Faculty of Fisheries and Marine Sciences & Technology

The Impacts of Causeway Modifications on Water quality in Rekawa lagoon, Sri Lanka.

2026-06-12T09:48:31Z

The Impacts of Causeway Modifications on Water quality in Rekawa lagoon, Sri Lanka. Pathumika, G.H.A.S.; Asanthi, H.B.; Suwandhahannadi, W.K .; Athapaththu, K.S.S. Rekawa lagoon, a major coastal aquatic system on the southern coast of Sri Lanka that supports numerous ecosystem services, has experienced impaired ecological integrity due to construction activities near the lagoon mouth. Water exchange through the causeway has undergone several modifications and evolved from 23 pipes (30 cm diameter) in 1984, to a partial bridge (6.2 m) in 1999, then eight larger culverts (79 cm diameter) with a partial bridge in 2005, followed by a complete bridge in 2018. Although these modifications have a potential to change the water quality of the lagoon, a comprehensive scientific report in this regard is unavailable. The present study was designed to compare the water quality of lagoon in parallel to these modifications by using published historical literature together with field observations conducted in August 2024 selecting eight sampling sites (S1-S8) across the lagoon. Salinity, Temperature, pH, Dissolved Oxygen, Nitrate nitrogen, Orthophosphate, Total dissolved solids, Total suspended solids, Chlorophyll-a, Turbidity, Chemical oxygen demand, Secchi depth and Electrical Conductivity were measured, and the Lagoon Water Quality Index (L-WQI) was calculated. Salinity levels recorded in 1994, 2002, and 2005 were 4.81±0.66 ppt, 5.7±4.4 ppt, and 8.1±0.6 ppt, respectively, while the value increased to 9.78±0.94 ppt in 2024. Significant differences (p < 0.05) were observed in salinity, temperature, pH, and Secchi depth between historical water quality and present findings, demonstrating notable improvements in lagoon water quality over time. L-WQI of study sites were range from 49.42 ± 0.52 to 56.70 ± 0.12. L-WQI were significantly different (p<0.05) among sites, where two sites (S2 and S6) were classified under “critical condition”, while the remaining sites were categorised as “good condition”. Present findings revealed that the causeway modifications have significantly altered the water quality dynamic of Rekawa lagoon, and the L-WQI indicated that, restoration efforts have improved water quality, but specific areas are still facing localized pollution and nutrient loading. This study recommends sustainable management strategies and conservation programs to preserve ecological health, support local livelihoods, and ensure the long-term sustainability of the Rekawa Lagoon ecosystem.

Applying generalized additive models to predict benthic macroinvertebrate diversity in relation to water quality: A Case study, Mawarala stream, Sri Lanka.

2026-06-12T09:39:19Z

Applying generalized additive models to predict benthic macroinvertebrate diversity in relation to water quality: A Case study, Mawarala stream, Sri Lanka. Sivalingam, P.; Prasangika, K.D.; Atapaththu, K.S.S.; Gamage, T.P.D. Freshwater ecosystems harbor exceptional biodiversity, yet they remain highly sensitive to changes in physical and chemical conditions, making continuous monitoring essential for evaluating their ecological health. Benthic macroinvertebrates have been identified as suitable bio-indicators because they exhibit varying degrees of sensitivity to different environmental stressors, and they are specific to habitats. In this study we assessed the relationship between water quality physicochemical parameters and the diversity of benthic macroinvertebrates found in the Mawarala Stream located in Southern Sri Lanka. Water quality parameters that we monitored included temperature, pH, dissolved oxygen (DO), biological oxygen demand (BOD), electrical conductivity, total dissolved solids (TDS), total suspended solids (TSS) and nitrates selecting four sites of the stream. A total of sixteen macroinvertebrate families belonging to nine orders were recorded. Hydropsychidae, Dermestidae, and Simuliidae were the most abundant families, whereas Aeshnidae, Paludomidae, and Corydalidae occurred in low abundances. Correlation analysis revealed a strong negative correlation between TSS and diversity (p < 0 .05); pH, DO and temperature had weak, non-significant correlations. A multiple regression model (R² = 0.27) was insufficient to accurately explain the complex ecological patterns; therefore, a generalized additive model (GAM) was developed using TSS, DO, and pH as predictor variables, while temperature was removed due to statistical non-significance. The final GAM provided an improved fit to the observed data (adjusted R² = 0.627; deviance explained = 69.6%) and yielded a lower Akaike Information Criterion value (AIC = 70.39). The predictive capability was thought to be limited due to both the small sample size and large ecological variability. Overall, the study emphasizes how TSS, DO, and pH affect the diversity of macroinvertebrates and supports the use of GAMs in tropical freshwater bioassessment. It also highlights the need for larger datasets to improve the predictive accuracy of streams in Sri Lanka.

Assessing the role of wetland ecosystem services and their support for sustainable livelihood of local community: A case study in Kirala Kele Wetland, Matara.

2026-06-12T09:40:30Z

Assessing the role of wetland ecosystem services and their support for sustainable livelihood of local community: A case study in Kirala Kele Wetland, Matara. Shiron, R.; Karunarathna, A.C.; Caspersz, D.; Atapaththu, K.S.S. Wetlands are vital ecosystems offering valuable goods and services to the local community. However, there is a gap in understanding the economic contributions of the Kirala Kele Wetland (KKW), located in Matara District, Sri Lanka, to the nearby community. This understanding is important because demonstrating this economic value is necessary to drive policies that balance ecological conservation with sustainable livelihoods. Accordingly, this study assesses the direct economic role of KKW and analyzes the socioeconomic determinants affecting community dependence on wetland resources for their sustainable livelihoods. Additionally, this study aims to assess the perception of the local community on KKW’s intangible ecosystem services and environmental concerns. A mixed-method research design was employed, consisting of survey of 184 households and 6 Key Informant Interviews (KII) in three Grama Niladhari divisions adjacent to KKW. This study used the market-price valuation method to estimate annual wetland-derived household economic value (WDHEV) and used statistical analyses (Mann–Whitney U tests, Spearman correlation, and multiple linear regression) to identify socioeconomic determinants of wetland resource use. Additionally, qualitative thematic analysis assessed community perceptions towards KKW. The key results show that 74.5% of households surveyed gain direct economic benefits from KKW. Among economically dependent households, the mean annual WDHEV was LKR 413,069.80 (USD 1,381), consisting of an average of 48.9% of their total annual household income. Further statistical analysis showed that KKW serves as a vital “safety net” for low-income households sustaining their livelihoods. The Regression analysis (R² ≈ 0.25) showed that distance to the wetland and the presence of agricultural land significantly affected the WDHEV, whereas variables age, household size, education level, and involvement in wetland conservation activities had no significant effect. The qualitative thematic analysis identified the cultural, regulating, and supporting ecosystem services of KKW. At the same time, pollution, invasive species, illegal waste disposal, and governance failures were identified as leading to significant environmental degradation on KKW, which threatens the sustainability of local livelihoods. This study contributes an analysis about both the tangible and intangible benefits to local communities which urban wetlands provide, thus contributes an understanding of the importance in conserving them. The policy and practice implications are that evidence-based policies promoting community-based co-management are crucial to balance ecological preservation with community economic well-being. Further, management strategies should prioritize enforcing conservation regulations, control pollution, and promoting sustainable alternative livelihoods to reduce pressure on wetland resources.

Feasibility of introducing integrated rice-fish farming in Hambantota District, Sri Lanka.

2026-06-12T04:58:04Z

Feasibility of introducing integrated rice-fish farming in Hambantota District, Sri Lanka. Kumara, H.K.R.S.; Atapaththu, K.S.S.; Herath, S.S.; Vidanapathirana, N.P.; Rathnayaka, R.M.K.T.; Marasinghe, M.M.K.I. This study examined the feasibility of introducing integrated rice fish farming (IRFF) system among rice farmers in the Hambantota District, Sri Lanka, by assessing their knowledge, perceptions, misconceptions, constraints and perceived potentials. A cross-sectional study design with a two-stage sampling procedure was employed. Data were collected from 100 randomly selected farmers under major irrigation schemes using structured questionnaires and individual interviews. Statistical analyses included chi-square tests, Pearson correlation and binary logistic regression to identify factors influencing willingness to adopt. Results showed that younger, better-educated and land-owning farmers with smaller landholdings were more willing to adopt IRFF system, while older and more experienced farmers were less receptive. Knowledge and perception were positively associated with feasibility to adopt, whereas constraints had a significant negative effect. Logistic regression confirmed knowledge, perception and constraints as the most decisive predictors of adoption feasibility, with higher knowledge and favourable perceptions substantially increasing feasibility and constraints reducing it. Although myths did not directly affect feasibility, they were negatively correlated with knowledge and perceptions, suggesting an indirect influence. The findings suggest that the feasibility of introducing IRFF system may be enhanced by improving farmer knowledge and perceptions through targeted extension and demonstration programs, while addressing institutional and resource-related constraints.