Mathematics – Logic
Scientific paper
Dec 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011e%26psl.312...48m&link_type=abstract
Earth and Planetary Science Letters, Volume 312, Issue 1, p. 48-58.
Mathematics
Logic
Chemical Weathering, Solute Fluxes, Global Carbon Cycle, Erosion, Climate Change
Scientific paper
The role of fluid residence time and catchment length scales in controlling the chemical composition of rivers is evaluated by comparing numerical simulations and scaling arguments to concentration-discharge data from small catchments. The analysis suggests that poorly-crystalline aluminosilicates are an important control on the composition of stream waters and therefore chemical equilibrium between the dissolving and precipitating phases determines the maximum concentration and the maximum silicate weathering flux. The modeling results suggest that the residence time of fluid relative to the residence time required to approach chemical equilibrium can be used to assess the controls on solute fluxes in small catchments, and possibly larger rivers. Catchments that show little variability in concentration with discharge (or "chemostatic behavior") likely have average fluid residence times that exceed the time required to reach chemical equilibrium. Conversely, decreases in concentration with increasing discharge are explained by average residence times shorter than required to approach chemical equilibrium, resulting in dilution. Solute fluxes are also strongly impacted by the distribution of fluid residence times in a basin. The fluid residence time model provides an alternative framework for assessing both the relationship between discharge and concentration observed for individual catchments, and controls on the solute fluxes of rivers. If fluid residence times are a dominant control on weathering fluxes, the chemistry of different rivers could vary entirely as a function of the nature subsurface flow paths and the composition of the system at equilibrium, which is complex to predict and strongly coupled to biological processes, temperature and the composition of the system. As a result of thermodynamic and hydrologic restrictions on the amount of weathering, global solute fluxes may depend more strongly on the geometry, relief, runoff and permeability of basins then on temperature and rates of erosion.
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