Sources and export of nutrients associated with integrated multi-trophic aquaculture in Sanggou Bay, China

Abstract

Field observations were made from 2012 to 2014 at an integratedmulti-trophic aquaculture (IMTA) site in Sanggou Bay (SGB), China, tocharacterize the nutrients associated with aquaculture activities, andto assess the effects of aquaculture on nutrient cycles in the bay.Dissolved inorganic and organic nutrient levels were measured in rivers,groundwater, and SGB. Seasonal variations in nutrient concentrationswere detected in the rivers, particularly enrichment of dissolvedinorganic nitrogen (DIN) and silicate (DSi). Nutrient concentrationsshowed considerable seasonal variation, with higher and significantlydifferent concentrations occurring in autumn than in the other seasons.The composition and distribution of nutrients were also affected by thespecies being cultured. Dissolved organic nitrogen and phosphorus (DONand DOP) accounted for 27 to 87% of total dissolved nitrogen and 34 to81% of total dissolved phosphorus, respectively. Phosphorus may be apotentially limiting nutrient for phytoplankton growth in summer.Nutrient budgets were developed based on a simple steady-state boxmodel. These showed that bivalve aquaculture was the major source ofPO43-(contributing 64% of total influx) and led to increased riverinefluxes of PO43-. The results indicated that substantial quantities ofnitrogen and DSi accumulated in sediments or were transformed into otherforms (e.g. phytoplankton cell composition or particles). Largequantities of DIN and PO43- were removed from the bay through harvestingof seaweeds and bivalves, which represented up to 64 and 81% of totaloutflux, respectively. The results show that aquaculture activities playthe most important role in nutrient cycling in SGB.