ECOLOGY AND MACROBENTHIC FAUNAL DIVERSITY OF SOME FLOODPLAIN WETLANDS OF RIVER GANGA IN WEST BENGAL

Floodplain wetlands of West Bengal, locally known as beels, offer diverse ecological attributes and diversified faunal elements of which macrozoobenthic communities of some floodplain wetlands of river Ganga located in the districts of Maida, Murshidabad and Nadia in West Bengal have been investigated and reported in the present communication. It may be mentioned that although sotne reports (MandaI and Moitra, 1975; Sarkar, 1989, 1992; Mukherjee and Nandi, 2004; Banerjee and Banerjee, 2005) are available regarding benthos from freshwater wetlands of West Bengal, but very little is known on the benthic fauna of floodplain lakes of lower Ganga river basin of \Vest Bengal, and hence the present study. Studies on faunal resources of wetlands in West Bengal mostly pertain to southern part of West Bengal (De et a/., 1989; Ghosh, 1990; Nandi et a/., 1993, 1999, 2001a, b, 2005, 2007; Mukherjee and Nandi, 2004).


INTRODUCTION
Floodplain wetlands of West Bengal, locally known as beels, offer diverse ecological attributes and diversified faunal elements of which macrozoobenthic communities of some floodplain wetlands of river Ganga located in the districts of Maida, Murshidabad and Nadia in West Bengal have been investigated and reported in the present communication.It may be mentioned that although sotne reports (MandaI and Moitra, 1975;Sarkar, 1989Sarkar, , 1992;;Mukherjee and Nandi, 2004;Banerjee and Banerjee, 2005) are available regarding benthos from freshwater wetlands of West Bengal, but very little is known on the benthic fauna of floodplain lakes of lower Ganga river basin of \Vest Bengal, and hence the present study.Studies on faunal resources of wetlands in West Bengal mostly pertain to southern part of West Bengal (De et a/., 1989;Ghosh, 1990;Nandi et a/., 1993Nandi et a/., , 1999Nandi et a/., , 2001aNandi et a/., , b, 2005Nandi et a/., , 2007;;Mukherjee and Nandi, 2004).

Study Area:
Six floodplain wetlands of Ganga river basin in West Bengal, two frOll1 each of MaIda, Murshidabad and Nadia districts, were selected from rural and urban environments (Table I Sagardighi (SD), Murshidabad : This wetland with a water area of about 149.8 ha is located at about 25 km northwest of Berhampur.It is highly infested with aquatic weeds.
Bhandardaha beel (BD), Murshidabad : It has the water area of about 330 ha.It is located at about 32 km southeast of Berhampur town.This wetland is also highly infested with macrophytes during the course of investigation.
Hasadanga beel (HO), Nadia: This wetland is shallow and located at about 30 km southeast of Krishnanagar Sadar.It is situated in between northwest of lalangi river and southwest of Bhagirathi river.The water area is about 66.65 ha, which is mainly infested with water hyacinth at its margin.
Haarkhali beel (HK), Nadia: This wetland is situated near Puratan Sambhunagar at about 18 km east of Krishnanagar, in between lalangi and Churni rivers with an approximate water area of 250 acre and highly infested with weeds.were rneasured in the field and in the laboratory, chietly following standard IlH.;lhuJ~ 01 ,\PHA (1998) and Mukherji and Nandi (2004).The qualitative benthic samplings wcr~ June with tilL: ai.j of a box-type sampler and sieve.

RESULTS AND DISCUSSION
The physiographic features of selected wetlands, physico-chemical paralneters of water of the wetlands and the benthic faunal elements inhabiting the selected wetlands are presented in Tables 1, 2 and 3.These include seven water parameters (  (Sarkar, 1992).In all 18 species of aquatic invertebrates have been recorded froIH MaIda, Murshidabad and Nadia districts (0 ' Malley, 1990;Distrit Gazetters).It seems floodplain wetlands of these districts are less rich in diversity of benthic fauna in comparison to Rabindra Sarovar and Subhas Sarovar, representing 29 species each.However, monthly intensive or at least seasonal surveys are needed to ascertain the actual richness of benthic species occurring in these wetlands.
) for survey work.The geographical locations of these wetlands are shown in the Fig.I The brief descriptions of six selected wetlands are as follows: Golbaka-Haripur beel (GHB), MaIda: This wetland is located at about 50 kIn north west of MaIda town, and is situated near Ratua.The total area of the wetland is about 30 ha which is moderately infested with marginal macrophytes.Barasagar Dighi (BSD), Maida: This wetland is situated near Sadhullapur (It about 22 km northeast of MaIda town with water area covering about 83 ha.It is infested with low growth of macrophytes.

Table - I
. Physiographic features of the selected wetlandsThe surveys \vcrc condutcd during 2004 and 2005.Physico-chcInical paranlCh:r~ t)f the \\ ~ll(:l Table-2) and 29 benthic ~pecies belonging to 3 phyla, representing 19 families under 7 major groups/classes (Table 3).It is evident froln the Table-2 that the water in all these selected floodplain wetlands is alkaline with poor to lnoderatc dissolved oxygen to support aquatic life.From Table-3 it is, however.revealed that gastropod molluscan macrobenthos representing 12 species belonging to 5 families don1inate these wetlands over the other benthic ommunities viz., annelids (5 species), insects (7 species), crustac~ans (3 species), etc.Among the selected wetlands, Barasagardighi of MaIda district represents the highest macrozoobenthic diversity harbouring 21 species under 16 farnilies.The lowest Illa<'TPocnthlL' diversity of 13 species under 9 families was observed in the Hasadanga beel of Nadia district.

Table - 2
. Physio-chemical parameters of the sleeted wetlands in premonsoon season