Lijin Station Research Articles

Surface Water Resource Accessibility Assessment of Rural Settlements in the Yellow River Basin

Analyzing the spatial relationship between humans and water is crucial for regional development and water allocation schemes, particularly in the face of extreme water scarcity in the Yellow River Basin. A quantitative evaluation model of surface water resource accessibility (SWRA) has been developed, with rural settlements serving as the research unit. This model is built upon three key dimensions: topography, distance, and surface water resources within the Yellow River Basin. The results show that: (1) The SWRA range spans from 0.13 to 0.88, with an average value of 0.47 and a standard deviation of 0.05. Higher SWRA values are concentrated in the eastern and western regions, while lower values are predominantly found in the central area. (2) The gradient of SWRA across the 12 catchments, from low to high, is as follows: Sanmenxia station, Lanzhou station, Shizuishan station, Longmen station, Tongguan station, Toudaoguai station, Xiaolangdi station, Huayuankou station, Lijin station, Gaocun station, Ai Shan station, and Tangnaihai station. (3) At the city scale, the SWRA values are generally higher in the eastern areas of 10 cities, with one exception being higher in the west. Conversely, in the western areas of nine cities, the SWRA values are lower. The remaining cities exhibit SWRA values at a medium level. The correlation coefficient between primary industry gross domestic product (GDP) and SWRA is 0.271 (N = 56, Sig = 0.043, in 0.05 level, the correlation is significant), which confirms that SWRA serves as a factor influencing GDP and is appropriately designed for assessing water accessibility. Consequently, managers can utilize SWRA results to make informed decisions regarding regional development and water allocation.

Accumulation and migration of particulate trace metals by artificial flood event of the Yellow River: From Xiaolangdi reservoir to estuary

Reservoir construction increasingly alters the natural transport of riverine water and sediment to the sea, including the trace metals and other pollutants. In 2018, an intensive flood event and 412 million tons of sediment were released from the Xiaolangdi dam during the water-sediment regulation of Yellow River, one of the world's largest sediment releases. During the artificial flood event, the surface sediments in Xiaolangdi Reservoir (XLD) and the Yellow River estuary, suspended sediments at Lijin Station were collected. The concentration and speciation of particulate Cr, Ni, Cu, Zn, Cd and Pb, as well as the major geochemical composition were analyzed, to characterize the behaviors of the metals from the reservoir to estuary mixing zone, and elucidate the controlling mechanisms. The results showed that for exogenous phases, Cr, Ni, Cu and Zn were likely bound to the FeMn oxides, whereas Pb and Cd were mainly adsorbed in the carbonates. The trace metals in XLD were stably combined with fine-grained bottom sediments at high concentrations before dam release. During the delivery from reservoir to downstream channel, the binding of Cr, Ni and Cu with FeMn oxides was markedly enhanced. Pb and Cu showed obvious migration from carbonates to FeMn oxides, and Cd and Pb were even released into the water. The accumulation and migration of trace metals were controlled by the adsorption of fine-grained components, especially FeMn oxides and carbonates, and influenced by the oxidizing processes. After entering the estuary, the trace metals were greatly scavenged by reservoir-sourced fine particles, tended to bound to organic matter affected by the reducing environment. Our results suggest that dam regulation and artificial flood events will likely alter the existing forms and redox state of trace metals and the potential environmental effects should be considered.

Quantitative Analysis of the Influence of the Xiaolangdi Reservoir on Water and Sediment in the Middle and Lower Reaches of the Yellow River

The Xiaolangdi Reservoir is the second largest water conservancy project in China and the last comprehensive water conservancy hub on the mainstream of the Yellow River, playing a vital role in the middle and lower reaches of the Yellow River. To study the effects of the construction of the Xiaolangdi Reservoir (1997-2001) on the runoff and sediment transport in the middle and lower reaches of the Yellow River, runoff and sediment transport data from 1963 to 2021 were based on the hydrological stations of Huayuankou, Gaocun, and Lijin. The unevenness coefficient, cumulative distance level method, Mann-Kendall test method, and wavelet transform method were used to analyze the runoff and sediment transport in the middle and lower reaches of the Yellow River at different time scales. The results of the study reveal that the completion of the Xiaolangdi Reservoir in the interannual range has little impact on the runoff in the middle and lower reaches of the Yellow River and a significant impact on sediment transport. The interannual runoff volumes of Huayuankou station, Gaocun station, and Lijin station were reduced by 20.1%, 20.39%, and 32.87%, respectively. In addition, the sediment transport volumes decreased by 90.03%, 85.34%, and 83.88%, respectively. It has a great influence on the monthly distribution of annual runoff. The annual runoff distribution is more uniform, increasing the runoff in the dry season, reducing the runoff in the wet season, and bringing forward the peak flow. The runoff and Sediment transport have obvious periodicity. After the operation of the Xiaolangdi Reservoir, the main cycle of runoff increases and the second main cycle disappears. The main cycle of Sediment transport did not change obviously, but the closer it was to the estuary, the less obvious the cycle was. The research results can provide a reference for ecological protection and high-quality development in the middle and lower reaches of the Yellow River.

Impact of a water-sediment regulation scheme on nutrient variations at the Lijin station of the Yellow River

The water-sediment regulation scheme (WSRS) imposed on dams throughout the Yellow River not only alleviates siltation in the downstream section but also alters the nutrient characteristics, which indirectly affects the enrichment of nutrients in the estuary. Nevertheless, the long-term changes in the nutrient contents and their causes in the lower Yellow River (LYR) remain unclear, and the nutrients characteristics during the years with and without WSRS have yet to be compared. Therefore, the purpose of this study was to explore the variations in the nutrient contents and limitations at the Lijin station on the LYR over the past decade, especially during the annual WSRS period, and to compare the water quality characteristics at Lijin between the years with and without WSRS. The results reveal that WSRS significantly changed the seasonal nutrient concentrations (nitrogen, phosphorus and silicon) at the Lijin station. The fluxes of these nutrients during WSRS (excluding 2016 and 2017) accounted for 11.64–40.63% of the total annual fluxes. The N concentration in the LYR was higher than that in some global rivers, while the concentrations of dissolved inorganic phosphorus (DIP) and dissolved silica (DSi) were lower than the average levels in other rivers. In addition, higher values of dissolved inorganic nitrogen (DIN), DSi and the Redfield ratio indicated that the growth of phytoplankton at the Lijin station was strongly restricted by P. However, during the 2 years without WSRS (2016 and 2017), the proportions of the nutrient fluxes in June were less than 66% of those in the WSRS period in other years. Additionally, there was a potential Si limitation in June in these 2 years. Furthermore, due to the occurrence of floods upstream of the Yellow River and the low-level operation of the Xiaolangdi Reservoir, the fluxes of nutrients during WSRS in 2018 were approximately 0.90–4.20 times those during the same period in 2009–2015 and 6.30–35.76 times those in June 2016 and June 2017. This study shows that WSRS effectively changes the nutrient balance in the LYR and provides a reference for the multi-objective collaborative optimization of WSRS to improve siltation and control flood in the LYR.

Impact of water-sediment regulation on the concentration and transport of dissolved heavy metals in the middle and lower reaches of the Yellow River

Anthropogenic activities in river basins, especially large-scale water conservancy projects, have notably impacted the physical, chemical and ecological environments of estuaries and coastal areas. In this paper, the effects of water and sediment regulation (WSR) on the concentration and transport of heavy metals in the Yellow River were studied based on a continuous daily heavy metal survey in both the middle reaches (Xiaolangdi station) and lower reaches (Lijin station) of the Yellow River during the WSR period in 2019. The results indicated that the variation in the water oxidation-reduction environment of the Xiaolangdi reservoir during the WSR process exerted an important impact on the concentrations of dissolved Cu, Cd, Pb, Cr and As at the Xiaolangdi station but exerted almost no influence on the concentration of dissolved Ni. At Lijin station, the dissolved heavy metal content first increased and then decreased in the first stage, which mainly depended on the release of heavy metals from resuspended sediments. In the second stage, the heavy metal content gradually decreased due to adsorption onto fine particles discharged from the reservoir. The dissolved heavy metal flux during the water-sediment regulation scheme (WSRS) period accounted for 16.9–33.4% of the annual total dissolved heavy metal flux. WSRS changed transport of water and sediment. The dissolved heavy metal concentrations at the Xiaolangdi station were mainly controlled by the discharge of water and sediments from the Xiaolangdi reservoir, while the dissolved heavy metal concentration at the Lijin station was largely affected by the sediments resuspended from downstream riverbeds and the water and sediment scheduling mode of the Xiaolangdi reservoir. Dissolved heavy metal transportation was highly influenced by the WSR process within a short time. Human intervention, especially WSRS operation, apparently alters the natural states of both the mainstream and estuarine environments of the Yellow River.

Variability of heavy metal transport during the water–sediment regulation period of the Yellow River in 2018

To understand the impacts of the human-induced flood event on heavy metal (HM) transport, spatiotemporal variations in contents and fluxes of metals (Cr, Ni, Cu, Zn, As, Pb, Cd), Pb stable isotopes and characteristics of water and sediment transport into the sea during Water-Sediment Regulation Scheme (WSRS) in Yellow River (YR) were studied based on field investigation at Xiaolangdi Reservoir (XLD), Lijin Station and Yellow River estuary (YRE). The HM transport was significantly controlled by hydrological process and dominated by particulate form with strong associations with particle size and suspended sediment concentration (SSC). In first stage, dissolved heavy metal (DHM) and particulate heavy metal (PHM) contents both increased significantly as coarser sediment with a mixed source of downstream river channel and XLD, while that maintained higher value for stable source of fine-grained XLD sediment in second stage. The HMs into the sea were mainly originated from upper and middle reaches but also contributed by human emissions from downstream area. As the source of HMs into the sea, the downstream area also acted as an important sink, especially in first stage, playing a role of buffering and filtration. During WSRS, the YR discharged 49%–60% of annual HM flux into the sea, and the second stage is the main transport period, leading to a great alternation in geochemical composition of the YRE sediment.

The variation and attribution analysis of the runoff and sediment in the lower reach of the Yellow River during the past 60 years

Abstract The water and sediment regimes of the Yellow River are the basis of decision-making of major projects of the Yellow River. Based on water and sediment data at the Huayuankou station, Gaocun station, Aishan station, and Lijin station in the lower reach of the Yellow River, the Mann–Kendall test, the T-test for differences, wavelet analysis, slope change ratio method and the double cumulative curve method were applied to analyze the runoff and sediment regime alteration. The results show that the water and sediment of the lower Yellow River have a significant downward trend, and the annual sediment decreases significantly compared with the annual runoff. The annual runoff and sediment of the four hydrological stations changed around the 1980s and 1990s, respectively. The water and sediment of hydrological stations have periodic variations on multiple time-scales, but the variation scales are different. Precipitation, human activities and other factors lead to the decreasing trend of water and sediment in the lower Yellow River, and their contribution rates to the change of water and sediment are also different. Precipitation contributed 0.15%–8.71% and 0.06%–22.32% to the reduction of runoff and sediment load at the hydrological stations, while human activities contributed 91.29%–99.85% and 77.68%–102.21% to the reduction of runoff and sediment load, respectively. Human activity is the main factor in runoff and sediment reduction.

Stepwise morphological evolution of the active Yellow River (Huanghe) delta lobe (1976–2013): Dominant roles of riverine discharge and sediment grain size

The presently active Yellow River (Huanghe) delta lobe has been formed since 1976 when the river was artificially diverted. The process and driving forces of morphological evolution of the present delta lobe still remain unclear. Here we examined the stepwise morphological evolution of the active Yellow River delta lobe including both the subaerial and the subaqueous components, and illustrated the critical roles of riverine discharge and sediment grain size in dominating the deltaic evolution. The critical sediment loads for maintaining the delta stability were also calculated from water discharge and sediment load measured at station Lijin, the last gauging station approximately 100km upstream from the river mouth. The results indicated that the development of active delta lobe including both subaerial and subaqueous components has experienced four sequential stages. During the first stage (1976–1981) after the channel migration, the unchannelized river flow enhanced deposition within the channel and floodplain between Lijin station and the river mouth. Therefore, the critical sediment supply calculated by the river inputs obtained from station Lijin was the highest. However, the actual sediment load at this stage (0.84 Gt/yr) was more than twice of the critical sediment load (~0.35 Gt/yr) for sustaining the active subaerial area, which favored a rapid seaward progradation of the Yellow River subaerial delta. During the second stage (1981–1996), the engineering-facilitated channelized river flow and the increase in median grain size of suspended sediment delivered to the sea resulted in the critical sediment load for keeping the delta stability deceasing to 0.29 Gt/yr. The active delta lobe still gradually prograded seaward at an accretion rate of 11.9km2/yr at this stage as the annual sediment load at Lijin station was 0.55 Gt/yr. From 1996 to 2002, the critical sediment load further decreased to 0.15 Gt/yr with the sediment grain size increased to 22.5μm; however, the delta suffered net erosion because of the insufficient sediment supply (0.11 Gt/yr). In the most recent stage (2002−2013), the intensive scouring of the lower river channel induced by the dam regulation provided relatively coarser sediment, which effectively reduced the critical sediment load to 0.06 Gt/yr, much lower than the corresponding sediment load at Lijin station (~0.16 Gt/yr). Consequently, the subaerial Yellow River delta transitioned to a slight accretion phase. Overall, the evolution of the active Yellow River delta is highly correlated to riverine water and sediment discharge. The sediment supply for keeping the subaerial delta stability is inconstant and varying with the river channel morphology and sediment grain size. We conclude that the human-impacted riverine sediment discharge and grain-size composition play dominant roles in the stepwise morphological evolution of the active delta lobe.

Developing policy for the Yellow River sediment sustainable control

The Yellow River of China is one exception where erosion and sediment delivery have successfully been reduced [1]. This riverwasonce theworld’s largest carrier of fluvial sediment load and peaked at about 1.6 Gt yr−1 in the middle of the last century [1–3]. The Yellow River is the birthplace of Chinese civilization, but throughout history it has produced frequent and catastrophic floods and droughts [3,4]. Over thousands of years, a diverse range of strategies and methods have been applied in attempts to control the sediment transport of the YellowRiver, but none have succeeded in completely eradicating this scourge [2]. Fortunately, since the 1970s, the sediment transport by the Yellow River has significantly declined [1–5]. Nearly 90% of the sediment load is originated and transported from the Loess Plateau in the middle reach [3]. The current input of sediment from the Loess Plateau is less than one quarter of what it was before 1980 [1], and the sediment export to the ocean at Lijin station is now only 10.7% of the 1950s’ level [6]. That is a reduction of 90% in sediment transport. This decline implies that the sediment load in this large river has been regulated to a near prehuman level, i.e. that prior to around 600 AD [7]. We argue that it is a time for the cessation of engineering constructions, more important is themaintenanceof a sustainable (i.e. little water consumption) vegetated ecosystem on the Loess Plateau for soil conservation, especially necessity is the establishment of an integrated basin-wide ecosystem and land-use management regime for sustainable water use and sediment regulation. DRIVING FORCES OF THE REDUCED SEDIMENT

Spatial and Temporal Variation in Erosion and Accumulation of the Subaqueous Yellow River Delta (1976–2004)

ABSTRACT Xing, G. P.; Wang, H. J.; Yang, Z. S., and Bi, N. S., 2016. Spatial and temporal variation in erosion and accumulation of the subaqueous Yellow River Delta (1976–2004). Yellow River Delta (YRD), one of the most heavily human-influenced delta systems, had undergone dramatic changes since 1976. To determine the erosion and accretion pattern of the subaqueous YRD, bathometry data as well as the sediment discharge from the Lijin station over the period of 1976 to 2004 were analyzed. The erosion and accretion pattern of the subaqueous YRD was delineated by 1) the northern abandoned delta lobe, consisted of the heavily eroded Diaokou (DK) and Shenxiangou (SXG) lobes; 2) the active delta lobe, comprised of Qingshuigou (QSG) and Q8 lobes and featuring fast progradation; 3) the Laizhou Bay (LZB) with slight accumulation. Three stages were summarized based on the evolution of the northern abandoned delta lobe. During 1976–1980, the northern abandoned delta was severely eroded due to the cutoff of sediment ...

Seasonal Variation and Sources of Dissolved Nutrients in the Yellow River, China.

The rapid growth of the economy in China has caused dramatic growth in the industrial and agricultural development in the Yellow River (YR) watershed. The hydrology of the YR has changed dramatically due to the climate changes and water management practices, which have resulted in a great variation in the fluxes of riverine nutrients carried by the YR. To study these changes dissolved nutrients in the YR were measured monthly at Lijin station in the downstream region of the YR from 2002 to 2004. This study provides detailed information on the nutrient status for the relevant studies in the lower YR and the Bohai Sea. The YR was enriched in nitrate (average 314 μmol·L−1) with a lower concentration of dissolved silicate (average 131 μmol·L−1) and relatively low dissolved phosphate (average 0.35 μmol·L−1). Nutrient concentrations exhibited substantial seasonal and yearly variations. The annual fluxes of dissolved inorganic nitrogen, phosphate, and silicate in 2004 were 5.3, 2.5, and 4.2 times those in 2002, respectively, primarily due to the increase in river discharge. The relative contributions of nutrient inputs to nitrogen in the YR were: wastewater > fertilizer > atmospheric deposition > soil; while to phosphorus were: wastewater > fertilizer > soil > atmospheric deposition. The ratios of N, P and Si suggest that the YR at Lijin is strongly P-limited with respect to potential phytoplankton growth.

Multi-scale variability of water discharge and sediment load into the Bohai Sea from 1950 to 2011

This paper examines the changes in the time series of water discharge and sediment load of the Yellow River into the Bohai Sea. To determine the characteristics of abrupt changes and multi-scale periods of water discharge and sediment load, data from Lijin station were analyzed, and the resonance periods were then calculated. The Mann-Kendall test, order clustering, power-spectrum, and wavelet analysis were used to observe water discharge and sediment load into the sea over the last 62 years. The most significant abrupt change in water discharge into the sea occurred in 1985, and an abrupt change in sediment load happened in the same year. Significant decreases of 64.6% and 73.8% were observed in water discharge and sediment load, respectively, before 1985. More significant abrupt changes in water discharge and sediment load were observed in 1968 and 1996. The characteristics of water discharge and sediment load into the Bohai Sea show periodic oscillation at inter-annual and decadal scales. The main periods of water discharge are 9.14 years and 3.05 years, whereas the main periods of sediment load are 10.67 years, 4.27 years, and 2.78 years. The significant resonance periods between water discharge and sediment load are observed at the following temporal scales: 2.86 years, 4.44 years, and 13.33 years. Water discharge and sediment load started to decrease after 1970 and has decreased significantly since 1985 for several reasons. Firstly, the precipitation of the Yellow River drainage area has reduced since 1970. Secondly, large-scale human activities, such as the building of reservoirs and floodgates, have increased. Thirdly, water and soil conservation have taken effect since 1985.

Characteristics Identification of Runoff and Sediment Flux Based on Wavelet Analysis Approach in Lower Yellow River

Due to the influences of climate change and human activities, the water and sediment flux of the Yellow River are certainly changing. This paper selects monthly time series of runoff and sediment flux from 1950 to 2009 for study at Lijin station, in lower Yellow River. A widely used identification method, wavelet analysis, is applied for recognizing changing point and cycle of the runoff and sediment respectively in multi-scale of annual, flood season and non-flood season. The results indicate that there are two significant changing points in 1985, 2002 year, and cycle recognized results are different in multi-scale as well as with different hydrology factors.

Sample entropy‐based adaptive wavelet de‐noising approach for meteorologic and hydrologic time series

AbstractDe‐noising meteorologic and hydrologic time series is important to improve the accuracy and reliability of extraction, analysis, simulation, and forecasting. A hybrid approach, combining sample entropy and wavelet de‐noising method, is developed to separate noise from original series and is named as AWDA‐SE (adaptive wavelet de‐noising approach using sample entropy). The AWDA‐SE approach adaptively determines the threshold for wavelet analysis. Two kinds of meteorologic and hydrologic data sets, synthetic data set and 3 representative field measured data sets (one is the annual rainfall data of Jinan station and the other two are annual streamflow series from two typical stations in China, Yingluoxia station on the Heihe River, which is little affected by human activities, and Lijin station on the Yellow River, which is greatly affected by human activities), are used to illustrate the approach. The AWDA‐SE approach is compared with three conventional de‐noising methods, including fixed‐form threshold algorithm, Stein unbiased risk estimation algorithm, and minimax algorithm. Results show that the AWDA‐SE approach separates effectively the signal and noise of the data sets and is found to be better than the conventional methods. Measures of assessment standards show that the developed approach can be employed to investigate noisy and short time series and can also be applied to other areas.

Water discharge variability of Changjiang (Yangtze) and Huanghe (Yellow) Rivers and its response to climatic changes

Infl uences of large-scale climatic phenomena, such as the El Nino/La Nina-Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO), on the temporal variations of the annual water discharge at the Lijin station in the Huanghe (Yellow) River and at the Datong station in the Changjiang (Yangtze) River were examined. Using the empirical mode decomposition-maximum entropy spectral analysis (EMDMESA) method, the 2- to 3-year, 8- to 14-year, and 23-year cyclical variations of the annual water discharge at the two stations were discovered. Based on the analysis results, the hydrological time series on the interannual to interdecadal scales were constructed. The results indicate that from 1950 to 2011, a significant downward trend occurred in the natural annual water discharge in Huanghe River. However, the changes in water discharge in Changjiang River basin exhibited a slightly upward trend. It indicated that the changes in the river discharge in the Huanghe basin were driven primarily by precipitation. Other factors, such as the precipitation over the Changjiang River tributaries, ice melt and evaporation contributed much more to the increase in the Changjiang River basin. Especially, the impacts of the inter-annual and inter-decadal climate oscillations such as ENSO and PDO could change the long-term patterns of precipitation over the basins of the two major rivers. Generally, low amounts of basin-wide precipitation on interannual to interdecadal scales over the two rivers corresponded to most of the warm ENSO events and the warm phases of the PDO, and vice versa. The positive phases of the PDO and ENSO could lead to reduced precipitation and consequently affect the long-term scale water discharges at the two rivers.

Conceptual Model for Simulating the Adjustments of Bankfull Characteristics in the Lower Yellow River, China

We present a conceptual model for simulating the temporal adjustments in the banks of the Lower Yellow River (LYR). Basic conservation equations for mass, friction, and sediment transport capacity and the Exner equation were adopted to simulate the hydrodynamics underlying fluvial processes. The relationship between changing rates in bankfull width and depth, derived from quasiuniversal hydraulic geometries, was used as a closure for the hydrodynamic equations. On inputting the daily flow discharge and sediment load, the conceptual model successfully simulated the 30-year adjustments in the bankfull geometries of typical reaches of the LYR. The square of the correlating coefficient reached 0.74 for Huayuankou Station in the multiple-thread reach and exceeded 0.90 for Lijin Station in the meandering reach. This proposed model allows multiple dependent variables and the input of daily hydrological data for long-term simulations. This links the hydrodynamic and geomorphic processes in a fluvial river and has potential applicability to fluvial rivers undergoing significant adjustments.

Research on Influences of Global Climate Change on Water Resources in the Yellow River Basin

The study explored global climate change influence on water resources in Yellow River basin. A HBV hydrological model was developed to simulate the rainfall-runoff relationship at the region. Importing the CCLM climate model data, runoff at Lijin station was obtained in 2000-2039. The results indicate: (1) the annual average runoff depth is 1213mm, runoff in summer is larger than in spring,autumn and winter. The water resources decrease in three months (March, April and Jun) and increase in other months. (2) for inter-annual variations, the water resources increases slightly, and increase trend is about 64.8mm/10a. Water resources are insufficient in 200-2016, and rise gradually from 2017. (3) for different decades, the water resources are lack relatively in 2001-2010 and 2011-2020, and the differences are-59.4mm and-76.0mm respectively. While, the water resources in 2021-2030 and 2031-2039 are abundant, and the differences are 90.6mm and 88.8mm respectively.

Spatial and seasonal variability of organic carbon transport in the Yellow River, China

Summary In this study, we examined the spatial and seasonal variability in the concentrations of dissolved and particulate organic carbon (DOC and POC) of the Yellow River. Weekly samples of water and suspended solids were collected along the main stem channel between July 2011 and July 2012 for the upstream Toudaoguai and Tongguan stations, and between August 2008 and July 2012 for the downstream Lijin station near the river mouth. The DOC export at the upstream two stations was primarily controlled by hydrological events such as melting of ice and snow with high DOC concentrations occurring in spring. In contrast, it was more affected by human activities, mainly reservoir regulation, at the lowermost Lijin station. Lower DOC concentration in the wet season indicates that most of the leachable DOC in surface soils may have largely been flushed away by spring floods. In addition, it is also likely due to dilution effect of the rapidly increased water discharge. As a result of low organic carbon content in the parent soils, the Yellow River sediments were characterized by low POC content (POC%). The averaged POC% at Toudaoguai, Tongguan, and Lijin was 0.48%, 0.47%, and 0.37%, respectively, which is significantly lower than the global mean of around 0.95%. The POC% decreased exponentially with total suspended solids (TSS) concentration. This is likely due to the dilution of riverine POC, because high TSS generally means a higher proportion of coarse sediments that have more mineral matter. During the study period, the total DOC and POC fluxes into the ocean were estimated at 0.06 × 10 12 g/yr and 0.41 × 10 12 g/yr, respectively. Combining our previous estimate of dissolved inorganic carbon (DIC) export shows that the Yellow River transports a carbon flux of 1.52 × 10 12 g/yr into the Bohai Sea, accounting for about 0.19% of the global total riverine carbon flux (DOC + POC + DIC). The extremely low DOC/POC ratio represents the lowest level among major world rivers, which is consistent with its intense soil erosion and highlights the effect of soil erosion on organic carbon export.

VARIATION OF SEDIMENT LOAD AT THE MAJOR TRIBUTARIES IN THE MIDDLE REACHES OF YELLOW RIVER AND ITS IMPACTS ON THE SEDIMENT FLUX TO THE SEA

The loess plateau plays a critical role in the sediment budget of Huanghe River and its flux to the sea.Here in this paper,we studied the variations in annual water discharge and sediment load in seven main tributaries in the middle reach of the Huanghe River.Annual water and sediment data have been acquired from seven major hydrographic stations for 7 tributaries(Huangfuchuan River,Kuyehe River,Wudinghe River,Yanhe River,Beiluohe River,Jinghe River and Weihe River) and the Tonguan Station in the middle reach of the Huanghe River in 1950-2009.Besides,we studied the annual sediment load of the seven major tributaries and several hydrological stations in the mainstream(Tongguan and Lijin).The results indicate that the annual water discharge and sediment load decreased sharply over the past 60 years,the total sediment loads have dropped from 13.5 108t/a in 1950s-1960s to only 3.4 108t/a in 2000-2009,with a reduction of about 75%.Time series data of sediment loads from the major tributaries and Lijin station indicate that tributaries in the loess plateau played a dominant role in the decrease in Huanghe sediment flux to the sea,while the rapid increases in water consumption and redistribution in the low reaches sinc the 1980s accelerated the reduction of sediment flux to the sea.

Water renewal time of the Yellow River mainstream based on reservoir action

This note analyzes the change in water renewal time characteristics based on reservoir action and then establishes calculation models for the water renewal time in the Yellow River mainstream. The results indicate that the amount of renewable water with reservoir action can meet the annual water demand and that water flows naturally at the Lijin station near estuary. Initial storage dynamics is an important factor in water resource renewable capacity at a certain time, and rational reservoir action can promote sustainable water resource utilization. When the initial storages in the Longyang Gorge reservoir are 9.343 and 5.343 billion m3, the water renewal times are 28 and 33.9 d, respectively. Flow stoppage appears in April and May.