Assessing soil redistribution of forest and cropland sites in wet tropical Africa using &amp;lt;sup&amp;gt;239+240&amp;lt;/sup&amp;gt;Pu fallout radionuclides

Wilken, Florian; Fiener, Peter; Ketterer, Michael E.; Meusburger, Katrin; Muhindo, Daniel; Oost, Kristof Van; Doetterl, Sebastian

doi:10.5194/soil-7-399-2021

Cited by 16 publications

(20 citation statements)

References 49 publications

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“…Isotopes of beryllium (meteoric 10 Be), plutonium ( 239+240 Pu) and caesium ( 137 Cs) are widely used in Earth sciences to reconstruct, for example, Earth's palaeomagnetic field [4][5][6], snow palaeoaccumulation rates [7], seafloor sedimentation rates [8] and denudation rates [9] and to determine the age of fluvial terraces [10][11][12], evaluate seawater exchange cycles [13] and long-distance Asian dust transport [14], among several other processes. More recently, these isotopic tools have been used to investigate soil erosion processes in various environments, such as grasslands and forests of the European Alps or the Rocky Mountains [15][16][17][18][19][20][21], in arable lands, forests and grasslands of tropical and subtropical areas and the wet-dry tropics [22][23][24][25][26], in forested mountainous regions [21,27], forests and arable lands under continental Mediterranean climates [28][29][30][31], in moraine landscapes used as farmlands and forests [2,[32][33][34][35], in loess regions that are dominated by agriculture [36][37][38][39][40] or in post-fire forests and deserts areas [41,42].…”

Section: Introductionmentioning

confidence: 99%

Meteoric 10Be, 137Cs and 239+240Pu as Tracers of Long- and Medium-Term Soil Erosion—A Review

et al. 2022

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Isotopes of meteoric 10Be, 137Cs, 239+240Pu have been proposed as a soil redistribution tracer and applied worldwide as an alternative method to classical field-related techniques (e.g., sediment traps). Meteoric 10Be provides information about long-term soil redistribution rates (millennia), while 137Cs and 239+240Pu give medium-term rates (decades). A significant progress in developing new models and approaches for the calculation of erosion rates has been made; thus, we provide a global review (n = 59) of research articles to present these three isotopes (meteoric 10Be, 239+240Pu and 137Cs) as soil erosion markers in different environments and under different land-use types. Understanding the dynamics and behaviours of isotopes in the soil environment is crucial to determine their usefulness as soil erosion tracers; thus, we discuss the chemical–physical behaviour of meteoric 10Be, 137Cs and 239+240Pu in soils. The application of these isotopes sometimes has strong limitations, and we give suggestions on how to overcome them or how to adapt them to a given situation. This review also shows where these isotopic methods can potentially be applied in the future. A lack in knowledge about soil redistribution rates exists particularly in loess-dominated areas where the tillage system has changed or in areas with strong wind erosion.

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Section: Introductionmentioning

confidence: 99%

Meteoric 10Be, 137Cs and 239+240Pu as Tracers of Long- and Medium-Term Soil Erosion—A Review

et al. 2022

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“…Furthermore, low N and P availability limits microbial growth and activities and therefore affects the cycling of organic matter (Jing et al, 2020;Liu et al, 2015). Thus, nutrient limitations in highly weathered tropical soil likely force plant communities to alter belowground and aboveground C allocation (Doetterl et al, 2015a;Fisher et al, 2013;Wright et al, 2011), with more roots growing in organic rich topsoil, reducing C input to deeper soil layers (Addo-Danso et al, 2018), thereby affecting SOC stocks.…”

Section: Introductionmentioning

confidence: 99%

Heterotrophic soil respiration and carbon cycling in geochemically distinct African tropical forest soils

Bukombe

Fiener

Hoyt

et al. 2021

SOIL

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Abstract. Heterotrophic soil respiration is an important component of the global terrestrial carbon (C) cycle, driven by environmental factors acting from local to continental scales. For tropical Africa, these factors and their interactions remain largely unknown. Here, using samples collected along topographic and geochemical gradients in the East African Rift Valley, we study how soil chemistry and fertility drive soil respiration of soils developed from different parent materials even after many millennia of weathering. To address the drivers of soil respiration, we incubated soils from three regions with contrasting geochemistry (mafic, felsic and mixed sediment) sampled along slope gradients. For three soil depths, we measured the potential maximum heterotrophic respiration under stable environmental conditions and the radiocarbon content (Δ14C) of the bulk soil and respired CO2. Our study shows that soil fertility conditions are the main determinant of C stability in tropical forest soils. We found that soil microorganisms were able to mineralize soil C from a variety of sources and with variable C quality under laboratory conditions representative of tropical topsoil. However, in the presence of organic carbon sources of poor quality or the presence of strong mineral-related C stabilization, microorganisms tend to discriminate against these energy sources in favour of more accessible forms of soil organic matter, resulting in a slower rate of C cycling. Furthermore, despite similarities in climate and vegetation, soil respiration showed distinct patterns with soil depth and parent material geochemistry. The topographic origin of our samples was not a main determinant of the observed respiration rates and Δ14C. In situ, however, soil hydrological conditions likely influence soil C stability by inhibiting decomposition in valley subsoils. Our results demonstrate that, even in deeply weathered tropical soils, parent material has a long-lasting effect on soil chemistry that can influence and control microbial activity, the size of subsoil C stocks and the turnover of C in soil. Soil parent material and its control on soil chemistry need to be taken into account to understand and predict C stabilization and rates of C cycling in tropical forest soils.

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“…Therefore, these low reference bulk samples were removed from further analysis. Bulking of Pu samples causing a dilution of the Pu activity should be avoided, particularly in areas of high erosion or low initial fallout (Wilken et al, 2021). Here, we were able to resolve the dilution problem due to the availability of Cs-137 data, as the Cs-137 to Pu-239+240 activity ratios were valuable in identifying the suitability of the reference samples.…”

Section: Pu-239+240 Distribution At the Reference Sitesmentioning

confidence: 92%

Validating Plutonium-239+240 as novel soil redistribution tracer – a comparison to measured sediment yield

Meusburger

Porto²,

Waldis³

et al. 2022

Preprint

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Abstract. Quantifying soil redistribution rates is a global challenge addressed with direct sediment measurements (e.g., traps), models and isotopic, geochemical and radiogenic tracers. The isotope of Plutonium, namely Pu-239+240, is a relatively new soil redistribution tracer in this challenge. Direct validation of Pu-239+240 as soil redistribution is, however, still missing. We used a unique sediment yield time series in Southern Italy, reaching back to the initial fallout of Pu-239+240 to verify Pu-239+240 as a soil redistribution tracer. Distributed soil samples (n=55) were collected in the catchment, and at potential undisturbed reference sites (n=22), Pu-239+240 was extracted, measured with ICP-MS and converted to soil redistribution rates. Finally, we used a Generalized Additive model (GAM) to regionalize soil redistribution estimates for the catchment. For the catchment sites, mean Pu-239+240 inventories were significantly reduced (16.8 ± 10.2 Bq m-2) compared to the reference inventory (40.5 ± 3.5 Bq m-2,) indicating the dominance of erosion. Converting these inventory losses into soil erosion rates resulted in an average soil loss of 22.2 ± SD 7.2 t ha-1 yr-1. The uncertainties of the approach stemmed mainly from the high measurement uncertainties of low-activity samples where samples have been bulked over depth. Therefore, we recommend taking incremental soil samples and extracting ~20 g of soil. The geographic coordinates and the flow accumulation best described the spatial pattern of erosion rates in the GAM model. Using those predictors to upscale Pu-derived soil redistribution rates for the entire catchment resulted in an average on-site loss of 20.7 t ha-1 yr-1, which corresponds very well to the long-term average sediment yield of 18.7 t ha-1 yr-1 measured at the catchment outlet and to Cs-137 derived soil redistribution rates. Overall, this comparison of Pu-derived soil redistribution rates with measured sediment yield data validates Pu-239+240 as a suitable retrospective soil redistribution tracer.

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Assessing soil redistribution of forest and cropland sites in wet tropical Africa using <sup>239+240</sup>Pu fallout radionuclides

Cited by 16 publications

References 49 publications

Meteoric 10Be, 137Cs and 239+240Pu as Tracers of Long- and Medium-Term Soil Erosion—A Review

Meteoric 10Be, 137Cs and 239+240Pu as Tracers of Long- and Medium-Term Soil Erosion—A Review

Heterotrophic soil respiration and carbon cycling in geochemically distinct African tropical forest soils

Validating Plutonium-239+240 as novel soil redistribution tracer – a comparison to measured sediment yield

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