Abstract
Rapid, low-cost methods for large-scale assessments of soil organic carbon (SOC) are essential for climate change mitigation. Our work explores the potential for citizen scientists to gather soil colour data as a cost-effective proxy of SOC instead of conventional lab analyses. The research took place during a 2-year period using topsoil data gathered by citizen scientists and scientists from urban parks in the UK and France. We evaluated the accuracy and consistency of colour identification by comparing “observed” Munsell soil colour estimates to “measured” colour derived from reflectance spectroscopy, and calibrated colour observations to ensure data robustness. Statistical relationships between carbon content obtained by loss on ignition (LOI) and (i) observed and (ii) measured soil colour were derived for SOC prediction using three colour components: hue, lightness, and chroma. Results demonstrate that although the spectrophotometer offers higher precision, there was a correlation between observed and measured colour for both scientists (R2 = 0.42; R2 = 0.26) and citizen scientists (R2 = 0.39; R2 = 0.19) for lightness and chroma, respectively. Foremost, a slightly stronger relationship was found for predicted SOC using the spectrophotometer (R2 = 0.69), and citizen scientists produced comparable results (R2 = 0.58), highlighting the potential of a large-scale citizen-based approach for SOC monitoring.
Highlights
Soils are the second largest active pool of carbon after the oceans, and account for more than three times the amount of carbon stored in the atmosphere and terrestrial vegetation combined [1]
Spectroscopic data were used to evaluate the accuracy of the visual soil colour measurements; we evaluated the level of precision afforded by the spectrophotometer by taking five measurements of the same soil solution
This study demonstrates that soil colour gathered by citizen scientists for soil colour–soil organic carbon (SOC) estimations is comparable with results obtained from spectrally derived colour (R2 = 0.58 ∼ 0.69)
Summary
Soils are the second largest active pool of carbon after the oceans, and account for more than three times the amount of carbon stored in the atmosphere and terrestrial vegetation combined [1]. The carbon storage capacity of soils has been a subject of great interest in recent environmental literature, exemplified by an increasing number of publications in mapping soil carbon stocks [2]. It has caught the attention of a wide audience, including policymakers, NGOs, and land managers. This growing interest is mainly due to the realization of soils’ key role as either a natural sink of carbon for climate change mitigation [3,4,5] or as a potentially large and uncertain source of CO2 emissions [6].
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