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A bio-matrix material (BMM) system is used to pretreat swine wastewater and reduce the nitrogen (N) concentration to the tolerance range of plants in constructed wetlands. In this study, rice straw (RS), wheat straw (WS), and corn stalk (CS) were applied to treat pollutants from swine wastewater, respectively. This one year-long field experiment make up for the lack of long-term experiments and mechanistic investigations of BMM. The pollutant removal efficiency, degradation process of crop straw, and the abundance of nitrogen cycling genes were determined in different BMM systems. The results showed that the removal efficiency of COD, TN, NH 4 + , and NO 3 , which were 32.81% and 32.99%, 35.3% and 34.97%, respectively. Moreover, the removal efficiency of COD was 30.81% in three BMM systems. Meanwhile, it was found that the dry matter (DM) degradation of crop straws was fast in the first 4-5 months. The degradation rates of cellulose, hemicellulose, and lignin were 94.19%, 94.36%, and 87.32%, respectively, in 1 year. The abundance of nitrogen cycling genes significantly increased by adding BMM, compared with CK (P < 0.05). This showed the abundance of the hzsB gene in RS was the highest, while nirK, nirS, AOA, and AOB were the highest in WS. The addition of RS and WS was better than that of CS in promoting the abundance of nitrogen cycling microorganisms. The results indicated that adding BMM could enhance the anaerobic ammonia oxidation, nitrification, and denitrification. This study not only extends our comprehension of BMM mechanisms in swine wastewater treatment but also serves as a guiding light for numerous farms in similar climate regions.- was the best in the initial 6 months. Furthermore, RS and WS exhibited favorable annual removal efficiency of TN and NH 4 + , which were 32.81% and 32.99%, 35.3% and 34.97%, respectively. Moreover, the removal efficiency of COD was 30.81% in three BMM systems. Meanwhile, it was found that the dry matter (DM) degradation of crop straws was fast in the first 4-5 months. The degradation rates of cellulose, hemicellulose, and lignin were 94.19%, 94.36%, and 87.32%, respectively, in 1 year. The abundance of nitrogen cycling genes significantly increased by adding BMM, compared with CK (P < 0.05). This showed the abundance of the hzsB gene in RS was the highest, while nirK, nirS, AOA, and AOB were the highest in WS. The addition of RS and WS was better than that of CS in promoting the abundance of nitrogen cycling microorganisms. The results indicated that adding BMM could enhance the anaerobic ammonia oxidation, nitrification, and denitrification. This study not only extends our comprehension of BMM mechanisms in swine wastewater treatment but also serves as a guiding light for numerous farms in similar climate regions., (© 2024. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Increased nitrogen (N) concentrations in water bodies have highlighted issues regarding nutrient pollution in agricultural catchments. In this study, the ammonium-N (NH 4 + -N), nitrate-N (NO 3 - -N), and total N (TN) concentrations were observed in the stream water and groundwater of two contrasting catchments (named Tuojia and Jianshan) in subtropical central China from 2010 to 2014, to determine the rice agriculture impacts on the hydrographic patterns, and N export characteristics of the catchments. The results suggested that greater amounts of stream flow (523.0 vs. 434.7 mm year -1 ) and base flow (237.6 vs. 142.8 mm year -1 ) were produced in Tuojia than in Jianshan, and a greater base flow contribution to stream flow and higher frequencies of high-base flow days were observed during the fallow season than during the rice-growing season, indicating that intensive rice agriculture strongly influences the catchment hydrographic pattern. Rice agriculture resulted in moderate N pollution in the stream water and groundwater, particularly in Tuojia. Primarily, rice agriculture increased the NH 4 + -N concentration in the stream water; however, it increased the NO 3 - -N concentrations in the groundwater, suggesting that the different N species in the paddy fields migrated out of the catchments through distinct hydrological pathways. The average TN loading via stream flow and base flow was greater in Tuojia than in Jianshan (1.72 and 0.58 vs. 0.72 and 0.15 kg N ha -1  month -1 , respectively). Greater TN loading via stream flow was observed during the fallow season in Tuojia and during the rice-growing season in Jianshan, and these different results were most likely a result of the higher base flow contribution to TN loading (33.5 vs. 21.3%) and greater base flow enrichment ratio (1.062 vs. 0.876) in Tuojia than in Jianshan. Therefore, the impact of rice agriculture on catchment eco-hydrological processes should be considered when performing water quality protection and treatment in subtropical central China.

Increasingly, the characteristics of nitrogen (N) loading have been recognized to be critical for the maintenance and restoration of water quality in agricultural watersheds, in response to the spread of water eutrophication. This paper estimates N loading and investigates its influencing factors in ten small watersheds variously dominated by forest and agricultural land use types in the subtropics of China, over an observation period of 23-29 months. The results indicate that the average concentrations of total nitrogen (TN), NH4 (+)-N, and NO3 (-)-N were 0.83, 0.07, and 0.46 mg N L(-1) in the forest watersheds and 1.49-5.16, 0.21-3.23, and 0.99-1.30 mg N L(-1) in the agricultural watersheds, respectively. Such concentrations exceed the national criteria for nutrient pollution in surface waters considerably, suggesting severe stream pollution in the studied agricultural watersheds. The average annual TN loadings (ANL) were estimated to be 1,640.8 kg N km(-2) year(-1) in the agricultural watersheds, 63.3-86.1 % of which was composed of dissolved inorganic N (DIN; comprising NO3 (-)-N and NH4 (+)-N). The watershed with intensive livestock production (i.e., the maximum livestock density of 2.66 animal units (AU) ha(-1)) exhibited the highest ANL (2,928.7 kg N km(-2) year(-1)) related to N loss with effluent discharge. The results of correlation and principle component analysis suggest that livestock production was the dominant influencing factor for the TN and NH4 (+)-N loadings and that the percentages of cropland in watersheds can significantly increase the NO3 (-)-N loading in agricultural watersheds. Therefore, to restore and maintain water quality, animal production regulations and more careful planning of land use are necessary in the agricultural watersheds of subtropical China.

Atmospheric nitrogen (N) deposition is currently high and meanwhile diffuse N pollution is also serious in China. The correlation between N deposition and riverine N export and the contribution of N deposition to riverine N export were investigated in a typical hilly red soil catchment in southern China over a two-year period. N deposition was as high as 26.1 to 55.8kgN/(ha·yr) across different land uses in the studied catchment, while the riverine N exports ranged from 7.2 to 9.6kgN/(ha·yr) in the forest sub-catchment and 27.4 to 30.3kgN/(ha·yr) in the agricultural sub-catchment. The correlations between both wet N deposition and riverine N export and precipitation were highly positive, and so were the correlations between NH4(+)-N or NO3(-)-N wet deposition and riverine NH4(+)-N or NO3(-)-N exports except for NH4(+)-N in the agricultural sub-catchment, indicating that N deposition contributed to riverine N export. The monthly export coefficients of atmospheric deposited N from land to river in the forest sub-catchment (with a mean of 14%) presented a significant positive correlation with precipitation, while the monthly contributions of atmospheric deposition to riverine N export (with a mean of 18.7% in the agricultural sub-catchment and a mean of 21.0% in the whole catchment) were significantly and negatively correlated with precipitation. The relatively high contribution of N deposition to diffuse N pollution in the catchment suggests that efforts should be done to control anthropogenic reactive N emissions to the atmosphere in hilly red soil regions in southern China., (Copyright © 2014. Published by Elsevier B.V.)

Changes in the landscape pattern can disturb legacy nitrogen (N) release by influencing hydrological and biogeochemical processes; thus, understanding the effects of landscape patterns on riverine N exports from legacy sources is critical for preparing water quality improvement strategies. In this study, an empirical statistical model that incorporates the net anthropogenic nitrogen input (NANI), runoff coefficient, and residential land area percentage was used to quantify the contribution of legacy sources to annual riverine ammonium nitrogen (NH4+–N), nitrate nitrogen (NO3−–N), and total nitrogen (TN) exports in eight adjacent agricultural catchments in subtropical southern China. The results indicated that annual riverine NH4+–N, NO3−–N, and TN exports from legacy sources ranged from 0.36–1.03, 3.09–4.89, and 3.94–6.79 kg ha−1 year−1, respectively, during the 2012–2017 period. Redundancy analysis (RDA) was used to analyze the interactions between legacy N release and landscape metrics at both the landscape and class levels. The RDA results suggested that higher dispersion, lower shape complexity, and greater heterogeneity in landscape patches can enhance the release of legacy N at the landscape level. In agricultural and residential areas, higher release of legacy N was associated with patches that are unfragmented and have a low shape complexity, whereas in woodland areas, the opposite was true. These analyses provide scientific support for preparing legacy N control strategies from the perspective of landscape ecology. [ABSTRACT FROM AUTHOR]

Swine wastewater contains high concentration of nitrogen (N), causing pollution of surrounding water bodies. Constructed wetlands (CWs) are considered as an effective ecological treatment measure to remove nitrogen. Some emergent aquatic plants could tolerate high ammonia, and play a crucial part in CWs to treat high concentration N wastewater. However, the mechanism of root exudates and rhizosphere microorganisms of emergent plants on nitrogen removal is still unclear. Effects of organic and amino acids on rhizosphere N cycle microorganisms and environmental factors across three emergent plants were investigated in this study. The highest TN removal efficiency were 81.20% in surface flow constructed wetlands (SFCWs) plant with Pontederia cordata. The root exudation rates results showed that organic and amino acids were higher in 56 d than that in 0 d in SFCWs plants with Iris pseudacorus and P. cordata. The highest ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) gene copy numbers were found in I. pseudacorus rhizosphere soil, while the highest nirS , nirK , hzsB and 16S rRNA gene copy numbers were detected in P. cordata rhizosphere soil. Regression analysis results demonstrated that organic and amino acids exudation rates were positive related to rhizosphere microorganisms. These results indicated that organic and amino acids secretion could stimulate growth of emergent plants rhizosphere microorganisms in SFCWs for swine wastewater treatment. In addition, the EC, TN, NH 4 +-N and NO 3 −-N were negatively correlated with organic and amino acids exudation rates, and abundances of rhizosphere microorganisms via Pearson correlation analysis. These results imply that organic and amino acids, and rhizosphere microorganisms synergically affected on the nitrogen removal in SFCWs. [Display omitted] • Root exudation and rhizosphere microorganisms were tested in treating to swine wastewater. • Higher abundance of nitrifiers were found in I. pseudacorus. • Higher abundance of denitrifiers and anammox bacteria were found in P. cordata. • TOA and TAA impacted on rhizosphere microorganisms. • TOA and TAA secretion by plants could impact on the concentration of N in wastewater. [ABSTRACT FROM AUTHOR]

How sediment bacterial community structure and diversity responds to different gradients of nitrogen (N) in swine wastewater is poorly understood. Here, the effects of different total nitrogen (TN) concentrations in swine wastewater on the microbial diversity and community composition in surface flow constructed wetlands (SFCWs) were investigated. The five concentration gradients included 2, 250, 300, 350, and 400 mg L−1. Under high N concentrations (>300 mg L−1), the Ace and Chao1 indexes increased, however, the Shannon index declined with increasing N concentration. The relative abundance of Chloroflexi, Acidobacteria and Actinobacteria showed an increasing trend. In contrast, under relatively low N concentrations (≤300 mg L−1), Shannon index increased with increasing N concentration. The relative abundance of Bacteroidetes and Verrucomicrobia exhibited an increasing trend with increasing N concentration. TN, NH 4 + and NO 3 − significantly influenced on the microbial community distribution and composition (P < 0.05). These findings provide evidence that N concentration of swine wastewater is powerful predictor of bacterial diversity and community composition in SFCWs. Image 1 • Microbial diversity and community were tested along gradients of swine wastewater. • Higher bacterial diversity was found in high N concentration. • Denitrifying bacteria increased in high N concentration. • N strongly drove bacterial community distribution in sediments. [ABSTRACT FROM AUTHOR]

• Harvesting of Myriophyllum elatinoides at 49 days is recommended. • Higher N concentrations in plant roots were found under high N conditions. • Aerobic bacteria increased at low N, while anaerobic bacteria increased at high N. • pH drove rhizosphere bacterial community distribution. In this study, Myriophyllum elatinoides growth under different nitrogen (N) concentrations (2, 250, 300, 350 and 400 mg L−1) and changes in rhizosphere bacterial community structure were investigated. High N (>300 mg L−1) concentrations caused reduction in M. elatinoides biomass. Growth tended to stabilize at 49 days. N concentration in roots were higher than that in stems and leaves under high N conditions. TN and NH 4 + removal efficiencies reached 84.0% and 87.2%, respectively, in M. elatinoides surface flow constructed wetlands (SFCWs). Rhizosphere bacterial diversity increased over time. Proteobacteria , Firmicutes , Cyanobacteria , and Bacteroidetes dominated at the phylum level. Genera Turicibacter , Allochromatium , and Methylocystis increased at low N (<300 mg L−1) concentrations, while Pseudomonas increased at high N concentrations over the experimental period. Redundancy analysis showed that pH was strongly correlated with changes in rhizosphere bacterial community structure. These findings helped to insight into N removal mechanism in M. elatinoides. [ABSTRACT FROM AUTHOR]

Base flow is recognized as an important hydrological pathway for NO 3 − –N export, however, the base flow contribution to NO 3 − –N loading in rice agriculture catchments remains unknown. In this study, stream discharge and NO 3 − –N concentration were observed in two contrasting rice agriculture catchments (named Tuojia and Jianshan) in subtropical central China between November 2010 and December 2013, to quantify the base flow contribution to NO 3 − –N loading and determine its relationship with rice agriculture. The results suggested that Tuojia produced more base flow (727.0 vs. 426.5 mm) and had higher base flow contribution to stream discharge (41.9% vs. 28.4%) than Jianshan did during the observation period, due to the more groundwater recharge associated with the higher areal proportion of rice agriculture in Tuojia. The average flow-weighted NO 3 − –N concentration in the base flow was higher in Tuojia than in Jianshan (1.43 vs. 1.07 mg N L −1 ), because rice agriculture could result in obvious N leaching into groundwater system. The NO 3 − –N loading via the base flow reached 0.27 kg N ha −1 month −1 in Tuojia, which contributed 36.5% of the NO 3 − –N loading via the stream discharge. These values were much greater than 0.12 kg N ha −1 month −1 and 27.3% in Jianshan. The more NO 3 − –N loading and greater base flow contribution in Tuojia were attributed to the more base flow and higher NO 3 − –N concentration in base flow associated with the intensive rice cropping. Specifically, the base flow contribution to the NO 3 − –N loading was greater during the fallow seasons than during the rice-growing seasons, likely due to the NO 3 − –N “landscape memory” effects from previous rice cropping seasons. Therefore, NO 3 − –N reduction practices in the rice agriculture catchments should be applied to mitigate the base flow contribution to NO 3 − –N loading in subtropical central China. [ABSTRACT FROM AUTHOR]

Highlights: [•] Rice agriculture affects nutrient chemical composition in stream water [•] Rice agriculture has a potential to degrade stream water quality [•] Influence of rice agriculture on nutrients in stream water is nonlinear [•] Influence is detectable when areal proportion of rice agriculture is >12–29% [Copyright &y& Elsevier]