Post-doctoral research 2013-
Recent research has recognized that consumers in aquatic systems, besides relying on indigenous primary production, can utilize terrestrial organic matter imported from the terrestrial surroundings. The relative importance of terrestrial organic matter for consumers in aquatic food webs (i.e. allochthony) remains unclear due to methodological limitations. Preliminary estimates indicate that as much as 70–90% of the dissolved organic matter in the Bothnian Bay (Scandanavia) has a terrestrial origin and thus it is likely that it plays an important role for consumers. Using δ13C, δ15N and δ2H stable isotopes I aim to (1) quantify allochthony in intermediate and top consumers, (2) determine patterns and control of allochthony in aquatic consumers across salinity gradients, and (3) to determine if the use of terrestrial organic matter by aquatic consumers repress or subsidize aquatic secondary production. This project is funded by the Kempe foundation and is integrated into the current ECOCHANGE programme being conducted in the Bothnian Bay.
Summary of previous research
Research Engineer 2011-2012
Phytoplankton production in lakes outside of high nitrogen deposition areas tend to be nitrogen-limited or co-limited by nitrogen and phosphorus. Part of my research examined nitrogen and phosphorus limitation seasonally along an altitudinal lake gradient in Abisko, Sweden. We found the lakes to be primarily nitrogen limited, except at the highest altitudes. Therefore, increased nitrogen deposition could increase phytoplankton production in these lakes, but only if combined with increased temperatures, as production was limited by temperature for a large part of the year (Bergström et al. 2013).
I am also involved in a large scale project (3 y, 6 lakes) measuring how nitrogen addition affects food web dynamics and pelagic-benthic linkages along a lake gradient of dissolved organic carbon concentrations.
I have been co-applicant and organiser of a large scale mesocosm experiment in Medimeer, France, as part of the MesoAqua programme. This experiment examined the effects of a sediment pulse on relative pelagic and benthic production and food web dynamics in a marine lagoon.
PhD thesis 2006-2011
Some of the major problems we face today are human induced changes to the nitrogen (N), phosphorus (P) and carbon (C) cycles. Predicted increases in rainfall and temperature due to climate change, may also increase dissolved organic matter inflows to freshwater ecosystems in the boreal zone. N, P, C and light, are essential resources that most often limit bacterial (BP) and phytoplankton production (PPr) in the pelagic zone of lakes. PPr and BP not only constitute the total basal C resource for the pelagic aquatic food web, but also influence ecosystem function and biogeochemical cycles.
During my doctoral studies at Umeå University, Sweden, within the LEREC group, I examined how N, P, C and light affect the relative and absolute rates of PPr and BP. This was studied along a wide latitudinal and trophic gradient using published data, and in two in situ mesocosm experiments in an oligotrophic lake. In the experiments I manipulated not only bottom-up drivers of production, but also top-down predation to examine how these factors interact to affect pelagic food web structure and function.
Globally the most important predictors of areal and volumetric PPr were latitude, total-N, and lake shape. BP tended to be relatively stable, therefore the BP:PPr ratio was primarily affected by changes in PPr (Faithfull et al. 2011). In Northern Sweden where N-deposition is low, PPr was primarily N-limited and BP was P- and C-limited, therefore bacteria and phytoplankton were not directly competing for nutrients (Faithfull et al. 2010). Although the energy pathway from bacteria to higher consumers is generally longer than from phytoplankton to zooplankton and fish, increased BP still stimulated the biomass of rotifers, calanoid copepods and planktivorous fish. This appeared to be mediated through intermediate bacterial grazers such as flagellates and ciliates (Faithfull et al. 2011; Faithfull et al. 2012). Interaction effects between top-down and bottom-up drivers were evident in middle of the food web (i.e. rotifers and ciliates), which suggests more effort should be made to examine these frequently overlooked trophic levels.
Honours thesis 2004
Cyanobacterial blooms are a considerable problem to water users and also tend to affect energy transfer through aquatic food webs negatively. Cyanobacteria can reach high cell concentrations rapidly under favourable conditions due to entrainment of resting stages (i.e. akinetes) from the sediments. During my honours thesis I studied the interactive effects of sediment location and salinity on the germination of Anabaena flos-aquae akinetes from a shallow, tidally influenced lake. Littoral sediments showed higher akinete germination rates than open water sediments and akinete germination was not affected by increasing salinity. Consequently sea-level rise and increased salinity in this lake will not influence akinete germination, although filament growth was negatively affected by increased salinity (Faithfull & Burns 2006).