Spatial and temporal distribution of nutrients and chlorophyll a, and their influential factors in Caofeidian coastal waters

Based on two cruises respectively carried out in May 2014 and August 2013 in Caofeidian coastal waters, temporal and spatial distributions of nutrients and chlorophyll a (Chl a), their influential factors and correlations with water temperature, salinity, chemical oxygen demand (COD) and suspended particle matter (SPM) were analyzed in this study.Trophic status and nutrient limitation were assessed, and changes of trophic status after land reclamation were discussed.The results showed dissolved inorganic nitrogen (DIN), dissolved inorganic phosphate (DIP) and dissolved silicate (DSi) were mainly affected by riverine inputs and sediment release with high values ordinarily occurred in inshore waters.Nutrient quality index (NQI) ranged from 1.07 to 2.23, indicating their oligotrophic or mesotrophic status.Nutrient limitations showed seasonal variations, which were Si limitation in spring and P limitation in summer.The high values of Chl a in spring were observed in eastern offshore waters and the northeastern bay, which was related to salinity, P and Si, while those in summer occurred near Caofeidian foreland and the northeastern bay, which was mainly related to P and Si.The comparison between historical data and this study revealed that in spring DIN, NQI and Chl a decreased in western sea areas and increased in eastern sea areas, which was possibly related to nutrients redistribution induced by spatial variations of tidal changes after reclamation, while in summer DIN and NQI decreased and Chl a increased in most study areas, suggesting nutrients were largely consumed by phytoplankton and influence of reclamation should be further discussed basing on phytoplankton community.