Mean NH4 Research Articles

Controlling internal nitrogen and phosphorus loading using Ca-poor soil capping in shallow eutrophic lakes: Long-term effects and mechanisms

Clean soil is a potential capping material for controlling internal nutrient loading and helping the recovery of macrophytes in eutrophic lakes, but the long-term effects and underlying mechanisms of clean soil capping under in-situ conditions remain poorly understood. In this study, a three-year field capping enclosure experiment combining intact sediment core incubation, in-situ porewater sampling, isotherm adsorption experiments and analysis of sediment nitrogen (N) and phosphorus (P) fractions was conducted to assess the long-term performance of clean soil capping on internal loading in Lake Taihu. Our results indicate that clean soil has excellent P adsorption and retention capacity as an ecologically safe capping material and can effectively mitigate NH4+-N and SRP (soluble reactive P) fluxes at the sediment-water interface (SWI) and porewater SRP concentration for one year after capping. The mean NH4+-N and SRP fluxes of capping sediment were 34.86 mg m−2 h−1 and -1.58 mg m−2 h−1, compared 82.99 mg m−2 h−1 and 6.29 mg m−2 h−1 for control sediment. Clean soil controls internal NH4+-N release through cation (mainly Al3+) exchange mechanisms, while for SRP, clean soil can not only react with SRP due to its high Al and Fe content, but also stimulate the migration of active Ca2+ to the capping layer, thus precipitating as Ca-bound P (Ca-P). Clean soil capping also contributed to the restoration of macrophytes during the growing season. However, the effect of controlling internal nutrient loading only lasted for one year under in-situ conditions, after which the sediment properties returned to pre-capping conditions. Our results highlight that clean Ca-poor soil is a promising capping material and further research is needed to extend the longevity of this geoengineering technology.

Isotopic imprints of aerosol ammonium over the north China plain

Atmospheric PM2.5 poses a variety of health and environmental risks to urban environments. Ammonium is one of the main components of PM2.5, and its role in PM2.5 pollution will likely increase in the coming years as NH3 emissions are still unregulated and rising in many cities worldwide. However, partitioning urban NH4+ sources remains challenging. Although the 15N natural abundance (δ15N) analysis is a promising approach for this purpose, it has seldom been applied across multiple cities within a given region. This limits our understanding of the regional patterns and controls of NH4+ sources in urban environments. Here, we collected PM2.5 samples using an active sampling technique during winter at six cities in the North China Plain to characterize the concentrations, δ15N and sources of NH4+ in PM2.5. We found substantial variations in both the concentrations and δ15N of NH4+ among the sites. The mean NH4+ concentrations across the six cities ranged from 3.6 to 12.1 μg m−3 on polluted days and from 0.9 to 10.6 μg m−3 on non-polluted days. The δ15N ranged from 6.5‰ to 13.9‰ on polluted days and from 8.7‰ to 13.5‰ on non-polluted days. The δ15N decreased with increasing NH4+ concentrations at all six sites. We found that non-agricultural sources (vehicle exhaust, ammonia slip and urban wastes) contributed 72%–94% and 56%–86% of the NH4+ on polluted and non-polluted days, respectively, and that during polluted days, combustion-related emissions (vehicle exhaust and ammonia slip) were positively associated with the proportion of urban area, population density and number of vehicles, highlighting the importance of local sources of particulate pollution. This study suggests that the analysis of 15N in aerosol NH4+ is a promising approach for apportioning atmospheric NH3 sources over a large region, and this approach has potential for mapping rapidly and precisely the sources of NH3 emissions.

Nitrogen Distribution and Inorganic Nitrogen Diffusion Flux in a Shallow Lake During the Low Temperature Period: A Case Study of the Baiyangdian Lake

The distribution of inorganic nitrogen across the sediment-water interface in Baiyangdian Lake, the largest shallow lake in North China, was examined during the low temperature period. Furthermore, the influence of inorganic nitrogen diffusion flux in sediment porewater on the overlying water quality was analyzed. The results showed that the mean TN concentration in the surface water ranged from 4.83 to 8.23 mg·L-1, the mean NH4+-N concentration ranged from 0.21 to 0.34 mg·L-1, and the mean NO3--N concentration ranged from 0.01 to 2.75 mg·L-1. TN exceeds the Class V water quality standard for surface water, indicating serious pollution. The mean TN content of the sediments ranged from 681 to 4365 mg·kg-1, of which TON was the main form of TN, accounting for 61.6%-93.1%. NH4+-N was the main form of TIN, with a mean content ranging from 28.9 to 116.3 mg·kg-1, and a mean NO3--N content of between 5.2 and 23.7 mg·kg-1, which is relatively low. The NH4+-N concentration in the porewater was 3 to 16 times that of the overlying water, showing a gradual accumulation trend. The diffusion flux ranges of NH4+-N, NO3--N, and NO2--N across the sediment-water interface were -0.55-4.09, -1.44-3.67, and -0.88-0.04 mg·(m2·d)-1, respectively. There was still a potential release risk during the low temperature period. A large amount of NH4+-N accumulated in the sediments during the low-temperature period, which may affect the quality of the overlying water after the temperature rises. Therefore, studying the distribution of nitrogen across the sediment-water interface, and the risk of internal release of inorganic nitrogen during the low temperature period, is of great significance for improving water quality in Baiyangdian Lake and understanding the internal nitrogen pollution of shallow lakes.

Are vegetated drainage ditches effective for nitrogen removal under cold temperatures?

Vegetated ditches are widely used to treat agricultural wastewater, but effective nitrogen removal at low temperatures remains a challenge because plants wilt in the winter. In this study, three simulated drainage ditches vegetated with Myriophyllum aquaticum were operated with low, medium, and high water levels to study ammonium nitrogen (NH4+-N) removal under cold temperatures. The M. aquaticum ditches had a mean NH4+-N removal efficiency of 75.8–86.8% throughout cold period. Based on nitrogen mass balance, plant uptake, sediment adsorption, and microbial removal accounted for 12.4–21.5%, 0.0–8.1%, and 38.9–54.6% of the influent total nitrogen loading, respectively. The accumulation of nitrate confirmed that intense microbial nitrification occurred in M. aquaticum ditches even at low temperature. These results suggest that M. aquaticum is appropriate as a cold-tolerant plant for NH4+-N removal in drainage ditches.

Distribution of nitrogen and phosphorus and estimation of nutrient fluxes in the water and sediments of Liangzi Lake, China.

Water samples and sediments from Liangzi Lake were taken and used to study the vertical distribution characteristics of nitrogen (N) and phosphorus (P) in both the overlying and pore water. Fluxes of ammonia (NH4+-N) and phosphate (PO43--P) were calculated using a one-dimensional transport-reaction model based on Fick's First Law. The results showed that the mean NH4+-N and NO3--N concentrations in the overlying water of Liangzi Lake were 2.59 and 0.46mgL-1, respectively. The mean PO43--P concentrations were lower than the detection limit. Both N and P displayed peaks at the sediment-water interface. For example, the mean concentration of ammonia in pore water in the surficial layer (0-5cm) was 4.29 ± 2.74mg·L-1, which was twice than that of the overlying water. Two PO43--P vertical profile regimes were identified; one had a gradually increasing trend, while the other first increased and then decreased. The mean orthophosphate concentration in the pore water of the surface layer (0-5cm) was 0.01 ± 0.01mg·L-1. The spatial distribution of ammonia flux values was highly heterogeneous. Using these data, the annual load contribution of autochthonous ammonia was calculated to be 481t a-1. Studying N and P pollution and fluxes in the lakes of urban drinking water sources facilitates the provision of protection measures.

The Physico-Chemical Quality of Effluents of Selected Sewage Treatment Plants Draining into River Rwizi, Mbarara Municipality, Uganda

As population increases in urban areas, the domestic and industrial activities increase resulting in an increase in the volumes of wastewater and anthropogenic pollution, hence posing a threat to public health and environment. This study assessed the physical chemical quality of two main sewage plant effluents discharging into River Rwizi. Effluent water samples were analyzed for dissolved oxygen, colour, turbidity, total suspended solid, total iron, phosphates, alkalinity, magnesium, calcium carbonate, temperature, pH, ammonium, electrical conductivity, chloride and nitrates. Parameters were analyzed following standard methods of APHA (1985). The values obtained were compared with EPA (2001), NWSC (2015) and NEMA (1999) standards for waste water. Results showed that the mean values most of the parameters tested were higher than the recommended EPA, NWSC and NEMA standards. The mean colour was 1627.67°C and 1414.33°C in Kakoba and Taso sewage effluents respectively compared to EPA (20-150), NWSC (500) and NEMA (300) standards (p > 0.05). The mean alkalinity was 1390.17 mg/l and 1308.33 mg/l for Kakoba and Taso respectively compared with EPA (400) and NWSC (800) standards. DO had a mean concentration of 68.27 mg/l and 63.03 mg/l in Taso and Kakoba respectively compared to EPA and NEMA standard of 5 mg/l. Mg was 243.29 mg/l and 246.49 mg/l in Kakoba and Taso sewage effluents respectively compared to NEMA standard for waste water of 100 mg/l (p > 0.05). The mean pH was 8.26 and 8.16 in Taso and Kakoba sewage effluents respectively compared to NWSC and NEMA standard of 6.0 - 8.0. Phosphate mean concentration levels were 32.2 mg/l and 27.11 mg/l for Taso and Kakoba respectively compared to standards of EPA (0.5 - 0.7 mg/l) and NEMA (10 mg/l). NO3 was 10 mg/l and 5.83 mg/l in Kakoba and Taso sewage effluents respectively compared to NWSC maximum permissible limit of 5 mg/l. The mean NH4 concentration was 385.33 mg/l (Kakoba) and 50.0 mg/l (Taso) compared to the EPA guideline range (0.2 - 4 mg/l). Chloride (Cl) had a mean of 833.33 mg/l in Kakoba compared to EPA (250 mg/l), NWSC and NEMA (500 mg/l) standards. Therefore the study recommends for effective treatment of waste effluents from Kakoba and Taso sewage treatment plants before recycling in order to avoid pollution of river Rwizi.

Concentration, Flux, and Emission Factor of N2O in Rivers with Different Nitrogen Pollution Features

In this study, 22 rivers in Tieling City were selected to study the concentration, flux, and emission factor (EF5r) of N2O. Based on the concentrations and components of nitrogen (N), the 22 rivers can be divided into ammonia nitrogen (NH4+)-polluted rivers (mean NH4+=5.86 mg·L-1), nitrate nitrogen (NO3-)-polluted rivers (mean NO3-=3.05 mg·L-1), and N-limited rivers[mean DIN (NH4++ NO3-)=1.04 mg·L-1]. Overall, the concentration of N2O ranges from 17.03 to 9028.60 nmol·L-1, with a mean value of 546.75 nmol·L-1 (mean saturation=6256%). The emission fluxes across the water-air interface range from 17.21 to 15655.3 μg·(m2·h)-1, with a mean value of 949.36 μg·(m2·h)-1, indicating that those rivers are net sources of atmospheric N2O. The concentration and flux of N2O observed in NH4+-polluted rivers are significantly higher than that in the NO3--polluted and N-limited rivers. According to the method proposed by the IPCC, EF5r varies greatly among the three types of rivers and the coefficient of variation of EF5r is 445%. The EF5r for NO3--polluted rivers is on average 0.0005, which is lower than the recommended value of 0.0025. However, the EF5r for NH4+-polluted rivers is on average 0.4456, which is 180 times the recommended value and may be caused by the lower NO3- concentration of those rivers. The EF5r of N-limited rivers averages 0.0050 and is two times the recommended value. Thus, it is necessary to assess the pollution status of N before calculating the EF5r for the riverine system. We suggest that the EF5r for NH4+-polluted and N-limited rivers should be calculated using[N2O]/[NH4+] and[N2O]/[DIN], respectively, without assessing the composition and concentration of N.

Inorganic nitrogen dynamics of throughfall following fertilization in a red pine stand

ABSTRACTInorganic nitrogen fluxes caused by rainfall and throughfall following fertilizer applications were measured in a red pine stand located in the Wola National Experimental Forest in Jinju, Korea. Fertilizer (N3P4K1 = 113:150:37 kg ha−1 yr−1) was applied for 2 years, and inorganic nitrogen fluxes were monitored from April 2011 to March 2013. Monthly variations in inorganic nitrogen concentrations were generally higher in the throughfall than in the rainfall, whereas monthly variations in concentrations were similar between the fertilized and control treatments. The mean NH4+ and NO3− concentrations during the study period were 0.39 and 0.21 mg L−1 for the rainfall, 1.06 and 1.06 mg L−1 for the control, and 1.01 and 0.89 mg L−1 for the fertilizer treatments, respectively. Inorganic nitrogen fluxes were generally higher during the growing season (May–October) than during the dormant season (November–April). Inorganic nitrogen fluxes were higher in the throughfall (17.03 kg ha−1 yr−1 in the control treatments and 14.93 kg ha−1 yr−1 in the fertilizer treatments) than in the rainfall (10.66 kg ha−1 yr−1). This result indicates that inorganic nitrogen concentrations and fluxes of throughfall are affected by the amount of throughfall rather than by fertilizer application in a red pine stand.

Quantification of nitrogen dry and wet deposition in Fujian tobacco planting area

In this study, the wet/bulk and dry atmospheric deposition of different inorganic nitrogen (N) species was investigated in the Fujian tobacco planting area from 2010 to 2014. Wet/bulk N deposition flux of inorganic N was monitored at five sites (Fuzhou, Shanghang, Changting, Taining, and Wuyishan) of Fujian by using precipitation gauges. While dry deposition fluxes of gaseous NH3, NO2, and HNO3 (gNH3, gNO2, and gHNO3), and particulate NH4+ and NO3− (pNH4+ and pNO3−) were estimated only at the Fuzhou site through multiplying monthly mean Nr concentrations obtained from DELTA (DEnuder for Long-Term Atmospheric sampling) system (gNH3, gHNO3, pNH4+, pNO3−) and passive samplers (gNO2) and the modeled monthly mean dry deposition velocities provided by the GEOS-Chem global chemical transport model. Annual mean NH4+-N, NO3−-N, and total inorganic N (TIN) concentrations in precipitation (rainwater and snow) were 0.21–1.05, 0.33–0.74, and 0.59–1.68mgNL−1, respectively, and the averages over the monitoring period were 0.55, 0.49, and 1.04mgNL−1, respectively. Across the five monitoring sites, the average annual wet/bulk N deposition was 17.6kgNha−1a−1, while that of NH4+-N and NO3−-N amounted to 9.2 and 8.4kgNha−1a−1, respectively. Wet/bulk deposition was lowest at Changting, but no significant differences were found between the other four sites. Annual mean atmospheric concentrations of gNH3, gNO2, gHNO3, pNH4+, and pNO3− were 1.87, 2.95, 0.45, 2.36, and 1.23μgNm−3, respectively. Gaseous NH3 concentrations were highest in summer and lowest in winter. In contrast, seasonal fluctuations in other measured Nr species (e.g., gNO2) were not as large as those of gNH3.The annual mean total dry deposition was estimated to be 9.6kgNha−1a−1, and those of the individual species, gNH3, gNO2, gHNO3, pNH4+, and pNO3− were estimated to be 4.1, 2.2, 2.0, 0.8, and 0.4kgNha−1a−1, respectively. Based on the similarities in wet deposition, if we assume a similar level of dry deposition at all the sites, the total (dry and wet) N deposition was 27.2kgNha−1a−1 on average, which twice the critical load (10–15kgNha−1a−1) for forest ecosystems, suggesting a risk of “N saturation” in the local natural environment.

Nitrogen removal by three types of bioretention columns under wetting and drying regimes

The behaviors of inorganic nitrogen species in three types of bioretention columns under an intermittently wetting regime were investigated. The mean NH4+—N, NO3−—N and total N (TN) removal efficiencies for the conventional bioretention column (Col. T1) are 71%, 1% and 41%, for layered bioretention column with less permeable soil layer (Col. T2) the efficiencies are 83%, 84% and 82%, and for the bioretention column with submerged zone (Col. T3) the values are 63%, 31% and 53%, respectively. The best nitrogen removal is obtained using Col. T2 with relatively low infiltration rate. Adsorption during runoff dosing and nitrification during the drying period are the primary NH4+—N removal pathways. Less permeable soil and the elevated outlet promote the formation of anoxic conditions. 30%–70% of NO3−—N applied to columns in a single repetition is denitrified during the draining period, suggesting that the draining period is an important timeframe for the removal of NO3−—N. Infiltration rate controls the contact time with media during the draining periods, greatly influencing the NO3−—N removal effects. Bioretention systems with infiltration rate ranging from 3 to 7 cm/h have a great potential to remove NO3−—N.

454 pyrosequencing-based characterization of the bacterial consortia in a well established nitrifying reactor.

This present study aimed to characterize the bacterial community in a well-established nitrifying reactor by high-throughput sequencing of 16S rRNA amplicons. The laboratory-scale continuous stirred tank reactor has been supplied with ammonium (NH(4)(+)) as sole energy source for over 5 years, while no organic carbon has been added, assembling thus a unique planktonic community with a mean NH(4)(+) removal rate of 86 ± 1.4 mg NH(4)(+)-N/(L d). Results showed a nitrifying community composed of bacteria belonging to Nitrosomonas (relative abundance 11.0%) as the sole ammonia oxidizers (AOB) and Nitrobacter (9.3%) as the sole nitrite oxidizers (NOB). The Alphaproteobacteria (42.3% including Nitrobacter) were the most abundant class within the Proteobacteria (62.8%) followed by the Gammaproteobacteria (9.4%). However, the Betaproteobacteria (excluding AOB) contributed only 0.08%, confirming that Alpha- and Gammaproteobacteria thrived in low-organic-load environments while heterotrophic Betaproteobacteria are not well adapted to these conditions. Bacteroidetes, known to metabolize extracellular polymeric substances produced by nitrifying bacteria and secondary metabolites of the decayed biomass, was the second most abundant phylum (30.8%). It was found that Nitrosomonas and Nitrobacter sustained a broad population of heterotrophs in the reactor dominated by Alpha- and Gammaproteobacteria and Bacteroidetes, in a 1:4 ratio of total nitrifiers to all heterotrophs.

Modelling the future distribution of ammonium nitrate concentrations in The Netherlands for 2020: The sensitivity to meteorological parameters

We present a parameterization developed to simulate Ammonium particle (NH4+) concentrations in the Operational Priority Substances (OPS) source-receptor model, without the necessity of using a detailed chemical scheme. By using the ratios of the main pre-cursor gases SO2, NO2 and NH3, and utilising calculations performed using a chemical box-model, we show that the parameterization can simulate annual mean NH4+ concentration fields to within ∼15% of measured values at locations throughout the Netherlands. Performing simulations for different decades, we find a strong correlation of simulated NH4+ distributions for both past (1993–1995) and present (2009–2012) time periods. Although the total concentration of NH4+ has decreased over the period, we find that the fraction of NH4+ transported into the Netherlands has increased from around 40% in the past to 50% for present-day. This is due to the variable efficiency of mitigation practises across economic sectors. Performing simulations for the year 2020 using associated emission estimates, we show that there are generally decreases of ∼8–25% compared to present day concentrations. By altering the meteorological fields applied in the future simulations, we show that a significant uncertainty of between ∼50 and 100% exists on this estimated NH4+ distribution as a result of variability in the temperature dependent emission terms and relative humidity. Therefore, any projections of future NH4+ distributions should be performed using well chosen meteorological fields representing recent meteorological situations.

Inorganic nitrogen deposition in China's forests: Status and characteristics

Nitrogen (N) deposition in China has been dramatically enhanced by anthropogenic emissions and has aroused great concerns of its impacts on forest ecosystems. This study synthesized data on ammonium (NH4+) and nitrate (NO3−) contents in bulk precipitation and throughfall from 38 forest stands in published literature to assess the status and characteristics of N deposition to typical forests in China between 1995 and 2010. Our results showed that ammonium dominated N deposition in this period, with a mean NH4+–N:NO3−–N ratio of ∼2.5 in bulk deposition and throughfall. Mean throughfall N deposition in China's forests was as high as 14.0 kg N ha−1 yr−1 for ammonium, 5.5 kg N ha−1 yr−1 for nitrate and 21.5 kg N ha−1 yr−1 for total inorganic N (TIN), respectively. Mean bulk deposition was 9.4 kg N ha−1 yr−1 for ammonium, 3.9 kg N ha−1 yr−1 for nitrate and 14.0 kg N ha−1 yr−1 for TIN, respectively. Canopy captured dry deposition, calculated as the difference between throughfall and bulk deposition, was thus approximately half of the bulk deposition. Spatial patterns of N deposition were in accordance with our urban hotspot hypothesis, showing a strong power-law reduction of ammonium with increasing distance to large cities but only slightly lower nitrate deposition. Our results suggest that high N deposition, especially of ammonium, exceeds critical N loads for large areas of China's forests.

A novel approach using the 15N tracer technique and benthic chambers to determine ammonium fluxes at the sediment–water interface and its application in a back-reef zone on Reunion Island (Indian Ocean)

The 15N tracer method and the benthic chamber technique were combined to evaluate NH4+ exchanges at the sediment–water interface. This novel approach consists in measuring NH4+ fluxes during a single in situ incubation in a sample of water enclosed in a benthic chamber placed over the sediment and in a subsample thereof concomitantly incubated in a bottle. Using this combined approach, the influx and efflux of NH4+ across the sediment–water interface can be simultaneously measured along with uptake and regeneration rates of NH4+ in the water column. Details of the experimental protocol and principles behind the calculations of N transport rates are given. We applied this approach to a tropical reef on Reunion Island (Indian Ocean). Experiments were carried out in triplicate at three stations with organic-poor, sandy sediments. At the three stations, the mean flux of NH4+ from the water column to the sediment (29.6–59.2μmolm−2h−1) was much higher than the mean NH4+ uptake rate by phytoplankton (3.0–4.0μmolm−2h−1) indicating that the removal of NH4+ from the water column must be due, for the most part, to uptake by benthic microalgae in the study area. The mean flux of NH4+ from the sediment to the water column (6.7–13.7μmolm−2h−1) was comparable to the mean regeneration rate in the water (7.4–9.9μmolm−2h−1) suggesting that the sediment may constitute a significant N source for phytoplankton in the back-reef zone on Reunion Island.

Increased methane uptake but unchanged nitrous oxide flux in montane grasslands under simulated climate change conditions

SummaryMontane grasslands of Central Europe are expected to be exposed to strong warming and to altered precipitation patterns, suggesting that biosphere–atmosphere–hydrosphere exchange of carbon (C) and nitrogen (N) compounds may be vulnerable to future climatic conditions. By transferring small lysimeters along an altitudinal gradient, we assessed the impact of climate change conditions on soil–atmosphere exchange of methane (CH4) and nitrous oxide (N2O) as well as on ammonium (NH4+) and nitrate (NO3−) in soil water in extensively managed montane grassland in southern Germany. Lysimeter transfer to lower altitude increased air and soil temperatures by more than 2°C and reduced summer precipitation as well as soil moisture throughout the year compared with a control transfer within the high altitude site. This simulation of climate change conditions almost doubled the CH4 sink strength from −0.11 to −0.19 g C m−2 year−1, which appeared to be mainly related to improved gas diffusion after reduced soil moisture. Mean NH4+ and NO3− concentrations in soil water (0.05 mg NH4+–N l−1 and 0.08 mg NO3−–N l−1) and N2O emissions (approximately 0.03 g N m−2 year−1) remained small and unaffected by climate change simulation. Our study suggests that expected climate change conditions will have positive effects on the non‐CO2 greenhouse gas balance in extensively managed montane grassland because of increased net CH4 uptake in soil. For N2O emission, we conclude that potential effects of management changes may override the small effects of simulated climate change on N2O emissions observed in this study.

Nitrogen Fate and Transport in a Conventional Onsite Wastewater Treatment System Installed in a Clay Soil: Experimental Results

Relationships between N transport and hydraulic function of onsite wastewater treatment systems (OWTSs) in clay‐textured soils are largely unknown. The objectives of this study were to quantify N concentrations in a clay soil and estimate denitrification in the vadose zone beneath a conventional OWTS. An OWTS installed in the Piedmont region of Georgia was dosed with residential strength wastewater three times per day for 2 yr. Soil near trench bottoms cycled between saturated and unsaturated conditions under the dosing schedule we used. Mean NH4–N concentrations decreased to <1 mg L−1 within 90 cm of trench bottoms due to adsorption, immobilization, and nitrification. Mean NO3–N concentrations increased as the drainfield matured and ranged from 10 to 25 mg L−1 near the end of the two year study period. Mean pressure heads and Cl− concentrations measured at 3.3 m and 6.6 m from trench inlets indicated that significantly more water infiltrated the drainfield at the 3.3 m position. Wet conditions at the 3.3 m position may have restricted nitrification, while dry conditions at the 6.6 m caused rapid nitrification. Nitrogen:chloride ratios suggested that 61% of N entering the drainfield was lost, potentially as volatile N‐species. The 30‐cm zone directly beneath the trenches had high biomass N and C contents (15 mg kg−1 N and 60 mg kg−1 C) and was presumably the most biologically active zone. The fate and transport of N was dynamic in this system due to variable moisture conditions near the trench‐soil interface which may have intermittently stimulated denitrification.

Nitrogen removal and microbial community profiles in six wetland columns receiving high ammonia load

This study aimed to investigate nitrogen mass removal rates and microorganisms in planted columns that simulate vertical flow constructed wetlands. Two synthetic wastewaters, with mean NH4–N concentrations of 471±19 and 475±17mg/L, were treated in six individual columns. Under steady hydraulic and pollutant loading, average NH4–N removal rate was in the range of 21–47g/m2d, and average TN removal was 0–27g/m2d. Higher redox potential values benefitted ammonia removal but limited TN removal. The supply of organic carbon, by adding glucose into the synthetic wastewater, slightly reduced ammonia removal rate, but significantly enhanced TN removal. The variation of temperature between 14°C and 20°C had no effect on nitrogen removal. The seeding of microorganisms using diluted activated sludge, and submerging the columns with treated effluent for three days per week, appeared to intensify aerobic microbial degradation activities; oxygen consumption reached 53–363g O2/m2d, which was equivalent to upward air flux of 0.18–1.21m3/m2d in individual columns. Fluorescence in situ hybridization analysis of bacterial mass revealed the population densities of nitrifying bacteria, and specific denitrifying bacteria (Azoarcus-Thauera-cluster, genus Hyphomicrobium, genus Paracoccus, and family Saprospiraceae). Denitrifier Azoarcus-Thauera-cluster was the dominant bacterial group (58% of all cells) when organic carbon is available. Without organic carbon, ammonium oxidizing bacteria (AOB) dominate microbial populations in the columns.

Geologic nitrogen and climate change in the geochemical budget of Kärkevagge, Swedish Lapland

While nitrogen is an essential nutrient for plant growth in the terrestrial environment and generally fixed by biological processes in soils, in Arctic and alpine environments N is a severely limited nutrient because of both climatic and soil constraints. It is widely believed that geologic nitrogen is such a small component of the nitrogen cycle that this source is generally not viewed as being a significant component. However, it has been estimated that in fact as much as 20% of the total nitrogen budget may be stored in geological materials and where N is severely limited such as in Arctic and alpine environments geologic N may in fact be a dominant source of N for biological processes. Nitrogen saturation may therefore have substantial impacts on geochemical cycles involving both soil and water chemistry.In order to determine the potential for the rocks and soils of Kärkevagge to be significant sources of N samples of the principal rock units of the valley along with soil developed on a variety of rock types were sampled. Ammonia/ammonium contents were determined using ion chromatography. Ammonia/ammonium contents of the sampled rock materials display a wide range of abundances with marble containing a mean NH4 abundance of 4300mgNkg, quartz schist 1600mgNkg, biotite schist 4300mgNkg, and garnet mica schist 4500mgNkg. Soil ammonia/ammonium abundances were found to be 1600mgNkg. N-pool abundances range from 2.5kgm3 for marble to 8.7 for garnet mica schist. Soil N-pools were found to be 3.0kgm3.The inorganic N present as ammonia/ammonium measured in bedrock represents substantial N-input into the geochemical budget. The N in bedrock originates from organically bound nitrogen associated with sediment or geothermal waters representing a mixture of sedimentary, mantle and meteoric sources. Nitrogen in the soil originates from the weathering of N-rich rocks, the presence of unweathered nitrate minerals or fluid inclusions released to the soil and ultimately to plants by assimilation by biota or nitrification. Geologic nitrogen in Kärkevagge rocks and soils may represent a large and reactive pool with the potential for considerable impact on the geochemical system.To investigate the potential responses of nitrogen release, as well as other nutrients to increasing CO2 concentration scenarios, flow-through leaching experiments were conducted on crushed rock samples and soils from the study area. Leaching experiments revealed two to three fold increases in both N and K release with a tripling of carbon dioxide concentrations. Ammonium shows more rapid release than potassium which suggests substantial changes in nitrogen cycling with increasing CO2 enrichment of the atmosphere.

A Comparative Study on the Growth and Nutrient Uptake Characteristics of Fifteen Wetland Species in Taihu Lake Region of China

Fifteen kinds of local wetland plants in Taihu Lake region of China were investigated on their respective growth conditions, biomass allocations and nutrient uptake capacities. The test plants were cultured in 3 L nutrient solutions for 28 days with NH4 +-N, NO3 --N and P concentrations of 38.5, 132.8 and 10 mg/L, respectively. Mean species total biomass ranged from 1.2-21.6 g/plant with above/below ground ratios (AG:BG) between 1.7-5.5. Mean NH4 +-N, NO3 --N and P uptake rates ranged from 3.7-14.3 mg/day (8.0-49.4 % of NH4 +-N supplied), 17.8-59.4 mg/day (17.8-59.6 %) of NO3 --N supplied and 1.71-4.61 mg /day (24.1-61.5 % of P supplied), respectively. Plant tissue N and P concentrations ranged between 28.2-606.1 mg N /plant and 4.1-53.1 mg P/plant, with AG:BG ratio between 1.7-7.0 and 1.6-4.6, respectively. The accumulation of N and P in plant tissues was significantly correlated with plant biomass and root surface area. Among the different species, C. generalis, T. latifolia, T. dealbata and L. salicaria were better than the other plants in above- and below-ground biomass, root surface area, nutrient uptake and storage rates. T. dealbata and L. salicaria were more suitable for year-round application in this area due to their tolerance of coldness.

Community Oxygen and Nutrient Fluxes in Seagrass Beds of Florida Bay, USA

We used clear, acrylic chambers to measure in situ community oxygen and nutrient fluxes under day and night conditions in seagrass beds at five sites across Florida Bay five times between September 1997 and March 1999. Underlying sediments are biogenic carbonate with porosities of 0.7–0.9 and with low organic content (<1.6%). The seagrass communities always removed oxygen from the water column during the night and produced oxygen during daylight, and sampling date and site significantly affected both night and daytime oxygen fluxes. Net daily average fluxes of oxygen (−4.9 to 49 mmol m−2 day−1) ranged from net autotrophy to heterotrophy across the bay and during the 18-month sampling period. However, the Rabbit Key Basin site, located in the west-central bay and covered with a dense Thalassia testudinum bed, was always autotrophic with net average oxygen production ranging from 4.8 to 49 mmol m−2 day−1. In November 1998, three of the five sites were strongly heterotrophic and oxygen production was least at Rabbit, suggesting the possibility of hypoxic conditions in fall. Average ammonium (NH4) concentrations in the water column varied widely across the bay, ranging from a mean of 6.9 μmol l−1 at Calusa in the eastern bay to a mean of 0.6 μmol l−1 at Rabbit Key for the period of study. However, average NH4 fluxes by site and date (−240 to 110 μmol m−2 h−1) were not correlated with water column concentrations and did not vary in a consistent diel, seasonal, or spatial pattern. Concentrations of dissolved organic nitrogen (DON) in the water column, averaged by site (15–25 μmol l−1), were greater than mean NH4 concentrations, and the range of day and night DON fluxes (−920 to 1,300 μmol m−2 h−1), averaged by site and date, was greater than the range of mean NH4 fluxes. Average DON fluxes did not vary consistently from day to night, seasonally or spatially. Mean silicate fluxes ranged from −590 to 860 μmol m−2 h−1 across all sites and dates, but mean net daily fluxes were less variable and most of the time contributed small amounts of silicate to the water column. Mean concentrations of filterable reactive phosphorus (FRP) in the water column across the bay were very low (0.021–0.075 μmol l−1); but site average concentrations of dissolved organic phosphorus (DOP) were higher (0.04–0.15 μmol l−1) and showed a gradient of increasing concentration from east to west in the bay. A pronounced gradient in average surficial sediment total phosphorus (1.1–12 μmol g DW−1) along an east-to-west gradient was not reflected in fluxes of phosphorus. FRP fluxes, averaged by site and date, were low (−5.2 to 52 μmol m−2 h−1), highly variable, and did not vary consistently from day to night or across season or location. Mean DOP fluxes varied over a smaller range (−8.7 to 7.4 μmol m−2 h−1), but also showed no consistent spatial or temporal patterns. These small DOP fluxes were in sharp contrast to the predominately organic phosphorus pool in surficial sediments (site means = 0.66–7.4 μmol g DW−1). Significant correlations of nutrient fluxes with parameters related to seagrass abundance suggest that the seagrass community may play a major role in nutrient recycling. Integrated means of net daily fluxes over the area of Florida Bay, though highly variable, suggest that seagrass communities might be a source of DOP and NH4 to Florida Bay and might remove small amounts of FRP and potentially large amounts of DON from the waters of the bay.