Impact of weed invasion on soil erosion, carbon and nitrogen fluxes to tropical streams

Impact of weed invasion on soil erosion, carbon and nitrogen fluxes to tropical streams

Closing date: 
31 October 2017
Study Type: 
PhD

Background

Land use change and weed invasion pose an increasing threat to tropical savannas of northern Australia. Over the last two decades, significant areas of savanna woodlands have been transformed due to grassy weed invasion, resulting in altered fire regimes and enhanced tree mortality (Setterfield et al., 2013). This process can transform native savannas to grasslands in this region in relatively short time periods (Ferdinands et al., 2006).

Tropical savannas occur in high rainfall environments and operate under highly seasonal hydrological regimes. Because of substantial throughputs of water and carbon during the wet season, the degradation of these ecosystems may have considerably higher impacts on soil and river ecology than similar land transformation in temperate areas (Wohl et al., 2012). Higher rates of precipitation are likely to increase the vulnerability of the sandy topsoils to erosion, which will ultimately cause higher carbon and nutrient inputs to streams. Changes in riverine carbon and nutrient fluxes can in turn have profound effects on water quality, habitat condition and the trophic state of aquatic systems.

While nutrient and carbon transport in undisturbed tropical streams has previously been quantified (e.g. McDowell and Asbury, 1994; Saunders et al., 2006), there has been limited work on the effects of land degradation on these riverine fluxes. There is an urgent need to determine how soil erosion rates, and riverine export of carbon and nutrients, change with weed invasion. Assessing the cumulative impacts of land transformation at different scales will help better inform land use planning and management practices in northern Australia. This is critical especially in an era of proposed expansion of primary production across northern Australia.

Objectives

This project will build upon ongoing work led by the supervisors and funded by an ARC Discovery (2016-2018) and a National Environmental Science Programme (NESP) grant (2017-2020). Both projects examine the impacts of land use change on carbon and water fluxes in northern Australia. OzFlux eddy covariance sites provide measures of carbon input and respiratory loss at unimpacted savanna sites of the region (AU-How, AU-Ad, AU-Daly), providing baseline data on the nature of carbon cycling in non-impacted, native savanna systems.

For this PhD proposal, three sub-catchments will be monitored that support different states of land degradation: (i) native savanna, (ii) moderate weed invasion and (iii) severe weed invasion. The candidate will combine novel remote sensing technology at the plot scale and high-frequency measurements of water, carbon and nutrient fluxes at the sub-catchment scale.

The aims of the project are:

  • to quantify soil erosion rates at the plot scale for each sub-catchment;
  • to quantify the riverine export of solutes (dissolved inorganic and organic carbon; nitrate) in each sub-catchment;
  • to assess the impact of weed invasion on carbon and nutrient cycling and their transfer to streams.

Supervisory team

Prof. Lindsay Hutley; Assoc. Prof. Samantha Setterfield (University of Western Australia); Dr Natalie Rossiter-Rachor; Dr Clément Duvert; Assoc. Prof. Shaun Levick.

Qualification requirements

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

Application

Enrolment to this project will be subject to the candidate obtaining a Research Training Program scholarship through Charles Darwin University. The deadline for applications is 31 October 2017 (details on how to apply at http://www.cdu.edu.au/research/ori/admissions). The living allowance for a RTP is $27,082 per year (2018) free of tax. A relocation allowance of up to $2,000 is also available. There is also a possibility of a top-up scholarship of $5,000 per year.

 

International applicants for whom English is not their first language must attain a satisfactory English language test score (Academic IELTS 6.5 with no band less than 6 or TOEFL 575).

Research environment – Contact

Charles Darwin University (CDU) is a young and dynamic university, which has developed an excellent research reputation in its short history. CDU has been ranked in the top 4 in Australia and New Zealand for research in Environmental Science (Reuters). The Research Institute for the Environment & Livelihoods (RIEL; http://riel.cdu.edu.au) provides a vibrant, multidisciplinary research environment that currently comprises around 50 scientists and 75 PhD students (roughly one-third international).

The project is aligned with the NESP – Northern Hub and partner researchers at the University of Western Australia.

For additional information on the position, please contact Lindsay Hutley (lindsay.hutley@cdu.edu.au), Samantha Setterfield (samantha.setterfield@uwa.edu.au), or Natalie Rossiter-Rachor (natalie.rossiter-rachor@cdu.edu.au).

References

Ferdinands K., Setterfield S., Douglas M., Barratt J., 2006. Africanising the tropical woodlands: canopy loss and tree death  following gamba grass Andropogon gayanus invasion. In: Proceedings of the 15thAustralian Weeds Conference, eds. R.G. Richardson and F.J. Richardson. Weed Management Society of South Australia, Adelaide. 296pp.

McDowell W.H., Asbury C.E., 1994. Export of carbon, nitrogen, and major ions from three tropical montane watersheds. Limnol. Oceanogr. 39, 111–125.

Saunders T.J., McClain M.E., Llerena C.A., 2006. The biogeochemistry of dissolved nitrogen, phosphorus, and organic carbon along terrestrial aquatic flowpaths of a montane headwater catchment in the Peruvian Amazon. Hydrol. Process. 20, 2549–2562.

Setterfield S.A., Rossiter-Rachor N.A., Douglas M.M., Wainger L., Petty A.M., Barrow P., Shepherd I.J., Ferdinands K.B., 2013. Adding fuel to the fire: the impacts of non-native grass invasion on fire management at a regional scale. PLoS One 8, e59144.

Wohl E. et al., 2012. The hydrology of the humid tropics. Nat. Clim. Change 2, 655–662.

lindsay-hutley's picture
Lindsay Hutley
Professor of Environmental Science