Browsing by Author "Malawaraaratchi, RN"

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item: Thesis-Full-text
A Study of the Negombo lagoon with respect to the salinity variation and pollution of the lagoon water and effects of proposed dredging activities
Malawaraaratchi, RN; Rathnayake, N; Samarawickrama, SP
Negombo Lagoon is a shallow basin estuary, located on the West coast of Sri Lanka, serving important functions including fishing and tourism. It drains water carrying nutrients and organic matter from the heavily populated catchment area and has faced the threat of the degradation of water quality. The objectives of this research are to study the seasonal and diurnal variation of salinity in the estuary, study the pollution status of the estuary; study the effects of dredging on the water quality and to recommend remedial measures. 17 sampling locations were selected for the study, which included points in the estuary and fresh water feeders. A Sampling programme of 6 days which covered both wet and dry weather as well as the spring and neap tidal periods was carried out. Salinity, nutrients and COD were measured at the flood and ebb tides. According to the salinity measurements, in the dry period, the estuary is fully mixed. Stratified conditions occur when the fresh water flow rate increases. Chl a measurements were used to assess the trophic state of the estuary and fresh water feeders. The estuary is eutrophicated both in the wet and dry periods and some locations are even hypertrophic. Out of the fresh water feeders, Hamilton canal is mesotrophic and has faced the threat of eutrophication. According to the literature, limiting potential of the tropical estuaries has been found to shift from N to P with higher fresh water flow rates and results of this study agree well with the above finding. Limiting P inflows is a remedial measure to improve the water quality. Where the loads of DIN and TN are concerned, Dandugam-Oya was found to bring the highest loads irrespective of the climatic conditions. Where the Phosphate loads are concerned, Ja-ela brings significant, constant loads on rainy season, while Dandugam-Oya brings the highest load with the highest flow rate. Out of the 7 dredging options studied, option 6 is the most feasible one.
item: Conference-Extended-Abstract
Salinity variation and pollution of the Negombo estuary
(2003) Malawaraaratchi, RN; Rathnayake, N; Samarawickrama, SP
Negombo estuary. which is 3170 ha in extent, serves important economic functions including fishing and tourism. It is characterized by high secondary production rates reflected in important biomass values for benthic and pelagic organisms. Estuarine plants and animals are adapted to high environmental variability and possess potentially valuable genetic characteristics. However it is under heavy and increasing pressure li'0111 human activities since it drains water carrying nutrients, organic matter and toxic. materials [rom the terrestrial environment .and the river system to the sea. The disposal of waste oil from the fishing anchorage located at the inlet and the direct discharge of partially and untreated effluents from the Ekala and Katunayake industrial zones are the major contributors of .pollution. The ad-hoc expansion of piers and landing points has lead the alterations in the flow patterns and thus the sedimentation in the channels. Newly formed sand shoals have· obstrncted the previously navigable areas. Unplanned development, unauthorized encroachments to the water body and the siltation have reduced the effective water area by 791 ha during the last three decades. The eventual fate of this basin estuary would be degradation by sedimentation and pollution.