INTRODUCTION:

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The Barak valley region of Assam is blessed with a good number of floodplain wetlands harbouring a great variety of aquatic macrophytes. Information on phytosociological data for AM in any waterbody is of immense importance to understand the wetland ecosystem. Several works have been done on the phytosociology of different macrophytic species in different freshwater bodies of India and abroad (Billore and Vyas, 1981; Biswas and Calder, 1984; Cottam and Curtis, 1956; Crowder et al., 1977; Dey, 1981; Dey and Kar, 1989; Hutchinson, 1975; Kar and Barbhuiya, 2000; Mishra, 1974; Purohit and Singh, 1981; Shah and Abbas, 1979; Unni, 1971; Zutshi et al., 1980). But very little literature is available in this context in Barak valley region of Assam. The present investigation was, therefore, undertaken to study the species composition, seasonal distribution, succession and phytosociology of different aquatic macrophytes in certain wetlands of the valley.

MATERIALS AND METHODS

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Monthly survey was done by quadrat method for collecting submerged aquatic macrophytes (AM), from January 1998 to December 1999. Qualitative and quantitative analysis of AM was done by Biswas and Calder (1984); Cottam and Curtis, (1956); Hutchinson (1975) and Mishra (1974). Specimens were identified up to genus/species level.

Equity and diversity status of the AM was studied using Shannon-Weaver (1949) function and the phyto-sociology was studied through X2 (chi-square) test.

RESULTS AND DISCUSSION

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AM exhibited a heterogeneous assemblage of 27 species in the studied wetlands (Table 1). Of these, Eichhornia crassipes, Salvinia cucullata, Azolla pinnata, Trapa bispinosa, Jussiaea repens and Cynodon dactylon, were found to occur throughout the year. During monsoon, floating varieties of AM, viz., E. crassipes, S. cucullata, A. pinnata, Nymphaea nouchali, Nymphoides cristatum, N. indicum, Nelumbo nucifera and Hygrorhiza aristata flourished and dominated the aqua-regime at a greater depth of the water. Vetiveria zizanoides was also a monsoon variety, which was found to occur in some of the studied wetlands. Conversely, the monsoon varieties of AM were succeeded by the winter emergent varieties, viz., Eleocharis acutangula, Scirpus eriophorum, Echinochloa stagnina, Sagittaria trifolia and Polygonum flaccidum.

Significant phytosocial association had been recorded among the different AM species. E.crassipes, S. cucullata and A. pinnata were found to be associated with each other among the floating varieties. Further, Hydrilla verticillata, Vallisneria spiralis and Trapa natans (L) var. biopinosa were found to be associated together showing heterogeneity. Phytosocial association was also observed among Nymphaea nouchali, Nymphoides indicum and N. cristatum; as well as Eleocharis acutangula, Echinochloa stagnia and Scirpus eriophorum. Further, significant (P< 0.05) phytosocial association between C.dactylon and E.crassipes (X2 12.44), C. dactylon and N. indicum (X2 10.21), H. aristata and E.crassipes (X2 13.87), and H. aristata and N. cristatum (X2 18.96) was recorded during the study period. However, none of the AM species were found to be associated with Euryale ferox, possibly because of its thorny body; and, thus it formed a monospecific unit.

Calculation of species diversity in the studied wetlands revealed the following values:
Biased estimate of H' = 2.015;
Expected value, E (H') = 2.014;
Variance of H' = 1.431 E_____3)

TABLE 1: SPECIES COMPOSITION AND SEASONAL DISTRIBUTION OF AQUATIC MACROPHYTES FOUND IN THE WETLANDS OF BARAK VALLEY REGION, ASSAM. ('+': present, '-': absent)

REFERENCES

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Address:

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Devashish Kar
1.) Department of Life Science,
Assam University,
Silchar - 11,
Assam

Monjurul Hoque Barbhuiya
2.) Department of Biology,
Sonai NGHS School,
Sonaimukh,
Cachar,
Assam

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