Exploring Carbon Sources in Jiaozhou Bay's Intertidal Zones

The intertidal zones of Jiaozhou Bay (JZB) are a key storage area for carbon, playing a big part in how organic matter moves and builds up. Yet, there aren't many studies that measure the sources of this organic matter. This study looked at 36 surface sediment samples from JZB to find out where the organic carbon (OC) comes from. The samples were tested for total organic carbon (TOC), the ratio of TOC to total nitrogen (TOC/TN), carbon isotope values (δ 13 C), and specific markers called biomarkers. The results showed that using only TOC/TN or δ 13 C can lead to mistakes in identifying OC sources, especially when there are C 3 plants, C 4 plants, and sewage outlets involved. Instead, a three-end-member model using both TOC/TN and δ 13 C values gave a better picture. This model found that marine productivity, or the growth of marine plants, was the main source of OC. In the western zones, about 74% of OC came from marine productivity, 14% from estuarine productivity (growth in estuaries), and 12% from C 4 plants. In the eastern zones, the numbers were 58% from marine productivity, 25% from estuarine productivity, and 17% from sewage outlets. The higher marine productivity in the west is due to the presence of a plant called Spartina alterniflora. In the east, more rivers flowing into JZB contributed to more estuarine productivity. The study also found that the biomarkers and OC contents matched well with the three-end-member model, supported by further analysis called principal component analysis (PCA). This study helps us understand that OC sources vary depending on the coastal environment and fills a gap in our knowledge about carbon cycles and protecting ecosystems in JZB's intertidal zones.