『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 km2 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 SiO2 a-1. This equals
an average specific flux of 2.26 t SiO2 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.
Keywords: Dissolved silica; North America; Nutrients; Global change』
1. Introduction
2. Methods
3. Results
4.1. General discussion
4.2. Land-cover and ecosystem influences
4.3. Extrapolation uncertainty
4.4. Projection uncertainty
4.5. Implications for marine systems
5. Conclusions
Acknowledgements
References