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Soil organic carbon (SOC) storage in paddy profiles plays an important role in regulating terrestrial carbon cycling and global climatic change. The changes in groundwater level may influence the accumulation characteristics of SOC fractions in paddy soil profiles. However, the characteristics of organic carbon storage in paddy profiles under different groundwater levels are not well recognized. In this work, effects of groundwater levels (high and low groundwater levels at 20 and 80 cm depths, respectively) on the distribution of SOC, particulate organic carbon (POC), and mineral-associated organic carbon (MAOC) in red paddy profiles (0–20, 20–40, and 40–60 cm depths) with 40 years of chemical fertilization (CF) and organic fertilization (OF) were investigated. The results showed that compared to a low groundwater level, a high groundwater level resulted in an increase in SOC, POC, and MAOC contents in the profiles. SOC and POC increased by 9.00 ~ 9.11% and 22.89 ~ 26.95% at 0–20 cm depth and increased by 24.02 ~ 52.42% and 36.69 ~ 76.94% at 20–40 cm depth, respectively. MAOC increased by 18.18 ~ 38.28% at 20–40 cm depth. No obvious changes were observed in SOC, POC, and MAOC at 40–60 cm depth between the two groundwater levels. At high groundwater level, the contents of aliphatic and aromatic carbon in soil profiles were higher, but the δ13C values were less than those at low groundwater level. MAOC constitutes main fraction of SOC in all soil profiles, and the values of MAOC/SOC increased obviously with depth. Moreover, the MAOC/SOC values in all soil layers were higher under low groundwater level than under high groundwater level. Correlation analysis showed that SOC, POC, and MAOC were positively correlated with Feo and significantly negatively correlated with Fed-Feo (P < 0.01) under two groundwater levels. Overall, distributions of SOC, POC, and MAOC were strongly influenced by groundwater levels, with higher levels leading to increased storage of these fractions in paddy soil profiles, particularly in 20–40 cm soil layer. MAOC is the main component of SOC in the paddy profiles, and higher groundwater levels are available for POC accumulation, especially for OF treatments. The δ13C value of SOC decreased with increasing groundwater level. These results suggested that groundwater level is a potential strategy to improve carbon sequestration in paddy soils, which offers new insights for understanding the influence of groundwater levels in distribution of SOC fractions in paddy profiles.

There is a growing understanding that methane hydrates (MHs) distributed globally in permafrost and deep sea sediments present an enormous unconventional reservoir of methane (CH4); however, there is also increasing concern about their role in the global climate change. The study focuses on the evaluation of the environmental conditions in the deep Adriatic Sea during the Last Glacial Maximum (LGM, 21.5–18.3 ka BP) and presently with respect to MHs potential occurrence. The MHs phase stability diagram was calculated in order to evaluate the methane hydrate stability zone (MHSZ) by using the Croatian Legacy Data and the digital bathymetry map of the Adriatic Sea obtained from the Croatian Hydrocarbon Agency (CHA). Environmental data from different surveys published in the scientific literature were used to assess the environmental conditions in the deep Adriatic Sea during the LGM and present. The sea level rise of 100 m since the end of the LGM was taken into consideration. The volume of methane in place (MIP) as an estimation of the amount of CH4 stored in MHs deposits at standard conditions of pressure and temperature (SPT, T0 = 273.15 K, P0 = 0.101325 MPa) was calculated by using combined gas law VSPT = (P×V/T) × (TSPT/PSPT). Evaluation of the MHs phase stability diagram for the Adriatic Sea in present environmental conditions has revealed that MHs are exactly at the boundary of stability. This has been calculated for the potential temperature of 13 °C, the salinity of 3.87% (data measured at the E2-M3A deep ocean observatory of the Southern Adriatic), and the average geothermal gradient of 17 °C km−1 reported in the literature and verified by the Croatian Legacy Data of CHA. According to the published literature, LGM deep sea temperature was 2–4 ° C lower and seawater was saltier. Consequently, the estimation of MHSZ during the LGM taking into consideration the temperature of 10 °C and salinity of 3.98% revealed a potential deposit of methane in place (MIP) of more than 415 × 109 m3, the majority of which probably dissociated in the sea/atmosphere system in the last 18 ka. The results have shown that MHs reservoir in the deep sea Adriatic basin shows boundary instability for MHs occurrence which might be of importance for studying the role of MHs in climate change. Further research is needed as follows: (1) thermodynamic modeling in order to understand if the MHs dissociation is concluded; and (2) in the case of the transient condition, seismic data analysis in order to reveal the presence of a relic bottom simulating reflection.

Anthropic activities induce severe metal(loid)s contamination of many sites, which is a threat to the environment and to public health. Indeed metal(loid)s cannot be degraded, and thus accumulate in soils. Furthermore, they can contaminate surrounding ecosystems through run-off or wind erosion. This study aims to evaluate the phytostabilization capacity of Salix viminalis to remediate As and Pb highly contaminated mine site, in a biochar-assisted phytoremediation context and to assess biochar particle size and dose application effects. To achieve this, mesocosm experiments were conducted using the contaminated technosol and four different size fraction of one biochar as amendment, at two application rates (2 and 5%). Non-rooted cuttings of Salix viminalis were planted in the different mixtures. In order to characterize the mixtures, soil pore waters were sampled at the beginning and at the end of the experiment and analyzed for pH, electrical conductivity, and metal(loid) concentrations. After 46 days of Salix growth, roots, stems, and leaves were harvested and weighed, and As and Pb concentrations and distributions were measured. Soil fertility improved (acidity decrease, electrical conductivity increase) following biochar addition, whatever the particle size, and the Pb concentration in soil pore water decreased. Salix viminalis did not grow on the non-amended contaminated soil while the biochar amendment permitted its growth, with a better growth with the finest biochars. The metal(loid)s accumulated preferentially in roots. Fine biochar particles allowed S. viminalis growth on the contaminated soil, allowing this species to be used for technosol phytostabilization.

Sediment contamination in US waterways is an expensive and complicated issue, and as acceptance of nontraditional sediment remediation strategies broadens, novel and efficient methods to assess and monitor the bioavailability of hydrophobic organic contaminants (HOCs) in contaminated sediments will play an important role. In this project, solid phase microextraction (SPME) fibers inside perforated steel tubes were used as in situ passive samplers to measure polycyclic aromatic hydrocarbon (PAH) concentrations in sediment before and after treatment with activated carbon (AC). Two modes of waterjet amendment injection were used to apply the AC. In the first treatment, a single 2-min injection was shot into the center of a test vessel, and in the second treatment, multiple 7-s injections in a grid were placed in sediment. In the single injection, no treatment was observed 5 cm away from the injection, while at 2.5 cm, >90 % decrease of PAH pore water concentration was observed, indicating a similar bioavailability decrease. In the multiple injection experiment, >90 % PAH pore water level reductions were observed throughout the test vessel. Highly contaminated and less contaminated sediments were mixed with 0–5 % AC by weight to develop AC treatment curves. Over 99 % reduction in PAH pore water concentrations and bioavailability was observed in the less contaminated sediment at 3 % AC, while 99 % reduction was never reached even at 5 % AC addition in the highly contaminated sediment. Different treatment curves were observed for the different contaminated sediments. In situ equilibration times were 120, 215, and 250 h for phenanthrene, pyrene, and benzo(a)anthracene, respectively. The results show that in situ SPME is a viable method to observe AC treatment and evaluate reductions in pore water concentrations and bioavailability.

Data from the Elbe River and its tributaries indicate, despite extensive improvement in water quality during the last 15 years, that the respective sediment situation of many priority pollutants has not reached an acceptable level. For the coming decades, risks for downstream sites and stakeholders will persist, mainly due to secondary sources originating from historical pollution of soils and sediments in the catchment area. In practice, a catchment-wide assessment of historical contaminated soil and sediment should apply a three-step approach: (i) Identification of substances of concern (s.o.c.) and their classification into ’hazard classes of compounds’; (ii) identification of areas of concern (a.o.c.) and their classification into ‘hazard classes of sites’; (iii) identification of areas of risk (a.o.r.) and their assessment relative to each other with regard to the probability of polluting the sediments in the downstream reaches. The conversion of this concept has to consider the underlying philosophy of the EU Water Framework Directive, particularly with respect to the analysis and monitoring of priority substances in solid matrices. However, major deficiencies are still in the assessment and prognosis of resuspension processes, and potential approaches to fill this gap are described both in theory and from examples of the Elbe River. The sediment stability testing facilities consist of a unique triple set developed by innovative experimental laboratory and field research. The instrumental facilities consisting of a tube corer and a pressurized channel allow one to measure not only the onset of erosion (critical bed shear stress), but also the erosion rate for different sediment layers. Undisturbed sediment samples were taken from contaminated sites, e.g. in near-bank groyne fields and floodplains, using (i) core sampler (diameter 14 cm, length 150 cm) for sediment erodibility depth profiling and (ii) box sampler (30*70 cm2 top view area, 28 cm depth) for comparing and upscaling the results from the laboratory to the field. Sediment properties such as grain size spectrum (laser beam attenuation), water and gas content were analyzed by a non-intrusive, high frequency, capacity measurement method and bulk density by γ-ray. Sediment core samples from flooded areas in the Middle Elbe indicate, that, except from the uppermost 5 cm and at a depth of from 47 to 48 cm, where the critical shear stress is very low (0.5 Pa), the critical bottom shear stress is between 1.2 Pa and 3.4 Pa, i.e. at a moderate level. Major reasons for the distinct heterogeneity of the erosion stability are differences in consolidation processes, grain size distribution and in the composition of stabilizing exudates in the individual sediment layers. Similar to the erosion stability depth profile, the metal data exhibit short-range heterogeneities; the variations in the individual layers can be explained by different proportions of fine grained components and by an improvement of suspended matter quality in the course of time. A comparison of the metal contents of embanked alluvial soils and unembanked alluvial areas suggests the following causal chain: Recent floodplain areas at low mean water levels exhibiting high concentrations of organic carbon represent the most highly contaminated sites. On the other hand, insignificant pollution has occurred on alluvial areas, which were embanked already at pre-industrial times. In the case of flood events, due to the combination of flooding probability and flow conditions, the most favorable conditions for the deposition of nutrient- and contaminant-rich suspended particulate matter are found in the low level depressions with low current. Within a typical river section of 1 km length in the lower middle Elbe, the groyne fields are recognized as dominant, slack-water zones containing the following nutrient and trace metal loads (reference year 2001, anthropogenic proportions): 287 t organic carbon, 17.6 t phosphorous, 17.4 t nitrogen, and 16.7 t sulfur; 8.6 t zinc, 1.1 t copper, 0.9 t lead, 0.4 t chromium, and 0.2 t nickel, respectively. The estimated nutrient and pollutant loads, deposited on the floodplains and in the river course, clearly demonstrate the specific sink function of both sites. At the same time, however, the results suggest, in contrast to the deposits in the floodplains, that sediments within the river course may partly be remobilized. This means that the longterm sink function can at least temporarily become a significant source character, involving the hazard of a substantial deterioration of the downstream sections of the river basin. In view of the findings of relative low erosion stabilities of groyne field sediments and, in particular, after the extreme Elbe flood from August 2002, a prime question relates to the remobilization risks of these sediments typically enriched in contaminants and nutrients. The combined view on substances, areas and processes of concern in the Elbe catchment - with special emphasis on historical contamination of floodplain soils and sediments, as well as on groyne field sediments, as significant secondary sources of pollution - is a typical example for the holistic river basin approach of the European Water Framework Directive (WFD), both with respect to assessment of ecological risks and the development of remediation measures. In the latter respect, recent developments in ‘soft’ (geochemical and biological) techniques on contaminated soils and sediments, both with respect to policy aspects as well as to technical developments have led to a stimulation of in-situ remediation options, such as sub-aqueous depots, active capping, and application of natural attenuation processes. Limited financial resources require a direction of investments to those sites with the highest efficiencies in risk reduction. Establishing a rough sediment dynamic model, building on tributary/Elbe dilution factors, sedimentation data, suspended particulate matter monitoring data as well as calculations of long-term costs and benefits, based on risk management, could be essential steps in a basin wide river management.

Sorbitol and mannitol have profound effects on plant growth, involving plant photosynthesis, respiration and developmental processes, and are also associated with plant health as rhizosphere exudates. However, studies on soil microbial activity and the quality of sugar alcohols as carbon source additives, especially amendments with sorbitol and mannitol, are rarely studied. Soil nutrients, enzyme activities and microbial communities were measured at 0.25, 0.5 and 1.0 mg sorbitol or mannitol per gram (fresh weight) soil (i.e. mass ratio of sugar alcohol to fresh soil). Increasing soil concentrations of the sugar alcohols led to significantly increased soil concentrations of available potassium and NO3−-N, reduced soil pH and enhanced soil enzyme activities. Soil nutrient levels were enhanced by the sugar alcohols, despite decreasing NO3−-N and available P contents, relative to the control, with mannitol having a greater effect than sorbitol at the same concentration. These two sugar alcohols altered the composition of the soil microbial communities, significantly increasing the soil bacterial communities involved in nitrogen fixation and ureolysis, as well as the proportions of Pseudomonadaceae and Verrucomicrobiaceae which were significantly positively correlated with a variety of enzymes in the soil, particularly invertases. In addition, Xanthomonadaceae, Sphingomonadaceae and Blastocatellaceae were significantly positively correlated with the soil NO3−-N concentration. Sorbitol and mannitol improved soil nutrient environment, accelerated soil nutrient cycling and had screening and improvement effects on soil microbial communities, while mannitol had greater potential than sorbitol.

The nature of dissolved organic matter (DOM) strongly influences heavy metal sorption onto soil. However, the constituents and structures of DOM change continuously as DOM is subjected to microbial decomposition and photodegradation at natural field scales. Thus, this study was designed to explore the effects of chemical changes of DOM on heavy metal sorption onto farmland soil in natural degradation. Fresh DOM (FDOM) and degraded DOM (DDOM) both were extracted from the straw of maize which was extensively planted in Loess Plateau, China. The characteristics of DOM were determined by Fourier transform infrared spectroscopy (FTIR), elemental analysis, excitation-emission matrix (EEM) fluorescence spectra, UV-visible spectra (UV-vis), nuclear magnetic resonance (NMR), and molecular weight analysis. Farmland loess soil in Loess Plateau and heavy metal Cu(II) which can easily form a complex with DOM in soil were employed to investigate the effects of DOM dynamic changes on Cu(II) sorption onto loess through batch tests. Compared with FDOM, DDOM changed significantly in composition including oxygen content, functional group species, aromatic properties, and molecular weight distribution. Oxygen content, aromaticity, and low-molecular-weight fraction (<3 kDa) decreased while aromatic substitution and high-molecular-weight fraction (>10 kDa) increased for DDOM. For these changes, the effects of FDOM and DDOM on heavy metal Cu(II) sorption onto loess were significantly different due to DOM-Cu(II) binding ability varied with FDOM degradation. FDOM promoted Cu(II) sorption onto loess at Cu(II) concentration below 400 mg l−1 while inhibited above 400 mg l−1, but DDOM always showed inhibition effects on Cu(II) sorption onto loess. Moreover, both the promotion and inhibition effects depended mainly on the initial concentrations and pH values of FDOM and DDOM. The results of the present study demonstrate that chemical characteristics of FDOM and DDOM are greatly diverse in components, functional group species, molecular weight distribution, etc. although they are from the same source. The apparent differences can explain their distinct effects on copper sorption onto loess soil. Hence, future researches are supposed to focus on the dynamic changes of DOMs when evaluating their influence on heavy metals environmental behaviors under actual conditions.

In China, soil heavy metal pollution has become a major environmental problem, posing a serious threat to sustainable development. To remediate Pb-contaminated soil more efficiently, quickly, and inexpensively, a micro-nano-sized (2 μm) magnetic composite (MFH) was prepared. The synthesized materials were characterized by using various techniques such as SEM, TEM, XRD, and VSM. In order to study the reaction mechanism of MFH with Pb(II) in soil, the adsorption of Pb(II) by MFH was investigated. The results showed that MFH had good treatment effects on soils with different levels of lead contamination. The smaller water-soil ratio makes MFH more efficient in treating Pb-contaminated soil. MFH has the best remediation effect on neutral soil with pH = 7, followed by acidic lead-contaminated soil. With the prolongation of treatment time, the removal rate of total lead increased rapidly and reached a relatively stable level in about 8 h, with a total lead removal of 101.05 μg g−1. In addition, the high temperature favored the removal of Pb. However, the increase of ionic strength inhibited the removal of total Pb from the soil by MFH. The Pb(II) adsorbed by MFH material can be recovered by magnetic separation, and the recovery rate can reach more than 88% with good recovery and regeneration ability. In short, MFH is an efficient soil in situ remediation material.