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PhD Studentship: Human alteration of the nitrogen cycle: Implications for denitrification and nitro

Employer
Global Academy Jobs
Location
United Kingdom
Closing date
Jan 22, 2018

Job Details

Details

The magnitude of the human alteration of the global nitrogen (N) cycle due to agricultural intensification and industrial development is way bigger than any other elemental cycle on earth. The use of synthetic N fertilizer and fossil fuel results in the emission of reactive N (Nr) into air, which over time is re-deposited on land. As a result, soils under natural ecosystems including forests are now exposed to excessive Nr deposition. This additional Nr input supports forest growth, but its amount in soils in some regions is way above the forest growth demands. Thus too much of this good thing is indeed an environmental quality concern leading to higher greenhouse gas nitrous oxide (N2O) emission, for example.

Denitrification is the only dominant natural process in soils responsible for removing the Nr permanently by converting it back into the non-pollutant dinitrogen (N2) gas. However, during this process N2O gas is also produced when Nr availability is high. Simply too much of the Nr deposition locks the soils in a vicious cycle of swapping one pollutant for another thus negating the benefits of the enhanced biomass production. There is a need to better understand the controls of the denitrification processes in soils so that forests could be managed in way that N2O emission in to air is reduced. This PhD project would address two key challenges:

  1. Methodological challenge: Among available methods, the 15N gas-flux method has the advantage of providing field measurements, but it may stimulate denitrification due to the added 15N tracer. Accounting for the stimulatory contribution of 15N tracer to denitrification if any, is thus imperative for robust measurements.
  2. Mechanistic challenge: Depending on soil conditions, denitrification varies by an order of magnitude in space and time. A better understanding of the controlling factors such as the quality of soil organic carbon (SOC), soil moisture, temperature and nitrate content in forest soils is needed for modelling the response of denitrification and N2O emission from forest soils to Nr deposition.

 

Project aims: To evaluate the performance of in situ 15N Gas-Flux method in quantifying denitrification and to elucidate the implications of differences in SOC quality in influencing denitrification and N2O emission from soils under mature and restored forests exposed to chronic Nr deposition.

Soil cores will be collected from two restored and a mature forest site of the Birmingham Institute for Forest Research (BIFoR). The cores will be incubated using the He/O2 gas flow system at Rothamsted Research for performance evaluation of the 15N Gas flux method. Following laboratory incubation, in situ denitrification will be determined in the field together with high frequency measurement of soil moisture and temperature using a novel sensing technology called FO-DTS. The abundance of soil SOC and its potential sources using elemental C/N ratios, d13C and d15N values as well as lipid biomarkers (hydrocarbons, alcohols/sterols, fatty acids, lignin-derived phenols) will be determined to elucidate key controls of SOC on denitrification.

 

Funding Notes

In addition to completing an online application form, you will also need to complete and submit the CENTA studentship application form available from www.centa.org.uk.

CENTA studentships are for 3.5 years and are funded by the Natural Environment Research Council (NERC). In addition to the full payment of their tuition fees, successful candidates will received the following financial support.

Annual stipend, set as £14,553 for 2017/18

Research training support grant (RTSG) of £8,000

CENTA students are required to undertake 45 days training throughout their PhD including a 10 day placement.


References

Sgouridis, F., A. Stott, and S. Ullah. 2016. Application of the 15N-Gas Flux method for measuring in situ N2 and N2O fluxes due to denitrification in natural and semi-natural terrestrial ecosystems and comparison with the acetylene inhibition technique. Biogeosciences 13, 1821–1835

Groffman, et al. 2012. Terrestrial denitrification: challenges and opportunities. Ecological Processes 1-11; DOI: 10.1186/2192-1709-1-11

Sgouridis, F. and S. Ullah. 2015. Relative magnitude and controls of in situ N2 and N2O fluxes due to denitrification in natural and seminatural terrestrial ecosystems using 15N tracers. Environmental Science and Technology 49, 14110 −14119

Cárdenas et al. 2003. Biogenic gas emissions from soils measured using a new automated laboratory incubation system. Soil Biology and Biochemistry 35:867-870

Gontharet et al. 2014. Distribution and sources of bulk organic matter (OM) on a tropical intertidal mud bank in French Guiana from elemental and isotopic proxies. Chemical Geology 376: 1-10.

Krause, S.; Taylor, S. L.; Weatherill, J.; Haffenden, A.; Levy, A.; Cassidy, N. J.; Thomas, P. A. Fibre‐optic distributed temperature sensing for characterizing the impacts of vegetation coverage on thermal patterns in woodlands. Ecohydrology 2013, 6, 754-764.

Company

Global Academy Jobs works with over 250 universities worldwide to promote academic mobility and international research collaboration. Global problems need international solutions. Our jobs board and emails reach the academics and researchers who can help.

"The globalisation of higher education continues apace, driving in turn the ongoing development of the global knowledge economy, striving for solutions to the world’s problems and educating a next generation of leaders and contributors."

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