Anthropogenic disturbance of the global nitrogen (N) cycle has more than doubled the amount of reactive N circulating in the terrestrial biosphere alone. Exchange of reactive/non-reactive nitrogen gases between land and atmosphere are strongly affecting Earth’s atmospheric composition, air quality, global warming, climate change and human health. This session seeks to improve our understanding of a) how intensification of reactive N use, land management and climate change affects the pools and fluxes of nitrogen in terrestrial and aquatic ecosystems, b) and how reactive N enrichment of land and water will affect the future carbon sink of natural ecosystems as well as atmospheric exchanges of reactive (NO, N2O, NH3, HONO, NO2 and non-reactive N (N2) gases with implications for global warming, climate change and air quality. We welcome contributions covering a wide range of experimental and modelling studies, which covers microbes-mediated and physico-chemical transformations and transport of nitrogen across the land-water-air continuum in natural ecosystems from local to regional and global scales. Furthermore, the interactions of nitrogen with other elemental cycles (e.g. phosphorus, carbon) and the impacts of these interactive feedbacks for soil health, biodiversity and water and air quality will be explored in this session. Latest developments in methodological innovations and observational and experimental approaches for unraveling the complexities of nitrogen transformations and transport will also be of interest.
vPICO presentations: Mon, 26 Apr
Within in the United States some 54 km3 of water is withdrawn annually for public supply. Around 16% of this water is subsequently lost through leakage as it moves through distribution networks. These processes not only have implications both economically and for water security, but the substantial redistribution of water has also been shown to cause significant perturbations in elemental cycling. Due to its importance for ecological health and global food production, this research attempts to quantify the nitrogen (N) fluxes associated with a range of Public Water Supply processes, such as abstraction and leakage. Using county level data sets, these N fluxes will be determined across the contiguous United States, and the significance of results evaluated through comparisons with other quantified N fluxes. Assessments will also be made on how the absolute and relative significance of these fluxes may change in the future, such as due to evolving water demands as a result of the combined drivers of changing climate and increasing population. Outputs from the US will form part of a wider global assessment, including comparisons with less developed countries.
How to cite: Flint, E. M., Ascott, M. J., Gooddy, D. C., Surridge, B. W. J., and Stahl, M. O.: Understanding current and future impacts of public water supply on global nitrogen cycling, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15033, https://doi.org/10.5194/egusphere-egu21-15033, 2021.
In order to assess peatland carbon sink potential under multiple global change perturbations, we examined the individual and combined effects of long-term warming and enhanced nitrogen (N) and sulfur (S) deposition on ecosystem CO2 exchange at one of the longest-running experiments on peatlands, Degerö Stormyr poor fen, Sweden. The site has been treated with NH4NO3 (15 times ambient annual wet deposition), Na2SO4 (6 times ambient annual wet deposition) and elevated temperature (air +3.6 C) for 23 years. Gross photosynthesis, ecosystem respiration and net CO2 exchange were measured weekly during June-August using chambers. After 23 years, two of the experimental perturbations: N addition and warming individually reduced net CO2 uptake potential down to 0.3-0.4 fold compared to the control mainly due to lower gross photosynthesis. Under S only treatment ecosystem CO2 fluxes were largely unaltered. In contrast, the combination of S and N deposition and warming led to a more pronounced effect and close to zero net CO2 uptake potential or net C source. Our study emphasizes the value of the long-term multifactor experiments in examining the ecosystem responses: simultaneous perturbations can have nonadditive interactions that cannot be predicted based on individual responses and thus, must be studied in combination when evaluating feedback mechanisms to ecosystem C sink potential under global change.
How to cite: Larmola, T., Maanavilja, L., Kiheri, H., Nilsson, M., and Peichl, M.: Impacts of long-term warming and enhanced nitrogen and sulfur deposition on carbon sink potential in a boreal peatland, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1210, https://doi.org/10.5194/egusphere-egu21-1210, 2021.
Dissimilatory nitrate (NO3−) reduction to ammonium (DNRA) and denitrification (DNF) are major dissimilatory NO3− reduction processes, competing for the available NO3− under anoxic conditions. The competition among these processes leads to different fates of NO3− in soil, i.e., loss of nitrogen (N) as benign N2 or potent greenhouse gas (nitrous oxide, N2O), or retaining of N by converting NO3− to ammonium. Unfortunately, little is known about the soil-environmental factors controlling the NO3− partition. Here we report DNF and DNRA in soils from the top and bottom of the hillslope.
We sampled soils from a hillslope of forest to generate a soil-environmental gradient. The soil-environmental factors including soil pH, available carbon (potassium chloride-extractable organic carbon: EOC), NO3−, and microbial C and N (MBC and MBN) were determined. We incubated the soils under anoxic condition (i.e., helium atmosphere) and applied a 15N isotope pairing technique to quantify the potential rates of DNRA and DNF. Briefly, we incubated the soil under anoxic condition (i.e., helium atmosphere) to remove any N oxides and oxygen, then we added 15NO3− (99.9%) and measured the production rates of 15NH4+, 30N2, and 46N2O.
The results showed that (1) a good gradient of the soil-environmental variables was observed along the hillslope from top to bottom, including pH (top–bottom; 3.95–4.78), EOC:NO3− (184–18.7), and MBC: MBN (8.2–6.3); (2) DNRA rate tended to be higher at the top of the hillslope with DNF being nearly inactive, resulting in a dominance of DNRA (59–97%), while the trend was reversed at the bottom, with DNF rates being much higher and dominantly contributing to NO3− reduction (89–97%); and (3) during DNF process, the magnitude of N2O production rates was comparable or even higher than that of N2 in the soils from the bottom of the hillslope. The ratio of the N2O to N2 production (N2O:N2) was much higher in the soils from the top despite the low DNF rates.
The remarkably different patterns of DNRA and DNF rates and relative contributions between the top and bottom of the hillslope are controlled by the EOC:NO3−: DNRA was preferred over DNF when NO3− was limited (i.e., high EOC:NO3−) because more free energy is liberated per unit of NO3− reduced for DNRA as compared to DNF. The substantial production of N2O at the bottom of the hillslope indicates that previous studies that considered only 30N2 production rate could have highly underestimated the DNF rate. The high N2O:N2 at the top is likely caused by the low pH as well as the dominance of fungi, of which the N2O reductase is generally lacking, pointing to the key roles of soil pH and microbial community structure in regulating the product stoichiometry of N2O and N2 in DNF.
How to cite: Du, J., Zheng, J., Shibata, M., Wang, Z., Watanabe, T., and Funakawa, S.: Dissimilatory nitrate reduction processes along a forest hillslope, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10536, https://doi.org/10.5194/egusphere-egu21-10536, 2021.
Anthropogenic activities, and in particular the use of synthetic nitrogen (N) fertilizer, have a significant influence on soil nitrous oxide (N2O) emission from oil palm plantation on tropical peatland. Finding a suitable N rate for optimum N uptake efficiency and yield with low environmental impact and production cost is crucial for the economic growth of Malaysia’s oil palm sector. However, studies on the impact of N fertilizers on N2O emissions from tropical peatland are limited. Thus, long-term monitoring was conducted to investigate the effects of N fertilization on soil N2O emissions. This study was conducted in an oil palm (Elaeis guineensis Jacq.) plantation located in a tropical peatland in Sarawak, Malaysia. Monthly soil N2O fluxes were measured using the closed-chamber method in a control (T1, without N fertilization), and under three different N treatments: low N (T2, 31.1 kg N ha−1), moderate N (recommended rate) (T3, 62.2 kg N ha−1), and high N (T4, 124.3 kg N ha−1), from January 2010 to December 2013 and from January 2016 to December 2017. The only N fertiliser rate to significantly increase (p<0.05) annual cumulative N2O emissions was 124.3 kg N ha-1 (T4). Increased in water-filled pore space (WFPS) (>70%) with a decrease in both N2O flux and nitrate (NO3−) implies that complete denitrification has taken place. Increased in NO3- uptake by oil palm with an increase in WFPS decreased NO3- concentration in soil, resulting in the reduction of N2O emission. This study highlights the importance of WFPS on denitrification and N uptake by oil palm in tropical peatland. This needs to be taken into account for the accurate assessment of N dynamics in oil palm plantations on tropical peatland in order to enhance N fertilization management strategies and counteract anthropogenic activities that produce greenhouse gases.
Keywords: WFPS, oil palm yield, NO3-, N uptake
How to cite: Chaddy, A., Melling, L., Ishikura, K., and Hatano, R.: N fertilization effects on N2O fluxes from oil palm plantation on tropical peatland, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10546, https://doi.org/10.5194/egusphere-egu21-10546, 2021.
The world’s acute reactive nitrogen (Nr) deposition is chronically eroding the biospheric integrity and undermining earth system’s resilience to be in an accommodatable state. The present study comprehensively attempts to decipher the dry depositions of atmospheric inorganic Nr along with other major ions through dustfall fluxes. Authentic atmospheric dust samples were collected by incorporating a surrogate-surface approach at an agriculturally intensive rural site in Indo-Gangetic plain of India over a year-long temporal scale from October 2017-September 2018. The mean (±Standard Error) dry deposition fluxes of NH4+-N and NO3--N during the whole study period were observed as 0.41±0.09 kg ha-1 yr-1 and 6.51±1.58 kg ha-1 yr-1, respectively. The total percent ionic contribution to the dustfall flux was observed 2.95% and the descending order of their percent contribution in total ionic fluxes were observed as SO42- (31.46%) > Cl- (15.74%) > K+ (15.04%) > Ca2+ (13.97%) > Na+ (10.23 %) > NO3- (7.06%) > Mg2+ (4.43%) > F-(1.62%) > NH4+ (0.44%). The relative dominance of NO3--N over NH4+-N fluxes was maintained in all seasons during the whole monitoring period which could be attributed to the competitive exclusion of NH4+-N from acid-base neutralization reactions by other strong base cations in dustfall. Size-distribution and morphological analysis of dust particles from Scanning Electron Microscope images signified the anthropogenic involvement in shaping the dominant mode of particle-size distribution in dust fall fluxes which culminated into the dominance of fine-mode fraction over course-mode in dustfall.
How to cite: Naseem, M. and Kulshrestha, U.: Dry deposition fluxes of NH4+-N and NO3--N at a rural site of Indo-Gangetic Plain, India., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7776, https://doi.org/10.5194/egusphere-egu21-7776, 2021.
Laboratory studies indicated that soil could produce considerable nitrous acid (HONO) emissions, which is the main primary source of hydroxyl radical (OH) in the troposphere. However, very few field observations of HONO emission from soil were reported. In order to relate laboratory results and field measurements, we measured HONO emissions from 7 representative agricultural soils (rice, vegetables, orchards, peanuts, potatoes, sugarcane and maize) in Guangdong under controlled laboratory conditions, and took flux measurements on 2 of them (rice and vegetables) by dynamic chambers in the field. Generally, release rates of HONO from the seven soils increased with temperature and varied with soil moisture, and the optimum release rates can be reached under specific values of water-filled pore space (WFPS), which is considered to be beneficial to nitrification. The seven soils' optimum release rates ranged from 1.24 to 43.19 ng kg-1 s-1, and the Q10 (It is defined as the multiple of the increase of soil gas emission rate when the temperature increases by 10℃) ranged from 1.03 to 2.25. Formulas were deduced from the lab results to express HONO emissions for every soil. Flux measurements on two soils varied around -1 to 4 ng N m-2 s-1, and both showed similar diurnal variations with peaks around noontime and very low even negative values during nighttime. There were good correlations between HONO fluxes and soil temperature (R2=0.5). Furthermore, irrigation enhanced the HONO emission substantially. However, a large discrepancy existed between soil HONO emissions measured in lab and low HONO fluxes in field. More investigations are needed to explain the paradox.
How to cite: Han, B., Cheng, P., Yu, Y., Yang, W., Tian, Z., Li, H., Gong, Y., Chen, B., and Tian, Y.: Laboratory and field measurements of HONO emissions from agricultural soils in Guangdong of China , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14992, https://doi.org/10.5194/egusphere-egu21-14992, 2021.
Nitrous acid (HONO) can produce hydroxyl radicals (OH) by photolysis and plays an important role in atmospheric photochemistry. Over the years, high concentrations of HONO have been found in the Pearl River Delta region (PRD), which may be one of the reasons for the high atmospheric oxidation capacity. A comprehensive atmospheric observation was conducted at an urban site in Guangzhou from 27 September to 9 November 2018. During the period, HONO ranged from 0.02 to 4.43 ppbv with an average of 0.74±0.70 ppbv. The combustion emission ratio (HONO/NOx) of 0.9±0.4% was derived from 11 fresh plumes. The primary emission rate of HONO during night was calculated with the emission source inventory data to be between 0.04±0.02 and 0.30±0.15 ppbv/h. And the HONO produced by the homogeneous reaction of OH+NO at night was 0.26±0.08 ppbv/h, which can be seemed as secondary results from primary emission. They were both much higher than the increase rate of HONO (0.02 ppbv/h) during night. Soil emission rate of HONO at night was calculated to be 0.019±0.0003 ppbv/h. Deposition was the dominant removal process of HONO during night, and a deposition rate of at least 2.5 cm/s is required to balance the direct emissions and OH+NO reaction. Correlation analysis shows that NH3 and relative humidity (RH) may participate in the heterogeneous transformation from NO2 to HONO during night. In the daytime, the average primary emission Pemis was 0.12±0.01 ppbv/h, and the homogeneous reaction POH+NO was 0.79±0.61 ppbv/h, which was even larger than the unknown sources PUnknown (0.65±0.46 ppbv/h). The results showed that the direct and indirect contributions of primary emission to HONO are great at the site, both during daytime and nighttime. Similar to previous studies, PUnknown was suggested to be related to the photo-enhanced reaction of NO2. The mean OH production rates by photolysis of HONO and O3 were 3.7×106 cm-3·s-1 and 4.9×106 cm-3·s-1, respectively. We further studied the impact of HONO on the atmospheric oxidation by a Master Chemical Mechanism (MCM) box model. When constraining observed HONO in the model, OH and O3 increased 59% and 68.8% respectively, showing a remarkable contribution of HONO to the atmospheric oxidation of Guangzhou.
How to cite: Yu, Y., Cheng, P., Li, H., Yang, W., Han, B., Yu, X., Zhang, M., Song, W., Huang, Z., and Yuan, B.: Budget of nitrous acid (HONO) and its impacts on atmospheric oxidation capacity at an urban site in Guangzhou of China, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6907, https://doi.org/10.5194/egusphere-egu21-6907, 2021.
Some studies show that photolysis of nitrate and deposited nitrate and gas nitric acid (HNO3) on the ground surface is much faster than that of HNO3. The former mechanism has been considered as a possible daytime HONO source and discussed in many laboratory and field studies. Although this mechanism is also coupled into some three-dimensional chemical transport models, the effect of large changes in the ratio of photolysis rate of nitrate to that of HNO3 (RAT) on HONO concentrations has not been assessed and will be discussed here by using the updated WRF-Chem model. Simulations indicate that in the morning, this mechanism only resulted in a HONO increase of a few ppt, while the heterogeneous reaction of NO2 enhanced HONO by about 150 ppt; in the afternoon, however, this mechanism led to a significant HONO increase, with its contribution to HONO concentrations being close to the contribution of the heterogeneous reaction of NO2. In some heavily nitrate-polluted areas, this mechanism contributed more than 80% of HONO concentrations during the afternoon. Large changes in RAT produced a substantial impact on HONO concentrations. When RAT was altered from 15 to 100, increase of HONO concentrations was enhanced by about 6 times. Our results suggest that more laboratory and field studies on the photolysis rates of nitrate and deposited nitrate and HNO3 on the ground surface are still needed.
How to cite: Guo, Y., An, J., and Zhang, J.: Assessment of the impact of large changes in the ratio of photolysis rate of nitrate to that of gas nitric acid on HONO concentrations simulated by a 3-D chemical transport model, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2471, https://doi.org/10.5194/egusphere-egu21-2471, 2021.
Plastic-shed vegetable production system is becoming the main type of vegetable production in China, while excessive irrigation and fertilization input lead to significant N loss by leaching, runoff, and gaseous N. The current study established a field experiment to investigate the effects of drip irrigation and optimized fertilization on vegetable yield, water and fertilizer efficiencies and N2O emission in a typical intensive plastic-shed tomato production region of China. The treatments include CK (no fertilization, flood irrigation), FFP (farmers’ conventional fertilization, flood irrigation), OPT1 (80% of FFP fertilization, flood irrigation), OPT2 (80% of FFP fertilization, drip irrigation). N2O isotopocule deltas, including δ15Nbulk, δ18O and SP (the 15N site preference in N2O), have been used to investigate microbial pathways of N2O production under different treatments. Our results showed: i) optimized fertilization and drip irrigation significantly improved the fertilizer and water use efficiency without reducing tomato yield, ii) compared with flood irrigation, drip irrigation decreased soil WFPS and soil ammonium content, but increased soil nitrate content. When soil moisture was higher than 60%WFPS, drip irrigation led to a decrease of N2O emission with lower N2O SP signature observed than that of food irrigation, suggesting a reduction of denitrification derived N2O. In contrast, drip irrigation significantly increased N2O emission and N2O SP value when soil moisture status was lower than 55% WFPS, which may be due to the enhanced nitrification or fungal denitrification derived N2O.
How to cite: Xu, X., Wu, D., Zhang, W., Ni, B., Yang, X., and Meng, F.: Drip irrigation affects N2O emission differently depending on soil moisture status in an intensive vegetable production system, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15035, https://doi.org/10.5194/egusphere-egu21-15035, 2021.
Identification of nitrate sources and fate in basins with complex backgrounds is essential for understanding the controlling factors of regional groundwater nitrates pollution and its prevention. In this study, hydrochemistry, the concentration of dissolved nitrogenous species, multiple isotopes (δD-H2O, δ18O-H2O, δ15N-NH4+, δ15N-NO3- and δ18O-NO3-) and Bayesian model (SIMMR) were applied to identify the nitrate sources and major transformation processes under different land uses and complicated hydrological conditions in Qingyi River basin with an area of 8700km2, east China. A total of 28 groundwater samples of forest-dominated areas in mountainous, forest-farmland in piedmont, and farmland-residential in plain were collected in Jul 2019. The results showed that concentrations of N species, hydrochemistry and isotopic composition had significantly differences under distinctive backgrounds generally. In mountainous area, nitrate concentrations were as low as of 1.9-6.3mg/L, and low TDS (23.6-60.8mg/L), depleted δD-H2O(-43.3±6.7‰) and δ18O-H2O (-7.2±1.0‰) were observed with δ15N-NO3- values of +1.1±0.8‰, which implies that 18.4% and 81.6% of groundwater nitrate were from soil organic nitrogen (SON) and atmosphere precipitation (AP), respectively. In piedmont areas, moderate nitrate(1.0-35.6mg/L), TDS(91.6-253.9mg/L), and relative enriched δD-H2O(-40.1±4.1‰), δ18O-H2O(-6.7±0.5‰) were detected with δ15N-NO3- values +2.8±2.2‰, and the SIMMR model suggested 37.3% nitrates were derived from SON and 31.1% from chemical fertilizers (CF) .With increasing of residential areas, higher TDS(186.5-643.8mg/L) and nitrate(5.4-58.5mg/L) as well as enriched δD-H2O(-38.6±6.5‰) and δ18O-H2O(-6.4±0.7‰) indicated higher anthropogenic inputs in plain areas with δ15N-NO3- values +6.3±2.3‰, with the origins of 31.8% SON and 30.9% manure&sewage (M&S). From the recharge and runoff areas to the discharge areas, major nitrate sources altered from SON to CF and M&S due to variation of land uses, and the denitrification became the dominant process rather than nitrification owing to gradually decreasing oxidization condition. Incomplete nitrification was proved by negative correlations of δ15N-NH4+ and δ15N-NO3- in recharge and runoff areas. And the occurrence of obvious denitrification was deduced by low redox parameters and major ions in discharge zone. Finally, a conceptual model was proposed to reveal the pattern of groundwater nitrate sources and fate in Qingyi River Basin. This study provided a reliable and integrated approach for recognition and understanding of the nitrate sources and fate in large watershed under complicated land-uses and hydrological conditions.
Keywords: groundwater; nitrate, sources identification; δ15N-NH4+; Qingyi River basin
How to cite: Huang, X., Jin, M., and Zhang, Z.: Identification of groundwater nitrate sources and transformation processes under different land uses and complicated hydrological conditions in Qingyi River Basin, east China, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1901, https://doi.org/10.5194/egusphere-egu21-1901, 2021.
The spatiotemporal changes of nitrate in agricultural watersheds are of global concern. Although numerous studies have explained the source and transformation mechanism of nitrate in groundwater and surface water, the transformation mechanism in groundwater remains poorly understood because of different hydrogeological and climatic conditions. Based on a field investigation and sampling, this study revealed the sources and transformation mechanism of nitrogen in surface water and groundwater in a karst agricultural watershed by comprehensively using water chemistry data, isotope components, and a Bayesian model (simmr). The results indicated that:1)Local agricultural activities have controlled the changes of δ15N-NO3-, δ18O-NO3- and δ15N-NH4+ in groundwater. The difference is that the concentration of NO3- is significantly affected by rainfall. However, the contribution of rainfall to groundwater NO3- is relatively small (<9%), indicating that there is a dual influence mechanism of leaching in the watershed that controls the concentration of groundwater NO3-, while agricultural activities control its isotope changes;2)The study observed that after fertilization, due to the influence of ammonia volatilization and nitrification, δ15N-NO3-, δ18O-NO3- in groundwater showed a simultaneous decrease, while δ15N-NH4+ showed an increasing trend, which may be due to the result of incomplete nitration of NH4+ in the vadose zone;3)According to the calculation results of the simmr model, in the two main fertilization periods in October 2018 and April 2019, the contribution of chemical fertilizers to groundwater NO3-reached the peak value(65% and 69%), which is in line with the seasonal variations of δ15N-NO3-, δ18O-NO3-and δ15N-NH4+;4)The surface water in the watershed is mainly supplied by groundwater, and the contribution of chemical fertilizers to surface water NO3- is generally higher than that of groundwater. This may be caused by the drainage of rice fields containing chemical fertilizers into the river.
How to cite: Cao, M.: Transformations and nitrate sources in an agricultural watershed(Quanshui River, China): An investigation using hydrogeochemistry, isotopes, and a Bayesian model, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3618, https://doi.org/10.5194/egusphere-egu21-3618, 2021.
The identification of nitrate (NO3-) sources and biogeochemical transformations is critical for understanding and controlling diffuse pollution in surface water in drainage basins. This study combines water chemistry, environmental isotopes (δ2HH2O, δ18OH2O, δ15NNO3, and δ18ONO3), with land use data and a Bayesian isotope mixing model (Simmr), for reducing the uncertainty in estimating the contributions of different pollution sources in a Karst drainage basin of Jinan, North China. 64 samples were collected from Yufu River (YFR) of Jinan city in September and December, 2019. The results revealed that the NO3−-N (4.41mg/L) was the predominant form of inorganic nitrogen in YFR watershed, accounting for about 58% of total nitrogen (8.06 mg/L). There were significant temporal and spatial variations in nitrate concentrations in the area. The nitrate concentration in time was low in December and high in September, while the process of first rising and then attenuating from upstream to downstream in space. Moreover, according to the surface water flow path, different biogeochemical transformations were observed throughout the study area: microbial nitrification was dominant in the upstream with elevated NO3−-N concentrations; in the middle stream a mixing of different transformations, such as nitrification, denitrification, and/or assimilation, were identified, associated to moderate NO3−-N concentrations; whereas in the downstream the main process affecting NO3−-N concentrations was assimilation, and/or denitrification, resulting in low NO3−-N concentrations. Water chemical and dual isotope of δ15NNO3 and δ18ONO3 indicated that the river water was significantly affected by soil organic nitrogen and ammonium fertilizer inputs. Simmr mixing model outputs revealed that soil organic nitrogen (SON 55.5%) and ammonium fertilizer inputs(AF 29.5%) were the primary contributors of N pollution, whereas nitrate fertilizer(NF 7.1%), sewage & manure (M&S 3.6%), and atmospheric deposition (AP3.4%) played a less important role. The chemical fertilizer (AF and NF) and SON collectively mean contributing > 50 % of nitrate both in September and December in the watershed. Therefore, reducing fertilizer application and adopting water-saving irrigationare key to control nitrate pollution in the area. The results provide scientific basis for the water quality protection and sustainable water management in the study area or similar areas.
How to cite: Zhang, J. and Jin, M.: Identifying source and transformation of riverine nitrates in a karst watershed, North China: comprehensively using major ions, multiple isotopes and Bayesian model, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2059, https://doi.org/10.5194/egusphere-egu21-2059, 2021.
Pyrite is the most common sulfide mineral occurring in sedimentary and igneous rocks and globally contributes a greater flux of sulfate. Large quantity of reactive nitrogen as fertilizers for agricultural production has been released into the environment in China over recent decades. Sulfuric acid formed by oxidative weathering of pyrite (OWP) and nitric acid formed by oxidation of reducing nitrogen fertilizer (ONF) through neutralization with carbonate minerals can counteract CO2 drawdown from chemical weathering. Here, we use the multiple isotopes (13C-DIC, 34S and 18O-SO42–, 15N and 18O-NO3–, and 18O and D-H2O) and water chemistry, as well as historical hydrochemical data to assess the roles of strong acids in chemical weathering and the carbon cycle in a karst river system (Chishui River, southwestern China). The variations in alkalinity and the δ13C-DIC along with theoretical mixing models demonstrate the involvement of strong acids in carbonate weathering. However, the strong acid weathering flux determined by δ13C-DIC and mixing models is considered to be overestimated due to the effects of photosynthesis and degassing of CO2 on δ13C-DIC signal. The protons liberated from OWP and ONF can be constrained by water chemistry and isotope techniques with the use of a Bayesian isotope mixing model. The strong acid weathering flux determined using proton information is higher that determined by δ13C-DIC and mixing models. This suggests that the additional protons derived from OWP and ONF might be consumed in other ways without affecting the δ13C-DIC signals, such as the neutralization of acidic waters. These results indicate that OWP and ONF coupled with carbonate dissolution significantly enhanced the coupling cycles of carbon, nitrogen and sulfur in this river system.
How to cite: Xu, S., Li, S.-L., Su, J., Yue, F.-J., Zhong, J., and Chen, S.: Assessing the effects of oxidation of pyrite and reducing nitrogen fertilizer on chemical weathering and the carbon cycles in a karst river system by using multiple isotopes, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3682, https://doi.org/10.5194/egusphere-egu21-3682, 2021.
The increase of affected river reaches by reservoirs has drastically disturbed the original hydrological conditions, and subsequently influenced the nutrient biogeochemistry in the aquatic system, particularly in the cascade reservoir system. To understand the seasonal variation of nitrogen (N) behaviors in cascade reservoirs, hydrochemistry and nitrate dual isotopes (δ15N-NO3− andδ18O-NO3−) were conducted in a karst watershed (Wujiang River) in southwest China. The results showed that NO3−–N accounted for almost 90% of the total dissolved nitrogen (TDN) concentration with high average concentration 3.8 ± 0.4 mg/L among four cascade reservoirs. Higher N concentration (4.0 ± 0.8 mg/L) and larger longitudinal variation were observed in summer than in other seasons. The relationship between the variation of NO3−–N and dual isotopes in the profiles demonstrated that nitrification was dominated transformation, while assimilation contributed significantly in the epilimnion during spring and summer. The high dissolved oxygen concentration in the present cascade reservoirs system prevented the occurrence of N depletion processes in most of the reservoirs. Denitrification occurred in the oldest reservoir during winter with a rate ranging from 18 % to 28 %. The long-term record of surface water TDN concentration in reservoirs demonstrated an increase from 2.0 to 3.6 mg/L during the past two decades (~ 0.1 mg/L per year). The seasonal nitrate isotopic signature and continuously increased fertilizer application demonstrated that chemical fertilizer contribution significantly influenced NO3−–N concentration in the karst cascade reservoirs. The research highlighted that the notable N increase in karst cascade reservoirs could influence the aquatic health in the region and further investigations were required.
How to cite: Chen, S., Yue, F.-J., Liu, X.-L., Zhong, J., Yi, Y.-B., Wang, W.-F., Qi, Y., Xiao, H.-Y., and Li, S.-L.: Seasonal variation of nitrogen biogeochemical processes constrained by nitrate dual isotopes in cascade reservoirs, Southwestern China , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16166, https://doi.org/10.5194/egusphere-egu21-16166, 2021.
The recent discovery of comammox Nitrospira performing complete ammonia oxidation to nitrate has fundamentally renewed the 120-year-held perspective of “two-step” nitrification. Rivers are known as the “Arteries” of the Earth, coupling the biogeochemical cycling of continents and oceans. Frequent human activities usually increase nitrogen load, and nitrifying microorganisms are crucial for the management of nitrogen load in rivers. The ecological roles of truncated nitrifiers, including canonical ammonia-oxidizing bacteria, ammonia-oxidizing archaea and nitrite-oxidizing bacteria in rivers have been fully understood, however, investigations of the newly discovered comammox Nitrospira are very scarce. To fill this gap, we used the metagenomic shotgun sequencing to provide the first biogeographic patterns of comammox Nitrospira in the Yangtze River over a 6030 km continuum.
First, ten novel comammox genomes (71~96% completeness) were reconstructed with the metagenome assemblies from fluvial water in the upper reach and surface sediments from the middle reach to the estuary. Gene arrangements in ammonia oxidation-related gene clusters of these novel genomes were more complex and diverse than those of the previously discovered ones. For instance, multi-copy amoA or amoB genes, peptidases, cupredoxin and fkpA-cytochrome c-nirK gene sets were first found within the ammonia oxidation-related gene clusters of comammox Nitrospira, which might confer them advantages in adapting to the relatively oligotrophic environments and stabilizing the ammonia-oxidation process in rivers. Taxonomic analysis demonstrated that all riverine comammox genomes (constituting four new species) belonged to clade A. Based on the phylogenies of their 37 “elite” conserved marker genes, we further separated all reported comammox clade A into five sublineages, named clade A-Ia, A-Ib, A-Ic and A-IIa, A-IIb. The reclassified sublineages were sufficiently divergent to be meaningful in expanding the taxonomic/functional diversity and improving the phylogenetic resolution.
Second, based on the improved phylogenetic resolution, we explored the biogeographic patterns of planktonic and benthic comammox Nitrospira subjected to natural and anthropogenic factors along the Yangtze River. Our study revealed the wide existence of comammox Nitrospira and their significant contributions to nitrifier abundances, constituting 30% and 46% of ammonia-oxidizing prokaryotes (AOPs) and displaying 30.4- and 17.9-fold greater abundances than canonical Nitrospira representatives in water and sediments, respectively. Comammox Nitrospira were found to contribute more to nitrifier abundances (34~87% of AOPs) in typical oligotrophic environments with a higher pH and lower temperature, particularly in the plateau (clade B), mountain and foothill (clade A-Ic) of the upper reach. Environmental selection determined the niche replacement of planktonic comammox Nitrospira by canonical ammonia-oxidizing bacteria and Nitrospira sublineages I/II from upstream to downstream, leading to a higher spatial turnover rate than observed for the benthic counterpart, while the dissimilarity of benthic comammox Nitrospira was moderately driven by geographic distance. A considerable decrease (83%) in benthic comammox Nitrospira abundance occurred immediately downstream of the Three Gorges Dam, which was consistent with a substantial decrease in the overall bacterial taxa in sediments.
Together, this study highlights the previously unrecognized dominance of comammox Nitrospira in major river systems and underlines the importance of revisiting the distributions of and controls on nitrification processes within global freshwater environments.
How to cite: Liu, S., Wang, H., and Ni, J.: Biogeographic patterns of complete ammonia oxidizers (comammox) within the Yangtze River continuum, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7121, https://doi.org/10.5194/egusphere-egu21-7121, 2021.
Nitrogen is the primary limiting nutrient in high latitude ecosystems. Biological nitrogen fixation (BNF) by microorganisms associated with cryptogamic covers, such as cyanolichens and bryophytes, is an important source of new reactive nitrogen in pristine, high-latitude ecosystems. BNF is catalyzed by the enzyme nitrogenase, for which three isoforms have been described; the canonical molybdenum (Mo) nitrogenase which requires Mo in its active site and two alternative nitrogenases, the vanadium and iron-only nitrogenases. The low availability of Mo on land has been shown to limit BNF in many ecosystems from the tropical forest to the arctic tundra. Alternative nitrogenases have been suggested as viable alternatives to cope with Mo limitation of BNF, however, field data supporting this long-standing hypothesis have been lacking.
Here, we elucidated the contribution of the vanadium nitrogenase to BNF by cyanolichens across a 600 km latitudinal transect in eastern Canadian boreal forests. We report a widespread activity of the vanadium nitrogenase which contributed between 15 to 50% of total BNF rates on all sites. Vanadium nitrogenase contribution to BNF was more robust in the northern part of the transect. Vanadium nitrogenase contribution to BNF also changed during the growing season, with a three-fold increase between the early (May) and late (September) growing season. By including the contribution of the vanadium nitrogenase to BNF, estimates of new N input by cyanolichens increase by up to 30%, a significant change in these low N input ecosystems. Finally, we found that Mo availability was the primary driver for the contribution of the vanadium nitrogenase to BNF with a Mo threshold of ~ 250 ng.glichen-1 for the onset of vanadium based BNF.
This study on N2-fixing cyanolichens provides extensive field evidence, at an ecosystem scale, that vanadium-based nitrogenase greatly contributes to BNF when Mo availability is limited. The results showcase the resilience of BNF to micronutrient limitation and reveal a strong link between the biogeochemical cycle of macro- and micronutrients in terrestrial ecosystems. Given widespread findings of Mo limitation of BNF in terrestrial ecosystems, additional consideration of vanadium-based BNF is required in experimental and modeling studies of terrestrial biogeochemistry.
How to cite: Bellenger, J.-P., Darnajoux, R., Magain, N., Renaudin, M., Lutzoni, F., and Zhang, X.: Ecosystem scale evidence for the contribution of vanadium-based nitrogenase to biological nitrogen fixation. , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7892, https://doi.org/10.5194/egusphere-egu21-7892, 2021.
Terrestrial ecosystems worldwide are experiencing increasing atmospheric nitrogen (N) deposition because of fossil-fuel combustion and fertilizer applications. As a C4 feed crop, sweet sorghum (Sorghum bicolor L.) is widely used in the arid region of China since its high sugar content, good palatability and high yield. However, impacts of atmospheric N deposition on production of sweet sorghum are poorly understood in arid land ecosystems where soils are typically low in plant available N. At Hui Autonomous Region, Ningxia, China, a complete random block design was used to study the effects of four levels of N additions (45, 169, 197, and 224 kg ha-1 year-1) on sorghum, node number, stem diameter, leaf number, plant height, yield per plant, dry matter, and sugar Brix of stem. Nitrogen application significantly affected the above parameters. When the amount of N applied was 224 kg ha-1 year-1, the plant height (mean ± standard deviation, 256.9 cm ± 10.7, n=9), stem diameter (16.9 mm ± 1.1 ,n=9), number of leaf (10.8 ± 1.3, n=6) and node (4.9 ± 0.4, n=9), and dry matter per unit area (1.48 t ha-1 ± 0.3, n=9) was highest. While N application did not affect sugar Brix of stem. Therefore, N deposition plays a linearly positive role in enhancing the productivity of sweet sorghum in the arid region of China.
Keywords: Agronomic traits, C4 plant, Feed crop, Nitrogen addition
How to cite: Liu, W., Sun, L., Lan, J., and Li, Y.: Nitrogen deposition enhanced productivity of sweet sorghum (Sorghum bicolor L.) in the arid region of China, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10759, https://doi.org/10.5194/egusphere-egu21-10759, 2021.
Increasing evidence suggests that alkaline mineral amendments from industrial wastes (e.g., phosphorus tailing, PT) have potential to ameliorate soil acidification and improve agriculture sustainability. However, the effects of such amendment on nitrous oxide (N2O) production remain elusive. To fill this knowledge gap, an incubation experiments were conducted with an acidic soil of pH 4.80 treated with i) control (CK, no amendments), ii) urea at 60 mg N kg-1 (U), iii) 10 g kg-1 amendments (S) and iv) 10 g kg-1 amendments plus urea at 60 mg N kg-1 (S+U). A 184-h experiment was conducted with a robotized incubation system for monitoring real-time gases (O2, N2O, N2, CO2) dynamics. Results from this batch experiment showed that the soil pH was significantly increased with the amendment addition (S and S+U) from 4.80 to above 6.00. Meanwhile, the mineralization, nitrification and denitrification processes were stimulated with the amendment addition. The N2O production was reduced by an average of 65.7% with the amendment addition compared to that without the amendment application. After incubation, higher N2 productions were observed from the soil with amendment addition (S and S+U) than untreated soil (P<0.05). The findings suggest that the N2O emissions from acidic soils can be considerably controlled by valorization of PT.
How to cite: Yin, J., Liu, R., and Chen, Q.: Mitigation of nitrous oxide emissions from an acidic soil by valorization of industrial waste, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14027, https://doi.org/10.5194/egusphere-egu21-14027, 2021.
In China, amounts of organic manure as basal fertilizer application along with flooding irrigation usually resulted in large N2O emissions from intensively protected vegetable soils. However, little attention paid on the N2O emission bursts after application of manure, in a newly established vegetable soil with a low-nitrate content. The nitrification inhibitor, 3,4-dimethylpyrazole phosphate (DMPP), can be used to reduce N2O emissions from agricultural soils, little is known about how DMPP affect N2 emissions and gaseous nitrogen (N2O+N2) losses. Here, we conducted a microcosm experiment in a robotized incubation system under an aerobic (O2/He) condition. Dried chicken manure was applied with and without DMPP to a protected vegetable soil. Two drying-rewetting events occurred during the 19 days monitoring period, and the relevant soil properties (e.g., NO2-, WFPS, DOC, DON, SMBC) were analyzed. Our results showed DMPP addition strongly retarded soil nitrification process that kept a higher NH4+ concentration than that of only manure application. A significant decline of NO2- and NO3- concentration was found in a manure-treated soil with DMPP addition. Clearly, DMPP addition significantly reduced N2O emissions from the protected vegetable soil by 77.0% and remarkably decreased N2 emissions and overall N2O+N2 losses (compared with manure alone) by 51.9% and 54.0%, respectively. Pearson analysis showed that soil N2O fluxes were significantly related to soil WFPS, NH4+, SMBC (P<0.01) and SMBN (P<0.05), whereas N2 fluxes were significantly correlated with soil WFPS, SMBC (P<0.01), NO2-, NH4+ and SMBN (P<0.05) during the whole incubation. The fluxes of N2O+N2 were positively correlated with WFPS, NO2-, SMBC and SMBN, whereas negatively correlated with NH4+ (P<0.05). Moreover, the ratio of N2O to N2O+N2 (N2O/(N2O+N2)) was positively correlated with NO3- (P<0.05), and negatively correlated with DOC, DON and SMBC (P<0.01). An aggregated boosted tree (ABT) analysis further indicated that the relative influence of WFPS, SMBC and NH4+ on N2O fluxes were 19.4%, 14.9% and 12.8%, respectively. Moreover, the relative influence of WFPS on N2 fluxes was the largest (47.4%), followed by SMBC and SMBN (14.3% and 9.66%, respectively). In addition, the relative influence of WFPS, SMBN and SMBC on N2O+N2 losses were 32.6%, 17.0% and 12.6%, respectively, and the relative influence of SMBC, DOC and NO2- on N2O/(N2O+N2) were 22.5%, 20.2% and 11.1%, respectively. In conclusion, our data show that DMPP combined with manure can significantly reduce N2O and N2 emissions in a low-nitrate newly established vegetable soil, and their emissions were strongly affected by WFPS.
How to cite: Liu, Y., Yin, J., and Cao, W.: Nitrification inhibitor DMPP mitigated N2O emissions and decreased N2 losses in a low-nitrate vegetable soil after application of manure , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10794, https://doi.org/10.5194/egusphere-egu21-10794, 2021.
A common approach to reduce N loss is inclusion of inhibitors with the fertilizer formulation. However, the performance of commercially available inhibitors is often highly unpredictable, with efficacies lasting for few weeks or even only days, for reasons that are still poorly understood. Furthermore, how repeated use of these inhibitors affect soil microbes and nitrogen (N) transformation remains elusive. In the current study, we investigated the response of the community compositions of critical N-cycling biomarkers involved in nitrification and denitrification (including amoA, nxrA, nxrB, narG, nosZ), potential nitrification rates (PNR) and N2O emissions to repeated addition of urease and nitrification inhibitors (nBPT, DMPP) based on a 4-year field experiment. The results demonstrated that 4 years of fertilization significantly affected the community structure of nitrifiers, except AOA. Repeated addition of inhibitors significantly reduced N2O emissions (P ˂ 0.05) and changed the community structure of bacterial-amoA, nxrB, narG and nosZ compared to urea application alone (P ˂ 0.05), but the effects of DMPP and nBPT on N2O emissions and soil microbes were different. Inhibitors had no significant effect on the soil PNR and archaeral-amoA and nxrA. Based on structural equation modeling, amendment with the inhibitors reduced N2O emissions through directly affecting NH4+-N substrate availability for soil microbes and subsequently changing community composition of AOB. These findings help to disentangle the interplay of nBPT and DMPP with soil microbes and N2O emissions in North China Plain.
How to cite: Zhang, W., Liu, R., and Meng, F.: How repeated use of urease and nitrification inhibitors affect soil microbes and N2O emissions in North China Plain? , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15030, https://doi.org/10.5194/egusphere-egu21-15030, 2021.
One of the most important measures to reduce ammonia (NH3) and nitrous oxide (N2O) fluxes from crop production is the adoption of low-emission application techniques for slurry. Application techniques may also impact dinitrogen (N2) emission, as they can influence denitrification activity by changing slurry and soil aeration (e.g. by injection techniques), nitrate formation (e.g. by adding nitrification inhibitors) and the pH value (e.g. by slurry acidification). However, measuring N2 emissions and following pathways of slurry nitrogen (N) transformation under field conditions is still challenging.
Thus, we set up a field experiment using undisturbed soil cores with growing winter wheat as small lysimeters. Cattle slurry treatments include the following application techniques: trailing hose with and without acidification (H2SO4), slot injection with and without nitrification inhibitor (DMPP). Soil cores without slurry application were used as control. In a first step, soil nitrate was 15N labelled by homogeneous injection of a K15NO3 solution (98 at% 15N, equal to 4 kg N ha-1). One week later, we applied 72 kg N ha-115N-labelled slurry (NH4+ labelled at 65 at% 15N). NH3 emissions were measured by Dräger-Tube method (Pacholski, 2016). N2O and N2 emission were measured using the 15N gas flux method with N2-depleted atmosphere (Well et al., 2018). To close the N balance and follow the different N transformation pathways, 15N losses by leaching, 15N uptake by plant and residual 15N in roots, plant residues, microbial biomass and soil were analysed by IRMS.
N2O emission were very low (up to 0.1 kg N2O-N ha-1) and not significantly different between treatments during the experimental period of 60 days. Since the N2O/(N2+N2O) ratio of denitrification (N2Oi) was also very low, most labelled N was lost via N2 (up to 3 kg N ha-1). Nevertheless, the major gaseous loss pathway was NH3 with up to 8 kg N ha-1 in the trailing hose treatment. Slot injection significantly reduced NH3 emission, while N leaching losses were up 5 kg N ha-1. Recovery of 15N was higher in the soil N pool (32-48 %) than in plants (19-37 %) and roots (5-7 %). Total 15N recovery was almost complete, indicating that the experiment was able to catch the relevant N pathways.
Pacholski, A., 2016. Calibrated passive sampling-multi-plot field measurements of NH3 emissions with a combination of dynamic tube method and passive samplers. Journal of visualized experiments: JoVE 109, e53273.
Well, R., Burkart, S., Giesemann, A., Grosz, B., Köster, J., Lewicka-Szczebak, D., 2018. Improvement of the 15N gas flux method for in situ measurement of soil denitrification and its product stoichiometry. Rapid Communications in Mass Spectrometry 33, 437–448.
How to cite: Buchen-Tschiskale, C., Flessa, H., and Well, R.: Applying slurry with different techniques in spring – which pathway does the nitrogen take?, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-674, https://doi.org/10.5194/egusphere-egu21-674, 2021.
Fertilizing arable soils with liquid manures affects gaseous N losses to the atmosphere including NO, N2O and N2 as well as nitrate leaching. These emissions impair nitrogen use efficiency of crops and contribute to the greenhouse effect and stratospheric ozone destruction and pollution of aquatic resources. Their extent depends on the complex interaction between manure application techniques and properties of manures and soil. Whereas the types of manure effects on N transformations and associated gaseous fluxes are known, their prediction is still poor because previous investigations mostly excluded N2 flux.
Our mesocosm experiment addresses the questions, (1) how liquid manure fertilization and its application mode impact N2, N2O and CO2 fluxes from agricultural soil, and (2) how the water and dissolve organic carbon content and the pH of the manure amended soil change between the soil layers. We use these data to set up a dataset to test and develop new biogeochemical model approach to describe the manure-soil interactions.
A sandy arable soil (Fuhrberg, Germany) was used for the experiments and amended with artificial slurry (artificial liquid and cow digestate mixture) in various treatments. The soil was incubated in laboratory incubation systems over 10 days. N2, N2O and CO2 fluxes were quantified by gas chromatography and isotope-ratio mass spectrometry. Incubations were conducted with (surface or injected application) or without (control) of slurry treatment and initial water content was adjusted equivalent to 40% and 60% water-filled pore space. The environmental conditions were kept constant during that experiment.
The average N2+N2O flux decreased at the 40% WFPS surface and injected treatments with 70% and 60%, respectively, compared to the non-fertilized control. For the 60% WFPS surface and injected treatments, the average N2+N2O flux increased with more than 610% and 1690%, respectively. The results show that the initial water content and the application method can influence drastically the N2+N2O flux of the manure amended soil.
How to cite: Grosz, B., Well, R., and Burkart, S.: The impact of liquid organic fertilization and associated application techniques on N2 and N2O fluxes from agricultural soils, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8305, https://doi.org/10.5194/egusphere-egu21-8305, 2021.
Biogeochemical processes in soils largely control the atmospheric mixing ratio of nitrous oxide (N2O). The growing use of nitrogen (N) fertilizer in agriculture drives anthropogenic N2O emissions, which currently surpass projections with some of the highest emissions. In order to adapt mitigation strategies and to model the future N cycle it is crucial to fully understand N2O emission pathways in a changing climate. The underlying processes, attributed to microbial transformation of N, primarily occur via the oxic nitrification and anoxic denitrification pathways. These processes depend greatly on soil, plant and ecosystem properties, which in turn rely on meteorological drivers (e.g. air temperature and precipitation). This means that the many environmental factors that drive microbial activity and N2O emissions in soils are vulnerable to climate change, including extreme events such as droughts. Consequently, the rates of nitrification and denitrification are expected to be strongly impacted by changing climatic conditions, which could also alter the N2O production and consumption dynamics across the soil profile.
This study aims to understand how N2O production and consumption pathways respond to the individual and combined effects of warming, elevated atmospheric CO2 concentration, and drought-rewetting events in managed mountain grassland. For the first time, we use online, in-situ stable isotopic measurements of both surface N2O emissions and of N2O across the soil profile to distinguish pathways for N2O production and consumption. Different modeling approaches will be used to reconstruct production and consumption dynamics from soil gas isotopic measurements, and to upscale results to examine global relevance.
How to cite: Stoll, E., Harris, E., Diaz-Pines, E., Reinthaler, D., Radolinski, J., Glatzel, S., Zechmeister-Boltenstern, S., Pötsch, E., and Bahn, M.: Using online N2O isotopic measurements to understand grassland N2O emission processes in a changing climate , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5125, https://doi.org/10.5194/egusphere-egu21-5125, 2021.
Diurnal variations in soil nitrous oxide (N2O) emissions have been documented for nearly four decades yet consensus on their significance is still lacking. Resolving this question is important as soil N2O emissions have some of the highest uncertainties in national greenhouse gas inventories. A major challenge for understanding diurnal variation is that conventional measurements rarely operate at temporal frequencies that can observe and report this phenomenon. Some higher frequency studies have observed daytime peaking of soil N2O emissions and often ascribe it to the diurnal oscillation of soil temperature. However, night-time peaking and irregular diurnal N2O patterns have also been reported in a number of studies.
To investigate the prevalence and characteristics of diurnal N2O variability, we systematically reviewed published studies that measured N2O at high temporal frequencies (≥ 5 times/day). We identified 46 published studies covering cropland, grassland and forest soils; and extracted sub-daily N2O flux data and other soil parameters, yielding 286 individual days of data. Diurnal variability of N2O emissions were found in ~80% of the data, with ~60% peaking during the day and ~20% at night. Diurnal N2O patterns were associated with non-diurnal factors including soil texture and land use but the relationship between soil temperature and N2O flux was inconsistent, with strong positive correlations (R > 0.7) only found in one-third of the datasets.
This talk explores the implications of the review results on the time of sampling using conventional approaches (single time-point flux measurements), and the potential drivers of diurnal N2O variations for future research. In addition, this talk will also introduce a novel automated measurement technique allowing flux measurements at high temporal resolutions and how its application could enable experimental investigations of potential drivers of diurnal N2O variability.
How to cite: Wu, Y. F., McNamara, N., Whitaker, J., and Toet, S.: Investigating the diurnal variability of nitrous oxide emissions from soils , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12807, https://doi.org/10.5194/egusphere-egu21-12807, 2021.
The main prerequisites for denitrification are availability of nitrate (NO3-) and easily decomposable organic substances, and oxygen deficiency. Growing plants modify all these parameters and may thus play an important role in regulating denitrification. Previous studies investigating plant root effects on denitrification have found contradictive results. Both increased and decreased denitrification in the presence of plants have been reported and were associated with higher Corg or lower NO3- availability, respectively. Accordingly, it is still unclear whether growing plants stimulate denitrification through root exudation or restrict it through NO3- uptake. Furthermore, reliable measurements of N2 fluxes and N2O/(N2O+N2) ratios in the presence of plants are scarce.
Therefore, we conducted a double labeling pot experiment with either maize (Zea mays L.) or cup plant (Silphium perfoliatum L.) of the same age but differing in size of their shoot and root systems. The 15N gas flux method was applied to directly quantify N2O and N2 fluxes in situ. To link denitrification with available C in the rhizosphere, 13CO2 pulse labeling was used to trace C translocation from shoots to roots and its release by roots into the soil.
Plant water uptake was a main factor controlling soil moisture and, thus, daily N2O+N2 fluxes, cumulative N emissions, and N2O production pathways. However, N fluxes remained on a low level when NO3- availability was low due to rapid plant N uptake. Only when both N and water uptake were low, high NO3- availability and high soil moisture led to strongly increased denitrification-derived N losses.
Total CO2 efflux was positively correlated with root dry matter, but there was no indication of any relationship between recovered 13C from root exudation and cumulative N emissions. We anticipate that higher Corg availability in pots with large root systems did not lead to higher denitrification rates, as NO3- was limiting denitrification due to plant N uptake. Overall, we conclude that root-derived C stimulates denitrification only when soil NO3- is not limited and low O2 concentrations enable denitrification. Thus, root-derived C may stimulate denitrification under small plants, while N and water uptake become the controlling factors with increasing plant and root growth.
How to cite: Rummel, P. S., Well, R., Pfeiffer, B., Dittert, K., Floßmann, S., and Pausch, J.: Nitrate and water uptake, rather than rhizodeposition, control denitrification in the presence of growing plants, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1223, https://doi.org/10.5194/egusphere-egu21-1223, 2021.
Accurate models of soil N cycling are an important tool for optimizing N use efficiency within agricultural systems and predicting N emissions to the environment. However, within such models, denitrification remains a challenge to describe and predict. One issue in achieving accurate denitrification estimates is the limited number of soil N2 flux datasets that can be used to validate model estimates. Measurements of soil denitrification, which include both N2O and N2 fluxes, are challenging, however, due to methodological limitations for the measurement of N2 and the heterogeneity of denitrification in soils.
As part of the DFG-research unit “Denitrification in Agricultural Soils: Integrated Control and Modelling at Various Scales (DASIM)”, we are building on previous data collected from laboratory incubations to take in situ field measurements. We use soil flushing and stable isotope techniques, combined with real-time monitoring of soil conditions, to assess the response of soil denitrification to a variety of control factors. These include: soil texture, previous crop, irrigation, and fertilizer application, in addition to the ambient changes in field conditions over one growing season of winter wheat. Both natural abundance and 15N labeling of the soil mineral N pool will be used to assess denitrification pathways.
Here we introduce the experimental field setup, summarize key elements of method testing and present early results of N2 and N2O. Once complete, this data set will provide valuable insight into the temporal and spatial heterogeneity of denitrification in agricultural soils. Data will be used to calibrate newly developed DASIM models as well as denitrification sub-modules of existing biogeochemical models.
How to cite: Matson, A., Lempio, D., Höppner, F., and Well, R.: Field measurements of soil denitrification using 15N gas flux, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12482, https://doi.org/10.5194/egusphere-egu21-12482, 2021.
Nitrous oxide (N2O) is a major greenhouse gas whose presence in atmosphere is continuously increasing. Hence it’s important to understand its production and consumption mechanisms. During the summer of 2020, we conducted lab experiments using heavy nitrogen tracers of Potassium Nitrate 15N 98% atom (Sigma Aldrich) and Ammonium Chloride 15N 98% atom (Sigma Aldrich) under different moisture conditions to get an insight into N2O production mechanisms and on their dependence on soil moisture. We applied the tracer to peat samples (Kärevere, Estonia) placed in 36 (12 control, 12 nitrate treatment & 12 ammonia treatment) plastic buckets (radius-10cm, height-20cm) with soil height of 10 cm and a 10 cm head space left for gas collection. We installed oxygen sensors, water table indicators and temperature sensors on all buckets. We focused on studying physical conditions (soil oxygen, temperature, water table and soil moisture), gas (N2O) emission data, soil chemistry, gas isotope 15N, soil isotope and soil microbiology to get a complete picture of the processes involved in production of N2O gas. Under the ammonia treatment, emissions increased more than ten-fold which could be due to multiple processes of the nitrogen cycle in play. N2O emissions increased as the oxygen conditions shifted from anoxic (Omg/L=0) to sub-oxic (Omg/L=0.5–6) and then decreased as oxygen conditions reached the oxic (Omg/L>6) state. Furthermore, we witnessed negative site preference and 18O values during the nitrate treatment indicating nitrifier-denitrification. Under the ammonia treatment, we recorded both negative as well as high positive site preference values indicating presence of multiple production mechanisms. This was expected as ammonia triggers multiple processes in the nitrogen cycle. In some samples, we observed N2O consumption with little change in site preference as compared to the N2O producing samples. This indicates some bacterial-denitrification along with the prevailing nitrifier-denitrification. We also observed that under both treatments, heavy oxygen increased with increasing site preference. This indicates reduction of N2O (Ostrom et al, 2007) as redox supports 15N and 18O enrichments. After these lab experiments, we conducted the same experiment at a large scale in a drained peatland forest in Agali, Estonia. In this experiment, we established 1m2 triangle-shape mesocosms using experimental draining and flooding to achieve varying oxygen conditions. Preliminary results of qPCR analysis of N-cycle control genes support the domination of ammonia oxidation and denitrification as sources of N2O.
How to cite: Masta, M., Gadegaonkar, S., Sepp, H., Espenberg, M., Pärn, J. P., Kirsimäe, K., and Mander, Ü.: Isotope and microbiome analysis indicates variety of N-cycle processes controlling N2O fluxes in a drained peatland forest soil, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10809, https://doi.org/10.5194/egusphere-egu21-10809, 2021.
Coastal wetlands, including mangrove and melaleuca forests, are globally important due to their capacity in sequestering carbon and nitrogen, and intercepting nutrient pollution from vast, nutrient-rich, tropical riverine networks. Despite this, the environmental drivers controlling soil biogeochemistry in these ecosystems remain poorly understood. Here we conducted a study across gradients of restoration and land-use in the mangrove forest of Xuan Thuy National Park in the Red River Delta, northern Vietnam and the melaleuca forest of U Minh Thuong National Park in the Mekong River Delta, southern Vietnam. We investigated nitrogen transformation processes and greenhouse gas production in mangrove and melaleuca forest soils using a 15N-Gas flux method to determine rates of denitrification, and its relative contribution to soil N2O emissions. We found that denitrification was a more dominant source of N2O in the melaleuca soils, despite higher rates of denitrification in the mangrove soils resulting from more complete denitrification in the mangroves. N2O and CO2 emissions were significantly higher from the melaleuca soils. Disturbance and subsequent recovery or restoration of these forests did not have a significant effect on soil biogeochemistry. The mangrove system, therefore, may remove excess nitrogen and improve water quality while maintaining low emissions of greenhouse gases whereas melaleucas process nutrients at a cost of N2O and CO2 emissions. Melaleucas, however, may act as a significant CH4 sink at least partially balancing these emissions.
How to cite: Comer-Warner, S., Nguyen, A., Nguyen, M., Wang, M., Turner, A., Sgouridis, F., Krause, S., Le, H., Kettridge, N., Nguyen, N., and Ullah, S.: The role of land-use change and restoration on nitrogen processing in tropical coastal wetlands of Vietnam, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1619, https://doi.org/10.5194/egusphere-egu21-1619, 2021.
Treatment wetlands are widespread measures to reduce agricultural diffuse pollution. Systems that are often planted with emergent macrophytes such as Typha spp. and Phragmites spp. are efficient to reduce nutrients, particularly nitrogen and phosphorus compounds. While many experiments have been conducted to study the emission of carbon dioxide (CO2) and methane (CH4), little attention has been paid for the emission of nitrous oxide (N2O). Few studies have been shown that usually N2O emission from water saturated ecosystems such as wetlands is low to negligible. In Vända in-stream treatment wetland that was built in 2015 and located in southern Estonia, we carried out first long term N2O measurements using floating chambers. The total area of the wetland is roughly .5 ha; 12 boardwalks, each equipped with two sampling spots, were created. Samples were collected biweekly from March 2019 through January 2021. In each sampling campaign water table depth, water and air temperature, O2 concentration, oxygen reduction potential, pH and electrical conductivity were registered. Water samples for TN, NO3-N, NO2-N, TOC, TIC and TC were collected from inflow and outflow of the system in each sampling session and the average concentrations were 5.1 mg/L, 3.68 mg/L, <0.1 mg/L, 41.2 mg/L and 28.7, respectively. Our results showed a very high variability of N2O emission: the fluxes ranged from -4.5 ug m-2 h-1 to 2674.2 ug m-2 h-1 with mean emission of 97.3 ug m-2 h-1. Based on gas samples (n=687) we saw a strong correlation (R2 = -0.38, p<0.0001) between N2O emission and water depth. The average N2O emission from sections with the water table depth >15 cm was 45.9 ug m-2 h-1 while sections with water table depth <15 cm showed average emission of 648.3 ug m-2 h-1. The difference between these areas was more than 10 times. Water temperature that is often considered as the main driver had less effect to the N2O emission. For instance, at lower temperatures, when the emissions from deeper zones decreased, there was no temperature effect on emissions from shallow zones. We also saw that over the years the overall N2O emission followed clear seasonal dynamics and has a slight trend towards lower emissions. This can be related to the more intensive vegetation growth that has been increased from ~40% in 2019 to approximately 90% in 2020. Our study demonstrates that the design of the wetland is not only important for the water treatment, but it can also determine the magnitude of greenhouse gas emissions. We saw that even slight changes in water table depth can have a significant effect on the annual N2O emission. Thus, in-stream treatment wetlands that have water table depth at least 15 cm likely have remarkably lower N2O emissions without losing water treatment efficiency.
How to cite: Kasak, K., Kill, K., Uuemaa, E., and Mander, Ü.: Design of the treatment wetland determines nitrous oxide emission, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7340, https://doi.org/10.5194/egusphere-egu21-7340, 2021.
Stable isotope fingerprinting is widely applied to plant-soil-groundwater systems in an aim to identify and even quantify the sources of nitrates found in groundwater. Frequently, in such studies, the δ15N and δ18O values of nitrogen sources, such as inorganic fertilizers and manure, are directly compared to the isotope signatures of nitrate encountered in groundwater bodies below agricultural watersheds. We submit that the underlying assumptions (conservative behavior of isotope composition, rapid transfer from surface to groundwater) may only be realistic under very specific conditions whereas, in most cases, significant isotope effects exerted by the soil-microbial-plant system on the δ15N and δ18O values of nitrate need to be taken into account when attempting a quantitative apportionment of sources of groundwater nitrate.
We hypothesise that the isotopic signature of nitrate exported from below the root zone and migrating towards the groundwater will reflect the nitrogen isotope composition of the soil organic N pool, rather than the isotope composition of source fertilizer or organic amendments, due to processes that reset source isotope compositions within soil N pools. We test this hypothesis using empirical observations from a diversity of settings, in France, Spain and Canada with a relatively constant historic anthropogenic N source or a simple and well constrained landuse history. Furthermore, through the use of a process-based model (SIMSONIC, Billy et al., 2010) we estimate to what extent the isotopic composition of the predominant N input to the soil-microbial-plant system and the soil N pool has been modified in an attempt to consider these changes in source apportionment studies elucidating the sources of groundwater nitrate.
This research was supported through the Consortium award MUTUAL, by the LE STUDIUM® Loire Valley Institute for Advanced Studies via its SMART LOIRE VALLEY (SLV) fellowship programme, co-funded by the H2020 Marie Sklodowska-Curie programme, Contract No. 665790.
Billy C., Billen G., Sebilo M., Birgand F., Tournebize J. (2010) Nitrogen isotopic composition of leached nitrate and soil organic matter as an indicator of denitrification in a sloping drained agricultural plot and adjacent uncultivated riparian buffer strips. Soil Biology and Biochemistry, 42, 108-117.
How to cite: Otero, N., Sebilo, M., Mayer, B., Gooddy, D., Lapworth, D., Surridge, B., Petelet-Giraud, E., and Kloppmann, W.: Modelling the impact of soil processes on the N and O isotope signatures of nitrate in groundwater, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12432, https://doi.org/10.5194/egusphere-egu21-12432, 2021.
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