Optimization of extraction method for quantitative analysis of Si/Al in soil phytoliths

Elemental information carried by phytoliths plays a crucial indicative role in geochemical research.For instance,it serves as an indicator of the carbon pool effect in phytoliths and aids in the elucidation of silicon sources.However,early extraction methods for soil phytoliths primarily focused on obtaining their morphological and quantitative information,lacking efficient techniques for quantitative elemental analysis.In this study,we aimed to extract Si/Al information from soil phytoliths.Considering the need for complete extraction of phytolith,six extraction methods were developed and further by alkaline dissolution to determine Si/Al.Six methods were compared in terms of enrichment capacity,the weight of extracted phytoliths,and Si/Al differences.The results indicated that the addition of Ammonia-Catechol in the commonly used heavy liquid flotation method effectively improved phytolith extraction capability and the accuracy of Si/Al results.Additionally,the inclusion of an acetic acid step before alkaline dissolution further removed surface-adsorbed impurities and enhanced the analytical quality of Si/Al in phytolith.The comparison of the data in this study with other published data shows that our method is relatively robust.The improved method proposed in this study can provide a new idea for the quantitative analysis of other elements in soil phytoliths.

Nitrous oxide (N_2O) emissions from a mesotrophic reservoir on the Wujiang River,southwest China

Aquatic ecosystems have been identified as a globally significant source of nitrous oxide(N_2O) due to continuous active nitrogen involvement, but the processes and influencing factors that control N_2O production are still poorly understood, especially in reservoirs. For that, monthly N_2O variations were monitored in Dongfeng reservoir(DFR)with a mesotrophic condition. The dissolved N_2O concentration in DFR displayed a distinct spatial–temporal pattern but lower than that in the eutrophic reservoirs. During the whole sampling year, N_2O saturation ranging from 144% to 640%, indicating that reservoir acted as source of atmospheric N_2O. N_2O production is induced by the introduction of nitrogen(NO_3^-, NH_4^+) in mesotrophic reservoirs, and is also affected by oxygen level and water temperature. Nitrification was the predominate process for N_2O production in DFR due to well-oxygenated longitudinal water layers.Mean values of estimated N_2O flux from the air–water interface averaged 0.19 μmol m^(-2)h^(-1) with a range of 0.01–0.61 μmol m^(-2)h^(-1). DFR exhibited less N_2O emission flux than that reported in a nearby eutrophic reservoir, but still acted as a moderate N_2O source compared with other reservoirs and lakes worldwide. Annual emissions from the water–air interface of DFR were estimated to be 0.32×10~5 mol N–N_2O, while N_2O degassing from releasing water behind the dam during power generation was nearly five times greater. Hence, N_2O degassing behind the dam should be taken into account for estimation of N_2O emissions from artificial reservoirs, an omission that historically has probably resulted in underestimates. IPCC methodology should consider more specifically N_2O emission estimation in aquatic ecosystems, especially in reservoirs, the default EF5 model will lead to an overestimation.

CO_2 emission and organic carbon burial in the Xinanjiang Reservoir

In order to understand the effect of river impoundment on carbon dynamics, a large reservoir in a subtropical area, the Xinanjiang Reservoir, was investigated in detail. CO_2 emissions from the water–air interface was studied, as was organic carbon burial in sediment. The results show a significant seasonal difference in CO_2 emissions. River impoundment led to the enhancement of aquatic photosynthesis, generating large amounts of authigenic organic carbon that was then buried in sediment.

Using seismic surveys to investigate sediment distribution and to estimate burial fluxes of OC, N, and P in a canyon reservoir

As a high-precision survey method,seismic surveying has been increasingly applied to inland water research,although its application to artificial reservoirs has remained limited.As a special artificial water body,reservoirs have important effects on the fluvial transport of material from land to ocean,and inevitably have complex terrain which can complicate and distort the results of seismic surveys.Therefore,there are still some problems need to be resolved in the application of seismic surveys in reservoirs with complex terrain.For this study,the Dongfeng Reservoir located in the upper reaches of the Wujiang River was chosen as an example to test the seismic survey method.Our testing showed that(1)because of the complex underwater terrain,the signal-to-noise ratio of the echo signal in canyon reservoir is low,making it difficult to determine sediment layers thicknesses in some areas;and(2)due to the large spatial heterogeneity of sediment distribution,insufficient density of cross-sections can lead to inaccurate interpolation results.To improve the accuracy of calculations,a mathematical method was used.Ultimately,the total burial mass of sediment was estimated at 2.85 x 107 tons,and the average burial rates of total organic carbon,total phosphorus,and total nitrogen were estimated at 0.194,0.011,and 0.014 g cm-2 year-1,respectively.These values were close to the results of previous studies and hydrographic station data,indicating that seismic survey can be a reliable and efficient method for the mapping of reservoirs.

Effects of river damming on biogenic silica turnover:implications for biogeochemical carbon and nutrient cycles

Rivers link terrestrial ecosystems and marine ecosystems, and they transport large amounts of substances into oceans each year, including several forms of silicon(Si), carbon(C), and other nutrients. However, river damming affects the water flow and biogeochemical cycles of Si, C, and other nutrients through biogeochemical interacting processes. In this review, we first summarize the current understanding of the effects of river damming on the processes of biogeochemical Si cycle, especially the source, composition, and recycling process of biogenic silica(BSi). Then, we introduce dam impacts on the cycles of C and some other nutrients. Dissolved silicon in rivers is mainly released from phytolith dissolution and silicate weathering. BSi in suspended matter or sediments in most rivers mainly consists of phytoliths and mainly originates from soil erosion. However, diatom growth and deposition in many reservoirs formed by river interception may significantly increase the contribution of diatom Si to total BSi, and thus significantly influence the biogeochemical Si,C, and nutrient cycles. Yet the turnover of phytoliths and diatoms in different rivers formed by river damming is still poorly quantified. Thus, they should be further investigated to enhance our understanding about the effects of river damming on global biogeochemical Si, C and nutrient cycles.

Distribution of functional microorganisms and its significance for iron, sulphur, and nitrogen cycles in reservoir sediments

The biogeochemical cycles of sulphur(S),iron(Fe)and nitrogen(N)elements play a key role in the reservoir ecosystem.However,the spatial positioning and interrelationship of S,Fe and N cycles in the reservoir sediment profile have not been explored to a greater extent.Here,we measure the gradients of Fe^(2+),SO_(4)^(2-),NO_(3)^(-),NH_(4)^(+),DOC,TC and TN in the pore water of the sediment,and combining the vertical distribution of the functional microorganisms involved in S,Fe and N cyclings in the sediments to determine the redox stratification in the sediment.It is found that the geochemical gradient of S,Fe and N of the reservoir sedimentary column is mainly defined by the redox process involved in the related functional microorganisms.According to the type of electron acceptor,the sediment profile is divided into 3 redox intervals,namely aerobic respiration(0–10 cm),denitrification/iron reduction(10–28 cm)and sulfate reduction(28–32 cm).In the aerobic respiration zone,NH_(4)^(+)is oxidized by aerobic AOB to NO_(3)^(-)(0–5 cm),and Fe^(2+)is oxidized by microaerobic FeRB to Fe^(3+)(3–10 cm).In the denitrification/iron reduction zone,Acinetobacter and Pseudomonas,as the dominant NRB genera,may use nitrate as an electron acceptor to oxidize Fe^(2+)(11–16 cm).The dominant genera in SOB,such as Sulfururvum,Thiobacillus and Thioalkalispira,may use nitrate as an electron acceptor to oxidize sulfide,leading to SO_(4)^(2-)accumulation(14–24 cm).In the sulfate reduction zone,SO_(4)^(2-)is reduced by SRB.This study found that functional microorganisms forming comprehensive local ecological structures to adapt to changing geochemical conditions,and which would be potentially important for the degradation and preservation of C and the fate of many nutrients and contaminants in reservoirs.

Carbon dioxide emissions from the Three Gorges Reservoir,China

Carbon dioxide(CO_2) emission from the rivertype reservoir is an hotspot of carbon cycle within inland waters. However, related studies on the different types of reservoirs are still inadequate. Therefore, we sampled the Three Gorges Reservoir(TGR), a typical river-type reservoir having both river and lake characteristics, using an online system(HydroCTM/CO_2) and YSI-6600v2 meter to determine the partial pressure of carbon dioxide(pCO_2)and physical chemical parameters in 2013. The results showed that the CO_2 flux from the mainstream ranged from 26.1 to 92.2 mg CO_2/m^2h with average CO_2 fluxes of 50.0 mg/m^2h. The CO_2 fluxes from the tributary ranged from-10.91 to 53.95 mg CO_22/mh with area-weighted average CO_2 fluxes of 11.4 mg/m^2h. The main stream emits CO_2 to the atmosphere the whole year; however, the surface water of the tributary can sometimes act as a sink of CO_2 for the atmosphere. As the operation of the TGR, the tributary became more favorable to photosynthetic uptake of CO_2 especially in summer. The total CO_2 flux was estimated to be 0.34 and 0.03 Tg CO_2/year from the mainstream and the tributaries, respectively. Our emission rates are lower than previous estimates, but they are in agreement with the average CO_2 flux from temperate reservoirs estimated by Barros et al.(Nat Geosci 4(9):593–596, 2011).

Interception, degradation and contributions of terrestrial organic carbon obtained from lignin analysis in Wujiang River, southwest China

Understanding the fate of terrestrial organic carbon(OC)in a cascade impoundment system is critical for recognizing the role of carbon sink for reservoirs.Surface sediments collected from eight cascade reservoirs across the Wujiang River,southwestern China,were analyzed for elemental and stable carbon isotopic(δ^13C)composition,and lignin phenols(∑8 andΛ8)to investigate the spatial distribution,contribution,origin and degradation of sedimentary terrestrial OC.The values of total organic carbon(TOC)and∑8 exhibited a remarkable reduction along the upstream-downstream transect suggesting the trapping effect of cascade-damming.A relatively broad range ofδ^13C(-26.61 to-25.54%,95%CI)and C/N(6.80-18.20)indicated mixed allochthonous/autochthonous OC sources in surface sediments.The quantitative simulation indicates that the OC of the sediments mainly was derived from terrestrial organic matter.Soilderived OC rather than C_(3)vascular plant-derived OC makes a major contribution to sedimentary terrestrial OC in reservoirs on karst terrain.As evidenced by lignin compositions andδ^13C,the predominant vascular plant origins of terrestrial OC along the Wujiang River are non-woody angiosperm C_(3)plants.The aged reservoirs showed a trend of increasing contribution of autochthonous OC,which potentially weaken the role of carbon sink for reservoirs.The relationship between runoff inputs,watershed area/water surface area ratios,and water residence time and Λ8 were explored,indicating the natural and anthropogenic influences on terrestrial OC remains very complex in a cascade-damming river.

Astrocytic modulation of potassium under seizures

The contribution of an impaired astrocytic K^+ regulation system to epileptic neuronal hyperexcitability has been increasingly recognized in the last decade.A defective K^+ regulation leads to an elevated extracellular K^+ concentration([K^+]o).When[K^+]o reaches peaks of 10-12 mM,it is strongly associated with seizure initiation during hypersynchronous neuronal activities.On the other hand,reactive astrocytes during a seizure attack restrict influx of K^+ across the membrane both passively and actively.In addition to decreased K^+ buffering,aberrant Ca^2+ signaling and declined glutamate transport have also been observed in astrogliosis in epileptic specimens,precipitating an increased neuronal discharge and induction of seizures.This review aims to provide an overview of experimental findings that implicated astrocytic modulation of extracellular K^+ in the mechanism of epileptogenesis.

Altered synaptic currents,mitophagy,mitochondrial dynamics in Alzheimer's disease models and therapeutic potential of Dengzhan Shengmai capsules intervention

Emerging research suggests a potential association of progression of Alzheimer's disease(AD)with alterations in synaptic currents and mitochondrial dynamics.However,the specific associations between these pathological changes remain unclear.In this study,we utilized Aβ42-induced AD rats and primary neural cells as in vivo and in vitro models.The investigations included behavioural tests,brain magnetic resonance imaging(MRI),liquid chromatography-tandem mass spectrometry(UPLC-MS/MS)analysis,Nissl staining,thioflavin-S staining,enzyme-linked immunosorbent assay,Golgi-Cox staining,transmission electron microscopy(TEM),immunofluorescence staining,proteomics,adenosine triphosphate(ATP)detection,mitochondrial membrane potential(MMP)and reactive oxygen species(ROS)assessment,mitochondrial morphology analysis,electrophysiological studies,Western blotting,and molecular docking.The results revealed changes in synaptic currents,mitophagy,and mitochondrial dynamics in the AD models.Remarkably,intervention with Dengzhan Shengmai(DZSM)capsules emerged as a pivotal element in this investigation.Aβ42-induced synaptic dysfunction was significantly mitigated by DZSM intervention,which notably amplified the frequency and amplitude of synaptic transmission.The cognitive impairment observed in AD rats was ameliorated and accompanied by robust protection against structural damage in key brain regions,including the hippocampal CA3,primary cingular cortex,prelimbic system,and dysgranular insular cortex.DZSM intervention led to increased IDE levels,augmented long-term potential(LTP)amplitude,and enhanced dendritic spine density and length.Moreover,DZSM intervention led to favourable changes in mitochondrial parameters,including ROS expression,MMP and ATP contents,and mitochondrial morphology.In conclusion,our findings delved into the realm of altered synaptic currents,mitophagy,and mitochondrial dynamics in AD,concurrently highlighting the therapeutic potential of DZSM intervention.

Flux of organic carbon burial and carbon emission from a large reservoir: implications for the cleanliness assessment of hydropower

Accurately quantifying the budget of carbon sources and sinks in hydropower reservoirs is important for evaluating the cleanliness of hydroelectricity. However, current research on carbon emissions from reservoirs has rarely taken into account the organic carbon(OC) buried in sediment. Only greenhouse gas emissions from the water-air interface at reservoirs have been examined, which would result in an overestimation of the greenhouse effect of reservoirs. In November 2017, this study investigated the distribution of sediment in the Hongfeng Reservoir(HFR) in southwest China, a typical large hydropower reservoir, by using an underwater seismology monitoring system. We estimated the flux of OC into sediment using the results of a sediment survey and a dataset compiled from references. Our results show that, the HFR retained 200,715 t of OC in the sediment since its impounding after dam construction to the sampling year of 2017, when the average burial flux was 3,521 t-C aà1(106 g C aà1) and the modern burial flux was 5,449 t-C aà1. After excluding the exogenous OC, the modern valid carbon sink of the sediment was 4,632 t per year. Under the current state of the reservoir, taking the modern valid carbon sink value, the carbon emissions from the reservoir's surface, and the discharge water from the dam into consideration, the net carbon sink of the HFR is found to be 1,098.9 t-C aà1. If the hydroelectricity generated by the reservoir is converted to a carbon sink, then the total net carbon sink becomes 12,972.9 t-C aà1.This work argues that both reservoir sediment and hydroelectricity are important carbon sinks and both should be included in assessments of the greenhouse effects of reservoirs.

Quantification of TOC and TN in reservoir sediments using Fourier transform infrared spectroscopy

This study aims to quantitatively assess the total organic carbon(TOC)and total nitrogen(TN)content of reservoir sediments in southwest China using Fourier transform infrared spectroscopy(FTIRS).FTIRS measurements were performed on 187 sediment samples from four reservoirs to develop calibration models that relate FTIR spectral information with conventional property concentrations using partial least squares regression(PLSR).Robust calibration models were established for TOC and TN content.The external validation of these models yielded a significant correlation between FTIR-inferred and conventionally measured concentrations of R^(2)=0.88 for TOC,R^(2)=0.90 for TN.This method can be performed with a small sample size and is non-destructive throughout the simple measurement process.The TOC and TN content in the sediment can be determined with high effectiveness without being overly expensive,making it an advantageous method when measuring a large number of samples.