Environmental impacts of abandoned dredged soils and sediments Available options for their handling, restoration and rehabilitation

Aim and background  

In the process of creating safe navigable waterways for oil exploitation, the companies operating in the Niger Delta generate tons of sulfidic spoils. These are often deposited over bank, mostly upon fringing mangroves, and abandoned. This leads to a myriad of environmental problems. The extent of these impacts is not exactly known, but was inferred from the activities of oil companies operating in the area. This paper describes the impacts following the disturbance of sulfidic sediment through dredging and by subsequent poor spoil management practices. Environmental impacts of exposed and abandoned sulfidic sediments. The practice of dumping and abandoning sulfidic dredged spoils along canal banks triggers a series of environmental problems leading to extreme acidification, heavy metal pollution, and general habitat degradation which prevent the re-colonization of the sites by native species. The resultant spoil dumps remain bare for several years and they become colonized by invasive species later. Later still they may become attractive to the local population as sites for houses, fishing camps and home gardens, which is nevertheless regarded as a positive impact.     

Characterization of contaminant migration potential in the vicinity of an in-place sand cap

Purpose  

This study characterized the chemical transport potential of polycyclic aromatic hydrocarbons (PAHs) and total petroleum hydrocarbons (TPH) in the vicinity of a sand cap placed in the nearshore zone of a tidal marine embayment.     

Endocrine disruption in a terrestrial isopod under exposure to bisphenol A and vinclozolin

Background, aim, and scope  

In the past decade there has been an increasing awareness about the possible consequences of human and wildlife exposure to endocrine disrupting compounds (EDCs). Bisphenol A (BPA) and vinclozolin (Vz) are EDCs which impacts on vertebrates have been largely investigated. Nevertheless, research on invertebrate effects, especially on soil organisms, are still largely under-represented. This work aims to extend the limited ecotoxicological datasets available and to provide tools to assess the effects of EDCs on the terrestrial species, using Porcellio scaber (Crustacea: Isopoda) as a model organism.     

Effect of 7-year application of a nitrification inhibitor, dicyandiamide (DCD), on soil microbial biomass, protease and deaminase activities, and the abundance of bacteria and archaea in pasture soils

Purpose

The nitrification inhibitor dicyandiamide (DCD) has been shown to be highly effective in reducing nitrate (NO₃ ^?) leaching and nitrous oxide (N₂O) emissions when used to treat grazed pasture soils. However, there have been few studies on the possible effects of long-term DCD use on other soil enzyme activities or the abundance of the general soil microbial communities. The objective of this study was to determine possible effects of long-term DCD use on key soil enzyme activities involved in the nitrogen (N) cycle and the abundance of bacteria and archaea in grazed pasture soils.

Materials and methods

Three field sites used for this study had been treated with DCD for 7 years in field plot experiments. The three pasture soils from three different regions across New Zealand were Pukemutu silt loam in Southland in the southern South Island, Horotiu silt loam in the Waikato in the central North Island and Templeton silt loam in Canterbury in the central South Island. Control and DCD-treated plots were sampled to analyse soil pH, microbial biomass C and N, protease and deaminase activity, and the abundance of bacteria and archaea.

Results and discussion

The three soils varied significantly in the microbial biomass C (858 to 542 μg C g^?1 soil) and biomass N (63 to 28 μg N g^?1), protease (361 to 694 μg tyrosine g^?1 soil h^?1) and deaminase (4.3 to 5.6 μg NH₄ ⁺ g^?1 soil h^?1) activity, and bacteria (bacterial 16S rRNA gene copy number: 1.64?×?10⁹ to 2.77?×?10⁹ g^?1 soil) and archaea (archaeal 16S rRNA gene copy number: 2.67?×?10⁷ to 3.01?×?10⁸ g^?1 soil) abundance. However, 7 years of DCD use did not significantly affect these microbial population abundance and enzymatic activities. Soil pH values were also not significantly affected by the long-term DCD use.

Conclusions

These results support the hypothesis that DCD is a specific enzyme inhibitor for ammonia oxidation and does not affect other non-target microbial and enzyme activities. The DCD nitrification inhibitor technology, therefore, appears to be an effective mitigation technology for nitrate leaching and nitrous oxide emissions in grazed pasture soils with no adverse impacts on the abundance of bacteria and archaea and key enzyme activities.     

Modeling impacts of climate change on carbon dynamics in a steppe ecosystem in Inner Mongolia,China

Purpose  

In this study, a process-oriented biogeochemistry model, denitrification–decomposition (DNDC), was employed and adapted to interpret and integrate the field observations that the tested ecosystem was a weak sink of atmospheric carbon dioxide (CO₂) in 2004 but a strong source in 2005 during the growing seasons. Then we applied the model to predict long-term impacts of climate change on carbon (C) dynamics in the semiarid grassland.     

Effect of soil sealing on the microbial biomass,N transformation and related enzyme activities at various depths of soils in urban area of Beijing,China

Purpose  

Sealing of soils prevents the exchange of gas, water and nutrient between soil and other environmental compartments, and affects urban N flux, thereby resulting in certain negative impacts on soil functioning and urban environment. However, little information is available on the biogeochemical cycling and biological activities after sealing of soils in urban areas. The aim of this study was to assess the effects of soil sealing on N transformation and associated microbial properties.     

Temporal dynamics of iron-rich, tropical soil organic carbon pools after land-use change from forest to sugarcane

Background, aim, and scope  

Land-use change can significantly influence carbon (C) storage and fluxes in terrestrial ecosystems. Soil–plant systems can act as sinks or sources of atmospheric CO₂ depending on formation and decomposition rates of soil organic matter. Therefore, changes in tropical soil C pools could have significant impacts on the global C cycle. This study aims to evaluate the impacts of long-term sugarcane cultivation on soil aggregation and organic matter, and to quantify temporal dynamics of soil organic matter in cultivated sugarcane plantation soils previously under a tropical natural secondary forest.     

Effects of vegetation restoration and slope positions on soil aggregation and soil carbon accumulation on heavily eroded tropical land of Southern China

Background aim and scope  

Soil organic carbon (SOC) accumulation is strongly affected by soil erosion and deposition that differ at slope positions of a watershed. However, studies on the effects of topography on soil aggregation and SOC dynamics, especially after the implementation of vegetation restoration, are rare. Poorly understood mechanisms and a lack of quantification for the suite of ecological benefits brought by the impacts of topography after planting further obstructed our understanding of terrestrial ecosystem carbon (C) sequestration. The purposes of this study are to (1) quantify the impacts of vegetation restoration on size and stability of soil aggregates and the sequestration of C in soil and (2) to address the impacts of various slope locations on aggregates and SOC distribution.     

Impact of in-season split application of nitrogen on intra-panicle grain dynamics,grain quality,and vegetative indices that govern nitrogen use efficiency in sorghum

Background

The correct rate and timing of nitrogen (N) has the potential to improve sorghum productivity through modified grain yield components and quality. The impacts of in-season split application of N have little documentation.

Aim

An experiment was conducted to determine the optimum rate and timing of N to relate vegetative indices that govern nitrogen use efficiency and to maximize grain yield and quality under different soil types.

Methods

Pioneer 86P20 was grown in three environments on two different soil types following a completely randomized block design with nine N application treatments. Treatments included differing N rates applied at critical developmental stages of sorghum (planting, panicle initiation, and booting), accompanied with high temporal aerial phenotyping.

Results

Opportunities to increase grain protein content while using split N applications were observed, with panicle initiation identified as a critical developmental stage. In-season split application of N enhances grain yield under low soil mineral N. Split application of 31 kg N ha⁻¹ each at the time of planting, panicle initiation, and booting emerged as optimum N treatment to increase protein content in sorghum. Vegetative indices, that is, normalized difference vegetation index and normalized difference red edge index are capable of predicting grain yield and protein content, respectively. Intra-panicle grain numbers and weights were altered significantly at different portions within panicles, with an opportunity to enhance yield potential at the bottom portion. The strong stay-green trait in this hybrid locked a large proportion of nitrogen in the leaves, which warrants the need for balancing stay-green and senescence in sorghum improvement programs.

Conclusions

Findings highlight that in grain sorghum remobilization of residual leaf N into grain is a target to increase yield and grain quality. An optimized stay-green trait balanced with senescence is recommended for enhancing sorghum yield potential.     

Enhanced sorption of polycyclic aromatic hydrocarbons by soil amended with biochar

Purpose  

Polycyclic aromatic hydrocarbon (PAHs) are ubiquitous pollutants in agricultural soils in China. Biochar is the charred product of biomass pyrolysis, which is widely applied to soils to sequestrate atmospheric carbon dioxide and guarantees a long-term benefit for soil fertility. Knowledge about the impacts of various biochars on soil sorption affinity remains obscure. In this study, we evaluated the effects of various biochars on PAHs sorption to biochar-amended agricultural soil.     

Application of bioassays with <Emphasis Type="Italic">Enchytraeus crypticus</Emphasis> and <Emphasis Type="Italic">Folsomia candida</Emphasis> to evaluate the toxicity of a metal-contaminated soil,before and after remediation

Purpose  

A contaminated soil was amended to reduce bioavailability of metals (As, Cd, Cu, Pb, and Zn) and to modify its potential environmental impacts. Reproduction toxicity tests using two different soil invertebrates, Enchytraeus crypticus and Folsomia candida, were used to evaluate efficiency of soil amendments to reduce metal availability.     

Leaching impacts Ni toxicity differently among soils but increases its predictability according to nitrification assay

Purpose  

Deriving toxicity thresholds through bioassays has become the scientific basis for the risk assessment of metal contamination in soils, but few studies have been reported for Ni toxicity in Chinese soils. In addition, although leaching has been recommended to increase the ecological relevance of the output of soil toxicity bioassays, its impacts on Ni threshold and soil solutions in soils remained to be shown. Therefore, in this study, 17 soils were collected throughout China and were assessed for Ni toxicity using substrate-induced nitrification (SIN) assay for both un-leached and leached treatments. Meanwhile, soil solutions of all Ni treatments were extracted and analyzed. This study provides information for the development of a terrestrial biotic ligand model (TBLM) for Ni in Chinese soils.     

Identification of most susceptible soil parameters for Latosol under simulated acid rain stress using principal component analysis

Purpose  

Acid rain is a problem of increasing agricultural, environmental, and ecological concerns worldwide. In recent years, coupled studies have been conducted to evaluate impacts of simulated acid rain (SAR) on Latosol in China. However, no efforts have been devoted to investigating which soil parameters are most sensitive to the influences of SAR. In this study, we addressed the issue using the principal component analysis (PCA) and principal factor analysis (PFA) techniques.     

Decomposition of Bacillus thuringiensis (Bt) transgenic rice residues (straw and roots) in paddy fields

Background, aim, and scope  

Genetic modification of commercial crops may affect their decomposition and nutrient cycling processes in agricultural ecosystems. Intensive rice cultivation under partially submerged conditions (paddy rice) is an important and widespread cropping system, particularly in the tropics, yet there is little data on the decomposition of Bt rice residue under field conditions. We investigated straw and root decomposition of rice modified to express the Cry1Ab protein of Bacillus thuringiensis (Bt) to kill lepidopteran pests, compared with a parental non-Bt isoline. The objective of this study was to assess the possible impacts of cry gene transformation of rice on residue decomposition under intensive rice cultivation with long period of submergence.     

Nitrogen deposition influences nitrogen isotope composition in soil and needles of <Emphasis Type="Italic">Pinus massoniana</Emphasis> forests along an urban-rural gradient in the Pearl River Delta of south China

Purpose  

Atmospheric nitrogen (N) deposition remains globally and regionally a significant N source in forest ecosystems, with intensive industrial activities. Stable N isotope ratio (δ¹⁵N) is a useful indicator widely adopted to assess environmental and ecological impacts of anthropogenic N inputs. On the basis of temporal changes in tree ring δ¹⁵N established recently, the present study investigated the influence of N deposition on δ¹⁵N in needles of Masson pine (Pinus massoniana L.) and forest soil along an urban–rural gradient in the Pearl River Delta of south China.     

Incipient motion for gravel particles in clay-silt-gravel cohesive mixtures

Purpose

Incipient motion plays an instrumental role in understanding various aspects of sediment transport, such as river bed aggradation and degradation, channel design, bank erosion, scour around bridge piers, and water quality issues.

Materials and methods

Experiments were conducted to study the incipient motion of gravel particles in three types of bed material, i.e., gravels only, silt-gravel mixture, and clay-silt-gravel mixture. The clay content varied from 10 to 50% in the clay-silt-gravel mixture while silt and gravel were in equal proportion by weight. Samples were taken out from the prepared cohesive bed for the determination of their bulk density, unconfined compressive strength, and water content. The incipient motion was observed visually, which corresponded to the beginning of movement of gravel particles in the mixture. The shear stress corresponding to incipient motion was computed using measured flow depth and slope of water surface. The physical appearance of the top layer of cohesive bed was observed visually at the end of experiment.

Results and discussion

The effects of clay content, water content, unconfined compressive strength, and bulk density of the mixture on the critical shear stress were investigated using the data collected in this study on clay-silt-gravel mixture along with the data from previous studies. A relationship is proposed for the computation of critical shear stress of gravel particles in the cohesive mixtures. The physical appearance of the top surface of the bed for clay-silt-gravel mixture has also been investigated with varying percentages of clay content in the mixture.

Conclusions

High clay percentage significantly increased the critical shear stress. The presence of silt lowers the critical shear stress especially when there is low clay content (up to 20%) in the mixture. The clay content along with the bulk density was found to be the dominant parameters that affect the incipient motion of the gravel particles in the cohesive mixtures. The proposed relationship for critical shear stress was found to be in good agreement with the observed ones.

     

Changes of soil particle size fraction along a chronosequence in sandy desertified land: a fundamental process for ecosystem succession and ecological restoration

Purpose

Soil is composed of particles of different sizes. A fraction of soil particles with different sizes has many vital effects on soil properties such as soil texture, soil porosity, and soil nutrient content. We intended to explore what change took place in soil particle distribution along the chronosequence of restoration and to address what implication this change has for ecosystem restoration.

Materials and methods

Six restoration ecosystem sites were selected to form a chronosequence in a sandy desertified region, northern China. We examined the relative content of soil particles with different sizes and established an index of enrichment ratio to reflect the change trend of soil particle size fraction.

Results and discussion

It was showed that soil substrate in this region is mainly composed of coarse sand (>0.25 mm) and fine sand (0.25–0.10 mm), the fraction of which are averagely 23.62 and 57.07 %, respectively. These characteristics make soil coarse, loose and erodible, and to be one of the reasons why sandy desertification was quickly developed in this region. In sandy desertification process, the grades of soil particles were air-classified. Fine sand was strongly enriched 1.36 times than average level, while very fine sand (0.10–0.05 mm) and silt and clay (<0.05 mm) were strongly diluted 0.14 and 0.22 times than average level, respectively. Along with the chronosequence of restoration, very fine sand and silt and clay were deposited and markedly enriched. This change in soil particle size fraction along the chronosequence has many fundamental roles for the subsequent restoration succession of sandy land ecosystem, such as promoting plant growth, strengthening soil anti-erodibility, leading to species replacement and community succession.

Conclusions

From this research, it could be concluded that the response of soil particle size fraction to ecological restoration in sandy desertified lands is ecologically valuable, demonstrating that a positive cycle between plant and soil was formed to strengthen the stability of soil-plant system, and the ecosystem has the ability of self-recovering or self-organizing.

     

The importance of dust material in urban soil formation: the experience on study of two young Technosols on dust depositions

Purpose

The volume of dust deposition on the soil surface in Moscow is big enough and make several tens of grams per square meter annually. The role of dust as a soil-forming material is especially high in places with practically no other soil parent materials. It is necessary to consider solid atmospheric precipitation as a parent soil material in urban conditions and its impact on soil properties.

Materials and methods

Samples of two soil bodies were taken near two major highways of Moscow, and airborne solid deposit samples were collected from the roadside barrier in summer and from plant leaves after snowmelt. The fallout samples were studied by methods used for soil because of its silicate matrix (Si～30 % total). Main complex characteristics of samples were obtained by chemical analysis and with a scanning electron microscope with energy-dispersive X-ray spectrometer. Bulk elemental composition, available phosphorus and potassium, carbonates, organic carbon and oil hydrocarbon contents, pH, redox potential, magnetic susceptibility, and particle-size distribution of dust and soils were determined.

Results and discussion

Near the highways, where the process of dust transfer is activated, there are possibilities of dust inclusion into soil and formation of new soil horizons on these deposits. Pedofeatures are formed during a very short period of time. The soil-forming processes are connected with both soil organic matter and mineral compound transformation. Chemical properties of the studied soils correspond to those of usual Moscow soil horizons and dust samples studied previously by Prokofyeva et al. (2011) and Prokof’eva et al. (2015). It was established that atmospheric solid aerosol imports organic carbon, carbonates, and other salts; pollutants such as oil hydrocarbons; and heavy metals into the soil. Airborne deposits influence soil physical properties by enriching the soil with clay and coarse silt fractions.

Conclusions

Investigation of dust deposit composition provides data for characterizing material being continuously deposited on the urban soil surface. The atmospheric fallouts together with construction waste and natural rocks provide the common geochemical properties of urban soils.

     

Soil porosity in physically separated fractions and its role in SOC protection

Purpose

Processes that lead to soil organic carbon (SOC) protection depend on both soil porosity and structure organization, as well as chemical and biological properties. In particular, the soil micro-nano porosity (<30 μm) regulates microorganism accessibility to the soil pore system and offers surfaces for organic carbon adsorption and intercalation into soil minerals. The aim of this work was to investigate how pore size distribution can selectively protect specific carbon pools in different aggregate size fractions, by considering the effects of long-term application of farmyard manure (FYM) and mineral (Min) fertilization.

Materials and methods

Macroaggregates (250–2000 μm), microaggregates (53–250 μm), and silt–clay (<53 μm) fractions of three different soils (clayey, peaty, and sandy) were separated by wet sieving technique and then subjected to chemical and physical analysis. Sample porosity and pore size distribution were analyzed using mercury intrusion porosimetry (MIP), while SOC chemical structure was characterized by means of nuclear magnetic resonance (¹³C cross-polarization–magic angle spinning nuclear magnetic resonance (CP MAS ¹³C NMR)) and diffuse reflectance infrared Fourier transform (DRIFT) spectroscopies.

Results and discussion

Results showed that FYM increased organic (OC) and humic carbon (HC) content compared to the Min fertilization and unfertilized soils. However, it caused a gradual decrease in O,N-alkyl C, and alkyl C of humic C from macroaggregate to silt–clay fractions, suggesting an advanced state of humic component degradation as revealed by CP MAS ¹³C NMR, DRIFT analyses. MIP analysis showed a clear increase of micropores (5–30 μm) and cryptopores (0.0035–0.1 μm) from macroaggregate to silt–clay fractions, while minor differences were observed among the treatments. The application of principal component analysis to mineral soil fractions identified the formation of three main clusters, where (i) macroaggregates of clayey soil were mainly associated to cryptopores and OC and (ii) microaggregates and silt–clay fraction were mainly isolated by carbonyl C, ultramicropores, and total porosity. The third cluster was associated with medium and fine sand of the sand soil fraction as coupled with O,N-alkyl C, anomeric C, mesopores, and HC/OC ratio.

Conclusions

Overall, this study indicates that pore size distribution may be a valuable indicator of soil capacity to sequester carbon, due to its direct influence on SOC linkages with soil aggregates and the positive effects against SOC decomposition phenomena. In this context, micropore- to nanopore-dominated structures (e.g., clayey soil) were able to protect OC compounds by interacting with mineral surfaces and intercalation with phyllosilicates, while meso/macropore-dominated structures (i.e., sandy soil) exhibited their low ability to protect the organic components.

     

Effects of nitrogen fertilizer application rates on nitrate nitrogen distribution in saline soil in the Hai River Basin,China

Background and Objectives  

Soil nitrate nitrogen (NO₃ ⁻-N) accumulation is related closely to NO₃ ⁻ leaching, which is an important issue in groundwater pollution, especially in intensive agricultural areas with saline soils where volumes of water are used in irrigation to avoid salt accumulation in the root zone. However, in the saline environment in Hai River Basin, China, the importance of detailed research into NO₃ ⁻-N distribution in the root zone has not been adequately recognized. Considering the impacts of eco-environmental system N and crop production, the present study aimed at contributing to an understanding of the effects of N application rate on soil NO₃ ⁻-N distribution, NO₃ ⁻-N residue, N loss, and maize (Zea mays L.) yield in this region.