Dissolved organic carbon (DOC) is a critical component of aquatic carbon cycling and a key indicator of water quality in lake ecosystems. As the largest river-connected freshwater lake in China, Poyang Lake exhibits dramatic seasonal water level fluctuations (WLFs) and substantial spatial heterogeneity in hydrological connectivity. However, the drivers and mechanisms regulating DOC dynamics across its hydrologically distinct sub-lakes remain poorly understood. Based on quarterly monitoring data (2019–2022) from ten sampling sites in two typical regions—the relatively enclosed Cuoji Lake and the highly interconnected Nanji Wetland—this study investigated the spatiotemporal variations of DOC and identified the dominant controlling factors. Results showed that DOC concentrations in Cuoji Lake ranged from 0.54 to 4.61 mg/L (mean: 2.46 ± 0.07 mg/L) with significant seasonal fluctuations, peaking in the dry season (January: 3.52 mg/L) and declining in the flood season (July: 2.58 mg/L). In contrast, DOC in Nanji Wetland varied from 1.52 to 9.61 mg/L (mean: 3.82 ± 1.72 mg/L) without significant temporal variation. The correlation heatmap revealed no significant relationship between DOC and water level in either sub-lake, indicating that WLFs are not the dominant driver. Instead, hydrological connectivity, shaped by geomorphological enclosure, mediated DOC responses. Cuoji Lake’s seasonal DOC pattern was modulated indirectly by hydrological changes, while Nanji Wetland’s stability reflected a balance between allochthonous inputs and autochthonous production. Additionally, DOC was positively correlated with nutrients (NH4+-N, PO₄3−-P, TP), COD, chlorophyll a, and phytoplankton biomass, highlighting joint regulation by internal biogeochemical processes. These findings clarify the multi-factor regulation of DOC in hydrologically heterogeneous sub-lakes, emphasizing hydrological connectivity, organic matter sources, nutrients, and phytoplankton rather than water level as the main regulators shaping DOC dynamics in Poyang Lake’s sub‑lakes. The results provide scientific support for carbon cycling assessment and water quality management in large river-connected lakes.

Duckweed exhibits distinct advantages over other aquatic plants in phytoremediation. Bioaugmentation is a promising approach for enhancing the treatment performance of various wastewater treatment systems, including duckweed-based systems (DS). However, there is a lack of suitable inoculants for field-scale DS bioaugmentation, and the long-term viability and mechanisms of these inoculants are still poorly understood. To address this, a single strain (Pseudomonas sp. DWP1) and a mixed culture (activated sludge) were separately added into two carrier-enhanced DS to systematically evaluate their application potential for DS bioaugmentation by comparing with another control DS over a year. The results indicated that adding strain DWP1 and activated sludge increased the dissolved oxygen concentration and oxidation-reduction potential of pond water. Meanwhile, they promoted duckweed growth (by 64.95% and 41.39%, respectively), enhanced nutrient recovery (by 68.97% and 44.83% for nitrogen, and 71.43% and 42.86% for phosphorus, respectively) and pollutant removal in the DS, and reduced CH4 emission (by 68.88% and 33.16%, respectively) from the DS. Compared with activated sludge, strain DWP1 had a more significant impact on microbial diversity, community composition, and the relative abundance of dominant assemblages probably due to its high adaptability and successful survival in the duckweed system, which results in the better bioaugmentation performance of strain DWP1 in terms of duckweed biomass production, water purification, and carbon emission reduction in the DS. Therefore, strain DWP1 has greater application potential than activated sludge for the bioaugmentation of the DS.

Dissolved Organic Carbon (DOC) is a core environmental factor that sustains aquatic ecosystem stability and regulates the structure and function of lake ecosystems. Poyang Lake, the largest river-connected freshwater lake in China, is characterized by extreme seasonal water level fluctuations (WLFs). To clarify the coupling mechanisms between WLFs and DOC concentrations and identify key influencing environmental factors, quarterly monitoring was conducted at ten sampling sites in two typical regions (the relatively enclosed Cuoji Lake and the extensively interconnected Nanji Wetland) from 2019 to 2022. Results showed that DOC concentrations in Cuoji Lake ranged from 0.54 to 4.61 mg/L (mean: 2.46 ± 0.07 mg/L) with significant seasonal differences (peak: 3.52 mg/L in dry-season January; trough: 2.58 mg/L in flood-season July), while those in Nanji Wetland varied from 1.52 to 9.61 mg/L (mean: 3.82 ± 1.72 mg/L) without marked temporal variation. WLFs were identified as the dominant driver of DOC dynamics, exhibiting a strong negative correlation: flood-season high water diluted DOC through enhanced hydrodynamic mixing, while dry-season low water accelerated vegetation litter decomposition and inhibited DOC transportation, leading to DOC accumulation. Additionally, DOC concentrations were positively correlated with ammonia nitrogen, phosphate, chemical oxygen demand, chlorophyll a, and water temperature. Nutrients promoted microbial decomposition of organic matter, and phytoplankton (dominated by Bacillariophyta and Chlorophyta; Cyanobacteria accounted for 7.06% in Cuoji Lake and 16.02% in Nanji Wetland) released photosynthates, both contributing to DOC accumulation. This study reveals the coupling relationship between WLFs and DOC concentrations, supplements key parameters for global seasonal lake carbon flux estimation, and provides scientific support for wetland carbon cycle conservation, water quality management, and algal bloom prevention in Poyang Lake and similar aquatic ecosystems worldwide.

To elucidate the driving factors and regulatory mechanisms of epilithic algal communities in subtropical rural rivers, we investigated the water physicochemical parameters, sediment characteristics, phytoplankton, macroinvertebrates, and epilithic algal communities in the Shilipu and Xiabu Rivers during the summer period (June and August 2023). A total of 131 epilithic algal species belonging to five phyla were identified, with Cyanobacteria, Chlorophyta, and Bacillariophyta constituting the dominant groups. Core dominant species included Lyngbya sp. C. Agardh, 1824, Oscillatoria sp. Vauch., 1803, and Gomphonema sp. Agardh, 1824. Epilithic algal communities exhibited significant monthly differences, with both biomass and abundance being significantly higher (p < 0.05) in August than in June. Environmental factors, encompassing both abiotic and biotic parameters, collectively explained 56.76% and 56.99% of the variation in epilithic algal abundance and biomass, respectively. Water physicochemical parameters and phytoplankton biomass emerged as the core driving factors. Both showed highly significant positive correlations with epilithic algal abundance (R = 0.26, p < 0.001; R = 0.27, p < 0.001) and biomass (R = 0.21, p < 0.001; R = 0.27, p < 0.001). Sediment factors exerted a mild regulatory effect (abundance: R = 0.13, p < 0.05; biomass: R = 0.17, p < 0.01) by releasing nutrients to supplement the water column. The impact of macroinvertebrates was weak and biomass-dependent, showing only a weakly significant positive correlation with epilithic algal biomass (R = 0.12, p < 0.05). This study reveals the synergistic regulatory effects of abiotic and biotic factors on epilithic algal communities in subtropical rural rivers, where elevated external nutrient input attenuates the competitive effects of phytoplankton and the grazing pressure of macroinvertebrates. This provides a scientific basis for the ecological monitoring and restoration of similar river systems.

This study analyzed phytoplankton monitoring data (2019-2023) from the middle-lower reaches of the Xin River to clarify cyanobacterial spatiotemporal distributions and their environmental drivers. Sixty-six phytoplankton genera across seven phyla were detected, with Chlorophyta being the dominant phylum, followed sequentially by Bacillariophyta and cyanobacteria. The inter-annual variation of phytoplankton biomass ranged from 2.42 to 11.46 mg/L, while the cyanobacteria biomass varied from 0 to 2.63 mg/L, accounting for 7.54% of the total phytoplankton biomass. The dominant cyanobacteria species included Microcystis, Planktothrix, and members of Phormidioideae, with the dominant species showing some heterogeneity across different regions. For the study area, the average River Trophic Status Index (RSI) was recorded as 54.89, indicating seasonal water quality variations: favorable during the dry season; slightly polluted in most river sections during the rising period; moderately polluted in most sections during the wet period; and generally slightly polluted during the rece ssion period. Statistical analyses (Pearson correlation and redundancy analysis (RDA)) revealed that cyanobacteria and their dominant species had significant correlations (p < 0.05) with environmental factors including total phosphorus (TP), orthophosphate (PO4 3--P), dissolved total nitrogen (DTN), chemical oxygen demand (CODMn), Secchi Depth (SD), were the primary environmental factors driving the spatiotemporal distribution of cyanobacteria. This study provides for the first time an earlier seasonal emergence of cyanobacteria in lake entrance areas, addresses the domestic gap concerning inadequate attention to small and medium-sized rivers (e.g., the Xin River) relative to large lakes such as Taihu Lake and Chaohu Lake and holds crucial reference value for early warning systems aimed at preventing cyanobacterial encroachment into Poyang Lake.

In Northeast China, waterlogging has emerged as a significant challenge due to climate change, particularly during the June–August period when spring maize (Zea mays L.), at the post-tasseling phase, impedes a comprehensive understanding of responses and the development of resistance technologies. 2-(3,4-dichlorophenoxy) triethylamine (DCPTA) is suitable for the entire lifecycle of various economic and food crops, improving crop quality and enhancing stress resistance. The study investigated the ear leaf photosynthesis in relation to the root antioxidant systems’ differential responses of spring maize to waterlogging among the tasseling (VT), vesicle (R2) and dough (R4) stages, and the exogenous DCPTA regulating effect. Results revealed that waterlogging inhibited root physiological activity due to oxidative damage. Consequently, the stomatal restriction and non-stomatal restriction on photosynthesis appeared successively, and R4 was the most sensitive stage. Pretreatment with DCPTA reduced stomatal restriction by maintaining water transfer to the leaf through maintaining root physiological activity via enhanced ascorbate–glutathione cycle. Delayed non-stomatal restriction appeared due to relatively stable chlorophyll content and photosynthetic activities, and VT stage exhibited the highest susceptibility to DCPTA. The study provides a necessary theoretical foundation for comprehending the physiological mechanisms underlying yield formation of spring maize under waterlogging stress in Northeast China, and offers valuable insights for the development of chemical regulation technology.

To elaborate on the effects of hydraulic projects and physicochemical factors on the spatiotemporal distribution of phytoplankton communities, we monitored the phytoplankton communities and related water parameters in the Ganjiang River’s main channel over a five-year period. The survey revealed 65 species across six phyla, with Chlorophyta, Cyanophyta and Bacillariophyta as the most diverse groups. Phytoplankton abundance and biomass exhibited significant seasonal variations (p < 0.001), peaking in summer and autumn and reaching their lowest values in winter and spring. Spatially, phytoplankton abundance and biomass were not significantly different (p > 0.05), the abundance and biomass of Cyanophyta were higher in the two reservoir areas compared to the upstream sampling points. This suggests that the hydraulic projects altered the river’s flow and velocity, which led to a succession in phytoplankton community composition. Correlation analysis showed a strong positive association between the abundance and biomass of both Cyanophyta and Chlorophyta and water temperature (p < 0.001), but showed a significant negative relationship with nitrogen (p < 0.05). In contrast, Bacillariophyta abundance and biomass were positively and significantly correlated with ammonium nitrogen (p < 0.05). Redundancy analysis confirmed that water temperature and nitrogen are the primary environmental variables influencing the phytoplankton community’s succession. The direct alteration of river hydrodynamic characteristics by hydraulic projects, coupled with the reservoir-induced water stratification and its influence on vertical water temperature distribution, ultimately results in the profound reshaping of the phytoplankton community structure through coupled effects with nitrogen cycling. The findings from this study can scientifically inform the ecological scheduling, water quality management and water supply security of the Ganjiang River basin’s cascade reservoirs.

Iron and calcium salts are two commonly used inactivators of sediment phosphorus (P). However, there is limited research on the effectiveness of their combined use. In this study, two enclosures (each 600 m2) were constructed in a eutrophic sub-lake within Poyang Lake (the largest freshwater lake in China), to examine the inhibitory effect of iron-calcium combined treatment (Fe&Ca treatment) on sediment P release. Subsequently, a sediment incubation experiment was conducted to investigate the impact of Fe treatment alone, Ca treatment alone, and Fe&Ca treatment on sediment P release fluxes and P fractions. The enclosure experiment demonstrated that the Fe&Ca treatment resulted in a decrease of 0.65 times in non-apatite inorganic P (NAIP) content in sediment, and an increase of 2.87 times in apatite P (AP) content. The sediment P release in the treated enclosure was significantly reduced by up to 90% under alkaline conditions compared to the control enclosure. In the sediment incubation experiment, Fe&Ca treatment effectively restrained P release and enhanced sediment AP content while reduced NAIP content. The transformation from NAIP to AP was likely primarily driven by Ca treatment, while Fe&Ca treatment stabilized water pH and consequently inhibited the release of sediment P and nitrogen. This study is the first to validate this transformation pathway and its inhibitory effect on P release. These findings emphasize the effectiveness of iron and calcium combination for minimizing the risk of P release from sediments, thereby offering a promising approach for in situ P control in lakes.

Eutrophication of water bodies significantly accelerates water quality degradation, leading to the decline of aquatic organisms. To evaluate the synergistic restoration effects of submerged macrophyte Hydrilla verticillata and filter-feeding bivalve Anodonta woodiana on hypereutrophic water, a 40-day mesocosm simulation experiment in hypereutrophic aquatic ecosystems was conducted by setting up four treatments: control group (CK), A. woodiana group (Aw), H. verticillata group (Hv), and combined H. verticillata + A. woodiana group (HA). The results indicated that the combined application of H. verticillata and A. woodiana significantly reduced total phosphorus (TP), chlorophyll a (Chl a) concentration, and turbidity in the water, with removal rates reaching 58.3%, 60.6%, and 85.4%, respectively. The introduction of A. woodiana substantially altered the algal community composition. At the end of the experiment, the average proportion of cyanobacteria in the CK and Hv groups was 55.6%, whereas in the Aw and HA groups it decreased to 36.0%. Both total phosphorus and water-soluble phosphorus contents in H. verticillata tissues were significantly lower in HA compared to Hv, indicating that the combined treatment could reduce the risk of internal phosphorus release after H. verticillata senescence. These findings collectively demonstrate that the combination of H. verticillata and A. woodiana represents an efficient and environmentally friendly ecological restoration technology of eutrophic waters.

Iron (Fe) and calcium (Ca) are two commonly used sediment phosphorus (P) inactivators. However, both have limitations when used alone, and few studies have investigated the effectiveness of their combined use. In this study, two sediments with different nutrient levels (high-nutrient sediment, HS, and low-nutrient sediment, LS) were selected to study the effects of adding ferric chloride alone (Fe treatment), calcium hydroxide alone (Ca treatment), and their combined addition (Fe&Ca treatment) on the P release flux and P fractions in the sediments. The results showed that Fe treatment significantly inhibited P release from HS and LS, and their P fluxes at the end of the experiment were −0.137 mg·m ^−2 ·d ^−1 and −0.135 mg·m ^−2 ·d ^−1 , respectively. In terms of P removal and fluxes, the efficacy of Fe&Ca treatment was comparable to that of Fe treatment alone. However, Fe&Ca treatment exhibited superior inhibitory effects on total nitrogen and ammonia nitrogen compared to Fe treatment alone. In addition, the Fe&Ca and Ca treatments significantly increased the sediment apatite P content and decreased the non-apatite inorganic P content, whereas the Fe treatment significantly decreased the apatite P content. The inhibitory effects of Fe&Ca on P in both sediments were greater than that of Ca alone, and there was no significant difference between the Fe&Ca and Fe treatments. This study showed that the combined treatment of Fe and Ca can effectively make up for the deficiencies of the single treatment method, demonstrating significant synergistic effects, thus providing a practical and efficient method for in situ control of the release of nutrients in lake sediments.

Phosphorus (P) is a critical nutrient that limits primary productivity in aquatic ecosystems. Submerged macrophytes exhibit strong capabilities for P absorption and sequestration. The P content and its fractional composition within these plants directly reflect the bioavailability of P in the ambient environment, thus providing a sensitive measure of their physiological and ecological responses to environmental changes. This study employed a sequential extraction method to partition the total plant P (TPplant) into water-soluble P (H2O-P), non-reactive organic P (NaOH-P), and calcium-bound P (HCl-P). Field surveys on submerged macrophytes in two lakes with contrasting trophic statuses were conducted to characterize interspecific variations in P fractions within submerged macrophytes and their responses to environmental changes. The study revealed a robust positive correlation between H2O-P (in contrast to NaOH-P and HCl-P) and TPplant contents, indicating that H2O-P serves as a reliable indicator for inferring the TPplant. Moreover, species characterized by a high proportion of H2O-P are more sensitive to eutrophication. There is significant interspecific variation in the H2O-P content within submerged macrophytes. The divergence in H2O-P content among these plants may be attributed to their inherent ecological strategies.

Currently, the issue of eutrophication and cyanobacterial blooms persists in water bodies worldwide, prompting the exploration of various treatment methods. This study conducted a comparative analysis of eutrophic water bodies using ferric chloride-modified zeolite (FMZ) and calcium hydroxide-modified zeolite (CMZ) combined with Elodea nuttallii (E. nuttallii) for removal and purification effects. The results revealed that the addition of E. nuttallii had a sustained inhibitory effect on phosphorus release, maintaining stability with lower Turbidity(Tur) and stabilized pH within the range of 8.5-9. FMZ demonstrated rapid reduction in dissolved phosphorus concentration, achieving a removal rate of 96% within 3 days. The combined plant group of CMZ and FMZ exhibited synergistic effects with E. nuttallii, achieving an impressive total phosphorus (TP) removal rate of 80.13% and a total nitrogen (TN) removal rate of 48.77%. Additionally, chlorophyll a (Chl a) concentration decreased from 100.74 +/- 24.72 mu g l-1 to 49.96 +/- 2.08 mu g l-1. The phytoplankton community composition indicated that diatoms thrived in low temperatures and high NH4 conditions. Under the same low Total Nitrogen to Total Phosphorus (TN:TP) ratio, high TP concentrations were associated with cyanobacteria dominance, while green algae dominated in other scenarios. This comprehensive approach demonstrates the potential efficacy of CMZ and FMZ combined with E. nuttallii in addressing eutrophic water bodies and mitigating cyanobacterial blooms.

Dredging, adsorbent inactivation, and phytoremediation are commonly used to control internal nitrogen and phosphorus sediment loads in eutrophic still-water ecosystems, such as lakes and ponds. However, the effectiveness of these remediation techniques has not been verified for rivers, lakes, and reservoirs with large disturbances. In this study, a calcium-loaded clay granular adsorbent (CRB) was prepared as an alternative to commercial adsorbents, and an experiment was conducted on the ecological restoration effects of both dredging and adsorbent single treatments as well as combined treatments on eutrophic flowing water. The enhancement effect of phytoremediation on the above restoration techniques was investigated. The results indicated that CRB inactivation treatment reduced the phosphorus and turbidity of the water by 63% and 80%, respectively and increased the total nitrogen and permanganate index (CODMn) by 25% and 101% before phytoremediation, respectively compared to the control group. There were no significant differences in the nutrient indexes of the sediment and water between the dredging treatment and the control group, but dredging enhanced the effect of the CRB treatment. Compared with the CRB treatment, the total nitrogen and CODMn of water in the dredging and combined CRB treatments decreased by 13% and 15%, respectively. Phytoremediation significantly improved the effectiveness of the dredging and adsorbent treatments, both individually and in combination. Additionally, there were notable differences in the growth rates of the submerged plants and the contents of different phosphorus speciation among the plant species. Selecting suitable plant species is recommended when implementing phytoremediation methods. This study highlights that the combination of multiple restoration techniques is effective for eutrophic flowing water. The results provide a guide for the ecological restoration of flowing water.

Eutrophication and its resulting harmful algal blooms greatly reduce the ecosystem services of natural waters. The use of modified clay materials to assist the phytoremediation of eutrophic water is a promising technique. In this study, ferric chloride and calcium hydroxide were respectively loaded on red soil for algal flocculation and phosphorus inactivation. A two-by-two factorial mesocosm experiment with and without the application of ferric- and calcium- loaded red soil (FA), and with and without planting the submerged macrophyte Vallisneria natans was conducted for the in-situ repair of eutrophic water and sediment. Furthermore, field enclosure application was carried out to verify the feasibility of the technology. At the end of the mesocosm experiment, the total phosphorus, total nitrogen, and ammonia nitrogen concentrations in water were reduced by 81.8 %, 63.3 %, and 62.0 %, respectively, and orthophosphate phosphorus concentration in the sediment-water interface decreased by 90.2 % in the FA + V. natans group compared with those in the control group. The concentration and proportion of chlorophyll-a in cyanobacteria decreased by 89.8 % and 71.2 %, respectively, in the FA + V. natans group. The content of active phosphorus in V. natans decreased and that of inert phosphorus increased in the FA + V. natans group, compared with those in the V. natans alone group, thus may reducing the risk of phosphorus release after decomposing of V. natans. The sediment bacterial diversity index did not change significantly among treatments. Field enclosure application have also been successful, with chlorophyll-a concentration in the water of treated enclosure decreased from above 200 μg/L to below 10 μg/L, and phosphorus concentration in the water decreased from >0.6 mg/L to <0.02 mg/L. These results demonstrated that the FA in combination with submerged macrophyte planting had great potential for the in-situ remediation of eutrophic water, especially those with severe algal blooms.

The application of plant hormones such as indoleacetic acid (IAA) has attracted increasing attention for enhancing the potential of phytoremediation. Research suggests that Cinnamomum camphora is resistant to heavy metals and suitable for soil remediation. However, the mechanism of how IAA would alleviate the cadmium (Cd) stress in C. camphora remains unclear. This study evaluated the effects of IAA application on the Cd uptake by C. camphora seedlings in Cd contaminated soils, with growth, physiological, and biochemical characteristics explored. Results showed that the Cd accumulation in C. camphora increased with the rising soil Cd concentrations. Under the Cd stress, especially for the high-level stress, the growth and photosynthesis of C. camphora declined, while the peroxidase activity, the contents of malondialdehyde (MDA) and osmotic regulators (including soluble sugars, soluble proteins, proline) increased on contrary. The IAA application in general alleviated the negative influences of Cd stress on C. camphora by enhancing the Cd accumulation in plants, promoting biomass and the photosynthetic efficiency, improving the superoxide dismutase activity, but reducing the contents of MDA and osmotic regulators. Overall, C. camphora has a good defense system with high capabilities in Cd tolerance and accumulation, which are conducive to its normal growth and metabolism under the Cd stress, and therefore is suitable for remediating Cd contaminated soils.

The increasing demand for environmentally friendly agricultural practices has driven the need for diversified crop cultivation to optimize crop productivity while minimizing carbon footprints (CFs). However, the impacts of crop diversification on crop production and environmental benefits are still poorly understood. In this study, conducted at two sites in the Yellow River Delta, China, we investigated the effects of legume intercropping, specifically maize/soybean (M/S) and maize/peanut (M/P) systems, on crop productivity, economic return, ecosystem economic budget (NEEB), CF, and carbon sustainability index (CSI) in comparison to conventional monocrops. Crops were grown in replicated field plots and fertilized in their strips according to common practice for monocrops. Compared to the expected averages of monocrops, maize/legume intercropping demonstrated higher crop yields, with M/S achieving a 37% and 43% increase at the two sites, respectively, and M/P achieving an 11% and 20% increase. The higher overyielding in M/S was attributed to stronger selection effects, i.e., interspecific facilitation. However, the complementarity effects induced by the competitive dominance of maize were similar in both intercropping systems. Additionally, M/S exhibited greater potential for improving net revenues compared to M/P. Life cycle assessments revealed lower CFs in the intercropping systems compared to monocultures. M/S reduced CFs per unit of area by 26.8% at both sites, CFs per unit of maize equivalent energy yield by 25% and 33%, and CFs per unit of revenue by 20% and 25% at the two sites, respectively. M/P also resulted in reduced CFs, albeit to a lesser extent. Intercropping enhanced the CSI, with the highest values observed in the M/S system. However, both intercropping systems showed limited effects on soil C sequestration. Overall, our results highlight that maize/legume intercropping is a feasible approach to enhance crop productivity while reducing CFs. The M/S system outperformed the M/P system in terms of crop yields, economic benefits, and CF reduction. However, the intercropping systems showed limited effects on SOC storage. This study provides important implications for sustainable agriculture by appropriate crop diversification.

A long-term field experiment was conducted to study the diversity of soil bacterial communities and the response of crop growth to biochar application, in order to provide a scientific basis for the rational application of biochar in agricultural fields. Four treatments were applied at 0 (B0 blank), 5 (B1), 10 (B2), and 20 t·hm-2(B3) to investigate the effects of biochar on soil physical and chemical properties, soil bacterial community diversity, and growth of winter wheat using Illumina MiSeq high-throughput sequencing technology. The results showed that soil water content, pH value, soil organic carbon, total nitrogen, nitrate nitrogen content, winter wheat biomass, nitrogen uptake, and yield showed an increasing trend with the increase in biochar amount. The high-throughput sequencing results showed that the B2 treatment significantly reduced the alpha diversity of the bacterial community at the flowering stage. The overall response of soil bacterial community composition to different application rates of biochar and phenological phases was taxonomically consistent. In this study, Proteobacteria, Acidobacteria, Planctomycetes, Gemmatimonadetes, and Actinobacteria were the dominant bacterial phyla. The relative abundance of Acidobacteria decreased, but the relative abundance of Proteobacteria and Planctomycetes increased with biochar application. The results of redundancy analysis, co-occurrence network analysis, and PLS-PM analysis indicated that bacterial community compositions were closely associated with soil parameters such as soil nitrate and total nitrogen. The average connectivity between 16S OTUs was higher under the B2 and B3 treatments (16.966 and 14.600) than under the B0 treatment. The variation in soil bacterial community (89.1%) was regulated by biochar and sampling period and partly explained the changes in the growth dynamics of winter wheat (0.077). In conclusion, biochar application could regulate the changes in the soil bacterial community and promote crop growth after seven years of application. It is suggested that 10-20 t·hm-2 biochar should be applied in semi-arid agricultural areas to achieve sustainable agricultural development.

Understanding how phytoplankton interacts with local and regional drivers as well as their feedbacks is a great challenge, and quantitative analyses of the regulating role of human activities and climate changes on these feedback loops are also limited. By using monthly monitoring dataset (2000-2017) from Lake Taihu and empirical dynamic modelling to construct causal networks, we quantified the strengths of causal feedbacks among phytoplankton, local environments, zooplankton, meteorology as well as global climate oscillation. Prevalent bidirectional causal linkages between phytoplankton and the tested drivers were found, providing holistic and quantitative evidence of the ubiquitous feedback loops. Phytoplankton exhibited the highest feedbacks with total inorganic nitrogen and ammonia and the lowest with nitrate. The feedbacks between phytoplankton and environmental factors from 2000 to 2017 could be classified by two groups: the local environments (e.g., nutrients, pH, transparency, zooplankton)-driven enhancement loops promoting the response of the phytoplankton, and the climate (e.g., wind speed)-driven regulatory loops suppressing it. The two counterbalance groups modified the emergent macroecological patterns. Our findings revealed that the causal feedback networks loosened significantly after 2007 following nutrient loading reduction and unsuccessful biomanipulation restoration attempts by stocking carp. The strength of enhancement loops underwent marked decreases leading to reduced phytoplankton responses to the tested drivers, while the climate (decreasing wind speed, warming winter)-driven regulatory loops increased– like a tug-of-war. To counteract the self-amplifying feedback loops, the present eutrophication mitigation efforts, especially nutrient reduction, should be continued, and introduction of alternative measures to indirectly regulate the critical components (e.g., pH, Secchi depth, zooplankton biomass) of the loops would be beneficial.

ABSTRACT: The combined pollution of antibiotics and heavy metals in the livestock industry wastewater has drawn considerable attention. In this study, a hybrid material of Cu-Mn binary oxide (CMBO) was used to activate persulfate (PS) for the enhanced co-removal of arsenite [As(III)] and tetracycline (TC) from water. Although the two pollutants posed a mutual impact on the removal efficiency of each other by using CMBO, the addition of PS could improve their co-removal performance remarkably. Sufficient experimental explorations confirmed the mechanism for TC removal was changed from adsorption to degradation, thus alleviating the impact effect of As(III) on TC removal. The by-products after TC degradation might compete for the oxidation and adsorption active sites with As species. The spectroscopic analysis results indicated that As(III) was directly adsorbed via inner-sphere complexation or removed through an “oxidation-adsorption” process with electrons transferred to Mn oxides or reactive oxygen species. The radicals played a dominant role in the co-removal process. Two possible pathways for TC degradation were proposed based on the HPLC–ESI–MS results assisted with DFT calculations. This contribution shed a new light on the technologies towards the co-removal of combined contaminants from water.

Bacterivorous nematodes are abundant in petroleum-contaminated soils. However, the ecological functions of bacterivorous nematodes and their impacts together with the addition of organic materials on the activity and diversity of microorganisms in petroleum-contaminated soils remain unknown. To assess such effects, six treatments were established in this study, including uncontaminated nematodes-free soil (Control), petroleum-contaminated soil (PC), petroleum-contaminated soil + 5 nematodes per gram dry soil (PCN), and petroleum-contaminated soil + 5 nematodes per gram dry soil + 1% wheat straw (PCNW), or + 1% rapeseed cake (PCNR), or + 1% biochar (PCNB). Results showed that the enzyme activities in the six treatments generally increased firstly and then decreased during the incubation period. Compared with Control, the invertase activity in PCNW, PCNR, and PCNB increased by 80.6%, 313.5%, and 12.4%, respectively, whereas the urease activity in PC, PCN, PCNW, PCNR, and PCNW increased by 1.2%, 25.5%, 124.3%, 105.3%, and 25.5%, respectively. Petroleum pollution, inoculation of bacterivorous nematodes, and the addition of organic materials all significantly boosted the concentrations of phospholipid fatty acids (PLFAs) of soil bacteria, actinobacteria, and total microorganisms, and increased the concentrations of both G+ and G− bacteria PLFAs and the ratio of G−/G+. The concentration of fungi PLFAs and the ratio of fungi to bacteria were significantly higher in PCNW and PCNR than those in other treatments. Overall, adding bacterivorous nematodes and organic materials to the petroleum-contaminated soil significantly improved soil microbial activity and community structure, suggesting that bacterivorous nematodes could be used for the bioremediation in petroleum contaminated soils.