Concentrations In Soil Pore Water Research Articles

Dune soil nitrogen leaching for Chinese-yam cultivation: Impact of microbe-decomposable slow-release fertilizer

Chinese yam production is thriving in Aomori Prefecture, a cold and snowy region in Japan. Recently, there has been an increasing risk of nitrogen leaching in Chinese-yam fields, which consist of sandy soil, due to localized torrential rain. The relationships between the type of fertilizer used for Chinese-yam cultivation, the amount of nitrogen (N) leaching, and the timing of leaching remain unknown. Therefore, this study aimed to fill this knowledge gap by investigating the effects of different fertilizers (fast-acting and/or slow-release fertilizer) and irrigation practices (conventional and/or excessive irrigation) in order to mitigate the detrimental impact of nitrogen leaching on groundwater quality. An enhanced mathematical model and the spatiotemporal dynamics of inorganic nitrogen concentration in soil pore water were evaluated the negative impact of nitrogen leaching on the groundwater environment was evaluated. The results showed that the combined use of slow-release fertilizers could significantly reduce nitrate-nitrogen concentration in soil-water, especially during the harvest season. This study demonstrated that cultivating Chinese yam with a fertilizer application system that includes the use of slow-release fertilizer can diminish the negative impact of nitrogen leaching on the groundwater environment, contributing to our understanding of sustainable agricultural practices in regions facing similar environmental challenges. Therefore, our findings represent an important advancement providing new approaches to maintaining productivity while mitigating the adverse impacts on groundwater environments, as well as offering guidelines for agricultural practices in regions facing similar environmental challenges.

Efficient co-stabilization of arsenic and cadmium in farmland soil by schwertmannite under long-term flooding-drying condition

Simultaneously stabilizing of arsenic (As) and cadmium (Cd) in co-contaminated soil presents substantial challenges due to their contrasting chemical properties. Schwertmannite (Sch) is recognized as a potent adsorbent for As pollution, with alkali modification showing promising results in the simultaneous immobilization of both As and Cd. This study systematically investigated the long-term stabilization efficacy of alkali-modified Sch in Cd–As co-contaminated farmland soil over a 200-day flooding-drying period. The results revealed that As showed significant mobility in flooded conditions, whereas Cd exhibited increased soil availability under drying phases. The addition of Sch did not affect the trends in soil pH and Eh fluctuations; nonetheless, it led to an augmentation in the levels of amorphous iron oxides and SO42− concentration in soil pore water. At a dosage of 0.5% Sch, there was a notable decrease in the mobility and soil availability of As and Cd under both flooding (34.5% and 53.6% at Day 50) and drying conditions (27.0% and 29.4% at Day 130), primarily promoting the transformation of labile metal(loid) fraction into amorphous iron oxide-bound forms. Throughout the flooding-drying treatment period, Sch maintained stable mineral morphology and mineralogical phase, highlighting its long-term stabilization effect. The findings of this study emphasize the promising application of Sch-based soil remediation agents in mitigating the challenges arising from As–Cd co-contamination. Further research is warranted to explore their application in real farmland settings and their impact on the uptake of toxic metal(loid)s by plants.

Size-dependent vector effects of microplastics on bioaccumulation of hydrophobic organic contaminants in earthworm: A dual-dosing study

The potential of microplastics to act as a vector for anthropogenic contaminants is of rising concern. However, directly quantitatively determining the vector effects of microplastics has been rarely studied. Here, we present a dual-dosing method that simulates the chemical bioaccumulation from soil and microplastics simultaneously, wherein unlabeled hydrophobic organic contaminants (HOCs) were spiked in the soil and their respective isotope-labeled reference compounds were spiked on the polyethylene microplastics. The comparison of the bioavailability, i.e., the freely dissolved concentration in soil porewater and bioaccumulation by earthworm, between the unlabeled and isotope-labeled HOCs was carried out. Relatively higher level of bioavailability of the isotope-labeled HOCs was observed compared to the unlabeled HOCs, which may be attributed to the irreversible desorption of HOCs from soil particles. The average relative fractions of bioaccumulated isotope-labeled HOCs in the soil treated with 1 % microplastics ranged from 6.9 % to 46.4 %, which were higher than those in the soil treated with 0.1 % microplastics. Treatments with the smallest microplastic particles were observed to have the highest relative fractions of bioaccumulated isotope-labeled HOCs, with the exception of phenanthrene, suggesting greater vector effects of smaller microplastic particles. Biodynamic model analysis indicated that the contribution of dermal uptake to the bioaccumulation of isotope-labeled HOCs was higher than that for unlabeled HOCs. This proposed method can be used as a tool to assess the prospective vector effects of microplastics in complex environmental conditions and would enhance the comprehensive understanding of the microplastic vector effects for HOC bioaccumulation.

Pre-activated biochar by fertilizers mitigates nutrient leaching and stimulates soil microbial activity

BackgroundPrevious studies have suggested that the targeted application of biochars in agricultural soils may benefit soil health and crop production. Physico-chemical properties of soils after biochar addition have been explored, but less is known about how microbial parameters respond. Therefore, impact of biochar (NB), mineral fertilizer-activated biochar (AB), or mineral fertilizer (MF) application on selected chemical and microbial parameters of lettuce-planted soil was evaluated in a pot experiment.ResultsIn comparison to the control, soil enzymes activities, related to carbon (C), nitrogen (N), and phosphorus (P) cycling, and their content in plant biomass, were significantly increased by the addition of mineral fertilizer with or without biochar (MF, NB + MF). Conversely, microbial respiration (basal and substrate induced) was highly responsive to the activated biochar amendment (AB) as compared to other treatments. N, P, and potassium (K) concentrations in soil pore water were stabilized by the mineral fertilizer-activated biochar, indicating reduced leaching and the likelihood of increased longevity of these nutrients in soils. Enhanced carbon acquisition and mitigated nitrogen acquisition in soil of the most experimental treatments were coupled with higher crop (lettuce) biomass.ConclusionsOur study demonstrates that the application of biochar both with and without mineral fertilizer has the potential to enhance microbial activity and fertility in the tested agricultural soil, but that leaching of fertilizer-borne nutrients may be mitigated by the activation process.Graphical

Revising the EPA dilution-attenuation soil screening model for PFAS

Per and polyfluoroalkyl substances (PFAS) have been shown to be ubiquitous in the environment, and one issue of critical concern is the leaching of PFAS from soil to groundwater. The risk posed by contaminants present in soil is often assessed in terms of the anticipated impact to groundwater through the determination of soil screening levels (SSLs). The U.S. Environmental Protection Agency (EPA) established a soil screening model for determining SSLs. However, the model does not consider the unique retention properties of PFAS and, consequently, the SSLs established with the model may not represent the actual levels that are protective of groundwater quality. The objective of this work is to revise the standard EPA SSL model to reflect the unique properties and associated retention behavior of PFAS. Specifically, the distribution parameter used to convert soil porewater concentrations to soil concentrations is revised to account for adsorption at the air-water interface. Example calculations conducted for PFOS and PFOA illustrate the contrasting SSLs obtained with the revised and standard models. A comparison of distribution parameters calculated for a series of PFAS of different chain length shows that the significance of air-water interfacial adsorption can vary greatly as a function of the specific PFAS. Therefore, the difference between SSLs calculated with the revised versus standard models will vary as a function of the specific PFAS, with greater differences typically observed for longer-chain PFAS. It is anticipated that this revised model will be useful for developing improved SSLs that can be used to enhance site investigations and management for PFAS-impacted sites. SynopsisThe widely used EPA SSL model is revised for PFAS applications to account for adsorption at the air-water interface.

Cover crop mixtures versus single species: Water quality and cash crop yield

Cover crops promote environmental health and agricultural production, but most research in the Midwest focuses solely on winter cereal rye (<i>Secale cereal</i> L.) (CR). We evaluated cover crop mixtures compared to single species in terms of cover crop biomass (<i>n</i> = 32 site-years), cash crop yield (<i>n</i> = 32), and subsurface water quality (<i>n</i> = 17) spanning six sites and seven years in Iowa. Before soybeans (<i>Glycine max</i> [L.] Merr), the single species was CR and the mixture species were CR, radish (<i>Raphanus sativus</i>), and rapeseed (<i>Brassica napus</i>). Before corn (<i>Zea mays</i> L.), the single species was oats (<i>Avena sativa</i>) and the mixture species were oats, radish, and hairy vetch (<i>Vicia villosa</i>). Before soybeans, average fall growth of CR in the single species was significantly greater than or similar to the mixture. Fall growth before corn with oats was significantly less than or similar to the oat mixture. Before soybeans/during soybean growth, both cover crop treatments had significantly lower spring nitrate-nitrogen (NO₃-N) concentrations in soil pore water than the control, and single species had lower concentrations than mixtures. Even with mostly winterkill cover crops before corn, spring NO₃-N concentrations of soil pore water were significantly lower in the single species treatment than in the no cover treatment. Cover crop treatments had no influence on corn yield overall and slight negative influence on soybean yield at two of the sites. We propose the following to increase diversity of cover crops in the Midwest: CR before soybeans, oats and/or an oat mixture before corn, and introducing brassicas and hairy vetch in southern Iowa. In this project, these diverse species were possible after broadcast seeding in late August, and that would be our planting recommendation to promote fall growth.

Evaluating the release and metabolism of ricinine from castor cake fertilizer in soils using a LC-QTOF/MS coupled with SIRIUS workflow

Castor cake is a major by-product generated after castor oil extraction and has been widely used as an organic fertilizer. Once applied to soil, a toxic alkaloid ricinine in castor cake may be released into soils and subsequently taken up by crops, which poses a potential threat to food safety and human health. However, the environmental fate of castor cake derived ricinine in agroecosystems remains unclear. In this study, the release and metabolism of ricinine in soils were conducted using soil pot experiments with different castor cake application rates. The analytical methodology of ricinine quantification in soil pore water was first established using solid phase extraction (SPE) coupled with liquid chromatography quadrupole time-of-flight mass spectrometry (LC-QTOF/MS). A non-target screening workflow associated with LC-QTOF/MS and SIRIUS platform was further developed to identify ricinine metabolites in soil pore water. After castor cake application, the ricinine concentrations in soil pore water significantly increased to 297–7990 μg L−1 at 1 day and then gradually decreased to 62.1–3460 μg L−1 at 7 days and 1.70–279 μg L−1 at 14 days for the selected two tested soils with castor cake application rates of 2, 10, and 20 g castor cake/kg soil. In addition, two ricinine metabolites R-194 and R-180 were tentatively identified and one ricinine metabolite N-demethyl-ricinin was confirmed through authentic reference standard for the first time by the developed non-target screening workflow. This study highlights the release and metabolism of toxic alkaloid ricinine in soils once applied castor cake as an organic fertilizer. Ricinine could be released into soil pore water in a short-term after castor cake application and then undergo demethylation, hydroxylation, and hydroxylation followed by methylation metabolisms over time in agroecosystems.

PFAS concentrations in soil versus soil porewater: Mass distributions and the impact of adsorption at air-water interfaces.

Determining the risk posed by PFAS leaching from soil to groundwater requires quantification of the magnitude and temporal/spatial variability of PFAS mass discharge from the vadose zone, which is governed in part by the concentrations of PFAS in soil porewater. Porewater concentrations are impacted and mediated by the properties of the PFAS and soil, multiple transport and fate processes, and site conditions. The objective of this research was to delineate the relationship between soil porewater concentrations and soil concentrations, based on a comprehensive model of PFAS mass distribution within a soil sample volume. Measured parameters representing solid-phase sorption and air-water interfacial adsorption are used to illustrate the impact of soil and PFAS properties on the distribution of representative PFAS between soil and soil porewater. Literature data reported for soil and soil porewater concentrations of several PFAS obtained from outdoor lysimeter experiments are used to test the distribution model. Soil-to-porewater concentration ratios predicted with the model compared very well to the measured concentration ratios. The nondimensional distribution coefficient that describes the distribution of PFAS mass amongst all domains within a soil sample was observed to be a function of PFAS molecular size. Numerical simulations conducted for a model fire-training source area were used to illustrate the ranges in magnitude of soil versus porewater concentrations for representative field conditions. The results of the measured and simulated data sets demonstrated the importance of air-water interfacial adsorption for the distribution of the longer-chain PFAS within soil samples. PFAS soil porewater concentrations are anticipated to range from ng/L to mg/L depending upon soil concentrations, which in turn depend upon the nature of the site.

Characterization of Plant Accumulation of Pharmaceuticals from Soils with Their Concentration in Soil Pore Water.

Predicting plant uptake of pharmaceuticals from soils is very challenging because many pharmaceuticals are ionizable compounds, which experience highly variable sorption/desorption and transformation processes in soils. This study aimed to elucidate how the equilibrium between sorbed and dissolved phases influences radish uptake of 15 pharmaceuticals from three soils with different properties. After 30 days of uptake, the accumulation of acetaminophen, carbamazepine, lamotrigine, carbadox, trimethoprim, and triclosan in radish ranked as Riddles > Capac > Spinks soil. In contrast, radish accumulation of caffeine, lincomycin, monensin, tylosin, sulfadiazine, and sulfamethoxazole exhibited the opposite order of Riddles < Capac < Spinks soil. Oxytetracycline and estrone demonstrated similar accumulation in radish grown in the three soils. Accumulation of pharmaceuticals in radish demonstrated no apparent relation with their concentration in soils. However, we identified strong positive correlation between pharmaceutical accumulation in radish and their corresponding concentration in soil pore water. These results reveal that pharmaceutical in soil pore water is the dominant fraction bioavailable to plant uptake. Relatively constant root concentration factors (RCFs) on the basis of pharmaceutical concentration in soil pore water, compared to the highly variable RCFs derived from soils, suggest that pore water-based RCF is superior for describing pharmaceutical accumulation in plants grown in soils. We recommend that pharmaceuticals in soil pore water should be evaluated and included in modeling their uptake by plants.

Root exudates increased arsenic mobility and altered microbial community in paddy soils

Root exudates are crucial for plants returning organic matter to soils, which is assumed to be a major source of carbon for the soil microbial community. This study investigated the influence of root exudates on the fate of arsenic (As) with a lab simulation experiment. Our findings suggested that root exudates had a dose effect on the soil physicochemical properties, As speciation transformation and the microbial community structure at different concentrations. The addition of root exudates increased the soil pH while decreased the soil redox potential (Eh). These changes in the soil pH and Eh increased As and ferrous (Fe(II)) concentrations in soil porewater. Results showed that 40 mg/L exudates addition significantly increased arsenite (As(III)) and arsenate (As(V)) by 541 and 10 times respectively within 30 days in soil porewater. The relative abundance of Fe(III)-reducing bacteria Geobacter and Anaeromyxobacter increased with the addition of root exudates, which enhanced microbial Fe reduction. Together these results suggest that investigating how root exudates affect the mobility and transformation of As in paddy soils is helpful to systematically understand the biogeochemical cycle of As in soil-rice system, which is of great significance for reducing the health risk of soil As contamination.

Oyster shell amendment reduces cadmium and lead availability and uptake by rice in contaminated paddy soil.

Contamination with cadmium (Cd) and lead (Pb) in rice and paddy soil threatens food safety and human health. This study determined the effects of oyster shell amendment (0, 6, and 12gkg-1) on the mobility and uptake of Cd and Pb by two rice plants (ZY18, japonica and DL5, indica) in contaminated paddy soil. Oyster shell amendment significantly increased the pH of soil and pore water, and decreased the DTPA-extractable Cd concentration in soil, but not the Cd concentration in pore water. Furthermore, the DTPA-extractable Pb concentration in rhizosphere soil was not significantly influenced by oyster shell addition. Application of oyster shell reduced the Pb concentration in pore water and Pb uptake by both cultivars, but excessive application (12gkg-1) resulted in Cd accumulation in tissues for ZY18. Furthermore, oyster shell addition significantly increased the dissolved organic carbon, calcium, and magnesium concentrations in soil pore water, and decreased glutathione and phytochelatin levels in roots, all of which alleviated heavy metal toxicity and improved rice growth. These results demonstrate that amendment with the appropriate amount of oyster shell, combined with rice cultivar type, could simultaneously reduce Cd and Pb accumulation in rice grown in heavy metal-contaminated soil.

The risks of sulfur addition on cadmium accumulation in paddy rice under different water-management conditions

Recently, the application of sulfur (S) has been recommended to control the accumulation of cadmium (Cd) in rice in contaminated paddy soil. However, the effects of exogenous S on Cd transfer in paddy rice systems under different water-management practices have not been systematically investigated. Pot experiments were performed to monitor the composition of soil pore water and the Cd accumulation in iron plaque and rice tissue were compared under different S (0 and 200 mg/kg Na2SO4) and water (continuous and discontinuous flooding) treatments. Sulfur application significantly increased Cd concentrations in soil pore water under discontinuous flooding conditions, but slightly reduced them under continuous flooding. Moreover, the oxidation/reduction potential (Eh) was the most critical factor that affected the Cd levels. When the Eh exceeded −42.5 mV, S became the second critical factor, and excessive S application promoted Cd dissolution. In addition, S addition elevated the Cd levels in iron plaque and reduced the Cd transfer from the iron plaque to rice roots. In rice, S addition inhibited Cd transfer from the rice roots to the straw; thus, more Cd was stored in the rice roots. Nevertheless, additional S application increased the Cd content in the rice grains by 72% under discontinuous flooding, although this effect was mitigated by continued flooding. Under simulated practical water management conditions, S addition increased the risk of Cd contamination in rice, suggesting that S application should be reconsidered as a paddy fertilization strategy.

Cadmium uptake and transport processes in rice revealed by stable isotope fractionation and Cd-related gene expression

Multiple processes are involved in Cd transfer in rice plants, including root uptake, xylem loading, and immobilization. These processes can be mediated by membrane transporters and can alter Cd speciation by binding Cd to different organic ligands. However, it remains unclear which processes control Cd transport in rice in response to different watering conditions in soil. Herein, Cd isotope fractionation and Cd-related gene expression were employed to investigate the key regulatory mechanisms during uptake, root-to-shoot, and stem-to-leaf transport of Cd in rice grown in pot experiments with Cd-contaminated soil under flooded and non-flooded conditions, respectively. The results showed that soil flooding decreased the Cd concentration in soil porewater and, thereby, Cd uptake and transport in rice. Cd isotopes fractionated negatively from soil porewater to the whole rice (flooded: ∆114/110Cdrice-porewater = −0.15‰, non-flooded: ∆114/110Cdrice-porewater = −0.39‰), suggesting that Cd transporters preferentially absorbed light Cd isotopes. The non-flooded treatment revealed an upregulated expression of OsNRAMP1 and OsNRAMP5 genes compared to the flooded treatment, which may partially contribute to its more pronounced porewater-to-rice fractionation. Cd isotopes fractionated positively from roots to shoots under flooded conditions (∆114/110Cdshoot-root = 0.19‰). However, a reverse direction of fractionation was observed under non-flooded conditions (∆114/110Cdshoot-root = −0.67‰), which was associated with the substantial upregulation of CAL1 in roots, facilitating xylem loading of Cd-CAL1 complexes with lighter isotopes. After being transported to the shoots, the majority of Cd were detained in stems (44%–55%), which were strongly enriched in lighter isotopes than in the leaves (∆114/110Cdleaf-stem = 0.77 to 1.01‰). Besides the Cd-CAL1 transported from the roots, the expression of OsPCS1 and OsHMA3 in the stems could also favor the enrichment of Cd-PCs with lighter isotopes, leaving heavier isotopes to be transported to the leaves. The higher expression levels of OsMT1e in older leaves than in younger leaves implied that Cd immobilization via binding to metallothioneins like OsMT1e may favor the enrichment of lighter isotopes in older leaves. The non-flooded treatment showed lighter Cd isotopes in younger leaves than the flooded treatment, suggesting that more Cd-CAL1 in the stems and Cd-PCs in the older leaves might be transported to the younger leaves under non-flooded conditions. Our results demonstrate that isotopically light Cd can be preferentially transported from roots to shoots when more Cd is absorbed by rice under non-flooded conditions, and isotope fractionation signature together with gene expression quantification has the potential to provide a better understanding of the key processes regulating Cd transfer in rice.

Response of Iron and Cadmium on Yield and Yield Components of Rice and Translocation in Grain: Health Risk Estimation

Rice consumption is a major dietary source of Cd and poses a potential threat to human health. The aims of this study were to examine the influence of Fe and Cd application on yield and yield components, dynamics of Cd in pore water, translocation factors, daily dietary intake, and estimation of human health risks. A pot experiment was performed under glasshouse conditions where rice cultivars (Langi and Quest) were cultivated in two dissimilar soils under different levels of Cd (0, 1.0, and 3.0 mg kg−1) and Fe (0, 1.0, and 2.0 g kg−1). The results showed that variation in two rice cultivars in terms of yield and yield-related components was dose dependent. Cadmium concentration in soil pore water was decreased over time and increased with increasing Cd levels but decreased with Fe application. Translocation factors (TFs) from root to straw (TFroot-straw) or straw to husk (TFstraw-husk) were higher than root to grain (TFroot-grain) or straw to grain (TFstraw-grain). The Quest cultivar had 20% lower Cd than the Langi cultivar. Application of Fe at the rate of 1 and 2 g kg−1 soil reduced Cd by 23 and 46%, respectively. Average daily intake (ADI) of Cd exceeded the permissible limit (5.8 × 10−3 mg −1 kg−1 bw per week) when rice plant subjected 1 and 3 mg kg−1 Cd stress with or without Fe application. Results also indicated that ADI value was lower in the Quest cultivar as compared to the Langi cultivar. Estimation of human health risk revealed that the non-carcinogenic risks (HQ &amp;gt; 1) and carcinogenic risks (CR &amp;gt; 1.0 × 10−4) increased with increasing Cd levels in the soil. The application of Fe decreased the human health risks from rice consumption which is more pronounced in Fe 2.0 than in Fe1.0 treatments. The rice cultivar grown in soil-1 (pH 4.6) showed the highest health risks as compared to soil-2 (pH 6.6) and the Quest cultivar had lower health risks than the Langi cultivar.

Belowground productivity varies by assessment technique, vegetation type, and nutrient availability in tidal freshwater forested wetlands transitioning to marsh.

Wetlands along upper estuaries are characterized by dynamic transitions between forested and herbaceous communities (marsh) as salinity, hydroperiod, and nutrients change. The importance of belowground net primary productivity (BNPP) associated with fine and coarse root growth also changes but remains the dominant component of overall productivity in these important blue carbon wetlands. Appropriate BNPP assessment techniques to use in various tidal wetlands are not well-defined, and could make a difference in BNPP estimation. We hypothesized that different BNPP techniques applied among tidal wetlands differ in estimation of BNPP and possibly also correlate differently with porewater nutrient concentrations. We compare 6-month and 12-month root ingrowth, serial soil coring techniques utilizing two different calculations, and a mass balance approach (TBCA, Total Belowground Carbon Allocation) among four tidal wetland types along each of two river systems transitioning from freshwater forest to marsh. Median values of BNPP were 266 to 2946 g/m2/year among all techniques used, with lower BNPP estimation from root ingrowth cores and TBCA (266–416 g/m2/year), and higher BNPP estimation from serial coring of standing crop root biomass (using Smalley and Max-Min calculation methods) (2336–2946 g/m2/year). Root turnover (or longevity) to a soil depth of 30 cm was 2.2/year (1.3 years), 2.7/year (1.1 years), 4.5/year (0.9 years), and 1.2/year (2.6 years), respectively, for Upper Forest, Middle Forest, Lower Forest, and Marsh. Marsh had greater root biomass and BNPP, with slower root turnover (greater root longevity) versus forested wetlands. Soil porewater concentrations of NH3 and reactive phosphorus stimulated BNPP in the marsh when assessed with short-deployment BNPP techniques, indicating that pulses of mineralized nutrients may stimulate BNPP to facilitate marsh replacement of forested wetlands. Overall, ingrowth techniques appeared to represent forested wetland BNPP adequately, while serial coring may be necessary to represent herbaceous plant BNPP from rhizomes as marshes replace forested wetlands.

Effect of biochar amendment on mobility and plant uptake of Zn, Pb and Cd in contaminated soil

This study aimed to assess the effect of rice straw biochar application as a soil amendment on the mobility, availability, speciation and plant uptake of Zn, Pb and Cd in contaminated soil. A pot experiment with maize (Zea mays L.) was conducted using different rates 0, 1, 2, and 5% (w/w) of rice straw biochar. The soil pore water properties; pH, EC, and DOC concentration, the dissolved metal concentrations in soil pore water as well as plant metals uptake were determined at the end of the experiment. The BCR sequential extraction procedure was adopted to determine the effect of biochar on speciation and partitioning of the studied metals.Results showed that the application of biochar is significantly increased the plant shoots biomass by 94.5% with 5% biochar rates compared to untreated soil. Similarly, the soil pore water properties pH, EC, and DOC concentration were also increased with biochar addition compared to untreated soil. The dissolved metal concentrations were decreased in soil pore water with the increasing of biochar rates by 92%, 81.5%, and 90% for Zn, Pb and Cd, respectively at 5% biochar rate. In the same trend, the plant metals uptake reduced significantly with the increasing of biochar dose. Compared to untreated soil, the BCR sequential extraction showed that the biochar addition induced the transformation of the exchangeable metal fractions to oxidizable and residual fractions. These results confirmed the ability of rice straw biochar to immobilize the studied metals and therefore reducing their bioavailability and their uptake by plant.

Are long-term exposure studies needed? Short-term toxicokinetic model predicts the uptake of metal nanoparticles in earthworms after nine months

Uptake of most metal nanoparticles (NPs) in organisms is assumed to be mainly driven by the bioavailability of the released ions, as has been verified in controlled and short-term exposure tests. However, the changeability of NPs and the dynamic processes which NPs undergo in the soil environment, bring uncertainty regarding their interactions with soil organisms over a long period of time. To assess the potential impacts of long-term exposure scenarios on the toxicokinetic of metal NPs, earthworms Eisenia fetida were exposed to soils spiked with pristine Ag-NP, aged Ag-NP (Ag2S-NP) and ionic Ag for nine months, and results were compared to those from a similar short-term (28 days) experiment, conducted under similar conditions. Overall, there were no statistical differences between long-term accumulation patterns in earthworms exposed to pristine Ag-NP and AgNO3, while for Ag2S-NP, the amount of Ag internalized after 9 months was five times lower than for the other treatments. Average Ag concentrations in soil pore water in all treatments did not change over time, however the soil pH decreased and electrical conductivity increased in all treatments. Metallothionein concentrations in exposed earthworms were not statistically different from levels in untreated earthworms. Finally, the short-term toxicokinetic models predicted the bioaccumulation in earthworms exposed to Ag-NP, AgNO3 after nine months on the whole. Although the bioaccumulation for Ag2S-NPs was somewhat under-predicted, the rate of accumulation of Ag2S-NPs is much lower than that of Ag-NPs or AgNO3 and thus potentially of lower concern. Nevertheless, better understanding about the exposure kinetics of Ag2S-NP would help to address potential nano-specific toxicokinetic and toxicodynamics, also of other sulfidized metal NPs.

Conversion of degraded farmlands to orchards decreases groundwater recharge rates and nitrate gains in the thick loess deposits

Conversion of farmlands to orchards has been reported to greatly influence groundwater recharge and quality; however, it has not been fully discussed in regions with arid climate and thick unsaturated zones. This study attempted to connect land use with groundwater recharge and quality in an arid region covered by loess up to 350 m deep. We collected 1300 soil samples for 26 profiles of 10 m deep, which is deep enough for the water and solutes in soil to be under steady state. We selected sampling sites under farmlands and different deep-rooted fruit trees (i.e., apple and apricot) of varying ages. Based on mass balance methods, we determined the chloride concentrations in soil pore water to estimate the recharge rates, and estimated the groundwater pollutant gains by employing nitrate as pollution index. The mean diffuse recharge was estimated as 3.2 ± 1.5–82.3 ± 44.5 mm yr−1 accounting for 1.7 ± 0.8–13.7 ± 7.4% of mean annual precipitation, and the values under farmlands can be reduced by up to 60% after conversion to deep-rooted fruit trees. The mean groundwater nitrate gains ranged 0.7 ± 0.4–16.5 ± 10.4 kg hm−2 yr−1, and the conversion decreased groundwater nitrate gains by up to 90%. The reduced nitrate pollution to groundwater is different from those regions with shallow vadose zones or humid climate where groundwater pollution is getting more severe with increasing fertilizer application. The reduced recharge was found to be the primary control, but it would extend the lifetime of the risk associated with groundwater pollution from nitrate gains. Our results provide useful information for management of agriculture and groundwater resources in regions with thick vadose zones.

Root Uptake of Imidacloprid and Propiconazole Is Affected by Root Composition and Soil Characteristics.

Residual pesticides in soil may be taken up by crops and negatively affect food safety. The uptake mechanism of imidacloprid and propiconazole was studied using wheat roots. The factors affecting root uptake were also studied with different crops and in different soils. Imidacloprid and propiconazole were taken up by wheat roots mainly through the symplastic and apoplastic pathways, respectively. Root protein and lipid contents were the main factors affecting the uptake and accumulation of imidacloprid and propiconazole by different crop roots, respectively. The uptake of imidacloprid and propiconazole in soil by wheat plants was linearly correlated with their concentrations in soil pore water, which were governed by soil characteristics. These results are helpful for understanding and estimating crop uptake of residual pesticides in soils.

Drivers of bacterial diversity along a natural transect from freshwater to saline subtropical wetlands

Tropical coastal wetlands provide a range of ecosystem services that are closely associated with microbially-driven biogeochemical processes. Knowledge of the main players and their drivers in those processes can have huge implications on the carbon and nutrient fluxes in wetland soils, and thus on the ecosystems services we derive from them. Here, we collected surface (0–5 cm) and subsurface (20–25 cm) soil samples along a transect from forested freshwater wetlands, to saltmarsh, and mangroves. For each sample, we measured a range of abiotic properties and characterised the diversity of bacterial communities using 16S rRNA gene amplicon sequencing. The alpha diversity of bacterial communities in mangroves exceeded that of freshwater wetlands, which were dominated by members of the Acidobacteria, Alphaproteobacteria and Verrucomicrobia, and associated with high soil pore-water concentrations of soluble reactive phosphorous, and nitrogen as nitrate and nitrite (N-NOX−). Bacterial communities in the saltmarsh were strongly stratified by depth and included members of the Actinobacteria, Chloroflexi, and Deltaproteobacteria. Finally, the mangroves were dominated by representatives of Deltaproteobacteria, mainly Desulfobacteraceae and Synthrophobacteraceae, and were associated with high salinity and soil pore-water concentrations of ammonium (N-NH4+). These communities suggest methane consumption in freshwater wetlands, and sulfate reduction in deep soils of marshes and in mangroves. Our work contributes to the important goal of describing reference conditions for specific wetlands in terms of both bacterial communities and their drivers. This information may be used to monitor change and assess wetland health and function.