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The recent expansion of shellfish mariculture could significantly impact the ocean carbon cycle and its associated biogeochemical processes. To understand the source and fate of particulate organic carbon (POC), a summer cruise was conducted from September 8 to 10, 2022, at a mussel farm on Gouqi Island and its adjacent areas located in the East China Sea. Parameters included in situ temperature and salinity, contents of dissolved oxygen (DO), suspended particulate matter (SPM), POC, and chlorophyll a (Chl a), as well as the stable carbon isotopic composition (δ13C) of organic matter in particle and sediment samples, which were analyzed to facilitate a comparative assessment of the areas inside and outside the mussel farm. The POM was much fresher (POC/Chl a < 150) inside the farm with little impact from sediment resuspension (lower SPM content, 11.6 ± 6.6 mg/L), while a significant influence of sediment resuspension was found outside the farm (SPM > 20 mg/L, POC/Chl a > 150). A two end-member mixing model showed that 82.0 ± 6.0% of POC originated from marine algae within the farm, much higher than that outside the farming area (66.1 ± 7.8%). Moreover, elevated DO saturation but relatively low Chl a concentration within the farm suggested continuous algae consumption following potential high productivity. The averaged δ13C values were similar among suspended POC, sinking POC, and sedimentary organic carbon within the farm, implying the fast export and burial of POC. This is likely due to the filter-feeding habits of mussels, who ingest fresh POC and then pack it as fecal pellets that rapidly settle into the sediment. This study sheds light on the distribution and sources of POM inside and outside the mussel farm on Gouqi Island, enhancing our understanding of the marine carbon cycle on shellfish farms and providing insights into the underlying biogeochemical processes. [ABSTRACT FROM AUTHOR]

Noise pollution is considered an important aspect of global environmental issues. The construction of urban rail transit is gradually increasing, leading to excessive noise pollution in rail transit projects. The noise during construction has negatively impacted both the construction workers and residents in the surrounding neighborhoods. Therefore, monitoring and managing the noise is very important. In this study, noise sensors and sound level meters were employed to monitor the noises produced in an urban rail transit project. Then, Cadna/A software was utilized to simulate the noise characteristics. Based on the results, it was found that daytime noise has a maximum of 89.5dB(A), which exceeds the standard. To alleviate the noise impacts, a noise reduction scheme was put forward. The implementation of the noise reduction scheme is predicted to have an effect, resulting in an approximate 10-20dB reduction in noise level. The implementation of the scheme will allow the construction noise of the case projects to meet the national standard. This study addresses the research gaps related to construction noise in urban rail transit projects and provides valuable references for the noise control of urban rail transit projects in China. [ABSTRACT FROM AUTHOR]