Monitoring sedimentary areas from mine waste products with Sentinel‐2 satellite images: A case study in theSEof Spain

Abstract

Torrential rainfall regimes, among others, are the origin of accelerated soil erosion. The Spanish southeastern Mediterranean region is characterised by an arid climate regime affected by extreme erosion episodes with an important loss of sediments. Soil erosion effects are even more noticeable in areas where soil has been anthropically degraded, as in the mining district of Sierra Minera de Cartagena. The present research focuses on monitoring and mapping the changes in the sediment distribution of iron oxides and hydroxyl (OH−) bearing minerals caused by a cold drop known in Spanish as 'DANA' in September 2019 on the Rambla del Beal. This short rambla is fed by sediments from its drainage basin and by mining residues, irrigating a wide agricultural area. When discharges overflow the rambla channel, residues spread over its floodplain and reach the ecological protected coastal lagoon Mar Menor. The objective of the study was mapping the mineral distribution of the mining materials eroded from the source areas and sedimented in Rambla del Beal during a DANA. The study was carried out using a pre‐ and a post‐DANA image from the Sentinel‐2 satellite. After masking vegetation, urban areas and water bodies, different band ratios (B4/B3, B11/B12, B8A/B6) and a Spectral Angle Mapper (SAM) classification were applied. Sediment deposits were identified in wider areas after the DANA. Iron oxides increased their extension by 11.08% in the central area (B3/B4 with R2 of 0.84) and hydroxyl‐bearing minerals increased by 8.95% in the Rambla del Beal's headwaters (B11/B12 with R2 of 0.71). The SAM classification (with a 0.1 rad threshold and an overall accuracy of 87.33%) allowed the differentiation and classification of two ferric iron oxides (haematite and goethite) and one iron hydrous sulphate mineral (jarosite). Additionally, band ratio images were spatially overlaid with the soil land uses map layer of the cadastre in order to plot the land uses most affected by the transported sediments during the DANA. These results highlighted agricultural land as the areas (land uses) most affected by iron oxides deposition, as oxidation processes occur more rapidly in these areas. However, grassland and scrubland were the areas with the highest content of hydroxyl‐bearing minerals, as water is accumulated in these places, which favours hydrolysis reactions. Highlights Torrential events can relocate large volumes of contaminated sediments from former mining areas. Sentinel‐2 allows monitoring mine waste iron‐sulphate changes caused by weathering alteration. Spatial mineralogical pattern in sediments is controlled by geomorphology and flood dynamics. The proposed digital image analysis allows mapping short‐term evolution of mine waste sediments.

Let's give a voice to young soil researchers

“…On soil organic carbon, Tadiello et al (2023) carry out a global meta‐analysis to explore the effects of conservation agriculture, with a focus on Mediterranean and humid subtropical areas. Looking at soil monitoring and contamination, Rodríguez et al (2022) develop a tool for monitoring antibiotics in soils, while Pereira et al (2023) use a remote‐sensing approach to evaluate mine waste sediments. Regarding soil biodiversity, Burton et al (2023) use global databases to model how the soil biota responds to land use and soil properties, observing a local soil biodiversity reduction in all land uses compared with the undisturbed baseline.…”