Terrestrial ecosystem growth and sustainability relies on access to mineral-derived nutrients such as phosphorus, calcium, magnesium, and potassium. The result is a routing of some of these elements into living biomass and litter before they are discharged to streams, leading to a significant influence of ecosystem dynamics on river chemistry.

At the scale of large river catchments, this routing is observable through the difference between elemental supply to catchments through rock weathering and corresponding elemental riverine export (Charbonnier et al. 2022). This is illustrated by two non-nutrient elements lithium (Li) and sodium (Na) and two bio-cycled elements potassium (K) and barium (Ba) across 20 of the largest world river catchments. Overall, the fluxes of elemental release from rock weathering are aligned with those of riverine export for both Li and Na, while the export fluxes of the two nutrients K and Ba are lower than their estimated geogenic inputs. This apparent depletion in mineral-derived nutrient river fluxes is attributed to two factors:

1. their long-term storage in soil and living biomass, and
2. episodic, poorly gauged erosive export of coarse organic debris from catchments.

Isotope constraints support this hypothesis, suggesting that the observed catchment-scale difference between nutrient and non-nutrient fluxes is evidence for the pervasive influence of biological uptake on rock-derived nutrients in river chemistry. 

Where local lithology does not offer an essential nutrient in sufficient abundance for ecological needs, or where rates of rock weathering are too low to match ecosystem demand for mineral-derived nutrients, exogenous dust inputs can serve as compensation. At an instrumented catchment located in Mt-Lozère, southern France, Saharan dust offers an additional source of calcium (Ca) to the watershed (Reina et al. 2025). Shallow soils, vegetation and stream water are all significantly enriched in Ca relative to the calcium-poor local granitic bedrock. Isotopic constraints again provide further evidence for the role of dust inputs to soil chemistry, and allow us to calibrate a reactive transport model accounting for the effect of dust addition and dissolution to soil, water, and vegetation chemistry. Our model results show the propagation of this exogenous input into the local weathering profile over the past ~15 kyr, and quantify alteration to mineral-specific reaction rates due to the addition of carbonate-rich dust.

Through this combination of field observations, geochemical tracing, and reactive transport modeling, our approach enables us to map the routing of mineral-derived nutrients through ecosystems. This quantitative capacity opens the possibility to leverage long-term monitoring of river solute chemistry to infer shifts in ecosystem nutrition under the influence of climate- or land-use change.

Critical zone, weathering, nutrient cycles, isotopes, geochemistry, dust, rivers, streams, reactive transport

Julien Bouchez

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