Abstract:
Hypoxic events are becoming frequent in some estuaries and coastal waters due to
over-enrichment of anthropogenic nutrients, organic matter, and/or due to restricted
water circulation. The coastal lagoons and estuaries of Sri Lanka are facing high
population pressure and lacking sufficient infrastructure. Coastal lagoons may receive
high anthropogenic inputs of natural or untreated nitrogen and phosphorus wastes,
and consequently result in hypoxic conditions while sluggish circulation occurred. In
this study, we examined the spatiotemporal variability of eutrophication and hypoxia in
the Negombo Lagoon, one of the most productive and sensitive coastal ecosystems
in Sri Lanka. Based on seasonal measurements of dissolved oxygen, nutrients,
chlorophyll-a (Chl-a), particulate and dissolved organic carbon (POC and DOC),
we concluded that eutrophication and hypoxia occurred in both the dry and wet
seasons. The main contributing factors were high seawater temperature and poor water
circulation in the dry season and high nutrient loading combined with elevated POC and
DOC inputs in the wet season.