Elemental geochemical evidence for the river-derived sources of trace metals in surface sediments from Hangzhou Bay, East China Sea

Coastal estuaries are often heavily subject to riverine influences by the inputs of sediment from terrestrial sources. Hangzhou Bay (HZB) is threatened by the riverine derived trace metals from two large rivers of Qiantang River (QTR) and Yangtze River (YZR). However, previous studies mainly focused on the incidental transport from the largest river in China (YZR) and failed to simultaneously evaluate the contributions of these two rivers, especially the directly flowing river of QTR, by their trace elemental geochemical composition and distribution. Herein, a comprehensive study identified the river-derived sources of multiple trace metals in surface sediments which transported from both of the rivers. The sampling stations were separated into three regions of YZR, HZB, and QTR based on their spatial distributions of sediment grain size and components. The significant variations for most of the trace metals concentrations, except for Cd, Th, and U, were found among three regions (χ2 ≥ 8.22, p ≤ 0.016). The highest concentrations in HZB were mainly resulted from the grain size effect (68.82% of the total variance), while the highest concentrations of Sr, Cd, and Ba in YZR and Zr and Hf in QTR were attributed to the anthropogenic source (11.90%) and mineral composition (6.21%) of river basins. After normalized the diversity of multiple trace metals concentrations and the influence of grain size by ratios of Igeo and EFLi, three regions were effectively distinguished. It was indicated that As, Cd, and Sb were enriched in the sediments of rivers by anthropogenic source (EFLi > 1.5 and/or Igeo > 1). The results evidenced that, after removing the influence of grain size, elemental geochemical composition of the surface sediments confidently identified the river-derived anthropogenic sources of the enriched trace metals from two major rivers, and largely from YZR.

Recent Declines in Nutrient Concentrations and Fluxes in the Lower Changjiang River

To elucidate nutrient variation patterns and trends over various timescales under combined effects of human activities and climate change, nutrient concentrations were monitored monthly in Lower Changjiang (Yangtze) River from November 2016 to August 2020. They were also monitored daily during an extreme flood in July 2020. Over daily and seasonal timescales, the Changjiang River discharges had a dominant influence on nutrient concentrations. By combining existing data over recent decades with those from the current study, we found that turning points for concentration trends for most nutrients emerged in the recent decade (2010-2020), i.e., 2012 for NO3-, PO43-, and NH4+ and 2014 for SiO32-. After these turning point years, NO3-, SiO32-, and PO43- concentrations decreased at annual rates of 2.953, 3.746, and 0.108 μM/year, respectively. Regarding NO3- and PO43-, their concentrations and fluxes increased from 1960s to 2012, similar to the increasing trends of anthropogenic N and P fertilizer inputs from the drainage basin. After 2012, concentrations and fluxes of NO3- and PO43- showed significant decreasing trends, largely due to the control of N and P fertilizer usage. A comparison among eight rivers in East and South China (including the Changjiang River) indicated that basin latitudes were essential to determining areal nutrient yields, implying that latitude-related factors, such as temperature, precipitation, and areal population density, significantly impacted nutrient fluxes. This study emphasized that the deteriorating Changjiang River aquatic environment (which lasted from 1960s to 2010) has been successfully terminated over the last 10 years in 2010s.

Seasonal variation of heavy metals in suspended sediments downstream the Three Gorges Dam in the Yangtze River

High sediment flux in large rivers provide sufficient dilution to the heavy metals' concentration. However, sediment starvation caused by hydrological engineering in recent decades has been reported worldwide. Thus, a study is necessary on the influences of recent declining sediment flux on heavy metal pollution change in the suspended sediments. In this study, heavy metal concentrations and speciation (Cd, Pb, Zn, Cu, Co, Ni, and Cr) in suspended sediments were investigated downstream the Three Gorges Dam (TGD) during dry and flood seasons. Substantial changes of Pb, Zn, Cd, and Cu along the river channel were found which were constrained by the dilution efficiency of suspended sediment during the dry season. High proportion of labile fraction revealed anthropogenic sources of heavy metal. Moreover, the historical trend of metal content illustrated TGD construction together with anthropogenic influx both contribute to the increasing environmental risk in the Yangtze River basin.

Carbonate chemistry variability in the southern Yellow Sea and East China Sea during spring of 2017 and summer of 2018

Marginal seas are highly productive and disproportionately large contributors to global air-sea CO₂ fluxes. Due to complex physical and biogeochemical conditions, the southern Yellow-East China Sea is an ideal site for studying carbonate chemistry variability. The carbonate system was investigated in the area in spring of 2017 and summer of 2018. Dissolved inorganic carbon (DIC) and total alkalinity (TA) concentrations were higher in the SYS than the ECS due to material from carbonate weathering and erosion carried by the Yellow River. High pH and low DIC and TA were observed in the Zhe-Min Coastal Current in spring due to high primary productivity caused by Changjiang River input and the Taiwan Warm Current. Temperature and biological activity were the primary drivers controlling the partial pressure of CO₂ (pCO₂) in the SYS, pCO₂ was controlled by primary productivity related to nutrients carried by the Changjiang River and physical mixing in the Changjiang River plume and inner/middle shelves of the ECS, whereas temperature was the dominant factor determining pCO₂ distributions in the ECS outer shelf waters influenced by the Kuroshio Current. Overall, the entire study area shifted from a CO₂ sink (-4.18 ± 5.60 mmol m^-2 d^-1) to a weak source (1.02 ± 4.87 mmol m^-2 d^-1) from spring to summer. Specifically, the SYS and ECS offshore waters changed from CO₂ sinks in spring to sources in summer, while the Changjiang River plume was always a CO₂ sink.

Evolution of the Upper Yellow River as Revealed by Changes in Heavy-Mineral and Geochemical (REE) Signatures of Fluvial Terraces (Lanzhou, China)

Despite decades of study, the factors that controlled the formation and evolution of theupper reaches of the Yellow River, including uplift of the northeastern Tibetan Plateau, Pliocene-Pleistocene climate change, and autogenetic processes are still poorly constrained. The stratigraphicrecord of such paleogeographic evolution is recorded in the sequence of nine terraces formed duringprogressive incision of the Yellow River in the last 1.7 Ma. This article investigates in detail forsediment provenance in terraces of the Lanzhou area, based on heavy-mineral and geochemical(REE) signatures. Two main provenance changes are identified, pointing each to a majorpaleogeographic reorganization coupled with expansion of the upper Yellow River catchment andenhanced sediment fluxes. The first change took place between the deposition of terrace T9 (formedaround 1.7 Ma) and terrace T8 (formed around 1.5 Ma), when rapid fluvial incision point to tectoniccontrol and active uplift of northeastern Tibetan Plateau. The second change took place betweendeposition of terrace T4 (formed around 0.86 Ma) and terrace T3 (formed around 0.14 Ma), duringa period of low incision rates and notably enhanced sediment fluxes as a response to enhanced EastAsian Summer Monsoon and consequently increased precipitations, pointing instead chiefly toclimatic control.

Impact of mining on metal concentration in waters of the Zuari estuary, India

The rationale of the current study was to establish that mining and associated activities are the chief sources of trace metal contamination in the Zuari estuary, Goa. Surface and bottom water samples were collected monthly, at 11 stations, starting from the mouth of the estuary, covering a stretch of 35 km towards the head during the period of ban on mining in Goa as per the directions of the Honourable Supreme Court of India. The water samples were analysed for physicochemical parameters and metals (Fe, Mn, Zn, Cr, Cu and Pb). Spatial variation of metals (Zn, Cr and Cu) indicated high concentrations at the mouth region, revealing that they are derived by resuspension of bottom sediments at higher salinities, while metals Fe, Mn and Pb showed higher concentrations at the head region, indicating that these are derived from freshwater discharge. Seasonal variation of metals revealing high concentrations during non-monsoonal months was attributed to a high rate of evaporation and intense anthropogenic activities except Pb. Contamination factors and enrichment factors of metals were calculated to assess the degree of metal contamination and relative abundance of pollutants, respectively. Sources of metals into the estuary were discussed by using principal component analysis. Correlation coefficients were calculated to find out the dynamics among the physicochemical factors and trace metals. The study exemplified that concentrations of trace metals in waters of the Zuari estuary were significantly less when compared to the periods of rampant mining activity around Goa, indicating that mining can influence the concentration of metals in the Zuari estuary.

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.

Characterization of the Particle Size Fraction associated with Heavy Metals in Suspended Sediments of the Yellow River

Variations in the concentrations of particulate heavy metals and fluxes into the sea in the Yellow River were examined based on observational and measured data from January 2009 to December 2010. A custom-built water elutriation apparatus was used to separate suspended sediments into five size fractions. Clay and very fine silt is the dominant fraction in most of the suspended sediments, accounting for >40% of the samples. Cu, Pb, Zn, Cr, Fe and Mn are slightly affected by anthropogenic activities, while Cd is moderate affected. The concentrations of heavy metals increased with decrease in particle size. For suspended sediments in the Yellow River, on average 78%-82% of the total heavy metal loading accumulated in the <16 μm fraction. About 43% and 53% of heavy metal in 2009 and 2010 respectively, were readily transported to the Bohai Sea with "truly suspended" particles, which have potentially harmful effects on marine organisms.

Analysis and evaluation of the source of heavy metals in water of the River Changjiang

In order to analyze and evaluate different trace metals on surface water of the Changjiang River, concentrations of dissolved trace metals (Cu, Ni, Fe, Co, Sc, Al, Zn, Pb, Cd, Se, As, Cr, and Hg), major elements (Ca and Mg), and nutrient (NO3- were measured. Samples were taken at 76 positions along Changjiang River in flood and dry seasons during 2007-2008. Spatial distributions identified two main large zones mainly influenced by mineral erosion (sites 1-22) and anthropogenic action (sites 23-76), respectively. Principal component analysis (PCA) and hierarchical cluster analysis were used to identify the variance distinguishing the origin of water. Four significant components were extracted by PCA, explaining 74.91% of total variable. Cu, Ni, Fe, Co, Sc, Al, Ca, and Mg were mainly associated with the weathering and erosion of various rocks and minerals, while an anthropogenic source was identified for Cd and As. Although erosion was one source of Pb and Zn, they were also input by atmospheric deposition and industrial pollutions. NO3- and Se were mainly associated with agriculture activities. However, Hg and Cr showed different sources. CA confirmed and completed the results obtained by PCA, classifying the data into two large groups representing different areas. Group 1 referred to the upper reaches which represented samples mainly corresponding to natural background areas. Group 2 referred to the middle and lower reaches including samples under anthropogenic influence. Meanwhile, group 2 was subdivided into three new groups, representing agricultural, industrial, and various artificial pollution sources, respectively.

Identification and evaluation of hydrogeochemical processes on river Cooum, South India

The salient features of the river water chemistry and the seasonal variations on the individual chemical parameter were evaluated and characterized. The order of abundance of the ions in the water is determined for both seasons. The contribution of chemical weathering to the water chemistry has been determined using the (Ca(2+) + Mg(2+))/(Na(+) + K(+)) ratio, ternary, and Gibb's diagrams. The results show that the chemical composition of river water during premonsoon is controlled mainly by evaporation-crystallization, while in the postmonsoon, the rock-water interaction dominates. The unique characteristic of the river water is the linear relationship among the principal ions. Hydrochemical characteristics of ions in the water were studied using 1:1 equiline diagrams. The nature of the water samples was determined using the piper diagram. The influence of trace metals on the chemical composition and the quality of the river water in the study area has been assessed using Wilcox and US Salinity Laboratory diagrams.

Strontium isotopic compositions of dissolved and suspended loads from the main channel of the Yangtze River

The concentrations of Sr and (87)Sr/(86)Sr isotopic ratios have been measured in the dissolved loads from the main channel of the Yangtze River. The result shows that the Yangtze River mainstream water has considerably higher Sr concentration (202-330 microg kg(-1)) and slightly lower (87)Sr/(86)Sr ratio (0.7098-0.7108) than the global average runoff values of dissolved Sr (78 microg kg(-1)) and (87)Sr/(86)Sr ratio (0.7119). The (87)Sr/(86)Sr values of 0.7098-0.7108 in river waters result from the intense weathering of carbonate and evaporate rocks that enriched in the Yangtze River drainage basin. The calculated result based on the end-member mixing model shows that about 91% of total dissolved Sr are derived from the weathering of carbonate and evaporate rocks and the other 9% derived from the weathering of silicate rock. The Yangtze River transports about 1.86 x1 0(11)g yr(-1) (2.12 x 10(9)mol yr(-1)) of dissolved Sr annually to the East China Sea, with an average (87)Sr/(86)Sr of 0.7108. The calculated "(87)Sr(excess) flux" of the Yangtze River is about 2.12 x 10(7)mol yr(-1), indicating the important impact on seawater Sr isotope evolution. The measured (87)Sr/(86)Sr ratios of suspended particulate matters in the Yangtze River water ranging from 0.7178 to 0.7252, are about 0.015 higher than that of corresponding dissolved loads, reflecting more important contribution of silicate particles in suspended particulate matters and preferential dissolution of carbonate rocks during basin weathering.