The Acidification Coupled with Eutrophication of the Coastal Waters of Bolinao, Pangasinan, Philippines

English Abstract:

Ocean acidification is becoming a global concern due to its potential effects on marine resources. In coastal areas, an emerging problem is ocean acidification due to eutrophication resulting from human activities. The coastal water of Bolinao, Pangasinan, Philippines has become eutrophic due to increased nutrient loading from unconsumed fish feeds in fish cages. Mariculture is a big industry in Bolinao. In over a decade, the area has experienced decreased oxygen levels leading to hypoxia, fish kills, and algal blooms. The decomposition of organic matter from unconsumed fish feeds results not only to high nutrient buildup but also increased CO₂ and acidity in the area. Nutrients (ammonia, nitrate, nitrite, phosphate and silicate), total alkalinity (TA), dissolved inorganic carbon (DIC), pH, dissolved oxygen (DO), aragonite saturation state (Ω_arg) and partial pressure of carbon dioxide (pCO₂) were measured to determine the combined effect of acidification and eutrophication in Bolinao. Monitoring results have shown an increase in nutrients by 30% to 70% in over a decade. Total alkalinity (TA) data have a good correlation with salinity showing lower TA values in less saline waters. High DIC values were obtained from shallow stations with depth less than 5 meters. pH exhibited a clear seasonal cycle showing low pH values during the start and toward the end of the year while it increased from April to August. Lowest pH values were obtained from high residence time areas compared to areas which are near the opening of the channel. The eutrophic and acidified coastal waters of Bolinao are already affecting the seagrass and coral reef ecosystems in the area.