Fig 1.
(a) Geographic outline of the study area in the Emilia-Romagna Region, Northern Italy.
(b) The upper Val d’Arda-Mignano watershed. The main elevation peaks, elevation distribution, hydrographic elements, and other relevant toponyms are represented on the map. The location and distribution of sampling sites (fluvial sediments) are also reported. Base Map: Digital Terrain Model 5x5, Ed. 2014 (© Archivio Cartografico, Regione Emilia-Romagna; https://metasfera.regione.emilia-romagna.it/ricerca_metadato?uuid=r_emiro:2016-08-08T155835) (c) Explanatory excerpt showing the location of some sampling sites along the main channels and stream tributaries (d, e, f, g, h, i). Base Map: Technical Regional Map 1:5,000 (© Archivio Cartografico, Regione Emilia-Romagna; https://metasfera.regione.emilia-romagna.it/ricerca_metadato?uuid=r_emiro:2017-11-24T113154).
Fig 2.
Schematic methodological workflow used in the present study.
Fig 3.
Identification of the bands A, B, C, and D, within specific wavenumber regions, on a smoothed, baseline-corrected spectrum.
Table 1.
Indices for SOM characterization calculated as FTIR band ratios, used in the present study.
Table 2.
Terrain variables used in the present study, along with their geomorphological significance. Sources: [92,94–102].
Table 3.
Lithological groups of the upper Val d’Arda-Mignano watershed. Shapefile data derived from the Geological Units database of the Emilia-Romagna Region [1:10,000 scale; 110]. The description of the lithological groups was adapted from the Geological Sheet 198 – Bardi [1:50,000 scale; 59].
Table 4.
LULC types of the upper Val d’Arda-Mignano watershed. Shapefile data derived from Land use database of the Emilia Romagna Region [1:10,000 scale; 111].
Fig 4.
The three experimental designs employed in the present study: (a) ‘Upstream areas Exp_1’, (b) ‘Sources and sinks Exp_2’, (c) ‘Hazard areas Exp_3’.
The coloured areas delimited in the three experimental designs were used to extract values from the feature variables. This methodology was replicated for each of the 73 sediment samples (Fig 1b). Base Maps: Hillshade Map derived from DTM 5x5, Ed. 2014 (© Archivio Cartografico, Regione Emilia-Romagna; https://metasfera.regione.emilia-romagna.it/ricerca_metadato?uuid=r_emiro:2016-08-08T155835) and Technical Regional Map 1:5,000 (© Archivio Cartografico, Regione Emilia-Romagna; https://metasfera.regione.emilia-romagna.it/ricerca_metadato?uuid=r_emiro:2017-11-24T113154). Maps produced using the Esri© ArcMap software (version 10.3.1; ArcGIS).
Table 5.
FTIR Indices calculated for the 73 fluvial sediment samples in the upper Val d’Arda-Mignano watershed (cfr. Table 1).
Table 6.
Spearman’s rank correlation coefficients among the calculated FTIR indices (cfr. Table 1).
Fig 5.
Spatial distribution of FTIR indices (Table 1) within the upper Val d’Arda watershed (Fig 1b): (a) A/B, (b) A/D, (c) B/D, (d) C/D.
Values are classified into 10 classes according to the Jenks natural breaks method, for a better visual representation. Base Map: Hillshade Map derived from DTM 5x5, Ed. 2014 (© Archivio Cartografico, Regione Emilia-Romagna; https://metasfera.regione.emilia-romagna.it/ricerca_metadato?uuid=r_emiro:2016-08-08T155835). Maps produced using the Esri© ArcMap software (version 10.3.1; ArcGIS).
Fig 6.
Terrain variables of the upper Val d’Arda-Mignano watershed derived from GIS-based terrain analysis: (a) Elevation, (b) Flow Accumulation, (c) Slope, (d) Aspect, (e) Profile curvature, (f) Tangential curvature, (g) General curvature, (h) Total curvature, (i) Downslope Distance Gradient, (j) SAGA Wetness Index, (k) Terrain Ruggedness Index, (l) Stream Power Index, (m) Channel Network Base Level, (n) Vertical Distance to Channel Network.
Variables (a), (c), (d), (j), (k), (m), and (n) are displayed in the full range. Variables (b) and (l) are displayed by applying a stretching factor of 0.5 standard deviations for a better visual representation. Variables (e), (f), (g), (h), and (i) are displayed by applying a stretching factor of 2.5 standard deviations. Data source: all the maps are derived from the Digital Terrain Model 5x5, Ed. 2014 (© Archivio Cartografico, Regione Emilia-Romagna; https://metasfera.regione.emilia-romagna.it/ricerca_metadato?uuid=r_emiro:2016-08-08T155835). Maps produced using the SAGA software (version 8.1.1).
Fig 7.
Soil properties of the upper Val d’Arda-Mignano watershed: (a) SOC stock, (b) SOC %, (c) Clay %, (d) Silt %, (e) Sand %, (f) Skeleton %, (g) pH, (h) lithological groups, and (i) LULC types.
All the variables are displayed in the full range. (h) Lithological groups (Table 3): LI_1, Silicified Calcilutites and Silty Clays; LI_2, Varicoloured Clays and Shales; LI_3, Carbonate Turbidites; LI_4, Ophiolitic/Sedimentary Breccias and Olistoliths; LI_5, Arenaceous-Pelitic Turbidites. (i) LULC types (Table 4): LU_1, Coniferous forests; LU_2, Beech forests; LU_3, Oak, hornbeam and chestnut forests; LU_4, Riparian vegetation; LU_5, Cultivated fields; LU_6, Anthropic areas; LU_7, Bare surfaces/Rocky outcrops; LU_8, Sparse vegetation in evolution; LU_9, Meadows; LU_10, Bushes and shrubs. Data sources: (a) https://datacatalog.regione.emilia-romagna.it/catalogCTA/dataset/r_emiro_2023-08-09t162508; (b) https://datacatalog.regione.emilia-romagna.it/catalogCTA/dataset/r_emiro_2023-08-09t160758; (c, d, e, f) https://datacatalog.regione.emilia-romagna.it/catalogCTA/dataset/r_emiro_2023-08-02t140310; (g) https://datacatalog.regione.emilia-romagna.it/catalogCTA/dataset/r_emiro_2023-08-02t144815; (h) https://datacatalog.regione.emilia-romagna.it/catalogCTA/dataset/r_emiro_2017-06-12t113543; (i) https://geoportale.regione.emilia-romagna.it/catalogo/dati-cartografici/pianificazione-e-catasto/uso-del-suolo/layer-9 [106–111]. Maps produced using the SAGA software (version 8.1.1).
Table 7.
Models’ performance metrics for the three experiments (cfr. Fig 4).
Fig 8.
Permutation-based variable importance for the selected variables in the best-performing experiment for each FTIR index: (a) A/B, Experiment 1; (b) A/D, Experiment 1; (c) B/D, Experiment 3; (d) C/D, Experiment 1.
Fig 9.
Accumulated Local Effect (ALE) plots using the RF model for assessing A/B index, Experiment 1.
Fig 10.
Accumulated Local Effect (ALE) plots using the RF model for assessing A/D index, Experiment 1.
Fig 11.
Accumulated Local Effect (ALE) plots using the RF model for assessing B/D index, Experiment 3.
Fig 12.
Accumulated Local Effect (ALE) plots using the RF model for assessing C/D index, Experiment 1.