Zucheng Wang

Northern peatlands are important pools of soil organic carbon (SOC) and show a fine‐scale feature of hummocks and hollows. However, there remains uncertainty about the magnitude of SOC–climate feedbacks because of the knowledge gap about the fine‐scale spatial pattern and temperature sensitivity ( Q ₁₀ ) mechanism of SOC decomposition. We collected peatland soils from the Greater Khingan Mountains in Northeastern China to investigate how soil enzyme kinetics control the hummock–hollow pattern of the Q ₁₀ of SOC decomposition. Results revealed that soil enzyme kinetic parameters (maximum reaction velocity [ V _max ] and Michaelis constant [ K _m ]) were greater in hollows compared to hummocks. In the 0–15 cm depth, the catalytic efficiencies ( K _cat ) of β‐1,4‐glucosidase (BG) and acid phosphatase (AP) were greater in hollows than in hummocks, but the K _cat of 4‐N‐acetylglucosaminidase (NAG) was reversed. In the 15–30 cm depth, the K _cat of NAG and AP was greater in hollows than in hummocks, but the K _cat of BG was reversed. Except for the K _m of NAG, all enzyme kinetic parameters increased with rising temperature. The Q ₁₀ values of V _max and K _m were greater in hummocks than in hollows, with Q ₁₀ values of V _max ranging from 1.48 to 2.22 and from 1.12 to 2.12 for hummocks and hollows, respectively. Similarly, the Q ₁₀ values of K _m ranged from 0.70 to 1.67 and from 0.55 to 1.50 for hummocks and hollows, respectively. A positive correlation was observed between V _max and K _m , indicating that increases in K _m may counterbalance increases in V _max as temperature rises. The Q ₁₀ values for SOC decomposition were greater in hummocks than in hollows, with average Q ₁₀ values of 3.5 and 1.5 when temperature increased from 5°C to 15°C, respectively. Soil TP and the Q ₁₀ – V _max of NAG and AP have emerged as the best predictors of Q ₁₀ values for SOC decomposition, and they were positively correlated with the Q ₁₀ values for SOC decomposition. The larger phosphorus content and the high temperature sensitivity of hydrolase activities on hummocks suggest they would have a high potential for carbon mineralisation in the background of climate warming. These findings suggest that soil enzyme kinetic parameters and their Q ₁₀ provide valuable tools for predicting the response of microbially mediated SOC decomposition to climate warming scenarios.

Peatlands are important reservoirs of terrestrial carbon (C), whose fate can have implications for the global C cycle and climate change. Many peatlands around the world have been drained for agriculture and forestry and restored later on hoping to reduce C emissions and improve water quality. However, the actual effects of these management practices remain unclear. To address this, we investigated the concentration and quality of dissolved organic C (DOC) and water chemistry (nutrient and Fe concentrations) in the surface water (creeks and ditches) of the natural, drained, and restored areas along an elevation gradient of the Baijianghe (BJH) peatland in northeast China from 2017 to 2020. We found significantly higher DOC concentrations in the natural than the drained area, with a heavier, more fulvic, and less aromatic DOC composition upslope, but the difference in DOC quality became smaller downslope. Restoration, on the other hand, did not bring DOC concentrations or quality back to the natural conditions within 2 years. These variations in DOC concentration and quality were closely associated with dissolved Fe concentration, highlighting the role of the Fe redox cycle, as Fe(II) can catalyse phenol oxidation activities and promote DOC production. Vegetation also affected DOC characteristics, as the drained and restored areas were dominated by shrubs with woodier tissues, which probably released less in amount but more recalcitrant DOC. Our study features rare side‐by‐side comparisons between pristine, drained, and restored areas of the same peatland, and sheds light on factors affecting peatland DOC under different management practices.

Melting snowpack can release semi-volatile organic contaminants (SVOCs) to both terrestrial and aquatic ecosystems, resulting in high ecological risk. The dynamics of polycyclic aromatic hydrocarbon (PAH) released from snowpack under controlled laboratory (intense melting) and field (melt/freeze melyting) snowmelt experiments was investigated in this study. In the laboratory: dissolved organic carbon (DOC) controlled the first flush of dissolved PAHs released from snowpack, except for napthelene, which is also affected by its solubility. The particles released early from snowpack usually contained high PAH concentrations (more than 100 μg g⁻¹) and those released at the end contained low PAH concentrations (μg g⁻¹). The total PAH release pattern was determined by composition of all PAHs, including type 2 enrichment with a final peak and type 4 enrichment with double-peak. In field melting: all dissolved PAHs were released constantly, except naphthalene, which also showed a first flush but to a lesser extent. DOC controlled the release pattern of all detected dissolved PAHs from snowpack. High PAH concentrations were observed in particles released from snowpack at both the beginning and the end of the melting event. Concentrations of both total PAHs and PAH compositions in meltwater showed an increasing trend with melting time (from 1.3 to 4.0 μg l⁻¹ and from 1.7 to 5.3 μg l⁻¹ in meltwater from each of the two snowpacks), which coincided with Type 3 enrichment. Overall, our results suggest intense melting of snowpack results in the shift of some hydrophobic PAH compositions from Type 2 to Type 4 enrichment, depending on their partition coefficients. In contrast, melting with melt/freeze cycles may cause the shift of PAHs from Type 2 to Type 3 enrichment. Our study indicates changes of the melting scenarios due to global warming could affect dynamics of SVOCs released from snowpack, which is useful for risk management for water and soil quality.

Organic contaminants in agricultural soils are widely reported; however, their accumulation patterns are quite different among regions. This study reports the distribution, accumulation and risk assessment of polycyclic aromatic hydrocarbons (PAHs), dichlorodiphenyltrichloroethane (DDT) and hexachlorocyclohexane (HCH) in soils from the Corn Belt of northeast China at a regional scale. Concentrations of PAHs, DDT and HCH were 306‐5300, 6.00–82.0 and 4.07–15.6 ng g ⁻¹ , respectively. Source analysis suggests PAHs were derived from regional combustion of biomass and coal, except where sites are strongly affected by local sources. The DDT and HCH residues in soils are likely to be derived from previous agricultural applications that have persisted due to slow microbiological degradation under low mean temperatures. Precipitation was only significantly correlated with PAH concentrations, suggesting that precipitation affected PAH but not DDT and HCH distributions at a regional scale. Positive correlations between DDT concentrations and total organic carbon (TOC) contents of soils suggest hydrophobic organic contaminants were associated with organic matter. In contrast, TOC contents were correlated with PAHs in alfisols but not in pedocals. Pedocals contained mainly high molecular weight PAHs, indicating that eluviation affected the accumulation of less hydrophobic organic contaminants. Different correlations between low‐molecular‐weight PAH and HCH concentrations with TOC contents were found in alfisols, suggesting that contaminant structure may also affect the accumulation of less hydrophobic organic contaminants in these soils. Risk analysis suggested that potential ecological risks related to soils in the Corn Belt may lead to reduced maize production and the potential for human health risks in the future. Highlights: Few studies focus on regional‐scale factors that affect organic contaminant accumulation in soils. Environmental process affects less hydrophobic organic contaminant distribution at regional scale. Precipitation and eluviation affected accumulation of less hydrophobic contaminants in soils. PAH and OCP residues in the soil of maize fields may pose ecological risks affecting future crop production and human health.