e - poz 2 - Central Institute of Brackishwater Aquaculture

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The sediment texture showed that sand was the major fraction (44.7 %) followedby the clay (31.3 %) and silt (18.7). Studies conductd by Murthy and Veerayyar 1972) during the pre barrage phase showed a silty sand condition, which wasgrddudlly paving the way for a silty clay with the clayey fraction increasing overthe years as observed during the present investigation. Samples collected from theoppo5lte side of the barrage during March, April and October 1996 had theslit + clay fract~on only less than 5 %. This suggests an accummulation of the claydnd silt In the stagnant portion of the lake over the years. Stations 1-3 hads~gnlfitantly high portion of the clay (42.0 %) and silt (22.1%) compared to theother stations lav. 27.8 % and 17.6 % respectively). Stations 1&2 were(omparatlvely less influenced by the monsoon flow (Fig. 4).The study revealed that the water and sediment characteristics showed wides1)atial and temporal differences before and after the construction of the barrage,ttit, differences being more pronounced at the south end of the lake.Plankton Biomass1 he vdr~atlons In the plankton b~omass (senllng volume) with respect to the5f>d50115 and the sampllng stations were determined durcng 1994-96 The preriionsoon perltxl showed the hlghest mean value for the plankton b~omass (4 7n,l/mJ) followed by the post-monsoon (4 4 mllml) and monsoon (34 ml/ml)p~r1Od5 The barrage remains open t~ll early December, the b~omass during thepost monsoon sedson was decided by the outflow to the sea The closure of thebarrage thereafter allowed the environment to be stat~c, and the phytoplanktoncould util~ze the trapped nutrients and flourish Low biomass values observedduring the monsoon period In the present study could be due to the dllut~on of thewater mass and the transport of the b~omass to the sea by the heavy monsoondischarge froni the four rivers The post-monsoon was the recovery season for theblonldss as the plankton could ut~lize nutrients received through the runoff Thedens~ty of organlsrns In the samples presented a more real~st~c and rellable Indexof the abundance than the volume, since the suspended sllt and dirt ~nfluenced theb~omass determlnatlon
The mean biomass varied from 6.6 mVm3 to 0.3 mVml The values were generallyhigh in stations 1,3 and 5. These stations are located nearer to the areas of humansettlement on ttte western fringe. The average highest value was recorded atStation 5 near the denser settlements. At this station, the average biomass was 11mg/L during October to February reflecting the inflow of the nutrients during themonsoon flow. At Station 1, near to the opening end of the city canals to the Lake,the biomass was as high as 13.5 mum'during this period. The canals receive theeffluents from the urban settlements and are known as the worst polluted segmentof the entire Kuttanad region. At the extreme south of the lake, this station had theleast influence of whatever feeble salinty incursion occurred to the Sector. Thisportion remained stagnant through out the summer season. All the three Stat~onsthat depicted high biomass concentration were on the western fringes of the lake,least influenced by the river.flow even during the monsoon season.PhytoplanktonThe net phytoplankton population in the 12 stations of the Vembanad wasinvestigated for a period of two years during 1994-96. At various sampling sltes,phytoplankton had a density variation between 17797 and 60613 unitlm' w~th anaverage value of 30682 unitdmJ. The overall density for the sector was higher lorthe green algae (42.6 %). The blue greens were concentrated at Station-1 w~th 'Ipercentgae contribution upto 70.6 %. Anacystis and Tr~chodesm~urn were ,~lsoabundant at this place, indicating a eutrophic condition. The overall contr~hut~onby the greens and the desmids were prevalent during the monsoon and postmonsoonmonths indicating an improvement in the water condition due to thrmonsoon inflow. The green algae represented by 24 species contributed to thrhigh phytoplankton abundance in the 12 stations of the Vembanad lake. Thr I)rcbmonsoon period (34796 ndmJ) showed a maximum numer~cal abundanctafollowed by the monsoon (32773 no/ml) and the post monsoon (24934 nolm')period (Table 6).Studies conducted during the prebarrage phase by Gopinathan et a/. (1974) In theCochln estuary, a part of the Vembanad Lake, observed a maximum phytoplanktonabundance in the pre-monsoon and monsoon periods. Compared to the prcbarrage phase, the diversity has been found on a higher s~de In the presentinvestigation, ~nfluenced by the prevalence of freshwater condition during the
Page 2 and 3: Ecology and Fisheries Investigation
Page 4: The Vembened take on the south-west
Page 7 and 8: The lakc had already been reclatd c
Page 9 and 10: from the orig~nal marine environmen
Page 11: of this century. The current lwei o
Page 14 and 15: The project was implemented partial
Page 16 and 17: The barrage at Thanneerrnukkom acro
Page 18 and 19: INvISTGATIONS ON THE FISHERY ECOLOG
Page 21 and 22: Several literatures are available o
Page 23 and 24: ECOLOGICAL INVESTffiATtONS WRING 19
Page 25 and 26: so.
Page 31 and 32: summer. The pure saline forms that
Page 33 and 34: eporxd by Nair et al. (1983) was di
Page 35 and 36: lhJm md tabqodr Onty m spxlcr m6emd
Page 37: A view of the endangered fish speci
Page 41 and 42: Urcrobrachium rosenbergir 57 930 47
Page 43 and 44: The study reveals that the Thanneen
Page 45 and 46: BIBLIOGRAPHY ON VEMBANAD LAKEAnon.
Page 48 and 49: m,T.R. Mii(l. Y. nd Wli, C. M. 1984
Page 50 and 51: Smlathan, P., MccoJuMkr~y, N. I., r
Page 52: I. E-. Mu. bid. E d.I. lndln FWI. A

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