Shuwei Zheng

Reliable quantification of morphological evolution in shallow-water lakes constitutes a long-standing challenge for limnological studies, which is essential to advance sustainable lake-basin management. Poyang Lake is a typical shallow-water lake, featuring a basin composed of narrow channels and extensive shallow bottomlands. This geomorphological feature leads to a variety of eco-environmental problems. Using the Google Earth Engine (GEE) platform and field-measured water level data, this study constructed a volume change model (VCM) to estimate changes in water storage (volume) across water levels ranging from 8 m to 14 m in Poyang Lake during 1989–2025. In the VCM, annual surface water areas at the two characteristic water levels (8 m and 14 m, approximating the 25th and 75th percentiles of the long-term water-level record) were first derived. Thus, the volume changes reflect lake-basin morphological change rather than hydrological variability. The results show that lake volume (8–14 m) decreased by 2515.5 × 10⁴ m³ over 1989–2025, an equivalent of 3018.6 × 10⁴ t sediment for the lake basin material. Specifically, the lake basin experienced deposition (1092.0 × 10⁴ t), erosion (2052.0 × 10⁴ t) and deposition (3984.0 × 10⁴ t) during 1989–1999, 1999–2007 and 2007–2025, respectively. The volume change model can effectively quantify lake volume change. Intense basin-wide precipitation led to net sediment deposition during 1989–1999, while large-scale unregulated sand mining operations were closely associated with an increase in the lake volume in 1999–2007. Since 2007, enforced sand-mining regulations have greatly reduced in-lake sand extraction. The sediment input change and sand-mining regulations lead to net sediment accumulation across the Poyang Lake basin.

Man-made floods from dams are intentional for different purposes, e.g., spreading sediment and helping deltaic development. Less is known about their effects on slack-water deposits (SWDs) in downstream channels. Since the implementation of the Water and Sediment Regulation Project (WSRP) through a large dam on China’s Yellow River (YR) in 2002, the dynamic sedimentary environment of the river has undergone significant changes. To understand the sedimentary responses of the downstream channels to the man-made floods, this study was conducted following a 24-day man-made flood period in 2021 to investigate SWDs on the floodplains. Sediment samples were collected from four floodplain sites in the lowermost reach of the YR. The study showed that the median grain size (D₅₀) of the man-made flood SWDs on the floodplains ranges from 17 to 131 μm, with an average of 44.14 μm, classifying them as fine-grained deposits. Spatially, D₅₀ of 57.2% of the sampled SWDs exhibited an increasing trend from the riverbank to the main channel. This finding indicates that during the deposition process of floodplain floods, differences may exist in the direction perpendicular to the riverbank. Along the upstream-to-downstream direction, no obvious regularity was observed. Moreover, there is no positive correlation between sediment discharge and the average grain size of suspended sediment. These findings indicate that large man-made floods by a dam will not allow finer particles to settle. Such changes in sediment transport may have a long-term effect on Yellow River deltaic development and stability.

Anthropogenic activities and climate change have increased the stress on the world’s estuaries over the past decades. Limited knowledge exists about how estuarine receding responds to human interference, particularly the geomorphic dynamics of channels and sandbars. Here, we evaluate the topographic evolution of the upper Yangtze River Estuary (YRE), the largest branch reach with frequently shifting sandbars, from 1994 to 2019. Our results show that a net channel erosion of 9.59 × 10⁸ m³ occurred in the upper YRE, equivalent to an annual erosion depth of 8.67 cm. On the contrary, sandbars with a large area increased from 47.68 km² to 70.88 km², showing the opposite development of estuarine channels. Reduced riverine sediment supply may have been responsible for the estuarine channel erosion, and river engineering may have contributed to intense erosion in local areas. Also, the engineering projects were likely the main reason for the stability and growth of the sandbars. This study reveals the branching channel–sandbar system of the upper YRE in response to anthropogenic and climatic change forcing. The knowledge gained from this study can be applied to other similar estuarine systems around the world, helping develop sustainable strategies for the utilization and protection of the world’s estuaries and deltas.

The urban heat island (UHI) effect has become increasingly prevalent and significant with the accelerated pace of urbanization, posing challenges for urban planners and policymakers. To reveal the spatiotemporal variations of the urban heat island effect in Jinan City, this study utilized Landsat satellite images from 2009, 2014, and 2019, employing the classic Mono-Window algorithm to extract land surface temperature (LST). Additionally, Geodetector was introduced to conduct a detailed analysis of the relationship between LST in Jinan City and land cover types (vegetation, water bodies, and buildings). The results indicate a significant increase in the severity of the urban heat island effect in Jinan from 2009 to 2019, with the central urban area consistently exhibiting a high-intensity core heat island. Suburban areas of Jinan show a clear trend of merging their heat island effects with the central urban area. The combined area of strong cool island effect zones and cool island effect zones within water bodies reaches 89.7%, while the combined proportion of heat island and strong heat island effect zones in building areas is 62.2%. Vegetation cover (FVC) exerts the greatest influence among all factors on the intensity level of the urban heat island effect. These findings provide a reliable basis for decision-making related to urban planning and construction in Jinan City.

Climate change and human activities affect regional sediment transport and ecological environment construction. Investigating sediment transport and its influencing factors in the Yihe River Basin (YHRB) will provide guidance for regional soil and water conservation and sustainable development. We analyzed the chronological changes, cycles, spatial distribution and influencing factors using Mann–Kendall (M-K) trend analysis, wavelet analysis, and the Pettitt mutation point (PMP) test, then quantified the role of precipitation and human activities in sediment transport changes. The results showed that annual precipitation decreased marginally, whereas sediment load has noticeably declined. Four precipitation cycles were observed: 4–8a, 9–14a, 16–19a, and 20–28a, where 9–14a was dominant; sediment transport cycles were tracked: 3–5a, 9–15a, and 30a, where 30a was dominant with a decreasing trend. The sediment load was higher in the central, northern, and southwestern sub-basins of the YHRB, while it was lower in the southeast. The contribution of human activities and precipitation changes to sediment transport was 73.14% and 26.86% in transitional phase I (1965–1980) and 71.97% and 28.03% in transitional phase II (1981–2020), respectively. Hydraulic engineering construction, water resource development, land-use changes, and soil and water conservation measures intercepted precipitation and sediment, making them the primary factor affecting sediment transport changes in the YHRB.

Grain size analysis of flood sediments is a key method for understanding the sedimentary environments of rivers worldwide; however, there is limited knowledge of how to effectively reflect the sedimentary environment of lower Yellow River (Huang He) flood events using grain size parameters. In this study, two widely used grain size analysis methods, the graphic method (GM) and moment method (MM), were compared, and their applicability to flood sediment analysis in the lower Yellow River was evaluated. Modern flood sediments (n = 143) in the lower Yellow River featured a fine-grained texture and were classified as silty sand (4.95 ≤ Φ ≤ 5.03) characterized by an inadequate sorting ability. The grain size distribution patterns obtained using the GM and MM revealed positive and extremely positive deviations with sharp and flat peaks, respectively. A strong correlation (0.6966 ≤ R² ≤ 0.9961) was observed between the mean grain size and the sorting coefficient obtained using the GM and MM. Thus, both methods were deemed suitable and could be used interchangeably. Our results indicate that the MM should be applied to assess skewness because it provided comprehensive information regarding flood sediments in the lower Yellow River, whereas the GM is recommended for kurtosis analysis, as it highlighted the primary sedimentary dynamics during flood events. Methods must be selected based on the sedimentary environment when analyzing grain size parameters.

Reduction in river discharge and sediment load has left deltaic lobes in the world’s many river deltas starving, but knowledge of how the subaqueous topography of these abandoned subdeltas responds to environmental changes is limited. In this study, we aimed to determine the long-term dynamics of the subaqueous seabed of abandoned delta lobes to advance current knowledge. As a case study, we selected an abandoned subdelta on the Yellow River Delta of the Bohai Sea, China, for which three-decade long (1984–2017) bathymetric data and long-term river discharge and sediment load records are available. We analyzed the seafloor surface change and quantified the void space from the sea water surface to the seafloor. In addition, we surveyed the seafloor surface with an M80 unmanned surface vehicle carrying a multibeam echo sounder system (MBES) in 2019 to obtain high-resolution microtopography information. We found that a net volume of 5.3 × 10⁸ m³ of sediment was eroded from the study seabed within an area of 3.6 × 10⁸ m² during 1984–2017. This volumetric quantity is equivalent to 6.89 billion metric tons of sediment, assuming a bulk density of 1.3 t/m³ for the seabed sediment. The seabed erosion from 0 to −5 m, from −5 to −10 m, and below −10 m has showed a similar increasing trend over the past 33 years. These findings suggest that seabed erosion in this abandoned subdelta will very likely continue, and that other abandoned delta lobes in the world may have been experiencing similar seabed erosion due to the interruption of the sediment supply and sea level rise. It is not clear if the seabed erosion of abandoned delta lobes would have any effect on the stability of the coastal shoreline and continental shelf.

Deltaic channels are significant landforms at the interface of sediment transfer from land to oceanic realms. Understanding the dynamics of these channels is urgent because delta processes are sensitive to climate change and adjustments in human activity. To obtain a better understanding of the morphological processes of large deltaic channels, this study assessed the evolution and response mechanism of the South Channel and South Passage (SCSP) in the Yangtze Estuary between 1983 to 2018 using hydrology, multibeam echo sounding and historical bathymetry datasets. Decadal changes in riverbed volume and erosion/deposition patterns in the SCSP were assessed. The results showed that the SCSP experienced substantial deposition with a total volume of 26.90 × 10⁷ m³ during 1983–2002, but significant bed erosion with a total volume of 26.04 ×10⁷ m³ during 2003–2010. From 2011 to 2018, the estuarine riverbeds shifted from erosive to depositional, even though the deposition was relatively marginal (0.76 ×10⁷ m³). We inferred that the SCSP have most likely changed from a net erosion phase to a deposition stage in response to local human activities including sand mining, river regulation project, and Deep Water Channel Regulation Project). The channel aggradation will possibly continue considering sea level rise and the ongoing anthropogenic impacts. This is the first field evidence reporting that the lowermost Yangtze River is reaching an equilibrium state in terms of channel erosion and, in fact, the Yangtze River Estuary channels are beginning to aggrade. The findings have relevant implications for the management of the Yangtze River and other lowland alluvial rivers in the world as global sea level continues rising and human intervention on estuarine systems persists.

The global demand for sand and gravel is at 50 billion tons per year, far exceeding global resource capacities. It reached 7.6 billion tons in 2021 in the Yangtze River Basin (YRB), China. However, production is severely limited in the YRB. Therefore, the incongruity between the supply and demand of river sand is prominent. Wise management of decreasing sand resources in the YRB has become critical since the Three Gorges Dam became operational in 2003. This study synthesized spatial and temporal changes in sand mining activities and quantities along the Yangtze River and its major tributaries from 2004 to 2020. Results from the study show that the mining amount during the period reached 76.2 million tons annually. At the same time, riverine suspended sediment discharge (SSD) downstream of the Three Gorges Dam decreased largely. SSD reduction leads to riverbed erosion, further limiting the riverine sand and gravel sources for mining. Thus, alternative sand and gravel resources, as well as optimizing supply/demand balance, are necessary for sustainable development. There is an urgent need to assess the relationship between river sand resources and exploitation in the YRB for creating a sand and gravel data management system in order to cope with the increasing incongruity between their supply and demand.

Analyzing cultivated land input behavior (CLIB) at the scale of rural households links with cultivated land-use efficiency (CLUE), this study examined the Yimeng Mountain area in northern China, supported by field survey data from 737 rural households. This research systematically analyzed the characteristics of CLIB of different types of rural households, measured the CLUE of different types of rural households by using a data envelopment analysis (DEA) model, and explored the influence of CLIB on CLUE based on the Tobit regression model. The results show (1) significant differences in the characteristics of the CLIB of different types of rural households in the Yimeng Mountain area. Among them, the highest land, labor, and capital inputs were I part-time rural households (I PTRH), followed by full-time rural households (FTRH). In contrast, II part-time rural households (II PTRH) and non-agricultural rural households (NARH) had higher levels of non-agricultural employment; however, their input levels gradually declined. (2) The CLUE of the sample rural households was generally low and had considerable potential for improvement. Regarding the types of rural households, as the degree of part-time employment increased, the CLUE showed an inverted U-shaped trend of first increased and then decreased, namely, I PTRH > FTRH > II PTRH > NARH. This finding indicates that appropriate part-time employment could help to promote investment in agricultural production and improve the CLUE. (3) The CLIB of rural households had significant effects on CLUE; the literacy of the agricultural labor force, yield-increasing input per unit area, per capita household income, share of agricultural income, operation scale of cultivated land, effective irrigation rate of cultivated land, and soil and water conservation rate of cultivated land had positive effects on improving CLUE. Even so, there was still significant heterogeneity in the degree of influence of different rural household types. The study concluded with some policy recommendations from the perspective of different rural household types to provide references for optimizing farming inputs and improving CLUE.