Organic geochemical proxies (OC, OC/TN, δ13C, and lignin oxidation products) were measured in a 271 cm long sediment core collected from central Jiaozhou Bay, northern
China, to study the response of terrestrial and marine organic carbon burials to the surrounding urbanization. Terrestrial
organic carbon content was constantly low from the bottom of the core to ~150 cm depth, indicating a stable and low level
of terrestrial input before urbanization. Thereafter, it increased up to ~20 cm depth, suggesting that increased human activities
and land-use changes during urbanization likely enhanced the flux of terrestrial organic carbon to the bay. Overall, 5–38%
of the total organic carbon was terrigenous, which was derived from a mixture of woody and non-woody angiosperms and moderately
degraded. Marine organic carbon content did not increase notably during urbanization. It increased from the bottom of the
core to ~180 cm and stayed at high levels until it decreased in the top 20 cm. It was affected by multiple factors, including
grain size and nutrient composition. These results demonstrate the different influences of urbanization on terrestrial and
marine organic carbon cycles and suggest the importance of discriminating between these two organic carbon pools in the reconstruction
of their historical changes. 相似文献
Dissolved organic matter (DOM) is a critical component in aquatic ecosystems, yet its seasonal variability and reactivity remain not well constrained. These were investigated at the land-ocean interface of a subtropical river (Minjiang River, SE China), using absorption and fluorescence spectroscopy. The annual export flux of dissolved organic carbon (DOC) from the Minjiang River (5.48 × 1010 g year?1) was highest among the rivers adjacent to the Taiwan Strait, with 72% occurring in spring and summer. The freshwater absorption coefficient a280, DOC-specific UV absorbance SUVA254 and humification index HIX were higher, while the spectral slope S275–295 and biological index BIX were lower in summer than in winter. This suggests intensified export of terrestrial aromatic and high molecular weight constituents in the rainy summer season. Six fluorescent components were identified from 428 samples, including humic-like C1–C3, tryptophan-like C4 and C6, and tyrosine-like C5. The freshwater levels of four components (C1, C2, C4, and C6) were lower while that of C5 was higher in the wet season than in the dry season, suggesting contrasting seasonal variations of different constituents. Laboratory experiments were performed to assess the effects of photochemical and microbial degradation on DOM. Photo-degradation removed chromophoric and fluorescent DOM (CDOM and FDOM) effectively, which was stronger (i) for high molecular weight/humic constituents and (ii) during summer under higher solar radiation. Microbial degradation under laboratory controlled conditions generally showed little effect on DOC, and had smaller impact on CDOM and FDOM in winter than in summer. Overall, this study showed notable seasonal changes in the chemical composition and reactivity of DOM at the land-ocean interface, and demonstrated the significant effects of photo-degradation.