Browsing by Author "Samaraweera, S. A. P. T."

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Change detection of vegetation cover in Kurunegala district by using remote sensing approach
(Faculty of Science, University of Kelaniya Sri Lanka, 2024) Imbulana, I. B. A. C.; Jayasinghe, V. S.; Peramune, P. R. S. N.; Samaraweera, S. A. P. T.; Weerasinghe, V. P. A
The amount of vegetation cover has reduced over time due to the rapid increase in population, expansion and intensification of agricultural activities, and unsustainable use of resources worldwide. This leads to significant negative impacts on the ecosystems. Although several studies have been carried out on vegetation change in Sri Lanka, there is little or no information available in Kurunegala District. Therefore, the objective of the present study was to assess the extent of changes in areas with healthy vegetation cover in Kurunegala District of Sri Lanka, through examining the Normalized Vegetation Index (NDVI) over a period of 10 years from 2013 to 2023. NDVI was employed to determine the growth condition of vegetation. Remote sensing data from Landsat-8 OLI/TIRS images were used to perform NDVI analysis. The area was classified into no vegetation and vegetation and the values above 0.3 were considered as the vegetation. The obtained NDVI maps were reclassified, and the resulting maps were converted to vector maps. The final values were used to compute the area under no vegetation and vegetation. The results of the present study indicated a significant vegetation cover change between 2013 and 2023. The results revealed a conversion of 1424.95 km2 area from no vegetation to vegetation and a conversion of 550.57 km2 area from vegetation to no vegetation. In addition, 669.98 km2 of no vegetation area and 2253.35 km2 of vegetation area have remained unchanged. The vegetation area, which was initially 2804.32 km2 in 2013, had expanded to 3678.79 km2 in 2023, reflecting a 31.18% transformation of no vegetation areas to vegetation areas. Thus, it can be concluded that the vegetation cover area in the year 2023 had increased compared to 2013. However, NDVI does not differentiate between various types of vegetation, such as agricultural crops and forests, which is a limitation of this study. Enhancing sustainable land management, strengthening environmental policies, promoting community involvement and continuous monitoring are crucial for further expansion of the vegetation cover in Kurunegala District
Impact of Wastewater Treatment Plant on the Quality of Water in the Canals Passing Through Kurunegala City
(Faculty of Science, University of Kelaniya Sri Lanka, 2023) Samaraweera, S. A. P. T.; Najim, M. M. M.
Water scarcity is a growing concern worldwide, leading to the adoption of innovative treatment solutions. Urban stormwater drains collect runoff and wastewater released from many urban entities. Canals passing through Kurunegala city have been a traditional means of irrigation but also serve as stormwater drains collecting polluted water causing public health problems. Communities have complained about commercial establishments, residents, institutions, and hospitals releasing untreated wastewater into these canals. In response, the Greater Kurunegala Sewage Treatment Plant (GKSTP) was commissioned to address the issue in 2018. The GKSTP is not covering the whole city and is not operated up to its maximum capacity (73% of the capacity is operated). This study aimed to investigate the impact of wastewater treatment by the GKSTP on water quality in canals passing through Kurunegala City. Water samples were collected from seven sampling sites along the canals during the dry (DS) and wet (WS) seasons. Physical, and chemical parameters were measured to determine the water quality from each sampling point. The study employed General Linear Model (GLM) to assess the spatial and temporal variations in physicochemical parameters of water. Cluster analysis identified patterns, and Analysis of Similarities evaluated the significance. Distance-based Redundancy Analysis analyzed overall parameter influence on seven locations. The effectiveness of the GKSTP in improving water quality was evaluated using the Water Quality Index (WQI). Physicochemical parameters of water along Kurunegala city canals exhibited notable spatial and temporal variation (pWQI>69) in the canals. The GKSTP has a positive impact on the water quality of the canals, with significant reductions observed on key indicators of organic pollution and sedimentation, such as BOD5 and TSS. Improvements have been noted in nitrate levels, indicating a reduction in acidity and nutrient pollution. These findings suggest that the GKSTP is partially effective in removing pollutants from the canals. Unconnected areas need to be connected to the GKSTP to improve the effectiveness of the treatment plant.
Impacts of a partially connected wastewater treatment plant on the water quality of stormwater drains used as an irrigation source
(2024) Samaraweera, S. A. P. T.; Najim, M. M. M.; Alotaibi, Bader Alhafi; Traore, Abou
Urban stormwater drains in Kurunegala City collect runoff and untreated wastewater, leading to public health problems. The Greater Kurunegala Sewage Treatment Plant (GKSTP) was commissioned in 2018 and currently operates at 73% of its capacity to combat public health issues. This study assessed the water quality of canals, comparing it with standards and pre- GKSTP conditions. Water samples were collected from seven sites during dry and wet seasons, and physicochemical parameters were measured. The data underwent spatial and temporal analysis using the general linear model (GLM). Additionally, cluster analysis and distance-based redundancy analysis were employed. The water quality index (WQI) was employed to evaluate the effectiveness of the treatment plant. The study revealed significant spatial and temporal variations in physicochemical parameters along the canals (p < 0.05, GLM), with higher pollution levels during wet months. The WQI improved from 35 (2005) to 49 at present, indicating enhanced water quality (p < 0.05, ANOVA), although it remains unsatisfactory. This study provides novel insights into the limitations of conventional wastewater treatment practices, demonstrating that merely treating wastewater and discharging it back into canals is insufficient. Research underscores the importance of rethinking treated wastewater reuse in achieving multiple sustainable development goals (SDGs). This approach offers a pragmatic path forward for enhancing water security and environmental] sustainability globally.
Insights into the effects of interspecific larval competition on Aedes aegypti (L.) and Aedes albopictus (Skuse) mosquitoes and dengue transmission
(Faculty of Science, University of Kelaniya Sri Lanka, 2024) Shalinda, K. A. N.; Jayasooriya, G. A. J. S. K.; Gunathilaka, R. A. K. M.; Samaraweera, S. A. P. T.; Ganehiarachchi, G. A. S. M.
In Sri Lanka, both Aedes aegypti and Aedes albopictus mosquitoes are prevalent and contribute to the transmission of dengue, a significant public health concern with high morbidity and mortality rates. Ae. aegypti predominates in urban environments and is a primary driver of dengue outbreaks, whereas Ae. albopictus, adaptable and found in both urban and rural areas, poses a persistent threat. While the effects on their life history and morphometrics when reared in isolation have been well investigated, the effects of their coexistence, which more closely reflect real-life scenarios in many parts of Sri Lanka, have not been thoroughly explored. Thus, this study addresses this gap by investigating the effects of interspecific larval competition on key biological parameters of both Ae. aegypti and Ae. albopictus, specifically focusing on larval duration, survival rates, and body size, particularly wing length. The study was conducted in the School of Entomology at the Medical Research Institute (MRI) in Colombo 08, Sri Lanka. The experimental design involved controlled laboratory settings where Ae. aegypti and Ae. albopictus larvae were reared either in isolation or in mixed-species groups. Eggs of both species, obtained from laboratory cultures, were hatched using the vacuum method to synchronize hatching times. Larvae were reared in 100 mL transparent plastic containers, with fifty larvae of each species reared separately and twenty-five larvae of each species reared together in mixed-species containers, each filled with 50 mL of distilled water. Larvae were fed with finely ground commercial fish food (Apex©), and feeding amounts were increased daily according to larval instar needs. Wing length was determined by mounting the separated wings on slides and measuring the radius vein length using a scale-mounted light microscope. Statistical analyses, including two-sample t-tests, were conducted using MINITAB 14 (Minitab Inc., 2004) to assess the effects of interspecific competition. Results indicate that both Ae. aegypti and Ae. albopictus exhibited longer larval durations when reared in mixedspecies conditions. Survival rates were not statistically significant for Ae. aegypti (p > 0.05) but increased in mixed-species environments, whereas survival of Ae. albopictus was significantly reduced in mixed-species conditions (p < 0.05). Morphometric analyses revealed significant differences in wing length between males and females of both species (p < 0.05). In males, wing length differences were not statistically significant (p > 0.05), but Ae. aegypti tended to have longer wings compared to Ae. albopictus in mixed-species environments. However, in females, wing length was significantly higher in Ae. aegypti and lower in Ae. albopictus (p < 0.05) when reared in mixed-species environments. In conclusion, interspecific competition between Ae. aegypti and Ae. albopictus influences larval development, survival rates, and body size differently for each species. Mixed-species conditions result in prolonged larval stages, altered survival rates, and distinct morphometric changes (i.e. wing length), with Ae. aegypti demonstrating characteristics suggestive of relative strength or competitive advantage compared to Ae. albopictus. The findings highlight the intricate dynamics of interspecific competition among Aedes mosquito species, emphasizing the need to consider these ecological interactions in strategies for controlling mosquito populations and mitigating dengue transmission, leading to more effective disease prevention efforts.
Preparation and laboratory evaluation of herbal stick formulations using mosquito repellent plant materials against Aedes aegypti and Aedes albopictus
(Faculty of Science, University of Kelaniya Sri Lanka, 2024) Fernando, M. U. D.; Jayasooriya, G. A. J. S. K.; Samaraweera, S. A. P. T.; Ganehiarachchi, G. A. S. M.
Dengue, caused by Aedes mosquitoes, remains a significant public health issue. Current vector control methods have been unable to effectively reduce the Aedes populations, thereby failing to control dengue transmission rates. This study has attempted to develop an effective and practical tool for the control of dengue transmission by dengue vectors, Aedes aegypti and Aedes albopictus by reducing vector population and human-vector contact using mosquito repellent plant materials. In the current study, to prepare the incense herbal sticks Ocimum Basilicum, Tagetes erecta, Mentha piperita, Syzygium aromaticum, Cinnamomum verum, Salvia rosmarinus, Laurus nobilis and Cymbopogon nardus were used as herbal materials while saw dust, charcoal powder and “Patta” powders were used as inactive ingredients. The final weight of the herbal stick was 1.5 g and three different herbal formulas were prepared. Adult mosquitoes were reared in the laboratory from eggs collected via ovitraps deployed in various locations. F1 generation of mosquitoes were used and, their age of exposure was 2 weeks. Ytube experiments (n = 21) were conducted to assess the repellent activity of incense sticks impregnated with different herbal extracts. Additionally, smoke toxicity tests were performed on adult female mosquitoes. Statistical analyses were conducted using JMP 5.01 (SAS Institute Inc., 2002). Data were initially tested for homogeneity of variances using O’Brien’s test (p < 0.05). For homogenous variances, ANOVA was applied; if variances were heteroscedastic, data transformation was attempted to rectify the issue. Persistent heteroscedasticity led to the use of Welch ANOVA. Significant treatment effects were further analyzed using the Tukey-Kramer HSD test (p < 0.05) to compare the mean values. Test results clearly indicated that all three treatments resulted in significant reductions in attraction of both A. aegypti (F2,6 = 10.23, p < 0.05); and A. albopictus (F2,6 = 13.07, p < 0.05). Among the three formulations, incense stick that contains 45 % of active ingredients acted as the best repellent to Aedes species. The smoke toxicity test results depicted that both Aedes species showed significant toxicity to three treatments i.e. 5%, 25% and 45%, p < 0.01). The highest mortality was obtained with 45% of active ingredients, followed by moderate toxicity at 25%, and the lowest mortality at 15%, demonstrating a dose-response relationship. Therefore, incense sticks that contain 45 % herbal ingredients could be recommended as supplementary method to reduce human-vector contact to both A. aegypti and A. albopictus mosquito species. For further improvement, long-term monitoring procedures should be established to evaluate the long-term effectiveness and user acceptability of these mosquito repellent formulations.