Urbanizations have increased the loadings of reactive nitrogen in urban riverine environments. However, limited information about dissimilatory nitrate reduction processes and associated contributions to nitrogen removal is available for urban riverine environments. In this study, sediment slurry experiments were conducted with nitrogen isotope-tracing technique to investigate the potential rates of denitrification, anaerobic ammonium oxidation (anammox) and dissimilatory nitrate reduction to ammonium (DNRA) and their contributions to nitrate reduction in sediments of urban river networks, Shanghai. The potential rates of denitrification, anammox and DNRA measured in the study area ranged from 0.193 to 98.7 nmol N g−1 h−1 dry weight (dw), 0.0387–23.7 nmol N g−1 h−1 dw and 0–10.3 nmol N g−1 h−1 dw, respectively. Denitrification and DNRA rates were higher in summer than in winter, while anammox rates were greater in winter than in summer for most sites. Dissolved oxygen, total organic carbon, nitrate, ammonium, sulfide, Fe(II) and Fe(III) were found to have significant influence on these nitrate reduction processes. Denitrification contributed 11.5–99.5%% to total nitrate reduction, as compared to 0.343–81.6% for anammox and 0–52.3% for DNRA. It is estimated that nitrogen loss of approximately 1.33 × 105 t N year−1 was linked to both denitrification and anammox processes, which accounted for about 20.1% of total inorganic nitrogen transported annually into the urban river networks of Shanghai. Overall, these results show the potential importance of denitrification and anammox in nitrogen removal and provide new insight into the mechanisms of nitrogen cycles in urban riverine environments.

Developed landscapes are exposed to changes in hydrology and water chemistry that limit their ability to mitigate detrimental impacts to coastal water bodies, particularly those that result from stormwater runoff. The elevated level of impervious cover increases not only runoff but also contaminant loading of nutrients, metals, and road salt used for deicing to water bodies. Here we investigate the impact that road salt has on denitrification in roadside environments. Sediments were collected from a series of forested and roadside wetlands and acclimated with a range of Cl− concentrations from 0 to 5000 mg L−1 for 96 h. Denitrification rates were measured by the isotope pairing technique using 15N–NO3−, while denitrifying community structures were compared using terminal restriction fragment length polymorphism (T-RFLP) of nitrous oxide reductase genes (nosZ). Chloride significantly (p < 0.05) inhibited denitrification in forested wetlands at a Cl− dosage of 2500 or 5000 mg L−1, but the decrease in denitrification rates was less and not significant for the roadside wetlands historically exposed to elevated concentrations of Cl−. The difference could not be attributed to other significant changes in conditions, such as DOC concentrations, N species concentrations, or pH levels. Denitrifying communities, as measured by T-RFs of the nosZ gene, in the roadside wetlands with elevated concentration of Cl− were distinctly different and more diverse compared to forested wetlands, and also different in roadside wetlands after 96 h exposures to Cl−. The shifts in denitrifying communities seem to minimize the decrease in denitrification rates in the wetlands previously exposed to Cl. As development results in more Cl− use and exposure to a broad range of natural or manmade wetland structures, an understanding of the seasonal effect of Cl on denitrification processes in these systems would aid in design or mitigation of the effects on N removal rates.

Many lakes and rivers are enriched with high levels of suspended sediments (SPS). Denitrification occurring on suspended sediments (DSS) may play an important role in nitrogen removal in water columns with high SPS concentrations. Poyang Lake, with dramatic hydrologic variations, has high spatial and seasonal variation of SPS, and we hypothesized that DSS and nitrogen removal in this lake would vary similarly. DSS in Poyang Lake was determined by the traditional acetylene-inhibition method combined with a batch mode assay. Laboratory simulation experiments were also conducted to examine the factors controlling denitrification occurring on SPS. Seasonally, DSS rates at 15 sampling sites in Poyang Lake were 0.63 ± 0.24, 0.29 ± 0.17, 0.25 ± 0.18, and 0.52 ± 0.37 μmol N·L−1·d−1, respectively in spring, summer, autumn, and winter. Spatially, average DSS rates were higher in the northern lake area, which is connected to the Yangtze River, than in the upstream and central lake area. Lowest DSS rates occurred in semi-closed bay and dish lakes. Spatial and seasonal variations of DSS rates were affected by a combination of factors, in which nitrate concentrations, SPS composition, and concentrations of organic-SPS were the most important. These influencing factors were seasonally dependent, with nitrate concentrations having stronger effects on DSS during wet seasons than dry seasons. Results from a multiple stepwise regression model also demonstrated that DSS tended to occur on fine particles (e.g., clay particles, <4 μm). Evaluation of annual nitrogen loss by DSS was estimated according to the seasonal water budget and DSS rates in Poyang Lake. The total nitrogen loss by DSS was estimated to be 10800 ± 6090 t, which accounted for 2.8–9.9% of the nitrogen input, and this proportion was comparable to nitrogen removal by sediment denitrification. This result confirms that DSS was an important nitrogen sink in this large, turbid lake.

In this study, basic sediment properties, nutrient flux, and nitrogen cycle (including denitrification, anaerobic ammonium oxidation [anammox], nitrification, and dissimilatory nitrate reduction to ammonium [DNRA]) were investigated at two sampling sites with different tree ages in the mangrove region of the Jiulong River Estuary, China. The results show that sediments at mangrove flat area have relatively strong capability to reduce NO3−, in which the DNRA rate is relatively high (204.53±48.32μmolNm−2h−1), which is approximately 75.7–85.9% of the total NO3− reduction, while the denitrification and anammox rates are relatively low – only approximately 5.6–9.5% and 8.5–14.8% of the total NO3− reduction, respectively. Thus, in the nitrogen-enriched subtropical mangrove system, DNRA is the main pathway to reduce NO3−, and most of the input nitrogen is conserved as NH4+ in the system, which assures high productivity of the mangrove system.

We utilize N and C species concentration data along with δ15N values of NO3− and δ13C values of dissolved inorganic C to evaluate the stoichiometry of biogeochemical reactions (mineralization, nitrification, anammox, and denitrification) occurring within a subsurface wastewater plume that originates as treated wastewater injection and enters the coastal waters of Maui as submarine groundwater discharge. Additionally, we compare wastewater effluent time-series data, injection rates, and treatment history with submarine spring discharge time-series data. We find that heterotrophic denitrification is the primary mechanism of N loss within the groundwater plume and that chlorination for pathogen disinfection suppresses microbial activity in the aquifer responsible for N loss, resulting in increased coastal ocean N loading. Replacement of chlorination with UV disinfection may restore biogeochemical reactions responsible for N loss within the aquifer and return N-attenuating conditions in the effluent plume, reducing N loading to coastal waters.

A novel aerobic denitrification and biomineralization strain CN86 was isolated from the Qu Jiang artificial lake. Based on phylogenetic characteristics, the isolated strain was identified as Acinetobacter species. Strain CN86 was confirmed to have the ability to perform simultaneous denitrification and biomineralization. Exponential decay equation was used for the matching of kinetic processes on denitrification and biomineralization. A highest nitrate removal rate was achieved at the pH7.0, organic concentration of 1.5g/L and temperature of 30°C. An optimal hardness removal rate was obtained at the pH9.0, organic concentration of 2.0g/L and temperature of 30°C. Strain CN86 is a suitable candidate for the simultaneous removal of nitrate and hardness in groundwater treatment.

Acinetobacter sp. J25 exhibited good denitrification and high algicidal activity against toxic Microcystis aeruginosa. Response surface methodology (RSM) experiments showed that the maximum algicidal ratio occurred under the following conditions: temperature, 30.46°C; M. aeruginosa density, 960,000cellsmL−1; and inoculum, 23.75% (v/v). Of these, inoculum produced the maximum effect. In the eutrophic landscape water experiment, 10% bacterial culture was infected with M. aeruginosa cells in the landscape water. After 24days, the removal ratios of nitrate and chlorophyll-a were high, 100% and 87.86%, respectively. The denitrification rate was approximately 0.118mgNO3−–N·L−1·h−1. Moreover, the high-throughput sequencing result showed that Acinetobacter sp. J25 was obviously beneficial for chlorophyll-a and nitrate removal performance in the eutrophic landscape water treatment. Therefore, strain J25 is promising for the simultaneous removal of chlorophyll-a and nitrate in the eutrophic landscape water treatment.

This study aimed to investigate microbial responses to nitrate stimulation in oiled mangrove mesocosm. Both supplementary oil and nitrate changed the water and sediment chemical properties contributing to the shift of microbial communities. Denitrifying genes nirS and nirK were increased several times by the interaction of oil spiking and nitrate addition. Bacterial chao1 was reduced by oil spiking and further by nitrate stimulation, whereas archaeal chao1 was only inhibited by oil pollution on early time. Sampling depth explained most of variation and significantly impacted bacterial and archaeal communities, while oil pollution only significantly impacted bacterial communities (p<0.05). Despite explaining less variation, nitrate addition coupled with oil spiking enhanced the growth of hydrocarbon degraders in mangrove. The findings demonstrate the impacts of environmental factors and their interactions in shaping microbial communities during nitrate stimulation. Our study suggests introducing genera Desulfotignum and Marinobacter into oiled mangrove for bioaugmentation.

Oysters provide a critical habitat, are a food resource for higher trophic levels and support important commercial fisheries throughout the world. Oyster reefs can improve water quality by removing phytoplankton. While sediment denitrification may be enhanced adjacent to oyster reefs, little is known about nitrification and denitrification associated with living oysters and their shells. We measured nitrification and denitrification in living oysters (Crassostrea virginica and Crassostrea gigas) and empty oyster shells. Nitrification was similar between live oysters and empty oyster shells, however, denitrification was enhanced significantly on living oysters compared to shells. This is the first demonstration of nitrification and denitrification associated with living oysters and their shells. Our data suggest that loss of historic oyster reefs has likely affected the resilience of estuaries to eutrophication. The additional benefit of oyster mediated denitrification should be considered in restoration of oyster reefs as a tool for managing eutrophication.

Due to nitrogen load reduction policies, wastewater treatment facilities (WWTFs) have upgraded to tertiary treatment — where denitrification reduces and removes nitrogen. Changes to the stable isotopic composition of nitrate inputs after upgrades or how it transfers to the estuary have not been assessed in Rhode Island. We investigate whether these upgrades impact the isotopic signature of nitrate inputs to Narragansett Bay. Samples from rivers and WWTFs discharging to Narragansett Bay characterize the anthropogenic source nitrate (NO3−) isotopic composition (δ15N–NO3− and δ18O–NO3−) and temporal variability. At one WWTF, tertiary treatment increased effluent nitrate δ15N–NO3− and δ18O–NO3− values by ~16‰. Riverine values increased by ~4‰, likely due to the combination of decreases in N and upgrades. Combined river and WWTF flux-weighted isotopic compositions showed enriched values and an amplitude reduction in monthly variability. When seasonal isotopic means are significantly different from other sources, δ15N–NO3− may be a useful tracer of inputs.