Spatial and temporal variation of nutrient cycling in Vembanad lake

Abstract- The Vembanad Lake is the largest estuarine lagoon system in Kerala. This lake consists of a complex system of backwaters, marshes, small islands, mangrove forests and network of canals. Recently, there is a trend of degradation of this highly valuable system. Studies on the spatial and temporal variation in nutrient cycling in Vembanad Lake have been carried out in pre-monsoon and monsoon in the year 2018. 21 stations were selected in Vembanad Lake from Thevara ferry to Aroorkutty region. We have studied the general hydrography,nutrients, and metals in both water and sediment. Assessment of sediment contamination was also done using geochemical indices like contamination factor, geoaccumulation index and pollution load index. CHNS ratio of sediment was also studied.
By statistical analysis it was found that there was no spatial variation reflected in water or sediment. Seasonal significant difference was observed only for certain parameters. The nutrient in water showed a seasonal variation with increased concentration in monsoon season. The flood happened in 2018 August had an effect on certain parameters. There was a drastic increase in the hardness of water in post flood/monsoon period.
Most of metals showed an increase in its concentration in monsoon being a contradiction to earlier studiesand the assessment of contamination indices also pointed towards the effect of flood in the Lake. In monsoon season / post flood the sediment contamination according to pollution load index was reduced to ever time low. This may be due to the effect of flood which caused the fluxing of upper layer of sediments. Based on contamination factor and geoaccumulation index Cu is the important pollutant among metals. CHNS ratio of the sediments remains normal when compared to the earlier studies.