Carbon and microbes in a degrading palsa mire are distinct from a peatland and a wider connected sub-Arctic fluvial system

Sep 29, 2026

Climate change is reshaping biogeochemical cycling of carbon and nutrients across northern peatland and permafrost regions, which store some of the largest terrestrial carbon stocks. Lateral carbon transfer remains insufficiently studied, particularly in small streams and catchments receiving high organic-matter loads and acting as carbon-degradation hotspots. This study links dissolved organic matter (DOM) quantity and quality with microbial community data from a small sub-Arctic catchment containing degrading palsa permafrost mire and spring thawing subcatchments. Palsa thaw ponds show higher DOM concentrations, more aromatic DOM, and distinct microbial communities; dissolved organic carbon export rates are comparable at sampling, while local DOM processing is greater in the palsa site. Ultra-small Patescibacteria are abundant and dominate community composition across sampled waters.

LanguageEnglish

CategoryResearch & Report

FormatPDF

Pages14

Reading Time35 min

AccessFree to download

Abstract

Introduction

Carbon and nutrient cycling in northern peatlands and permafrost

Role of DOM quality in microbial degradation

Microbial community assembly and DOM processing

Knowledge gaps and focus on Patescibacteria

ISME Communications, 2025, 5(1), ycaf240 [https://doi.org/10.1093/ismeco/ycaf240](https://doi.org/10.1093/ismeco/ycaf240) Advance access publication: 18 December 2025 Original Article Carbon and microbes in a degrading palsa mire are distinct from a peatland and a wider connected sub-Arctic fluvial system Nea Tuomela 1 , *, Samu Elovaara 2 , Jenni Hultman 3 , Hermanni Kaartokallio 2 , David N. Thomas 1 1 Faculty of Biological and Environmental Sciences, University of Helsinki, Viikinkaari 1, 00790 Helsinki, Finland 2 Finnish Environment Institute (SYKE), Latokartanonkaari 11, 00790 Helsinki, Finland 3Natural Resources Institute Finland (LUKE), Latokartanonkaari 9, 00790 Helsinki, Finland *Corresponding author. Faculty of Biological and Environmental Sciences, University of Helsinki, Viikinkaari 1, 00790 Helsinki, Finland. [E-mail:](E-mail: nea.tuomela@helsinki.fi)[ nea.tuomela@helsinki.fi](E-mail: nea.tuomela@helsinki.fi) Abstract Climate change is altering the biogeochemical cycling of carbon and nutrients in the northern peatland and permafrost regions, which provide two of the largest terrestrial carbon storages. Lateral transfer of carbon needs to be more widely studied, especially in smaller streams and catchments, as they receive high loading of organic matter and are hotspots of carbon degradation. In this study, we combined measurements of dissolved organic matter (DOM) quality and quantity with microbial community data from a small subArctic catchment. Our aim was to understand how the catchment is affected by two subcatchments: Degrading palsa permafrost mire and peatland thawing in spring. The small thaw ponds in the palsa mire were clearly distinct from the rest ofthe catchment and ponds in the peatland: Palsa ponds had higher DOM concentration, more aromatic DOM, and distinctive microbial communities compared with the peatland ponds and the rest of the catchment. Dissolved organic carbon export rates from the palsa and peat sites were comparable at the time of sampling, but local DOM processing was higher in the palsa site. We also detected high abundances of ultra-small Patescibacteria, which dominated the microbial community composition in all the sampled waters. Graphical abstract Keywords: microbial communities; carbon cycling; arctic; permafrost peatland; biogeochemistry; palsa; peat; river catchment; thaw ponds Received: 18 March 2025 . Revised: 22 August 2025 . Accepted: 12 December 2025 © The Author(s) 2025. Published by Oxford University Press on behalf of the International Society for Microbial Ecology. This is an Open Access article distributed under the terms of the Creative Commons Attribution License ([https://creativecommons.org/licenses/by/4.0/](https://creativecommons.org/licenses/by/4.0/)), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited. Introduction Northern peatlands and permafrost are two of the largest reservoirs of organic carbon on Earth, storing a total of 415 Pg C, of which 185 Pg of carbon is in permafrost peatlands [1] . The Arctic is undergoing rapid warming [2 , 3], which is leading to the mobilization and release of soil organic carbon from permafrost [4] . Palsas, isolated peat mounds with a permafrost core, are especially vulnerable to increasing temperatures and changing rainfall patterns [5] and drastic degradation of palsas has been detected pan-Arctic [6–8] . Following permafrost degradation, organic matter and nutrients can be released into ponds and streams, to be transported and transformed [1 , 9–11] . Fluxes of dissolved organic matter (DOM) are highly seasonal, with highest export rates during spring freshet [12] . However, with permafrost thaw changing the hydrology, DOM export patterns and quality can change [11 , 13 , 14] . The properties of DOM along with temperature and nutrient availability determine whether it is degraded or transferred further downst

FAQs

What is the main goal of the study?

To understand how a small sub-Arctic catchment is affected by two subcatchments: degrading palsa permafrost mire and spring peatland thawing, using DOM and microbial community data.

How do palsa thaw ponds differ from the rest of the catchment?

Palsa ponds have higher DOM concentration, more aromatic DOM, and distinctive microbial communities compared with peatland ponds and other parts of the catchment.

What did the study find about dissolved organic carbon export and DOM processing?

Dissolved organic carbon export rates from palsa and peat sites were comparable at sampling, but local DOM processing was higher at the palsa site.

Sep 29, 2026

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