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The Yellow River is the mother river of the Chinese nation. The source region of the Yellow River is an important region for water conservation in China. The hydro-ecological environment of the Yellow River source region is very fragile. Therefore, the variation processes of runoff and sediment discharge in the Yellow River source region have become the subject of considerable concern in recent years. However, the source region of the Yellow River has been studied relatively little, and the influence of these two process in the source region of the Yellow River remains unclear. In this paper, precipitation, runoff, sediment discharge, and their interactions in the source region of the Yellow River from 1956 to 2018 were analyzed using several different time-series evaluation methods, such as Spearman's rank correlation coefficient method, the ordered clustering analysis method, and the double-mass curve method. Furthermore, the impact of Huangheyuan hydropower station on these hydrological elements was analyzed in relation to the few other human activities in Sanjiangyuan National Nature Reserve. The results indicated that the precipitation in the source region of the Yellow River increased significantly, the sediment discharge decreased non-significantly, and there was no significant change in runoff over this time period. The years 1995 and 2011 were probable mutation points of the sediment discharge series, and the mutation point of the precipitation series was likely 2001. The Huangheyuan hydropower station is the main reason for the decrease in annual sediment discharge in the source region of the Yellow River. [ABSTRACT FROM AUTHOR]

Multivariate hydrological series become nonstationary under the changing environment. In this paper, a new method is proposed to study the change in the dependence structure between runoff and sediment sequences. First, a moving cut transfer entropy is proposed to detect the sudden change point in the dependence structure between runoff and sediment. Then, the Gumbel copula with a new parameter estimation method (MEE) is employed to construct the dependence structure of runoff and sediment before or after the change point for situation with small samples. The new method is applied to the annual runoff and sediment discharge series in Xiliugou River, China. It is found that the dependence structure between runoff and sediment changed abruptly in 2000. The joint probabilistic characteristics of the annual runoff and sediment discharge during the period of 1960–1999 are built based on the values of RMSEs and AICs. The joint distribution of the annual runoff and sediment discharge during the period of 2000–2016 is constructed by the Gumbel copula with MEE. Moreover, the synchronous encounter probability of runoff and sediment decreases from 0.76 to 0.63, and the asynchronous encounter probability rises from 0.24 to 0.37, after the runoff and sediment discharge series presents a significant change in the dependence structure. [ABSTRACT FROM AUTHOR]

Soil erosion has become more serious in semiarid areas around the world. However, the discrimination of the impact of concurrent climate change and human activity on soil erosion in a particular study area remains a challenge. Check dams are important engineering measures to prevent soil erosion on the Chinese Loess Plateau, and the dam sediments, as the product of soil erosion, are related to both climate change and human activities in a small watershed. The present study selected a check dams sediment profile in the upper Jinghe Basin on the Chinese Loess Plateau as a case study. Based on AMS 14C dating and 137Cs measurement, we established the soil erosion timescale and employed multiple methods including magnetic susceptibility, particle size, and minerals to trace the soil erosion history. We compared them with a local hydrometeorological record in the Jinghe Basin to explore the relationship between soil erosion and human activities. AMS 14C and 137Cs results indicated that the profile was deposited since 1953. The results of magnetic susceptibility, particle size, and minerals revealed 3 soil erosion phases during the last 60 years. Soil erosion in this region is not only related to precipitation changes, but also closely related to human activities. Prior to the Reform and Opening-up in China in 1978, climatic change played a leading role in check dams sedimentation and hydrological changes. Subsequently, despite accelerated soil erosion associated with the family contract responsibility system, the check dams, afforestation and a warmer climate mitigated the soil erosion to some extent, runoff and sediment load continued to decrease. Since 1999, China's Grain for Green project has greatly reduced the runoff and sediment load. However, the policy of filling gullies and creating land since 2010 should be reconsidered carefully in terms of all aspects, including the eco-environment, hydrological cycle, and economics. [ABSTRACT FROM AUTHOR]

Runoff and sediment discharge have displayed great reductions due to climate change and enhanced various human activities during recent decades in the Jialing River, China, with significant environmental and social implications. The water balance equation, double mass curve, and linear regression analysis were employed to quantify the contributions of climate change and human activities to runoff and sediment discharge reductions in the Jialing River during 1960–2017. The results indicated that the annual runoff of the Jialing River exhibited a significant decreasing trend of − 2.75 × 108 m3 every year (P < 0.05) but no significant abrupt change occurred, while annual sediment discharge significantly decreased by 0.03 × 108 t every year (P < 0.05) with a significant abrupt change in 1990 (P < 0.05). Climate change led to a great reduction (82.2%) in annual runoff from 1960 to 2017 in the Jialing River, whereas the contribution of climate change to sediment discharge reduction in the human-affected period (1990–2017) was only 4.55% and precipitation inclined to increase sediment discharge in recent years (2010–2017). The reduced sediment discharge in the 1990s was mostly due to the implementation of soil–water conservation programs and the reduction after 2000 was due to the development of reservoirs as well as the implementation of soil–water conservation programs. The results provided references to develop various human activities better and drew great attention to strengthening basin management. [ABSTRACT FROM AUTHOR]

Purpose: Significant changes in the runoff and sediment load have been detected in many catchments of the Loess Plateau. These changes are expected to be influenced by the interplay of climate variability and human activities. Quantitatively evaluating these effects is crucial for framing climate variability adaptation measures and the assessment and management of regional water resources. Materials and methods: Based on the annual rainfall, runoff, and sediment load data taken over the period from 1974 to 2013 and using data from 112 flood events, this study investigates the runoff and sediment load variations at the annual scale and distinguishes the impacts of climate variability and human activities at the event scale. The Mann-Kendall test and Pettitt's test are employed to detect the trends and abrupt change points of the annual runoff and sediment load. Rainfall and land surface conditions play a dominant role in the runoff and sediment yield of flood events. However, vegetation recovery, which benefits from the Grain-for-Green project and the construction of check dams has greatly changed the land surface condition, resulting in a reduction in streamflow energy, hydrological connectivity, and flood peaks. Therefore, for two flood events with similar rainfall conditions but different runoff and sediment yield, the differences in the runoff and sediment load within paired events may be attributed to the changes in the land surface condition induced by human activities. Results and discussion: The results showed that the annual runoff and sediment load has significantly decreasing trends (p < 0.05). The abrupt changing point was detected in 1996, dividing the runoff and sediment load series into a baseline period (1974–1995) and a changing period (1996–2013). At the flood event scale, the hysteresis analysis showed that the counter-clockwise and figure-eight loops are the main patterns for both of the periods. The relationships between the runoff depth (H) and sediment yield (SY) varied greatly in 2007–2013 compared with those during 1974–1989. Human activities accounted for an average of 47 and 81% for the changes in the runoff and sediment load, respectively, and the remainder was attributable to climate variability. Conclusions: Human activities have a greater effect on the sediment load reduction in the Xichuan River catchment, while climate variability accounted for more of the runoff changes. [ABSTRACT FROM AUTHOR]

The Loess Plateau of China has experienced a lengthy drought and severe soil erosion. Changes in precipitation and land use largely determine the dynamics of runoff and sediment yield in this region. Trend and mutation analyses were performed on hydrological data (1981-2012) from the Yanwachuan watershed in the Loess Plateau Gully Region to study the evolution characteristics of runoff and sediment yield. A time-series contrasting method also was used to evaluate the effects of precipitation and soil and water conservation (SWC) on runoff and sediment yield. Annual sediment yield declined markedly from 1981 to 2012 although there was no significant change in annual precipitation and annual runoff. Change points of annual runoff and annual sediment yield occurred in 1996 and 1997, respectively. Compared with that in the baseline period (1981-1996), annual runoff and annual sediment yield in the change period (1997-2012) decreased by 17.0% and 76.0%, respectively, but annual precipitation increased by 6.3%. Runoff decreased in the flood season and normal season, but increased in the dry season, while sediment yield significantly declined in the whole study period. The SWC measures contributed significantly to the reduction of annual runoff (137.9%) and annual sediment yield (135%) and were more important than precipitation. Biological measures (forestland and grassland) accounted for 61.04% of total runoff reduction, while engineering measures (terraces and dams) accounted for 102.84% of total sediment yield reduction. Furthermore, SWC measures had positive ecological effects. This study provides a scientific basis for soil erosion control on the Loess Plateau. [ABSTRACT FROM AUTHOR]

We analyze the variability of sediment discharge and runoff in the Hekou-Longmen segment in the middle reaches of the Yellow River, China. Our analysis is based on Normalized Difference Vegetation Index (NDVI), sediment discharge, runoff, and monthly meteorological data (1961-2010). The climate conditions are controlled via monthly regional average precipitation and potential evapotranspiration (ET) that are calculated with the Penman-Monteith method. Data regarding water and soil conservation infrastructure and their effects were investigated as causal factors of runoff and sediment discharge changes. The results indicated the following conclusions: (1) The sediment concentration, sediment discharge, and annual runoff, varied considerably during the study period and all of these factors exhibited larger coefficients of variation than ET and precipitation. (2) Sediment discharge, annual runoff, and sediment concentration significantly declined over the study period in a linear fashion. This was accompanied by an increase in ET and decline in precipitation that were not significant. (3) Within paired years with similar precipitation and potential evapotranspiration conditions (SPEC), all pairs showed a decline in runoff, sediment discharge, and sediment concentration. (4) Human impacts in this region were markedly high as indicated by NDVI, and soil and water measurements, and especially the soil and water conservation infrastructure resulting in an approximately 312 Mt year of sediment deposition during 1960-1999. [ABSTRACT FROM AUTHOR]

Determining abrupt changes in runoff and sediment load may not only enhance identification of the principal driving factors for such changes but also help establish effective countermeasures for serious water deficit by managers in the Yellow River basin. We used the Mann-Kendall trend test and linear regression to determine trends and abrupt changes of runoff and sediment load during the period between 1950 and 2005, based on monthly hydrological data. Results show that runoff and sediment load decreased from 1950 to 2005, on annual or monthly time scales. Their changes are divided into three stages: fluctuating stage (1950-1970), slowly decreasing stage (1970-1980) and accelerated decreasing stage (1980-2005). The relationship between runoff and sediment load was most significant, and it can be expressed as a linear regression function. Precipitation was one of the most important climate factors affecting runoff before 1985, and the impact of human activities on runoff decrease grew strongly after 1985. Water balance analysis of the Yellow River basin indicates that natural climate change contributed about 55.3% and human activities about 44.7% to the runoff decrease after 1986. [ABSTRACT FROM AUTHOR]

To reflect the historical changes, the vertical profiles of concentrations, enrichment factors and burial fluxes of potential harmful elements (PHEs: Ga, Ge, Mo, In, Sn, Sb, Te, Tl, Bi, W and V) were determined in two sediment cores collected from Bohai Bay. Sediment accumulation rates and chronologies were obtained from Pb activity-depth profiles. Two sediment accumulation rates in core 2 were observed: a higher rate of 4.78 mm/year before the 1960s and 2.93 mm/year since then. The sediment accumulation rate in core 6 was 2.82 mm/year. The PHE concentrations and burial fluxes exhibited an obvious variation with the depth due to the natural and anthropogenic inputs. Especially, the higher concentrations and burial fluxes of PHEs occurred in the 1960s and 1980s, matching the large runoff and industrial development. Enrichment factors (EFs) of PHEs were computed in order to evaluate their potential sources. Results showed that the EFs of Sb, Te and Bi were higher than 1.5, revealing the anthropogenic inputs; however, the EFs of other PHEs were lower than 1.0, indicating the natural inputs. Moreover, the high EFs of Sb, Te and Bi appeared in the surface or subsurface layers, indicating that the extent of anthropogenic contamination enhanced in recent years. Sequential extraction technique was used to study the ecological risks of PHEs. Results revealed that the ecological risks of Mo, Te and Bi in both cores and Sb and W in core 2 were medium due to their high availability in the exchangeable and carbonate-bound fractions. [ABSTRACT FROM AUTHOR]

The article presents abstracts of several studies on environmental geochemistry. Some of the abstracts presented include "Biogeochemical Cycling of Nutrients in Karstic Catchments, Southwestern China: Linkages to Changes of Eco-Environments," by Congqiang Liu and "Emerging Organic Contamination in China," by Guibin Jiang and colleagues.