Impacts of coastal aquaculture on sedimentary phosphorus speciation and fate: Evidence from a seaweed cultivation area off Nan'ao Island, South China.

How aquaculture impacts the coastal phosphorus (P) cycle remains poorly understood. Here we compared different P species from two sedimentary records off Nan'ao Island, South China, with core S1 collected in a large seaweed cultivation area and core S2 in a non-mariculture area. The results showed that the concentration of total P (TP) in sediment cores varied from 143.67 to 400.92 μg/g, and organic P (OP) was the dominant P species. The TOC/OP ratios in the two sediment cores were higher than the Redfield ratio in 26 samples (52%) from core S1 and 39 samples (78%) from core S2, suggesting that terrestrial organic matter was an important carbon source to Shen'ao Bay. The lack of change in Ex-P (exchangeable or loosely sorbed P) and OP in the area around core S1 since the 2000s may be due to the large-scale seaweed cultivation.