Qingqing Cao

The water quality purification of constructed wetlands (CWs) with adsorbent materials has been extensively studied, yet the impact on the improvement in water quality of natural sediment wetlands (SWs) remains unclear. In this study, CWs and SWs were established with biochar and activated carbon substrates, and high and low nitrogen (N) and phosphorus (P) pollution loads were applied. Additionally, relevant studies on the purification efficiencies of artificial wetlands under different pollution loads were reviewed. Results showed that the purification capacities of biochar and activated carbon were affected by the pollution load, and that there was significant interaction between the pollution load and wetland type (P = 0.000). The removal efficiencies of NH₄⁺, NO₃⁻, and total P in CWs were significantly higher than those in SWs. In particular, the removal stability of NO₃⁻ was higher in the BCW (77.12%) and ACW (75.94%) under high pollution loads (P = 0.000). As the pollution load increased, the TP removal efficiency of SWs decreased from 86.56% to 75.97%, while the addition of biochar significantly enhanced removal efficiency (94.57%). The BSW experiment was more efficient in purifying P and NH₄⁺ than ASW or SW. ACWs presented lowest microbial diversity and richness while higher metabolism of chemoheterotrophy and nitrate reduction. This study confirms that the addition of B can promote the sustainability of SW purification, and that both biochar and activated carbon exhibited varying adsorption characteristics in different wetland types. It demonstrates the improved purification potential in biochar added SWs.

Conversion of curtilage land into cropland or grassland can have substantial effects on soil nutrition and microbial activities; however, these effects remain ambiguous. This is the first study to compare the soil organic carbon (SOC) fractions and bacterial communities in rural curtilage, converted cropland, and grassland compared with cropland and grassland. This study determined the light fraction (LF) and heavy fraction (HF) of organic carbon (OC), dissolved organic carbon (DOC), microbial biomass carbon (MBC), and the microbial community structure by conducting a high-throughput analysis. Curtilage soil had significantly lower OC content, the DOC, MBC, LFOC and HFOC of grassland and cropland soils were 104.11%, 55.58%, 264.17%, and 51.04% higher than curtilage soil averagely. Cropland showed notably high bacterial richness and diversity, with Proteobacteria (35.18%), Actinobacteria (31.48%), and Chloroflexi (17.39%) predominating in cropland, grassland, and curtilage soil, respectively. Moreover, DOC and LFOC contents of converted cropland and grassland soils were 47.17% and 148.65% higher than curtilage soil while MBC content was 46.24% lower than curtilage soil averagely. Land conversion showed more significant effects on microbial composition than land-use differences. The abundant Actinobacteria and Micrococcaceae population and the low MBC contents indicated a “hungry” bacterial state in the converted soil, whereas the high MBC content, Acidobacteria proportion, and relative abundance of functional genes in the fatty acid and lipid biosynthesis indicated a “fat” bacterial state in cropland. This study contributes to the improvement of soil fertility and the comprehension and efficient use of curtilage soil.

Studying the CO₂-assimilation potential under the effect of glucose addition is of great significance to completely comprehend the dynamic carbon cycle in wetland ecosystems. Rhizospheric sediments (RS) and bulk sediments (BS) were selected, with the addition of glucose (G) or not, and two experimental pots (RSG and BSG) and two control pots (RS and BS) were formed. Then, within 45 h of glucose addition, the sediments were sampled at intervals of 4 h for dynamic monitoring. The bacterial communities encoded by CO₂-assimilating function genes (cbbL) and the corresponding activities of key enzyme (ribulose-1,5-bisphosphate carboxylase oxygenase, RubisCO), and the light fraction (LF) and heavy fraction (HF) of organic carbon (C) and nitrogen (N) of the samples were determined. The results demonstrated that the dynamic processes of glucose deposition and degradation occurred in sediments from RSG and BSG, with the greatest depositions of 2.35 and 2.48 mg·g⁻¹ in the 4th and 12th hour, respectively. The contents of LFOC, LFON, HFOC, and HFON decreased by 171.70%, 125.45%, 8.40%, and 68.17% in the RSG pot, and decreased by 221.55%, 102.61%, 0.07%, and 74.74% in the BSG pot, respectively, which suggested the dominant activities of C and N mineralization. The FT-MIR of LF showed different changes of typical chemical bonds between RSG and BSG during the process, which further indicated irregular and inconsistent mineralization activities. The RubisCO activities in the rhizospheric sediments (52.14 nmol (g·min)⁻¹ on average) were substantially greater than in the bulk sediments, which indicated the high potential of carbon assimilation in rhizospheric sediments. Moreover, it showed a lower trend in BSG, BS, and RS, but an increasing trend in RSG after the glucose addition, albeit the effects were recovered in the 45th hour. The cbbL-containing bacteria were more abundant in the rhizospheric sediments than in the bulk sediments, and this effect was higher than that of the glucose addition. Proteobacteria were the dominating phylum with mean values of 93.49%, and Burkholderiales was found to be the dominant order (37.74% on average). Moreover, the changes in bacterial composition between the rhizospheric sediments and bulk sediments were more pronounced than they were during the process. Therefore, the effects of glucose degradation on RubisCO activity and cbbL-containing bacteria were transient, but the effects on organic matter fractions were straightforward, which probably further change the bacterial abundance and composition.

High-ring polycyclic aromatic hydrocarbons (PAHs, Benzo[b]fluorathene (BbFA), etc.) are difficult to biodegrade in the water environment. To address this issue, an innovative method for the preparation of MnO₂ nanoflower/graphene oxide composite (MnO₂ NF/GO) was proposed for adsorption removal of BbFA. The physicochemical properties of MnO₂ NF/GO were characterized by SEM, TEM, XRD, and N₂ adsorption/desorption and XPS techniques. Results show that the MnO₂ NF/GO had well-developed specific surface area and functional groups. Batch adsorption experiment results showed that adsorption capacity for BbFA was 74.07 mg/g. The pseudo-second-order kinetic model and Freundlich isotherm model are fitted well to the adsorption data. These show electron-donor-acceptor interaction; especially π-π interaction and π complexation played vital roles in BbFA removal onto MnO₂ NF/GO. The study highlights the promising potential adsorbent for removal of PAHs.

The influence of Alternanthera philoxeroide (alligator weed) invasion on wetland organic matter (OM) accumulation and bacterial changes is rarely studied, but is possibly an important step for revealing the invasion mechanism. Thus, the distribution characteristics of light fraction organic carbon and nitrogen (LFOC and LFON), and heavy fractions organic carbon and nitrogen (HFOC and HFON) were analyzed. Sampling was done on two sediment depths (0–15 cm and 15–25 cm) of invaded and normal habitats of two natural wetlands and two constructed wetlands, and bacterial taxa and composition in surface sediments were also analyzed by high-throughput sequencing. In the surface sediments, the LFOC and LFON contents were significantly higher in the constructed wetlands (0.791 and 0.043 g·kg⁻¹) than in the natural wetlands (0.500 and 0.022 g·kg⁻¹), and the contents of the C and N fractions were also prominently higher in the invaded areas than in normal wetland habitats. The OM storage was relatively stable. Proteobacteria (55.94%), Bacteroidetes (5.74%), Acidobacteria (6.66%), and Chloroflexi (4.67%) were the dominant bacterial phyla in the wetlands. The abundance of Acidobacteria, Actinobacteria, and Gemmatimonadetes were significantly higher in the invaded areas than in the normal habitats. The relative high abundance-based coverage estimator (ACE) index in the constructed wetlands and invaded areas suggested the corresponding high bacterial diversity. The significant and positive relationship between Acidobacteria and organic nitrogen concentrations suggested their potential and positive interrelationships. This study demonstrated that the alligator weed invasion could significantly change the compositions of sediment organic matterand bacteria, thus further changing the nutrition cycle and wetland microhabitat.

As a significant reservoir of organic carbon (OC), natural wetlands play an important role in mitigating greenhouse effects. To determine what factors might influence OC, we analyzed the distributions of dissolved organic carbon (DOC), light fraction organic carbon (LFOC), and heavy fraction organic carbon (HFOC) in sediments taken from the Yanghe River Wetland (YRW) and assessed the effects of several environmental variables on the distribution of the different carbon types. The microbial community abundances and compositions of the sampled sediments were analyzed by 16S rRNA amplicon sequencing. Redundancy analysis (RDA) was used to reveal the environmental factors that affect the distribution of OC. The DOC and LFOC contents varied significantly in the research area, while HFOC content showed no variation. The DOC content was significantly affected by sediment pH, vegetation height, and microbial abundances, and the LFOC content was significantly affected by water pH. We also proposed a novel indicator to study the microbial effect on the distribution of OC content in wetlands: weighted abundance of related microbes (WARM). This study identifies the environmental factors that could affect the distribution of OC in a riverine wetland and outlines the calculation of a novel indicator.

The aim of this study was to explore the distribution characteristics, sources, ecological risks and health indexes of heavy metals in greenhouse vegetable soils (GVS) of vicennial cultivation. Concentrations of chromium (Cr), nickel (Ni), copper (Cu), zinc (Zn), cadmium (Cd), and lead (Pb) were detected, and principle component analysis and cluster analysis were conducted. The potential ecological risk index and health index of the metals were also calculated to evaluate their multi-effects. Concentrations of Ni, Cu, Zn, Cd, and Pb reached peaks in GVS duration of 6-10 or 11-15 years, representing the high metal accumulation. Additionally, concentrations of Cr were significantly higher during the first decade than the second decade of GVS duration, which may be related to its bio-accumulation and leaching. Metals in soil depths of 20-40 cm showed a trend of intensive accumulation, especially in the second decade of duration. Cluster analysis revealed that Cr, Ni, and Zn were mostly from similar anthropogenic activities, and significantly high Cd in the studied area indicated the excessive human input. Furthermore, risk index demonstrated that GVS duration of 6-10 years was in moderate ecological risk and GVS duration of the second decade had a high health index.