Role at Cawthron
Simon is an ecosystem ecologist who researches nutrient cycling and food web processes. A common theme running through his research is identifying sources and pathways of nitrogen pollution and quantifying food web impacts. Simon has applied this research across the aquatic spectrum from headwater streams through to lakes and estuaries. Examples of this research include identifying and examining how nitrogen derived from invasive gorse affects streams and the macroinvertebrate communities; and, how nutrient recycling by food webs (i.e. nutrient excretion) mediates the response of lakes to increased catchment runoff.
While Simon’s research is applied in nature, he draws strongly on theoretical understanding of ecosystem and community ecology. This has been applied to a variety of applications ranging from lake restoration plans and analysis of monitoring data through to expert evidence on regional water quality policy and investigating novel monitoring tools. Simon has also worked on several MBIE funded research projects and contracted reports for regional councils and NGOs.
Technical skills, experience and interests
- Preparing technical advice and expert evidence related to nutrient limits and management.
- 10 years’ experience applying stable isotope biogeochemistry to applied environmental questions.
- Development of methods for quantifying NH4+ δ15N and NO3- δ15N & δ18O and has widely applied bulk δ13C & δ15N as well as compound-specific amino-acid δ15N analyses on a range of food web samples.
- Molecular ecology techniques (e.g. eDNA) for both streamlined routine biodiversity monitoring, as well as novel insights into aquatic food web structure.
- Broad modelling background having experience with a range of mechanistic models from simple Lotka-Volterra predator-prey models through to highly resolved hydrodynamic fluid models.
- Experience using a range of statistical models to analyse data, including expertise in using Bayseian mixing models to estimate diet composition in food webs.
- Stewart SD, Young MB, Harding JS and Horton WT 2019. Invasive Nitrogen-Fixing Plant Amplifies Terrestrial–Aquatic Nutrient Flow and Alters Ecosystem Function. Ecosystems.
- Stewart SD, Hamilton DP, Baisden WT, Verburg P and Duggan IC 2018. The role of mobile consumers in lake nutrient cycles: A brief review. Hydrobiologia: 818: 11–29.
- Stewart SD, Hamilton DP, Baisden WT, Dedual M, Verburg P, Duggan IC, Hicks BJ and Graham BS 2017. Variable littoral-pelagic coupling as a food-web response to seasonal changes in pelagic primary production. Freshwater Biology 62: 2008.
- Cyr H, Collier KJ, Clearwater SJ, Hicks BJ and Stewart SD 2017. Feeding and nutrient excretion of the New Zealand freshwater mussel Echyridella menziesii (Hyriidae, Unionida): Implications for nearshore nutrient budgets in lakes and reservoirs. Aquatic Sciences 79: 557.
- Rogers KM, Sim M, Stewart SD, Phillips A, Cooper J, Douance R, Pyne R and Rogers P 2015. Investigating C-4 sugar contamination of manuka honey and other New Zealand honey varieties using carbon isotopes. Journal of agricultural and food chemistry 62: 2605-2614.