Monitoring Land Use Changes and their Impacts on the Productivity of Negombo Estuary, Sri Lanka Using Time Series Satellite Data

Eutrophication and Hypoxia in Tropical Negombo Lagoon, Sri Lanka

“…In the present study, surface water temperatures were in the range 27.8-33.1 • C, with a mean value of 30.1 ± 1.0, i.e., similar to previously reported results for this lagoon (Gammanpila, 2010). Such high temperatures, coupled with the slow water circulation resulting from the very narrow connection to the Indian Ocean (Dahanayaka et al, 2012), mean that the Negombo Lagoon is at risk of experiencing hypoxic events (Hearn and Robson, 2001;Tyler et al, 2009). Moreover, the mean DO concentration we recorded in the Dandugam Oya river outflow (2.76 mg l −1 ) was considerably lower than that recorded by Gammanpila (2010) 10 years earlier (6.7 ± 2.1 mg l −1 ), which suggests that the lagoon is prone to hypoxic events in the near future.…”

“…In recent years, mangroves have been planted around the lagoon by local residents for the purpose of subsequent landfill. The area of mangrove vegetation in some areas has increased to form new islets consequently narrowing the channels (Dahanayaka et al, 2012). This has also led to sediment deposition, further enhance choking the channels.…”

“…The presence of these pollutants and the subsequent eutrophic conditions may result in depletion of dissolved oxygen which is thought to be responsible for the fish kill events reported in the lagoon and surrounded waters (Dahanayaka et al, 2012;Narangoda et al, 2015;National Aquatic Resources Research and Development Agency, 2019). Dahanayaka et al (2012) reported elevated chlorophyll-a (Chl-a) concentrations in the dry season as evidence for the above sequence of events, but nutrient and dissolved oxygen (DO) data were not available.…”

Anthropogenic nitrogen pollution threats and challenges to the health of South Asian coral reefs

“…In recent years, high levels of organic and inorganic nutrient pollution have been reported in the coastal waters along parts of the west coast, south of Negombo (Hettige et al, 2014), inferred along parts of the eastern coast (Perera, 2019), or measured in coastal lagoons (Gammanpila, 2010;Harris and Vinobaba, 2013), while oil and organic nutrient pollution has been reported within fishing areas along the southern coast (Niroshana et al, 2013;Weerasekara et al, 2015). Common indicators of coastal nutrient enrichment, such as increased chlorophyll concentrations or decreased dissolved oxygen levels, have not been widely recorded from Sri Lankan coastal waters (Bandara, 2003;BOBLME, 2013), and only rarely within surface water and estuarine settings (Silva, 1996;Dahanayaka et al, 2013). Recent observations of high biological oxygen demand in coastal harbor settings may have multiple origins, including fish processing, oil and grease discharge, and sewage input (Bandara, 2003;Niroshana et al, 2013;Weerasekara et al, 2015;Manage et al, 2022).…”