Distribution characteristics of reactive silicon in six water bodies in the Yangtze River Basin in China.

Terrestrial silicon (Si) from biogeochemically weathered rocks and soils into oceans must pass through several water bodies, resulting in some Si immobilized. Hence, the knowledge on Si distribution characteristics in different water bodies at a basin scale is helpful to understand Si immobilization. A total of 65 surface sediments and corresponding overlying water samples were sampled from six water bodies (Dianchi Lake, DL; Dadu River, DR; Tuojiang River, TR; Honghu Lake, HL; Donghu Lake, DhL; Taihu Lake, TL) in the Yangtze River Basin of China, total dissolved Si (TDSi) in overlying water and exchangeable Si (Ex-Si), active non-biogenic Si (NBSi), and total acid dissolved Si (TADSi) in sediments were analyzed. Water chemical parameters (pH, EC, and TDP) and sediment components (LOI, TN, TP, and TADFe) showed that the water environment characteristics of six water bodies differed. TDSi differed among regions and between lakes and rivers, significantly higher in water bodies in the upper reaches and rivers than the middle or lower reaches and lakes (p < 0.05), respectively. Ex-Si in sediments in the upper reaches was significantly higher than in the middle or lower reaches (p < 0.05), except for DhL, whose Ex-Si was the highest. Mean TADSi and active NBSi were significantly higher in lakes than rivers (p < 0.05). Oxidation of sediments significantly increased TDSi in overlying water and active NBSi in sediments (p < 0.01). Si forms in six water bodies significantly depended on components of the sediments (e.g. active Ca2+, Mg2+, Fe, and Al3+) and water chemical parameters (p < 0.05). Our results suggest that immobilization of Si in water bodies in the Yangtze River Basin depends on the types of water bodies and sediments, lakes and Fe-Al dominated sediments have a high potential to immobilize Si, but anthropogenic interference should not be ignored.

A Novel Data Augmentation Method for Improving the Accuracy of Insulator Health Diagnosis.

Performing ultrasonic nondestructive testing experiments on insulators and then using machine learning algorithms to classify and identify the signals is an important way to achieve an intelligent diagnosis of insulators. However, in most cases, we can obtain only a limited number of data from the experiments, which is insufficient to meet the requirements for training an effective classification and recognition model. In this paper, we start with an existing data augmentation method called DBA (for dynamic time warping barycenter averaging) and propose a new data enhancement method called AWDBA (adaptive weighting DBA). We first validated the proposed method by synthesizing new data from insulator sample datasets. The results show that the AWDBA proposed in this study has significant advantages relative to DBA in terms of data enhancement. Then, we used AWDBA and two other data augmentation methods to synthetically generate new data on the original dataset of insulators. Moreover, we compared the performance of different machine learning algorithms for insulator health diagnosis on the dataset with and without data augmentation. In the SVM algorithm especially, we propose a new parameter optimization method based on GA (genetic algorithm). The final results show that the use of the data augmentation method can significantly improve the accuracy of insulator defect identification.

Unexpected spatial stability of water chemistry in headwater stream networks.

Understanding how water and solutes enter and propagate through freshwater landscapes in the Anthropocene is critical to protecting and restoring aquatic ecosystems and ensuring human water security. However, high hydrochemical variability in headwater streams, where most carbon and nutrients enter river networks, has hindered effective modelling and management. We developed an analytical framework informed by landscape ecology and catchment hydrology to quantify spatiotemporal variability across scales, which we tested in 56 headwater catchments, sampled periodically over 12 years in western France. Unexpectedly, temporal variability in dissolved carbon, nutrients and major ions was preserved moving downstream and spatial patterns of water chemistry were stable on annual to decadal timescales, partly because of synchronous variation in solute concentrations. These findings suggest that while concentration and flux cannot be extrapolated among subcatchments, periodic sampling of headwaters provides valuable information about solute sources and subcatchment resilience to disturbance.

A piezoelectric-driven nanoindentation system for scanning electron microscope with improved analog compensation method.

This paper presents a novel piezoelectric-driven nanoindentation system for a scanning electron microscope (SEM) with an improved analog compensation (IAC) method. This system mainly consists of a piezoelectric-driven indenter head, a rectangle-shaped transducer, and a nanopositioner module. Compared with the state-of-the-art piezoelectric-driven nanoindentation system with a circle-shaped transducer, the proposed nanoindentation system is capable of multi-direction operation inside a SEM with a rectangle-shaped transducer. Self-matched semiconductor strain gauges are selected as the position sensor for the piezoelectric-actuator. The Wheatstone bridge output voltage cannot achieve a zero temperature coefficient because the temperature coefficients of self-matched semiconductor strain gauge pairs become significantly different from each other after installation in practice. An IAC method is proposed to compensate the temperature coefficients further. Compared with the existing analog compensation method, the IAC method solves the problem of amplifier saturation and improves the sensitivity of the self-matched semiconductor strain gauge pairs position sensor by 27%. The multi-direction operation results inside a standard SEM HITACHI SU5000 validate the advantage of the developed nanoindentation system.

Available acid consumption capacity of sediments in six water bodies in the Yangtze River Basin in China.

Acid-base reactivity is a fundamental property of sediments and is responsible for sediments' multiple roles in aquatic ecosystems. However, little information currently exists about the composition, magnitude, and change of the available acid consumption capacity (AACC) of sediments. To optimize reaction conditions, we developed operational procedures to determine AACC using base titration to recover surplus acid in suspensions. We characterized the sediment AACC of Dianchi Lake (DL), Daduhe River (DR), Tuojiang River (TR), Honghu Lake (HL), Wuhan Donghu Lake (DhL), and Taihu Lake (TL) in the Yangtze River Basin, China. The procedure demonstrated that reacting 40 mL 0.1 M HCl with fresh sediments equivalent to 1.0 g dry weight for 4 h and recovering surplus acid in the suspension by NaOH titration to an endpoint pH of 3.0 could determine sediment AACC. Sediment AACC in the Yangtze River Basin had high regional variability. The mean magnitude of AACC among sites was ranked DL > DR > DhL > TR > HL > TL, which is extremely similar to their geographical location from the upper to lower reaches of the Yangtze River Basin. Qualitative results from acid titration curves showed that more components contributed to AACC in DL, DR, TR, and DhL sediments than to those in HL and TL sediments. The correlation between AACC and the total amount of multivalent cations released indicated that AACC depended significantly on labile acid-soluble minerals that contain multivalent cations (Fe3+, Fe2+, Ca2+, Al3+, Mg2+, and Mn2+) (p < 0.01). Based on the contribution percentages of multivalent cations to AACC, sediment AACC of six water bodies were divided into two types: Ca-Mg dominated (DL, DR, and TR) and Fe-Al dominated (HL, DhL, and TL). We suggest that sediment AACC complexing with pH can contribute to a better description of the acid-base characteristics of sediments.

A Multi-Site Analysis of the Prevalence of Food Insecurity in the United States, before and during the COVID-19 Pandemic.

BACKGROUND: The coronavirus disease 2019 (COVID-19) pandemic profoundly affected food systems including food security. Understanding how the COVID-19 pandemic impacted food security is important to provide support and identify long-term impacts and needs. OBJECTIVE: The National Food Access and COVID research Team (NFACT) was formed to assess food security over different US study sites throughout the pandemic, using common instruments and measurements. This study presents results from 18 study sites across 15 states and nationally over the first year of the COVID-19 pandemic. METHODS: A validated survey instrument was developed and implemented in whole or part through an online survey of adults across the sites throughout the first year of the pandemic, representing 22 separate surveys. Sampling methods for each study site were convenience, representative, or high-risk targeted. Food security was measured using the USDA 6-item module. Food security prevalence was analyzed using ANOVA by sampling method to assess statistically significant differences. RESULTS: Respondents (n = 27,168) indicate higher prevalence of food insecurity (low or very low food security) since the COVID-19 pandemic, compared with before the pandemic. In nearly all study sites, there is a higher prevalence of food insecurity among Black, Indigenous, and People of Color (BIPOC), households with children, and those with job disruptions. The findings demonstrate lingering food insecurity, with high prevalence over time in sites with repeat cross-sectional surveys. There are no statistically significant differences between convenience and representative surveys, but a statistically higher prevalence of food insecurity among high-risk compared with convenience surveys. CONCLUSIONS: This comprehensive study demonstrates a higher prevalence of food insecurity in the first year of the COVID-19 pandemic. These impacts were prevalent for certain demographic groups, and most pronounced for surveys targeting high-risk populations. Results especially document the continued high levels of food insecurity, as well as the variability in estimates due to the survey implementation method.

Evidence of colloids as important phosphorus carriers in natural soil and stream waters in an agricultural catchment.

Colloids (1-1,000 nm) are important phosphorus (P) carriers in agricultural soils. However, most studies are based on colloids from soil waters extracted in the laboratory, thus limiting the understanding of the natural transfer of colloidal P along the soil-to-stream continuum. Here, we conducted a field study on the colloidal P in both natural soil waters and their adjacent stream waters in an agricultural catchment (Kervidy-Naizin, western France). Soil waters (10-15 cm, Albeluvisol) of two riparian wetlands and the adjacent stream waters were sampled monthly during wet seasons of the 2015-2016 hydrological year (seven dates in total). Ultrafiltration at three pore sizes (5 kDa, 30 kDa, and 0.45 µm) was combined with inductively coupled plasma mass spectrometry (ICP-MS) to investigate variability in colloidal P concentration and its concomitant elemental composition. Results showed that colloidal P represented, on average, 45 and 30% of the total P (<0.45 µm) in the soil waters and stream waters, respectively. We found that colloidal P was preferentially associated with (a) organic carbon in the fine nanoparticle fraction (5-30 kDa) and (b) iron-oxyhydroxides and organic carbon in the coarse colloidal fraction (30 kDa-0.45 µm). The results confirmed that colloidal P is an important component of total P in both soil waters and stream waters under field conditions, suggesting that riparian wetlands are hotspot zones for the production of colloidal P at the catchment scale, which has the potential to be transported to adjacent streams.

Thin-layer fine-sand capping of polluted sediments decreases nutrients in overlying water of Wuhan Donghu Lake in China.

Capping water body sediments with a thin layer of sand is an effective technique to decrease nutrient concentrations in the water column and accelerate ecological restoration of eutrophic water bodies. However, long-term effects of thin-layer sand capping in shallow lakes are reported less often. Using clean fine sand and geotextile mats as capping materials for sediments collected from Wuhan Donghu Lake in China, we designed a 290-day tank experiment with 3 cm of sand capping at four percentages of sediment coverage from 25 to 100% and a control (no capping). We monitored total nitrogen (TN), total phosphorus (TP), nitrate (NO3-), ammonia (NH4+), and soluble reactive phosphorus (SRP) in the overlying water every 7 days. Mean TN and NO3- concentrations were significantly the lowest (P < 0.05) at 50% coverage. Further increase in coverage kept them slightly fluctuating. NH4+ concentration was significantly lowest (P < 0.05) at 75% coverage. The relation between coverage and mean TP and SRP concentrations indicated that 75% coverage significantly decreased (P < 0.05) them, and increasing coverage to 100% decreased them even more. The fluxes of TN and TP estimated between sediments and overlying water showed that the thin fine-sand layer significantly increased the function of sediments as a sink of TN from overlying water and the potential of a sand layer to block release of TP from sediments (P < 0.05). Our results suggested that if thin-layer sand capping were applied to Wuhan Donghu Lake, more than 50% coverage is required to decrease nutrients in the lake's water.

River network alteration of C-N-P dynamics in a mesoscale agricultural catchment.

The majority of freshwater ecosystems worldwide suffer from eutrophication, particularly because of agriculture-derived nutrient sources. In the European Union, a discrepancy exists between the scale of regulatory assessment and the size of research catchments. The Water Framework Directive sets water quality objectives at the mesoscale (50-500 km2), a scale at which both hillslope and in-stream processes influence carbon (C), nitrogen (N) and phosphorus (P) dynamics. Conversely, research catchments focus on headwaters to investigate hillslope processes while minimising the influence of river processes on C-N-P dynamics. Because hillslope and river processes have common hydro-climatic drivers, the relative influence of each on C-N-P dynamics is difficult to disentangle at the mesoscale. In the present study, we used repeated synoptic sampling throughout the river network of a 300 km2 intensively farmed catchment, spatial stochastic modelling and mass balance calculations to analyse this mesoscale conundrum. The main objective was to quantify how river processes altered C-N-P hydrochemical dynamics in different flow, concentration and temperature conditions. Our results show that flow was the main control of alterations of C-N-P dynamics in the river network, while temperature and source concentration had little or no influence. The influence of river processes peaked during low flow, with up to 50% of dissolved organic carbon (DOC) production, up to 100% of nitrate (NO3) retention and up to 50% of total phosphorus (TP) retention. Despite high percentages of river processes at low flow, their influence on annual loads was low for NO3 (median of -10%) and DOC (median of +25%) but too variable to draw conclusions for TP. Because of the differing river alteration rates among carbon and nutrients, stoichiometric ratios varied greatly from headwaters to the outlet, especially during the eutrophication-sensitive low-flow season.

A Novel Stick-Slip Nanopositioning Stage Integrated with a Flexure Hinge-Based Friction Force Adjusting Structure.

The piezoelectrically-actuated stick-slip nanopositioning stage (PASSNS) has been applied extensively, and many designs of PASSNSs have been developed. The friction force between the stick-slip surfaces plays a critical role in successful movement of the stage, which influences the load capacity, dynamic performance, and positioning accuracy of the PASSNS. Toward solving the influence problems of friction force, this paper presents a novel stick-slip nanopositioning stage where the flexure hinge-based friction force adjusting unit was employed. Numerical analysis was conducted to estimate the static performance of the stage, a dynamic model was established, and simulation analysis was performed to study the dynamic performance of the stage. Further, a prototype was manufactured and a series of experiments were carried out to test the performance of the stage. The results show that the maximum forward and backward movement speeds of the stage are 1 and 0.7 mm/s, respectively, and the minimum forward and backward step displacements are approximately 11 and 12 nm, respectively. Compared to the step displacement under no working load, the forward and backward step displacements only increase by 6% and 8% with a working load of 20 g, respectively. And the load capacity of the PASSNS in the vertical direction is about 72 g. The experimental results confirm the feasibility of the proposed stage, and high accuracy, high speed, and good robustness to varying loads were achieved. These results demonstrate the great potential of the developed stage in many nanopositioning applications.

Release of dissolved phosphorus from riparian wetlands: Evidence for complex interactions among hydroclimate variability, topography and soil properties.

In agricultural landscapes, establishment of vegetated buffer zones in riparian wetlands (RWs) is promoted to decrease phosphorus (P) emissions because RWs can trap particulate P from upslope fields. However, long-term accumulation of P risks the release of dissolved P, since the unstable hydrological conditions in these zones may mobilize accumulated particulate P by transforming it into a mobile dissolved P species. This study evaluates how hydroclimate variability, topography and soil properties interact and influence this mobilization, using a three-year dataset of molybdate-reactive dissolved P (MRDP) and total dissolved P (TDP) concentrations in soil water from two RWs located in an agricultural catchment in western France (Kervidy-Naizin), along with stream P concentrations. Two main drivers of seasonal dissolved P release were identified: i) soil rewetting during water-table rise after dry periods and ii) reductive dissolution of soil Fe (hydr)oxides during prolonged water saturation periods. These mechanisms were shown to vary greatly in space (according to topography) and time (according to intra- and interannual hydroclimate variability). The concentration and speciation of the released dissolved P also varied spatially depending on soil chemistry and local topography. Comparison of sites revealed a similar correlation between soil P speciation (percentage of organic P ranging from 35-70%) and the concentration and speciation of the released P (MRDP from <0.10 to 0.40mgl-1; percentage of MRDP in TDP from 25-70%). These differences propagated to stream water, suggesting that the two RWs investigated were the main sources of dissolved P to streams. RWs can be critical areas due to their ability to biogeochemically transform the accumulated P in these zones into highly mobile and highly bioavailable dissolved P forms. Hydroclimate variability, local topography and soil chemistry must be considered to decrease the risk of remobilizing legacy soil P when establishing riparian buffer zones in agricultural landscapes.

An innovative approach for sequential extraction of phosphorus in sediments: Ferrous iron P as an independent P fraction.

Accurate identification of phosphorus (P) forms is crucially important for understanding the geochemical cycle of P; however, until now the role of ferrous iron P (Fe(II)-P) buried in sediments has been completely ignored in nearly all sequential extraction procedures developed. Using sediment cores sampled from Donghu Lake in Wuhan, China, this study explored a modified version of widely used sequential P extraction method (SEDEX; Ruttenberg, 1992) in which Fe(II)-P was identified as an independent fraction. Based on the high selectivity of the extractant (0.2% 2,2'-bipyridine+0.1 M KCl) and the dissolution equilibrium of P, procedures for extracting Fe(II)-P were optimized using a 1:100 solid:liquid ratio and extraction at 50 ± 1 °C for 24 h. The sedimentary P extracted was divided into five fractions: loosely-bound P, Fe(II)-P, CDB-P, Ca-P and O-P. Fe(II)-P was the predominant fraction in fresh sediments in Donghu Lake, accounting for 15.7-49.9% of TP, with a mean of 31.6%. The mean values of Ca-P, O-P, CDB-P and loosely-bound P were 28.4%, 22.7%, 17.1% and 4.3%, respectively. Combined with component analysis of extracts and recovery experiments of standard reference minerals (vivianite, Fe3(PO4)2·8H2O) in natural sediments, extraction of Fe(II)-P with 0.2% 2,2-bipridine and 0.1 M KCl was robust, with a good recovery rate (88.7-100.6%) and little of the Ca-P dissolved. It is possible to use this innovative SEDEX not only to distinguish the contribution of different P matrices in fresh sediments, but also to investigate the transformation of sedimentary P under different redox conditions. Therefore, greater focus on Fe(II)-P is necessary, because it is a major sink for the geochemical process of sedimentary P.

Groundwater control of biogeochemical processes causing phosphorus release from riparian wetlands.

Because of the high sorption affinity of phosphorus (P) for the soil solid phase, mitigation options to reduce diffuse P transfer usually focus on trapping particulate P delivered via surface flow paths. Therefore, placing riparian buffers between croplands and watercourses has been promoted worldwide, sometimes in wetland areas. To investigate the risk of P-accumulating riparian wetlands (RWs) releasing dissolved P into streams, we monitored molybdate-reactive P (MRP) in the soil pore water of two RWs in an agricultural watershed. Two main mechanisms released MRP under the control of groundwater dynamics. First, soil rewetting after the dry summer period was associated with the presence of a pool of mobile P, limited in size. Its mobilization started under water saturated conditions caused by a rise in groundwater. Second, anoxic conditions at the end of winter caused reductive dissolution of Fe (hydr)oxides along with a release of MRP. Comparison of sites revealed that the first MRP release occurred only in RWs with P-enriched soils, whereas the second was observed even in RWs with low soil P status. Seasonal variations in stream MRP concentrations were similar to concentrations in RW soils. Hence, RWs can act as a key component of the P transfer continuum in agricultural landscapes by converting particulate P from croplands into MRP transferred to streams.