With this data, we expand the data set characterizing the Critical Zone geochemistry along the Chilean Coastal Cordillera provided by Oeser et al. (2018). This data set completes the results of bulk geochemical analysis of bedrock and regolith with those of bulk analysis of major plants and those of the bio-available fraction in saprolite and soil (determined using a modified sequential extraction method on bulk regolith samples after Arunachalam et al., 1996;He et al., 1995;Tessier et al., 1979). For all those compartments of the Earth’s Critical Zone, we further present radiogenic (87Sr/86Sr) and stable (δ88/86Sr) strontium isotope ratios. A detailed graphical presentation and discussion of this data as well as method description is given in Oeser and von Blanckenburg, (2020a): Do degree and rate of silicate weathering depend on plant productivity? and Oeser and von Blanckenburg, (2020b): Strontium isotopes trace biological activity in the Critical Zone along a climate and vegetation gradient.
Using this data, we were thus, able to determine weathering rates and nutrient uptake along the “EarthShape” climate and vegetation gradient in the Chilean Coastal Cordillera and to identify the sources of mineral nutrients to plants. Ultimately, we were able to budget inventories, gains and losses of nutritive elements in and out of these ecosystems and to quantify nutrient recycling. We found that the weathering rate does not increase from north to south along the climate gradient. Instead, the increase in biomass growth rate is accommodated by faster nutrient recycling. Instead, the increase in biomass nutrient demand is accommodated by faster nutrient recycling. In the absence of an increase in weathering rate despite a five-fold increase in precipitation and NPP, we hypothesize that plant growth might in fact dampen weathering rates. Radiogenic and stable Sr isotopes in combination with mass balance calculations were used to detect the Sr sources and quantify its fluxes in four ecosystems along the “EarthShape” climate and vegetation gradient. Estimated whole-plant Sr isotope compositions reveal a preferential uptake of light Sr from soil solution and subsequent export of fractionated organic material from the ecosystems. This export correlates well with erosion rate E and potentially impairs the ability for direct Sr acquisition from solid plant debris and thus reduces the recycling factor of Sr and possibly Ca and that of other mineral nutrients, too.
All samples are assigned with International Geo Sample Numbers (IGSN), a globally unique and persistent Identifier for physical samples. The IGSNs are provided in the data tables and link to a comprehensive sample description in the internet.
Tables included in this data publication:
Table S1: Chemical composition, radiogenic strontium (87Sr/86Sr), stable strontium (δ88/86Sr), and molar Ca/Sr ratios of representative bedrock samples from Pan de Azúcar, Santa Gracia, La Campana, and Nahuelbuta
Table S2: Weathering indices CDF and τ, radiogenic strontium (87Sr/86Sr), stable strontium (δ88/86Sr), and molar Ca/Sr ratios of the 2 × 4 regolith profiles.
Table S3: Concentration of the bio-available fraction, comprised of the water-soluble and the exchangeable fraction.
Table S4: Concentration of the water-soluble and the exchangeable fraction, and the relative amount of the bio-available fraction (pooled water-soluble and exchangeable fraction) on bulk regolith.
Table S5: Chemical composition of the study sites’ single plant organs along with their respective radiogenic strontium (87Sr/86Sr), stable strontium (δ88/86Sr), and molar Ca/Sr ratios
Concentrations of in-situ-produced cosmogenic 10Be in river sediment are widely used to estimate catchment-average denudation rates. Typically, the 10Be concentrations are measured in the sand fraction of river sediment. However, the grain size of bedload sediment in most bedrock rivers covers a much wider range. Where 10Be concentrations depend on grain size, denudation rate estimates based on the sand fraction alone are potentially biased. To date, knowledge about catchment attributes that may induce grain-size-dependent 10Be concentrations is incomplete or has only been investigated in modelling studies. Here we present an empirical study on the occurrence of grain-size-dependent 10Be concentrations and the potential controls of hillslope angle, precipitation, lithology, and abrasion.
We first conducted a study focusing on the sole effect of precipitation in four granitic catchments located on a climate gradient in the Chilean Coastal Cordillera. We found that observed grain size dependencies of 10Be concentrations in the most-arid and most-humid catchments could be explained by the effect of precipitation on both the scouring depth of erosion processes and the depth of the mixed soil layer. Analysis of a global dataset of published 10Be concentrations in different grain sizes (n=73 catchments) – comprising catchments with contrasting hillslope angles, climate, lithology, and catchment size – revealed a similar pattern. Lower 10Be concentrations in coarse grains (defined as “negative grain size dependency”) emerge frequently in catchments which likely have thin soil and where deep-seated erosion processes (e.g. landslides) excavate grains over a larger depth interval. These catchments include steep (> 25°) and humid catchments (> 2000mm yr-1). Furthermore, we found that an additional cause of negative grain size dependencies may emerge in large catchments with weak lithologies and long sediment travel distances (> 2300–7000 m, depending on lithology) where abrasion may lead to a grain size distribution that is not representative for the entire catchment. The results of this study can be used to evaluate whether catchment-average denudation rates are likely to be biased in particular catchments.
Samples from the Chilean Coastal Cordillera were processed in the Helmholtz Laboratory for the Geochemistry of the Earth Surface (HELGES). 10Be/9Be ratios were measured at the University of Cologne and normalized to the KN01-6-2 and KN01-5-3 standards. Denudation rates were calculated using a time-independent scaling scheme according to Lal (1991) and Stone (2002) (St scaling scheme) and the SLHL production rate of 4.01 at g-1 yr-1 as reported by Phillips et al. (2016)
The global compilation exists of studies that measured 10Be concentrations in different grain sizes from the same sample location. We only included river basins of <5000 km2 which measured 10Be concentrations in at least one sand-sized fraction <2 mm and at least one coarser fraction >2 mm. Catchment parameters have been recalculated using a 90-m SRTM DEM.
The data are presented in Excel and csv tables. Table S1 describes the characteristics of the samples catchments, Table S2 includes the grain size dependent 10Be-concentrations measured during this study and Table 3 the global compilation of grain size dependent 10Be-concentrations. All samples of this study (the Chilean Coastal Cordillera) are assigned with International Geo Sample Numbers (IGSN). The IGSN links are included in Table S2 and in the Related References Section on the DOI Landing Page. The data are described in detail in the data description file and in van Dongen et al. (2018) to which they are supplementary material to.
The effects of climate and topography on soil physico-chemical and microbial parameters were studied along an extensive latitudinal climate gradient in the Coastal Cordillera of Chile (26° - 38°S). The study sites encompass arid (Pan de Azúcar), semiarid (Santa Gracia), mediterranean (La Campana) and humid (Nahuelbuta) climates and vegetation, ranging from arid desert, dominated by biological soil crusts (biocrusts), semiarid shrubland and mediterranean sclerophyllous forest, where biocrusts are present but do have a seasonal pattern to temperate-mixed forest, where biocrusts only occur as an early pioneering development stage after disturbance. All soils originate from granitic parent materials and show very strong differences in pedogenesis intensity and soil depth.
Most of the investigated physical, chemical and microbiological soil properties showed distinct trends along the climate gradient. Further, abrupt changes between the arid northernmost study site and the other semi-arid to humid sites can be shown, which indicate non-linearity and thresholds along the climate gradient. Clay and total organic carbon contents (TOC) as well as Ah horizons and solum depths increased from arid to humid climates, whereas bulk density (BD), pH values and base saturation (BS) decreased. These properties demonstrate the accumulation of organic matter, clay formation and element leaching as key-pedogenic processes with increasing humidity. However, the soils in the northern arid climate do not follow this overall latitudinal trend, because texture and BD are largely controlled by aeolian input of dust and sea salts spray followed by the formation of secondary evaporate minerals. Total soil DNA concentrations and TOC increased from arid to humid sites, while areal coverage by biocrusts exhibited an opposite trend. Relative bacterial and archaeal abundances were lower in the arid site, but for the other sites the local variability exceeds the variability along the climate gradient. Differences in soil properties between topographic positions were most pronounced at the study sites with the mediterranean and humid climate, whereas microbial abundances were independent on topography across all study sites.
In general, the regional climate is the strongest controlling factor for pedogenesis and microbial parameters in soils developed from the same parent material. Topographic position along individual slopes of limited length augmented this effect only under humid conditions, where water erosion likely relocated particles and elements downward. The change from alkaline to neutral soil pH between the arid and the semi-arid site coincided with qualitative differences in soil formation as well as microbial habitats. This also reflects non-linear relationships of pedogenic and microbial processes in soils depending on climate with a sharp threshold between arid and semi-arid conditions. Therefore, the soils on the transition between arid and semi-arid conditions are especially sensitive and may be well used as indicators of long and medium-term climate changes. Concluding, the unique latitudinal precipitation gradient in the Coastal Cordillera of Chile is predestined to investigate the effects of the main soil forming factor – climate – on pedogenic processes.
The data presented here is part of the German-Chilean Priority Program “EarthShape” (Earth Surface Shaping by Biota), funded by the German Research Foundation (DFG). We provide the basic background data, which includes investigations into the influence of climate, vegetation and topography on pedogenesis and microbial abundances. The data are supplementary material to Bernhard et al. (2018).
All tables are available as one Excel file, as individual tables in .csv format in a zipped archive and as PDF file. The samples are assigned with International Geo Sample Numbers (IGSN) and linked to a comprehensive sample description in the internet.
The content of the five data tables is:
Table S1: Soil profile field description for the EarthShape study sites
Table S2: Soil physico-chemical properties for the depth increment samples in the four study sites
Table S3: Soil physico-chemical properties for the horizon samples in the four study sites
Table S4: Relative microbial abundances in the four study sites
Table S5: Plant species and abundance (% cover) in the four study sites