Long-term monitoring of dissolved organic matter using a multi-analytical approach reveals spruce decline as a primary driver of soil solution browning
Abstract
Surface water browning is a widespread phenomenon in the Northern Hemisphere, although its underlying drivers remain debated. In this study, we combined 20 years of dissolved organic carbon (DOC) measurements with five years of optical characterization in soil solutions collected at multiple depths from two contrasting forest plots in the Strengbach catchment (Vosges Mountains, France): a spruce stand affected by dieback and a beech stand. We developed a conceptual framework to interpret the optical properties of DOC in soil solutions, based on commonly used indices and distinguishing between two endmembers: litter-derived and microbialderived signatures. Our results reveal a marked browning in soil solutions associated with spruce decline, characterized by increasing DOC and aromaticity. DOC concentrations increased significantly at several soil depths between 2004 and 2024, with an intensified increase following bark beetle infestation in 2013, reaching up to 2 ppm-C/year at 5 and 30 cm depth. This increase was accompanied by a shift towards more litter-derived DOC and a concomitant decrease in microbial-derived signatures, exacerbated in deeper soil solutions. A soil sequence representing a post-decline gradient further demonstrated that spruce decline increased soil lignin content, resulting in higher DOC and aromaticity in soil solutions, driven by litter input changes. The reduced microbial activity following clear-cut may explain the lower microbial signature. Overall, the disturbance of forest cover associated with spruce decline is a major driver of soil solution browning, raising concerns regarding the quality of downstream surface waters.
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BibTeX
@article{saphy2026longterm,
title = {{Long-term monitoring of dissolved organic matter using a multi-analytical approach reveals spruce decline as a primary driver of soil solution browning}},
author = {Adrien Saphy and Marie-Noëlle Pons and Sophie Rihs and Jeremy Masbou and Emilie Beaulieu and Marie-Claire Pierret},
journal = {Geoderma},
year = {2026},
month = aug,
doi = {10.1016/j.geoderma.2026.118012},
url = {https://univoak.hal.science/hal-05851465v1},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Long-term monitoring of dissolved organic matter using a multi-analytical approach reveals spruce decline as a primary driver of soil solution browning
AU - Adrien Saphy
AU - Marie-Noëlle Pons
AU - Sophie Rihs
AU - Jeremy Masbou
AU - Emilie Beaulieu
AU - Marie-Claire Pierret
PY - 2026
DA - 2026/08/29
JO - Geoderma
DO - 10.1016/j.geoderma.2026.118012
UR - https://univoak.hal.science/hal-05851465v1
AB - Surface water browning is a widespread phenomenon in the Northern Hemisphere, although its underlying drivers remain debated. In this study, we combined 20 years of dissolved organic carbon (DOC) measurements with five years of optical characterization in soil solutions collected at multiple depths from two contrasting forest plots in the Strengbach catchment (Vosges Mountains, France): a spruce stand affected by dieback and a beech stand. We developed a conceptual framework to interpret the optical properties of DOC in soil solutions, based on commonly used indices and distinguishing between two endmembers: litter-derived and microbialderived signatures. Our results reveal a marked browning in soil solutions associated with spruce decline, characterized by increasing DOC and aromaticity. DOC concentrations increased significantly at several soil depths between 2004 and 2024, with an intensified increase following bark beetle infestation in 2013, reaching up to 2 ppm-C/year at 5 and 30 cm depth. This increase was accompanied by a shift towards more litter-derived DOC and a concomitant decrease in microbial-derived signatures, exacerbated in deeper soil solutions. A soil sequence representing a post-decline gradient further demonstrated that spruce decline increased soil lignin content, resulting in higher DOC and aromaticity in soil solutions, driven by litter input changes. The reduced microbial activity following clear-cut may explain the lower microbial signature. Overall, the disturbance of forest cover associated with spruce decline is a major driver of soil solution browning, raising concerns regarding the quality of downstream surface waters.
SN - 0016-7061
SN - 1872-6259
ER -