Biodegradability of dissolved organic carbon in permafrost soils and aquatic systems: a meta-analysis

[摘要] As Arctic regions warm and frozen soils thaw, the large organic carbon poolstored in permafrost becomes increasingly vulnerable to decomposition ortransport. The transfer of newly mobilized carbon to the atmosphere and itspotential influence upon climate change will largely depend on thedegradability of carbon delivered to aquatic ecosystems. Dissolved organiccarbon (DOC) is a key regulator of aquatic metabolism, yet knowledge of themechanistic controls on DOC biodegradability is currently poor due to ascarcity of long-term data sets, limited spatial coverage of available data,and methodological diversity. Here, we performed parallel biodegradable DOC(BDOC) experiments at six Arctic sites (16 experiments) using a standardizedincubation protocol to examine the effect of methodological differencescommonly used in the literature. We also synthesized results from 14 aquaticand soil leachate BDOC studies from across the circum-arctic permafrostregion to examine pan-arctic trends in BDOC.

An increasing extent of permafrost across the landscape resulted in higherDOC losses in both soil and aquatic systems. We hypothesize that the uniquecomposition of (yedoma) permafrost-derived DOC combined with limited priormicrobial processing due to low soil temperature and relatively short flowpath lengths and transport times, contributed to a higher overallterrestrial and freshwater DOC loss. Additionally, we found that thefraction of BDOC decreased moving down the fluvial network in continuouspermafrost regions, i.e. from streams to large rivers, suggesting thathighly biodegradable DOC is lost in headwater streams. We also observed aseasonal (January–December) decrease in BDOC in large streams and rivers, but sawno apparent change in smaller streams or soil leachates. We attribute thisseasonal change to a combination of factors including shifts in carbonsource, changing DOC residence time related to increasing thaw-depth,increasing water temperatures later in the summer, as well as decreasinghydrologic connectivity between soils and surface water as the thaw seasonprogresses. Our results suggest that future climate warming-induced shiftsof continuous permafrost into discontinuous permafrost regions could affectthe degradation potential of thaw-released DOC, the amount of BDOC, as wellas its variability throughout the Arctic summer. We lastly recommend astandardized BDOC protocol to facilitate the comparison of future work andimprove our knowledge of processing and transport of DOC in a changingArctic.

[学科分类] 地球化学与岩石