http://ir.lib.ruh.ac.lk/handle/iruor/20933 Mon, 08 Jun 2026 20:21:28 GMT 2026-06-08T20:21:28Z http://ir.lib.ruh.ac.lk/handle/iruor/20977 A comparative analysis on diel vertical migration of zooplankton in littoral and limnetic zones of a reservoir in Sri Lanka. Jayawardhane, S.S.; Jayasinghe, U.A.D.; Wijewardene, L.N. Diel Vertical Migration (DVM) is a behavior displayed by many zooplankton in freshwater and marine habitats to avoid the visual predation risk. Usually, they perform a behavior pattern of ascending to the upper pelagic region during the nighttime and descending to deeper water layers during the daytime. The present study aimed to investigate the DVM of zooplankton in a tropical reservoir and compare the differences if any in limnetic and littoral zones. The research was conducted in Hambegamuwa reservoir in Monaragala District, Sri Lanka. Zooplankton samples and abiotic data were collected at four-hour intervals throughout 24 hours in each sampling day. Three sampling days from dry season to rainy season (August 2023 to November 2023) were considered. All data were collected at fixed depths i.e. surface and 3 ft in the littoral zone and surface, 3 ft and 6 ft in the limnetic zone. Three main zooplankton phyla were identified as Rotifera, Arthropoda and Sarcomastigophora, and were quantified as individuals L-1. They included seven genera of Rotifera and two genera of Arthropods. Canopy cover, aquatic vegetation and other hydrological parameters were different between the littoral and limnetic zones. In the limnetic zone, the DO had a significant negative correlation with depth (r= -0.828) and turbidity had a significant positive correlation with depth (r= 0.626). In the limnetic zone, the bottom layer exhibited the highest percentage abundance values of zooplankton in the morning, while the topmost layer has higher values during the darker hours The results exhibited that only the limnetic zone possessed a DVM pattern of zooplankton. Same taxonomic group exhibited different DVM patterns at limnetic and littoral zones. In littoral zone, only the phylum Sarcomastigophora exhibited DVM. Abundant food availability and shelter from vegetation reducing predation risk might be the reasons for the absence of the DVM pattern in the littoral zone. Fri, 08 Nov 2024 00:00:00 GMT http://ir.lib.ruh.ac.lk/handle/iruor/20977 2024-11-08T00:00:00Z http://ir.lib.ruh.ac.lk/handle/iruor/20973 Evaluation of acute toxicity of textile dye (reactive red 123) on Chlorella vulgaris and Spirulina platensis. Thinujan, M.; Maithreepala, R.A.; Asanthi, H.B.; Atapaththu, K.S.S. Microalgae are an ecologically important group of organisms in the aquatic environment due to their major role as primary producers. They are highly vulnerable to an array of stresses including different types of manmade chemical products, including textile dyes. Although many of textile dyes are known to be emerging environmental toxicants in aquatic environments, information on their toxicity on aquatic microalgae is limited Therefore, the present study was designed to assess the stress responses of aquatic microalgae using Chlorella vulgaris (Green algae) and Spirulina platensis (Blue-green algae) against reactive red 123 (RR123) which is frequently used in textile industries. C. vulgaris and S. platensis were exposed to solutions with six concentrations (0 (control), 80, 120, 160, 200, and 240 mgL-1) of RR123 dye. Each concentration with three replicates was exposed to the above two species for 96 hours following standard guidelines (Organization for Economic Co-operation and Development guidelines 201). At the end of the experiment, algae growth rate, growth inhibition, pigment contents (chlorophyll-a, chlorophyll-b, and carotenoids), H2O2 contents, and morphological changes of algae exposed to different concentrations were compared. A risk assessment was performed to determine the risk by using the EC50 value. The highest growth rates of both algae were observed in the control groups, and growth rates decreased in a concentration-dependent manner where the lowest growth was exhibited in algae exposed to the highest dye concentration (240 mgL-1). The EC50 values for the toxicant were 122.21 and 71.91 mgL-1 for C. vulgaris and S. platensis respectively. The pigment contents of both algae decreased with increasing the exposure level. After 96 hours of exposure, the EC50 values for the toxicant's effect on chlorophyll-a, chlorophyll-b, and carotenoid of C. vulgaris were 99.5, 101.45, and 105.5 mgL-1, respectively, while the same values of S. platensis, were 38.45, 38.5, and 39 mgL-1respectively. Present findings indicate that S. platensis is more vulnerable than C. vulgaris for RR123 dye, and their responses against the tested dye were species-specific. The findings of this study are important to clarify the interaction between textile dye waste and aquatic microalgae, and such information would benefit in formulating criteria for aquatic ecosystem management. Fri, 08 Nov 2024 00:00:00 GMT http://ir.lib.ruh.ac.lk/handle/iruor/20973 2024-11-08T00:00:00Z http://ir.lib.ruh.ac.lk/handle/iruor/20971 Determination of the maximum permissible level of tannin in wastewater released to surface waters. Luxshayan, P.; Maithreepala, R.A.; Sanjaya, H.L.K. Tannins are found in many field herbs and legumes. They are astringent and bitter plant polyphenols that bind, precipitate or shrink proteins and certain other organic compounds. Tannin is released to the environment by the industries that are based on plant materials as their raw materials. The dissolution of Tannic Acid (TA) in water affects the physiochemical parameters of wastewater. This change can cause toxic effects on living organisms and change the ecosystem balance. As phytoplankton are the base of a food chain, Chlorella vulgaris was used for the estimation of the minimum tolerance level of TA in this study. Chlorella vulgaris is resistant to harsh conditions and invaders. Different concentration of TA of concentrations from 0 ppm to 100 ppm at an interval of 10 ppm and from 100 ppm to 1000 ppm at an interval of 100 ppm was prepared and the change of physiochemical parameters such as pH, Chemical Oxygen Demand (COD) , Salinity, Conductivity, TDS, Temperature of water was measured. The limit was determined at the concentration of TA which breaches any of the water quality standard published by Central Environmental Authority (CEA) of Sri Lanka. The parameters such as pH and Chemical Oxygen Demand showed rapid variations even at smaller concentrations. At a TA concentration of 70 ppm, the pH goes below the permissible level of 6.0 and at a concentration of 200 ppm of TA the COD goes above the permissible level of 250 ppm. An acute toxicity assessment was carried out after providing suitable laboratory conditions for the growth of Chlorella vulgaris. During acute toxicity assessment, primary producers survived up to a concentration of 60 ppm. The cell count increases slightly in the first day for control setup, 50 ppm, 60 ppm, and 70 ppm. The rate of increase was more in 60 ppm than in 50 ppm compared to 0 ppm. Though, 70 ppm shows slight increase in day 1 afterwards the cell count was constant throughout 4 days. The cell count change in 80 ppm and 90 ppm concentration showed sudden increase in day 1 and afterwards the cell count was constant throughout 4 days. Therefore our, study suggests that the maximum permissible level for Tannin in wastewater released to the environment should be less than 60 ppm. Fri, 08 Nov 2024 00:00:00 GMT http://ir.lib.ruh.ac.lk/handle/iruor/20971 2024-11-08T00:00:00Z http://ir.lib.ruh.ac.lk/handle/iruor/20970 Present status of beach seine fishery in southern coast of Sri Lanka. Imasha, K.I.C.; Deepananda, K.H.M.A.; Bandara, E.G.K.Y.C. Beach seine fishery is one of Sri Lanka's oldest fishing methods. The study aims to assess the status of beach seine harbors and fisheries activities, direct and indirect involvement of people, target species, management strategies, and factors influencing the status of the beach seine fishery in Matara, Tangalle and Galle fisheries administrative districts. Data was collected from October to November in 2023 by using standard ethnographic methods. Galle district has the majority of beach seine harbors (62.5%) on the southern coast while Matara district has the least (6.25%). Tangalle district has the highest number of active beach seines (62.41%), followed by Galle (30.08%) and Matara (7.52%). Anchovies were identified as the main target species and 75% of beach seine harbors primarily use cod ends with mesh size of 5 mm. Beach seine sites typically have 10-15 skilled crew and 20-40 temporary laborers. Ninety percent of harbors are impacted by the southwest monsoon restricting fishing activities from October to April. Beach seine operations follow a rotational sequence, either on a daily basis or through a time-based method. The catch on the southern coast includes various coastal pelagic and demersal fish species, such as those from the families Engraulidae, Clupeidae, Carangidae, Trichiuridae, Sphyraenidae, Lactaridae and Scombridae. Profits are divided equally, with one half is given to the owner and the other half to permanent workers, while a portion of the yield is given to temporary workers. Most of the interviewed fishermen believe that purse seine fishing activities negatively affect beach seine harvests leading to the decreased interest among the younger generations. Further studies and management strategies are vital to prevent the collapse of this traditional fishing method. Proper analysis of coastal constructions should consider local community opinions as well. Addressing illegal fishing methods, and providing reliable fishing equipment and government subsidies are recommended for maintaining the sustainability of this fishing method. Fri, 08 Nov 2024 00:00:00 GMT http://ir.lib.ruh.ac.lk/handle/iruor/20970 2024-11-08T00:00:00Z