I have tested different ways of measuring P cycling in streams at the sediment water interface. I have provided a mathematical derivation linking the Elovich equation (used in bottle and flume studies) to the exponential decay equation (used in nutrient spiralling studies) - Demars 2008. This allowed to directly compare the results of different methods and showed the bottle method to be inadequate (Stutter et al 2010). I have also combined a stoichiometric approach with whole stream metabolism and nutrient spiralling studies to partition P cycling into the abiotic, algal and bacterial compartments.
Impact of point source pollution on P cycling
I have tested experimentally the effect of P reduction and addition from sewage treatment plant at the river reach and catchment scale (e.g. Demars et al 2005 Hydrology & Earth System Sciences, Stutter et al 2010).
Integrating carbon, nitrogen and phosphorus cycling
Current work investigates experimentally the effect of adding dissolved organic carbon (DOC) on N and P cycling in upland streams at Glensaugh research station. The fate of added DOC has been traced through the food-web using stable isotopes in collaboration with Nikolai Friberg (NIVA, Norway), Barry Thornton (The James Hutton Institute), Joanna Kemp (SEPA Aberdeen, Scotland) and Baptiste Marteau (University of Aberdeen, Scotland). The in-stream interactions between the elements is being modelled combining whole stream metabolism, stoichiometry, nutrient spiralling and isotopic tracers.
This work is currently expanded as part of the Turf2Surf NERC project, notably in collaboration with Paul Withers (Bangor University, Wales) and Joshua Thompson (now at Smithsonian Environmental Research Centre, USA). Comparative surveys in C, N, P spiralling studies were carried out along contrasting carbon gradients in the Conwy (Wales) and Ribble (England) river basins. Further experimental work integrating nutrient diffusive substrata with metabolic chambers is being carried out at the James Hutton Institute in collaboration with Marc Stutter to investigate the effects of temperature, nutrients and light on humic acid degradation.