Spatial distributions of δ13C, δ15N and C/N ratios in suspended particulate organic matter of a bay under serious anthropogenic influences: Daya Bay, China

Abstract

Stable isotopic signatures (δ¹³C and δ¹⁵N) and C/N ratios of suspended particulate organic matter (POM) were investigated from the surface water of Daya Bay during summer and winter of 2015. The relatively high δ¹³C_POM values suggested the input of ¹³C-depleted terrigenous organic matter was low in Daya Bay. There were significant correlations between δ¹³C_POM values and chlorophyll a concentrations both during summer and winter, suggesting the δ¹³C_POM values were mainly controlled by the phytoplankton biomass in the surface water. The distribution of δ¹⁵N_POM values was more complicated than that of δ¹³C_POM and displayed low values in the outer bay and the Dan'ao River estuary. ¹⁵N-depleted ammonia originating from industrial wastewater might have strongly influenced the water quality and stable isotopic signatures of POM near the Dan'ao River estuary. The δ¹³C_POM and δ¹⁵N_POM values strongly reflect the influences of anthropogenic activity and eutrophication in Daya Bay.

Keywords: Anthropogenic activity; Daya Bay; Eutrophication; Particulate organic matter; Stable isotope.