Abstract. For more than two decades, research groups in hydrology, ecology, soil science, and biogeochemistry have performed cryogenic water extractions (CWEs) for the analysis of δ2H and δ18O of soil water. Recent studies have shown that extraction conditions (time, temperature, and vacuum) along with physicochemical soil properties may affect extracted soil water isotope composition. Here we present results from the first worldwide round robin laboratory intercomparison. We test the null hypothesis that, with identical soils, standards, extraction protocols, and isotope analyses, cryogenic extractions across all laboratories are identical. Two standard soils with different physicochemical characteristics along with deionized (DI) reference water of known isotopic composition were shipped to 16 participating laboratories. Participants oven-dried and rewetted the soils to 8 and 20 % gravimetric water content (WC), using the deionized reference water. One batch of soil samples was extracted via predefined extraction conditions (time, temperature, and vacuum) identical to all laboratories; the second batch was extracted via conditions considered routine in the respective laboratory. All extracted water samples were analyzed for δ18O and δ2H by the lead laboratory (Global Institute for Water Security, GIWS, Saskatoon, Canada) using both a laser and an isotope ratio mass spectrometer (OA-ICOS and IRMS, respectively). We rejected the null hypothesis. Our results showed large differences in retrieved isotopic signatures among participating laboratories linked to soil type and soil water content with mean differences compared to the reference water ranging from +18.1 to −108.4 ‰ for δ2H and +11.8 to −14.9 ‰ for δ18O across all laboratories. In addition, differences were observed between OA-ICOS and IRMS isotope data. These were related to spectral interferences during OA-ICOS analysis that are especially problematic for the clayey loam soils used. While the types of cryogenic extraction lab construction varied from manifold systems to single chambers, no clear trends between system construction, applied extraction conditions, and extraction results were found. Rather, observed differences in the isotope data were influenced by interactions between multiple factors (soil type and properties, soil water content, system setup, extraction efficiency, extraction system leaks, and each lab's internal accuracy). Our results question the usefulness of cryogenic extraction as a standard for water extraction since results are not comparable across laboratories. This suggests that defining any sort of standard extraction procedure applicable across laboratories is challenging. Laboratories might have to establish calibration functions for their specific extraction system for each natural soil type, individually.
Since the late 1970s, several long-term ecological studies were conducted to better understand the biogeochemical functioning of Norway spruce stands in the Ardennes as these nutrient-poor ecosystems were subject to high levels of acid deposition and exhibited symptoms of tree health decline. Between 1978 and 2009, acid deposition declined sharply, especially sulfur and to a lesser extent nitrogen deposition. The aim of this study was (i) to determine if the Norway spruce stands recovered after the reduction of acid deposition and (ii) to explain why such a recovery occurred or not. Therefore, we collected data from different projects carried out in the Ardennes to characterize the long-term temporal trends in soil solution chemistry, foliar nutrition, and crown condition. In parallel, a model describing the nutrient cycling in forests (NuCM) was calibrated and used to check the consistency of the observed temporal trends and to explain them. The soil solution concentration of most of the elements decreased between 1978 and 2002, which was ascribed to a decrease in atmospheric deposition. For potassium, a decline in the exchangeable pool was also showed based on the simulation carried out with NuCM. As nitrogen (N) deposition remained at an elevated level, Norway spruce stands were progressively saturated in N and mineral nutrition became more and more unbalanced. Except the foliar N and Al concentration that remained constant and increased respectively, the foliar concentration of all other nutrients decreased between 1993 and 2009, which can be explained by the decrease in ion concentration in solution. These nutritional disorders weakened trees and were probably exacerbated during the 2003 summer drought, after which symptoms of vitality loss progressively appeared. In these N-saturated ecosystems, the N cycle was disrupted by this health decline, which increased NO 3 À leaching reinforcing soil acidification and risk of aluminum (Al) toxicity.
Abstract. For more than two decades, research groups in hydrology, ecology, soil science and biogeochemistry have performed cryogenic water extractions for the analysis of δ2H and δ18O of soil water. Recent studies have shown that extraction conditions (time, temperature, and vacuum) along with physicochemical soil properties may affect extracted soil water isotope results. Here we present results from the first worldwide round robin laboratory intercomparison. We test the null hypothesis that with identical soils, standards, extraction protocols and isotope analyses, cryogenic extractions across all laboratories are identical. Two ‘standard soils’ with different physicochemical characteristics along with deionized reference water of known isotopic composition, were shipped to 16 participating laboratories. Participants oven-dried and rewetted the soils to 8 % and 20 % gravimetric water content, using the deionized reference water. One batch of soil samples was extracted via pre-defined extraction conditions (time, temperature, and vacuum) identical to all laboratories; the second batch was extracted via conditions considered routine in the respective laboratory. All extracted water samples were analyzed for δ18O and δ2H by the lead laboratory (Global Institute for Water Security, GIWS, Saskatoon, CA) using both a laser and an isotope ratio mass spectrometer (OA-ICOS and IRMS, respectively). We rejected the null hypothesis. Our results showed large differences in retrieved isotopic signatures among participating laboratories linked to soil type and soil water content with mean differences to the reference water ranging from +18.1 ‰ to −108.4 ‰ for δ2H and +11.8 ‰ to −14.9 ‰ for δ18O across all laboratories. In addition, differences were observed between OA-ICOS and IRMS isotope data. These were related to spectral interferences during OA-ICOS analysis that are especially problematic for the clayey loam soils used. While the types of cryogenic extraction lab construction varied from manifold systems to single chambers, no clear trends between system construction, applied extraction conditions, and extraction results were found. Rather, differences between isotope results were influenced by interactions between multiple factors (soil type and properties, soil water content, system setup, extraction efficiency, extraction system leaks, and each lab’s internal accuracy). Our results question the usefulness of cryogenic extraction as a standard for water extraction since results are not comparable across laboratories. This suggests that defining any sort of standard extraction procedure applicable across laboratories is challenging. Laboratories might have to establish calibration functions for their specific extraction system for each natural soil type, individually.
15Regoliths encompass different materials from the fresh bedrock to the top of the organic 16 horizons. The occurrence and evolution of these materials are determined by deposition, 17 erosion and weathering processes that are specific for each region. The origin and interaction 18 of the regolith layers are still important issues in the study of critical zone functioning. 19Studies that attempt to understand the processes responsible for the structure and the 20 evolution of regoliths often focus either on the soil or on the bedrock compartment, and often 21 from a narrowly focused approach using just a single tool such as major element patterns or 22 mineralogy. This limits the understanding of the complete regolith composition and evolution. 23The present study proposes the combination of mineralogy, major and trace element 24 concentrations, and Sr-Nd-Pb-U isotopes as an extremely useful procedure for tracking the 25 Pleistocene Periglacial Slope Deposits (PPSD). The data allowed the differentiation of three 29 compartments within the regolith: 1) the organic compartment, where low 206 Pb/ 207 Pb and 30 87 Sr/ 86 Sr isotopic ratios reflected the impact of atmosphere-derived components; 2) the PPSD 31 compartment, whose upper horizons were characterised by the presence of atmosphere-32 derived particles rich in Cd, Sn, Sb, Hg and Pb and by relatively low 206 Pb/ 207 Pb and 87 Sr/ 86 Sr 33 ratios, whereas the lower horizons showed Nb enrichments in their matrix and a mineralogical 34 composition pointing to ancient volcanic events; and 3) the weathered slate compartment, 35 whose weathering progression and genetic relationship with the PPSD were particularly well 36 tracked with 87 Sr/ 86 Sr and 143 Nd/ 144 Nd isotope ratios, ( 234 U /238 U) activity ratios and positive 37Ce anomalies. The results prove the efficiency of radiogenic isotopes measurements 38 combined with the analysis of major and trace elements to complete regolith studies. 39Moreover, these isotopes and elements are shown to be potential geochemical tracers of 40 exchange processes at the water-mineral interface. This approach allows for the first time the 41 description of an evolution scheme of a complete slate regolith, which covers a large part of 42 the Rhenish Massif. 43 44
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