Seasonal phosphorus variation in coastal water affected by the land-based sources input in the eutrophic Zhanjiang Bay, China

Abstract

Phosphorus (P), a significant biogenic element, plays a key role in the primary productivity of estuarine and coastal ecosystems. The study determined that the seasonal dynamics of total dissolved P (TDP)in the coastal area of the Zhanjiang Bay (ZJB) were largely affected by land-based sources. The TDP concentration had significant seasonal variations in the ZJB (P < 0.01), and the annual mean TDP concentration was 3.30 ± 1.12 μmol L−1 in the coastal waters and 30.37 ± 55.07 μmol L−1 in the estuaries and sewage outlets. The spatial distribution of TDP demonstrated a decreasing trend from the top to the mouth of the ZJB. In the TDP composition, dissolved inorganic P (DIP) was the major fraction of the TDP in land-based sources and seawater. Moreover, the ZJB is annually subjected to a load of 3848.07 tons TDP through the land-based input sources, accounting for 10.4%, 37.0% and 52.6% in the dry, normal, and wet seasons, respectively. Most of the monitoring stations in ZJB coastal water did not meet the Grade IV national water quality standard. Both the coastal water and land-based water sources were seriously polluted by P. This study revealed that land-based source inputs played a key role in the P biogeochemistry process in the ZJB. A land-ocean integrated P pollution control strategy should be effectively implemented for water quality improvement and eutrophication mitigation in the ZJB.