Use of multiple isotopes to evaluate the impact of mariculture on nutrient dynamics in coastal groundwater

Abstract

Nitrogen and phosphate dynamics in groundwater and surface waters (aquaculture ponds and effluents and drainage channels) in the two seasons (April and September 2015) were investigated in a reclaimed coastal region in China. Multiple isotopes (δ¹⁵N-NO₃^-, δ¹⁸O-NO₃^-, δ²H-H₂O, and δ¹⁸O-H₂O) associated with the concentrations of dissolved inorganic nitrogen and phosphate were analyzed to assess the environmental impact of mariculture on coastal waters. Low phosphate concentration in the effluents was released from aquaculture ponds. Nitrate accounted for a larger proportion of dissolved inorganic nitrogen in September in aquaculture ponds and effluents and drainage channels. The groundwater in the mariculture zone was enriched with dissolved nitrogen components. In the offshore direction, seawater and precipitation were supplement of the groundwater, with nitrate deriving from mixing aquaculture effluents and wastewater. Denitrification occurred in groundwater in September 2015.

Keywords: Groundwater; Isotopes; Mariculture; Nitrate; Nitrate sources; Nitrogen transformation; Nutrients.