Distribution, key controlling factors and potential ecological role of particulate nitrogen and phosphorus in Daya bay

Particulate nutrients have been proved to be the important components of nutrients in seawater.In this study, particulate nitrogen (PN) and particulate phosphorus (PP) were measured in four different seasons to investigate the seasonal distribution patterns and their potential ecological roles in Daya bay.The results showed that the concentrations of PN and PP ranged from 2.63 to 26.24 μmol/L (averaged 8.20 μmol/L) and 0.11 to 3.71 μmol/L (averaged 0.39 μmol/L), respectively.The main component of PN was particulate organic nitrogen (PON), accounting for 65.0%; while PP was made up by 63.4% particulate inorganic phosphate (PIP).Meanwhile, PN and PP accounted for 24.8% and 37.0% of total phosphorus (TP) and total nitrogen (TN), respectively.PN and PP showed a decreasing trend from the inner bay to the outer bay except in winter.Runoff input and phytoplankton were considered to be the main factors controlling the spatial distribution as well as contents of particulate nutrients.In addition, the average PIN/PIP value in Daya bay was 13.2±11.1, which was close to the Redfield ratio (16:1).However, average DIN/DIP ratio (49.1±39.7) was much higher than 16:1.These combined results suggested that particulate nutrients probably played an important role in buffering and regulating nutrient structure in Daya bay.