Mid-infrared spectroscopy determines the provenance of coastal marine soils and their organic and inorganic carbon content

Lewis Walden; Oscar Serrano; Zefang Shen; Mingxi Zhang; Paul Lavery; Zhongkui Luo; Lei Gao; Raphael A Viscarra Rossel

doi:10.1016/j.scitotenv.2024.174871

Mid-infrared spectroscopy determines the provenance of coastal marine soils and their organic and inorganic carbon content

Sci Total Environ. 2024 Nov 1:949:174871. doi: 10.1016/j.scitotenv.2024.174871. Epub 2024 Jul 20.

Authors

Lewis Walden¹, Oscar Serrano², Zefang Shen³, Mingxi Zhang³, Paul Lavery², Zhongkui Luo⁴, Lei Gao⁵, Raphael A Viscarra Rossel³

Affiliations

¹ Soil & Landscape Science, School of Molecular & Life Sciences, Faculty of Science & Engineering, Curtin University, GPO Box U1987, Perth, WA 6845, Australia. Electronic address: lewis.walden@curtin.edu.au.
² Centro de Estudios Avanzados de Blanes, Consejo Superior de Investigaciones Científicas, Blanes 17300, Spain; School of Science & Centre for Marine Ecosystems Research, Edith Cowan University, Joondalup, WA 6027, Australia.
³ Soil & Landscape Science, School of Molecular & Life Sciences, Faculty of Science & Engineering, Curtin University, GPO Box U1987, Perth, WA 6845, Australia.
⁴ Institute of Applied Remote Sensing and Information Technology, College of Environmental and Resource Sciences, Zhejiang University, Hangzhou 310058, China.
⁵ Environment Business Unit, Commonwealth Scientific and Industrial Research Organisation, Waite Campus, Urrbrae, SA 5064, Australia.

PMID: 39038672
DOI: 10.1016/j.scitotenv.2024.174871

Abstract

Vegetated coastal ecosystems (VCE), encompassing tidal marshes, mangroves, and seagrasses, serve as significant 'blue' carbon (C) sinks. Improving our understanding of VCE soils and their spatial and temporal dynamics is essential for conservation efforts. Conventional methods to characterise the dynamics and provenance of VCE soils and measure their total organic carbon (TOC) and inorganic carbon (TIC) contents are cumbersome and expensive. We recorded the mid-infrared (MIR) spectra and measured the TOC and TIC content of 323 subsamples across consistent depths from 106 soil core samples. Using the spectra of each VCE, we determined their mineral and organic composition by depth. We then used a regression tree algorithm, cubist, to model TOC and TIC contents. We rigorously validated the models to test their performance with a 10-fold cross-validation, bootstrapping, and a separate random test dataset. Our analysis revealed distinct mineralogical and organic MIR signatures in VCE soils that correlated with their position within the seascape. The spectra showed decreased clay minerals and increased quartz and carbonate with distance from freshwater inputs. The mineralogy of tidal marsh and mangrove soils differed with depth, showing larger absorptions due to carbonate and quartz and weakening clay minerals and organics absorptions. The mineralogy of the seagrass soils remained the same with depth. The cubist models to estimate TOC and TIC content were accurate (Lin's concordance correlation, ρ_c≥ 0.92 and 0.93 respectively) and interpretable, confirming our understanding of C in these systems. These findings shed light on the provenance of the soils and help quantify the flux and accumulation of TOC and TIC, which is crucial for informing VCE conservation. Moreover, our results indicate that MIR spectroscopy could help scale the measurements cost-effectively, for example, in carbon crediting schemes and to improve inventories. The approach will help advance blue C science and contribute to the conservation and protection of VCE.

Keywords: Blue carbon; Ecosystem services; Mid-infrared spectroscopy; Soil inorganic carbon; Soil organic carbon; Vegetated coastal ecosystems.