Land-use Drives Seasonal Riverine Si Cycling at the Landscape Scale

Silicon (Si) is an important element in the environment and is required for diatom production. Bedrock type, weathering rate and terrestrial vegetation are factors known to influence dissolved Si fluxes at the landscape scale, however the combined effect of these factors, along with anthropogenic influences on Si concentration and seasonal Si cycling is yet unknown. Using the provincial water quality monitoring network dataset (PWQMN) provided by the Ontario Ministry of Environment (Canada), Satellite data from The Ontario Land Cover Database (OMNR), we tested several factors that may influence dissolved silica (DSi) concentration and the annual DSi concentration range (as a proxy for seasonal cycling) for 79 river and stream monitoring stations within 53 distinct sub-watersheds in Ontario, Canada, for the years 2005 to 2011 in single and multivariate analyses. Our results indicate that the annual average DSi concentration is not affected by land-use type. The annual range in DSi, however, is positively influenced by the percent of land under agriculture, and negatively influenced by the amount of land covered by forests. Because average DSi is not affected by land-use, increased N and P loads associated with agricultural activity mean lowered Si:N and Si:P ratios in river water. Increased annual DSi range implies changes to both the timing and the quantity of Si delivered to downstream coastal environments, which may have implications for seasonal diatom production and carbon sequestration.