Nutrients distributional characteristics and eutrophication in the sea-surface microlayer and subsurface water in the Jiaozhou Bay
胶州湾微表层和次表层海水中营养盐的分布特征及富营养化研究

Based on observed nutrient data collected in the sea-surface microlayer (SML) and subsurface water of Jiaozhou Bay during 6 cruises in summer (June, July and August) and autumn (September, October and November) of 2010, the distributional characteristics and spatio-temporal variations of nutrients and the enrichment extents of N, P, Si in the sea-surface microlayer were studied and the water quality status was assessed by using the assessment model of potential eutrophication. Results showed that in the sea-surface microlayer and subsurface water, the concentrations of nutrients decreased gradually from the inner bay to the bay mouth. The mean concentrations of dissolved inorganic nitrogen (DIN), phosphate and silicate in the sea-surface microlayer of Jiaozhou Bay in summer were 0.296, 0.026 and 0.618 mg·L-1, respectively, and those in autumn were 0.369, 0.028 and 0.592 mg·L-1. In contrast, the mean concentrations of DIN, phosphate and silicate in the subsurface water in summer were 0.240, 0.025 and 0.506 mg·L-1, respectively, and those in autumn were 0.292, 0.028 and 0.580 mg·L-1. The sea-surface microlayer displayed an obvious enrichment for N and Si nutrients in different degrees, with the mean enrichment factors ranging from 1.48 to 1.96 dependent on sea surface conditions and seasons. No enrichment was observed for phosphate. In the whole cruises, the contents of nutrients in Jiaozhou Bay in July were the lowest, which might be attributed to the peak of Chl-a concentration. Water eutrophication and moderate-phosphorus-limitied potential eutrophication appeared in the northeast area and moderate nutrition or oligotrophy was observed in the other areas. In addition, the potential eutrophication level in the sea-surface microlayer was higher than that in the subsurface water.