Submarine groundwater discharge-driven nutrient fluxes in a typical mangrove and aquaculture bay of the Beibu Gulf, China

Abstract

To understand the role of submarine groundwater discharge (SGD) in a mangrove combined aquaculture ecosystem, groundwater samples and timeseries observations (27 h) of 224Ra, 223Ra, and nutrients were obtained during wet and dry seasons in Zhenzhu Bay, a typical mangrove and aquaculture ecosystem along the Beibu Gulf in China. The SGD rates in Zhenzhu Bay were estimated to be 22.3–44.5 cm/d in the wet season and 41.1–58.1 cm/d in the dry season, which were 0.8–1.6 and 9.8–14.1 times higher than the corresponding river water discharge values, respectively. Furthermore, SGD-driven dissolved inorganic nitrogen, dissolved inorganic orthophosphate, and dissolved inorganic silicate accounted for 72%, 56%, and 60% of the total nutrient input, respectively, during wet season, which increased to 93%, 98%, and 89% during dry season. The findings highlight that SGD plays an important role in the dissolved inorganic nutrient sources of Zhenzhu Bay, and that the effective utilization and management of the bay should consider SGD.