Abstract:
Eutrophication has emerged as one of the main threats to surface water bodies. The parameters for assessing
eutrophication are not generally measured regularly from the lakes of India as part of monitoring programmes
and it is necessary to express the trophic status in terms of secondary indicator variables that are included in the
routine analysis by the State/Central government. In this paper, the trophic status of Ashtamudi Lake has been
studied, considering its international importance and socio-economic relevance. The cause and response vari ables such as total phosphorus, Secchi disc depth, chlorophyll-a and the secondary indicator variables such as pH,
turbidity, DO, EC, Salinity, TDS and BOD were analysed during the pre-monsoon season. The lake was pre dominantly classified as eutrophic, with some areas coming under a hypereutrophic state. A comparison was
made among the five methods of water quality index by the use of secondary indicator variables to identify the
appropriate method for simulating trophic status and the WQI based on the logarithmic method considering pH,
turbidity, DO and BOD was identified to predict the trophic state very well. Further, the application of numerical
strategy such as fuzzy logic was used to determine water quality indexes and trophic status, which can define the
quality of a water body as a consequence of the variation of environmental parameters. The developed approach
was further validated by using historical data for the years 2013–2015, which were regularly monitored by the
Kerala State Pollution Control Board. The trophic state predicted by the approach was found to be in agreement
with that estimated using Carlson's method. Thus the developed model, based on secondary indicator parameters
that are readily available from government agencies, can be used to assess the trophic state of lakes, thereby
assisting policy makers to frame regulations to minimize eutrophication.
