MSc

The present investigation entitled ―Pollution study of Vembanadu lake and
wetland rice ecosystem‖ was carried out at the College of Agriculture, Vellayani during
the period 2019 to 2021 to assess the extent of pollution in Vembanad lake and wetland
rice ecosystem. The lake is part of the Vembanad-Kol wetland system, which stretches
from Alappuzha in the south to Azheekkode in the north, making it India's longest lake.
The lake is fed by five rivers, including the Achenkovil, Manimala, Meenachil,
Muvattupuzha and Pampa which are all prominent rivers in central Kerala. Samples of
water and sediment from lake as well as soil and field water from paddy fields were
collected during post monsoon and summer season. Samples collected from the two
representative sites Kumarakom and Thanneermukkom were subjected to physical,
chemical and biological analysis.
Results of the analytical study of lake water revealed that among the physical
properties, turbidity and colour were above the acceptable limit of BIS drinking water
quality criteria and did not varied significantly with seasons. Chemical properties of
water viz. pH, BOD, COD, NH4-N and Fe were also above the acceptable limit. pH, EC,
K, Na, Ca and Mg varied significantly with season. Electrical conductivity and the
cationic nutrients were found to be higher in summer than post monsoon season. Trace
metals viz. Mn, Cu, Zn, Al, Pb and Cd were not detected in lake water samples in either
of the seasons. Total bacteria and coliform count exceeded the acceptable limit of
drinking water quality criteria in the study area. Pesticide residues were not detected in
the lake water samples.
Sample analysis of the sediment revealed that NO3- N recorded a mean value of
28.00 mg kg1
at Kumarakom and 36.17 mg kg1
at Thanneermukkom. Aluminium varied
from 342.00-474.00 mg kg1
at Kumarakom while at Thanneermukkom was 348.00-
468.00 mg kg1
. For Pb, mean value of 0.71 mg kg1
and 0.72 mg kg1was obtained at
Kumarakom and Thanneermukkom respectively. Seasonal variation was observed for the
chemical properties viz. pH, EC, extractable K, Ca, Mg, S, and Mn. Parameters EC,
cationic nutrients except Al, trace metals viz. Mn, Cu, Zn and Pb were found to be
highest during summer season while pH, organic carbon, NO3- N, NH4-N, P, Al were
highest during post monsoon. Cadmium was not detected in sediment samples collected
in both the seasons. Pesticide residue analysis of sediment samples revealed the presence
of DDT (0.024 mg kg1
).
Soil samples from padashekaram of Kumarakom were slightly acidic while it was
moderately acidic at Thanneermukkom. At Kumarakom and Thanneermukkom organic
carbon was high, available N and K were medium and low in available P. At both
locations, secondary nutrients were sufficient. Among micronutrients, Fe toxicity and
deficiency of Cu and Zn were observed. Chemical parameters of soil were significantly
influenced by the seasons. Cationic nutrients and EC were high in summer while pH and
organic carbon were high in post monsoon season. Pesticide residue analysis of the soil
samples revealed the presence of cypermethrin, chlorpyrifos and ethion. Textural class of
soil sample ranged from sandy loam to sandy clay loam.
In the field water samples from padashekaram, trace element Fe was detected.
Among the chemical properties pH, EC, S, K, Na, Ca, Mg varied significantly with
season.
Pollution study of Vembanad lake revealed that lake water is polluted with respect
to most of the biological, physical and chemical properties. Hence it is important to
develop water quality monitoring and management strategies for conserving and
sustaining the natural resources from environmental pollution and ecological degradation.