Browsing by Author "Dahanayaka, D.D.G.L."

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Assemblages of macro-invertebrates in the Negombo estuarine ecosystem in relation to the locations of drainage outlets
(University of Kelaniya, 2006) Dahanayaka, D.D.G.L.; Jayamanne, S.C.; Wijeyaratne, M.J.S.
Assessing the potential of satellite and ground spectral data for Chlorophyll-a monitoring in Lake Kasumigaura, Japan
(IEEE, 2014) Dahanayaka, D.D.G.L.; Tonooka, H.; Wijeyaratne, M.J.S.; Minato, A.; Ozawa, S.
The suitability of a handheld spectrometer and ASTER satellite data for monitoring Chlorophyll-a (Chl-a) in Lake Kasumigaura, Japan was tested in July 2010 to December 2013. ASTER based Chl-a retrieval algorithms were developed support with in-situ Chl-a, MODIS OC3 Chl-a and Kakemaoki and Koshin automated water quality monitoring stations Chl-a. ASTER VNIR band ratio were regressively analyzed with the corrected MODIS Chl-a and automated station values obtained for each ASTER date on a day by day basis. The regression equation of the ASTER band ratio (B1/B2), with highest correlation was used to generate high-resolution Chl-a distribution maps. Significant correlation between the ratio of the reflectance peak at 705 nm and the Chl-a absorption at 678 nm and the in-situ Chl-a content was observed and these reflectance ratios were used to establish spectrometric Chl-a estimation algorithms. Proposed algorithms can be successfully adopted to determine localized environmental effects in the Lake.
Assessment of invasion of Najas marina, Linnaeus 1753 in Madu Ganga estuary, Sri Lanka using ASTER data of Terra satellite
(Institute of Biology, Sri Lanka, 2015) Silva, T.M.S.D.G.; Dahanayaka, D.D.G.L.; Wijeyaratne, M.J.S.
Benthic Invertebrates of a Tropical Estuary in the Western Coast of Sri Lanka
(2008) Dahanayaka, D.D.G.L.; Jayamanne, S.C.; Wijeyaratne, M.J.S.
Change detection in the channel segment of Negombo Estuary, Sri Lanka using time series satellite data and its possible impacts on estuarine productivity
(The Asian Fisheries Society, 2011) Dahanayaka, D.D.G.L.; Tonooka, H.; Wijeyaratne, M.J.S.; Minato, A.; Ozawa, S.
CHLOROPHYLL-A MONITORING IN SRI LANKAN ESTUARIES USING ALOS/ANVIR-2 DATA
(International Geo Science and Remote Sensing symposium, 2012) Dahanayaka, D.D.G.L.; Tonooka, H.; Wijeyaratne, M.J.S.; Minato, A.; Ozawa, S.
Coastal water body database to monitor the water quality and land use changes from remote sensing data
(Remote Sensing Society of Japan (RSSJ), 2012) Dahanayaka, D.D.G.L.; Tonooka, H.; Wijeyaratne, M.J.S.; Minato, A.; Ozawa, S.
Comparison of three chlorophyll-a estimation approaches using ASTER data acquired over Sri Lankan coastal water bodies
(Malaysian Journal of Remote Sensing & GIS (MJRS&GIS), 2015) Dahanayaka, D.D.G.L.; Tonooka, H.; Wijeyaratne, M.J.S.; Minato, A.; Ozawa, S.
In the present study, we compare the following Chlorophyll–a (Chl-a) estimation algorithms using ASTER data acquired over Sri Lankan coastal water bodies: (1) the simple band-ratio algorithm with simple atmospheric correction using dark object subtraction (DOS); (2) the single band-ratio algorithm with radiative transfer-based atmospheric correction using ENVI’s FLAASH software including MODTRAN; and (3) our previously proposed algorithm based on combinations of ASTER and corrected MODIS Ocean Color-3 (OC3) data. First, several ASTER band ratios were regressively analyzed with in-situ Chl-a data acquired from the Negombo estuary and Puttalam lagoon in the west coast of Sri Lanka, and the band ratio with the highest correlation was selected. Then, time-series Chl-a distribution maps with the spatial resolution of ASTER/VNIR (15 m) were generated using the above three methods, and compared with the in-situ Chl-a data. Based on the result obtained, the FLAASH and ASTER/OC3 based methods showed high correlation with the in-situ Chl-a values (R2 = 0.96 and 0.92 respectively), while the DOS based method showed low correlation (R2 = 0.61), which indicates that the ASTER/OC3 based method will give equivalent performance to the FLAASH based method even though it does not need user-based atmospheric correction like the DOS and the FLAASH based methods.
Development of coastal water body database on KISSEL server
(IEEE, 2012) Dahanayaka, D.D.G.L.; Tonooka, H.; Wijeyaratne, M.J.S.; Minato, A.; Ozawa, S.
Monitoring of coastal water bodies in all the relevant aspects was highly important for the sustainable use of those. To achieve this all the research findings should be easy access and presenting those in a user friendly manner will be more advantage. In Sri Lanka, there was not fully or never developed database on research findings especially on coastal water bodies. Thus we developed a Sri Lankan coastal water body database (CWBDS) on KISSEL server system which can be benefitted all the interest communities including general public. Presently it include water quality data over two decades of lagoons and estuaries and in near future it will update with support from universities and research organizations including research on biodiversity, fisheries, land use, socio economics, topography, water circulation, pollution etc.
Diversity of macrobenthic community in the Negombo estuary, Sri Lanka with special reference to environment conditions
(Sri Lanka Association form Fisheries and Aquatic Resources, 2006) Dahanayaka, D.D.G.L.; Wijeyaratne, M.J.S.
Emerging ICT applications for strengthening of fisheries information system; A Sri Lankan experience
(Department of Zoology and Environmental Management, University of Kelaniya, Kelaniya, Sri Lanka., 2016) Wimalasena, H.D.; Dahanayaka, D.D.G.L.; Amaralal, K.H.M.L.
At present, information and communication technologies (ICTs) are used across the fisheries and aquaculture sectors in Sri Lanka for resource assessment, capture or culture to processing and commercialization. Especially in fisheries sector, ICT is widely used in applications such as Global Positioning Systems (GPS) for navigation and location finding, mobile phones for trading, information exchange, and emergencies, Satellite Remote Sensing (RS) for fishery forecasting and culture site selection, and radio for communication with fishers. But usage of web-based information and networking resources of these sectors are still emerging in Sri Lanka. Efficient information sharing system among resource users and fishery managers are essential for the sustainable management of aquatic resources. To fulfill this requirement, National Aquatic Resources Research and Development Agency (NARA) had foreseen the setting up of a user friendly system and launched the ‘Fisheries Information Centre (FIC) on 07th May 2013, to provide timely and accurate information on fisheries related problems for all stakeholders. The aim of this paper is to discuss the present status of the FIC and its role on development of Sri Lankan fisheries sector with evolving ICT applications. At the initial phase, FIC provided mobile phone interface to connect with the centre for their information needs. It can facilitate dialogue among fisheries communities and with government planners, researchers, and technical experts in sharing information for improvement in the efficiency and profitability of the fisheries industry. Through this dialogue FIC is able to disseminate scientific and legislative information, professional experiences and good practices to the fisheries sector (fishing, aquaculture, fish processing and marketing). From the start, FIC was successfully engaged to solve more than 500 telephone queries, which were categorized under academic and research related services (37%); consumer and industry services (33%); fishermen welfare and disaster related services (8%); trade and investment related services (6%); general comments and communications (16%). Delivering extension services such as conducting workshops for fishers and fishery related stakeholders, policy makers and politicians is another goal of FIC. Further, fisheries related information such as weather conditions, natural disasters, market fish prices, fishery forecasting etc. is also disseminated through the FIC. As the internet is emerging as a tool with potential to contribute to the development of Fisheries in developing countries like Sri Lanka, FIC focused on Setting up of a Web Portal for efficient information sharing between local and foreign stakeholders in near future.
Eutrophication Trends in Bolgoda North Lake, Sri Lanka
(Department of Zoology, University of Kelaniya, Kelaniya, Sri Lanka, 2014-06) Perera, B.D.C.; Wijeyaratne, M.J.S.; Dahanayaka, D.D.G.L.; Tonooka, H.; Minato, A.; Ozawa, S.
Chlorophyll-a (Chl-a) concentration in the Bolgoda North Lake (06.400 – 06. 480 N; 079. 550 -079. 580 E), which is a shallow brackish water body situated in the western coastal region of Sri Lanka, was determined through correlating Advanced Space-borne Thermal Emission and Reflection Radiometer (ASTER) optical sensor data with in-situ data measured from April 2013 to October 2013 in 05 sampling sites. ASTER band ratio of B1/B2 which gave the highest correlation with in-situ Chl-a data was used to generate 15 m resolution Chl-a distribution maps. Chl-a distribution maps generated using ASTER data indicated that most areas of Bolgoda North Lake were eutrophic. Some regions of the Weras Ganga which flows into the Lake showed very high Chl-a concentrations during April indicating hypereutrophic conditions while in June, September and October these areas indicated eutrophic conditions. Observations on land use pattern revealed that industrial zones border these areas. High Chl-a concentrations were also observed in the areas bordered by the lands with low income houses from which household waste as well as sewage are discharged directly to the lake. Chl-a distribution maps developed for 2005, 2008, 2010 and 2011 revealed that eutrophication of the Bolgoda North Lake has gradually increased in the recent past. This may possibly be due to the increase in the industrial effluents as a result of industrial development in the area and also due to increased population of low income groups that live in some areas bordering the lake.
Evaluation of Chlorophyll retrieval algorithm using an intermittently closed tidal estuary: The Chilaw lagoon in the west coast of Sri Lanka
(Remote Sensing Society of Japan (RSSJ), 2011) Dahanayaka, D.D.G.L.; Tonooka, H.; Wijeyaratne, M.J.S.; Minato, A.; Ozawa, S.
Feasibility Study for the Estimation of the Chlrophyll-a Using ASTER Data in an Eutrophic Lake, Sri Lanka
(Japan Geoscience Union, Japan., 2014) Dahanayaka, D.D.G.L.; Tonooka, H.; Wijeyaratne, M.J.S.; Minato, A.; Ozawa, S.
The objective of this study is to evaluate the performance of the previously proposed band ratio approach in estimating Chl-a in Bolgoda Lake, Sri Lanka as a representative example of Case II waters. Lake is located at western province in an area with lot of industries and also with some agricultural activities. Considerable amount of industrial effluents are discharged into it. Illegal filling and also encroachment has occurred in the recent past. This study focused on to determine the trends in eutrophication via Chl-a changes during the recent past, make predictions and recommend mitigatory measures and suggest precautionary measures to restore the environment. From March to December 2013, water samples at 5 points of Lake were collected once per month parallel to ASTER overpass and Chl-a of each sample was measured using a laboratory spectrophotometer. Cloud-free ASTER scenes acquired over Lake under clear sky conditions were selected during 2000 to 2013 for Chl-a estimation and trend analysis. All the ASTER images were atmospherically corrected using FLAASH and in-situ Chl-a data on Lake were regressively analyzed with atmospherically corrected three ASTER VNIR band ratios such as B1/B2 of the same date. Finally, the regression equation of the band ratio with highest correlation (B1/B2; R2 = 0.78) was used to develop algorithm for generation of 15-m resolution Chl-a distribution maps using atmospherically corrected time series satellite imageries in day by day basis. This method applied for ASTER band 1/2 ratio due to Chl-a is positively correlated with the green band reflectance and negatively correlated with the red band reflectance. Therefore, the reflectance ratio of green and red bands becomes a robust parameter to estimate the Chl-a content. According to the ASTER based Chl-a distribution maps it is clearly evident that eutrophication of the Bolgoda Lake has been gradually increased from 2005-2011. Further, results showed that there were significant eutrophic conditions throughout the year 2013 in several parts of the Lake and considerable spatial heterogeneity with higher concentrations being recorded water stagnant areas and in water adjacent to freshwater outlets. It is clear that Bolgoda Lake is apparently a disposal site of various discharges of factories in addition to poor drainage and sewage systems present in this area. Highly unplanned urbanization and absolutely lack of adequate waste disposal management facilities in industries close to Lake have resulted in pollution of water. If the present trend of waste disposal and unplanned urbanization continue, they would create enormous environmental problems in future. Results of the present study showed that information from satellite remote sensing can play a useful role in determining the changes in Chl-a related to eutrophication in Bolgoda Lake and in the development of time series Chl-a distribution maps. Such information is important for the future predictions, development and management of this area as well as in the conservation of biodiversity. Therefore we recommend incorporation with this technique for routine monitoring of water quality using multi satellite data such as ASTER in inland water bodies like Bolgoda Lake in the future.
In-vitro and in-vivo Seed Germination Percentage of Typha angustifolia
(International Postgraduate Research Conference 2019, Faculty of Graduate Studies, University of Kelaniya, Sri Lanka, 2019) Madushani, K.P.K.; Amarasinghe, M.D.; Ratnayake, R.M.C.S.; Dahanayaka, D.D.G.L.
Typha is a cosmopolitan genus and T. angustifolia is considered an alien invasive plant species in Sri Lanka. Extensive distribution of T.angustifolia is observed in Bundala wetland complex during the recent past. Seed germination is an important process that contributes to plant distribution and invasiveness. Therefore, this study aimed to investigate the in-vitro and in-vivo seed germination of T.angustifolia seeds to evaluate the percentatge seed germination of Typha seeds. Typha seeds were collected from Bundala wetland complex, Hambantota, Sri Lanka (6°12′50″N; 81°13′30″E) during the South West monsoon windy season (seed dispersing period). Typha seeds were cleaned with distilled water and settled in distilled water to select the most viable seeds, which sink to the bottom of the container, whereas non-viable seeds float. Seed viability was tested by placing 50 seeds on cavity slides with 3% 2,3,5-triphenyltetrazolium chloride (TTC) solution and percentage seed viability was calculated after incubating in dark for 8 hours. For the seed germination test, 50 seeds were placed on a layer of Whatman grade no. 1 filter paper (pH 7) in 90mm petri dishes and watered weekly. Seed was counted as germinated when the radical reached 2 mm. For seedling emergence test, 50 seeds were sown in lagoon soil in trays at 0.5 cm depth, which were collected from Bundala wetland complex and they were weekly irrigated with distilled water. A seedling was considered emerged when the hypocotyl was fully erect. All tests were replicated 5 times. Finally the percentage seed germination and percentage seedling emergence were calculated. Results indicate that there is a significant difference (p<0.05) between seed viability in TTC test and seed germination in petri dishes/ seedling emergence in soil trays. TTC test resulted in 87.2±7.2% seed viability, but only 51.2±2% of seedlings germinated in soil trays. Seedlings were emerged after 2 to 3 weeks of sowing. However radicals were failed to appear in petri dishes. Therefore, results conclude that even though T.angustifolia bear numerous viable seeds they show moderate percentage seed germination in wetland soils. It may be due to seed dormancy and further investigations are recommended to evaluate the effect of seed dormancy on distribution of T. angustifolia.
Integration of multisource data for chlorophyll-a monitoring in Negombo estuary, Sri Lanka
(IEEE, 2011) Dahanayaka, D.D.G.L.; Tonooka, H.; Wijeyaratne, M.J.S.; Minato, A.; Ozawa, S.
In order to estimate chlorophyll-a concentration (Chl-a) for tropical coastal estuarine environments using satellite optical sensor, observations were conducted from 1987 to 2009 in Negombo estuary, Sri Lanka, with support with available in-situ measurements. Landsat band ratios were regressively analyzed with available in-situ Chl-a data. This relationship was used for correcting MODIS OC3 Chl-a values, and then ASTER band ratios were regressively analyzed with the corrected MODIS values. The regression equations obtained for ASTER and Landsat were used to develop algorithms for generation of 15m and 30m resolution Chl-a distribution maps, respectively, in Negombo estuary using atmospherically-corrected time-series imageries. The results indicate that some parts of the estuary have increased eutrophication conditions during 1987-2009.
Macrobenthic Community Structure in Relation to Land Based Pollution - Case Study in a Tropical Estuary in the West Coast of Sri Lanka
(Ibaraki University, Hitachi, Japan, 2009) Wijeyaratne, M.J.S.; Dahanayaka, D.D.G.L.; Jayamanne, S.C.
Macrozoobenthic community structure in the channel segment, Negombo estuary, Western coast of Sri Lanka
(National Aquatic Resources Research and Development Agency, 2006) Dahanayaka, D.D.G.L.; Jayamanne, S.C.
Ctrannesl r:gmenot f the Negomboe stuary (7o6'- 7ol2'N, 79o49'- 79o53'E) is very importantf or the continuation of estuarine functrons through exchange of water between sea and the estuary, but are subjected to changes due to vario'rs anthropogenic activities such as planting mangroves, boat and fishing gear operations and discharge of industrial effluents. A survey was carried out in August 2005 to study the community structure of the macrozoobenthic coinmunity in the channel segment in relationt o the environmentalf actorsa nd antlrropogenica ctivities.E leven stations,a ccuratelyr ecorded using a hadd held GPS were sampledu sing a Petersong rab and macrobenthosw ere separatedb y wet sieving ancl identified up to the lowest possible level. At each sampling site, the depth and salinity were measured and the presence of sea grasses and mangroves was recorded. The anthropogenic activities that are carried out at each sampling site such as disposal of sewage and fishing were also noted. I'he diversity of macrobenthos was determined using Shannon-Wiener and Pielou's indices respectiveiy.T he similarities amongt he macrobenthicc ommunitiesa t different sites were determined using Bray-Curtis similaritv coefficient, ordinations of Non-parametric Multidimensional Scaling (MDS) and the BIO-ENV function was used to relate the multivariate community structure to environtnentavl ariablesa nd to determinet he most responsiblev ariablesf or the inter-sitev ariability of the benthic community using PRIMER-5 software package (Version 5.2.2). Thirty-two species of invertebratecso nsistingo f 3 specieso f polychaetesl,4 specieso f gastropods,'7s pecieso f bivalves and 8 specieso f crustaceansw ere recordedd uring the presents tudy.N eritids andH ydrobiirls were the mosi abrndant gastropods whiie Venerids wbre the most abundant bivalves. Salinity of water changed from 17 to 30g/kg and the water depth changedifrom 0.3 to 2.5 m. Highest diversity (2.031) was recorded in association of sea grasses and lowe$t (0) in highly pblluted site near Dutch canal. As indicated by Bray-Curtis similarity index and MDS ordination, two sample sites located at the mouth of the estuarya nd upper left region of Munnakkate clearly separatedfr om the other sites which rnay be explainedb y the presenceo f trvo specieso f biValvesi n theses ites. Resultso f the Spearmanra nk correlationc oefficients for permutationso f envirohmentalv ariableso f the BIO-ENV function indicate that the combination of abundanceo f sea grassesa nd mangr.ovesm ostly affect the abundanc"a :id diverslry, .rlm acrobenthosi n the channels egmento f the Negombo estuary
Monitoring eutrophication trends in Bolgoda North Lake, Sri Lanka by Satellite Remote Sensing
(Central Fisheries Research Institute (CFRI) Trabzon, Turkey in cooperation with Japan International Cooperation Agency (JICA), Japan, 2016) Dahanayaka, D.D.G.L.; Perera, B.D.C.; Wijeyaratne, M.J.S.; Tonooka, H.
This study was aimed to determine the present level and past trends of eutrophication of the Bolgoda North lake, Sri Lanka using in situ Chlorophyll-a (Chl-a) measurements and remote sensing data obtained from Advanced Space-borne Thermal Emission and Reflectance Radiometer (ASTER) satellite data. From March to October 2013, Chl-a, nitrate and phosphate contents of the lake were measured once a month on the days of ASTER overpass and using standard laboratory methods. Cloud-free ASTER images of the lake for the 2000-2013 period were atmospherically corrected using Fast Line-ofsight Atmospheric Analysis of Hypercubes (FLAASH) and in-situ Chl-a data were regressed with atmospherically corrected three ASTER Visible and Near Infrared band ratios of the same date. The green/red band ratio, which had the highest coefficient of determination, was used to develop algorithm for generation of 15-m resolution Chl-a distribution maps. Results indicated that eutrophication of this lake has increased from 2008 to 2011. Heavy eutrophic conditions were noted in several regions of the lake in 2013, especially in water stagnant areas and adjacent to freshwater inlets. Unplanned urbanization and inadequate facilities for waste management have resulted in heavy eutrophication of the water body. If the present trends of waste disposal and unplanned urbanization continue, enormous environmental problems would be resulted in future.
Monitoring land use changes and their impacts on the productivity of Negambo Estuary, Sri Lanka using time series satellite data
(Asian Fisheries Society, 2012) Dahanayaka, D.D.G.L.; Tonooka, H.; Wijeyaratne, M.J.S.; Minato, A.; Ozawa, S.