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    Spatial variations of macrobenthic assemblage structure along paddy-based runof- river irrigation system: A case study from Colombo, Sri Lanka
    (Faculty of Science, University of Kelaniya Sri Lanka, 2023) Dasanayaka, D.M.P.I.; Najim, M.M.M.
    In a paddy-based run-of-river irrigation system, quality of water varies spatially along the river, which influences the biodiversity present in an aquatic ecosystem. With the spatial variations, macrobenthic fauna living along a run-of-river system also vary. The major objective of this study was to analyze the spatial variation of macrobenthos along a run-of-river irrigation system. The selected study area is located in Uduwana near Homagama in Colombo District. The study paddy field is mainly irrigated using two natural streams which are named Kalu Ganga athu ela and Thel Ela and irrigated water is drained to a natural stream named Kunu Ela. Four sampling sites were taken judgmentally as covering different areas of the run-of-river irrigation system. A random sampling technique was employed, and two bottom sediment samples were collected using a Peterson grab sampler on monthly basis from each sampling site between September 2022 to February 2023 (Maha cultivation season). Sediments were wet sieved through 0.5 mm mesh and collected macrobenthos were identified using standard keys. Total abundance, species richness, species evenness, and species heterogeneity were determined separately for the four sites. The spatial variation of total abundance between the four sites was analyzed using one-way ANOVA in MINITAB version 17.0. Similarities of macrobenthos community assemblages were assessed using Bray-Curtis similarity clustering method using PRIMER. A total of 8 macrobenthic taxa (Pila globosa, Lymnaea pinguis, Gyraulus saigonensis, Melanoides turberculata, Hirudo sp., Glyphidrilus sp., Paratelphusa sp., and Chironomidae sp.) were observed from sampling sites. Lymnaea pinguis and Chironomidae sp. dominated in sediment samples and accounted for more than 70% of the total macrobenthic abundance. Sampling site 2 recorded the highest total abundance (N=350) and site 1 recorded the lowest total abundance (N=115) throughout the sampling period. The species richness of the macrobenthic communities was similar in sites 1, 3, and 4 (S=6) while the species richness was 5 in site 2. Since the benthic community was mainly dominated by Lymnaea pinguis, the lowest species heterogeneity (H’) and species evenness (J) values were observed in sampling site 2 (H′ = 0.11; J = 0.79). According to the results of ANOVA, the abundance of Pila globosa, Lymnaea pinguis, and Gyraulus saigonesis showed spatial variations. The cluster analysis separated site 2 from other sites, indicating that the macrobenthic taxa in site 2 are varied compared to the other three sites. Thus, the results revealed that there were spatial variations in the distribution pattern of macrobenthos along a paddy-based run-of-river irrigation system. It is recommended to extend the sampling period to include both Yala and Maha cultivation seasons with more sampling sites to get a better understanding of the spatial variations in the distribution patterns of macrobenthos along the paddy-based run-of-river irrigation system.
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    Salinity Development in the Dry Zone of Sri Lanka – a Review
    (Salinity Development in Sri Lanka-Abstract, 2008) Najim, M.M.M.; Jayakody, K.P.K.
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    Health implications related to mismanagement of domestic and municipal wastewater in Sri Lanka.
    (Sage Publishers, India., 2011) Najim, M.M.M.; Rajapakshe, I.H.
    TRADITIONALLY IN SRI LANKAN villages domestic wastewater, especially grey-water generated from kitchens and bathrooms of a household, fl ows along open unlined wastewater drains and is collected in a garden pool known as kohila wala or vegetation pool. This pool is a kind of traditionally constructed wetland. Main vegetation type cultivated in the wetland is kohila (Lasia spinosa) which is used as a leafy and stem vegetable. Medicinal and other important plants are also grown along the drains that utilise the wastewater and its nutrients. This system of grey-water disposal and utilisation was always kept separate from the black-water disposal system as the latter is disposed to individual cesspits located in home gardens. In the traditional sys tem, natural capacity to treat wastewater without any harmful effects to groundwater was possible due to low population density and land availability. With the population expansion in urban centres, the land value increased and land area available for the traditional wastewater treatment process shrank.
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    Adapting Sri Lanka to Climate Change: Approaches to Water Modelling in the Upper Mahaweli Catchment Area
    (Climate Change Research at Universities. Springer, Cham, 2017) Gunawardena, M.P.; Najim, M.M.M.
    Water flow and water quality changes in surface water bodies due to climate change is a major problem worldwide, typically in river eco-systems. To address these issues, proper monitoring of river flow variations and water quality is necessary, but daily monitoring and data collection is greatly time consuming and costly. Therefore, a study was done with the objectives to calibrate and validate the HEC-HMS 3.5 and HEC-RAS 4.1.0 models to simulate flow variation and water quality variations respectively in Nillambe Oya, Sri Lanka. The development of such models are a significant requirement in the present scientific world to predict river flow and water quality variations as an adaptation for the climate change. The HEC-HMS 3.5 model was used to generate flow which is needed for HEC-RAS 4.1.0. Daily flow data for five years (from October 1991 to September 1996) were used to calibrate the HEC-HMS 3.5 model and another set of daily flow data for five years (from October 1994 to September 1999) were used to validate the model. HEC-RAS 4.1.0 model was calibrated using water quality data collected and analyzed in five days. The validity of the calibrated model was evaluated using water quality data collected in the other four days. The calibrated and validated HEC-HMS 3.5 model reliably predicted the flow in Nillambe Oya. The calibrated and validated HEC-RAS 4.1.0 model simulated Dissolved Oxygen (DO), Biological Oxygen Demand (BOD) and Nitrate Nitrogen (NO3-N) splendidly. Orthophosphates was also predicted reliably by the model, but the simulation of organic Phosphorus was not that sensible.
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    Climate Change Induced Variations in Rainfall Patterns and Potential Adaptation Options of DL1b Agro-Ecological Zone of Sri Lanka: A Case Study
    (Institute of Biology Sri Lanka, Colombo., 2020) Udayanga, L.N.W.B.A.; Najim, M.M.M.
    An analysis of the shifts and trends of climate patterns with respect to wet and dry events and rainfall seasonality is vital for the effective planning and management of water resources in tropical countries such as Sri Lanka, which have agriculture-based economies. Hence, temporal and spatial variations of climate extremes and rainfall seasonality in Sri Lanka, were evaluated in the DL1b Agro-Ecological Zone through the Standardized Precipitation Index (SPI) and Seasonality Index (SI) utilizing 58 years of daily rainfall data of five selected localities. The Chi-square test of independence was used to statistically compare the percentage occurrence of each event recorded during 1961-1988 and 1989-2018. The dryness of all study areas denoted increments in terms of both severity and frequency of occurrence in accordance with SPI. However, among the studied localities of the DL1b agro-ecological zone, only the increment of dryness in Vavuniya remained statistically significant (Χ2 (df = 4) <9.78; P=0.04) at 95% level of confidence. Rainfall seasonality of the localities was characterized with a markedly seasonal climatic condition with a long, dry season (0.95 – 0.97) with no significant variations and shifts. Cultivation of low water demanding crops, adjustment of cropping seasons, use of more efficient water smart irrigation methods, implementation of agro-forestry systems and employment of smart and integrated watershed management practices could be recommended as potential adaptation measures to compensate the impacts of climatic change.
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    A Mathematical Model for Control of Drainage in an Irrigation System
    (Emerging Challenges to Food Production and Security in Asia, Middle East, and Africa. Springer, Cham, 2021) Hajiyev, A.; Rustamov, Y.; Najim, M.M.M.
    Mathematical models describing the estimation of optimal amounts of water depend on various parameters such as the quality of soil that depends on many random factors. Investigation methods and approaches of the random processes of those parameters play an important role. In irrigation systems, drainage systems are widely used to achieve multiple objectives and it is necessary to pay attention to the choice of mathematical models that are adequately describing the processes of drainage and control of groundwater levels. An algorithm for the regulation and prevention of salinization of arable land and swampy areas in addition to an estimation of the amount of drainage water, have been proposed. Behaviour of the groundwater (temporal variation) is analysed applying the proposed model. Under the given conditions, it was derived that for an isotropic and homogeneous case, the level of the priming relative to axis x is approximately stable. A change in other parameters leads to the reduction of the effectiveness of drainage system and, consequently, to decreasing the level of water. Hence, using some engineering processes, it is necessary to increase the velocity of water through the drainage system.
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    Seasonal Variation of Rainfall at Attanagalu Oya Basin
    (Geo-Informatics Society of Sri Lanka, Peradeniya. Sri Lanka., 2012) Waniganethti, D.; Najim, M.M.M.; Halwatura, D
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    Trends in Dry and Wet Events of Rainfall in Aththanagalu Oya Basin
    (Geo-Informatics Society of Sri Lanka, Peradeniya. Sri Lanka, 2014) Udayanga, N.W.B.A.L.; Najim, M.M.M.
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    Quantitative analysis of water quality and heavy metals in water, sediments and tissues of Grey Mullet (Mugil cephalus) from the Negombo estuary
    (Colombo Journal of Multi-Disciplinary Research, 2015) Mendis, B.R.C.; Najim, M.M.M.; Kithsiri, H.M.P
    The objectives of this study were to assess the levels of water quality and heavy metals of the water, sediments and fish tissues in the Negombo estuaries. For this study, samples were collected from sixteen sampling locations during the one year study period from January to December 2014. The results revealed that the average concentrations of ammonia, nitrate, pH, electrical conductivity, total suspended solids of 0.215±0.4mg/l, 1.08±0.98mg/l, 7.8±0.28, 29.6±1.56ms/cm, 29.2±0.35mg/l, levels were below the maximum permissible limits. Biochemical Oxygen Demand 24.8±1.3mg/l and Chemical Oxygen Demand 469.0±36.5mg/l levels were much higher than the permissible threshold limits of industrial wastewater quality standards for CEA,(2001) Sri Lanka. The results indicated that the concentrations (ppm) of heavy metals in water were Pb,0.01±0.0003; Cd,0.015±0.003; Hg,0.013±0.001; Zn,0.695±0.06; Cu,0.03±0.02; Cr,0.055±0.004 and Fe,0.485±0.04 respectively. The sediments concentrations (mg/kg) were Pb,7.95±0.95; Cd,1.06±0.23; Hg,0.001±0.52; Cu,0.042±3.2; Cr,14.30±1.5, Zn,154.25±3.2 and Fe,78.6±101.2 respectively. The concentrations (mg/kg) of metals in the fish tissues were Pb,0.57±0.48; Cd,1.045±0.28; Hg,0.05±0.046; Zn,119.2±111.3; Cu,4.60±1.64; Cr,5.22±2.49 and Fe,32.8±59.3 respectively. The highest concentrations of pollution status were recorded in the Northern region of the estuary.
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    Bioaccumulation of Heavy Metals in the Selected Commercially Important Edible Fish Species Gray Mullet (Mugil cephalus) from Negombo Estuary.
    (Journal of Environmental Professionals Sri Lanka,, 2015) Mendis, B.R.C.; Najim, M.M.M.; Kithsiri, H.M.P.; Azmy, S.A.M.
    Consumption of fish contaminated with non essential heavy metals such as Pb, Hg and Cd metals which exceed the required limits pose a risk to human health. Bioaccumulations of heavy metals in fish depend on several factors such as increased levels of industrial pollution and domestic solid waste dumping in the estuary. Based on the pollution inputs into the estuary, it is considered that different localities within the estuary are polluted at different rates. The objectives of this study were to determine the non essential heavy metals concentration in fish tissues and assess the seasonal variations in the ecosystem. For this study, fish tissue samples were collected from nine sampling locations along the North (n =3), South (n=2), West (n=2), and East (n=2) parts of the estuary for a period of one year from January to December 2014. Fish tissue heavy metals levels were analyzed employing standard methods. Results revealed that the average concentrations (mg/kg) varied from Pb 0 to 0.15 ± 0.06, Cd 0.35 ± 0.16 to 1.04 ± 0.28 and Hg 0.0005 ± 0.0004 to 0.05 ± 0.046 mg/kg respectively. The detected levels were below the maximum permissible limits for hazardous substances in fish and fishery products for recommendation of FAO. The detected lead, mercury and cadmium contents in fish tissue were below the standard limits defined for each element < 0.5 mg/kg < 0.05 mg/kg and < 0.05 mg/kg respectively. Significant differences (P< 0.05) were observed for Pb and Hg depending on fish tissues. The levels of Pb and Hg metals in muscle tissue were lower than the standard limit for FAO. The value obtained on Cd 1.04 ± 0.28 mg/kg concentration was much higher than the permissible threshold limit observed in the north, south, east and west regions. The most prominent increases in Pb and Cd metal concentrations in fish tissue were found during the October, November and December study of 2014, which corresponded to peak periods from October, November and December which apparently coincided with the second inter monsoon of the island respectively.