Research ArticleAPPLIED ECOLOGY

Global patterns of dust and bedrock nutrient supply to montane ecosystems

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Science Advances  06 Dec 2017:
Vol. 3, no. 12, eaao1588
DOI: 10.1126/sciadv.aao1588
  • Fig. 1 Fluxes of bedrock and dust in eroding soils.

    Inputs of soil from dust (D) and bedrock (B) are balanced by outputs from chemical and physical erosion (collectively termed E) on an eroding hillslope. E is a proxy for the sum of inputs from D and B because in steady state, D + B = E and the DSI is equal to fd. All inputs and outputs reflect total mass flux from both inorganic and organic fractions. Several previous studies have explicitly included dust in the soil mass balance of an eroding hillslope (1618). Here, we adopt the conceptual model of Ferrier et al. (18), which considers net inputs and outputs over an entire watershed (that is, from ridge to channel), consistent with resolution of both the global dust models and the catchment-wide 10Be-based erosion rates.

  • Fig. 2 The DSI in mountain catchments around the world.

    (A) DSI calculated from a compilation of 10Be-based erosion rates (24) and a global model of LGM dust fluxes (28). (B) DSI from (A) in relation to modern MAP and mean annual temperature (MAT) for each sampling location, with modern biomes delineated by dashed lines [after the work of Whittaker (33)]. (C) Same as (B) except that DSI is inferred using modern instead of LGM dust fluxes. The star indicates a DSI of 0.15 calculated from direct observations of dust fluxes and 10Be-based erosion rates in the southern Sierra Nevada, California (20, 34). The uncertainty in individual DSI estimates is approximately an order of magnitude due to the order-of-magnitude uncertainty in dust deposition rates (28).

  • Fig. 3 Soil residence times, dust fluxes, and DSI from the global database.

    (A) Bivariate density plot of DSI and catchment-wide erosion rates. Here, DSI is calculated from 10Be-based erosion rates (24) and LGM dust fluxes (28). It is commonly higher at sites with longer soil residence times, calculated for a 1-m-thick soil with a density of 1.8 g cm−3 (see Materials and Methods). The gray region marks estimated residence times that are greater than or equal to 20,000 years, highlighting instances where soils may harbor legacies of dust accumulation from the LGM, when fluxes were much higher than they are today. (B and C) DSI is also high at sites with high dust input rates, and there is little correlation between rates of erosion and dust deposition. Together, these observations suggest that erosion rates and dust input rates contribute roughly equally to observed global patterns in DSI.

  • Fig. 4 Erosion rates and dust fluxes in the southern Sierra Nevada, California.

    (A) Four southern Sierra Nevada catchments where erosion rates have been measured by both 10Be and sediment yields. The star indicates the location of the Providence dust collection site in the study of Aciego et al. (20). (B) 10Be-based erosion rates (see Materials and Methods), sediment yield-based erosion rates (38), and modeled LGM and modern dust fluxes (28) for eight southern Sierra Nevada catchments. Observed dust deposition rate from the Providence dust collection site is also displayed. P concentration in dust collected at the Providence dust collection site is 2.5 times greater than the average P concentration in local bedrock (20), suggesting that the modeled DSI is underestimated at this site. Error bars reflect propagated analytical uncertainty in 10Be-based erosion rates and SEM of seven measurements for sediment yield-based erosion rates. The range for dust fluxes represents order-of-magnitude uncertainty in modeled dust fluxes and observed range in measured dust fluxes at the dust collection site (20).

  • Fig. 5 Nd isotopes reveal plant utilization of dust-derived nutrients.

    εNd measurements in bedrock, soil, and pine needles are combined with εNd measured in dust collected nearby (Fig. 4) in previous work (20). fd,Nd reflects the fraction of Nd that is dust-derived based on a two-component isotopic mixing model. Errors bars show internal reproducibility (1 SD).

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/3/12/eaao1588/DC1

    fig. S1. Combination of existing global data sets.

    fig. S2. Systematically higher DSI in soils with longer residence times.

    fig. S3. Comparison of LGM-based DSI estimates and modern DSI estimates in Idaho.

    table S1. Global DSI estimates from 10Be-based erosion rates (24) and global models of modern and LGM dust fluxes (28).

    table S2. DSI estimates for the southern Sierra Nevada and central Idaho.

    table S3. Nd isotopic measurements (εNd) of southern Sierra Nevada bedrock, soil, and pine needles.

    table S4. fd,Nd for southern Sierra Nevada soils and pine needles.

    table S5. P/Nd ratios of southern Sierra Nevada bedrock.

    table S6. P and Nd concentrations of southern Sierra Nevada dust and bedrock.

  • Supplementary Materials

    This PDF file includes:

    • fig. S1. Combination of existing global data sets.
    • fig. S2. Systematically higher DSI in soils with longer residence times.
    • fig. S3. Comparison of LGM-based DSI estimates and modern DSI estimates in Idaho.
    • Legends for tables S1 to S6

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    Other Supplementary Material for this manuscript includes the following:

    • table S1 (Microsoft Excel format). Global DSI estimates from 10Be-based erosion rates (24) and global models of modern and LGM dust fluxes (28).
    • table S2. (Microsoft Excel format). DSI estimates for the southern Sierra Nevada and central Idaho.
    • table S3. (Microsoft Excel format). Nd isotopic measurements (εNd) of southern Sierra Nevada bedrock, soil, and pine needles.
    • table S4. (Microsoft Excel format). fd,Nd for southern Sierra Nevada soils and pine needles.
    • table S5. (Microsoft Excel format). P/Nd ratios of southern Sierra Nevada bedrock.
    • table S6. (Microsoft Excel format). P and Nd concentrations of southern Sierra Nevada dust and bedrock.

    Download Tables S1 to S6

    Files in this Data Supplement: