Tidal Flat Soil Research Articles

Research on adhesion properties of tidal flat soil on metal surface and discrete element simulation

The adhesion property of soil on the metal surface was tested by the orthogonal experiment with 4 factors and 3 levels based on piston pull out method. A regression model of adhesion stress and the factors including moisture content(X1), pressing time(X2), settling time(X3) and separation velocity (X4) was established. The experiment results show that the influence of each factor on adhesion stress is ranked as X1≈X2≈X3>X4>X3X4, and the adhesion stress shows an ‘S’ curve with the increase of separation velocity. The DEM parameters of the soil were calibrated based on the test results, and the contact and disturbance state of soil particles during the test were studied by discrete element method (DEM) using JKR model. The simulation tests show that the maximum adhesion stress occurs when the particles are about to separate from the probe surface, and the soil disturbance state is hierarchical.

Source and stability of soil organic carbon jointly regulate soil carbon pool, but source alteration is more effective in mangrove ecosystem following Spartina alterniflora invasion

Spartina alterniflora invasion seriously affects blue carbon function in mangrove ecosystems. However, the mechanisms by which S. alterniflora invasion affects the sources and stability of soil organic carbon (SOC) in mangrove ecosystems have not been fully elucidated. In this study, stable isotopes and nuclear magnetic resonance spectroscopy techniques were used to investigate the impacts of S. alterniflora invasion on SOC sources, decomposition characteristics, and SOC pool stability in the Zhangjiang Estuary, Fujian Province, China. The results showed that SOC content in the mangrove was 8.25–51.46 g kg−1, which was 21.3 % and 93.4 % higher than those in the S. alterniflora and tidal flat, respectively. Additionally, the SOC storage at depths of 0–30 cm was 26.0 % and 96.9 % higher in mangrove than in S. alterniflora and tidal flats, respectively. The values of soil δ13C and δ15N were lower, whereas the C/N ratio was higher in mangrove than in S. alterniflora. A Bayesian stable isotope mixing model revealed that mangrove plant tissues were the highest contributor to SOC (40.8 ± 18.7 %) in mangrove topsoil because of litter effects. However, in the S. alterniflora and tidal flat ecosystems, SOC was mainly derived from allochthonous sources with particulate organic matter (POM) proportions of 72.1 ± 3.3 % and 56.4 ± 5.3 %, respectively. Alkyl C (16.3–41.4 %) was the dominant functional group in all soils, followed by O-alkyl C and aromatic C. Alkyl C, A/O-A, and hydrophobicity index (HI) were significantly lower in S. alterniflora soil than in mangrove and tidal flat soils. Therefore, the SOC sources and stability, including fractions and chemical composition, were substantially altered in mangrove ecosystems after S. alterniflora invasion, leading to decreases in SOC pools. Nevertheless, source alteration was more effective in mangrove wetland invaded by S. alterniflora. These findings may provide new perspectives regarding blue carbon sources, decomposition, stabilization, and sequestration in mangrove wetlands invaded by S. alterniflora.

Plant invasion strengthens the linkages between dissolved organic matter composition and the microbial community in coastal wetland soils

Exotic plant invasion dramatically alters soil carbon transformation and shapes the structure and diversity of the microbial community in coastal wetlands. However, it remains unclear how the dissolved organic matter (DOM) optical components and chemical composition and their linkages with soil microorganisms change with increasing time since invasion. Here, we explored the impacts of Spartina alterniflora (S. alterniflora) invasion on DOM compositions and relationships with microbial communities along a short-term chronosequence (i.e., 3-, 5-,10-, and 15-year) in the Yellow River Delta. The results showed an increase in the soil water content, soil organic carbon, dissolved organic carbon, and C/N ratio along the invasion chronosequence, whereas bulk density showed the opposite trend. Moreover, invaded wetland soils had a higher abundance of total phospholipid fatty acids, gram-positive bacteria (G + ), gram-negative bacteria (G-), and fungi than tidal flat soils. The DOM in invaded wetland soils was mainly composed of endogenous protein-like components, and the proportion of autochthonous DOM increased over invasion time. The DOM was characterized by low molecular weight, low aromatic content, and low hydrophobic compounds in S. alterniflora wetland soils, whereas in tidal flat soils, the humification degree and DOM molecular weight were higher. The soil microbial communities exhibited stronger linkages with various environmental variables and DOM fluorescence components in invaded wetlands based on redundancy analysis (RDA) and correlation analysis using Mantel tests. Structural Equation Model (SEM) revealed that the soil microbial abundance and community structure induced by increasing S. alterniflora invasion time were the most important drivers of DOM content and chemical composition. The findings of this work provide a better understanding of labile carbon pool turnover in coastal wetlands invaded by S. alterniflora.

Saline–Alkaline Characteristics during Desalination Process and Nitrogen Input Regulation in Reclaimed Tidal Flat Soils

Coastal salt-affected soils account for a large area all around the world. Soil salinity and pH are two important parameters affecting soil quality. Investigating the correlation of electrical conductivity (EC) and pH at different soil depths in saline soil was useful for quickly assessing the saline–alkaline characteristics. During the natural desalination process in the field area of reclaimed lands, the phenomena of pH increase and nitrogen accumulation may occur. A field sampling experiment was conducted in slightly saline soil affected by natural desalination and newly reclaimed heavily saline soil. A series of soil–water ratio extracts consisting of 1:2.5, 1:5, 1:10, 1:20, and 1:40 was designed to measure the EC and pH for simulating the saline–alkaline characteristics during the soil desalination process. Meanwhile, for reasonable utilization of the naturally ameliorated slightly saline soil which consists of a high content of nitrogen, a plastic mulching (PM) accompanied with nitrogen (N) fertilizer addition experiment in maize cultivation plots was designed. Results showed that a significant correlation of EC and/or pH existed in all ratios of soil extracts, and the slightly saline soil had a higher nitrogen content (1.06 g kg−1). The EC was negatively correlated with pH at a depth of 0~100 cm in the coastal saline soil, which indicated the increase of pH value and alkalization during its natural desalination. Furthermore, PM treatments showed no significant difference with N treatments in soil bulk density and soil water content in the slightly saline soil. The PM and N treatments obtained similar grain yield, which was between 6.2 and 6.5 t ha−1. The soil salinity decreased in all treatments and the harvest index was largest in PM treated plots. Our study was beneficial for rapidly monitoring saline–alkaline characteristics and sustainable utilization of coastal saline soil resources. In addition, we should focus far more on pH improvement during the desalination process and rational utilization of chemical fertilizer for obtaining sustainable benefits in the coastal saline soil.

Complexity of clay minerals and its effects on silicon dynamics in hypersaline coastal wetland soils, Brazil

Context Tidal dynamics and high evaporative rates in hypersaline tidal flat (HTF) soils favour a range of clay reactions and the formation of complex clay assemblages. HTFs have a geochemical environment conducive to mineral reactions, and therefore, clay mineral alteration controls essential nutrients in coastal wetlands. Aims The crystallochemical characteristics of clay minerals from two HTFs were studied to provide insights into the complexity of fine clay assemblages in HTF soils and their effects on Si biogeochemistry. Methods The fine clay fraction (<0.2 μm) from these HTFs were investigated using X-ray diffraction (XRD) modelling, XRF, FTIR, TEM–EDS, and silicon sequential extractions. Key results The results have indicated the presence of endmembers and R0 mixed-layered minerals such as kaolinite, smectite, illite, kaolinite–smectite (K–S), kaolinite–illite (K–I), illite–smectite (I–S), and illite–vermiculite (I–V). In general, K–S was the dominant mineral in the samples, occurring in a range of kaolinite layers. Alteration of detrital kaolinite to other mixed-layered minerals occurs in soils, leading to silicon removal from the soil solution because of mineral genesis. There is Mg enrichment at the expense of Al in the samples, and bio-opal appears to be the source of Si for the kaolinite alteration process. Conclusions Our findings indicate that clay authigenesis is an important factor controlling Si dynamics in HTF soils, acting as a sink of Si during the formation of new clay phases. Implications Chemical reactions involving clay minerals are critical for deepening our understanding of the biogeochemistry of wetland soils.

Soil organic carbon storages and bacterial communities along a restored mangrove soil chronosequence in the Jiulong River Estuary: From tidal flats to mangrove afforestation

Among many ecological services provided by mangrove ecosystems, soil organic carbon (SOC) storages have recently received much attention owing to the increasing atmospheric partial pressure of dissolved CO2 (pCO2). Bacteria are fundamental to ecosystem functions and strongly influence the coupling of coastal carbon, nitrogen, and sulfur cycling in soils. The SOC storage and bacterial communities along a restored mangrove soil chronosequence in the Jiulong River Estuary were explored using the 16S rDNA sequencing technique. The results showed the SOC storage in the 100 cm soil profile was 103.31±5.87 kg C m−2 and 93.10±11.28 kg C m−2 for mangroves with afforestation ages of 36 and 60 years, respectively. The total nitrogen (TN) and total sulfur (TS) contents exhibited significant correlations with the SOC in the mangrove soils, but only TN and SOC showed significant correlation in tidal flat soils. Although the tidal flats and mangroves occupied the contiguous intertidal zone within several kilometers, the variations in the SOC storage along the restored mangrove soil chronosequence were notably higher. The Functional Annotation of Prokaryotic Taxa (FAPROTAX) database was used to annotate the metabolic functions of the bacteria in the soils. The annotation revealed that only four metabolic functions were enriched with a higher relative abundance of the corresponding bacteria, and these enriched functions were largely associated with sulfate reduction. In addition, the specifically critical bacterial taxa that were associated with the SOC accumulation and nutrient cycling, shaped the distinct metabolic functions, and consequently facilitated the SOC accumulation in the mangrove soils with various afforestation ages. The general homogenization of the microbial community and composition along the intertidal soil chronosequence was primarily driven by the reciprocating tidal flows and geographical contiguity.

Evaluation of Pedotransfer Functions for Estimating Soil Water Retention Curve of Ap Horizon Soils for Various Soil Series of Reclaimed Tidal Flat Soil

This investigation was to evaluate the applicability and prediction accuracy of pedotransfer function (PTF) to estimate the water retention curves of Ap horizon soils for five soil series which cannot be directly used to cultivate upland crops other than rice because of their high salinity. Soil water retention curves (SWRCs) were obtained from 150 undisturbed soil samples collected from the Ap horizons of which soil textures were grouped into sandy loam with high contents of sand (>60%) and low clay contents (<10%) and silt loam with relatively high silt content (>60%) and low sand content (<10%). Soil-water retention characteristics between 0 to −50 kPa and −50 to −1500 kPa were measured using the sandbox, kaolin-plate, and pressure chamber methods, respectively. The SWRCs were also estimated by Rawls and Brakensiek PTF (RB-PTF). The measured SWRCs of sandy loam and silt loam were compared against those obtained from RB-PTF. The SWRCs estimated with the modeled data closely fit the measured data of sandy loam and silt loam although saturated volume water content (θs) and residual volume water content (θr) of RB-PTF were higher than those of the measured mean for both soil textures. The air entry point (α) and the steepness of the water-retention curve (n) were higher in sandy loam than those of silt loam. SWRCS estimated by the RB-PTF yielded the best fit of all soil samples from the five series, whereas the MBE values less than zero indicate that θv measured at the water potentials is under-predicted. The r2 values greater than 0.9 for sandy loam and silt loam represent RB-PTF and are suitable for predicting SWRCs in RTFS because the measured data points do not vary around the estimated regression line.

인과순환구조 분석을 활용한 지속가능한 수변도시의 그린 인프라 도입 및 식재기반 계획 : 부산 에코델타시티를 중심으로

Busan Eco-Delta city is being developed under the paradigm of eco-friendly waterfront cities with goals such as sustainable development, ecosystem service improvement, and climate change response, etc. To do this, it is necessary to analyze the key variables that appear in common in recognition of the planting base environment and introduction of green infrastructure and to analyze the integrated system. Therefore, the purpose of this study is to analyze the causal loop structure to construct planting base and introduce green infrastructure in realizing a sustainable waterfront city. First, the causal loop structure of the planting base environment according to tidal-flat soil, mountain soil, and dredged sediment was analyzed using system thinking in system dynamics methodology. As a result of integrating individual causal loop structures, key variables of the planting base environment were soil hardness, organic matter in soil, soil pH, soil salinity, and plants growth variables. Second, when introducing green infrastructure (urban forests, wetlands, grasslands) to the planting base, constraints were derived and presented as a causal loop structure. In urban forests, the values of soil hardness, slope, soil pH, soil salinity, soil drainage, and plant growth should be taken into consideration. In wetlands, variables of soil hardness, soil permeability, soil moisture, wetland water level fluctuation, and wetland water depth should be taken into consideration. In grasslands, consideration of the variables of soil hardness, soil drainage and permeability, soil pH, and plant growth needed. The green infrastructure introduced in this study is important in that it can respond to climate change as well as environmental pollution. It is expected that the results of this study can be used as the basis for a green infrastructure plan in the process of developing Busan Eco-Delta city.

Expression and biochemical characterization of a novel chitinase ChiT-7 from the metagenome in the soil of a mangrove tidal flat in China

Chitinases play an important role in the process of chitin bioavailability. In this study, we cloned a new chitinase gene and characterized its recombinant protein. The new 1251 bp gene of chitinase (ChiT-7) was cloned from the metagenome of the mangrove tidal flat soil in the city of Zhangzhou in Fujian Province (China) by genome walking. The gene encoded a mature protein with 381 amino acids, which manifested certain sequence similarity (59% identity) to characterized GH18 chitinases. The mature protein of ChiT-7 was successfully expressed in E. coli BL21 (DE3). After purification, the specific activity of the recombinant enzyme was 0.63 U/mg at the optimal pH of 6.0 and the optimal temperature of 45 °C. The rChiT-7 was active over a wide pH range, and the residual enzyme activity reached 80% or higher at 30 °C–50 °C. rChiT-7 hydrolyzed colloidal chitin with (GlcNAc)2 and GlcNAc as the main final products. Structural analysis of ChiT-7 indicated that ChiT-7 could be a processive chitinase. rChiT-7 manifested characteristics analogous to those of fungi and actinomycetes and exhibited sequence homology.

Conversion behaviors of litter-derived organic carbon of two halophytes in soil and their influence on SOC stabilization of wetland in the Yangtze River Estuary.

Soil organic carbon (SOC) is both a product and a cause of soil development. Previous studies found that less carbon (C) is fixed by Phragmites communis than Spartina alterniflora in the Jiuduansha wetland of the Yangtze River Estuary. However, the P. communis zone presented higher contents of SOC and humus, which was mainly related to lower soil respiration (SR). It is not well known how different plants affect turnover of original SOC in the Jiuduansha wetland, and thus soil development and tidal flat evolution. In this study, in-field surveys and microcosm experiments were conducted to trace turnover of plant C and evaluate dynamics of SOC using stable C isotopic techniques. Spartina alterniflora decayed faster than P. communis, and more of its derived OC was lost through SR and leaching. Although S. alterniflora-derived OC suppressed the degradation of original SOC, it was consumed to a greater extent, making less supplementation to SOC. Phragmites communis-derived OC showed less degradability and accelerated the degradation of original SOC, but was more incorporated into new SOC and finally caused higher increase in SOC, specifically in bare tidal flat soil with poor original SOC. Overall, compared with S. alterniflora, P. communis-derived OC more effectively replaced the unstable original SOC, thereby improving the content and stability of SOC, especially for soil in early-development stages of tidal flats.

Metabarcoding reveals differences in fungal communities between unflooded versus tidal flat soil in coastal saline ecosystem

In the saline-affected ecosystem, fungi have huge potential to promote growth, induce disease resistance and enhance tolerance against salt-stress of host plants. Since areas of plowland are gradually decreasing, the reclamation of coastal saline lands could play a crucial role in maintaining agricultural productivity and crop security globally. Therefore, it is of great significance to explore the fungal diversity in the coastal saline ecosystem. Here, we collected saline soil samples from unflooded areas and tidal flat areas, the two typical distinct landforms in coastal saline ecosystems, and used ITS metabarcoding to depict the diversity of fungal communities. We found that fungal species evenness had a remarkably higher variation from the tidal flat compared to unflooded soil samples. Furthermore, we also confirmed that the fungal niches differentiation reports in the coastal saline ecosystem. Our ITS based DNA sequencing revealed that both unflooded and tidal flat soil were mainly composed of amplicon sequence variants (ASVs) belonging to Ascomycota (93.43% and 86.91% respectively). Based on our findings, understanding the associations and distinctions of fungal microbiome between unflooded soil and tidal flat could provide the basis for the development of reclamation in coastal saline lands.

Are hypersaline tidal flat soils potential silicon sinks in coastal wetlands?

Hypersaline tidal flats (HTF) are transitional ecosystems which play an important role over Si biogeochemistry in wetlands. Sources and sinks of Si in these ecosystems are directly dependent on pedogenesis and are strongly influenced by the readily soluble Si components, such as dissolved Si, adsorbed Si, and amorphous silicates. The aim of this study was to identify and assess the distribution of readily soluble Si pool in two HTFs on the Brazilian coast. We based our studies on sequential extractions of iron and silicon, modeling of the soil aqueous phase, and X-ray diffraction of the fine clay fraction. Our results show that mobile Si and adsorbed Si are present at very low levels in HTF soils, comprising <3% of the readily soluble Si pool. Silicon associated with Fe oxyhydroxides is the second largest component of the readily soluble Si pool, making up 8.7–40.8% of the Si extractions. The correlation between the ferrihydrite fraction and Si associated with Fe oxyhydroxides indicates a large control of Si by ferrihydrite. Amorphous Si makes up the dominant fraction, comprising 59–90% of the Si extractions. SEM images show the presence of diatoms, sponges, and phytoliths in the soils. Precipitation of pedogenic opal seems to occur in the soils due to a dry season at both sites. The clay assemblages are composed of the mixed-layer kaolinite-smectite (K-S), kaolinite-illite (K-I), and illite-smectite (I-S), and lesser amounts of kaolinite (K) and smectite (S) end-members. The presence of these clays indicates that HTF soils are conducive to the formation of mixed-layer minerals, which partially control Si dynamics. Our data indicate that HTF soils tend to accumulate Si by adsorption, (co)precipitation, and reactions involving clay minerals.

Role of Redox Processes in the Pedogenesis of Hypersaline Tidal Flat Soils on the Brazilian Coast

Core Ideas Iron and Mn movement followed by oxidation impose strong control on soil transformations. Sulfidization is not an active process in hypersaline tidal flat (HTF) soils. Coprecipitation of Mn and ferrihydrite controls the geochemistry of Mn in HTF soil. Hypersaline tidal flats (HTFs) represent transitional ecosystems where the ocean, land, and freshwater meet. These places are globally widespread and their soils are an important environmental component controlling chemical reactions in wetland ecosystems. Here, we present a pedogenic study of two HTFs on the Brazilian coast (northeast and southeast) based on the solid‐phase geochemistry of Fe and Mn and morphological studies. Broken and irregular topographies and strong expression of redoximorphic concentrations (e.g., mottles, nodules, and pore linings) are present throughout the soil profiles. Although lepidocrocite is the most abundant Fe fraction in these soils (more than 50% of all extractions), deeper horizons show pyrite as the main Fe fraction caused by the presence of buried mangrove soils. The more oxidizing conditions in these deeper horizons indicate that pyrite is not stable and is undergoing degradation. Iron released in this process is moving upward and precipitating as Fe oxides in more oxidized portions of the soil profile. Coprecipitation of Mn and ferrihydrite seems to be an important process controlling the geochemistry of Mn in HTFs. Our data indicate that deeper horizons have been transforming, driven mainly by water table oscillation and, consequently, redox processes. This process allows translocation of Mn2+ and Fe2+ throughout the soil profile, followed by oxidation and precipitation of Mn3+/4+ and Fe3+ oxides in preferential sites.

Effect of salinity on the decomposition of soil organic carbon in a tidal wetland

Climate warming and sea level rise have the potential to change the salt level of soil in tidal wetlands. And it is important to clarify the process and the mechanism of decomposition of soil organic carbon in a tidal wetland under varying salinities. The aim of this study was to evaluate the impacts of soil salinity on the decomposition rate of organic carbon (DROC) and dissolved organic carbon (DOC) in a tidal wetland. Two types of soil (surface soil in Suaeda salsa and bare tidal flat) were collected, air-dried, and homogenized. After adding different content of salt (0 g/L, 3 g/L, 6 g/L, 9 g/L, and 12 g/L), the soils were incubated for 28 days at stable room temperature (25 ± 2 °C) and added by deionized water to maintain the stability of soil moisture. The gases (CO2 and CH4) emission rates of each salt treatment were measured during 28-day incubation. DROC was determined by the sum of daily CO2-C emission rates and daily CH4-C emission rates in this study. Salt addition inhibited the process of gas emissions and DROC. Gases emission rates and DROC of two types of soil showed similar temporal trends, with distinctive drop in the beginning of experiment and no significant decrease followed. Significant difference of DOC among salt treatments was found in the bare tidal flat soil. Variations of partial correlation between DROC and soil salinity and DOC showed similar trends (e.g., in days 9–18, the positive effect of DOC on DROC was greatly promoted (R2 = 0.80, p < 0.001), and the negative effect of soil salinity was highly improved (R2 = 0.93, p < 0.001)). Soil properties, in particular DOC, may be primary factors accounting for the discrepancy of gases emission rates and DROC of two types of soil. Increased soil salinity had a negative effect on DROC during 28-day incubation. The impact of soil salinity and DOC on DROC were varied in different phases of laboratory experiment (soil salinity generally had increasingly negative relationship with DROC, but DOC showed most significantly positive relationship in the middle stage of incubation). Both the formation and consumption of DOC may be valuable for more detail research regarding to decomposition of soil organic carbon.

Low-Cd tomato cultivars (Solanum lycopersicum L.) screened in non-saline soils also accumulated low Cd, Zn, and Cu in heavy metal-polluted saline soils.

Many reclaimed tidal flat soils feature high salinity and heavy metal (HM) accumulation. Consumption of vegetables cultivated in this type of cropland may cause health risks. Low-Cd tomato cultivars (Solanum lycopersicum L.) were identified in non-saline soil in our previous studies (Tan et al. 2014). However, further research should determine whether these low-Cd cultivars will maintain in the repeatability and stability in saline soil and whether they have low accumulation abilities for accompanying metals (such as Zn and Cu). A soil-pot trial was implemented to measure Cd, Zn, and Cu concentrations in low- and high-Cd cultivars of both common and cherry-type tomatoes grown on HM-polluted reclaimed tidal flat saline soil. Then, cultivar differences in dissolution of Cd, Zn, and Cu in soil and their uptake and redistribution in plants were analyzed. Results showed that the cherry type accumulated more Cd, Zn, and Cu than the common type. Low-Cd cultivars of both types in saline soil accumulated low concentrations of Cd, Zn, and Cu in fruits. Low HM accumulation in fruits is partly attributed to a low root/shoot (R/S) biomass ratio. Low amounts of soil HMs were dissolved because of the low level of rhizosphere organic compounds, which possibly decreased HM uptake by the roots. Low-Cd cultivars of both tomato types had a higher ability to retain HMs in the roots than their high-Cd cultivars. These findings may provide a scientific guidance for the safe cultivation of HM-polluted saline soils.

Soil organic nitrogen composition and mineralization of paddy soils in a cultivation chronosequence in China

Soil organic nitrogen (SON) mineralization is a crucial process of nutrient dynamics for plant growth. However, impacts of long-term rice cultivation on SON composition and mineralization in paddy soils are few. This study examines the influence of long-term rice cultivation on SON composition and mineralization. The results provide useful data for long-term soil N fertility development and N biogeochemistry turnover in paddy soils. A chronosequence of rice paddy soils (50, 100, 300, and 700 years) was selected from uniform marine deposits with identical landscape and climate conditions. The paddy soil samples were obtained from Cixi, Zhejiang Province, China. SON of paddy soils, salt marsh soils (young soil), and tidal flat soils (control) was fractionized by the modified Bremner method. N mineralization was measured using a waterlogged incubation method. Soil total nitrogen (TN) increased from 0.47 to 2.00 g kg−1 with cultivation time, whereas soil pH dropped from 8.5 to 6.8. SON and its fractions (amino acid N, ammonium N, amino sugar N, and hydrolyzable unknown N) exhibited an exponential growth with cultivation time and stabilized rapidly at approximately 100 years, which might be caused by the paddy management such as fertilization, flooding, plowing in practice. However, the proportion of various fractionized N to TN did not follow a uniform trend with the cultivation time, suggesting the local paddy environment exerted an important impact on SON composition. Soil microbial C and N showed the same pattern with TN. The soil net mineralization rate of paddy soils was higher than those of salt marine and tidal flat soils. However, no significant difference was observed among the paddy soils with various cultivation times. These results demonstrate that reclamation and rice cultivation could improve soil N accumulation and availability. N stabilization was achieved within 100 years. Rice cultivation could maintain the sustainable long-term use of soil N.

Remediation of saline–sodic soil with flue gas desulfurization gypsum in a reclaimed tidal flat of southeast China

Salinization and sodicity are obstacles for vegetation reconstruction of coastal tidal flat soils. A study was conducted with flue gas desulfurization (FGD)-gypsum applied at rates of 0, 15, 30, 45 and 60Mg/ha to remediate tidal flat soils of the Yangtze River estuary. Exchangeable sodium percentage (ESP), exchangeable sodium (ExNa), pH, soluble salt concentration, and composition of soluble salts were measured in 10cm increments from the surface to 30cm depth after 6 and 18months. The results indicated that the effect of FGD-gypsum is greatest in the 0–10cm mixing soil layer and 60Mg/ha was the optimal rate that can reduce the ESP to below 6% and decrease soil pH to neutral (7.0). The improvement effect was reached after 6months, and remained after 18months. The composition of soluble salts was transformed from sodic salt ions mainly containing Na+, HCO3−+CO32− and Cl− to neutral salt ions mainly containing Ca2+ and SO42−. Non-halophyte plants were survived at 90%. The study demonstrates that the use of FGD-gypsum for remediating tidal flat soils is promising.

Use of flue gas desulfurization gypsum for leaching Cd and Pb in reclaimed tidal flat soil

A soil column leaching experiment was conducted to eliminate heavy metals from reclaimed tidal flat soil. Flue gas desulfurization (FGD) gypsum was used for leaching. The highest removal rates of Cd and Pb in the upper soil layers (0-30cm) were 52.7 and 30.5%, respectively. Most of the exchangeable and carbonate-bound Cd and Pb were removed. The optimum FGD gypsum application rate was 7.05kg·m(-2), and the optimum leaching water amount for the application was 217.74L·m(-2). The application of FGD gypsum (two times) and the extension of the leaching interval time to 20days increased the heavy metal removal rate in the upper soil layers. The heavy metals desorbed from the upper soil layers were re-adsorbed and fixed in the 30-70cm soil layers.

Effects of freshwater leaching on potential bioavailability of heavy metals in tidal flat soils.

Leaching experiments were conducted to investigate the effects of desalination levels and sediment depths on potential bioavailability of heavy metal (Cd, Cr, Cu, Fe, Mn, Ni, Pb, and Zn) in tidal flat soils. The data showed that both the desalination levels (p<0.001) and soil depths (p<0.001) had significant effects on the concentrations of acid-volatile sulfide (AVS). AVS concentrations generally exhibited increasing trends with an increase in depth and decreasing trends with enhanced desalination levels. The desalination levels had significant (p<0.05) effects on the concentrations of simultaneously extracted metal (SEM; Cd, Cr, Cu, Fe, Mn, Pb, and Zn). Moreover, the concentrations of SEM (Cd, Cr, Cu, Fe, Mn, Pb, and Zn) generally tended to decrease with an increase in the desalination level. The desalination treatment significantly reduced the ratios of SEM/AVS compared with control. However, the ratios of SEM/AVS increased with enhanced desalination levels in treatments. Results reveal that low desalination treatment is better for reducing toxicity to benthic organisms than high desalination treatment. Since these reclaimed tidal flats with low desalinisation are suitable for saline water aquaculture, transforming the present land use of reclaimed tidal flats from fresh water aquaculture into saline water aquaculture may reduce health risk of heavy metals remained in sediments. These results will also contribute to our understanding of the dynamic behavior of heavy metals in the reclamation of tidal flats during leaching and the role of the ratio of SEM/AVS predictions on assessing the ecological risks of reclaimed tidal flats.

환경정화 미생물에 의한 갯벌의 생물학적 정화에 대한 파일럿 규모의 연구

Tidal flats are continuously contaminated by human activities. This study assessed the bioremediation efficiency of tidal flat soil using microcosm reactors and microorganisms originating from the tidal area. We screened 135 bacterial strains that produce extracellu lar enzymes from the tidal area located in the North port of Incheon bay. Two bacterial strains (Pseudoalteromonas sp. and IC35 Halothiobacillus neapolitanus IC_S22) were selected and used in the microcosm reactors, which were specially designed to functionally mimic the ecological conditions of the tidal flats. Pseudoalteromonas sp. IC35 was se- lected based on its relatively high activity of the enzymes amylase, cellulose, lipase, and protease. Halothiobacillus neapolitanus IC_S22 was selected for oxidation of sulfur. The M1 and M2 microcosm reactors were operated by continuous feeding of seawater under the same conditions, but M2 was first inoculated with Pseudoalteromonas sp. IC35 before the seawater feeding. The initial COD in both the M1 and M2 microcosm reactors was 320 mg/l. The final COD was 21 mg/l (M1) and 7 mg/l (M2). The M3 and M4 microcosm reactors were operated by continuous feeding of seawater under the same conditions, but M4 was first inoculated with H. neapolitanus IC_S22. The initial sulfate concentration in both the M3 and M4 microcosm reactors was 660 mg/l, and the maximum sulfate concentration was 1,360 mg/l (M3) and 1,600 mg/l (M4).