover is
expressed as the percentage of total species that were gained and lost.
SEASONALITY OF BENTHIC DIATAOMS
86
6.5 Discussion
Physical and chemical parameters of water play an important role in species
community structure formation, particularly the primary producers, which form the
basis of the food chain. The study proposed two main outcomes, first indicated the
seasonal variation among water physical and chemical variables and second
differentiated the role of seasonal and anthropogenic activities with the aid of diatom
assemblages. Variables such as conductivity, biological oxygen demand and chemical
oxygen demand at Varthur (VR) and Yellammallappa chetty (YL) wetlands with higher
nutrient concentrations differed distinctly from that of Vaderahalli and Valley school
wetlands (Figure 10). Conductivity at VR and YL wetlands exceeded BIS limits due to
the continuous inflow of untreated sewage and industrial effluents influencing fish,
Figure 15. Percentage relative abundance of persistent taxa over 12 months and across 8
sampling sites.
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87
amphibians and microbial diversity. Fish gut samples of sewage fed lakes have showed
the accumulation of 50% carbon and 91% nitrogen (Roger, 1999). Elevated
conductivity and organic nutrients reflects contamination due to sewage inflow and
other anthropogenic activities (Muwanga and Barifaijo, 2006; Pandey et al., 2007;
Karbassi et al., 2007). Human activities on all spatial scale affect quality and quantity of
water in higher percentage than the natural or global climate change (Peters and
Meybeck, 2000; Pejman et al., 2009). Moderate quantity of organic carbon is required in
metabolic cycles of aquatic microorganisms, however, when it exceeds would result in
blooming of diatoms and geen algae. Other factors like availability of nutrients,
temperature and light internsity are responsible for varying diatom community
composition (Rosemond et al., 2000).
Second outcome was the influence of chemical drivers on diatom community
composition, which separated anthropogenically polluted wetlands and wetlands with
seasonal variations. The maximum growth of diatoms was observed in post monsoon
months (Karthick et al., press), and low abundance in monsoon season on epilithic
habitats (Nautiyal et al., 1996). The maximum taxa among recorded were cosmopolitan
and possibly meso-eutrophilic species except Achnanthidium and Cymbella. The
description of two new species belongs to genus Nitzschia from wetlands in Bangalore
indicates the rich biodiversity of the least studied urban region (Alakananda et al.,
2012b). The evolution in species tolerance and sensitivity range and development of
community structure explained the need for urban wetlands and biodiversity studies.
Dominant taxa such as N. palea and C. meneghiniana inhabited polluted wetlands
(Varthur & Yellamallappa) during entire year while taxa of genus Achnanthidium and
Cymbella were abundant at good water bodies (Vaderahalli & Valley School) (Figure 12).
Achnanthidium reflected the oligo to mesotrophic lake condition in terms of nutrients
and thus showed a seasonal pattern. Further polluted wetlands continued to receive
contaminated water throughout the year and hence bloom of taxa like C. meneghiniana,
which it is considered as indicators of trophic status (Mitrovic et al., 2009). Spatial
analysis summarized the water body and related human activities in its watershed that
are significant and deciding factor in balancing ecosystem health (Figure 13). Diatom
SEASONALITY OF BENTHIC DIATAOMS
88
assemblages at YL and VR wetlands were influenced by higher values of conductance
and lower oxygen saturation and were typified by the abundance of N. palea, G.
parvulum and C. meneghiniana. During the monsoon months, the abundance of these
species decreased drastically at outlet regions. C. meneghiniana was recorded to be more
dominant at pH of 7.7 to 7.9 and at increased EC (>900 µScm-1). This range of pH and
EC confines the distribution of C. meneghiniana to extremely eutrophic water condition.
Mitrovic et al., 2010 suggested that C. meneghiniana can bloom with maximum density at
faster rates at higher temperature as found in dry seasons. Presence of Achnanthidium
sp. was observed at all sampling sites of Vaderahalli whereas the abundance was
optimum at pH 8.1 to 8.2 and at EC 600 to 650 µScm-1 and abundance decreased at
elevated conductivity concentration. N. palea was distributed at all sampling sites and
revealed a wide range of optima though was less abundant at alkaline pH. N. palea was
also abundant at its optima of EC i.e., more than 850 µScm-1. While, low EC
concentration (<800 µScm-1) was limiting the distribution of N. palea. Although
cosmopolitan eutrophilic taxa are studied worldwide, the autecological preferences
have not been optimized because of spatial and seasonal change from temperate to
tropical region wetlands (van Dam et al., 1994; Blanco et al., 2008). Studies of the
autecology of seasonal dominant species and several indicator groups of diatoms and
other phytoplankton species would develop better understanding about species
habitation, prediction of bloom formation and subsequent management plans (Porter,
2008).
The percent species turnover was more than 50% at all sampling sites indicating
relationship between water quality and species turnover rate. Species turnover recorded
to be highest (more than 75%) at less polluted Vaderahalli followed by Valley school.
This trend is because of loss of one or more taxa during dry seasons and gained after
monsoons (Figure 14 and 15). Polluted wetlands (VR and YL) were characteristic of
moderate to less species turnover percent (<60%) and were comparable with former
wetlands reasoning that the dominant taxa were persistent throughout the studied year
(12 months). These wetlands in urban region in the threshold of eutrophication
inhabited pollution tolerant taxa. Soininen and Eloranta, 2004 recorded species
SEASONALITY OF BENTHIC DIATAOMS
89
turnover rate at Boreal stream wetlands, which was approx. 50% comparatively less
than tropical wetlands (Karthick et al., in press). Wischnewski et al., 2011 recorded a
stable diatom species turnover at wetlands of tibetean plateau over the past two
decades and revealed the change and impact of land cover is insignificant and this
might not be true in highly polluted regions. High persistence and relative abundance
of diatom species explained that the equal distribution might have minimized the loss
of species mainly in less disturbed sampling sites. The persistence of taxa could be due
to the regular metabolic process and cell division that provides species to occupy
habitat in all regions (Soininen and Heino, 2005).
6.6 Conclusion
Physical and chemical variables of wetlands influence several group of microorganisms,
its distribution or its ecology. Impact assessment is requisite with appropriate data to
facilitate interpretation on water quality and ecological values of an ecosystem. In our
study, diatoms provided reliable information on varying factors at seasonal and spatial
scales. Water quality patterns in polluted wetlands and relatively good water wetlands
were distinguished through diatom distribution analysis. Further diatom based
biomonitoring investigations, aid in understanding the role of spatial or anthropogenic
factors. Region specific taxa and its preferential studies would reflect the importance of
indicator species revealing pollution levels in aquatic ecosystems.