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Tanentzap Group: The role of algae in the Arctic carbon cycle


Supervisor: Andrew Tanentzap (Plant Sciences

Importance of the area of research:

Freshwaters are a major conduit for transporting carbon among the land, oceans, and atmosphere, but how much carbon is fixed and respired along the way by algae remains an uncertain but important flux in the global carbon cycle (Drake et al. 2017). Carbon enters inland waters through the export of either terrestrial organic matter or inorganic carbon released from soil respiration (e.g. free CO2 and CH4) and geological weathering (e.g. carbonate ions). Despite these different sources, few studies have identified which sources are photosynthetically-fixed within inland waters and the factors that influence this variation. This question may be especially important to resolve in the northern circumpolar region that has among the highest density of freshwaters and largest carbon stocks on Earth. Moreover, these carbon stocks have accumulated over hundreds to thousands of years, because frozen and waterlogged soils have slowed microbial decomposition. Rapid warming and drying of northern latitudes now risks accelerating the export of carbon into inland waters and could generate a positive feedback to global climate change.

What the project will involve:

The aim of this PhD is to understand the sources of photosynthetically-fixed carbon to algae in northern waters and their contribution to regional carbon budgets. The first part of this PhD will involve repeatedly surveying 30 Arctic streams using isotopic tracers (e.g. 13C and 14C; Ishikawa et al. 2014) and mass balance calculations (e.g. Rasilo et al. 2017). The student will use mixing models to estimate the contribution of different sources towards algal biomass and how these vary with landscape context, e.g. permafrost thaw and hydrology. The student will also monitor the productivity and biomass of algae and bacteria in these sites to quantify how much old (i.e. millennial-aged) carbon on an absolute basis is incorporated into the aquatic food web versus lost downstream. The second part of this PhD will involve combining information on algal resource use and biomass in different contexts and scaling up these results with geospatial data to revise regional carbon budgets. Finally, the student may develop an experiment to test how changes to soil carbon export influence algal carbon use.

What the student will be doing:

The student will design a multi-year field study and collect all the associated data, working in remote locations for long periods of time with a field assistant. In the lab, they will identify algal taxa and measure their biomass and productivity along with routine water chemistry. Isotope measurements will be outsourced to external laboratories. The student will also be responsible for performing statistical and geospatial analyses and hydrological modelling.

Training that will be provided:

The student will be given training in field work (including algal monitoring), experimental design, and statistical and hydrological modelling (including computer programming). The student will also be enrolled in a NERC postgraduate course in algal taxonomy and field identification skills.


  • Drake, T.W., Raymond, P.A., Spencer, R.G.M. 2018. Terrestrial carbon inputs to inland waters: A current synthesis of estimates and uncertainty. Limnology and Oceanography Letters 3:132-142.
  • Ishikawa, N.F., Uchida, M., Shibata, Y. 2014. Carbon storage reservoirs in watersheds support stream food webs via periphyton production. Ecology 95:1264-71.
  • Rasilo, D., et al. 2017. Transport and transformation of soil-derived CO2, CH4 and DOC sustain CO2 supersaturation in small boreal streams. Science of the Total Environment 579:902-912.




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