BIODIVERSITY AND ECOLOGY OF TWO ENDANGERED WETLANDS
OF TAMILNADUCOAST – KALUVELI AND OSUTERI
Manimekhalan M., Yoganand T.R.K., Rajan V., Amruth M., Ilangovan K. and Sharma C.B.S.R.
SalimAliSchool of Ecology and Environmental Sciences
PondicherryUniversity, Pondicherry 605 014, India.
Water storage systems play an important role in coastal management. Kaluveli and Ousteri are the major reservoirs along the East Coast of Tamilnadu and Pondicherry. Ecological status of these were studied to obtain the base line data on water, soil, flora, fauna and their interactions with local villages as a part of our ongoing work on the irrigation tanks of Tamil Nadu. Inferences were drawn from these so as to understand the system and help in maintaining it on a long-term basis. A combination of survey and analytical methods were employed in pursuit of our objectives.
Kaluveli is a fresh water swamp of about 70 sq.km. The soil is sandy-loamy to clayey. Water flows in from the local catchment. It is connected to the north to the Yedayanthittu estuary. The biodiversity is as follows: Plants 163 species; Butterflies: 19; Fishes 11; Amphibians: 6; Reptiles: 16; Birds: 120; Mammals: 15. The 14 villages continuously encroach this wetland for agriculture. The number of aquaculture farms functioning now are expected to increase and kill the wetland soon.
Ousteri is an ancient tank of about 15 sq.km. The soil is clayey. Water inflow is through Suthukeny channel from the Sankaraparani river and the local catchment. The biodiversity is as follows: Plants 101 species; Butterflies: 18; Fishes 10; Amphibians: 4; Reptiles: 20; Birds: 90; Mammals: 11. The major threats are pollution, eutrophication and encroachment for agriculture.
Since human settlements are intimately connected to the storage systems, developmental activities will continue ceaselessly. Therefore conservation has to be done simultaneously. The present experience underscores the urgent need for census and valuing of all coastal tanks preferably employing a Rapid Evaluation System.
With the increasing water scarcities, traditional knowledge is being applied to get the maximum potential from storage systems. Maintaining the ecological balance of the system has become important to utilise the resource of the system. The ecology and resourcefulness of the system have to be studied for a sustainable use of the system.
Tanks are structures that collect and store runoff water and bound by earthen embankments. There may be additional engineering works. This water is either used for paddy cultivation or for supplementary irrigation of dry crops. Since the income from irrigated crops is higher than from rain-fed crops, surface reservoirs have an impact upon productivity, employment and income in the rural sector.
There are about 40,000 tanks scattered throughout Tamilnadu, of which only 7,400 have an ayacut of more than 40 ha. Though the total potential under minor irrigation is one mha, the productivity is only one third of its potential because of improper management. The socio-political, technological and economic backgrounds have recently undergone a major change during the green revolution that has led to the breaking up of the traditional balances. This may further be aggravated under the impact of the new economic policies now pursued by the rulers. As 95% of the surface water in Tamilnadu is already being harvested, the need to improve the management and the efficiency of these systems is plainly urgent.
Most tanks are small farmer managed systems. The area, the associated people and the agro-economic conditions around the tanks are variable only slightly. Though 60% of Tamilnadu is drought prone, only a third of the annual precipitation is utilised. It is therefore imperative to lay stress on storage of rainfall. That is why the state became a land of ponds and tanks. Unfortunately, however many of these are being filled up and built upon. Thus Tamilnadu has been having more than its share of water shortage. The ecological status of Kaluveli and Ousteri were studied to obtain the base line data on water, soil, flora, fauna and their interactions with local villages as a part of our ongoing work on the irrigation tanks of Tamilnadu. Inferences were drawn from these to understand the system and for long-term maintainance . Since human settlements are intimately connected to the storage systems, infrastructure development and man induced will continue ceaselessly. Therefore conservation and development of the system has to go simultaneously. With the present study a model was developed for studing the coastal tanks through Census and Valuing employing a Rapid Evaluation System.
MATERIALS AND METHODS
1. Study area
Kaluveli, a large fresh water swamp is located in South Arcot District of Tamil Nadu about 20 km north of Pondicherry (12 5’-12 10’ N X 79 47’ – 79 55’ E) with an geographical area of 7040 ha, and a catchment of 75.7sq.Km. It is connected to Yedayanthittu estuary through a tidal creek Uppukali, 8 km further north. (Fig 1) Kaluveli is fed by precipitation of Northeast monsoons and foreshore areas of the Bay of Bengal. The rainfall pattern is asymmetrical falls during October-November.
Ousteri tank is located 10 km west of Pondicherry (11 57’ N X 79 45;E) in an area of 700ha, part of which is in TamilnaduState (Fig 2). The region has a tropical monsoon climate with an average rainfall of 125 cm/yr. The tank is characterised by the presence of input and output channels as well as' seasonal rainfall. Water is generally available for 6-9 months per year and is used for agriculture and domestic purposes. The rain fall regime is dissymmetrical and the water level fluctuates with the rainfall.
Combinations of different methods were adopted in the collection, analysis, interpretation and presentation of data. These include field survey of the tank environment for collecting soil and water samples, plant specimens, animal observations and to elicit anecdotal information, analysis of soil and water samples, identification of biota and interviewing the people and officials concerned with the tanks.
a. Field Survey
Reconnaissance of the tank was carried out during the first few field visits. Background information on the history, engineering, hydrological and climatic details of the tank were collected from local administration and public work departments.
Soil was collected from four regions foreshore, bed, ayacut and wastelands. Samples were analysed for the following parameters; texture, pH, electrical conductivity, nitrogen, phosphorus and potassium as per the standard methods of the Indian Standards Institution (1966).
Water samples were collected from inlet channel, stagnant water, outlet channel, dug or bore wells. The samples were analysed for the following parameters; pH, electrical conductivity, calcium, magnesium, sodium pottasium, carbonate, bicarbonate and chloride as per the standard methods prescribed by Indian Standard Institution (1966).
All habitats of all tanks were repeatedly surveyed for enumerating flowering plant species. The survey involved collection, preservation and identification of the specimens. A recent work on the regional flora (Matthew 1992) was used for identification.
Six animal classes were selected to study the species richness by check listing species during filed surveys. These are butterflies, fishes, amphibians, reptiles, birds and mammals.
Butterflies: Butterflies were net-trapped in and around the tanks.Their developmental stages, interactions with plants and other animals were also recorded. Specimens were identified with the help of standard keys. Fishes: The fish caught by the local fishermen were screened for different species. Specimens were identified with the help of Chandy’s work (1970). Amphibians and Reptiles: Various habitats like agriculture fields, afforested lands and other areas were randomly surveyed for these. These were also recorded during other field surveys. Identifications were made with the help of Daniel’s work (1983). Birds: Birds were sampled randomly in various habitats during morning and evening and identified using the treatise of Ali and Ripley (1987). Observations were made on their food habits and migratory status. Mammals: Various habitats in and around the tanks were surveyed for mammals. Also observations of the local people were noted and crosschecked with that of the investigators.
f. Culture Systems
Agriculture, aquaculture and social forestry of each tank was surveyed on the field and enquired from the local people and government officials. Perceptions of local people on their tank ecosystem were obtained by using a monitoring schedule. Background information was checked with the village headman or old and knowledgeable people.
Characteristics of Kaluveli
The soil of the tank bed, foreshore and ayacuts on the west are sandy loamy and clayey in nature. pH varied widely in the bed (4.5 – 8.4) and to a far less extent in the agricultural fields. Electrical conductivity also varied widely in the bed (0.1 – 5.3mS/cm) and foreshore (0.1 – 3.2mS/cm), but was consistently low in the ayacut, showing an increasing trend from south to north. The nutrients also varied more widely in the foreshore (N:30-135; P:1.2-62 and K:29-378) and in tank bed (N:65-88; P:1.9-129 and K:34-600) and to a far less extent in the ayacut (N:65-88; P:0.8-11; and .0-105). (Table 1)
The inflow into the lake depends mainly on the rainfall in the local catchment areas. During cyclones and when the fresh water inflow from catchment is less, seawater from the estuary flows in through the Uppukali Creek in the North. The pH of water has exhibited a narrow range both in the North (7.2 - 9.0) and South (6.9 - 8.7) Electrical conductivity, SAR, Ca, Mg, Na, K, CO, HCO, Cl have demonstrated variations in the Northern and Southern regions, the ranges being wider in the former. (Table 2)
There are total of 163 species belonging to 153 genera and 79 families. These include hydrophytes (6) grasses and sedges (17) climbers (20) shrubs (34) trees (34) and herbs (52). Diversity exists not only at the taxanomical level but also in habitat preferences. Suaeda maritima a halophyte occurs towards north near Kunimedu. Reeds are restricted to the middle part of the tank. Forest species like Flacourtia indica, Memecylon umbellatem, Albezia amara etc. and some scrub jungle species are widely scattered in the thickets. The hydrophytes are two species of Nymphaea, Nelumbo, Vallisneria and a pteridophyte Maselia. (Table 3)
There are 187 species distributed among 142 genera and 82 families. These include 19 Butterflies (from 6 families), 11 Fishes (from 8 families), 6 Amphibians (from 1 family), 16 Reptiles (from 9 families) and 15 Mammals (from 10 families) Many species are rare in distribution especially among mammals. For example, the bird Ruddy Sheldruck and the mammal Small Indian civet cat are endangered species. There are totally 118 bird species belonging to 92 genera and 50 families. They have varied food habits but majority are feeders of aquatic organisms. (Table 4)
e. Culture systems
Millets, groundnut and cashew are the usual crops around the tank. Paddy is cultivated in Southeast and Northeast only during monsoons. Fertilisers and pesticides are frequently used.
Aquaculture practice has started to emerge in the northern part, The water body has many species of fishes like Tilapia, Anabas and Mullets and crustaceans like crabs and prawns.
iii. Wetland forestry
Southwest part of the tank is full of Prosopis and Casuarina. In the foreshore, panchayats as well as private parties maintain casuarina, eucalyptus, piosopis and acacia plantations. Wastelands on the Auroville plateau have been completely re-vegetated with fast growing multipurpose tree species (Table 5).
There are about 14 villages around Kaluveli dependent on this tank for agriculture . The tank is exploited for fisheries, guano-enriched silt, grazing and collection of resource reed and firewood. Locals have reclaimed vast areas of the tank for agriculture.
There are no industries on the banks. But the run-off from the surrounding agricultural fields may contain pesticides. And the emerging aquaculture farms are likely to kill the system. Salinity due to the estuarine water intrusion is common.
Characteristic of Ousteri
Soil is clayey. pH ranges from 5.6 to 8.4 and electrical conductivity from 0.2 to 5.20mS/cm. The lime status was found to be Nil. Among the macro-nutrients, Nitrogen varies from 2.8 to 182 Kg/acre, Phosphorus from 2.8 to 55 Kg/acre and Potassium from 72 to 620. The Nitrogen distribution varied widely from very low to medium level (2.8-182), Phosphorous (2.8-55) and Potassium (72-620) showed variations from very low to very high, but the mean values indicate adequacy. It is moderate in nutrient status(Table 1)
The water is slightly alkaline and saline with pH ranging between 7.3 and 8.7 and electrical conductivity between 0.3 and 3.5. The range of cations were found to be as follows - Calcium: 0.6 and 9.4 Me/l, Magnesium: 0.4-6.2, Sodium: 0.1 -19.4 and Potassium: 0.02 - 0.11 Me/l. Anions like Carbonates ranged between 0.2 and 0.9 Me/l, Bicarbonates between 1.7 and 9.20 and Chlorides between 0.8 and 2.2 Me/l. High values of pH (8.2) is not substantiated by the E.C Value (0.63 units) which is relatively low. (Table 2).
In total there are 101 species distributed in 95 genera and 55 families. These are terrestrial, semi-terrestrial and aquatic variety colonising the tank bed, margins and other areas i.e. there are 6 habit types distributed among 4 habit guides. Of these 52 are found to have considerable economic and/or ecological importance. Commonly found hydrophytes are Vetiveria zizanioides, Typha angustata, Marselia and two species of Nymphaea (Table 3).
In total there are 153 species distributed among 123 genera and 78 families. Though many species of grasshoppers, dragon files, spiders, bugs and beetles were seen only butterflies (18 species), fishes (10), amphibians (4), reptiles (20), birds (82) and mammals (11) were checklisted. They were found in four habitat guilds. There are 90 species of birds belonging to 74 genera and 48 families. Their food habits range from Frugivory, nectarivory, insectivory feeding on aquatic and terrestrial organisms (Table 4, Table 4a).
e. Culture system
Culture systems include artificial and semi-natural ecosystems like agriculture, aquaculture, social forestry and private plantations (Table 6). These are an inseparable part of the tank system both structurally and functionally.
Paddy, sugarcane, millet and groundnut are cultivated in approximately an area of 1550 ha. of registered ayacut. This tank benefits the villages – Gudapakkam, Sendanattam, Villianur, Poraiyur, Oussudu, Odiyanpattu and Ozhukarai in Pondicherry and Perumbai in Tamilnadu. A total of 1465 ha is approximately benefited and harvested twice a year.
There is no managed aquaculture in Ousteri tank Tilapia mossambica a fish species introduced from Africa forms the main catch. The fish produce is leased out every year to private parties.
iii. Social forestry
Casuarina, eucalyptus, prosopis and acacia plantations are maintained by panchayats as well as by private parties. The North-Eastern banks are under prosopis plantation while others are scattered.
The seven villages are directly depenant on this tank. The natural fisheries benefit the local people. The tank serves as the main source of recharging ground water, which is extracted through wells and borewells.
Industrial waste is dumped from the Mettupalayam, Sedrapet industrial estates along the southern and eastern regions of the tank, further the rain water washes the pollutants from Sedrapet Industrial estate into the northwest region of the tank.
The tank ecosystem consists of all the areas and life around the water body, such as catchments, ayacut, villages, channels, wells, agriculture, animal husbandry, social forestry along with soil, water, plants, animals and supply channels. These systems have some features of irrigation reservoirs, natural lakes, shallow wetlands and riverine shorelines. Consequently subsystems vary from one another among tanks. A few may have micro-habitats as in the case of Kaluveli. But in all the tank areas, the water body functions as a ‘cornerstone’ of the region, serving the needs of soil, water, plants and animals of the surrounding villages . In other words, the villages depending on this ‘ epicenter’ appear as a part of the tank ecosystem and not vice versa. Thus, if the tank is not there, many villages will not exist. The current pilot work reveals the inputs that each tank needs based on the size and nature of the ecosystem, ayacut, catchment, associated villages, agriculture, aquaculture, flora, fauna and soil.
There are many wells around the tank both conventional and bored, reducing the direct dependency of the villages on the tank. But the wells are dependent on the tanks for their lateral recharge. In this connection it is necessary to study the dynamics of the lateral seepage for proper location of wells, the groundwater potential, its potability, level of water table and potential for recharge from tank waters.
In Kaluveli pH is around the neutral range and Ousteri recorded higher value and greater diversity, this may be due to the human activities and water inputs from its own catchments and supply channels. Electrical conductivity is uniform in Ousteri and very high in the case of Kaluveli due to seawater intrusion. Nitrogen content is high in Ousteri and potassium is lowest at Kaluveli. The data collected from these tanks indicate variations only with respect to a few parameters while most others are rather uniform and need low inputs, if plant culture has to be widened (Table 1and Table 2).