Mechanisms of carbon delivery, transport and evasion in tropical streams

Mechanisms of carbon delivery, transport and evasion in tropical streams

Closing date: 
31 October 2018
Study Type: 
PhD

 

Background

Headwater streams are tightly coupled to their surrounding terrestrial environment, with both surface and subsurface networks ensuring direct connectivity between hillslopes, riparian zones and streams. Because of this tight coupling, headwater streams receive large inputs of terrestrially-derived carbon, which they actively process, store and release1,2. The inflow of groundwater saturated with soil-respired CO2 is often the dominant source of dissolved inorganic carbon (DIC) to headwater streams3,4, whereas in-stream metabolism is often seen as a minor source of DIC due to short water residence times in the channel network5. However, the relative contributions of external (terrestrially-derived) versus internal (in-stream metabolism) carbon sources to the stream pool remain largely unconstrained.

A significant proportion of the DIC delivered to streams is rapidly released to the atmosphere as CO2 due to typically high turbulence6-8, but accurately capturing this highly localised evasion process remains difficult with existing methodologies. In wet-dry tropical areas, DIC delivery and evasion to and from streams may be particularly dynamic at seasonal and event scales, with disproportionately high rates during the wet season. Because tropical streams are likely to be major hotspots of terrestrial carbon export9-11, there is an urgent need for new observations and methodologies that contribute to reducing uncertainties on carbon fluxes to and from these systems.

Objectives

This PhD project will build upon ongoing work funded by ARC and NESP grants. The successful candidate will seek to improve understanding of the delivery and fate of terrestrially-derived carbon in tropical streams. Possible aims will include:

  • Assessing the dominant water flowpaths contributing to carbon delivery to streams, and the way these vary with varying flow regime;
  • Providing robust estimates of the CO2 evasion flux at a range of spatial and temporal scales;
  • Investigating in-stream carbon metabolism and delineating the provenance of dissolved carbon between internal and external sources.

The project will be based at Charles Darwin University (CDU), and will provide opportunity to work within an interdisciplinary team of biogeochemists, hydrologists, and carbon cycling scientists from CDU, the University of Washington and the University of Costa Rica.

Approach

The candidate will use Manton Creek as a study site to test their hypotheses. Manton Creek is a perennial stream located near Darwin, in a relatively undisturbed area representative of the native Australian tropical savanna. The project will combine hydrological and biogeochemical field techniques, including high-frequency measurements of dissolved solutes (CO2, organic carbon, oxygen, electrical conductivity), isotopic dating of water and carbon sources, and/or small-scale experiments to determine gas transfer velocities and internal metabolism rates.

Data analysis will involve a range of approaches such as time-series analysis, end-member mixing, coupled hydrology-biogeochemistry modelling, etc.

Supervisory team

Prof. Lindsay Hutley (CDU-RIEL); Dr Clément Duvert (CDU-RIEL); Dr David Butman, Asst. Prof. at the University of Washington (USA); Dr Christian Birkel, Assoc. Prof. at the University of Costa Rica.

Qualification requirements

Applicants are required to have a MSc or a BSc with 1st class honours (or equivalent) in a relevant science discipline such as hydrology, geochemistry, environmental science and/or ecology. The candidate must demonstrate strong numerical skills (Matlab or R) and significant fieldwork experience.

Application

All interested candidates are first required to make contact with Clément Duvert (clem.duvert@cdu.edu.au) to discuss their application.

Enrolment will then be subject to the candidate obtaining a Research Training Program scholarship through CDU. Note that the likelihood of obtaining an RTP scholarship is very high for candidates with a 1st class Honours (domestic) or with previously published peer-reviewed article(s) (international). The deadline for applications to the CDU Research Office is 31 October 2018, for a start of the PhD project in early 2019.

The RTP living allowance is $27,082 per year (2018 rate) free of tax. A relocation allowance of up to $2,000 is also available, and top-up scholarships can be applied for through external sources.

References

(1) Cole et al. 2007, Ecosystems  (2) Butman & Raymond 2011, Nature Geoscience  (3) Campeau et al. 2017, Scientific Reports  (4) Crawford et al. 2013, JGR: Biogeosciences  (5) Hotchkiss et al. 2015, Nature Geoscience  (6) Öquist et al. 2009, Environmental Science & Technology  (7) Campeau et al. 2018, JGR: Biogeosciences  (8) Deirmendjian & Abril 2018, Journal of Hydrology  (9) Regnier et al. 2013, Nature Geoscience  (10) Lauerwald et al. 2015, Global Biogeochemical Cycles  (11) Sawakuchi et al. 2017, Frontiers in Marine Science.

lindsay-hutley's picture
Lindsay Hutley
Professor of Environmental Science
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Clément Duvert
Research fellow