Microbial Nitrogen Removal Research Articles

Towards a better and more complete understanding of microbial nitrogen transformation processes in the rhizosphere of subsurface flow constructed wetlands: Effect of plant root activities

Plant rhizosphere is the most active hotspot for microbial nitrogen (N) removal in constructed wetlands (CWs), but the effects of plant root activities (i.e., radial oxygen loss, ROL and root exudates, REs) on different microbial N transformation processes, including nitrification, denitrification, anaerobic ammonia oxidation (anammox) and dissimilatory nitrate reduction to ammonia (DNRA) have not been comprehensively studied. In this study, N removal performance and transformation processes in the rhizosphere of CWs were investigated using rhizobox, planar optode system, and metagenomic approaches. Results suggested nitrification was promoted in the rhizosphere, due to the high dissolved oxygen (DO) concentration caused by ROL and the humic acid-like substance in REs, making the rhizosphere a higher removal efficiency of NH4+-N than in the nonrhizosphere. Out of expectation, the denitrification process was not promoted by the REs, the potential “carbon source”, but inhibited by the high DO concentration in the rhizosphere and the phenol-like substance (a kind of biological denitrification inhibitor) in REs. In addition, both anammox and DNRA processes were, for the first time, found to be inhibited in the rhizosphere. The humic acid-like substance in REs and ammonia-oxidation production hydroxylamine inhibited the activity of anammox microorganisms and genes, and there was a symbiotic relationship between anammox microorganisms and DNRA microorganisms. This study provides better and more complete insights into the biogeochemical cycle of N occurred in the rhizosphere of CWs.

Delineation of the complex microbial nitrogen-transformation network in an anammox-driven full-scale wastewater treatment plant

Microbial-driven nitrogen removal is a crucial step in modern full-scale wastewater treatment plants (WWTPs), and the complexity of nitrogen transformation is integral to the various wastewater treatment processes. A full understanding of the overall nitrogen cycling networks in WWTPs is therefore a prerequisite for the further enhancement and optimization of wastewater treatment processes. In this study, metagenomics and metatranscriptomics were used to elucidate the microbial nitrogen removal processes in an ammonium-enriched full-scale WWTP, which was configured as an anaerobic-anoxic-anaerobic-oxic system for efficient nitrogen removal (99.63%) on a duck breeding farm. A typical simultaneous nitrification-anammox-denitrification (SNAD) process was established in each tank of this WWTP. Ammonia was oxidized by ammonia-oxidizing bacteria (AOB), archaea (AOA), and nitrite-oxidizing bacteria (NOB), and the produced nitrite and nitrate were further reduced to dinitrogen gas (N2) by anammox and denitrifying bacteria. Visible red anammox biofilms were formed successfully on the sponge carriers submerged in the anoxic tank, and the nitrogen removal rate by anammox reaction was 4.85 times higher than that by denitrification based on 15N isotope labeling and analysis. This supports the significant accumulation of anammox bacteria on the carriers responsible for efficient nitrogen removal. Two distinct anammox bacteria, named “Ca. Brocadia sp. PF01” and “Ca. Jettenia sp. PF02”, were identified from the biofilm in this investigation. By recovering their genomic features and their metabolic capabilities, our results indicate that the highly active core anammox process found in PF01, suggests extending its niche within the plant. With the possible contribution of the dissimilatory nitrate reduction to ammonium (DNRA) reaction, enriching PF02 within the biofilm may also be warranted. Collectively, this study highlights the effective design strategies of a full-scale WWTP with enrichment of anammox bacteria on the carrier materials for nitrogen removal and therefore the biochemical reaction mechanisms of the contributing members.

Response of microbial community and biological nitrogen removal to the accumulation of nonylphenol in sequencing batch reactor.

The online version contains supplementary material available at 10.1007/s13762-023-04825-9.

Nitrogen loss from anaerobic ammonium oxidation coupled to Iron(III) reduction activity across estuarine and coastal wetlands of China: Spatial variations, controlling factors, and environmental implications

Anaerobic ammonium oxidation coupled with ferric iron reduction (Feammox) is a newly identified microbial nitrogen (N) removal process in natural ecosystems. However, little is known about the distributions of Feammox activity and their environmental drivers across estuarine and coastal wetlands at a continental scale. In this study, we determined the potential Feammox rates and related microbial diversities and abundances along the estuarine and coastal wetlands of China encompassing subtropical to temperate climate zones. Measured potential Feammox activity ranged from 0.05 to 0.23 mg N kg−1 d-1, and the process rates at the subtropical sites were generally higher than at the temperate sites. Partial least squares path model (PLS-PM) showed that the abundance of Fe reducing bacteria significantly and directly affected the potential Feammox rates, while sediment characteristics (mainly including sediment water content, Fe(III), TOC and NO3–) and geographical factors (longitude and latitude) had an indirect effect on the process rates. The N loss via the Feammox was approximately 1.72–7.89 kg N ha−1 year−1, accounting for 0.41–1.91 % of multi-annual average land-based inorganic N transported into the estuarine and coastal wetlands of China. Overall, this study reveals the distribution patterns and controlling factors of the Feammox process in estuarine and coastal wetlands of China, and provides a valuable database for N management in estuarine and coastal ecosystems.

Insights into microbial interactive mechanism regulating dissimilatory nitrate reduction processes in riparian freshwater aquaculture sediments

Aquaculture can substantially alter the accumulation and cycling of nutrients in sediments. However, the microbial mechanisms mediating sediment dissimilatory nitrate (NO3−) reduction in freshwater aquaculture ponds are still unclear, which rule the removal and retention of N element. In the present study, three microbial NO3− reduction processes in riparian aquaculture pond sediments (i.e., crab, shrimp and fish ponds) and natural freshwater sediments (i.e., lakes and rivers) were investigated via isotopic tracing and molecular analyses. The potential rates of denitrification, anaerobic ammonium oxidation (anammox) and dissimilatory nitrate reduction to ammonium (DNRA) significantly increased in the aquaculture ponds compared with the natural freshwaters. Denitrification contributed 90.40–94.22% to the total NO3− reduction (product as N2), followed by 2.49–5.82% of anammox (product as N2) and 2.09–5.18% of DRNA (product as NH4+). The availability of C and N substrates, rather than functional gene abundance, regulated the activities of NO3− reductions and microbiome composition. Microbial mechanism based on network analysis indicated that heterotrophic denitrifiers and DNRA bacteria (e.g., Bacillus, Micromonospora, Mycobacterium and Brachybacterium) determined the community structure and function for N conversions in aquaculture ponds, whereas the such microbial network in natural freshwater sediments was manipulated by autotrophic denitrifiers (e.g., Desulfuromonas, Polaromonas, Solitalea). Collectively, this study provides an in-depth exploration of microbial nitrogen removal in freshwater aquaculture areas and supports management strategies for N pollution caused by reclamation for aquaculture in riparian zones.

Enhanced susceptibility to oiling may limit denitrification recovery in marshes subjected to woody encroachment

Coastal salt marshes provide valuable ecosystem services but are subjected to multiple concomitant stressors that may impact their ability to provide those services. Global climate change has led to the poleward expansion of mangroves into salt marshes on each continent where mangroves and marshes co-occur. In the northern Gulf of Mexico, warming winter temperatures have resulted in the expansion of Avicennia germinans (black mangrove) into forb-dominated salt marshes, resulting in a shift in ecosystem structure that can impact the ecosystem services marshes provide, including biogeochemical processes such as nitrogen removal. There have been limited studies addressing how mangrove expansion impacts nitrogen removal rates in salt marshes, but it is possible that mangroves enhance microbial nitrogen removal capacity through more efficient oxygen translocation to sediments. However, mangroves are more sensitive to oiling (such as occurred during the 2010 Deepwater Horizon spill) than marsh plants, such as Spartina alterniflora, which have a higher turnover. Thus, even if they enhance nitrogen removal, if they cannot withstand disturbances such as oiling, there still may be a loss of function associated with woody encroachment. We conducted a field study to assess the impact of woody encroachment in mediating biogeochemical recovery 7 to 8 years after the Deepwater Horizon oil spill. We collected sediments from S. alterniflora- and A. germinans-dominated plots in the Chandeleur Islands (LA, United States), a chain of barrier islands in the northern Gulf of Mexico subjected to a range of oiling following the spill. We compared nitrate reduction rates (denitrification and dissimilatory nitrate reduction to ammonium), microbial community composition, and denitrifier marker gene abundance at sites subjected to light and moderate oiling using a combination of isotope pairing on sediment slurries, 16S sequencing, and qPCR. We predicted that overall, denitrification rates and microbial functional capacity would be enhanced in mangrove-dominated sediments. We also predicted that these enhancements would be diminished at the more intensely oiled site due to the higher susceptibility of A. germinans to oiling. Denitrification potential rates were higher in mangrove sediments at the lightly oiled site, whereas dissimilatory nitrate reduction to ammonium potential rates were higher in marsh sediments. Indicator analysis of 16S rRNA data selected putative sulfur cycling taxa as indicators of marsh sediments, suggesting that changes in oxygen availability associated with encroachment may be driving the differences in process rates. There was no difference in process rates between plant types at the moderately oiled site, where heavily weathered oil residue was still present. Sediment nutrient stocks were lower in moderately oiled mangrove plots than in lightly oiled mangrove plots, suggesting that sediment fertility recovery following the spill may have been slower in the mangroves, contributing to a change in ecosystem function. This study shows that woody encroachment has the potential to impact both the biogeochemical services that marshes provide and their response to and recovery from disturbances.

Start-up characteristics and microbial nitrogen removal mechanisms in ANAMMOX systems with different inoculations under prolonged starvation

The characteristics of lab-scale ANAMMOX system for efficient nitrogen removal were tested by different inoculations (anaerobic granular sludge (AGS) + anammox sludge (AMS), R1; AGS alone, R2) in continuous flow reactors following start-up under starvation. TN removal rates were above 90 % in both reactors. Microbial community analysis showed that the nitrogen removal was the combined results of anammox and partial denitrification (PD), Higher microbial growth rate triggered by quorum-sensing (QS) caused R1 to secrete more extracellular polymeric substances (EPS) and promoted the growth of its particle size. However, the overproduction of EPS destroyed the particle structure with time, and led to a deterioration of operational stability in R1. R2 showed better nitrogen removal stability to high nitrogen loading rate (NLR). This was due to higher endogenous organics within R2, which inhibited cell aggregation and EPS overproduction. But undeniably, R1 had higher specific anammox activity (SAA) with higher anammox bacteria (AAOB) abundance (The abundance of Planctomycetota in R1 and R2 were 21.2 %, 7.71 %). The results suggest that the operational stability was influenced by a combination of particle properties and microbial metabolism, and that the inoculation of AGS is more conducive to efficient and economic nitrogen removal in wastewater treatment under starvation.

Metagenomic analysis and nitrogen removal performance evaluation of activated sludge from a sequencing batch reactor under different salinities

The effect of salinity on the nitrogen removal performance and microbial community of activated sludge was investigated in a sequencing batch reactor. The NH4+-N removal efficiency was over 95% at 0–4% salinity, indicating that the nitrification performance of activated sludge was slightly affected by lower salinity. The obvious nitrite accumulation was observed with the increment of the salinity to 5%, followed by a notable decline in the nitrogen removal performance at 6% salinity. The salinity inhibited the microbial activity, and the specific rate of nitrification and denitrification was decreased by the increasing salinity obviously. Additionally, the lower activity of superoxide dismutase and peroxidase and higher reactive oxygen species content in activated sludge might account for the deteriorative nitrogen removal performance at 6% salinity. Metagenomics analysis revealed that the genes encoding the ABC-type quaternary amine transporter in the ABC transporter pathway were abundant in the activated sludge at 2% and 4% salinity, and the higher salinity of 6% led to the loss of the genes encoding the p-type Na+ transporter in the ABC transporter pathway. These results indicated that the salinity could weaken the ABC transporter pathway for the balance of osmotic pressure in activated sludge. The microbial activity and nitrogen removal performance of activated sludge were decreased due to the unbalanced osmotic pressure at higher salinity.

Crab bioturbation affects competition between microbial nitrogen removal and retention in estuarine and coastal wetlands

As the important benthic animal in coastal wetlands, crab bioturbation may significantly affect the nitrogen (N) budgets by regulating microbial N transformation processes. However, the response of interaction between different microbial N processes to crab bioturbation remains poorly understood. Here, a 30-day microcosmic experiment was conducted using sediment collected from the Yangtze Estuary wetland, followed by the determination of temporal variations of physicochemical parameters, N removal (denitrification plus anammox, which is defined as N2 production) and retention rates (nitrate dissimilatory reduction to ammonium, DNRA) as well as relevant gene abundances in response to different crabs densities. The results showed that crab bioturbation simultaneously promoted the rates of N2 production and DNRA processes. These two process rates were positively associated with the intensity of crab bioturbation, which was supported by molecular analysis of relevant functional gene abundance. Crab bioturbation was more beneficial to DNRA than N2 production. Due to this disproportionate stimulation, crab bioturbation increased the importance of DNRA, indicating that N retention was becoming more significant under crab bioturbation in estuarine and coastal wetlands. The variations of sediment total organic carbon and oxygen availability driven by crab bioturbation were the critical factors mediating the changes in microbial N removal and retention. Overall, our findings highlighted that crab bioturbation can affect the N budgets in estuarine and coastal wetlands by altering the competition between microbial N removal and retention.

Molecular analysis of microbial nitrogen transformation and removal potential in the plant rhizosphere of artificial tidal wetlands across salinity gradients

This study explored the microbial nitrogen transformation and removal potential in the plant rhizosphere of seven artificial tidal wetlands under different salinity gradients (0–30‰). Molecular biological and stable isotopic analyses revealed the existence of simultaneous anammox (anaerobic ammonium oxidation), nitrification, DNRA (dissimilatory nitrate reduction to ammonium) and denitrification processes, contributing to nitrogen loss in rhizosphere soil. The microbial abundances were 2.87 × 103–9.12 × 108 (nitrogen functional genes) and 1.24 × 108–8.43 × 109 copies/g (16S rRNA gene), and the relative abundances of dissimilatory nitrate reduction and nitrification genera ranged from 6.75% to 24.41% and from 0.77% to 1.81%, respectively. The bacterial 16S rRNA high-throughput sequencing indicated that Bacillus, Zobellella and Paracoccus had obvious effects on nitrogen removal by heterotrophic nitrifying/aerobic denitrifying process (HN-AD), and autotrophic nitrification (Nitrosomonas, Nitrospira and Nitrospina), conventional denitrification (Bradyrhizobium, Burkholderia and Flavobacterium), anammox (Candidatus Brocadia and Candidatus Scalindua) and DNRA (Clostridium, Desulfovibrio and Photobacterium) organisms co-existed with HN-AD bacteria. The potential activities of DNRA, nitrification, anammox and denitrification were 1.23–9.23, 400.03–755.91, 3.12–35.24 and 30.51–300.04 nmolN2·g−1·d−1, respectively. The denitrification process contributed to 73.59–88.65% of NOx− reduction, compared to 0.71–13.20% and 8.20–15.42% via DNRA and anammox, as 83.83–90.74% of N2 production was conducted by denitrification, with the rest through anammox. Meanwhile, the nitrification pathway accounted for 95.28–99.23% of NH4+ oxidation, with the rest completed by anammox bacteria. Collectively, these findings improved our understanding on global nitrogen cycles, and provided a new idea for the removal of contaminants in saline water treatment.

Nitrate Addition Increases the Activity of Microbial Nitrogen Removal in Freshwater Sediment

Denitrification and anammox occur widely in aquatic ecosystems serving vital roles in nitrogen pollution removal. However, small waterbodies are sensitive to external influences; stormwater runoff carrying nutrients and oxygen, flows into waterbodies resulting in a disruption of geochemical and microbial processes. Nonetheless, little is known about how these short-term external inputs affect the microbial processes of nitrogen removal in small waterbodies. To investigate the effects of NO3−, NH4+, dissolved oxygen (DO) and organic C on microbial nitrogen removal in pond sediments, regulation experiments have been conducted using slurry incubation experiments and 15N tracer techniques in this study. It was demonstrated the addition of NO3− (50 to 800 μmol L−1) significantly promoted denitrification rates, as expected by Michaelis-Menten kinetics. Ponds with higher NO3− concentrations in the overlying water responded more greatly to NO3− additions. Moreover, N2O production was also promoted by such an addition of NO3−. Denitrification was significantly inhibited by the elevation of DO concentration from 0 to 2 mg L−1, after which no significant increase in inhibition was observed. Denitrification rates increased when organic C was introduced. Due to the abundant NH4+ in pond sediments, the addition demonstrated little influence on nitrogen removal. Moreover, anammox rates showed no significant changes to any amendment.

Nitrite and nitrate reduction drive sediment microbial nitrogen cycling in a eutrophic lake

The anaerobic microbial nitrogen (N) removal in lake sediments is one of the most important processes driving the nitrogen cycling in lake ecosystems. However, the N removal and its underlying mechanisms regulated by denitrifying and anaerobic ammonia oxidation (anammox) bacteria in lake sediments remain poorly understood. With the field sediments collected from different areas of Lake Donghu (a shallow eutrophic lake), we examined the denitrifying and anammox bacterial communities by sequencing the nirS/K and hzsB genes, respectively. The results indicated that denitrifiers in sediments were affiliated to nine clusters, which are involved in both heterotrophic and autotrophic denitrification. However, anammox bacteria were only dominated by Candidatus Brocadia. We found that NO3− and NO2− concentrations, as well as Nar enzyme activity were the key factors affecting denitrifying and anammox communities in this eutrophic lake. The enrichment experiments in bioreactors confirmed the divergence of denitrification and anammox rates with an additional complement of NO2−, especially under a condition low nitrate reductase activity. The coupled denitrification and anammox may play significant roles in N removal, and the availability of electronic acceptors (i.e., NO2− and NO3−) strongly influenced the N loss in lake sediments. Further path analysis indicated that NO2−, NO3− and some N-related enzymes were the key factors affecting microbial N removal in lake sediments. This study advances our understanding of the mechanisms driving the of denitrification and anammox in lake sediments, which also provides new insights into coupled denitrification-anammox N removal in eutrophic lake ecosystems.

Treatment of Ammonium-Nitrogen–Contaminated Groundwater by Tidal Flow Constructed Wetlands Using Different Substrates: Evaluation of Performance and Microbial Nitrogen Removal Pathways

Treatment of Ammonium-Nitrogen–Contaminated Groundwater by Tidal Flow Constructed Wetlands Using Different Substrates: Evaluation of Performance and Microbial Nitrogen Removal Pathways

Artificial ponds as hotspots of nitrogen removal in agricultural watershed

Small waters, like ponds, are the most abundant freshwater environments, and are increasingly recognized for their function in ecosystem service delivery. In agricultural watershed, artificial ponds play an essential role in reducing nitrogen pollution. However, until now artificial ponds remain the least investigated part of water environments. The importance of microbial activities has seldom been discussed, which makes the microbial pathways and processes rates in nitrogen removal poorly understood. To illustrate the role of artificial ponds in microbial nitrogen removal in agricultural watersheds, 21 pond sediments and 11 soils are collected in an agricultural watershed of China. Results show that surface sediments in ponds carry significantly higher dissolved inorganic nitrogen (9.1–21.9 mg/kg) and total organic matter (64.8–113.0 g/kg) compared to the surrounding agricultural soils. High rates of microbial nitrogen removal in ponds (12.4–25.5 nmol N g−1 h−1) are observed, which are 2–9 times higher than those in dryland soils. In pond sediments, denitrification dominates (> 90% N-loss) the microbial nitrogen removal process with only a minor contribution of anaerobic ammonium oxidation. A high potential of N2O production (up to 9.4 nmol N g−1 h−1) occurs in ponds along with the rapid nitrogen removal. For denitrifier genes, nir gene are always more abundant than nosZ gene. Additionally, the nirS gene is more abundant under flooded conditions, while nirK gene prefers higher dissolved oxygen and NO3− in drylands. These findings highlight the ecosystem function of ponds in agricultural watersheds, and provide new ideas on pollution control and global nitrogen cycling.

Hotspots and trends of biological water treatment based on bibliometric review and patents analysis

In order to reveal the hotspots and trends of biological water treatment from the perspectives of scientific and technological innovation, both of the bibliometric review and patents analysis were performed in this study. The Web of Science Core Collection database and Derwent Innovation Index database recorded 30023 SCI papers and 50326 patents, respectively were analyzed via information visualization technology. The results showed that China ranked the first in both papers and patents, while the United States and Japan had advantages in papers and patents, respectively. It was concluded through literature metrology analysis that microbial population characteristics, biodegradation mechanism, toxicity analysis, nitrogen and phosphorus removal and biological treatment of micro-polluted wastewater were the research hotspots of SCI papers. Activated sludge process and anaerobic-aerobic combined process were the two mainstream technologies on the basis of patent technology classification analysis. Technology evolution path of biological water treatment was also elucidated in three stages based on the citation network analysis. Furthermore, the future directions including research on the law of interaction and regulation of biological phases and pollutants and the technology innovations towards the targeted biotransformation or selective biodegradation of pollutants and resource reuse of wastewater were prospected.

Microbial composition and nitrogen removal pathways in a novel sequencing batch reactor integrated with semi-fixed biofilm carrier: evidence from a pilot study for low- and high-strength sewage treatment.

The sequencing batch reactor (SBR) activated sludge process is a well-established technology for sewage treatment. One of the drawbacks of SBRs, however, total nitrogen (TN) removals is insufficient. By means of introducing four improvements, including semi-fixed biofilm carrier, sludge elevation mixing and change for the mode of influent and effluent, compliant standard for TN discharge was obtained in this novel SBR configuration during low- and high-strength sewage load. To illustrate the microbial compositions and functions of the attached biofilm on semi-fixed carrier and the suspended aggregates, as well as the nitrogen removal pathway, high throughput 16S rRNA gene amplicon sequencing, PICRUSt2 algorithm, and KEGG database were applied. The results revealed that (i) the microbial communities from suspended aggregates and biofilm samples were significantly different from each other; (ii) during low-strength sewage loads, TN removal was mainly by nitrification-denitrification. The suspended aggregates was responsible for denitrification, while the biofilm was focused on ammonium oxidation; (iii) during high-strength sewage loads, function of nitrate reductase from suspended aggregates was faded, and anammox and N assimilation by biofilm became dominant. Meanwhile, TN removal referring to the formation of L-glutamine via assimilation was the main pathway.

Start-Up Characteristics and Microbial Nitrogen Removal Mechanism in an Anammox System with Different Inoculations Under Prolonged Starvation

Start-Up Characteristics and Microbial Nitrogen Removal Mechanism in an Anammox System with Different Inoculations Under Prolonged Starvation

Start-Up Characteristics and Microbial Nitrogen Removal Mechanism in an Anammox System with Different Inoculations Under Prolonged Starvation

Start-Up Characteristics and Microbial Nitrogen Removal Mechanism in an Anammox System with Different Inoculations Under Prolonged Starvation

Structural Characteristics of Aerobic Granular Sludge and Factors That Influence Its Stability: A Mini Review

Current extensive research on aerobic granular sludge (AGS) largely focuses on improving its microbial biodiversity, settlement behavior, nitrogen and phosphorus removal efficiency, and shock load resistance. Great challenges that have to be faced are the bottleneck of slow-speed granulation and easy disintegration after granulation, which are key to the extended application of AGS technology. In the present review, the typical morphological structures of AGS are firstly summarized as well as the granulation model hypotheses, and then, we analyze the dominant microflora and their spatial distribution features. The influencing factors on particle structure stability are discussed thereafter on a macro and micro scale. Prospects and future research trends are also discussed based on the current study results for AGS technology.

Ditching Nutrients: Roadside Drainage Networks are Hotspots for Microbial Nitrogen Removal

AbstractHuman‐made stormwater control systems are biogeochemical hotspots, but construction and management may result in homogenization of their ecosystem structure. Roadside ditches are a ubiquitous part of the landscape, yet few studies have quantified their biogeochemical potential. We conducted a study to determine (a) nitrate (NO3−) removal potential through rate measurements and (b) microbial community structure using 16S rRNA gene (iTag) sequencing in roadside ditches draining predominantly forested, urban, and agricultural watersheds surrounding Mobile Bay, AL (USA). We found that nitrogen (N) removal rates by denitrification and anammox dominated over N‐retention by dissimilatory nitrate reduction to ammonium, accounting for upwards of 89% of NO3− reduction on average. There were no differences in soil characteristics between land use types, but denitrification potential rates in forested ditches were less than half of those in urban and agricultural ditches, possibly as a result of differences in vegetation management. Microbial alpha and beta diversity were largely homogenous across the three land use types. However, indicator species analysis revealed putative ammonia oxidizers (Nitrososphaeraceae and Nitrosomonadaceae), nitrate reducers (Gaiellales), and nitrous oxide reducers (Myxococcales) as significant groups in urban and agricultural ditches. We conclude that land use effects on N‐removal in these constructed drainage networks are mediated through key microbial groups and ditch vegetation management strategies. Further, roadside ditches have significant potential for reactive N removal in the landscape.