5th iLEAPS Science Conference Abstracts - A2

Abstracts – Session A2

The global nitrogen cycle: quantifying and modelling the flow of nitrogen through the land-atmosphere system


A201 - ORAL-0276: Gross rates of nitrogen transformation in tropical forest soils of Western Ghats, India

Sanjeev Kumar1, Niharika Sharma1, V. Ramaswamy2

1Physical Research Laboratory, Ahmedabad, India 2National Institute of Oceanography, Goa, India

The knowledge of sources and sinks of N2O along with rates of responsible biogeochemical processes in tropical soils, particularly Indian soils, is poorly understood. In order to fully understand the biogeochemical dynamics of N2O, it is essential to quantify the rates of fundamental processes involved. An attempt is being made to generate first data set of gross nitrification and mineralization rates from soils of different ecozones of India. In a first such study, 15N isotope dilution experiments were conducted in the forest soils of Western Ghats in India which experiences tropical hot and humid climate. Soils from two depth zones i.e., 0 -10 cm and 20-30 cm were collected in triplicates from five locations of these forests and were measured for gross nitrification rates, consumption rates, nitrate concentration and mean residence time. Gross nitrification rates in these soils varied from 0.16 to 3.87 mg NO3--N kg-1 d-1 and nitrate consumption rates ranged from 0.01-6.89 mg NO3--N kg-1 d-1. Negative consumption rates were also observed during the study. Consumption was found to be significantly correlated with gross nitrification (r=0.63, p<0.001) with general trend of higher consumption in bottom soils. C:N ratios was found to be low, indicating the high mineralization potential of the system. Residence time of NO3- was around 10 days with higher residence time at locations with low consumption to gross nitrification ratio. Availability of NO3- in these soils suggests potential for denitrification, which experiences heavy rainfall events and can lead to increased emissions of N2O, which needs to be confirmed.


A202 - ORAL-0420: Climate change amplifies gross nitrogen turnover in montane grasslands of Central Europe

Michael Dannenmann1, Changhui Wang2, Zhe Chen3, Sebastian Unteregelsbacher3, Haiyan Lu3, Silvia Gschwendtner4, Rainer Gasche3, Allison Kolar3, Michael Schloter4, Ralf Kiese3, Klaus Butterbach-Bahl3

1Karlsruhe Institute of Technology (KIT) Campus Alpin, Karlsruhe, Germany 2Institute of Botany, The Chinese Academy of Sciences, China, China 3Karlsruhe Institute of Technology (KIT), GARMISCH-PARTENKIRCHEN, Germany 4Helmholtz Zentrum Munchen, Munich, Germany

The carbon- and nitrogen-rich soils of montane grasslands are exposed to above-average warming and to altered precipitation patterns as a result of global change. To investigate the consequences of climatic change for soil nitrogen turnover, we translocated intact plant–soil mesocosms along an elevational gradient, resulting in an increase of the mean annual temperature by approx. 2 °C while decreasing precipitation from approx. 1500 to 1000 mm. Following three years of equilibration, we monitored the dynamics of gross nitrogen turnover and ammonia-oxidizing bacteria (AOB) and archaea (AOA) in soils over an entire year. Gross nitrogen turnover and gene levels of AOB and AOA showed pronounced seasonal dynamics. Both summer and winter periods equally contributed to cumulative annual N turnover. However, highest gross N turnover and abundance of ammonia oxidizers were observed in frozen soil of the climate change site, likely due to physical liberation of organic substrates and their rapid turnover in the unfrozen soil water film. This effect was not observed at the control site, where soil freezing did not occur due to a significant insulating snowpack. Climate change conditions accelerated gross nitrogen mineralization by 250% on average. Increased N mineralization significantly stimulated gross nitrification by AOB rather than by AOA. However, climate change impacts were restricted to the 2–6 cm topsoil and rarely occurred at 12–16 cm depth, where generally much lower N turnover was observed. Our study shows that significant mineralization pulses occur under changing climate, which is likely to result in soil organic matter losses with their associated negative impacts on key soil functions. We also show that N cycling processes in frozen soil can be hot moments for N turnover and thus are of paramount importance for understanding seasonal patterns, annual sum of N turnover and possible climate change feedbacks.


A203 - ORAL-0243: N flows across the soil in high deposition, non-agricultural sites in Italy

Guia Cecchini1, Anna Andreetta1, Aldo Marchetto2, Stefano Carnicelli1

1Università degli Studi di Firenze, Firenze, Italy 2CNR ISE, Pallanza, Italy

Atmospheric reactive nitrogen is a nonpoint-source pollutant, but emissions and depositions show strong geographical structures, major changes being visible within a few hundred km. It is then possible to assess their effects by comparing quite similar sites. Transfers of reactive N to fresh- or ground-waters are a major concern stemming from atmospheric N pollution; their monitoring is possible in non-agricultural sites, where N inputs only come from the atmosphere. Italy sees some of the highest N deposition loads, concentrated in northern Italy; in central-southern regions, remote sites receive low deposition loads.

The ICP-Forests network monitors N deposition and carries out assessments of critical loads (CL) and their exceedance. Presently, 6 sites also undergo monitoring of soil solution composition, which allows to assess whether N is flowing out of the main tree rooting zone. We developed a method to estimate chemical flows out of the root zone, using chloride as tracer. This method was validated by comparing both Cl- flows with other major chemical species and estimated water fluxes with precipitation data. The method was applied to N fluxes and results were compared with those of the last assessment of CL exceedance.

This evidenced regular N flux out of the rooting zone in sites showing medium to high CL exceedance, and no flux in sites with no exceedance. Absent or occasional N flux was observed in sites with low CL exceedance. These results indicate that the CL method has a potential for assessing site vulnerability to N deposition, while its parameterisation is susceptible to adjustments. The results also show that transfer of atmospheric N to natural waters is a real, measurable phenomenon.


A204 - ORAL-0156: Impacts of climate and management on water balance and nitrogen leaching from montane grassland soils of S-Germany

Jin Fu1, Rainer Gasche1, Klaus Butterbach-Bahl1, Ralf Kiese1

1Karlsruhe Institute of Technology, Institute of Meteorology and Climate research, Atmospheric Environmental Research, Garmisch-Partenkirchen, Germany

In this study water balance components as well as nitrogen and dissolved organic carbon leaching were quantified by means of large weighable grassland lysimeters at three sites (860, 770 and 600m a.s.l.) for both intensive and extensive management. Our results show that at E600, the site with highest air temperature (8.6°C) and lowest precipitation (981.9mm), evapotranspiration losses were 100.7mm higher as at the site (E860) with lowest mean annual air temperature (6.5°C) and highest precipitation (1359.3mm). Seepage water formation was substantially lower at E600 (-440.9mm) as compared to E860. Compared to climate, impacts of management on water balance components were negligible. However, intensive management significantly increased total nitrogen leaching rates across sites as compared to extensive management from 2.6 kg N ha-1 year-1 (range: 0.5-6.0 kg N ha-1 year-1) to 4.8 kg N ha-1 year-1 (range: 0.9-12.9 kg N ha-1 year-1). N leaching losses were dominated by nitrate (64.7%) and less by ammonium (14.6%) and DON (20.7%). The low rates of N leaching (0.8 – 6.9% of total applied N) suggest a highly efficient nitrogen uptake by plants as measured by plant total N content at harvest. Moreover, plant uptake was often exceeding slurry application rates, suggesting further supply of N due to soil organic matter decomposition. The low risk of nitrate losses via leaching and surface runoff of cut grassland on non-sandy soils with vigorous grass growth may call for a careful site and region specific re-evaluation of fixed limits of N fertilization rates as defined by e.g. the German Fertilizer Ordinance following requirements set by the European Water Framework and Nitrates Directive.

A205 - ORAL-0280: Some land management information is crucial to represent spatial variability of above-ground productivity

Emma Robinson1, Lina Mercado2, 1, Douglas Clark1, Sabine Reinsch3, Bridget Emmett3, Jack Cosby3, Simon Smart4, Ed Rowe1, Harry Harmens1, Helen Glanville5, Davey Jones5

1CEH, Wallingford, United Kingdom 2University of Exeter, Exeter, United Kingdom 3CEH, Bangor, United Kingdom 4CEH, Lancaster, United Kingdom 5Bangor University, Bangor, United Kingdom

A recent development of the Joint UK Land Environment Simulator (JULES) is the inclusion of the ECOSSE soil nitrogen (N) model. This allows a dynamic interaction of soil N with the hydrology, energy balance and carbon-cycle processes modelled by JULES, in particular improving the representation of N-limitation of vegetation productivity. While global estimates of soil N stocks and fluxes are limited, a regional-scale comprehensive field campaign was carried out in North Wales, UK, to measure key components of the C, N and P cycles within a single river catchment, covering a variety of representative UK vegetation types. Here we use these measurements to a) evaluate JULES model performance across a variety of ecosystems and also b) improve parameterisation of some key processes in JULES Key evaluation metrics included soil N content and above-ground net primary productivity (aNPP). We find that the standard model configuration of JULES does not represent well the variation of aNPP and soil N content across the studied land management gradient. Using observed site-level vegetation and soil properties (leaf N content, leaf mass per unit area, maximum rates of carboxylation and electron transport, and soil pH) as model input parameters helped to improve the model performance slightly. However, an important aspect of the N cycle is land management, in particular fertiliser application. We find that the inclusion of estimates of N fertiliser application at managed sites significantly improves the model's ability to represent spatial variation of productivity.


A206 - ORAL-0289: Long Term Large Scale simulations of freshwater nutrients across the UK

Victoria Bell1, Pam Naden, Ed Tipping, Helen Davies, Jessica Davies, Ulli Dragosits, Shibu Muhammed, John Quinton, Marianne Stuart, Andy Whitmore, Lianhai Wu, Sam Tomlinson, Ed Carnell, Giuseppe Formetta

1Centre for Ecology and Hydrology, Wallingford, United Kingdom

During recent decades and centuries, pools and fluxes of Carbon, Nitrogen and Phosphorus in UK rivers and ecosystems have been transformed by the spread and fertiliser-based intensification of agriculture (necessary to sustain human populations), by atmospheric pollution, by human waste (rising in line with population growth), and now by climate change.
The work described here examines the effects of this long-term nutrient enrichment on nutrient transfers from land to freshwaters and estuaries, with a focus on the freshwater component. A national-scale modelling environment has been developed, combining simple physically-based gridded models that can be parameterised using recent observations before application to long timescales. The Long Term Large Scale Integrated Model (LTLS-IM) consists of a suite of models that use readily-available driving data (climate, land-use, nutrient inputs, topography) as input. Terrestrial nutrient loads are estimated from agricultural and semi-natural areas and also take into account atmospheric deposition. Estimates of nutrients released from soils, along with estimates of human emissions, provide the input to a national-scale freshwater model which provides lateral routing of dissolved and particulate nutrients and within-river processing such as denitrification, decomposition and chlorophyll growth. The effects of groundwater storage and processes in lakes connected to the river network can also be included.
Following assessment against observations of terrestrial and freshwater nutrient fluxes for sites across the UK, the LTLS-IM has been run nationally for ~200 years (1800 to 2010), and the work presented here provides, for the first time, national, regional or catchment estimates of the origins and trends in freshwater nutrients in the period following the industrial revolution, and estimates nutrient fluxes to the sea. Ongoing work is now exploring the effects of future climate, waste water treatment and land-management scenarios on water quality, and the effects of nutrient enrichment on the development of eutrophication in rivers.

A207 - ORAL-0421: Comparison of nitrogen, carbon and greenhouse gas budgets from European forests, moorlands, croplands and grasslands

Ute Skiba1, Mark Sutton1, Christoff Ammann2, Christophe Flechard3, Benjamin Loubet4, Andreas Ibrom5

1CEH, Edinburgh, United Kingdom 2Agroscope Research Station, Reckenholzstr, Zurich, Switzerland 3INRA – UMRSAS, Rennes, France 4Institut National de la Recherche Agrognomique, Paris, France 5Technical University of Denmark, Kongens Lyngby, Denmark

Summary results from the European Nitrogen Flux Observing System of 13 ‘Super Sites’ for quantification of primarily nitrogen budgets, as well as carbon and greenhouse gases budgets, will be presented. This observation system operated over a 4.5 year period, as part of the NitroEurope Integrated Project (in short NEU IP) and funded under the 6th Framework Programme of the European Commission. The ‘Super Sites’ represent the main ecosystems and climate zones across Europe. Measurements of nitrogen and carbon import and export, using the same measurement protocols across all sites,  were made at the best available spatial and temporal resolution, to understand the differences between sites and to underpin modelling at the plot, landscape and European scale. The data demonstrate the influence of soil type, climate, landuse and land management on the import and export balances of carbon and nitrogen. In managed croplands and grasslands nitrogen fertiliser input and harvest losses dominated the nitrogen budgtes. Contrary, the rate of atmospheric nitrogen deposition had an important impact on nitrogen budgtes of forests and moorlands. The lower the N input rate, the lower were the N losses; and in remote regions, such as boreal Finland, the nitrogen cycling was almost a closed system. Contrary intensive, high N input agricultural fields were hotspots of the pollutants, N2O and NO3 (i.e. grazed grassland in Scotland). Carbon sequestration rates were largest in the forests, and reduced at intensively managed agricultural sites through exports soil N2O emissions, livestock and rice paddy CH4 emissions.


A208 - ORAL-0337: Exchange of ammonia and nitrogen oxide between fresh oilseed rape litter and the atmosphere in relation to the dynamics of organic matter and in response to climatic conditions

Raia Silvia Massad1, Varunesh Chandra1, Christophe Flechard2, Benjamin Loubet1

1INRA Agroparistech, Thiverval - Grignon, France 2INRA, Rennes, France

The atmospheric reactive nitrogen mainly composed of nitrogen oxides (NOx) and ammonia: (NH3) represent one of the main sources of air pollution from natural sources today. Soils and more specifically fresh plant litter play an important role in the exchanges of NH3 and NOx between plant surfaces and the atmosphere, particularly in anthropogenic ecosystems (Grasslands and croplands). Fresh vegetable litter is a complex system at the interface of the atmosphere, the soil and the living (Plants). Its physical, biological and chemical states depend on that of the adjacent soil (temperature, humidity, microorganisms, etc.), of the plants which are at its origin (C/N ratio, quality of organic matter, humidity, …) and the atmosphere (nitrogen deposition, concentration in CO2, temperature, precipitation, etc.). We conducted an experiment to characterize exchanges of NH3 and NOx from oilseed rape fresh litter both in the field with ambient conditions and laboratory with standardized conditions. Measurements and samplings were conducted at different periods so as to describe emissions for different litter ages and decomposition states. Preliminary results show that leaf litter is an important source of NH3 in the plant canopy, that its degree of decomposition highly affects NH3 and NOx emissions and that its wetness is an important control for the emissions.

A209 - ORAL-0336: Effects of Future Agricultural Ammonia Emission and Deposition on Air Quality through Vegetation Feedbacks

Xueying Liu1, Amos P. K. Tai1

1The Chinese University of Hong Kong, Shatin, Hong Kong

The world is facing the challenge of feeding an ever-growing population and simultaneous safeguarding the environment. In many parts of the world but very notably in China, excessive amounts of nitrogen fertilizer are applied to maximize crop production, often inducing unintended environmental consequences, including the substantial release of ammonia (NH3) into the atmosphere. Atmospheric NH3 emission of agricultural origins accounts for more than 50% of the total emission globally and over 80% for intensive agricultural areas in Asia. After chemical reaction and transportation, atmospheric NH3 deposits back onto the terrestrial ecosystem, modifies soil microbial processes and thus enhances vegetation growth.  As parameterizations for plant growth, leaf area index (LAI) and canopy height can potentially impact on serious environmental problems such as fine particulate matter (PM2.5) and ozone (O3) pollutions through biogeochemical and biogeophysical pathways. Here, we adopt an asynchronous coupling framework using the Community Earth System Model (CESM) to investigate how agriculture-induced atmospheric NH3 emission and deposition affect air quality via biosphere-atmosphere processes. We conduct two scenarios (current and future NH3 emission) to examine the corresponding vegetation responses, and then air quality responses driven by the change of 1) LAI only, 2) canopy height only and 3) both LAI and canopy height. We find that obvious enhancements for both LAI (around 0.4 m2 m-2) and canopy height (around 0.2 m) happen in the southeastern part of South America, Sub-Saharan Africa, Europe and southern China. Annual surface O3 increases in the US and Middle Russia through LAI pathway due to increased isoprene emission and decreased O3 dry deposition. PM2.5 level increases in eastern China and Moglia. Our results show that agricultural NH3 under future scenario has the potential to worsen air quality via vegetation feedbacks, thereby suggesting the need to formulate optimal strategies for future agricultural practices for environmental purpose.

A210 - ORAL-0318: Simulating the present-day and future global ammonia budget with the chemistry-climate model UKCA-CLASSIC

Claudia Steadman1, 2, David Stevenson2, Mathew Heal3, Colin Johnson4, Hana Pearce5, Nicholas Savage4, Luke Abraham6, 7, Mark Sutton1, David Fowler1

1Centre for Ecology and Hydrology, Penicuik, United Kingdom 2School of GeoSciences, The University of Edinburgh, Edinburgh, United Kingdom 3School of Chemistry, The University of Edinburgh, Edinburgh, United Kingdom 4Met Office, Exeter, United Kingdom 5Institute for Climate & Atmospheric Science, School of Earth & Environment, University of Leeds, Leeds, United Kingdom 6Centre for Atmospheric Science, Department of Chemistry, University of Cambridge, Cambridge, United Kingdom 7National Centre for Atmospheric Science, Cambridge, United Kingdom

Over the last century, large increases globally in fertiliser use and livestock have resulted in more reactive nitrogen being present in the Earth System, with effects including eutrophication and hypoxic zones, acidification, biodiversity loss, climate change, destruction of the ozone layer, and human health effects from aerosols and contaminated drinking water. Ammonia is a critical species in the nitrogen cycle as it volatilises from fertiliser and manure, and it is also the principal alkaline gas in the atmosphere. It therefore plays an important role in atmospheric chemistry, reacting with sulphuric and nitric acids to form ammonium aerosols, which serve as cloud condensation nuclei and negatively impact human health. Anthropogenic ammonia emissions are increasing rapidly, and are set to continue to do so this century due to increasing global temperatures and food production. We present details of the global ammonia budget as simulated by the chemistry-climate model UKCA coupled to the Unified Model, with the aerosol scheme CLASSIC, and we compare the model results with satellite and ground-based observations. We provide global distributions, deposition fluxes and lifetimes of ammonia and ammonium nitrate, quantifying the important processes that control reduced nitrogen in the present-day atmosphere, and its response to 21st century climate change.

A211 - ORAL-0020: Effects of ‘natural’ to ‘geoengineered’ nitrogen deposition on the carbon cycle

Taraka Davies-Barnard1, Pierre Friedlingstein1, Andy Wiltshire2

1University of Exeter, Exeter, United Kingdom 2Met Office, Exeter, United Kingdom

The terrestrial carbon cycle is dependent on the nutrient nitrogen, which comes from natural and anthropogenic deposition, and biological fixation. As atmospheric carbon dioxide concentrations increase, it is expected there will be increased plant productivity and carbon sequestration. However, how strong this ‘fertilisation’ effect will be somewhat dependent on availability of nitrogen. The anthropogenic deposition of nitrogen is likely to be a major contributor to the terrestrial nitrogen cycle, and therefore one of the key determinants of the carbon uptake by the terrestrial biosphere.
Using JULES-CN, a version of the UK’s land surface model that includes a carbon and nitrogen cycle, we explore a range of nitrogen deposition scenarios in a high CO2 world. We use the Representative Concentration Pathway (RCP) scenarios of nitrogen deposition to consider ‘realistic’ scenarios. We also use a variety of idealised nitrogen deposition scenarios, including one fixed at present-day deposition, pre-industrial deposition, and a high, ‘geoengineered’ nitrogen deposition.
We show the differences in carbon storage and net primary productivity between the different scenarios. We assess whether nitrogen fertilisation of areas which would not otherwise benefit from carbon dioxide fertilisation would provide a significant climate benefit.

A212 - ORAL-0077: Modeling and assessing effectiveness of intercropping as a sustainable agricultural practice for food security and air pollution mitigation

Ka Ming Fung1, Amos P. K. Tai1, Taiwen Yong2, Xiaoming Liu3

1Earth System Science Programme, Faculty of Science, The Chinese University of Hong Kong, Shatin, Hong Kong 2College of Agronomy, Sichuan Agricultural University, Sichuan, China 3Shehong Agricultural Technology Station, Sichuan, China

The fast-growing world population will impose a severe pressure on our current global food production system. Meanwhile, boosting crop yield by increasing fertilizer use comes with a cascade of environmental problems including air pollution. In China, agricultural activities contribute to 95% of total ammonia emissions. Such emissions are attributable to ~20% of the fine particulate matter (PM2.5) formed in the downwind regions, which imposes severe health risks to the citizens. Field studies of soybean intercropping have demonstrated its potential to enhance crop yield, lower fertilizer use, and thus reduce ammonia emissions by taking advantage of legume nitrogen fixation and enabling mutualistic crop-crop interactions between legumes and non-legume crops. We extend the scale of individual field studies to all Chinese provinces using the process-based biogeochemical model, DeNitrification-DeComposition (DNDC), which dynamically simulates plant growth, soil chemistry, and reactive nitrogen emissions. We revise DNDC further to capture the belowground interactions of intercropped crops, and conduct model experiments to investigate the effects of maize-soybean intercropping systems in different sites by comparing their performance with their monoculture counterparts. With intercropping, only 58% of fertilizer is required to yield the same maize production, corresponding to a reduction of ammonia emission by 43% over China. Using the GEOS-Chem global 3-D chemical transport model, we estimate that such ammonia reduction can lessen downwind inorganic PM2.5 by up to 2.1% (equivalent to 1.3 μg m-3). We find nationwide adoption of maize-soybean intercropping can raise the annual net income from crop production by USD45 billion (equivalent to +85% from current practices), with a US$0.61 billion and US$1.5 billion of savings on fertilizers and air pollution-related health costs, respectively. Our results can serve as a scientific base for policy makers to consider promoting intercropping as a national standard to secure a steady and sustainable food supply and mitigate air pollution simultaneously.