Seasonal fluctuation of nutrients and primary productivity of the coastal waters of Culaman, Malita, Davao Occidental

Abstract

The study was conducted to determine the nutrient and chlorophyll-a concentration of coastal water at Barangay Culaman, Malita, Davao Occidental between two seasons. One shot sampling was done during the rainy season on November 19, 2017, and November 26, 2017. It was also done during summer season on March 6, 2018, and March 11, 2018. Water samples were collected in the surface (5-10 cm depth) and subsurface (below 1m depth). Nutrients were analyzed in terms of their concentration expressed in mg/L, including ammonia, nitrate, nitrite, and phosphate. Chlorophyll-a was included being the most reliable index of primary productivity in seawater. Nitrate, nitrite, phosphate, and chlorophyll-a showed high concentration during rainy season while ammonia exhibited a high concentration during summer season. Further, nutrients were found in high concentrations from surface water compared to those from subsurface water. There were no significant differences in nutrient and chlorophyll-a concentrations between stations except for nitrate. In terms of its concentration between rainy and summer season, and between surface and subsurface waters, there were no significant differences in ammonia, nitrate, and phosphate.  However, significant differences in the concentrations of nitrite and chlorophyll-a between rainy and summer season and between surface and subsurface water samples were observed.  The prevailing levels of temperature, salinity, dissolved oxygen, and turbidity observed during sampling were found to be normal.