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Many of the world's largest deltas are increasingly threatened by impact of climate change and human activities. The Changjiang (Yangtze River) is among the largest river, and its change of delta has received extensive attention. However, many studies covered smaller delta areas, which cannot reflect the changes of the entire delta region. Here, we present an assessment of the Changjiang (Yangtze River) mega-delta (CMD) using 60 years of bathymetric data covering the entire study area in order to gain clear insight into the comprehensive morphological changes in the Anthropocene. The net deposition rate decreased from 3.47 cm/year over the period 1954–1986 to 0.074 cm/year for the period 2005–2013 in the subaqueous-delta because of a dramatic decline in the sediment load. In particular, as the sediment load further decline due to the implementation of soil and water conservation engineering since 1980s, slight erosion occurred at a rate of −0.0019 cm/year during 1986–2002. However, the subaqueous-delta converted to a balanced state from one of slight erosion, and the depocenter moved southward between 2002 and 2013. Consequently, the morphological change of the CMD went through the following periods: fast accumulation from 1954 to 1986, and balanced accumulation/erosion during 1986–2013 (conservative state in1986–2002 and steady state in 2002–2013). Moreover, the subaerial delta of the Changjiang experienced continued progradation; the area of the subaerial delta increased from 14,857.74 km2 in 1974 to 16,039.03 km2 in 2013 (7.9% increase), with a net progradation rate of 29.53 km2/year; and the most pronounced progradation occurred at Chongming Island and the eastern parts of Nanhui. An important reason for these changes was land reclamation, deep-water channel projects, and shore protection, despite a marked decrease in the river sediment supply. In the future, whether the accumulation/erosion balance continues to be maintained will be an urgent research in the CMD. [ABSTRACT FROM AUTHOR]

Highlights • The original spatial pattern of the natural geographical attributes was changed by human activities. • Different ecosystem components have different responses to human activities. • The establishment of reserved areas has a positive effect on the protection of Marine biodiversity. Abstract Using the marine biological valuation method, we selected five ecosystem components, namely, phytoplankton, microzooplankton, macrozooplankton, macrobenthos, and nekton, to evaluate the marine biodiversity value of Jiangsu's offshore areas in 2006 (early-term coastal development) and 2014 (mid-term coastal development), and the impact of human activities on the values were analyzed based on the differences between the two time periods. In general, the biological value (BV) of the Jiangsu offshore area changed in the context of high-intensity human activities, disrupting the original spatial pattern of the natural geographical attributes indicated by the BV in 2006. From the perspective of various ecosystem components, the impact on macrobenthos is long-lasting and significant, the impact on plankton is temporary and recoverable, and the presence of offshore structures leads to the formation of new habitats that attract new species and more predators (fishes), with the BV of nekton in the radial sand ridge area being higher than that in other marine areas. The results of our approach confirm the importance of areas that were previously identified for protection (particularly in the central regions). Our results also highlight the value of currently unprotected sites, mainly in the northern and southern regions. Highlighting the impact of high-intensity human activities on the BV of Jiangsu lays a foundation for developing future marine spatial plans and provides a scientific reference and basis for administrative departments to develop marine management decisions. [ABSTRACT FROM AUTHOR]

The water discharge and sediment load of rivers are changing substantially under the impacts of climate change and human activities, becoming a hot issue in hydro-environmental research. In this study, the water discharge and sediment load in the mainstream and seven tributaries of the Yangtze River were investigated by using long-term hydro-meteorological data from 1953 to 2013. The non-parametric Mann-Kendall test and double mass curve (DMC) were used to detect trends and abrupt change-points in water discharge and sediment load and to quantify the effects of climate change and human activities on water discharge and sediment load. The results are as follows: (1) the water discharge showed a non-significant decreasing trend at most stations except Hukou station. Among these, water discharge at Dongting Lake and the Min River basin shows a significant decreasing trend with average rates of − 13.93 × 10 8 m 3 /year and − 1.8 × 10 8 m 3 /year ( P < 0.05), respectively. However, the sediment load exhibited a significant decreasing trend in all tributaries of the Yangtze River. (2) No significant abrupt change-points were detected in the time series of water discharge for all hydrological stations. In contrast, significant abrupt change-points were detected in sediment load, most of these changes appeared in the late 1980s. (3) The water discharge was mainly influenced by precipitation in the Yangtze River basin, whereas sediment load was mainly affected by climate change and human activities; the relative contribution ratios of human activities were above 70% for the Yangtze River. (4) The decrease of sediment load has directly impacted the lower Yangtze River and the delta region. These results will provide a reference for better resource management in the Yangtze River Basin. [ABSTRACT FROM AUTHOR]

Based on data from the Datong hydrological station and 147 meteorological stations, the influences of climate change and human activities on temporal changes in water discharge and sediment load were examined in the Yangtze River basin from 1953 to 2010. The Mann–Kendall test, abrupt change test (Mann–Kendall and cumulative anomaly test), and Morlet wavelet method were employed to analyze the water discharge and sediment load data measured at the Datong hydrological station. The results indicated that the annual mean precipitation and water discharge exhibited decreasing trends of − 0.0064 mm/10 yr and − 1.41 × 10 8 m 3 /yr, respectively, and that the water sediment load showed a significant decreasing trend of − 46.5 × 10 6 t/yr. Meanwhile, an abrupt change in the water discharge occurred in 2003. The sediment load also exhibited an abrupt change in 1985. From 1970 to 2010, the climate change and human activities contributed 72% and 28%, respectively, to the water discharge reduction. The human-induced decrease in the sediment load was 914.03 × 10 6 t/yr during the 1970s and 3301.79 × 10 6 t/yr during the 2000s. The contribution from human activities also increased from 71% to 92%, especially in the 1990s, when the value increased to 92%. Climate change and human activities contributed 14% and 86%, respectively, to the sediment load reduction. Inter-annual variations in water discharge and sediment load were affected by climate oscillations and human activities. The effect of human activities on the sediment load was considerably greater than those on water discharge in the Yangtze River basin. [ABSTRACT FROM AUTHOR]

• Both soil-derived and autochthonous OC contributed approximately more than 40.0 %. • The POC derived from phytoplankton continues to increase influenced by TGD. • The decrease in POC was influenced by soil and water conservation. River is a crucial channel for the transport of terrestrial organic carbon (OC terr) into the sea, and has significant implications for the global carbon cycle. However, with the intensification of human activities within the watershed (such as dams and changes in land use), the sediment and OC terr output from rivers have significantly decreased. To study the influence of human activities on the provenance and transport of particulate organic carbon (POC) exported from the Changjiang River Basin (CRB), we collected suspended particulate matter samples during the rainy season of 2021. The POC content exhibited an increasing trend from the headwater zone to the estuary. Results of three-end-member mixing model indicated that both soil-derived and autochthonous OC (OC auto) contributed approximately more than 40.0 %. Notably, OC auto experienced a significant increase from the Three Gorges Dam (TGD) to estuary in the mainstem, attributed to the sediment interception effect of the TGD. The POC contents in the headwater zone and Jinshajiang River in 2021 were lower compared to those in 2007, which can be attributed to a decrease in cultivated land area and increase sediment trapping by cascade dams. Affected by TGD, the POC content in the middle and lower reaches as well as the delta zone first decreased in 2003 and then increased from 2007 to 2021. Additionally, the degradation of lignin phenols and n -alkanes was influenced by the TGD, which prolonged the retention time of terrestrial plants. Compared to previous studies, the decrease in soil-derived OC and increase in OC auto in CRB, influenced by dams and land use, could have long-lasting effect on carbon burial in the ECS. [ABSTRACT FROM AUTHOR]

Long-term organic matter (OM) burial in the ocean is essential to the global carbon cycle. Mud deposits, such as South Yellow Sea mud deposit (SYSMD) located in the central South Yellow Sea (SYS), are ideal for the study of long-term OM burial. A sediment core YS-A from the SYSMD was analyzed for lignin phenols and bulk OM properties to reveal the driving forces of sedimentary OM (SOM) fate during the Holocene. SOM burial was found to be dominantly influenced by sea level rise and increased East Asian summer monsoon during 11.0–7.0 ka BP. During 7.0–1.0 ka BP, the fate of SOM was controlled by El Niño Southern Oscillation on the millennial time scale, and correlated with East Asian winter monsoon variability on the centennial time scale. Remarkably, anthropogenic perturbation has gradually overwhelmed long-term climate control on the fate of SOM since 1.0 ka BP, and this phenomenon became more evident after 0.4 ka BP. • Sea level and East Asian summer monsoon controlled sedimentary organic matter (SOM) burial during 11.0–7.0 ka BP. • Climatic controlled on the fate of SOM during 7.0–1.0 ka BP. • Anthropogenic perturbation has gradually overwhelmed long-term climate control on the fate of SOM since 1.0 ka BP. [ABSTRACT FROM AUTHOR]