Journal of Soils and Sediments最新文献

Background and Aim

Continuous monocropping with high nitrogen (N) fertilizer input substantially increases greenhouse gas (GHG) emissions in maize-based agroecosystems in the North China Plain (NCP). Introducing soybeans as an intercrop with maize and partially substituting urea with manure might effectively decrease GHG emissions. The aim of this study was to quantify the synergistic effect of maize-soybean intercropping and manure on soil GHG emissions.

Methods

A two-year field experiment with three cropping systems (maize monocrop, soybean monocrop, and maize-soybean intercrop) and four N treatments (control, urea, manure, and manure + urea) was carried out at Luancheng Agro-Ecosystem Experimental Station in the NCP. All N treatments, except the control, received 150 kg N ha⁻¹season⁻¹, either full dose as a basal application or two equal split applications.

Results

Results showed that all treatments contributed as a net source of N₂O and CO₂ fluxes but acted as a net sink of CH₄ fluxes. In both cropping seasons, intercrops had significantly lower N₂O emissions compared to monocropping systems, with 38% and 14% less emissions than maize monocrops in 2018 and 2019, respectively. Additionally, maize monocrops had significantly higher soil CO₂ emissions than other systems, while maize-soybean intercropping had 12% and 13% less CO₂ emissions than maize monocrops in 2018 and 2019, respectively. Among fertilized treatments, manure-treated soils emit notably lower N₂O fluxes compared to sole urea treatments. In this study, N₂O and CO₂ fluxes had a strong positive correlation with soil mineral N concentrations, soil temperature, and moisture content. Possibly due to more efficient N utilization, intercrop soils exhibited significantly lower NH₄⁺ and NO₃⁻ concentrations, leading to reduced nitrification and denitrification in the system, resulting in lower N₂O emissions from maize-soybean intercrops.

Conclusion

Our findings indicate that intercropping maize and soybean reduces soil NH₄⁺ and NO₃^– concentrations, as well as significantly decreasing soil N₂O and CO₂ emissions when compared to traditional maize monoculture. Therefore, due to its potential for reducing soil GHG emissions, maize-soybean intercropping can be regarded as an effective alternative cropping system to the prevailing maize-dominant monoculture to develop a sustainable agroecosystem in the NCP region.

Purpose

The objective of this study was to investigate the spatiotemporal distribution patterns of two common heavy metals, Cd and Pb, in urban rivers in plains, and analyze the impact of weak hydrodynamics on the transport of heavy metals, and guide their ecological risk assessments in these regions.

Materials and methods

Two field surveys (wet and dry seasons) were conducted at a total of 36 sites in the tributaries of Gehu Lake, located in a plain region in China. The European Community Bureau of Reference (BCR) extraction method was employed to analyze the components of Cd and Pb. The Nemello index and ecological risk index were calculated to assess their pollution levels and ecological risks.

Results and discussion

Cd primarily accumulated at the river mouths, while Pb was predominantly concentrated near the discharge sources. The mobile fractions of Cd were more likely to be released and migrate downstream, and thus the total Cd content demonstrated a significantly negative correlation with these mobile forms (p < 0.05). In contrast, although Pb had a greater proportion of mobile fractions, they were readily re-adsorbed onto particles and settled near the source. The source area displayed notable pollution with Pb, whereas the downstream river mouth area posed a high risk of Cd pollution.

Conclusions

The results indicated that the weak river hydrodynamics within plains amplify the impact of heavy metal mobility on their behaviors, producing a “screening effect” on Pb and Cd and resulting in distinct distribution patterns in sediments. These findings can guide the ecological risk assessment of heavy metals in aquatic ecosystems within plains.

Purpose

Most forms of Mercury (Hg) in soil have significant destructive effect on ecosystems and food safety because of enormous toxicity. The existing treatment methods have drawbacks such as high energy consumption, complex operation, long remediation cycle, and secondary pollution. Therefore, this study aims to develop a governance method with low energy consumption, simple operation, short execution cycle, and no secondary pollution.

Methods

A new system was set up to remove leachable Hg²⁺ from soil and its performance was evaluated. The system consisted of photochemical vapor generator (PVG, for Hg²⁺ removal), dielectric barrier discharge (DBD) trapping reactor (for collection of removed Hg⁰). In the presence of organic acids, leachable Hg²⁺ was converted to gaseous Hg⁰ by UV irradiation in the PVG, and transported to the DBD trap by air for collection of the removed Hg²⁺. Soil samples in PVG were taken into glass tubes at specific time and then added aqua regia, analyzed using ICP-MS after digested in a boiling water bath. The performance of DBD trap was analyzed by connecting with ICP-MS.

Results

This study achieved the removal of leachable Hg²⁺ from soil under the UV excitation, the subsequent conversion of escaped gaseous Hg⁰ to solid and enrichment in DBD trap. The factors affecting the efficiencies of photochemical reaction, transport and collection were carefully investigated. Under the optimized conditions, the removal efficiency of 2.00 mg L⁻¹ leachable Hg²⁺ in soil reached 95.0% within 1 h. Even in the presence of 15 interfering ions separately containing 50 mg L⁻¹, good remediation effects can still be achieved. The capture rate of gaseous Hg⁰ by DBD trap is close to 100%. The system can achieve Hg pollution control in 10 types of soil, demonstrating great promotion value.

Conclusions

This system utilizes PVG theory and DBD low-temperature plasma device to construct a safe, green, simple, and inexpensive method for removing leachable Hg²⁺ from soil.

Graphical Abstract

Purpose

The Cr(VI) removal capacity of green synthesized nano-zero-valent iron (GnZVI) using tea polyphenols (TPs) remains limited. To improve their application in contaminated soil and groundwater, the GnZVI was modified. This is necessary for in-situ remediation of heavy metal-contaminated soil and groundwater.

Materials and methods

The GnZVI-based carbon-composite (L&GnZVI@BC) was successfully constructed via the synergistic effect of L-cysteine modification and biochar support. The Cr(VI) removal capacity and transportability of L&GnZVI@BC were investigated in soil–water system by batch and column experiments.

Results and discussion

Comparison with two materials of GnZVI separately modified by L-cysteine (L-GnZVI) or supported by biochar (GnZVI@BC)), GnZVI composite with a combination modification of L-cysteine and biochar (L&GnZVI@BC, L-cysteine/biochar/Fe = 0.1/0.1/1) showed a much higher Cr(VI) removal capacity in soil and groundwater. The synergistic effect of the reduction of L-cysteine functional groups and the dispersibility of biochar support can enhance the transportability of L&GnZVI@BC in water-saturated sand media for more Cr(VI) adsorption at neutral pH; while that improved the soluble Fe(II) released from composite for the higher reduction of Cr(VI) into Cr(III) at acidic pH. Particularly, L&GnZVI@BC favored more Cr(III) generation during transport in porous media at lower pH when applied in the treatment of Cr(VI) contamination.

Conclusion

This research highlights that the modification of both L-cysteine and biochar was beneficial to sufficient transport and efficient remediation in Cr(VI)-contaminated soil and groundwater environments at different pH ranges. This study’s results provide a theoretical support for the practical application of nZVI composites in in-situ remediation of Cr(VI)-contaminated soil and groundwater via an environmental-friendly approach.

Purpose

Arsenic (As) and antimony (Sb) are toxic elements that usually co-occur in paddy soils due to their chemical similarity. Those elements are redox-sensitive and shift their species across the soil–water interface (SWI) where redox potentials change in every millimeter. In the real world, the distribution and speciation of As and Sb in soils are often influenced by external redox disturbance, but their temporospatial response remains poorly understood. This study aimed to address this gap by introducing external disturbance by adding nitrate into the overlying water.

Methods

Daily changes in the profile of As, Sb, iron (Fe), and sulfur (S) were measured using ICP-MS and the In-situ Porewater Iterative (IPI) sampler array.

Results

The results revealed a rapid formation of a sink for As and Fe at the oxic-anoxic transition zone within one day, persisting for at least 6 days and extending to ~ 30 mm below the SWI. Moreover, Sb was re-mobilized in the same area as the As and Fe sink, but the re-mobilized Sb zone was weaker, lasting only 4 days and extending to ~ 20 mm below the SWI. The presence of aqueous ferrous Fe below the transition zone facilitated the formation of Fe and As sink, while the presence of aqueous sulfide below the transition zone hindered the development of the Sb source.

Conclusion

These findings highlight the importance of carefully evaluating the impact of nitrate-based fertilizers or stabilization reagents when applied in As and Sb contaminated soils.

Purpose

Soil Phosphorous (P) availability is critical for many important ecological processes and oil-contaminated soil remediation. Despites a few studies confirmed directly effects of crude oil exposure on soil Phosphorus-cycling (P-cycling), how soil microbes and functional genes affiliated with P-cycling respond to crude oil remains poorly understood.

Methods

Here, metagenomics was implemented to analyze variations in the microbial community structure and potential functions associated with P transformation in the coastal soil contaminated by crude oil.

Results

Results showed a dramatic scarcity of P in the contaminated soil. Microbial inorganic P solubilization was governed by genes gcd and ppx in CK soil. In contrast, genes encoding C-P lyase (phnGHIJKLN) and alkaline phosphatase (phoA) displayed significantly greater abundances in the contaminated soils. Taxa annotation revealed that oil contamination altered the structure of the P-cycling microbial community with a bias towards those with oligotrophic characteristics. Specifically, the oil-contaminated soils were characterized by a stronger contribution of Proteobacteria, Ascomycota and Firmicutes. Overall, the strategy for acquiring P in the CK is inorganic P solubilization, while it converted to organic P mineralization under petroleum contamination. Soil N/P ratio played a key role in affecting P-cycling functional genes.

Conclusion

Our results highlighted that oil contamination with unbalanced N/P ratio greatly altered the microbial strategy for obtaining available P (AP) in soil. A better understanding of P-cycling mechanism exposed to oil contamination and further scientifically regulating it may set the stage for in-depth improvement for current bioremediation practices.

Purpose

Polder soils develop from oceanic and lacustrine sediments covered with seawater, brackish water, and freshwater after artificial drainage. Because there are several concerns regarding the agricultural use of polder soils, soil genesis and properties have been considerably surveyed, mainly focusing on problematic soils developed from fine sediments. Although sediments have a wide range of particle size distributions due to different sedimentary conditions, particle size of parent materials have not been well addressed to understand the soil developmental process. In this study, Japanese polders with different reclamation ages and sedimentary conditions were surveyed to clarify the soil formation process and factors affecting pedogenesis.

Materials and methods

Soil samples were collected from 15 soil profiles in six Japanese polders under different land use types. Sedimentary conditions of polders were evaluated from particle size distributions using the hydrodynamic classification proposed by Pejrup (The triangular diagram used for classification of estuarine sediments: a new approach. Tide-influenced Sediment Environ Facies, pp 289–300, 1988). The major soil-forming factors of polders were extracted by principal component analysis (PCA) using general soil properties.

Results and discussion

Brackish lake and inner bay polders were characterized by calm hydrodynamic conditions comprising fine particles. Two polders reclaimed from a shallow inland sea were characterized by violent hydrodynamic conditions. Sandy sediments were also characteristic of immature soils reclaimed from a freshwater lake and an estuarine tidal flat. Soils on polders developed under calm hydrodynamic conditions enabled the accumulation of high total carbon content. The soil-forming process in the brackish bay oxidized pyrite, leading to an acidic soil reaction. Conversely, soils developed from sandy sediments were characterized by low iron content. The PCA extracted two factors explained by particle size and soil reaction relating to acidification and salt leaching.

Conclusion

Polder soils can be mainly discriminated by their particle size distributions, which are characterized by hydrodynamics under the sedimentary conditions, and the polder soil development is affected by water management in land uses after artificial drainage.

Purpose

Constructed wetlands have profound influences on efficient wastewater purification and treatment. However, what extent and how different kinds of constructed wetland can effectively influence the distribution of nutrients content and mineralization? Specially, whether the response of the changes of soil nutrients content and mineralization to different amounts of litter input was consistent? It has not been resolved.

Methods

In this study, five constructed wetland systems (i.e., the Circulating Water Treatment Pond 1 (CW), Recirculating Water Treatment Pond 2 (RCW), Reclaimed Water Treatment Pond (RW), Plant Oxidation Pond (POP), and Mixed Oxidation Pond (MOP)) in the Beijing Olympic Forest Park were studied. CW, RCW, and RW belong to the composite vertical-flow systems, while POP and MOP belong to the free surface systems. Field litter input (5 and 20 g, respectively) with five replicates applied to the constructed wetland systems were conducted. The contents of soil total carbon (TC), soil total nitrogen (TN), soil total phosphorus (TP), and phosphorus mineralization rates were quantified. Ordinary kriging interpolation was used to characterize the spatial distribution of soil TC, TN, TP and phosphorus mineralization rates.

Results

The results showed that the contents of soil TC and TN in the composite vertical-flow systems (CW, RCW, and RW) were greater than those in the free surface systems (POP and MOP), while it was contrary for the content of soil TP. Soil organic phosphorus (accounting for 45.80 ± 8.12%) and inorganic phosphorus (accounting for 51.81 ± 7.46%) were the main components of soil TP. Phosphorus mineralization rates in the composite vertical-flow systems were greater than the free surface systems. The phosphorus mineralization rates were the smallest in MOP (-2.06 mg·kg⁻¹·d⁻¹) and the highest in RW (0.32 mg·kg⁻¹·d⁻¹). Litter input decreased the contents of soil TC and TN in the composite vertical-flow systems and MOP, while increased in POP. Soil TP content after the litter input increased in CW, RCW, and MOP, while decreased in RW and POP. The litter input was beneficial for improving the phosphorus mineralization rates. The effects of 5 g litter input on the changes of the contents of soil TC, TN, TP and phosphorus mineralization rates were stronger than that of 20 g litter input.

Conclusion

Our study has supplemented the inconclusive results of the influences of different constructed wetlands and amounts of litter input on soil nutrient content and mineralization. The findings of this study could provide data support for better constructed wetland management, which could help the managers understand the mechanisms of improving the efficiency of wastewater treatment in constructed wetlands.