Spatiotemporal Assessment and Index-Based Evaluation of Coastal Water Quality at Selected Beaches in Southern Sri Lanka

Ramodh Niranga Jayawardena; Shynuga  Thirukeswaran; Sudeepa Ranasinghe; Pavithra  Jayawardhane; Nadeesha  Hettige; Shyamali Weerasekara

Authors

Ramodh Niranga Jayawardena National Aquatic Resources Research and Development Agency, Colombo 15, 01500 Sri Lanka
Shynuga Thirukeswaran National Aquatic Resources Research and Development Agency, Colombo 15, 01500 Sri Lanka
Sudeepa Ranasinghe National Aquatic Resources Research and Development Agency, Colombo 15, 01500 Sri Lanka
Pavithra Jayawardhane National Aquatic Resources Research and Development Agency, Colombo 15, 01500 Sri Lanka
Nadeesha Hettige National Aquatic Resources Research and Development Agency, Colombo 15, 01500 Sri Lanka
Shyamali Weerasekara National Aquatic Resources Research and Development Agency, Colombo 15, 01500 Sri Lanka

Keywords:

Coastal water quality index, Water quality, Sri Lanka’s coastline, Policies

Abstract

The coastline of Sri Lanka plays an important role in shaping the socioeconomic development through fisheries, tourism, and ecosystem services. However, the anthropogenic influence and the absence of systematic water quality assessments create serious challenges to coastal sustainability. This study evaluates the coastal water quality of Unawatuna, Mirissa and Polhena beaches through a spatiotemporal analysis and develops a Coastal Water Quality Index (CWQI). A total of 152 samples were collected across 19 sites between May to December 2023 and analyzed for pH, salinity, EC, TDS, DO, turbidity, TSS, phosphate, nitrate, and nitrite. Results were compared against ASEAN and regional marine water quality standards. Most of the parameters were within acceptable limits except for phosphate, highlighting the anthropogenic nutrient inputs. PERMANOVA and NMDS revealed spatial consistency in Unawatuna and Mirissa, while Polhena exhibited significant spatial variation, particularly in DO levels. October to November showed water quality deviations across all sites, linked to intermonsoon effects. CWQI results ranged from 14 (excellent) to 118 (poor), 14 (excellent) to 74 (good) and 17 (excellent) to 124 (poor) in Unawatuna, Mirissa and Polhena, respectively. Although overall water quality remained generally stable, an upward trend of CWQI values indicates a decline in water quality. These findings highlight the urgent need for monitoring and integrated coastal zone management strategies to maintain ecological resilience and support sustainable policy development.

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