Browsing by Author "Chandrasekara, W. U."

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Avian diversity in some human-altered landscapes in the Gampaha district, Sri Lanka
(Faculty of Science, University of Kelaniya, Sri Lanka., 2021) Liyanage, M. P.; Chandrasekara, W. U.
Although diversity and distribution of avifauna have been mostly studied in and around undisturbed and protected areas in Sri Lanka, there is a dearth of studies in human-altered landscapes. The present study, therefore, was carried out to investigate the variation of avifaunal diversity in some human-altered landscapes viz garbage dump site (Manelgama village), town area (Kiribathgoda town), coconut cultivation (Gonahena village), paddy field (Weboda village), rubber cultivation (Embaraluwa village), and a fish landing site and market (Negombo town) in the Gampaha district in Sri Lanka. Birds present at each selected landscape were identified and counted following the fixed-radius point count method (n=4 each) between 0700 hrs – 0800 hrs from August 2020 to March 2021. The degree of landscape alteration of each site was measured in terms of the number of buildings, tall trees (5m<), fruit trees, power line posts, TV antennas/disks and sound level concurrent to bird counting. The species richness (SR), species heterogeneity (H’) and species evenness (J) of the avifaunal communities in each landscape were calculated. Data on the avifaunal abundance and the degree of landscape alteration were analysed using ANOVA and PCA as appropriate. Altogether, a total of 1126 bird counts were recorded, and the birds belonged into 26 different species. Although characterized by low avian heterogeneity and low species richness, the total abundance of birds was high at highly altered landscapes viz garbage dumpsite (n=566; SR=9; H’=1.23), fish market (n=276; SR=8; H’=0.90), and the town area (n=119; SR=5; H’=0.96). The house crow (Corvus splendens), intermediate egret (Mesophoyx intermedia) and the rock pigeon (Columba livia) dominated the six sites with the relative abundances of 33.04%, 28.69% and 18.65%, respectively. It was also found that the abundance of these three bird species were significantly high in the above highly altered landscapes (p<0.05). In contrast, the paddy field recorded the highest H’ (2.5), SR (16) and the J (0.90) values. The H’, J and the SR of the avian communities were also found to be negatively correlated with the degree of habitat alterations in a way that the avifaunal diversity measures decreased with the increasing habitat alterations by anthropogenic activities. Further, the more tolerant and generalist avian feeders such as house crow, intermediate egret, and rock pigeon can be regarded as bio-indicator species in human-altered landscapes.
A comparative study of the effect of salinity on egg laying preference, egg hatchability, and larval survival of Aedes aegypti and Aedes albopictus (Diptera: Culicidae): a laboratory assessment
(Faculty of Science, University of Kelaniya Sri Lanka, 2024) Madhushani, M. H.; Chandrasekara, W. U.
Mosquitoes are notorious vectors that transmit pathogenic diseases, including dengue hemorrhagic fever. Since the salinity level affects the breeding behaviour of mosquito vectors, a laboratory assessment was conducted to study the variation of egg-laying preference, egg hatchability, and larval survival of two dengue vector mosquitoes, Aedes aegypti and Aedes albopictus, by exposing them to predetermined periods at varying salinity levels. In this assessment, the egg-laying preference, egg hatchability and larval survival of laboratory-raised Ae. aegypti and Ae. albopictus colonies were measured respectively at 5-day intervals for 25 days at 0 ppt, 5 ppt, 10 ppt, 15 ppt, and 20 ppt salinity levels (n = 3 each). The egg-laying preference, egg hatchability, and larval survival data, each against the salinity level, exposure period and the mosquito species, were analysed by 3-way ANOVA, while the differences in the measured parameters between the two species were analysed by a two-sample ttest. Results revealed that the egg-laying preferences of the two mosquito species did not differ significantly from each other (Ae. aegypti 34.73 ± 6.4 and Ae. albopictus; 35.01 ± 5.9) (p > 0.05). Both species laid eggs from the 5th day upon exposure to the test solutions, and the number of eggs gradually increased with the increasing exposure period. Neither species laid eggs at 15 ppt and 20 ppt salinity levels (p < 0.05). The hatchability of Ae. aegypti eggs (12.9 ± 1.2) were significantly higher than that of Ae. albopictus eggs (9.7 ± 0.6) (p < 0.05). The eggs of neither species hatched at 15 ppt and 20 ppt salinity levels (p < 0.05). The larval survival of both species was statistically similar to each other (p > 0.05), but the survival of both species gradually decreased with the increasing exposure period. The larvae of both species did not survive in 15 ppt and 20 ppt salinity levels (p < 0.05). Since the Aedes mosquitoes thrive in areas close to human dwellings, the addition of common table salt into discarded water-filled containers, both indoors and outdoors, to make the water salinity above 10 ppt (<10 g salt in 1 litre of water) could be used as a promising alternative vector control method in integrated vector management programmes.
Effects of hydrological regimes and limnological parameters on plankton community properties in tropical irrigation reservoirs: A Sri Lankan case study
(Lakes & Reservoirs, 2021) Weerakoon, S. N.; Chandrasekara, W. U.; Amarasinghe, U. S.
Water-level fluctuations are reported to be key processes influencing ecosystem structure and functions in lentic aquatic ecosystems such as reservoirs. The plankton community structure in reservoirs, being useful mon1toring tools as reservoir trophic status indicators, are influenced by water quality parameters and water-level fluctuations. The present study tested the hypothesis that plankton community properties in irrigation reservoirs are influenced by hydrological regimes and physical and chemical parameters. Accordingly, the effects of physical, chemical and hydrological parameters on plankton density and taxa richness were Investigated for 10 selected irrigation reservoirs of Sri Lanka. The relative reservoir level fluctuation (RRLF), an index of the magnitude of water-level fluctuation In relation to mean depth, had a positive influence on phytoplankton density. Because the RRLF positively influenced phytoplankton density, this index appeared to favour eutrophy in reservoirs. Canonical correspondence analysis (CCA) indicated both the phytoplankton and zooplankton community structure in the study reservoirs was influenced by physical and chemical characteristics. CCA also indicated the plankton taxa abundance and water quality parameters could be used for the trophic classification of irrigation reservoirs. The results of the present study highlight the need for examining attributes based on hydrological regimes in the context of reservoir water quality management.
Herpetofaunal diversity and endemism in a fragmented forest patch: a study in Dombagaskanda forest reserve
(2023) Sandeepa, S. P. M.; Chandrasekara, W. U.
Fragmented forest patches provide refuge for distressed animal forms including amphibians and reptiles (herpetofauna) but an array of adverse anthropogenic impacts often threatens them. Surrounded by human settlements, the Domabagaskanda Forest Reserve (DFR) is one such small, threatened, fragmented forest patch (area 192 ha) in the wet zone of the country. In this research, we studied the variation of the herpetofaunal diversity along a seasonal and spatial scale in the DFR and evaluated their endemism and conservation status against the National Red List 2012 of Sri Lanka. The research design included surveying herpetofauna within (viz. forest zone and monastery zone) and around the DFR (viz. outer buffer zone) during the wet season (November to December 2022) and dry season (January to March 2023) using a quadrat sampling strategy. The herpetofauna diversity in these three zones was calculated using the species richness (SR), Shannon-Weiver index (H’), and Pielou’s evenness index (J’). The canopy cover, air and soil temperature, humidity, and tree diameter in the quadrat sampling areas were also measured. A total of 125 individuals belonging to 14 reptilian and 11 amphibian species were identified. They showed a distinct spatial variation where their total abundance and diversity within the monastery zone were greater (N=40, SR=14, H’=2.507, J’=0.9501) than in the forest zone (N=26, SR=13, H’=2.418, J’=0.9427) and the peripheral buffer zone (N=21, SR=9, H’=1.934, J’=0.8801). They also showed a seasonal variation where their total abundance and diversity were higher during the dry season than in the wet season. Five (05) reptile and 08 amphibian species were endemic to Sri Lanka, representing 42% reptilian and 73% amphibian endemism. The endemism percentage (%) of herpetofauna within the DFR is 56.5%, which is 13 times higher than that in the outer buffer zone (4.6%). Of the 05 endemic reptile species, 02 are endangered, whereas of the 08 endemic amphibian species, 04 are endangered. Despite its small size, results suggest that the DFR is a rich biodiversity repository with a high herpetofaunal endemism, of which most are endangered. Results also insist on the grave need to protect and conserve small, fragmented forest patches, similar to DFR, from further human threats.
Impacts of rubber factory wastewater on the stream macrobenthic assemblages
(Faculty of Science, University of Kelaniya Sri Lanka, 2022) Dilhara, K. G. A.; Chandrasekara, W. U.
In this study, we assessed how the rubber factory wastewater effluents change the water quality and sediment quality parameters in some factory-associated streams, namely the Aswathu Oya, Gurugoda Oya, and Rakwatthe Ela, in the wet zone of Sri Lanka, and how such changes influence the inhabiting macrobenthic assemblages. For this assessment, we established 06 sampling sites at the Aswathu Oya based on the judgmental sampling technique [viz. Site A (rubber factory wastewater effluent canal, Site B (point of effluent discharge in the stream, Site C (50 m upstream control site), Site D (50 m downstream site from site B, Site D (100 m downstream site from Site B, and Site E (150 m downstream site from site B], measured some water quality parameters [viz. Dissolved oxygen (DO), Chemical oxygen demand (COD), Biological oxygen demand (BOD5), Conductivity, Total dissolved solids (TDS), Temperature (T), and pH] and sediment quality parameters [Organic matter content (OMC)] and, sampled the macrobenthic faunas in each site from December 2021 to January 2022 following standard field sampling techniques. We also retrieved the secondary research data from other streams that were also subjected to rubber factory wastewater effluents, namely Rakwatte Ela (2001) and Gurugoda Oya (2011), where both studies followed a similar sampling protocol. Data were analysed using univariate and multivariate statistical methods as appropriate. Although a certain degree of variation in data in the 03 temporal frames was noted, results revealed that all 03 streams share a common variation pattern in the water quality, sediment quality, and macrobenthic assemblages. For example, the COD, BOD5, OMC, conductivity, and TDS levels were elevated, and the DO level was reduced significantly (p<0.5; ANOVA) in the highly polluted A and B sites in all 03 streams. The abundance of some macrobenthic species, particularly the tubificids and chironomids, was also significantly high (p<0.5; ANOVA) in these 02 sites. In contrast, the COD, BOD5, OMC, conductivity, and TDS levels were low, but the DO level was significantly high in the furthest downstream site F and the upstream site C (p<0.5; ANOVA), but none of these parameters were significantly different between the two sites (p>0.05 ANOVA). The abundance of chironomids and tubificids was also significantly low in C and F sites compared to the highly polluted A and B sites (p<0.5; ANOVA). The species heterogeneity (H’), richness (SR), and evenness (J’) of the macrobenthic assemblages elevated at the furthermost site F, where they became almost the same as those in upstream control site C. Therefore, the changes made by the rubber factory effluents to the water/sediment quality and the macrobenthic assemblages in the factory-associated streams are never permanent and disappear within a relatively short stretch of 150 m along the streams, most probably due to dilution of wastewater along the stream and the pollution-tolerant tubificids and chironomids are excellent bioindicator candidates to detect such changes.
Macrobenthic diversity and their potential as bio-indicators in some urban reservoirs in the Western province, Sri Lanka
(Faculty of Science, University of Kelaniya, Sri Lanka., 2021) Perera, G. A. C. D.; Chandrasekara, W. U.
Studies addressing the macrobenthic diversity and their potential as bio-indicators in water quality assessment programmes are scarce in Sri Lanka. In this study, we investigated the macrobenthic diversity in relation to water quality parameters in some urban reservoirs in the Western province in Sri Lanka, and assessed their potential as bio-indicators in water quality assessment programmes. The reservoirs selected for the study were the Ihalagama tank, Peralanda tank, Kesbewa tank, Boralesgamuwa tank, Bolgoda Lake, and the Beira Lake. The abundance of macrobenthic faunas at randomly selected locations (n=9) in each reservoir, and the water quality parameters viz temperature, pH, conductivity, total dissolved solids, BOD5, dissolved nitrates, total dissolved phosphates and alkalinity of the overlying water at each location were measured using standard data collection methods between July, 2020 to January, 2021. The species richness (SR), species heterogeneity (H’) and species evenness (J) for the macrobenthic fauna in each reservior were calculated, and the abundance and water quality data were analyzed using ANOVA and PCA as appropriate. Altogether, thirteen macrobenthic taxa namely, Glyphidrilus sp., Limnodrilus socialis, Dero sp., Stratiomyd larva, Chironomid larva, Bellamya sp., Melanoides tuberculata, Gyraulus sp., Lymnaea sp., Paludomus sp., Thiara sp., Ancylus sp., and Mesostoma sp. were recorded from the six reservoirs. The tubificid worm L. socialis dominated in all the sediment samples and accounted for more than 94.7% of the total macrobenthic abundance where the highest relative abundance of this species was recorded at the Beira Lake (99.3%). The species richness of the macrobenthic community was the highest at the Ihalagama and Kesbewa tanks (SR=5), while it was the lowest at the Peralanda tank (SR=2). Since the benthic community was mainly dominated by L. socialis, the lowest species heterogeneity as well as the species evenness values were recorded at the Beira Lake (H՜ = 0.05; J = 0.03). Further, the water quality parameters varied among the selected reservoirs, where the Beira Lake registered significantly high BOD 5, dissolved nitrates, and total dissolved phosphates (p<0.05) than the other reservoirs, indicating a higher degree of eutrophication. In addition, the SR, J, and the H’ in the studied reservoirs decreased with the increasing levels of BOD5, dissolved nitrates, and total dissolved phosphates. Therefore, it was concluded that the abundance and diversity of macrobenthic faunas are primarily governed by water quality parameters, and the tubificid worm L. socialis can be used as a potential bio-indicator organism in water quality assessment programmes in urban reservoirs.
Variation of water quality parameters and brush park fish diversity: a study in Negombo estuary
(2023) Ratnayake, R. P. P.; Chandrasekara, W. U.
In the Negombo estuary, the brush park fishery is confined to two small zones along its Eastern Katunayake side and the Western Dungalpitiya side, with approximately 50 brush parks each. In this research, we investigated what factors, whether seasonal or water-quality related, contributed to the brush park fishery being confined into these two zones. Three (03) randomly selected brush parks were sampled from each zone during the rainy season (November to December 2022), and the fishes in each brush park were identified to the maximum possible taxonomic category and enumerated separately. Further, the water quality parameters within those selected brush parks were measured using standard field and laboratory procedures. This procedure was repeated for another set of 03 brush parks in each zone during the dry season (February to April 2023). The fish diversity in each brush park was calculated using the Shannon-Weiver (H’) and Pielou’s evenness (J’) indices. Fish abundance data and water quality data between the two zones and between the two seasons were analysed parametrically and nonparametrically as appropriate. Altogether, 18 taxa belonging to 16 finfish and shellfish families were recorded. Of the water quality parameters measured, the salinity, electrical conductivity, dissolved phosphates, and Ch-a increased significantly at both zones during the dry season. These water quality changes induced many marine species, including Siganus sp. and Acanthophagous berda to migrate into the two zones, resulting in Siganus sp. contributing about 42% and Acanthophagous berda contributing about 33% of the fish catch at Dungalpitiya and Katunayake, respectively. When the salinity, in particular, dropped near zero in both zones during the rainy season, these marine species migrated back. The same salinity drop induced the freshwater Macrobrachium rosenbergii to migrate into the two zones in large numbers during the rainy season, contributing about 61% and 30% of the fish catch at Katunayake and Dungalpitiya, respectively. It was apparent that M. rosenbergii dominates the brush park fish catch during the rainy season, while the marine Siganus sp. and A. berda dominate it during the dry season. The brush park fish diversity was higher in both zones during the dry season than in the wet season. For example, the SR, N, H’, and J’ at Katunayake during the dry season were 15, 425, 1.651, and 0.6098, while 7, 87, 0.5189, and 1.01 during the wet season. Results also suggest that the seasonal and zonal changes of salinity, dissolved phosphates, and Ch-a govern the brush park fish diversity in the Negombo estuary.