The Spatial and Temporal Distributions of Chlorophyll-a and Its Relationship With Main Environmental Factors in Zhanjiang Bay in 2009

The spatial and temporal distributions of chlorophyll-a in Zhanjiang Bay were surveyed in four seasons from Feb.to Nov.in 2009,and the relationship between chlorophyll-a and main environmental factors was studied.The chlorophyll-a ranged from 0.35 to21.52 mg/m3,with an annual average of 4.47 mg/m3.The seasonal change of chlorophyll-a was found in summer(6.50 mg/m3),followed by in winter(4.75 mg/m3),spring(3.58 mg/m3) and autumn(3.01 mg/m3) in turn.In horizontal distribution,the chlorophyll-a in winter was descending from middle Nansan Island sea area to coastal area and outside of the bay,while its degression was from outside bay to inner bay in spring,summer and autumn.The annual average distribution of the chlorophyll-a had a trend of descending from sea to coastal area.PCA analysis showed that the chlorophyll-a was significantly positive related to pH,salinity,but significantly negative correlated with NH+4-N,NO-3-N,SiO2-3-Si,PO3-4-P and DIN.Results indicated that the trophic status of the Zhanjiang Bay was middle-trophic or oligotrophic according to superficial chlorophyll-a as an assessment criterion.This was different from the criterion of nutrient and COD,suggesting the multiple ecological factors should be integratively considered for trophic assessment in this bay.