International Journal of Marine Science 2015, Vol.5, No.51: 1-11
2
role in providing a holistic picture of the ecosystem
(Armitage et al., 2003; Herzon and Helenius, 2008).
This study analyzed the oligochaete community
structure in paddy fields and channels in Kole paddy
fields which are part of Vembanad kole wetlands, a
Ramsar site. Kole wetlands are among the water-logged,
paddy cultivating areas in Kerala such as Kuttanad (in
Alappuzha, Kottayam and Pathanamthitta), Pokkali
(in Alappuzha, Ernakulam and Thrissur) and Kaipad
(in Kozhikode and Kannur) (Jayan and Sathyanathan,
2010). Kole wetlands were under rice cultivation for
the past 200 years since the erstwhile Maharaja
permitted to convert this wetland into paddy fields in
the early 18th century (Anon., 1989). The cyclical
nutrient recharging of the wetland during the flood
season made the area as one of the most fertile soils of
Kerala. Further they are noted for its high rice
production, even the term Kole in Malayalam (the
regional language in Kerala, India) means ‘bumper
yield of high returns in case flood does not damage
the crops’ (Johnkutty and Venugopal, 1993). Though
India stands first in area under rice cultivation, second
in rice production and has an agricultural based
economy (Balachandran 2007), the information on
oligochaete community in the paddy fields is limited
from India except the works by Ojha et al. (2010) and
Hegde and Sreepada (2014
)
.
Materials and Methods
Study area
The study area is a part of the Ponnani Kole lying
between Maranchery and Veliyamkodu in Malappuram
district (10
0
72’N 75
0
98’E) (Figure 1). The Kole
lands covering an area of 13,632 ha. spread over
Thrissur and Malappuram districts of Kerala
extending from northern bank of Chalakkudy river in
the South to the southern bank of Bharathappuzha
river in the North. The Viyyam dam is situated at the
downstream of end of Kole lands which prevents the
intrusion of salt water to the paddy fields. The Kole
lands are believed to be lagoons formed by the
recession of the seas centuries back. A shallow portion
of the sea along the western periphery of the main
land was isolated and they were gradually silted up
during rains making the lagoons shallow. The farmers
then bunded the fields, dewatered and raised paddy in
summer months. During the rains, the inflow into the
basin submerges all the kole areas. The area normally
remains flooded from June to January. Normally two
rice crops are raised in Kole wetlands, a summer crop
(
punja
in December/January- April/May) and an
additional crop
(
Kadumkrishi
) (Raj and Azeez, 2009).
The main crop is
Punja
(Summer crop). Towards the
end of the north east monsoon (October to December),
water from the paddy fields are pumped out and
sowing or transplanting is done by January.
Dewatering is done by centrifugal pumps or
petti
and
para
which is an indigenous pumping device. The
kole lands are dewatered after protecting the paddy
fields (
Padavu
or
Padashekharam
) with permanent
or temporary earthen bunds (
Mattoms
) (Johnkutty
and Venugopal, 1993). The crop is harvested in May,
soon after which the field gets flooded due to the
South West Monsoon (June to September).
Sampling procedure and methods
A total of five sampling stations were chosen, three
stations were paddy fields and two were channels.
Channels and paddy fields were separated by an earthen
bund. The field sampling was carried out for a complete
crop season ‘
punja
’ extending from January to May
2011 on a monthly basis for the study of oligochaetes
and environmental parameters.
As the water body was shallow (average depth 0.71 m),
water samples were collected using a locally fabricated
shallow water sampler of 1 litre capacity. The samples
were stored in plastic containers and kept frozen till
analysis. The sediment samples for the analysis were
collected using a Van Veen grab of size 0.45m
2
.
Temperature of the water and sediment samples were
measured in the field using a standard degree
centigrade thermometer of 0°C to 50°C range and
0.l°C accuracy. pH was measured using Systronics
digital pH meter model MK VI. Dissolved oxygen was
analyzed by modified Winkler method (Strickland and
Parsons, 1972). Organic carbon was determined by
Walkley - Black method then converted to organic
matter by multiplying with Van Bemmelen factor of
1.742 (Jackson, 1973). Particle size was analyzed using
particle analyzer Sympatrec T 100 laser diffraction
granulometer, made in Germany.
Sediment samples in replicate were collected for the
analysis of macrobenthos using a Van Veen grab of size
0.45m
2
. The samples were washed in the field itself
through a sieve of mesh size 500 μm and those that are
