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Based on data from river gauging stations, the multi-year variations in suspended sediment flux (SSF) from China's nine major rivers to the sea were examined. The decadal SSF decreased by 70.2%: from 1.81 Gt/year for 1954–1963 to 0.54 Gt/year for 1996–2005. The decrease in SSF was more dramatic in the arid northern region than in the wet southern r...
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... nine rivers studied here, the Songhuajiang, Liaohe, Haihe, Yellow, Huaihe, Yangtze, Qiantangjiang, Minjiang and Pearl rivers (listed from north to south), have a combined drainage basin area of 4.53 × 10 6 km 2 ( Fig. 1), which constitutes 74% of the total external drainage area and 47% of total area in China. The suspended sediment flux (SSF) from these rivers to the sea represents 85% of the total flux from China (DHMWR, 1997). Based on data from river gauging stations covering 52 years , we examine the temporal trend in total SSF from these rivers ...
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... of the exterior rivers of China flow from west to east into the Pacific Ocean due to the country's topography, and the rivers selected for this study drain the eastern part of China. They are located within a span of more than 30 degrees of latitude, which results in great variation in climate and hydrology among the rivers ( Fig. 1; Table 1). The southern rivers, such as the Table 1 Drainage area and averages of precipitation, water discharge, and suspended sediment flux (SSF) to the sea of nine major rivers in China Qiantangjiang, Minjiang and Pearl, lie within the humid zone (annual precipitation: >1400 mm) and have high vegetation coverage. These rivers have ...
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... well as of the other rivers for 1954-2005, were collected from the Ministry of Water Resources of China. Each of the rivers has a gauging station at the tidal limit to measure water and sediment fluxes to the sea, except for the Huaihe which has two, and the Pearl which has three, due to the existence of large tributaries in their lower reaches (Fig. 1). In the case of the Songhuajiang, Liaohe, Huaihe and Yangtze rivers, the gauging stations are far from the sea, because of the significant influence of tides, compared to some other rivers in the world (Syvitski & Morehead, 1999). Due to the short length of record for both the Haihe and Qiantanjiang rivers, the records for the other ...
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... decreasing trend in the other rivers, although most of these trends are not statistically significant. Regional responses to global climate change are complicated (Dore, 2005). The difference in precipitation between the Pearl and the other rivers may be due to their locations. The Pearl River is closer to the tropical seas than the other rivers (Fig. 1). The decrease in precipitation was relatively sharper in the northern rivers than in the southern ones (Fig. 3). For example, precipitation decreased by 14, 13, 18 and 7.4% in the Songhuajiang, Liaohe, Haihe and Yellow rivers, respectively, from 1954-1963 to 1996-2005. Less precipitation tends to result in less runoff and sediment ...
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... More than 70 percent of the world's large-and mediumsized cities are located in coastal areas, accounting for more than 60 percent of the world's economy and 50 percent of the world's total population [5][6][7][8][9]. However, in recent years, with global warming, sea level rise, reduction of sediment transport in river basins, offshore aquaculture, reclamation, and construction of various coastal projects, the area of tidal flats has rapidly decreased, their natural properties are gradually weakening, biodiversity is decreasing, and their ability to resist typhoons and storm surges has weakened, threatening people's lives and property safety [10][11][12][13][14]. It has been estimated that the total tidal flat area decreased globally by more than 20,000 km 2 between 1984 and 2016, representing a reduction of approximately 16 percent [15]. ...
... The sediment continued to be pushed offshore from the estuary, increasing the number of tidal flats [39,46]. According to relevant statistics, in recent decades, affected by the construction of reservoirs, industrial and agricultural water use, and a series of human activities, the amount of sand transported by rivers in Beibu Gulf has shown an obvious downward trend [11,[53][54][55][56]. For example, the suspended sediment content in the Nanliu River Basin decreased from an annual average of 0.16 kg/m 3 in 1972-2006 to an annual average of 0.11 kg/m 3 in 2007-2020 [57]. ...
Tidal flats are an important part of coastal wetland systems and play an irreplaceable role in maintaining the health of global coastal ecosystems, resisting natural coastal disasters, and sequestering blue carbon. For the coastal zone around Beibu Gulf, where tidal flats are densely distributed, the spatiotemporal characteristics of tidal flats evolution and its key driving factors remain unclear. This article took the Beibu Gulf as the study area, and constructed an integrated tidal flats extraction algorithm of “maximum spectral index composite (MSIC) + Otsu algorithm (OTSU) + DEM correction” based on the cloud computing platform of Google Earth Engine to realize a large-scope and high-accuracy automatic extraction of tidal flats. The results discovered that: (1) the tidal flats extraction method proposed in this study has high accuracy, with the overall accuracy of the confusion matrix reaching 93.9%, and the Kappa coefficient reaching 0.82. The user accuracy and mapping accuracy of the tidal flats are both greater than 85%. (2) In 35 years, the total tidal flats area of the Beibu Gulf has decreased by 683.9 km2, a reduction of 29%, and the average annual rate of change was -19.5 km2/a. (3) The fragmentation state of the tidal flats in Beibu Gulf intensified with time, and the natural driving forces of the tidal flats were mainly the rise in sea level, decrease in the amount of sediment in the river entering the sea, and expansion of mangrove trees. Human-driven forces were mainly coastal economic development and offshore aquaculture.
... In addition, with the increasingly changing structure of the coastline, a decrease in nonpoint source loads from the coast will lead to a decrease in sediment supply [53]. In previous studies, factors such as soil erosion [54], meteorological and hydrological conditions [55], dam construction [56], and sand mining [57] have all been well explained. PRE and SZB are important marine transportation areas (see in Figure 12), with the daily heavy discharge of pollutants from marine transportation potentially debasing water quality. ...
Shenzhen is a crucial city in the Guangdong–Hong Kong–Macao Greater Bay Area (GBA). With high-intensity land development and rapid population growth, the ocean has become an essential space for expansion, leading to significant variations in water quality in the coastal area of Shenzhen. Water clarity (Zsd) is a key indicator for evaluating water quality. We applied the quasi-analytical algorithm (QAA) to Sentinel-2 data and retrieved the Zsd of the coastal area of Shenzhen. By adjusting the red band for distinguishing water types, we avoided underestimating Zsd for clear water. This study pioneered the production of a 10 m Zsd product for the coastal area of Shenzhen from 2016 to 2021. The results showed that the coastal area of Shenzhen exhibited a spatial distribution pattern with low Zsd in the west and high in the east, with Pearl River Estuary (PRE: 0.41–0.67 m) and Shenzhen Bay (SZB: 0.30–0.58 m) being lower than Dapeng Bay (DPB: 2.7–2.9 m) and Daya Bay (DYB: 2.5–2.9 m). We analyzed the seasonal and interannual variations and driving factors of the four areas, where PRE and SZB showed similar variation patterns, while DPB and DYB showed similar variation patterns. PRE and SZB are important estuaries in southern China, significantly affected by anthropogenic activities. DPB and DYB are important marine aquaculture areas, mainly affected by natural factors (wind speed, precipitation, and sea level). The Zsd of the coastal area of Shenzhen, along with the analysis of its results and driving factors, contributes to promoting local water resource protection and providing a reference for formulating relevant governance policies. It also provides a practical method for assessing and monitoring near-shore water quality.
... Considerable research has been conducted on the impact of LULC and climate change on annual sediment load (i.e. sediment yield) at catchment scales (Dai et al. 2009;Hung et al. 2014;Camilo & Restrepo 2017;Kemper et al. 2019) and at continental scales (Syvitski 2003;Walling & Fang 2003;Wang et al. 2011;Syvitski et al. 2014;Moragoda & Cohen 2020). However, there has been less focus on how these factors and their interactions affect suspended sediment transport dynamics, i.e. short-term changes in suspended sediment concentration (SSC) at a location over days to months (Mount & Abrahart 2011;Roman et al. 2012;Murphy 2020). ...
Suspended sediment concentration (SSC) is an important attribute for water resources management. However, the interactions between climate and catchment characteristics that control the temporal variability of SSC in rivers are not fully resolved. The study aim is to evaluate how these variables influence spatial and seasonal variations in SSC dynamics at a continental scale. Daily SSC (mg/l) and site attribute data from 120 sites (USA) with minimum 10 years of record (1971–2000) were analysed. New indicators of SSC dynamics (magnitude and frequency) were developed and applied annually and seasonally. Geographically weighted regression (GWR) models were created for each ordinary least squares (OLS) regression model, and GWR coefficients were analysed by ecoregion. Land cover, rainfall and erosivity, baseflow index and soil texture were the most common variables in the OLS models. GWR coefficients displayed significant variation across the continent. Agricultural cover was positively associated with low frequency SSC events, while urban and forest cover predicted higher frequency events, except in the desert areas. PPT30 was generally a negative predictor for SSC magnitude, except the marine west coasts forests. These findings on catchment and climate controls on SSC will support future predictive models of SS transport dynamics.
HIGHLIGHTS
Influence of catchment and climate variables on short-term (day-month) suspended sediment transport dynamics were investigated using new indicators.;
Regression analysis identified land cover/land use, precipitation, baseflow index and soil clay content as significant predictor variables.;
Spatial modelling identified significant regional and seasonal differences in the influence of catchment and climate variables.;
... The TGD, the largest hydropower project worldwide, commenced operations in June 2003 (Zhou et al., 2021). As sediments are retained in the reservoir, there is a substantial reduction in the proportion of sediment outflow (Zheng, 2016) into the Yangtze River middle-lower reaches (Dai et al., 2008;Dai et al., 2009;Li et al., 2019;Lyu et al., 2020;Yan et al., 2021;Yang et al., 2018b) and, consequently, into the estuary (Milliman and Farnsworth, 2011;Tang et al., 2021). Moreover, the construction of cascade hydropower stations for water storage and utilization downstream of the Jinsha River, which is located at the Yangtze River upper reaches, further disrupts the inflow-outflow sediment proportion of the TGR, thereby significantly reducing the sediment proportion downstream of the dam (Dai et al., 2018;Dong et al., 2019;Li et al., 2018a;Wang et al., 2016b;Yang et al., 2022;Zhang et al., 2022). ...
... The volume of different particle sizes during restoration was not expected to exceed the average volume recorded prior to reservoir impoundment (Wang et al., 2016b). These predictions were verified through surveys conducted in 2003-2009(Chen et al., 2010Li et al., 2003). The long-distance scouring of the riverbed downstream of the TGD in [2003][2004][2005][2006][2007] was mainly attributed to the non-sufficient supply of riverbed sediments, especially fine particles (Li et al., 2003). ...
... The downstream replenishment of coarse sediments in the Yichang-Jianli reach majorly restored the volume to the average value recorded prior to the TGR operations in 2003-2009. In 1981-2002 (Table 4). ...
River hydrology and geomorphology are largely influenced by human activities. The operation of the Three Gorges Dam (TGD), which is the largest global hydropower project, has caused widespread concern because of its substantial influences on downstream water and sediment fluxes. This study assesses the influences of the Three Gorges Reservoir (TGR) impoundment on sediment sorting and spatial-temporal characteristics of downstream transport. The results indicate that the reservoir prevented the transport of 76% of the sediments from the upstream basin to the downstream area of the dam, and the discharge of fine (d ≤ 0.125 mm) and coarse particles (d > 0.125 mm) was lower than 25% (24% and 12%, respectively). The recovery of total and fine sediments along the lower reaches of the TGD since 2003 was lower than the respective average values before impoundment (1990–2002). The total volume and discharge ratio of coarse and fine sediments decreased owing to the increase in water level and discharge in the reservoir area. When the inflow was higher than 30,000 m³/s during the flooding season (May–October), the discharge ratio of fine and coarse sediments increased and remained stable, respectively. After the TGR operation commenced, the sediment reduction within 954.4 km downstream of the dam resulted in a long-distance cumulative scouring. However, coarse sediments were not considerably recovered owing to the gradual coarsening of the riverbed. The results of this study help clarify the influences of large dams on the sediment transport in alluvial river systems. This study provides an understanding of the effects of human activities in the evolution of the water-sediment-geomorphology system in rivers.
... First, the important quantities of aggregates being removed from Asian waterways lead to a decrease in the overall sediment load that rivers carry out to the sea, including the Yangtze and Pearl rivers in China (Chen et al., 2006;Chu et al., 2009;Du et al., 2016;Wu, C. et al., 2016). Chinese rivers yield one tenth of global sediment discharging into oceans, with the global consequences of massive China-based sediment withdrawals remaining widely unknown (Dai et al., 2009). Sand mining also leads to the removal of coarser sediments, leaving the water floor covered with finer particles and impacting river channel flow (Xu and Milliman, 2009;Xia et al., 2013). ...
Sand, gravel, and crushed rock – known as construction aggregates – are in high demand in the Asian region. Such demand is driven by high rates of urbanization, infrastructure development, and dam building: an unprecedented amount of sand is being extracted from the region's river, delta and estuary areas, only to be transported for infill or construction purposes elsewhere. This systematic scoping review examines the state of knowledge in the peer review literature on sand ecologies, livelihoods, and governance in Asia. We find that the literature mainly focuses on the ecological implications of sand mining, namely biotic and abiotic components: sand mining is linked with many forms of ecological degradation, although partial ecosystemic recovery may be possible when sand mining stops. In contrast, the limited analysis on livelihoods suggests that violence, work-related injuries, and precarious jobs are common for those working in the sand industry, with sand mining producing different types of work depending on the level of mechanization. We conclude by noting several gaps in the literature, including the narrow geographical focus (mainly India and China), the lack of attention to the intersection between sand mining and other anthropogenic disturbances, and the need to establish transparent sand governance processes within this region.
... The increasing trend of dam construction in the world indicates the need to investigate the environmental impacts of dams. Numerous studies have evaluated the environmental risk during the operational phases of the dammed reservoir (Babaei et al., 2021), focusing on the existing effects identified in the eco-environmental impact assessment including eutrophication and algae blooming (Stone, 2011), habitat deterioration , changes in aquatic ecosystems (Ruiz-González et al., 2013;Yan et al., 2015), sedimentation (Fu et al., 2008;Dai et al., 2009). ...
The presence of sulfur and iron in waste rocks produced during reservoir construction can generate acid rock drainage (ARD). Its environmental impact however, has often been neglected. Therefore, lab experiments were firstly conducted to simulate the release of main pollutants when the waste rocks having been submerged at the bottom of a reservoir in Guizhou Province, China. The impact of pollutants released on water quality during impounding was then predicted by a two-dimensional model MIKE21 coupled with ECO Lab module. Results showed that the argillaceous rock mainly produced acid and sulfate through oxidation. Based on release experiment, the model suggested that the average concentrations of TP, SO4²⁻, and Fe3＋ peaked rapidly in the cross section about 100 m downstream of the waste rock yards when water level reached 855 m. At this point, the average Fe3＋ concentration exceeded the standards of drinking water source and remained for 6 days, while the average TP concentration downstream exceeded the standards for 60 days. The water quality would meet the standards because of the dilution effect on pollutants when the water level was above 883 m. However, the release of phosphate from combined cycles of ”P-Fe-S” should be paid more attention during impoundment. Based on the simulation results and existing actual cases, it showed that the anaerobic environment caused by impoundment can significantly reduce the negative impact from ARD. The study would provide a new insight for the stacking of engineering waste rocks and environmental risk assessment of the reservoir under construction.
... There are three possible explanations. First, riverine SPM contents decreased due to human activities such as dam construction, soil conservation, and sand mining (Chu et al., 2009;Dai et al., 2009). Second, sediment deposition that mainly occurs with large particles within reservoir areas would also increase POC(%SPM) (Zhang et al., 2014). ...
Rivers serve as regulators of global climate by releasing greenhouse gases, burying particulate carbon, and connecting different ecosystem carbon pools. However, long-term organic carbon (OC) transport features across different Asian rivers are not well known due to unavailable data. Based on routinely monitored environmental and hydrological data during 2004-2018, this study investigated the spatiotemporal variations in dissolved (DOC) and particulate OC (POC) transport across 41 rivers in China. Across different rivers, both DOC (1.35 – 16.8 mg/L) and POC (0.27 – 4.48 mg/L) concentrations covered wide ranges. The DOC content was high in the north and low in the south, with significantly higher (t test, p < 0.01) values for rivers north of 30°N (5.39 ± 3.66 mg/L vs. 2.39 ± 1.14 mg/L). Human activities greatly influenced the riverine DOC and POC distributions. The riverine ammonia nitrogen (NH+ 4-N) content was positively correlated with DOC (r = 0.81 and p < 0.01) and explained 85.59% of its spatial variation. High vegetation coverage had significant effects on decreasing the riverine POC content, with r = -0.55 and p < 0.05. During 2004-2018, water pollution prevention and control strategies decreased DOC concentrations in 60.98% of rivers; meanwhile, anthropogenic vegetation restoration and dam construction led to POC content decreases in 90.48% of rivers. Importantly, along with DOC and POC changes, increasing DOC/POC ratios were found in 90.48% of the rivers, with 42.86% being significant, which indicated that Chinese rivers are losing their Asian features of low DOC/POC ratios due to artificial disturbance. This study is significant for accurately quantifying greenhouse gas emissions, carbon burial, and OC export to estuaries by Chinese rivers.
... To date, a large number of studies have indicated that runoff and the SSC in many large rivers are regulated by human activities, especially the reconstruction of navigation channels, construction of dams and reservoirs, and soil and water conservation projects, which have caused the amount of suspended sediment in certain large rivers to drastically decrease (Yang et al., 2002;Walling and Fang, 2003;Yang S. L. et al., 2015;Dai et al., 2016). It has been confirmed that human activities are the main factor leading to a reduction in the SSC in rivers flowing to the sea (Dai et al., 2009;Wu et al., 2012). For example, after the completion of the Three Gorges Dam in the Yangtze River, the SSC in the estuary immediately dropped by 40.3%, and the sediment load in the Yangtze River estuary was drastically reduced, resulting in a sharp decline in the wetland area (Yang et al., 2005;Wang et al., 2015;Wei et al., 2021). ...
Suspended sediment in the water body of rivers flowing into the sea is of great significance to the accumulation process in river basins and change pattern of landforms. In particular, small and medium rivers entering the sea in mountainous areas exhibit the characteristics of both mountains and streams, and the suspended sediment concentration (SSC) greatly contributes to the formation and evolution of deltas. However, scholars rarely give attention to the factors influencing changes in the SSC in small- and medium-sized mountainous rivers, and few studies have examined SSC changes in small- and medium-sized mountainous rivers. Here, based on daily SSC and flow data obtained at the Bobai Station and Changle Station, the percentile method and regression analysis method are employed to analyse the changes in SSC from the Nanliu River to the Beibu Gulf and possible influencing factors. The main research results indicate that 1) the SSC in river water bodies from 1965 to 2020 generally reveals a downwards trend, with significant annual variations. Specifically, the overall trend can be divided into three stages: 1) the SSC is the highest from 1965 to 1971, and the mean yearly SSC reaches 0.25 kg/m³; 2) the SSC is relatively high from 1972 to 2006, and the mean yearly SSC reaches 0.16 kg/m³; and 3) the SSC is the lowest from 2007 to 2020, and the mean yearly SSC reaches 0.11 kg/m³ 2) High values of the SSC are mainly concentrated in the flood season, and low SSC values mostly occur in the dry season. The monthly average SSC in the flood season from April to September and the dry season from October to March exhibits the characteristics of a decrease in the flood season and an increase in the dry season. Moreover, the peak SSC value in the watershed obviously occurs out of sync with the peak flow value. Generally, the former precedes the latter. 3) The curve of the flow rate-sediment ratio is an irregular clockwise rhombus. Moreover, the impact of tropical cyclones, land cover changes, regional GDP per capita, and engineering construction are crucial reasons for the observed variations in the SSC in the Nanliu River Basin. In this paper, the obtained research results provide an important guiding significance for the planning and management of water and sediment resources in the Nanliu River and offer a reference for hydrological planning of other river basins discharging into the sea.
... 已有研究表明, 河道砂石资源将面临资源枯竭的威胁及相关的社会和环境挑战 [40] . 主要河流的总 [41] . 通过对河道总输沙量和 湖泊自然沉积物减少的驱动因素的研究, 有学者认为输沙量减少可归为两个原因: 大坝建设 [42] 和天然 砂石开采 [23,43] . ...
Sand, gravel, and crushed rock—together referred to as construction aggregates—are the world’s most extracted solid materials by mass. China’s annual consumption of construction aggregates reached over 20 billion tons in 2018, accounting for nearly half of global consumption. This article provides an overview of the use of sand and gravel in China, including current supply and demand conflicts and the impacts of mining, transportation, and use. We highlight that: ① the national demand for sand and gravel has continued to grow in the last two decades; crushed rock has become the main source of construction aggregates, whereas the supply of river sand has significantly declined; and ② there are significant environmental, economic, and social challenges associated with sand and gravel mining, transportation, and use, including the emergence of illicit supply networks. We then discuss opportunities to ensure sand and gravel supply, minimize mining impacts, and promote sustainable trajectories for the Chinese aggregates industry. First, the quantification of the material flows and stocks of construction aggregates that includes geological and anthropogenic stocks is crucial to identify supply bottlenecks and ensure more efficient use of resources. This requires establishing a reliable data monitoring system. Second, the government should increase investment and establish relevant institutions to optimize supply systems and minimize their impacts, strengthen the regulatory framework, promote the uptake of alternative materials, and establish standards and implement best practices in the aggregates industry. Finally, interdisciplinary integrated research is needed to analyze the existing challenges associated with the supply of sand and gravel resources as well as the potential and risks of adaptation strategies.
... Thus, our results are robust, and they further motivate us to employ a multimodel SSC algorithm framework for a global assessment of SSC trend analysis in coastal mouths. The SSCs in river mouths are generally assumed to be driven by riverine inputs (Dai et al., 2009;Wright, 1989). Therefore, any significant deviation in SSCs presumably reflects changes in river flow that are themselves regulated by climate, dam construction, or changes in land use patterns. ...
Climate change and anthropogenic activities are affecting the hydrological conditions of rivers and may have altered nutrient and suspended sediments released into coastal seas. However, testing this hypothesis is difficult, confounded by the lack of observational data and the unavailability of globally accepted suspended sediment concentration (SSC) algorithms. Here, we analyzed the trends in SSC (2000-2020) at the mouths of 10 major Asian rivers using 10 available satellite-SSC algorithms. We identified spatially distinct trends, with SSC decreasing at the mouths of the Yellow, Pearl, and Indus rivers, and increasing trends at the mouths of the Narmada and Ganges-Brahmaputra rivers, while there were no significant trends at the mouths of the remaining rivers. River discharge, dams, and land use changes in basins individually did not suffice, but reproduced the observed SSC trends when used together. Our results imply that anthropogenic activities threaten the marine ecosystem more than climate forcing on Asian coasts.
