Dual Pollution Risks of Phosphorus and Heavy Metals in Cage Aquaculture: Implications for Larimichthys Crocea Farming

Abstract

Intensive cage aquaculture poses a potential environmental pollution risk, yet research on double pollution risk of phosphorus (P)-induced eutrophication and heavy metal accumulation remains limited. This study investigated the distribution characteristics and interrelationships of P and typical heavy metals (Cd, Pb, Cu, Cr, Zn, Hg, and As) in the overlying water and sediments under varying cage culture densities (small, medium, medium to large, and large) in the world’s largest cage aquaculture base for Larimichthys crocea located in Sansha Bay, a typical enclosed bay, with no cages as a control (reference stations). The results showed that (1) P concentrations in both overlying water and sediments with higher cage culture densities. Specifically, the total P (TP) and PO43--P in overlying water ranged from 1.23 to 4.91 mg·L-1 and 0.05 to 4.59 mg·L-1, respectively, while TP and available P in sediment ranged from 643.42 to 1879.12 mg·kg-1 and 210.37 to 769.35 mg·kg-1, respectively, with active P increasing and the residual P decreasing. (2) Heavy metal (Cu, Cd, Pb, Cr, Zn, As, Hg) exhibited similar trends to total P, accumulating more in higher-density cage culture areas. Variations were observed in active heavy metals among densities were minor. (3) Strong correlations between P and heavy metals were observed, particularly in medium-to-large and large density cage cultures, indicating a potential risk of P-induced eutrophication. A cage density of 250~400 was identified as a threshold to avoid combined pollution risks. This study provides theoretical guidance for sustainable breeding strategies for large yellow croaker in temperate nearshore waters.

Keywords: Cage culture, Large Yellow Croaker, phosphorus, Heavy metal, double pollution