Abstract

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Aim of the study was to document the aquatic macrophyte wealth of a perennial fresh water wetland ecosystem called Ambattur lake (ARL) through qualitative survey. ARL is situated in Thiruvallur district of south India. This is the very first of its kind on ARL, exhibited the wealth of macrophytes. A total of 56 plant species including 52 Angiosperm and 4 Pteridophyte were observed and collected from the lake. All the collected species were identified and checked with regional floras and available checklists. The most speciose families were Poaceae followed by Cyperaceae and Nymphaeaceae. Among five morpho-ecologic groups, emergent anchored with 30 species dominated the lake followed by floating and floating leaved anchored. Bioresource extraction was documented through contact and personal interviews with the local people. Anthropogenic pressure is escalating around the lake. Further qualitative and ecological assessments are needed to conserve this irreplaceable and invaluable perennial ecosystem.

Introduction

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Lakes are complex ecosystems which support many life-forms including several vascular hydrophytes. The value of wetlands is often ignored and they are considered as ‘wastelands’. Many of the World’s wetlands have been drained and converted for other profitable uses (1). Many wetlands harbour several kinds of economically useful macrophytes. Their ecological value is yet to be estimated.   Studies on aquatic macrophytes are in its initial phase in South India and it requires immediate attention (2, 3). Rivers, soil moisture and relatively shallow groundwater basins are the principal sources of water for human (4). One percent of the world’s surface is covered by various fresh water habitats including the lakes (5). They support life of 7 % of the estimated 1.8 million described species (6), including 25 % of the estimated vertebrates.  Aquatic macrophytes can be used as a tool in the determination of pollution and nutrient level (7), water quality and lake condition (8), trophic status of lakes (9), pollutant degradation (10) and decontaminate waste water (11).  Urbanisation, industrialisation and bursting human population are the major threats to the fresh water ecosystem. Human interference is the main reason for the shrinkage of area and reduction of mean depth of the lakes of Thiruvallur district (3). For the first time we present the aquatic macrophyte wealth of a perennial lake called Ambattur lake in Thiruvallur district of Tamil Nadu state, South India.

Methods

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Ambattur lake (ARL) (13°09’82” N, 80°13’89” E), perennial in nature located in Thiruvallur district of Tamil Nadu state, India  has the area about ca. 50 ha surrounded by industries and human settlement (Illustration 1). The mean maximum and minimum temperatures of Thiruvallur district are 33 ºC and 24 ºC respectively with relative average humidity 76.8%. The average annual rainfall is around 1108 millimetres with two thirds of the annual rainfall received during the north east monsoon (September-December). As on 2001 survey the human population is 2.75 million. Mean depth of water column is varying across the season; in rainy season (September-December) the mean depth is ca. 3.5 m while in summer it drops around ca. 1.0-1.5 m. High volume of water is available in October. So far no studies are available on the biotic wealth of ARL.

Qualitative floristic survey was made through regular field visit during 2003-09 to record the aquatic macrophytes wealth of ARL. Angiosperm and Pteridophyte macrophytes were observed and collected include submerged, submerged anchored and floating leaved anchored, emergent anchored and free floating. The collected plant specimens were identified and confirmed with regional floras (12, 13, 14, 15, 16, 17) and regional checklist for hydrophytes (3). Binomial and author citation of all collected hydrophytes were checked with International Plant Names Index (http://www.ipni.org/ipni/plantnamesearchpage.do). Further the extraction of bio-resources from the study area was carried out through personal interviews in the regional language (Tamil). Voucher specimens were deposited in Pachaiyappa’s College Herbarium, Chennai. Changes in mean depth of lakes were noted in the month of October of every year from 2003-2009.

Results

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Macrophyte wealth

A total of 56 species including 52 flowering plants and 4 Pteridophyte species spread in 44 genera and 28 families were recorded. Present study, the first of its kind in this lake showed the aquatic macrophyte wealth of ARL. The most speciose families were Poaceae with five species followed by Cyperaceae, Nymphaeaceae and Polygalaceae (4 each). Convolvulaceae, Hydrocharitaceae, Lemnaceae, Najadaceae and Scrophulariaceae were represented by three species each. Whereas, only one species each was recorded for Acanthaceae, Alismataceae, Amaranthaceae, Aponogetonaceae, Asteraceae, Brassicaceae, Ceratophyllaceae, Lythraceae, Mimosaceae, Pontederiaceae, Sphenocleaceae and Typhaceae (Illustration 2). Nahlik and Mitsch (2006) reported that tropical wetlands are dominated by floating aquatic macrophytes. Though ARL is a sub tropical perennial lake it is dominated by emergent anchored morpho-ecologic group with 30 species followed by floating (eleven), floating leaved anchored (seven), submerged anchored (six) and submerged group with two species. Species richness appears to be influenced by seasonal variations. In rainy season (September-December) 44 species were available whereas in summer season (April-June) as many as 49 species were recorded. Marsilea quadrifolia, Nasturtium indicum, Cyperus bulbosa, C. rotundus, Ludwigia adscendens and L. perennis mostly grow during summer in low depth areas near the embankment. Five species such as Lemna gibba, L. polyrrhiza, Wolffia globosa, Pistia stratiotes, Eicchorna crassipes and Salvinia molesta showed the seasonal appearance. Earlier Udayakumar and Ajithadoss (3) reported 45 species of angiosperm macrophytes from five ephemeral lakes with maximum species richness of 36 macrophytes in Palavedu lake, situated 13 km far from present study area in Thiruvallur district. Data on fresh water ecosystem, inhabiting life forms, species distribution and richness, comprehensive taxonomical and ecological information are needed to assess the impacts of developmental activities on freshwater ecosystem (18). During water filling period (September-December) surface of water in the lake was completely covered by the pioneer coloniser such as Lemna gibba, L. polyrrhiza and Wolffia globosa. Increasing exploitations on freshwater ecosystem for human uses adversely affect wetland dependent species. Ever increasing human populations exert pressure on the freshwater ecosystem (http://www.populationaction.org/Publications/
Reports/People_in_the_Balance/Summary.shtml). Increasing sedimentation in the lake due to both natural and man made causes affect water quality and clarity (19). Addition of silt during rainy season, run off of garbage from human settlement, and draining of waste water into the lake from industries have resulted shrinkage of mean depth of the lake ca. 10 cm each year.

Bioresource extraction

For people below poverty line (BPL) the lake is to certain extent functions as a bio-resource in a sustainable way. Alternanthera sessilis, (ponnankanni keerai in Tamil) a common green is available throughout the year and it is harvested from the lake for human consumption. Each day ca. 20 kg of A. sessilis is collected from the lake; small bundles of greens weighing 200 grams each are put on the market each priced 2-5 rupees. Considerable quantity of Marsilea quadrifolia   collected from the lake is used as pot herb. Ipomoea carnea an aggressive alien invasive weed introduced to India in the nineteenth century (12) finds a place in the flower market, ca. 25 kg day^-1 is collected from the bunds of the lake. In early days of rainy season tubers of Aponogeton natans collected from the low depth areas is cooked and eaten. Hydrilla verticillata a submerged anchored plant is collected from lake and used as an oxygenator in fish growing man-made ponds. Occasionally the leaves of Neptunia prostrata are used as a green. Flowers of sacred plants Nymphaea nouchali and Nelumbo nucifera are sold in the market; matured seeds are eaten raw or roasted, and made into flour to make nutritious meal. Presence of Ipomoea carnea, Pistia stratiotes, Eichhornia crassipes, Salvinia molesta showed the clear indication of invasion of alien species in this perennial ecosystem. However, a detailed  study about  the suitability of these plants  for human consumption as supplemental food  or as feed for the cattle  has to be carried out as these are growing  in water that is dangerously polluted both industrially as well biologically.

Conclusion(s)

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The studies on fresh water ecosystem are essential in this ever-changing environment to assess the values of lakes in developing countries like India. In-depth knowledge on macrophyte biology will pave path for the development of new management techniques and enhance the efficacy of present techniques of lake management (20). Inhabitants around the lake are unaware about the importance of flora and fauna. Human mediated activities such as building construction, accumulation of garbage, encroachment, industrialisation and quarrying of soil are escalating around ARL. Further studies on impacts of pollutants, nutrient load, microphyte wealth, seed germination strategies, water quality and ecological quantitative studies are needed to conserve this lake and its invaluable biota in an efficient way. Assessment of biota, continuous monitoring and conservation of lake are the important components to safeguard the biological wealth of lentic and lotic fresh water ecosystems.

Acknowledgement(s)

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The first author thank the Department of Science and Technology, Government of India, New Delhi for their financial support through a INSPIRE Fellowship (Ref. no: DST/INSPIRE Fellowship/2009/[xxxix]).

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Source(s) of Funding

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Department of Science and Technology, Government of India, New Delhi, India (Ref. No. DST/INSPIRE Fellowship/2009/[xxxix)

Competing Interests

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No

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