CONTENTS-
Abstract
Introduction
Study Area and Methodology
Results and Discussions
References

Lentic water bodies receive   nutrients from allochthonous and autochthonous   sources and they promote the succession of aquatic macrophytes.   The present study comprises nutrient condition of sediment and water, and its influence on the growth and diversity of aquatic plants.   During the study period (1999-2000), water and sediment samples were collected and analysed for calcium (Ca 2+ ), magnesium (Mg + ), sodium (Na + ), potassium (K + ), nitrates (NO 3 + ) and phosphates (PO 4 3- ).   Similarly aquatic macrophytes were collected and identified to know the distribution and diversity of macrophytes.    The present study concluded that, increase in the nitrate and phosphate concentration both in sediment and water, influence   the distribution and diversity of macrophytic vegetation and luxuriant growth with great succession of dominant species   was encountered.

Aquatic plants play a key role in biogeochemical cycles and food webs of living things in the lentic water bodies. On the other hand aquatic plants are primary producers of food in aquatic ecosystem, and further the absence of aquatic flora may also lead to the absence of fauna. Distribution of macrophytic plants and abundance also indicate the water quality.   In natural ecosystem, macrophytes   remove both toxic and non-toxic elements in the sediments and water (Narayana and Somashekar, 1997).   The trophic status is mainly influenced by the variety of communities and indicator species occurring at the source.   Moreover, metabolic activities of macrophytic communities accelerate the physico-chemical conditions of the stream. Submerged aquatic macrophytes are one of the most important components of the littoral zones of lakes.   Field studies conducted by Carpenter and Lodge (1986), Balls et al ., (1989) and Sondergaard et al ., (1996) evidenced that submerged macrophytes have an important role in restoration of shallow eutrophic lakes.   Therefore, from an engineering point of view, evaluation of life cycles of macrophytes is a key issue before using them in restoration of lakes (Carpenter and Adams, 1977; Asaeda and Bon, 1997).

Macrophytes also   take up a large amount of nutrients from the sediment and water. But after death and decay, the nutrient load is again increased in the sediment.    In the succeeding decomposition process, accumulated organic matter and nutrients are released, which has a significant influence on the lake ecosystem.   The release of ammonia and phosphorous raises the nutrient concentration in the overlying waters and the oxygen consumption in the chemical and biological decomposition process may decrease the dissolved oxygen level in the overlying waters as well as sediments (Jewell, 1971; Pereira et al ., 1994).

Sediment and water samples were collected from four sites namely Lakkavally, Rangenahally, Duglapura and Kadlekere ponds. The study area is located in malnad region (Western Ghat region) situated 15 kilometers away from Bhadra wild life sanctuary and Bhadra reservoir.   The   study area lies at latitude of 13º 42' 10" N and longitude 75º 38º 20" S. The source of water   to the ponds is from Bhadra canal linked from Bhadra river. Further the third sampling station namely Duglapura pond is considered as a reservoir, and    serves drinking water needs of   people of Tarikere.   The different physico-chemical parameters such as Ca 2+ , Mg + , Na + , K+, PO 4 -3 and nitrogen content ware analysed using the standard   methods (APHA, 1992).   Similarly, aquatic plants were also collected and preserved for identification. The   standard books and manuals were used for identification. (Fasset, 1975; Cook, 1974; Haslam, 1971; and Britto, 1991).

The present data reveals that the concentration of all inorganic ions in the sediment and water   are variable   from different ponds.   The average values of Ca 2+ , Mg 2+ , Na + , K + , PO 4 -3 and NO 3 +   are presented in Table 1.  

Table 1. Average values of Nutrient concentration in   water and sediment samples

Index

P 2 = Rangenahalli pond             S = Sediment samples

P 3 = Duglapura pond                (Values in mg/kg in sediment)

P 4 = Kadlekere pond                (Values in mg/l in water).

The results indicate that the calcium ions show higher concentration in water samples from Lakkvally pond compared to other sampling stations.   Similarly Mg + values   show   higher concentration in sediment at Lakkavally and Rangenahally.   Similarly the other parameters such as Na + and K + , phosphorous and nitrogen   show higher concentrations in sediment than water.  

Distribution of aquatic plants in each pond was determined   to understand the species diversity, abundance and occurrence of rare species.   The presence and absence of species was noted and is presented in Table 2.   In the present study twenty-eight different species of aquatic plants are identified from all the ponds.   But species distribution from each pond is greatly varied, which may be   due the physico-chemical characteristics of water and sediment.   The disturbance from human and domestic activity leads to the loss of macrophytic vegetation.

Table 2.   Distribution and species diversity of aquatic plants recorded from different ponds

Index : + = Present,   - = Absent.

It is confirmed that Lakkavally pond   is rich in few aquatic plants such as Ceratophyllum demersum, Jussiea repens, Monochoria vaginalis, Najas minor, pteris, Pista stratiotes and Polygonum sp .   The pond   receives water from surrounding paddy fields and sewage from Lakkavally town. Due to this, the pond has   become highly eutrophic. .   On the other hand, sediment load has increased due to the runoff   from paddy fields. Thus lake depth is slowly reduced, and it supports   rich   semi-aquatic plants such as Cyperus and other grass species.

Distribution and species diversity of macrophytic vegetation at Rangenahally pond supports   rich   aquatic and semi-aquatic plants.   The pond is surrounded by paddy fields, the run-off   has led to the increase   in nutrient load. In addition to this,   farmers   have encroached the catchment area of the lake and   now half of the lake is totally filled with sediment and covered with semi-aquatic plants like Polygonum members, Cyperus rotundus, Grass family, Ipomea aquatica and other plants.   Similarly, floating and submerged plants namely Azolla pinnata, Ceratophyllum demersum, Hydrilla verticillata, Jussia sp., Monochoria vaginalis, Nelumbo nucifera, Nymphaea sp. ,   Trapa bispinosa and pteridophytic plants such as pteris are abundant.

The third sampling station called as Duglapura pond is considered as a clean water pond,    because Bhadra canal water is linked to the pond for pumping   drinking water to Tarikere city.   Interestingly this pond also supports   a number of different species of aquatic and semi-aquatic plants. Interestingly Typha latifolia   covers    the pond and some of the semi-aquatic plants support rich   bird diversity.   Finally   Kadlekere pond,   has a half moon shaped structure and   is also surrounded by paddy fields.   Comparatively sediment load is less in Kadlekere and Duglapura ponds.

A number of investigators studied   the lentic ecosystem and concluded that the physico-chemical characters influence the growth, species distribution, indicator groups and pollution tolerant species   (Narayana and Somashekar, 2002).   The increasing concentration of phosphorous and nitrogen have important effects on the primary production.   Waglenska et al ., 1987 observed a close relationship between phytoplankton abundance and diversity of submerged macrophytes.   The dense stands of macrophytes release large amounts of inorganic nutrients (Dawidowicz et al ., 1987).

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Britto., S.J. (1991). Macrophytes collection Procedure. St.Joseph collage, Tiruchirapally, pp. 1-33.

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Cook, C.D.K.(1974). Water plants of the world. A manual for the identification of the genera of fresh water macrophytes. W.Junk.   B.V. Publishers, The Hague, pp 561.

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