Atmospheric nitrogen (N) deposition is believed to accelerate dissolved organic carbon (DOC) production and could lead to increased heavy metal mobility into water resources. We sampled intact soil cores from the Isle of Skye with low background N deposition history and having Serpentine rock known for its higher heavy metal concentrations including zinc (Zn), copper (Cu), nickel (Ni) and lead (Pb). The effects of 16 (16kgN) and 32 kg N ha⁻¹ year⁻¹ (32kgN), and liming with 32kgN (32kgN+Lime) on soil solution chemistry and heavy metal mobilization were investigated over the 15-month study. Nitrogen in deposition load was added at five ammonium (NH₄⁺) to nitrate (NO₃⁻) ratios of 9:1, 5:1, 1:1, 1:5 and 1:9 along NO₃⁻dominance. We found significant effects of load on Cu and NH₄⁺/NO₃⁻ ratio on pH, DOC and Zn in soil solution. However, under lime and ratio experimental factors, liming significantly influenced pH, DOC, Cu and Pb, and NH₄⁺/NO₃⁻ ratio pH, DOC, Ni and Zn whereas interactions between lime and ratio was significant for Ni and Cu. pH and DOC increased with N load, liming and NO₃⁻ dominance, and both correlated significantly positively. Liming under NH₄⁺ dominance enhanced DOC production due to supply of base cations in lime. Mobilization of Cu, Ni and Pb was driven by DOC concentrations and, therefore, increased with load, liming and NO₃⁻ dominance in deposition. However, in contrast, low pH and high NH₄⁺ dominance was associated with Zn mobilization in soil solution. On the contrary, despite of some patterns, heavy metals in soil HNO₃ extracts were devoid of any load, lime and NH₄⁺/NO₃⁻ ratio effects. Our study suggests that the effects of N load and forms in deposition on sites with high accumulated loads of metals need to be better quantified through soil solution partitioning models.

Nitrous oxide (N2O) is a devastating greenhouse gas mainly released from soils to the atmosphere. Pasture soils, particularly acidic in nature, are large contributors of atmospheric N2O through deposition of urine-N. Devising strategies for reducing N2O emissions in acidic soils are the utmost need of the time. Therefore, the present study was carried out to investigate the possible efficacy of dolomite application to reduce N2O emissions from urine treated acidic soil. Application of urine to soil enlarged the production of NH4+-N, NO3−-N, microbial biomass C (MBC) and dissolved organic C (DOC), resulting in higher N2O emissions as compared to the control (soil only). The highest N2O emission rate (1.35 μg N2O-N kg−1 h−1) and cumulative flux (408 μg N2O-N kg−1) occurred in urine only treated soil. Dolomite addition, especially higher application dose, greatly reduced N2O emissions through improved soil pH. The results suggest that increasing pH of acidic soils is a good applicable approach for reducing N2O emissions from urine-treated soils.

Rapid industrialization in China during the last three decades has resulted in widespread contamination of Cd in agricultural soils. A considerable proportion of the rice grain grown in some areas of southern China has Cd concentrations exceeding the Chinese food limit, raising widespread concern regarding food safety. In this review, we summarize rice grain Cd concentrations in national Chinese markets and in field surveys from contaminated areas, and analyze the potential health risk associated with increased dietary Cd intake. For subsistence rice farmers living in some contaminated areas of southern China who mainly consume locally-produced Cd-contaminated rice, their estimated dietary Cd intake is now comparable to that for the population in the region of Japan where the Itai-Itai disease was first reported. Interventions must be taken urgently to reduce Cd intake for these farmers. We also analyze i) the main reasons causing elevated grain Cd concentrations in southern China, ii) the dominant biogeochemical processes controlling the solubility of Cd in paddy soils, and iii) molecular mechanisms for the uptake and translocation of Cd in rice plants. Based on these analyses, we propose a number of countermeasures to address soil Cd contamination, including i) mitigation of Cd transfer from paddy soils to rice grain, and ii) intervention in those farmers who consume home-grown Cd-contaminated rice. Liming to increase soil pH to 6.5 and gene editing biotechnology are effective strategies to decrease Cd accumulation in rice grain. For these local farmers with high-Cd exposure risk, local governments should monitor the Cd concentration in their home-grown rice and exchange those high-Cd rice with low-Cd rice in order to reduce their dietary Cd intake.

Central European mountain bogs, among the most valuable and threatened of habitats, were exposed to intensive human impact during the 20th century. We reconstructed the subrecent water chemistry and water-table depths using diatom based transfer functions calibrated from modern sampling. Herbarium Sphagnum specimens collected during the period 1918–1998 were used as a source of historic diatom samples. We classified samples into hummocks and hollows according to the identity of dominant Sphagnum species, to reduce bias caused by uneven sampling of particular microhabitats. Our results provide clear evidence for bog pollution by grazing during the period 1918–1947 and by undocumented aerial liming in the early 90-ies. We advocate use of herbarized epibryon as a source of information on subrecent conditions in recently polluted mires.

The addition of calcium carbonate to catchments or watercourses – liming – has been used widely to mitigate freshwater acidification but the abatement of acidifying emissions has led to questions about its effectiveness and necessity. We conducted a systematic review and meta-analysis of the impact of liming streams and rivers on two key groups of river organisms: fish and invertebrates. On average, liming increased the abundance and richness of acid-sensitive invertebrates and increased overall fish abundance, but benefits were variable and not guaranteed in all rivers. Where B-A-C-I designs (before-after-control-impact) were used to reduce bias, there was evidence that liming decreased overall invertebrate abundance. This systematic review indicates that liming has the potential to mitigate the symptoms of acidification in some instances, but effects are mixed. Future studies should use robust designs to isolate recovery due to liming from decreasing acid deposition, and assess factors affecting liming outcomes.

Present study reports the laboratory and field scale application of different organic and inorganic amendments to immobilize cadmium (Cd) and lead (Pb) in a co-contaminated alluvial paddy soil. For that purpose, lime, biochar, Fe-biochar and two composite amendments (CA) composed of biochar, lime, sepiolite and zeolite (CA1: composite amendment 1) and manure, lime and sepiolite (CA2: composite amendment 2) were firstly tested in an incubation experiment to ameliorate Cd and Pb co-contaminated alluvial soil. It was observed that liming and CA2 elevated the soil pH and reduced DTPA extractable Cd and Pb in the incubated soil leading to higher metal immobilization. Therefore, efficiency of lime and CA2 was further investigated in field conditions with mid rice as the test crop to evaluate field scale immobilization and precise application rate for the tested soil type. DTPA and CaCl₂ extractable Cd (46 and 51%) and Pb (68 and 70%) in field soil were decreased with applied treatments. Speciation of Cd and Pb also promoted conversion of metal exchangeable contents to less-available forms. Activated functional groups on amendments’ surface (_OH bonding, C_O and CO, -O-H, Si–O–Si, carboxylic and ester groups) sequestered metals by precipitation, adsorption, ion exchange or electro static attributes. Application of lime at 2400 kg/acre (T4) and CA2 at 1200 kg/acre was more effective in reducing rice shoot and grains metal contents. Moreover, obtained results in terms of pH, extractable content, speciation and yield, and microanalysis of amendments highlights the remarkable efficiency of lime and composite amendment to sorb Cd and Pb providing the key evidence of these amendments for metals immobilization and environmental remediation. Considering these results, lime and CA2 are potential amendments for co-contaminated rice field especially in context of alluvial soil.

Rice is a major dietary source of the toxic trace metal Cd. Large variation in Cd concentration in rice grain was documented by global and regional surveys, with this variation difficult to predict from soil tests. Even within individual fields, a large spatial variation is often observed but the factors controlling this within-field spatial variation are still poorly understood. In the present study, we used field- and laboratory-based experiments to investigate the effects of a gentle slope gradient within paddy fields (a common farmers’ practice to facilitate water flow from the inlet to the outlet) on Cd availability and grain Cd concentrations in unlimed and limed soils. In our field experiments, a gentle slope resulted in large spatial variations in soil redox potential (Eh) and pH upon soil drainage during rice grain filling. As a result of these variations in Eh and pH, there was a 6- to 7-fold spatial within-field variation in grain Cd concentrations, which were the highest in the irrigation inlet area associated with higher Eh values and the lowest in the outlet area with lower Eh values. Our results highlight that soil Eh, and more importantly, field-moist soil pH during grain filling determine grain Cd concentration and accordingly, incorporating measurements of soil redox status (or water content) and pH of field moist soils (rather than air-dried soils) during grain filling may improve the prediction of grain Cd concentrations. Delaying drainage during grain filling or increasing soil pH by liming is effective in reducing grain Cd accumulation.

Keeping in view the expanding environmental pollution and irrigation water deficit, a pot experiment was performed for the upland (Huyou2, Hanyou737) and paddy rice cultivars (Taigeng8; Yixiang2292), to study soil liming effects on methane (CH₄) and nitrous oxide (N₂O) emission, bioavailability and accumulation of Cd, Pb in upland and paddy rice. Upland rice reduced 90% of soil CH₄ emission as compared to paddy conditions. Soil CH₄ emission decreased by 45% and 39% with dolomite, and it reduced by 35% and 33% with lime treatment both in upland and paddy conditions, respectively. Soil N₂O emission decreased by 44% and 52% with dolomite, and with the lime application, it was reduced by 37% and 44% for both upland and paddy conditions respectively. Reduction in soil DTPA-extractable Cd was between 37-53% and 43–80% with dolomite and 16–37% and 24–72% Cd decreased with lime application in upland and paddy conditions respectively. Soil DTPA-extractable Pb reduced by 27–44% and 25–53% with dolomite and 16–40% and 11–42% with soil-applied lime in upland and paddy conditions, respectively. Cd accumulation in rice grain was decreased by 47–88% and 62–79% with dolomite and 31–86% and 45–52% reduction by lime application in upland and paddy rice respectively. Rice grain Pb reduced by 58–91% and 66–78% with dolomite application and 32–71% and 44–71% with lime in upland and paddy rice, respectively. Our results showed that soil liming significantly reduced soil N₂O and CH₄ emission and Cd, Pb accumulation in rice grain, but dolomite was more effective as compared to lime. Altogether, results of this study suggest that upland rice can be cultivated in CdPb polluted soils with least soil CH₄ emission. Cd and Pb toxicity, accumulation, and N₂O emission in upland rice can be minimized by soil liming of 3 g kg⁻¹ and optimizing the nutrients composition of the soil.