Science Beneath Our Feet – Ruth Pereira

About Ruth Pereira

She is the author of 173 publications in international journals (Hindex of 41, and more than 6430 sections), 14 chapters in international books and 8 chapters in national books. Supervised 8 postdocs, 23 doctoral students (8 ongoing) and 61 master’s students (59 completed). All doctoral students held a FCT scholarship. She was PI of 6 international projects/ 12 national projects. Participated in 19/28 international/national projects. She has participated in several European and national evaluation panels of projects and grants. She was associated editor of Ecotoxicology and Environmental Safety journal for 5 years.

Comment on Froger et al., 2024, paper:

Under the scope of the new Soil Monitoring Law proposal (SML), under discussion between the Member States (MS), the European Parliament and the Commission, will request MS to characterize and monitor the evolution of soil health within their territory. In other aspects, the data collected will support decision-making on defining new soil management practices (for example aimed at increasing soil carbon storage) and for restoring soil health.

Soil monitoring at a continental scale is very recent (about 15 years). But at a lower geographical scale, while some MS have traditionally implemented its national soil information monitoring system (N-SIMS), with some doing so for decades, in others, existing data is scattered, obtained for different purposes or to address specific legal requirements, and not supported by harmonized sampling guidelines. Soil sampling design and methodology are crucial components of a soil monitoring framework that may determine the reliability of analytical results, or at least how they can be interpreted and support balanced decisions.

With the enforcement of the SML on the horizon, the LUCAS topsoil survey appears as the most promising approach to support the harmonization of soil health data collection, benefiting from the already existing network of sampling sites in the territory of the MS. Nevertheless, considering the relevance of data collected through N-SIMS, Froger and collaborators (2024) analyzed if these datasets, could be combined with the LUCAS topsoil survey and if the conclusions based, on various soil indicators, are consistent.

The authors start presenting several limitations of the previous soil sampling campaigns under the LUCAS topsoil survey (herein mentioned only as LUCAS): i) namely the low representativeness of land uses other than arable lands and grasslands; ii) the displacement of LUCAS sampling points between campaigns (80% displacements of about 10 m), iii) the reduced amount of analysis for some parameters (e.g. bulk density only in 10% of the sites in the 2018 campaign) and, iv) the modification of sampling depth (from 0-20 to 0-30 cm) between campaigns.

Regarding N-SIMS, the variability in soil monitoring also hampers the comparison between MS. The main differences found were related to aspects as soil monitoring strategies, sometimes land cover specific, soil sampling depths, the set of soil properties measured, site coverage area (km2), the overall coverage of the MS territory and the representativeness of different land cover and soil types. In a general way, cambisols and luvisols were oversampled to the detriment of others. Therefore, remarkable differences were found not only among N-SIMS but also when comparing with the LUCAS topsoil survey, despite being recognized that LUCAS 2022 campaign made an effort to correct some of these aspects.

The authors also selected three soil properties (clay, organic carbon-OC and pH_H20) to compare the results between N-SIMS and LUCAS, concluding that despite the differences between MS and land cover, only the results of clay content are consistent between monitoring systems. The analysis was complemented with the evaluation of two soil health indicators (OC/clay ratio and pHH2O classes), and it was found that the distribution of sites in OC/clay ratio and pH classes were different between MS and between N-SIMS and LUCAS. In what regards, the first indicator, sometimes the differences in the proportion of soils classified as very good were more related to OC content, while in other cases with clay content. As for pH, the discrepancies were especially observed for more acidic and intermediate pH levels.

Froger and co-authors (2024) suggested that the discrepancies observed between the soil parameters are likely due not only to differences in sampling design, but also on sampling protocols and analytical methods. Disparities in sampling depth may explain discrepancies in OC, between monitoring schemes, for some MS but not for others that have a sampling depth like the one of LUCAS (0-20 cm). Differences in sampling densities among different land uses and other methodological aspects, such as the removal of litter layer, may also play a role.

It was concluded that N-SIMS cannot be harmonized among MS and cannot be replaced by the LUCAS soil survey. They must be assumed to serve different and important purposes at national and supranational levels. The harmonization of analytical protocols among N-SIMS and with LUCAS is also not recommendable, as MS will lose the ability to to use their historical data and follow temporal evolution on their soils’ health. A concerted action may account for including some common measurements at N-SIMS, and collaboration with LUCAS can also serve the purpose of increasing sampling density and the requiring representativeness of soil types, land cover, land use, and climate in all the monitoring frameworks. Instead of pursuing the use of common protocols, the analysis of many common sites will contribute to generating “transfer functions” and for estimating the degree of uncertainty associated with the conversion of data obtained for soil parameters determined by different analytical protocols. The authors also highlighted the importance of considering deeper soil layer analysis in all the monitoring systems.

In summary, the careful reading of Froger and co-authors’ (2004) analysis confirms that the harmonization of sampling protocols and sampling design is indeed a complex task, even for more localized purposes, as to compare the effect of soil monitoring practices on soil health. Although each MS may follow its own N-SIMS, at the living labs (LL) level, for the sake of the transferability of practices between experimental sites or even between LL, the comparability of the results and, therefore, the harmonization of sampling and analytical methods is of utmost importance. That can be achieved by adopting the LUCAS topsoil survey methodology, which has a transboundary implementation. Experimental sites at LL and lighthouses should be complementary sites to increase the coverage of LUCAS topsoil survey, and this may be made in parallel with the other objectives of the experimental sites in addressing specific soil threats and the effectiveness of new soil management practices, which may require some adaptions of monitoring frameworks. Only through this way LL can effectively demonstrate their value to improve soil health at the continental scale, as it the objective of the EU Soil Mission.

Reference: Froger, C., Tondini, Elena, Arrouays, D., Oorts, K., Poeplau, C., Wetterlind, J., Putku, E., Saby, N.P.A., Fantappiè, M., Styc, Q., Chenu, C., Salomez, J., Callewaert, S.,  Vanwindekens, F.M., Huyghebaert, B., Herinck, J., Heilek, S., Harbo, L.S., de Carvalho Gomes, L. Lázaro-López, A., Bispo, A., 2024. Comparing LUCAS Soil and national systems: Towards a harmonized European Soil monitoring network. Geoderma Volume 449, 117027. https://doi.org/10.1016/j.geoderma.2024.117027