e - poz 2 - Central Institute of Brackishwater Aquaculture

The nutrients were highly influenced by dre monsoon discharges from the fourriven. The values (available nitrogen: 2C710, average: 213 pgk; availablephospho-rous: Tr.-72, average: 19 pgh) gradually declined during the postmonsoonand pre-monsoon months. The zones receiving the municipal discharge(Station-1) and runoff from agricultural lands and human inhabitation were r~cherIn phosphates and nitrates. The reduction in available phosphates could mainly beattributed to its loss to he sediment in the form of aluminium and iron-bound --- -phosphates at a lower pH. . Silicates had rich concentrations varying from 34.5 to47.0 mg/L (average: 38.5 mg/L).Sediment QualityThe temperature, pH, conductivity, organic carbon, available phosphorus, calciumcarbonate and texture properties of the sediinent were analysed (See Table 4 & 5).The pH of the sediment remained acidic in most of the stations during the studywith an average value of 5.3. The monsoon values were low (average: 4.7). Th~scould be due to the exposure of relatively higher acidic subsurface basin sodconsequent to monsoon turbulence and bottom currents. Available phosphate (av.34.2 mg/100gl in the sediment was high during the premonsoon consequent tothe phosphorous adsorption from the water column. The augmentation was alsoaided by the enrichment from the settled plankton and the subsequentphosphorous release through the microbial activities. The phosphate values forthe sediment phase had an invesre relationship with that of the water phase duringthe three seasons.The organic carbon content had an average value of 2.7% during 1996-97.Stattons 1-4 at the southern end of the lake had elevated levels of organic carb~on(3.27-5.49 %) compared to the 2.8 % reported for this part of the lake by Murthyand Veerayya (1972) during the prebarrage phase. This indicates an accumulationof organic matter in this part over the years. Predictably, the premonsoon seasoncharacterised by the stagnancy indicated higher values of organic carbon at all thestations. Free calcium carbonate was high during the premonsoon followed bythe monsoon and post-monsoon periods.