Browsing by Author "Amarasinghe, D. A. N. M."

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    Ichthyofaunal diversity of the SS Orestes shipwreck, Unawatuna, Sri Lanka
    (Faculty of Science, University of Kelaniya Sri Lanka, 2024) Amarasinghe, D. A. N. M.; Batugedara, B. D. I. M.; Handapangoda, H. M. K. D.; Senanayake, S. A. M. A. I. K.
    Artificial reefs, including shipwrecks, play a crucial role in enhancing marine biodiversity. The Unawatuna region has witnessed numerous shipwrecks over time, enriching the area’s maritime narrative. The SS Orestes shipwreck, located 4 km off the Unawatuna shore at a depth of 24 meters, provides a unique artificial reef environment. The present study was conducted to determine the ichthyofaunal diversity and species richness at the SS Orestes shipwreck, assessing the role of the shipwreck as a habitat for the fish community. The study was conducted once a month, between 9 a.m. to 12 p.m., from January 2024 to March 2024. Data on fish species were collected by using video surveys conducted by SCUBA diving. A GoPro hero 10 camera was used to collect relevant data. Fish species were identified to the lowest possible taxonomic level using standard keys and guides and then counted using video transects. Further, diversity indices (Shannon-Wiener diversity index and Simpson’s index of diversity) were calculated to determine the ichthyofaunal diversity at the study site. A total of 31 fish species belonging to 18 families were recorded at the SS Orestes shipwreck, indicating a rich and diverse marine ecosystem. The Shannon-Wiener diversity index was 2.79, and the Simpson’s index of diversity was 0.91, with an evenness value of 0.53. Family Pomacentridae (six species - Chrysiptera parasema, Neopomacentrus filamentosus, Amphiprion polymnus, Dascyllus trimaculatus, Chromis xanthochira, Neopomacentrus azysron) had the highest species richness among the ichthyofauna families. Family Lutjanidae (Lutjanus fulviflamma, Lutjanus kasmira, Lutjanus carponotatus, Lutjanus fulvus) had the highest individual fish count during the survey at a species level. Therefore, it can be concluded that SS Orestes shipwreck acts as an important artificial reef, fostering a diverse fish community and enhancing marine biodiversity. Further, the study site is important for fisheries, tourism, and scientific research.
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    Irrigation water quality index based suitability assessment of Mamunugama Tank cascade system
    (Faculty of Science, University of Kelaniya Sri Lanka, 2024) Amarasinghe, D. A. N. M.; Batugedara, B. D. I. M.; Handapangoda, H. M. K. D.; Senanayake, S. A. M. A. I. K.
    Tank cascade systems are considered as one of the traditional land water management systems that have been accepted as globally important agricultural heritage system. This study was conducted to assess the suitability of water for irrigation purposes in the Mamunugama Tank Cascade System (TCS), located in the Kurunegala district, specifically in terms of water quality parameters that affect irrigation. This TCS consists of six interconnected tanks: Ulpath Tank, Athaudagama Tank, Ihala Thimbiriyawa Tank, Mamunugama Tank, Kandubodagama Tank, and Weera Tank. Three water samples were collected from each tank on a monthly basis over a period of seven months, from August 2023 to February 2024. Water samples were analyzed for selected water quality parameters. The metals (Ca, Mg, Na, K) required for calculating the irrigation indices were analyzed using a Flame Atomic Absorption Spectrometer, while EC was measured using a conductivity meter. The HCO3- was determined using a titrimetric method. Irrigation suitability was assessed using sodium percentage (Na%), sodium adsorption ratio, permeability index (PI), magnesium hazard, Kelly’s Ratio, and salinity hazard. Sodium percentage ranged from 20.6 ± 3.5 % to 30.8 ± 4.8% during dry months, graded all tanks as good. In wet months, Na% ranged from 13.2 ± 4.4 to 36.6 ± 51, graded as excellent to good. The possible sources of sodium in the water could include natural weathering of minerals in the soil and agricultural runoff containing sodium-based fertilizers. The Sodium adsorption ratio ranged from 0.25 ± 0.09 to 0.78 ± 0.10. It was graded as excellent across all tanks in both dry and wet months. Athaudagama Tank (89.78 ± 51.50) and Wera Tank (99.52 ± 22.43) have suitable water quality during dry months, whereas the other tanks have moderately suitable water based on PI. During wet months, the PI ranged from 111.69 ± 23.01 to 192.97 ± 38.22, indicating that all tank water was suitable for irrigation. According to the Magnesium Hazard assessment, Mamunugama and Wera Tanks were unsuitable for irrigation in both dry and wet months, while the remaining tanks were suitable. Kelly’s Ratio was well below the threshold value in all the tanks during both dry and wet months. There was a notable increase in salinity hazard during dry months compared to wet months. The Irrigation Water Quality Index, based on the parameters sodium percentage, sodium adsorption ratio, permeability index, magnesium hazard, Kelly’s ratio and salinity hazard, rated the water in all tanks as good to excellent for irrigation. This indicates a stable water quality profile, with occasional shifts in certain parameters during different seasons.