Spatio-temporal distribution characteristics and sources of organic carbon in a typical mariculture Bay: A case study of Sansha Bay, China.

In the present study, a survey on the aquacultural environment and distribution characteristics of organic carbon were conducted in a typical mariculture bay of southeast China from January to August 2023. The spatio-temporal dynamics and sources of dissolved organic carbon (DOC) and particulate organic carbon (POC) were investigated, as well as the impact of mariculture on the coastal carbon cycles. The results showed that concentrations of DOC ranged from 0.488 mg/L to 2.674 mg/L, with an average of 1.118 ± 0.458 mg/L, being lowest in January and highest in August. DOC increased from the channel to the estuary in January and March, while the estuary was a high-value area in April. Then DOC concentrations decreased from west to east in May and June, while in August, DOC demonstrated an increasing trend from the west to the east. The concentrations of POC ranged from 0.012 mg/L to 0.309 mg/L, with an average of 0.091 ± 0.054 mg/L, being lowest in March and highest in June. POC increased from east to west. The highest concentrations of DOC and POC were found at bivalve and kelp cultivation areas. The non-culture area had the lowest concentrations of DOC and POC. The concentrations of POC in the bivalve-kelp multi-trophic aquaculture area were reduced by 19.063 % and 24.711 % compared to single bivalve or macroalgae aquaculture, respectively. Preliminary analysis of the source of organic carbon based on correlation analysis, C/N, POC/Chl-a ratios showed that the living phytoplankton and degraded organic matter were the main source of DOC. The sources of POC included microbial-derived organic matter, primary production and runoff inputs. This study provides a scientific basis for environmental management and planning of aquaculture in the semi-closed bays.