Linking carbon and iron cycles by investigating transport, fate and mineralogy of iron-bearing nanoparticles and colloids from peat-draining rivers - Scotland as a model for high-latitude rivers

Abstract

Iron plays an integral role in ocean biogeochemistry, regulating carbon transport and sequestration, and primary productivity via particulate phases. These particulate phases comprise nanoparticles and colloids that range in size below the traditional operational filter cut-off of 0.45 µm for ‘dissolved’ species. This means they are difficult to characterise mineralogically and often neglected as ‘dissolved iron’. Studies have investigated the covariation of iron with organic matter and the way that iron is transported from freshwater to saline systems. However, there remains a lack of understanding of the transport mechanisms. This understanding is imperative if we are to successfully apply iron biogeochemistry to climate models and begin to elucidate the role of iron in the environment. Therefore, there are ongoing efforts to find a reliable method to provide a mechanistic understanding of the transport of terrestrial, iron-bearing colloids and nanoparticles to the oceans. In their comprehensive 2012 review of the iron biogeochemical cycle, Raiswell and Canfield urge that we adopt a more mineralogical view to define the role of colloids and nanoparticles in aquatic (freshwater and marine) environments. The aim of my project was to develop a novel method using synchrotron-based Mössbauer techniques to investigate the speciation and mineralogy of iron in the nanoparticle and colloidal components of river and coastal waters. A cascade of filtering techniques was used to isolate these particles, to enable their quantification and characterisation. Here, I present an evaluation of these techniques for their applicability, and the results of the first successful SMS measurements, conducted at the European Synchrotron Radiation Facility, Grenoble (ID18, Nuclear Resonance Beamline).