Changes in dissolved silica mobilization into river systems draining North America until the period 2081–2100

Abstract

Dissolved silica (DSi) is an important control on algae abundance and species composition both in freshwater and marine ecosystems. Although continental and global budgets for DSi exist, understanding of the spatial variability of DSi cycles needs to be improved on those scales. In this study, an empirical model of DSi mobilization into river systems is extrapolated on a 1.4 km 2 grid to North America. To analyze changes in DSi mobilization patterns, DSi mobilization is estimated regionally for present day runoff and a runoff projection ensemble for the period 2081–2100. The model predicts present day annual DSi fluxes for the monitored area within 6% of the calculated fluxes. Possible biases by processes not directly represented by applied geodata are discussed (e.g. land use and ecosystem influences) and found to be only minor on the regional scale. Uncertainty of the results is discussed based on a literature review. The projected DSi-mobilization rates at high latitudes for the present day conditions may be overestimated. However, the projected change rate for the period 2081–2100 might even be underestimated, due to e.g. increased thawing in certain permafrost regions, which was not included in the model. The present DSi mobilization into North American rivers is estimated to 44.4 Mt SiO 2 a − 1 . This equals an average specific flux of 2.26 t SiO 2 km − 2 a − 1 . Applying the future runoff projection ensemble increases the specific DSi flux by 12.8%. For the present day conditions only 9% of the total area contributes to 50% of the DSi flux into river systems. This underscores the large regional differences on the North American continent. Analyses of tributary areas of distinct regional seas and coastal zones result in DSi mobilization increases of up to 68.3% for the Canadian Archipelago Basin tributary area. While in general a large increase at high latitudes is projected, in southern North America, slight decreases in DSi mobilization predominate. The highest DSi mobilization decrease of 13.3% is projected for the tributary rivers of the Gulf of California.