Seasonal distribution of dissolved iron in the surface water of Sanggou Bay, a typical aquaculture area in China

Sanggou Bay (SGB) is one of the largest aquaculture centers in China. Although iron is an essential biological element, little is known about its distribution in this bay. In this study, seasonal distributions of dissolved iron (dFe) in the surface water of SGB and its surrounding rivers and groundwater were investigated during the four seasons from April 2013 to January 2014. Our results indicate that SGB is a source of dFe on the bay scale. The average dFe concentrations in the surface water of SGB were 12.0 ± 6.29 nM in spring, 5.00 ± 2.92 nM in summer, 1.83 ± 0.42 nM in autumn, and 3.36 ± 2.06 nM in winter. External sources of dFe in SGB were ranked in the following order: atmospheric deposition > sediment diffusion > groundwater input > riverine input. The biological iron of the cultivated species (kelp, scallops, and oysters) was the main sink for dFe in SGB. The calculation of Fe^⁎_P (a tracer defined to quantify the degree of iron limitation in water relative to phosphorus) suggested that dFe was sufficient to support the biological utilization of dissolved inorganic phosphorus in spring and summer but was a potentially limiting factor for primary production in autumn.