| General note |
Vellayani lake with a spread area of about 3.98 km2 <br/>is the second largest fresh water lake<br/>in the Kerala state. The lake is located in the outskirts of Thiruvananthapuram District and lies<br/>between the North latitudes, 8024'90" and 80<br/>26'30" and East longitudes, 760 59'08" and 76 59'47".<br/>It is getting polluted consequent to the discharge of toxic contaminant from urban and agricultural<br/>areas. Lake of adequate baseline information is one of the major constrains challenging<br/>conservation & efficient use of freshwater resources. At present, the the lake Vellayani is<br/>disappearing in an unpredictable pace. Several reports have been published on the present<br/>condition of Vellayani lake. The area of the lake has been reduced to a little less than half the area<br/>of what previously existed (750 hectares in 1926). The scenic fresh water lake, at present is being<br/>strangulated by the invasive plant species. A thick layer of grass has made some portions near the<br/>banks as marshy grassland. Over the years, the lake has been filled with invasive plants such as<br/>Eichhornia crassipes, Limnocharis flava, Salvinia molesta, Salvinia auriculata, Cabomba<br/>Caroliniana, Lemna Minor and lotus (Cultivated for temple uses). All these indicates that the lake<br/>is under heavy threat mostly due human intervention. <br/> The present study was conducted as an attempt to evaluate the present geo-environmental<br/>status of the lake. Several physico-chemical parameters were analysed, which included<br/>Temperature, pH, EC, TDS, Turbidity, Salinity, TSS, Calcium, Magnesium, Sodium, Potassium, DO, CO2, Cl-, NO3, NO<br/>2, NH3, SO42-, PO4, SiO4,<br/>Alkalinity as well as heavy metals like Iron,<br/>Copper, Cadmium, Lead and Zinc. The Chl-a concentration was also estimated in the lake water,<br/>those concentrations showed that the lake was in oligotrophic. category. <br/>The physico-chemical parameters like EC, TDS, TSS, DO, CO2, NO2, NH3, PO4 as well<br/>as the heavy metal iron and cadmium. Highly significant correlation was found in the study, where<br/>EC strongly correlated with TDS & Salinity, pH strongly correlated with DO, PO4 with NO3, Mgwith HCO3 <br/>and TA and HCO3 with TA. SiO4 showed a strong negative correlation with K. As per<br/>the Gibb’s diagram, the samples fall in the rock-water interaction dominant area. Irrigation<br/>suitability of the samples were analyzed, various indices were considered to find the suitability and<br/>they were sodium percentage, sodium adsorption ratio (SAR), Kelly’s Ratio, Residual Sodium<br/>Carbonate, Potential salinity, Permeability Index and Mg Hazard. As per the Kelly’s ratio about<br/>64.31 percentage of samples were unsuitable for irrigation. All the samples belonged to the<br/>excellent category of sodium absorption ration classification. Salinity and alkalinity hazard class<br/>diagram (USSL) showed that all lake water samples fall under high salinity with low sodium (C3– S1) class. <br/>The Sodium percentage ratio index showed that almost 64% of the lake water samples<br/>fall under excellent category. The Wilcox diagram showed that about (78.57%) fell under<br/>permissible to doubtful. RSC values of the samples ranged from1.045to 0.0592. Based on the US<br/>Salinity Laboratory (1954), all the samples have values <1.25 meql-1 and are safe for irrigation<br/>purposes. Based on the Doneen criteria, all the collected samples came under Class ΙΙ which is<br/>categorized as good for irrigation. High values of potential salinity in the area can be ascribed to<br/>due to comparatively high values of chloride and sulphate content in the study area. About 99% of<br/>the samples were within the recommended limits and are suitable for irrigation purposes. As per<br/>WQI, only 14 % of samples came under excellent category. <br/>The higher values of nitrites, ammonia, phosphate, TDS and TSS along with the organic<br/>carbon content in the sediments (Krishnakumar and Baijulal, 2006), are suspected to be the reason<br/>for the growth of aquatic floating plantation in the lake. These parameters indicate that the water is<br/>mainly polluted by the agricultural and urban runoff. <br/>From the overall analysis, it was found that the lake water of Vellayani is portable for<br/>drinking water purposes only after pre-treatment. The overall irrigation suitability of the lake was<br/>found to be moderate. <br/>This study recommends to take proper action against unscientific agricultural activities<br/>and also recommends for the proper treatment of the lake water before using for irrigational as<br/>well as drinking water purposes. |