ENVIRONMENTAL SETTING IN VEMBANAD LAKE – HOW AQUACULTURE IN THE LACUSTRINE SYSTEM IS IMPACTED IN THE RECENT PAST?
Coastal Indian waters are well connected to estuarine systems which act as hub of aquaculture activities. A tropical well-mixed estuary along southwest coast of India is examined in this study to ascertain the impact of climate change. The study area is Vembanad Lake which has got diverse farming systems such as freshwater aquaculture system that operates below mean sea level conditions along the Kuttanad stretch, estuarine Pokkali system and coastal mariculture / aquaculture systems. Two data sets, one with compiled information on hydrology until the year 2000 and the other with in situ hydrographic data collected in 2018-19 were analyzed in this study to assess the impact of climate change n all the three aquaculture zones.
It was observed that the lower salinity ranges are skewed to freshwater with an order of ten differences showing low salinity of 0.02 ppt when compared with our bench mark data of 0.2 ppt (Menon et al, 2000). During pre-monsoon in the northern Vembanad, salinity stratification was not observed. In previous studies, rapid stratification of salinity was observed at the beginning of the monsoon, whereas the recent data shows stratification of salinity in the monsoon and post-monsoon. Temperature ranges between 24-320C. In the southern part, comparatively higher temperatures were observed during the post-monsoon than in northern part as in previous studies. Nitrite, nitrate, phosphate and silicate showed pronounced seasonal variations between the two studies indicating the increased impact of anthropogenic influence. In this study we discuss the effect of relevant environmental variables in Vembanad that has impacted the aquaculture operations on a regional scale. The study shows that major changes in the water quality structure of the lake are due to anthropogenic and climatic issues.
