New perspectives on microbiome and nutrient sequestration in soil aggregates during long-term grazing exclusion.

Grazing exclusion alters grassland soil aggregation, microbiome composition, and biogeochemical processes. However, the long-term effects of grazing exclusion on the microbial communities and nutrient dynamics within soil aggregates remain unclear. We conducted a 36-year exclusion experiment to investigate how grazing exclusion affects the soil microbial community and the associated soil functions within soil aggregates in a semiarid grassland. Long-term (36 years) grazing exclusion induced a shift in microbial communities, especially in the <2 mm aggregates, from high to low diversity compared to the grazing control. The reduced microbial diversity was accompanied by instability of fungal communities, extended distribution of fungal pathogens to >2 mm aggregates, and reduced carbon (C) sequestration potential thus revealing a negative impact of long-term GE. In contrast, 11-26 years of grazing exclusion greatly increased C sequestration and promoted nutrient cycling in soil aggregates and associated microbial functional genes. Moreover, the environmental characteristics of microhabitats (e.g., soil pH) altered the soil microbiome and strongly contributed to C sequestration. Our findings reveal new evidence from soil microbiology for optimizing grazing exclusion duration to maintain multiple belowground ecosystem functions, providing promising suggestions for climate-smart and resource-efficient grasslands.

Enhancing nitrogen and phosphorus removal in plant-biochar-pyrite stormwater bioretention systems: Impact of temperature and high-frequency heavy rainfall.

Global climate change and rapid urbanization have resulted in more frequent and intense rainfall events in urban areas, raising concerns about the effectiveness of stormwater bioretention systems. In this study, we optimized the design by constructing a multi-layer filler structure, including plant layer, biochar layer, and pyrite layer, and evaluated its performance in nitrogen (N) and phosphorus (P) removal under different temperatures (5-18 °C and 24-43 °C), rainfall intensity (47.06 mm rainfall depth), and frequency (1-5 days rainfall intervals) conditions. The findings indicate that over 775 days, the plant system consistently removed 62.3% of total nitrogen (TN) and 97.0% of total phosphorus (TP) from 103 intense rainfall events. Temperature fluctuations had minimal impact on nitrate nitrogen (NO3--N) and TP removal, with differences in removal rates of only 1.0% and 0.6%, respectively, among plant groups. Across the multi-layer structure, plant roots mitigated the impact of temperature differences on NO3--N removal, while high-frequency rainfall fluctuated the stability of NO3--N removal. Dense plant roots reinforced N and P removal by facilitating denitrification in the vadose zone (biochar) and strengthening denitrification processes. Biochar and pyrite contributed to stable microenvironments and diverse ecological functions, enhancing NO3--N and PO43- removal. In summary, the synergistic effects of the multi-layer filler structure improved and stabilized N and P removal, providing valuable insights for addressing runoff pollution in bioretention systems amidst rapid urbanization and climate change challenges.

Deep insights into the assembly mechanisms, co-occurrence patterns, and functional roles of microbial community in wastewater treatment plants.

The understanding of activated sludge microbial status and roles is imperative for improving and enhancing the performance of wastewater treatment plants (WWTPs). In this study, we conducted a deep analysis of activated sludge microbial communities across five compartments (inflow, effluent, and aerobic, anoxic, anaerobic tanks) over temporal scales, employing high-throughput sequencing of 16S rRNA amplicons and metagenome data. Clearly discernible seasonal patterns, exhibiting cyclic variations, were observed in microbial diversity, assembly, co-occurrence network, and metabolic functions. Notably, summer samples exhibited higher α-diversity and were distinctly separated from winter samples. Our analysis revealed that microbial community assembly is influenced by both stochastic processes (66%) and deterministic processes (34%), with winter samples demonstrating more random assembly compared to summer. Co-occurrence patterns were predominantly mutualistic, with over 96% positive correlations, and summer networks were more organized than those in winter. These variations were significantly correlated with temperature, total phosphorus and sludge volume index. However, no significant differences were found among microbial community across five compartments in terms of ß diversity. A core community of keystone taxa was identified, playing key roles in eight nitrogen and eleven phosphorus cycling pathways. Understanding the assembly mechanisms, co-occurrence patterns, and functional roles of microbial communities is essential for the design and optimization of biotechnological treatment processes in WWTPs.

Insights into carbon-neutral treatment of rural wastewater by constructed wetlands: A review of current development and future direction.

In recent years, with the global rise in awareness regarding carbon neutrality, the treatment of wastewater in rural areas is increasingly oriented towards energy conservation, emission reduction, low-carbon output, and resource utilization. This paper provides an analysis of the advantages and disadvantages of the current low-carbon treatment process of low-carbon treatment for rural wastewater. Constructed wetlands (CWs) are increasingly being considered as a viable option for treating wastewater in rural regions. In pursuit of carbon neutrality, advanced carbon-neutral bioprocesses are regarded as the prospective trajectory for achieving carbon-neutral treatment of rural wastewater. The incorporation of CWs with emerging biotechnologies such as sulfur-based autotrophic denitrification (SAD), pyrite-based autotrophic denitrification (PAD), and anaerobic ammonia oxidation (anammox) enables efficient removal of nitrogen and phosphorus from rural wastewater. The advancement of CWs towards improved removal of organic and inorganic pollutants, sustainability, minimal energy consumption, and low carbon emissions is widely recognized as a viable low-carbon approach for achieving carbon-neutral treatment of rural wastewater. This study offers novel perspectives on the sustainable development of wastewater treatment in rural areas within the framework of achieving carbon neutrality in the future.

Exogenous compound bacteria enhance the nutrient removal efficiency of integrated bioremediation systems: Functional genes and microorganisms play key roles.

With the continuous development of intensive mariculture, the application of the integrated bioremediation system of aquaculture wastewater (IBSAW) is increasingly promoted. However, the process and nutrients removal performance of the IBSAW need to be further optimized due to its immature technologies. In this study, exogenous compound bacteria (ECB) were added to IBSAW to investigate its pollutants removal efficiency and the relevant mechanisms. High-throughput sequencing and Geochip gene array were used to analyze the correlation between nutrients and bacteria, and the abundance of N and P cycling genes were quantified. Multivariable statistics, dimensionality reduction analysis, and network analysis were applied to explore the mechanisms of IBSAW operation. The results showed that the nutrients decreased significantly after adding ECB, with the brush treatment group significantly outperforming the ceramsite in removing NO3- and PO43-. Ceramsite has an advantage in removing NO2--N. The addition of ECB and different substrates significantly affected the composition of bacterial communities. The contents of nosZ and nirKS related to denitrification in the treatment groups were significantly higher than those in the control group, and the contents in the brush treatment group were significantly higher than that of ceramsite. The biomarkers Psychroserpens and Ruegeria on the biofilm of the brush treatment group were positively correlated with nirKS, while Mycobacterium, Erythrobacter and Paracoccus, Pseudohaliea in the ceramsite group were positively correlated with nirS and nirK, respectively. Therefore, it is speculated that the ECB significantly promoted the increase of denitrification bacteria by affecting the composition of bacterial communities, and the ECB combined with functional genera improved the efficiency of nutrients removal in the system. This study provided a reference for understanding the process and mechanism of nutrients removal, optimizing the wastewater purification technology of the IBSAW and improving the performance of the system.

Effects of combined microplastic and cadmium pollution on sorghum growth, Cd accumulation, and rhizosphere microbial functions.

The interaction between microplastics (MPs) and cadmium (Cd) poses a threat to agricultural soil environments, and their effects on plant growth and rhizosphere microbial community functions are not yet clear. In this study, energy sorghum was used as a test plant to investigate the effects of two types of MPs, polystyrene (PS) and polyethylene (PE), at different particle sizes (13 µm, 550 µm) and concentrations (0.1%, 1% w/w), and Cd, as well as their interactions, on the growth of sorghum in a soil-cultivation pot experiment. The results showed that the combined effects of MP and Cd pollution on the dry weight and Cd accumulation rate in sorghum varied depending on the type, concentration, and particle size of the MPs, with an overall trend of increasing stress from combined pollution with increasing Cd content and accumulation. High-throughput sequencing analysis revealed that combined MP and Cd pollution increased bacterial diversity, and the most significant increase was observed in the abundance-based coverage estimator (ACE), Shannon, and Sobs indices in the 13 µm 1% PS+Cd treatment group. Metagenomic analysis based on the Kyoto Encyclopedia of Genes and Genomes (KEGG) metabolic pathways revealed that 19 groups of metabolic pathways, including microbial metabolism and methane metabolism, differed significantly under combined MP and Cd pollution. Hierarchical clustering results indicated that Cd treatment and combined MP and Cd treatment affected the abundances of sorghum rhizosphere soil nitrogen (N) and phosphorus (P) cycling genes and that the type of MP present was an important factor affecting N and P cycling genes. The results of this study provide a basis for exploring the toxic effects of combined MP and Cd pollution and for conducting soil environmental risk assessments.

Deciphering the roles of attached and suspended sludges in simultaneous nitrogen and phosphorus removal in an IFAS system based on metagenomic analysis.

Integrated fixed-film activated sludge (IFAS) system, an improvement of the activated sludge process, combines the advantages of both attached sludge (AS) and suspended sludge (SS). This study aimed to fully decipher the roles of AS and SS in simultaneous N and P removal in an IFAS system through metagenomic analysis. It was found that AS contributed about 84.04%, 97%, and 95.12% to exogenous NO3--N reduction, endogenous NO3--N reduction, and endogenous NO2--N reduction, respectively. Compared with AS, SS exhibited a greater contribution to anaerobic P release (69.06%) and aerobic P uptake (73.48%). Nitrate and nitrite reductase enzymes showed higher activities in AS, while the activities of exopolyphosphatase and alkaline phosphatase D were more active in SS. P content further indicated that in AS, only a small amount of P was stored in EPS, with most presented intracellularly. In SS, the amount of P stored in EPS was found to be higher. Metagenomic analysis revealed genes related to the synthesis and degradation of endogenous carbon were higher in AS, whereas the TCA cycle exhibited higher activity in SS. P removal-related genes (such as ppk2, ppx, and adk) was significantly higher in SS than in AS. The alteration of genes associated with nitrogen metabolism suggested that the microbes in AS had a higher capacity for nitrification and denitrification. In summary, the discrepancy in the roles of AS and SS in N and P removal in IFAS can be attributed to variations in enzyme activity, P storage in EPS, microbial community composition, and functional gene abundance.

Electrocoagulation enhanced gravity driven membrane bioreactor for advanced treatment of rural sewage.

The daily discharge of rural sewage in China occupies 30 % of the national wastewater discharge, and developing an energy-efficient, easy to operate, and decentralized rural sewage treatment technology becomes an important task. In this work, a novel rural sewage treatment technology, Electrocoagulation enhanced Gravity-Driven Membrane Bioreactor (EC-GDMBR) was exploited for the rural sewage treatment under long-term operation (160 days). Two EC-GDMBRs with various module structures of ceramic membrane (horizontal module and side module) not only displayed the desirable effluent quality, but also sustained the stable flux (8-13 LMH). The electrocoagulation, electrooxidation, biodegradation, and separation in EC-GDMBRs were able to synergistically remove the particle matter, organic (CODCr effluent <11.6 ± 1.2 mg/L) and nutrients (NH3-N effluent <0.1 mg/L, TN effluent <8.5 mg/L, TP effluent <0.05 mg/L). Besides, the high permeability of ceramic membrane and large porosity of biofilm on its surface improved the sustainability of stable flux during the long-term operation. Moreover, by analyzing bacterial abundance, Extracellular Polymeric Substances, Adenosine Tri-Phosphate and Confocal Laser Scanning Microscopy, a large number of microorganisms grew and accumulated on the carrier, as well as formed the biofilm (23.46-659.9 µm), while Nitrobacteria (1.6-4.1 %) and Nitrate (0.01-0.06 %) exited in the carrier biofilms, promoting the nitrogen removal. Compared with EC-GDMBR with side module of ceramic membrane, EC-GDMBR with horizontal module of ceramic membrane has advantages in flux behavior, organic/nutrient removal, microbial abundance/activity, abundance of nitrogen removal functional bacteria and water permeability of biofilm, because the ceramic membrane of horizontal module can promote the uniform growth of biofilm and improve the uniformity of flow penetration distribution. In general, the findings of this work verify the reliability of EC-GDMBR for the sustainable operation of wastewater treatment and improve its application value of rural sewage treatment.

Treatment of nitrogen and phosphorus from sewage tailwater in paddy rice wetlands: concept and environmental benefits.

Domestic sewage tailwater (DSTW) reuse for crop irrigation is considered a promising practice to reduce water demand, mitigate water pollution, and substitute chemical fertilization. The level of the above environmental benefits of this water reuse strategy, especially when applied to paddy wetlands, remains unclear. In this study, soil column experiments were conducted to investigate the nitrogen and phosphorus fate in paddy wetlands subjected to different tailwater irrigation and drainage strategies, specifically, (i) TW1 and TW2 for regular or enhanced irrigation-drainage without N fertilization, (ii) TW3 and TW4 for regular irrigation with base or tillering N fertilizer, (iii) conventional fertilization N210, and (iv) no-fertilization controls N0. The results showed that the total nitrogen (TN), nitrate (NO3-), and total phosphorus (TP) removal rates from the paddies irrigated by DSTW ranged between 51.92 and 59.34%, 68.1 and 83.42%, and 85.69 and 86.98% respectively. Ammonia emissions from the DSTW-irrigated treatments were reduced by 14.6~47.2% compared to those paddies subjected to conventional fertilization (N210), similarly for TN emissions, with the exception of the TW2 treatment. Overall, it is established that the paddy wetland could effectively remove residual N and P from surface water runoffs, while the partial substitution of chemical fertilization by DSTW could be confirmed. The outcome of this study demonstrates that DSTW irrigation is a promising strategy for sustainable rice production with a minimized environmental impact.

Asymmetric response of aboveground and belowground temporal stability to nitrogen and phosphorus addition in a Tibetan alpine grassland.

Anthropogenic eutrophication is known to impair the stability of aboveground net primary productivity (ANPP), but its effects on the stability of belowground (BNPP) and total (TNPP) net primary productivity remain poorly understood. Based on a nitrogen and phosphorus addition experiment in a Tibetan alpine grassland, we show that nitrogen addition had little impact on the temporal stability of ANPP, BNPP, and TNPP, whereas phosphorus addition reduced the temporal stability of BNPP and TNPP, but not ANPP. Significant interactive effects of nitrogen and phosphorus addition were observed on the stability of ANPP because of the opposite phosphorus effects under ambient and enriched nitrogen conditions. We found that the stability of TNPP was primarily driven by that of BNPP rather than that of ANPP. The responses of BNPP stability cannot be predicted by those of ANPP stability, as the variations in responses of ANPP and BNPP to enriched nutrient, with ANPP increased while BNPP remained unaffected, resulted in asymmetric responses in their stability. The dynamics of grasses, the most abundant plant functional group, instead of community species diversity, largely contributed to the ANPP stability. Under the enriched nutrient condition, the synchronization of grasses reduced the grass stability, while the latter had a significant but weak negative impact on the BNPP stability. These findings challenge the prevalent view that species diversity regulates the responses of ecosystem stability to nutrient enrichment. Our findings also suggest that the ecological consequences of nutrient enrichment on ecosystem stability cannot be accurately predicted from the responses of aboveground components and highlight the need for a better understanding of the belowground ecosystem dynamics.

Identifying critical regions for nitrogen and phosphorus loss management in a large-scale complex basin: The Jialing River.

The determination of critical management areas for nitrogen (N) and phosphorus (P) losses in large-scale basins is critical to reduce costs and improve efficiency. In this study, the spatial and temporal characteristics of the N and P losses in the Jialing River from 2000 to 2019 were calculated based on the Soil and Water Assessment Tool (SWAT) model. The trends were analyzed using the Theil-Sen median analysis and Mann-Kendall test. The Getis-Ord Gi* was used to determine significant coldspot and hotspot regions to identify critical regions and priorities for regional management. The ranges of the annual average unit load losses for N and P in the Jialing River were 1.21-54.53 kg ha-1 and 0.05-1.35 kg ha-1, respectively. The interannual variations in both N and P losses showed decreasing trends, with change rates of 0.327 and 0.003 kg ha-1·a-1 and change magnitudes of 50.96% and 41.05%, respectively. N and P losses were highest in the summer and lowest in the winter. The coldspot regions for N loss were clustered northwest of the upstream Jialing River and north of Fujiang River. The coldspot regions for P loss were clustered in the central, western, and northern areas of the upstream Jialing River. The above regions were found to be not critical for management. The hotspot regions for N loss were clustered in the south of the upstream Jialing River, the central-western and southern areas of the Fujiang River, and the central area of the Qujiang River. The hotspot regions for P loss were clustered in the south-central area of the upstream Jialing River, the southern and northern areas of the middle and downstream Jialing River, the western and southern areas of the Fujiang River, and the southern area of the Qujiang River. The above regions were found to be critical for management. There was a significant difference between the high load area for N and the hotspot regions, while the high load region for P was consistent with the hotspot regions. The coldspot and hotspot regions for N would change locally in spring and winter, and the coldspot and hotspot regions for P would change locally in summer and winter, respectively. Therefore, managers should make specific adjustments in critical regions for different pollutants according to seasonal characteristics when developing management programs.

Preparation of high performance porous carbon by microwave synergistic nitrogen/phosphorus doping for efficient removal of Cu2+ via capacitive deionization.

Sargassum biochar has potential advantages as an electrode material due to its natural microscopic pore channels. However, conventional pyrolysis method is prone to thermal damage to the biochar, and incapable to form a complete pore structure resulting in poor biochar electrode performance. In this study, a strategy of microwave pyrolysis coupled with KOH activation was used to prepare nitrogen/phosphorus double-doped graded porous biochar (STC) using ammonium dihydrogen phosphate as dopant. The carbon material STC-1.24-800 prepared by the optimal parameters had a high specific surface area (SSA) of 1367.6 m2 g -1 and a total pore volume of 1.499 cm3 g-1. The precise inside-out heating characteristics of microwave facilitated the generation of suitable meso-micropore distribution ratios in carbon, and the graded porous structure provided abundant active sites for charge accumulation and ion diffusion. The doped nitrogen/phosphorus atoms responding to the microwave field, generated spin to promote microwave absorption, introducing surface structural defects to produce electron density differences. The change in the nature of the electron donor and its electron density enhanced the electrical conductivity and chemical stability of STC. Nitrogen/phosphorus polar surface functional groups improved hydrophilicity and wettability. STC-1.24-800 had a higher specific capacitance of 531 F g-1 and exhibits great cycle performance in capacitive deionization (CDI) applications (1.0 V, 50 mg L-1 Cu2+) as well as adsorption performance (56.16 mg g -1). The present work can provide a novel feasible idea for preparing diatomically doped graded porous biochar for CDI electrode application by microwave irradiation.

Weak transgenerational effects of ancestral nitrogen and phosphorus availabilities on offspring phenotypes in Arabidopsis thaliana.

Nutrient availability significantly regulates plant growth and metabolic functions, but whether and how the long-term exposure of ancestral plants to contrasting nutrient environments influences offspring phenotypic performance (i.e., transgenerational plasticity) remain poorly addressed. Here we conducted experimental manipulations using Arabidopsis thaliana with the ancestral plants grown in different nitrogen (N) and phosphorus (P) availabilities over eleven consecutive generations, and then examined the offspring phenotypic performance under the interactive effects of current and ancestral nutrient environments. We found that current rather than ancestral nutrient environments dominantly explained the variations in offspring plant traits (i.e., flowering time, aboveground biomass and biomass allocation fractions), suggesting the relatively weak transgenerational effects of ancestral N and P availabilities on offspring phenotypes. In contrast, increasing N and P availabilities in the offspring generation remarkably shortened the flowering time, increased the aboveground biomass, and altered biomass allocation fractions differentially among organs. Despite the overall weak transgenerational phenotypic plasticity, under the low nutrient environment, the offspring of ancestral plants from the low nutrient environment had a significantly higher fruit mass fraction than those from the suitable nutrient environment. Taken together, our findings suggest that A. thaliana exhibits a much stronger within- than trans-generational trait plasticity under contrasting nutrient availabilities, and may provide important insights into the understanding of plant adaptation and evolutionary processes under changing nutrient environments.

Nutrient released characteristics of struvite-biochar fertilizer produced from concentrated sludge supernatant by fluidized bed reactor.

With the exacerbating water eutrophication globally, it is important to recover nitrogen (N) and phosphorus (P) from sewage for recycle. In this study, coconut shell biochar and ethylene diamine tetraacetic acid (EDTA) were added into the designed fluidized bed reactor (FBR) to create struvite-biochar. N and P released from struvite-biochar and the recovery efficiency of N and P from concentrated sludge supernatant were analyzed. Results showed that the optimal operation condition for hydraulic retention time (HRT), pH, Mg/P molar ration, and addition amount EDTA were 90 min, 9.5, 1.2, and 0.2 g/L, respectively. The recovery efficiency of NH4+-N and PO43--P, and purity struvite for FBR were 34.41%-38.05%, 64.95-68.40%, and 84.15%, respectively. The recovery efficiency of NH4+-N and PO43--P were respectively increased by 7.23% and 5.36% when FBR with addition of 0.33 g/L coconut shell biochar, but purity struvite from struvite-biochar decreased by 45.70%. Contents of As, Cd, Pb, and Cr in struvite and struvite-biochar were all lower than Chinese Standard Limits of Fertilizer. Compared to commercial chemical fertilizer, such as superphosphate and urea, struvite-biochar and struvite have slowly released N and P. The amounts of released P, NO3--N and NH4+-N from struvite-biochar were higher than struvite during the five leaching times. Compared with struvite, the total amounts of released P, NO3--N and NH4+-N from struvite-biochar increased by 4.9%, 3.5% and 8.3%, respectively. Therefore, it is valuable to add biochar into FBR to recovery N and P from concentrated sludge supernatant and make struvite-biochar as a slow-release fertilizer.

Enhancement of organics and nutrient removal and microbial mechanism in vertical flow constructed wetland under a static magnetic field.

Low and unstable pollutant removal is regarded as the bottleneck problem in constructed wetlands (CWs) for wastewater treatment. This study investigated the effect of static magnetic field (MF) on enhancing the purification efficiency and microbial mechanism in vertical flow CW systems for treating domestic wastewater. The results showed that MF-CWs outperformed control systems in terms of treatment performance, with average removal efficiencies of COD, NH4+-N, TN, and TP reaching 92.58%, 73.58%, 72.53%, and 95.83%, respectively. The change of malondialdehyde (MDA), catalase (CAT), and superoxide dismutase (SOD) activity indicated that MF application was beneficial for plant health. Additionally, higher ammonia monooxygenase (AMO) activity in MF-CWs suggested the removal of NH4+-N was facilitated. The high-throughput sequencing results demonstrated that MF application could enrich the functional bacteria such as Patescibacteria phylum, mainly, including Gammaproteobacteria, Betaproteobacteria, and Alphaproteobacteria, which further accelerated pollutants transformation. These findings would be beneficial in understanding pollutant removal processes and their mechanism in CWs with MF application.

An updated review of the efficacy of buffer zones in warm/temperate and cold climates: Insights into processes and drivers of nutrient retention.

The transport of excess nutrients into freshwater systems constitutes a serious risk to both water quality and aquatic health. Vegetated buffer zones (VBZs) next to waterways are increasingly used in many parts of the world to successfully intercept and eliminate pollutants and other materials in overland flow, especially in warm or temperate regions. The major processes for the retention of pollutants in VBZ are microbial degradation, infiltration, deposition, filtration, adsorption, degradation, assimilation, etc. The effectiveness of the VBZ relies on several environmental factors, including BZ width, runoff intensity, slope, soil texture, temperature, vegetation type, etc. Among the reported factors, cold weather possesses the most detrimental impact on many of the processes that VBZ are designed to carry out. The freezing temperatures result in ice formation, interrupting biological activity, infiltration and sorption, etc. In the last twenty years, burgeoning research has been carried out on the reduction of diffuse nutrient pollution losses from agricultural lands using VBZ. Nonetheless, a dearth of studies has dealt with the problems and concerns in cold climates, representing an important knowledge gap in this area. In addition, the effectiveness of VBZ in terms of nutrient removal abilities varies from -136% to 100%, a range that reveals the incertitude surrounding the role of VBZ in cold regions. Moreover, frozen soils and plants may release nutrients after undergoing several freeze-thaw cycles followed by runoff events in spring snowmelt. This review suggests that the management and design of VBZ in cold climates needs close examination, and these systems might not frequently serve as a good management approach to decrease nutrient movement.

Potential linkage between WWTPs-river-integrated area pollution risk assessment and dissolved organic matter spectral index.

The direct discharge of wastewater can cause severe damage to the water environment of the surface water. However, the influence of dissolved organic matter (DOM) present in wastewater on the allocation of DOM, nitrogen (N), and phosphorus (P) in rivers remains largely unexplored. Addressing the urgent need to monitor areas affected by direct wastewater discharge in a long-term and systematic manner is crucial. In this paper, the DOM of overlying water and sediment in the WWTPs-river-integrated area was characterized by ultraviolet-visible absorption spectroscopy (UV-vis), three-dimensional excitation-emission matrix combined with parallel factor (PARAFAC) method. The effects of WWTPs on receiving waters were investigated, and the potential link between DOM and N, P pollution was explored. The pollution risk was fitted and predicted using a spectral index. The results indicate that the improved water quality index (IWQI) is more suitable for the WWTPs-river integration zone. The DOM fraction in this region is dominated by humic-like matter, which is mainly influenced by WWTPs drainage as well as microbial activities. The DOM fractions in sediment and overlying water were extremely similar, but fluorescence intensity possessed more significant spatial differences. The increase in humic-like matter facilitates the production and preservation of P and also inhibits nitrification, thus affecting the N cycle. There is a significant correlation between DOM fraction, fluorescence index, and N, P. Fluorescence index (FI) fitting of overlying water DOM predicted IWQI and trophic level index, and a(254) fitting of sediment DOM predicted nitrogen and phosphorus pollution risk (FF) with good results. These results contribute to a better understanding of the impact of WWTPs on receiving waters and the potential link between DOM and N and P pollution and provide new ideas for monitoring the water environment in highly polluted areas.

Effects of forest age on soil erosion and nutrient loss in Dianchi watershed, China.

Soil erosion and nutrient loss are important environmental and ecological problems in the Dianchi watershed in southwestern China. Woodlands-the primary land type in the Dianchi watershed-play an important ecological role in controlling soil and water loss. In this study, we compared soil erosion and loss of total organic carbon (TOC), total nitrogen (TN), and total phosphorus (TP) in woodlands of different ages, i.e., young forest, medium forest, and near-mature forest, at the Dongda River catchment in south-western Dianchi watershed. Furthermore, changes in stoichiometries in soil were analyzed. The average degree of erosion of each forest age stage was below moderate. Based on the non-arable soil erosion modulus models of 137Cs and 210Pbex, the soil erosion rates decreased gradually with the increasing forest age. The forest age affected soil nutrient distribution and loss. The losses of TOC and TP gradually decreased, while the losses of TN first increased and then decreased with the growth of forest age. TOC, TN, and TP were enriched in the topsoil. Forest age affected soil stoichiometry and soil nutrient supply level. In general, the forest can effectively reduce soil erosion and nutrient loss in the red soil area with the forest age increasing.

Understanding Responses of Soil Microbiome to the Nitrogen and Phosphorus Addition in Metasequoia glyptostroboides Plantations of Different Ages.

Nitrogen (N) and phosphorus (P) have significant effects on soil microbial community diversity, composition, and function. Also, trees of different life stages have different fertilization requirements. In this study, we designed three N additions and three P levels (5 years of experimental treatment) at two Metasequoia glyptostroboides plantations of different ages (young, 6 years old; middle mature, 24 years old) to understand how different addition levels of N and P affect the soil microbiome. Here, the N fertilization of M. glyptostroboides plantation land (5 years of experimental treatment) significantly enriched microbes (e.g., Lysobacter, Luteimonas, and Rhodanobacter) involved in nitrification, denitrification, and P-starvation response regulation, which might further lead to the decreasing in alpha diversity (especially in 6YMP soil). The P addition could impact the genes involved in inorganic P-solubilization and organic P-mineralization by increasing soil AP and TP. Moreover, the functional differences in the soil microbiomes were identified between the 6YMP and 24YMP soil. This study provides valuable information that improves our understanding on the effects of N and P input on the belowground soil microbial community and functional characteristics in plantations of different stand ages.

Simultaneous denitrification and iron-phosphorus precipitation driven by plant biomass coupled with iron scraps in subsurface flow constructed wetlands.

This study investigated the interaction between plant biomass and iron scraps and their influence on nitrogen (including nitrate and ammonia) and phosphorus removal in the subsurface flow constructed wetland. The results showed that with the addition of 0.5 g L-1 of plant biomass and 5.0 g L-1 of iron scraps, the nitrate, total nitrogen and total phosphorus removal were simultaneously improved. During 35 days of continuous operation, the plant biomass played main effect on the enhanced denitrification, accounting for about 57%, while iron scraps enhanced the other 43% of nitrogen removal and most phosphorus removal through precipitation inside the wetlands. Iron scraps could benefit the degradation of cellulose into low molecular carbohydrates by 10%, and the biomass could promote the oxidation of iron and increase the total phosphorus removal by 15%. Plant biomass coupled with iron scraps also improved simultaneously the richness, diversity and evenness of microbial community and promoted the abundance of Nitrospira (17.37%) and Thiobacillus (8.46%) in wetlands. In practice, putting iron scraps as matrix and placing plant biomass in the influent region would be a better choice. This research would provide a new method for effective utilization of plant biomass and iron scraps and further treatment of low-polluted wastewater in the wetlands.