Resuspension-driven organic matter dynamics in bivalve aquaculture systems: seasonal insights from Dinghai Bay, China

Understanding organic carbon dynamics in coastal bivalve aquaculture zones is essential for sustainable management, yet comprehensive studies on seasonal variations and aquaculture impacts remain limited. This study investigates the organic matter (OM) distribution and resuspension effects in Dinghai Bay, China, through field surveys in winter, summer, and autumn combined with controlled incubation experiments. Using the IsoSource approach with particulate organic carbon isotope (POC-δ 13 C) and amino acid (Asp/Glu) indices, we quantitatively assessed the contributions of resuspension, bacteria, phytoplankton, and terrestrial plants to particulate organic matter (POM). Results revealed significant seasonal resuspension patterns, with maximum intensity in winter driven by winds and minimal activity in summer during peak phytoplankton growth. Incubation experiments demonstrated that resuspension releases labile dissolved organic matter (DOM) from porewater, with microbial degradation being the dominant removal pathway in turbid waters. Additionally, clam-feeding experiments quantified their impact on water column chemistry, showing alterations in DOM composition (freshness) and decreased nutrient N/P ratios close to the Redfield ratio. Extrapolating the incubation results indicated that feeding activities reduced total suspended matter by 29% in the aquaculture area, but by less than 1% across the entire Dinghai Bay. Our results provide a new understanding of seasonal OM dynamics, resuspension impacts, and bivalve-aquaculture interactions, offering critical insights for sustainable coastal ecosystem management.