Quantifying biotic and abiotic Si fluxes in the Critical Zone with Ge/Si ratios along a gradient of erosion rates

Silicon (Si) is an important nutrient for many plant and algae species, the ultimate source of Si silicate mineral weathering reactions. These topics have inspired application isotope geochemistry to quantifying cycling in Critical Zone, though interpretations are often equivocal. Because germanium (Ge) similar that Si, Ge/Si ratio considered a tracer provides additional constraints on cycling. Here, we provide ratios three sites span gradient erosion rates thus time material spends zone before being removed. We present bulk rock, soil saprolite, clay-size fractions, biomass, river water from Central Swiss Alps, southern Californian Sierra Nevada, highlands Sri Lanka. Our data perform two functions. First, they insight into system. In particular, document presence substantial pool Ge biomass not associated with phytoliths, suggesting overall plants do discriminate against relative during uptake. also quantify preferential incorporation clay minerals. show secondary clays may be better proxy intensity (the fraction denudation achieved chemically) than solutes. minerals as well or even silicon isotopes proxies. Second, used conjunction develop catchment mass-balance model. It suggests export secondary, fractionated solids (largely material) becomes increasingly at shorter regolith residence times: 80−24+15% total solubilized rapidly eroding Alps site, vs. id="u2" overflow="scroll">32−20+22% slowly Lanka site. The results suggest surprisingly large contributor these catchments, likely equivalent 25 to110 % dissolved export.