[Effects of Biochar Addition on Soil Nitrogen Mineralization and Leaching Characteristics in Riparian Zone of Taihu Lake].

Nitrogen mineralization in riparian soil changes the migration and utilization efficiency of nitrogen, which is closely related to the control of water eutrophication. The differences in soil properties caused by land use alter nitrogen retention and transport capacity. Therefore, the soil of three land use types (woodland, grassland, and cultivated land) in the western riparian zone of Taihu Lake were selected for research on the dynamic changes in nitrogen mineralization amount using an incubation experiment and a leaching characteristics by soil column leaching experiment, and their environmental effects were also studied under different biochar addition conditions (0%, 1%, and 5%). The results showed that, in general, the addition of biochar inhibited nitrogen mineralization in forest land and grassland soil, whereas the effect of biochar on nitrogen mineralization in cultivated land was promoted in low concentrations but inhibited in high concentrations. Leaching experiments showed that the biochar addition reduced the loss of soil mineral nitrogen, and the reduction rate in ammonia nitrogen was 23.28%-39.79%, whereas there was little difference between the three land use types. The nitrate decreased by 17.20%-44.49%, and the reduction rate of cultivated land was smaller than that of forest land and grassland. In conclusion, the input of biochar into grassland and cultivated land can better maintain soil fertility and reduce soil nitrogen loss in riparian soil.

[Comparison of Available Nitrogen and Phosphorus Characteristics in the Land-Water Transition Zone of Different Watersheds and Their Environmental Significance].

In order to explore the characteristics and environmental significance of available nitrogen and phosphorus in different land-water transition zones, soil and sediment samples from three study areas, including the upstream watershed of Minjiang River (MJU), western watershed of Hongze Lake (HZW), and western watershed of Taihu Lake (THW), were collected and analyzed. The results showed that the contents of total nitrogen and phosphorus in THW were higher than those of other two study areas. The contents of nitrogen and phosphorus in sediments were higher than those in soils of HZW. The distribution trend of available nitrogen and available phosphorus was generally consistent with the distribution trend of total nitrogen and phosphorus. The proportions of available nitrogen and phosphorus in THW and HZW were much higher than those in MJU, and the proportions of available nitrogen and phosphorus in sediments were higher than those in soils. The physiochemical properties such as pH value, organic matter, and iron and aluminum oxides were related to the available nitrogen and phosphorus in the soil and sediment, but correlations between them were complex. The distribution patterns of available nitrogen and phosphorus in the soil and sediments of the land-water transition zone reflect the impacts of the natural environment and human activities, particularly those of the latter.

Rhizospheric pore-water content predicts the biochar-attenuated accumulation, translocation, and toxicity of cadmium to lettuce.

Metal bioavailability controls its behaviors in soil-plant system, especially involved in biochar amendment. This study compared a rhizospheric pore-water extraction against a BCR sequential extraction method to understand cadmium (Cd) bioavailability in two typical Chinese soils. Soils were spiked with five levels of Cd (CdCl2) and remediated with 3% corn-straw derived biochar. After 60 days of lettuce growth, Cd accumulation and enzyme activities in tissues were analyzed. Results showed that biochar increased soil properties (pH, CEC and SOM) compared to un-amended soils, but decreased contents of bioavailable Cd in soil pore-water (Cdpore-water) and BCR extracted Cd (CdFi+Fii). Contents of Cdpore-water were lower in yellow-brown soils than that in red soils. Pearson analysis showed that bioavailable Cd is negatively correlated with soil pH and CEC (p < 0.05). Cd accumulation in lettuce roots and leaves both were decreased by biochar addition, and the established linear equations proved that soil Cdpore-water is the best predictor for Cd accumulation in lettuce roots (r2 = 0.964) and in leaves (r2 = 0.953), followed by CdFi+Fii. Transfer factor (TF) values of Cd from roots to leaves were lower than 1, and slightly better correlated with soil Cdpore-water (r = -0.674, p < 0.01) than CdFi+Fii (r = -0.615, p < 0.01). Aggregated boosted tree (ABT) analyses indicated that soil properties together with Cdpore-water contribute more than 50% to root enzyme activities. Collectively, soil Cdpore-water is a promising predictor of Cd bioavailability, accumulation and toxicity in soil-plant system with biochar addition.

[Effects of Biochar Input on Changes of Available Nutrient Elements in Riparian Soils with Different Landuse Types].

Biochar, as a new environmentally friendly material, has been used to improve soil quality and for pollution remediation. Biochar input has a significant impact on available nutrients in the soil. Based on the different land use types (forestland, grassland, cultivated land, and barren land) in the riparian zone of Taihu Lake, the effects of biochar application on the available content of nutrients in different land use types of soil were compared, and the dynamics of nutrient change was also discussed. Results show that the addition of biochar can significantly affect the available nutrient content in riparian soil, however the influential degrees for carbon, nitrogen, and phosphorus were different. After the input of biochar, dissolved organic carbon in riparian soils showed a clear downward trend, while the available nitrogen increased slightly, and the available phosphorus increased significantly. For woodland, grassland, arable land and wasteland soils, the contents of dissolved organic carbon decreased by 33.3%, 27.4%, 29.5%, and 51.4%, while the contents of available nitrogen increased by 10.8%, 18.2%, 16.4%, and 15.2%, and the contents of available phosphorus increased by 40.0%, 50.2%, 34.0%, and 43.6%, respectively. Compared with the concentrations between the control group soil (CK) and the biochar additive group soil (BC), the concentrations of dissolved organic carbon and available phosphorus exhibited large differences between the two groups regarding available nitrogen concentrations. Among the four types of riparian soils, the effects of biochar on the availability of different nutrients were different.

Soil microbiome-induced changes in the priming effects of 13C-labelled substrates from rice residues.

Knowledge gap exists to understand the soil CO2 emission and microbial group response to substrates of whole plant residues and derived biochar. We used 13C-labelled substrates (rice straw, roots and biochar) to track influences of their decomposition on soil priming effect (PE) and phospholipid fatty acid (PLFA) composition during one-year incubation. Organic substrates at 1% (w/w) level increased soil pH, available nitrogen (AN) and available phosphorus (AP), especially during the first 45 days of incubation. After incubation, 44% of the added straw was mineralized to 13CO2, followed by roots (~35%) and biochar (~5%). Straw and roots amendment caused positive PE during 4-360 day of the incubation, where a lowest value of 41.9 mg C kg-1 was observed. Biochar amendment caused negative PE during 56-150 day of the incubation, where a largest value of -99.0 mg C kg-1 was observed. Analysis of 13C-labelled PLFA enabled the differentiation of microbial groups during substrates utilization. Gram positive bacteria (G+) and general bacteria groups were dominated in co-metabolizing both the native soil organic carbon (SOC) and substrates after straw and roots amendment. Gram negative bacteria (G-), especially identified by PLFA biomarkers cy17:0 and cy19:0, preferentially utilizes the 13C-labelled biochar but not promoting soil priming effect. Soil pH, SOC, AN and AP all explained changes of total and 13C-labelled PLFA contents (>75%, p < .05). Evidences showed that biochar is best in sequestering soil C pool, followed by straw and roots, and soil microbial groups in utilization of organic substances mediated SOC mineralization.

Effect of amendments on soil Cd sorption and trophic transfer of Cd and mineral nutrition along the food chain.

Phytotoxicity of cadmium (Cd) and its trophic transfer along a terrestrial food chain have been extensively investigated. However, few studies focused on the role of amendments on the trophic transfer of Cd and related mineral nutrients. In a 60-day pot experiment, soil Cd availability, accumulation of Cd, mineral nutrients (Ca and Si) in lettuce, and subsequent trophic transfer along the lettuce-snail system were investigated with or without 3% (w/w) soil amendment (biochar or micro-hydroxyapatite, µHAP). Soil CaCl2 extractable Cd (CdCaCl2) contents decreased by both amendments. µHAP amended soil increased the Freundlich sorption capacity of Cd2+ to a greater extent (15.9 mmol/kg) than biochar (12.6 mmol/kg). Cd, Ca and Si accumulation in lettuce tissues (roots and shoots) varied with amendment species and soil Cd levels. Linear regression analysis showed that root Cd contents are negatively correlated with root Ca and Si contents (r2 = 0.96, p < 0.05). But no significant correlation between shoot Cd and lettuce Ca and Si contents was found (p > 0.05). After 15 days snail feeding, nearly 90% content of Cd was found in snail viscera, while nearly 95% content of Ca was found in snail shells. Contents of Si distributed equally in snail tissues. Biomagnification of Cd, Ca and Si (TF > 1) was found in lettuce shoot - snail viscera system. Opposite tendency of TF variation between Cd and nutrient elements (Ca and Si) from shoots to snail tissues indicated that µHAP, rather than biochar, amendment is applicable to remediate soil Cd contamination in our study.

[Spatial Distribution of Organic Phosphorus in Sediment and Its Environmental Implication in the Upper Stream of Minjiang River].

In order to explore the effect of land use pattern on phosphorus distribution and the potential release capacity of stream sediment in the upper Minjiang River, this paper presented organic phosphorus forms and their spatial distribution characteristics of sediments in the upper Minjiang River by using the IVANOFF method and discussing the effects of physicochemical properties of sediments on the distribution of organic phosphorus forms. The results show that:①nitrogen and phosphorus contents of sediments in Jianxi and Shaxi catchments are higher than those in the Futunxi catchment, probably related to the large number of farmland runoff and municipal sewage near the Jianxi and Shaxi catchments and the large forest area around the Futunxi catchment;②contents in the sediments from three catchments and TP contents in the sediments from Jianxi and Futunxi catchments showed the order of upper reaches < middle reaches < lower reaches, which may be caused by the mountainous and forested areas in the upper reaches and the intensive human activities in the middle and lower reaches;③nitrogen phosphorus in sediments of the three catchments were mainly non-active organic phosphorus, which indicated that upper reaches of the Minjiang river were generally less affected by external pollution, and the relative proportion of organic phosphorus in the sediments of different catchments was relatively large, while the change in different sections of the same river was relatively small;④physicochemical properties of sediments had a significant impact on the morphology and distribution of organic phosphorus, among which the effects of organic matter, TP, and TN were the most obvious, but the effects on sediments in different river basins were different. Therefore, to protect the water quality of the upper Minjiang River, it is necessary to strengthen the control of the living and agricultural pollution sources near the catchments.

Effects of soil amendments on cadmium transfer along the lettuce-snail food chain: Influence of chemical speciation.

Cadmium (Cd) trophic transfer along the soil-lettuce-snail food chain was investigated using the root bags-based pot experiments. Two amendments (corn straw biochar and micro-hydroxyapatite (µHAP)) were investigated on Cd (0, 2.5, and 5 mg/kg soil) availability in soils, chemical distribution in plant cells and accumulation in snails. After 60 days, both the CaCl2 extractable Cd in rhizosphere soil (CdCaCl2,rhizo) and Cd accumulation in lettuce decreased with amendments addition. Biochar had a great capacity to reduce both Cd contents and toxicity-sensitive associated Cd (CdFi+Fii) percentages in lettuce roots at 2.5 mg/kg Cd contaminated soil; while µHAP generates a higher reduction in both Cd contents and chain transfer associated Cd (CdFi+Fii+Fiii) percentages in lettuce shoots at 5 mg/kg Cd contaminated soil. Linear regression showed that both contents of root CdFi+Fii and shoot CdFi+Fii+Fiii are better correlated with the CdCaCl2,rhizo (R2 > 0.70, p < 0.01). After 15 days feeding, almost 90% content of Cd accumulated in snail viscera. µHAP had a higher reduction in snail soft tissues Cd accumulation than biochar. Distributions of Cd in snail tissues are significantly correlated with CdFi+Fii+Fiii in shoots (viscera R2 = 0.835; soft tissue R2 = 0.771). Established quantitative relationships could be used to predict the bioavailability and transfer of Cd in terrestrial food chain in the presence of amendments.

Leaf aging effects on copper and cadmium transfer along the lettuce-snail food chain.

Metal bioavailability at root plasma membrane surfaces and chemical forms within cells putatively controls the trophic transfer processes. Accumulation and distribution of Cu or Cd in lettuce were investigated as a function of lettuce leaf aging through soil-solution culture experiments. Metal contents in snail tissues were examined after fed on young (interior) or old (exterior) age leaves for 15d, respectively. In both roots and leaves, Cu accumulation was higher than Cd by 3-90 fold. Regardless of 9.42 µmoL/L CuCl2 exposure, young leaves accumulated more Cu than old leaves, while higher Cu contents are found in snail tissues fed on old leaves. Opposite trends were observed for Cd. Copper as an essential element had a higher transfer factor (TF) than the non-essential element Cd in biomagnification from leaf to snail. Reasons involved in metal chemical forms within leaf cells, where higher percentages of toxicity and migration associated metal (Fi: inorganic form, Fii: water-soluble form and Fiii: pectate- and protein-integrated form) are found for Cu in old leaves (88.3-91.6%) and Cd in young leaves (86.8-94.5%). Metal activities at root plasma membrane surfaces ({M2+}0) and chemical forms in Fi + Fii + Fiii linearly correlated with metal accumulation in lettuce and snail tissues (R2 > 0.900, p < 0.001 for snails fed on old leaves). Our study incorporated both the chemical form approach and {M2+}0 into evaluating the trophic bioavailability of different metals along the lettuce-snail chain, which is important for mechanistic understanding of metal behaviors in the ecosystem.

[Spatial Distributions of Transferable Nitrogen Forms and Influencing Factors in Sediments from Inflow Rivers in Different Lake Basins].

It is necessary to investigate the distribution of nitrogen forms in river sediments to recognize the water environment quality. In this study, ion exchangeable form nitrogen(IEF-N), weak acid extractable form nitrogen (WAEF-N), strong alkali extractable form nitrogen (SAEF-N) and strong oxidation extractable form nitrogen (SOEF-N) in sediments were obtained by means of sequential extraction procedures.We analyzed the spatial variations of nitrogen forms in sediments from Taihu watershed (Dongtiaoxi River and Xitiaoxi River) and Hongzehu watershed (Anhe River and Suihe River), and expounded the influence factors of nitrogen form distribution. The results showed that the physicochemical properties of sediments from different watersheds varied in space. The concentrations of total nitrogen and nitrogen fractions also showed obvious changes in river sediments. As a whole, the concentrations of total nitrogen and transferable nitrogen in Taihu rivers were higher than those in Hongzehu rivers, but the former showed smaller spatial changes. Sediments from Taihu rivers showed the different concentration order of total nitrogen and transferable nitrogen comparing with those from Hongzehu rivers. The former followed the order of SOEF-N > SAEF-N > IEF-N > WAEF-N, and the latter followed the order of SOEF-N > SAEF-N > WAEF-N > IEF-N.The spatial varitions of transferable nitrogen fractions in Hongzehu rivers were prominent, which was associated with nitrogen sources. The spatial distributions of transferable nitrogen in sediments were obviously affected by their physicochemical properties, especially for organic matter and grain size.

Modeling the interaction and toxicity of Cu-Cd mixture to wheat roots affected by humic acids, in terms of cell membrane surface characteristics.

Responses of wheat (Triticum aestivum L.) seedling roots to the mixtures of copper (Cu), cadmium (Cd) and humic acids (HA) were investigated using the solution culture experiments, focusing on the interaction patterns between multiple metals and their influences on root proton release. A concentration-addition multiplication (CA) model was introduced into the modeling analysis. In comparison with metal ion activities in bulk-phase solutions, the incorporation of ion activities at the root cell membrane surfaces (CMs) (denoted as {Cu2+}0 and {Cd2+}0) into the CA model could significantly improve their correlation with RRE (relative root elongation) from 0.819 to 0.927. Modeling analysis indicated that the co-existence of {Cu2+}0 significantly enhanced the rhizotoxicity of {Cd2+}0, while no significant effect of {Cd2+}0 on the {Cu2+}0 rhizotoxicity. 10 mg/L HA stimulated the root elongation even under metal stress. Although high concentration of metal ions inhibited the root proton release rate (ΔH+), both the low concentration of metal ions and HA treatments increased the values of ΔH+. In HA-Cu-Cd mixtures, actions of metal ions on ΔH+ values were varied intricately among treatments but well modeled by the CA model. We concluded from the CA models that the electrostatic effect is vitally important for explaining the effect of {Cu2+}0 on the rhizotoxicity of {Cd2+}0, while it plays no unique role in understanding the influence of {Cd2+}0 on the rhizotoxicity of {Cu2+}0. Thus our study provide a novel way for modeling multiple metals behaviors in the environment and understanding the mechanisms of ion interactions.

[Characteristics and Pollution Source Analysis of Nutrients in Tributary Outlets of Xitiaoxi Watershed].

The input of tributary is the important source of nutrients to the main stream, and it is the key area for water pollution control of watershed. In order to explore the sources of nutrient and seek the effective measures to control the river pollution, the spatial and temporal variations of aquatic parameters and the output of nutrient flux in the tributary outlets of Xitiaoxi watershed were analyzed. The quantitative analysis concerning the contribution of pollution sources from 10 typical tributaries was carried out, using the PMF analytical model. The results showed that the TN and TP concentrations were higher in the middle and lower reaches. In the temporal scale, the concentrations of nutrients in the dry season were higher than those in the wet season. In the dry season, average concentrations of TN and TP were 4.25 mg·L-1 and 0.11 mg·L-1, respectively, compared to the corresponding values of 3.15 mg·L-1 and 0.09 mg·L-1 in wet season. Because of the differences of surrounding lands, the sources of nitrogen and phosphorus forms were various. The results of PMF(Positive Matrix Factorization) method identified the three nutrient sources as agricultural source, aquaculture source and municipal source. In different seasons and river reaches, the contribution rates of three sources were different. Agricultural source contributed nutrient largely to the tributaries in the upstream reaches, and the aquaculture source was the main contributor in the middle reaches, while the municipal source contributed more nutrient in the wet season than in the dry season. Therefore, to better improve water quality of Xitiaoxi watershed, the surrounding environment of tributary and the characteristics of nutrients in spatial and temporal variations should be considered.

[Distributions of phosphorus fractions in suspended sediments and surface sediments of Tiaoxi mainstreams and cause analysis].

Phosphorus is a primary nutrient showing the water quality status of river and inducing eutrophication, and a different phosphorus fraction can make diverse contributions to water quality. Four phosphorus forms of suspended sediments and surface sediments in Tiaoxi mainstreams were measured using a sequential extraction procedure, and the distributions of their forms were discussed. The results showed that the tropic status of Xitiaoxi River was inferior to that of Dongtiaoxi River as a whole, and the water quality in the middle reach of Dongtiaoxi River was better than that in the upper and lower reaches. The contents of nutrient elements in suspended sediments were significantly higher than those in surface sediment, which indicated an enrichment of nutrient in fine sediment. The percentages of the loosely absorbed phosphorus ( NH4Cl-P), the reductant phosphorus (BD-P) and the metal oxide bound phosphorus (NaOH-P) in the suspended sediment were higher than those in surface sediment, while the percentage of the calcium bound phosphorus (HCl-P) showed a reverse trend. Correlation analyses between phosphorus forms and chemical compositions of suspended sediments and surface sediments were performed. The results showed the phosphorus forms in suspended sediments and surface sediments of Xitiaoxi River had weak relationships with mineral components, while those in the Dongtiaoxi River had strong relationships with mineral, especially OM and clay mineral. The cause was associated with the geological setting and material sources in Tiaoxi watershed.

[Characteristics of heavy metals in sediments from different sources and their ecological risks in the lower reaches of the Yangtze River].

Characteristics of heavy metals in sediments from different sources are significant varied,which impact on the degree of damage for aquatic system. Samples from municipal, mining, industrial and port sources in the lower reaches of the Yangtze River were analyzed for major elements and Cu, Zn, Pb, Cd, Cr by ICP-AES and AAS. The results showed that the concentrations were moderately and relatively uniform for heavy metals in the municipal source, Cu, Pb were dominated for the mine source. Five metals had higher concentrations in industrial source, and Cd was the highest in sediments from port source. The enrichment factors of heavy metals in sediments were high, especially Cd, up to 7.3.Through principal component analysis of major elements and heavy metals, it is concluded that heavy metals of municipal source stem from the erosion of road surface and inner pipeline in cities, heavy metals of mine source come from the mining and the leaching of tailings, heavy metals of industrial source are mostly generated by mechanical debris and metal dissolution, heavy metals of port sources are mainly from the transport ships and the intensive gas emissions from vehicles. The ecological risks of these sediments were evaluated with the Hakanson ecological risk index. It is concluded that the single factors of the ecological hazards for metals are Cd > Cu > Pb > Cr > Zn, the comprehensive index of potential ecological risks for metals from different sources decrease with port source > industrial source > mine source > municipal source.