Wenhuan Yang

Traditional ecological ditch technology is unable to enhance the water quality purification effect of highly salty water and improve the salt tolerance of plants. BA (Bacillus amyloliquefaciens) has a positive effect in alleviating salt stress and promoting plant growth. However, the mechanism by which BA enhances plant stress resistance and improves nutrient removal efficiency in the ecological ditch system under high salt stress conditions remains unclear. The experiment constructed two ecological ditches of [P(substrate + plants) and PM (substrate + plants + BA)], and four different salinity treatments (5 g/L, 10 g/L, 15 g/L and 20 g/L) were set up to investigate the removal efficiency of nitrogen and phosphorus in water, and plant growth and physiological indicators, antioxidant enzyme activities and inorganic salt ion concentrations under different salinity stresses by adding BA. It also clarified the relationship between plant growth physiology and the response of water nutrient salts. The results show that the PM treatments for purifying nutrients performed significantly better than the P treatments under different salinity stresses, the removal rates of TN, TP and NH4⁺-N increased by 13.61–22.50%, and the effect was the best at a salinity of 15 g/L. BA enhanced the salt tolerance by increasing the activities of SOD (superoxide dismutase), POD (peroxidase) and CAT (catalase) of plants, reducing the content of MDA (malondialdehyde), lowering the concentration of Na⁺ and increasing the concentration of K⁺, improving the growth and activity of plant roots. Meanwhile, through a comprehensive evaluation, it was determined that BA has the most significant promoting effect on the growth of reed (Phragmites australis), and stronger plant root system is the key to improving the overall purification efficiency of the system. This research provides a theoretical basis for enhancing the water purification effect of high salinity water through ecological ditch technology.

In cold arid regions, the relationships between dissolved organic matter (DOM) characteristics and heavy metal distributions across ice, water, and sediment interfaces remain insufficiently resolved. This study characterized DOM spectral features and examined their associations with measured metal distributions in a typical frozen eutrophic lake using excitation–emission matrices coupled with parallel factor analysis (EEMs-PARAFAC), ultraviolet-visible absorption spectroscopy (UV-Vis), and Fourier-transform infrared spectroscopy (FTIR). Protein-like substances dominated ice DOM, whereas water and sediment-derived DOM contained more humified fluorescent components. Fluorescence indices confirmed a primarily biological origin across all media, with ice showing the highest autochthonous microbial contribution (BIX = 1.23) but the lowest humification (HIX = 0.26), suggesting a greater contribution of recently produced protein-like fluorescent DOM in the ice samples. Water DOM showed the highest average HIX (1.88), followed by sediment-derived DOM (0.61) and ice DOM (0.26). The measured hydrochemical conditions, including weak alkalinity, elevated total dissolved solids (TDS), and locally low dissolved oxygen, provide environmental context for differences in metal distributions. Exploratory Spearman analysis at 17 matched water stations identified the strongest DOM–metal associations for HIX-As (rho = 0.474, p = 0.054) and FI-Zn (rho = 0.471, p = 0.056), indicating that DOM optical properties provide testable indicators of metal-distribution patterns but should be combined with direct binding and speciation measurements for mechanistic confirmation. Because ice was collected in January 2021, whereas water and sediment were collected in October 2020, cross-medium differences are interpreted as between-campaign associations rather than synchronous partitioning. These findings provide a basis for targeted winter monitoring and future binding, speciation, and freeze-concentration experiments in shallow eutrophic lakes.

Microorganisms play a crucial role in biogeochemical cycling within wetland ecosystems. Soil-environment-mediated seasonal changes in microbial structure require further investigation. However, the factors driving seasonal variations in the microbial abundance and diversity in the Daihai wetlands remain unclear. This study employed high-throughput sequencing technology to examine the bacterial community structure and diversity in the lakeshore zone of Daihai across different seasons and to explore the seasonal variations in the bacterial community structure and the influence of driving factors. The results indicated that Pseudomonadota and Bacteroidota dominate in spring and Pseudomonadota abundance further increases in summer, while organic-matter-decomposing microorganisms (e.g., Actinobacteriota and Bacteroidota) dominate in autumn. Microbial diversity indices indicated a significantly greater diversity in spring than in summer and autumn (p < 0.05). Changes in environmental variables were strongly associated with bacterial community changes, with variations in total nitrogen, ammonium nitrogen, and soil moisture content being identified as potential key factors influencing seasonal bacterial diversity trends. Furthermore, bacterial community assembly in spring is driven by both stochastic processes and environmental selection, suggesting that abundant nutrients and organic matter promote bacterial diversity. The findings of this study provide a theoretical basis for wetland ecosystem restoration and conservation.

Aquaculture wastewater is rich in nutrients such as nitrogen and phosphorus. If discharged directly without treatment, it can cause eutrophication of water bodies and the proliferation of algae. This study explores the treatment of aquaculture wastewater using cerium nitrate and hydrogen peroxide. To improve the treatment efficiency of ammonia and nitrite in aquaculture wastewater, a Box–Behnken design with three factors at three levels was used to optimize the process of treating aquaculture wastewater with cerium nitrate and hydrogen peroxide. The optimal process conditions for removing ammonia and nitrite were determined to be a Ce(NO₃)₃ dosage of 0.18 g/L, an H₂O₂ reaction concentration of 1.0%, and a reaction time of 30 min. Under the optimal reaction conditions, the degradation rate of ammonia and nitrite can reach 80% or more. Finally, high-throughput sequencing technology was used to explore the impact of cerium nitrate and hydrogen peroxide treatment on microbial community structure and metabolic pathways. The results showed that, at the phylum level, the dominant positions of Actinobacteriota, Proteobacteria, and Bacteroidota were maintained throughout the entire culture period. At the genus level, the relative abundance of the hgcI_clade genus under Actinobacteriota significantly increased, becoming the main dominant genus throughout the culture period. Under the condition of adding cerium nitrate and hydrogen peroxide, the metabolic functions of the microbial community were enhanced. The addition of cerium nitrate and hydrogen peroxide increased the abundance of key nitrogen metabolism genes such as amo, hao, and nap, thereby enhancing the potential nitrification/denitrification capabilities of microorganisms. The combination of cerium nitrate and hydrogen peroxide showed positive effects in the treatment of aquaculture wastewater, providing a new strategy for the green treatment of wastewater.

When treating municipal wastewater, nitrogen removal is often limited due to low C/N, which needs to be compensated for by additional carbon source injections. This study investigated the feasibility of using industrial-waste polyglycolic acid (PGA) as a carbon source for denitrification in an SBR to obtain an economical carbon source. The results revealed that an optimal denitrification performance in a methanol-fed activated sludge system was achieved with a PGA dosage of 1.2 mL/L, a pH of 7–8, and a dissolved-oxygen (DO) concentration of 3 ± 0.5 mg/L. Under these conditions, all quality parameters for effluent water met the required criteria [COD < 50 mg/L; TN < 15 mg/L; NH₄⁺-N < 5(8) mg/L]. PGA enhanced the variety and richness of microbial communities, thereby markedly increasing the relative abundance of major phyla such as Proteobacteria and Bacteroidota and major genera such as Paracoccus and Dechloromonas. Furthermore, PGA upregulated the expression of nitrogen-metabolism-related genera, including amo, hao, nar, and nor, which improved the denitrification performance of the system. This study provides a reference for applying PGA as a carbon source for low-C/N-wastewater treatment and solid-waste utilization.

The comparative study of the transformation among sediment phosphorus (P) fractions in different lake types is a global issue in lake ecosystems. However, interactions between sediment P fractions, environmental factors, and microorganisms vary with the nutrient status of lakes. In this study, we combine sequential extraction and metagenomics sequencing to assess the characteristics of P fractions and transformation in sediments from different lake types in the Inner Mongolian section of the Yellow River Basin. We then further explore the response of relevant microbial and environmental drivers to P fraction transformation and bioavailability in sediments. The sediments of all three lakes exhibited strong exogenous pollution input characteristics, and higher nutritional conditions led to enhanced sediment P fraction transformation ability. The transformation capacity of the sediment P fractions also differed among the different lake types at the same latitudes, which is affected by many factors such as lake environmental factors and microorganisms. Different drivers reflected the mutual control of weakly adsorbed phosphorus (WA-P), potential active phosphorus (PA-P), Fe/Al-bound phosphorus (NaOH-P), and Ca-bound phosphorus (HCl-P) with the bio-directly available phosphorus (Bio-P). The transformation of NaOH-P in reducing environments can improve P bioavailability, while HCl-P is not easily bioavailable in weakly alkaline environments. There were significant differences in the bacterial community diversity and composition between the different lake types at the same latitude (p < 0.05), and the role of P fractions was stronger in the sediments of lakes with rich biodiversity than in poor biodiversity. Lake eutrophication recovery was somewhat hindered by the microbial interactions of P cycling and P fractions within the sediment. This study provides data and theoretical support for exploring the commonalities and differences among different lake types in the Inner Mongolian section of the Yellow River Basin. Besides, it is representative and typical for promoting the optimization of ecological security patterns in ecologically fragile watersheds.