Abstract:
Inland fisheries in Sri Lanka, primarily within reservoirs and tank cascade
systems, hold significant potential for sustainable fish farming and livelihood of peo-
ple. This study employed images of the Lake Water Quality 300 m version 1 (Near-
Real-Time) products of the Sentinel-3 OLCI (Ocean and Land Colour Instrument)
sensor obtained from the Copernicus Global Land Service for every 10 days during
May 2016 to December 2019 to evaluate the overall conditions and mean monthly
and annual variations and relationship of Lake Turbidity and Trophic State Index
(TSI) in Maduruoya reservoir (MO) and Senanayake Samudraya (SS). According to
the Carlson’s Trophic State Index, MO exhibited an upper mesotrophic status (TSI
52±0.54), while SS displayed a lower mesotrophic status (TSI 44.34±0.76). The SS
had a greater turbidity level (20.23±1.43 NTU) than MO (9.31±0.77 NTU). Higher
TSI levels were found in deeper areas and near the reservoir dam, while in contrast,
increased turbidity was observed in littoral zone compared to the dam area and middle
of the reservoirs. The TSI has reduced (34-46 NTU) with the onset of rains in the
second inter-monsoon and the North-East monsoon. TSI was increased in post rainy
seasons and with the beginning of the distinct dry period in the dry zone reservoirs
have experienced higher TSI levels (48.2-55.8 NTU). This verified the temporal var-
iation in the trophic status of reservoirs consist of lower values in the rainy season and
gradually increased over the dry period and vice versa. After the rainy season and
second inter-monsoon, higher turbidity (20.2-42.3 NTU) values were observed. The
turbidity was gradually reduced in the dry season (5.8-10.9 NTU). The regression
model between TSI and turbidity for SS (R2=0.86) had a stronger fit compared to the
model for MO (R2=0.51). It can be concluded that there are clear seasonal trends in
TSI and turbidity associated with the rainy season in MO and SS
