Simulating loss of primary silicate minerals from soil due to long-term weathering using Allogen: Comparison with soil chronosequence,lake sediment and river solute flux data

This paper presents ALLOGEN, a process model of soil mineral chemical weathering. Though designed principally to aid interpretation of lake sediment geochemical records by providing mass balance constraints for competing interpretations, the model is also applicable to more general questions about long-term weathering and soil development. The model is constructed around a generalised version of the mineral-weathering submodel of PROFILE, modified to minimise the need for site-specific data and to optimise performance for long-term change. Comparison with observed weathering rate data (river flux studies, chronosequences and lake sediment chemical stratigraphy) suggests that soil mineral depletion can be usefully simulated over timescales applicable to Quaternary and Holocene studies. To illustrate this, the plausibility of a weathering interpretation is demonstrated for sediment records at Lake Hope Simpson and Moraine Lake and the lake chronosequence at Glacier Bay. While long-term soil mineral depletion appears predictable, reliable simulation of past runoff quality is hampered by lack of a suitable long-term model for soil carbon.