Abstract

Research from biological and geological sources has highlighted the role of volcanoes in the outgassing of P, and thermal fixation and subsequent atmospheric oxidation of NO_x in volcanic environments. The impact of these nutrient fluxes on biological systems has been demonstrated on present-day Hawai'i, and here we consider the impact on the plant communities within a large igneous province (LIP). The Miocene Columbia River Basalt Province, the youngest LIP on Earth, contains many sedimentary interbeds between the flows of the major extrusive phase, and these interbeds preserve variable but often diverse palynofloras. By integration of palynofloral analysis with analysis of macronutrient levels in the interbeds it can be suggested that there may have been significantly elevated levels of P within the lava field proximal to the source vents, a distribution mirrored by Ca and Mg. Evidence for potential volcanogenic eutrophication is restricted to >10³ year duration interbeds, contemporary with eruptive activity elsewhere in the LIP. The geochemistry and palynology of other interbeds demonstrate nutrient deficiency, with a potential route to nutrient sufficiency available from long-term symbiotic N-fixation. Elsewhere within the Columbia River Basalt Province, this process is short-circuited by the imput of felsic ash from the nearby Cascades Range of volcanoes.