CHAPTER 6: SEASONALITY OF BENTHIC DIATOM …shodhganga.inflibnet.ac.in/bitstream/10603/35936/12/chapter 6.pdfSEASONALITY OF BENTHIC DIATAOMS 77 taxa gained and lost between months

SEASONALITY OF BENTHIC DIATAOMS

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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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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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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


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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


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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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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


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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.


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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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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


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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


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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.

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CHAPTER 6: SEASONALITY OF BENTHIC DIATOM …shodhganga.inflibnet.ac.in/bitstream/10603/35936/12/chapter 6.pdfSEASONALITY OF BENTHIC DIATAOMS 77 taxa gained and lost between months