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

Abstract

International audienceAs Arctic regions warm and frozen soils thaw, the large organic carbon pool stored in permafrost becomes increasingly vulnerable to decomposition or transport. The transfer of newly mobilized carbon to the atmosphere and its potential influence upon climate change will largely depend on the degradability of carbon delivered to aquatic ecosystems. Dissolved organic carbon (DOC) is a key regulator of aquatic metabolism, yet knowledge of the mechanistic controls on DOC biodegradability is currently poor due to a scarcity 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 standardized incubation protocol to examine the effect of methodological differences commonly used in the literature. We also synthesized results from 14 aquatic and soil leachate BDOC studies from across the circum-arctic permafrost region to examine pan-arctic trends in BDOC. An increasing extent of permafrost across the landscape resulted in higher DOC losses in both soil and aquatic systems. We hypothesize that the unique composition of (yedoma) permafrost-derived DOC combined with limited prior microbial processing due to low soil temperature and relatively short flow path lengths and transport times, contributed to a higher overall terrestrial and freshwater DOC loss. Additionally, we found that the fraction of BDOC decreased moving down the fluvial network in continuous permafrost regions, i.e. from streams to large rivers, suggesting that highly biodegradable DOC is lost in headwater streams. We also observed a seasonal (January–December) decrease in BDOC in large streams and rivers, but saw no apparent change in smaller streams or soil leachates. We attribute this seasonal change to a combination of factors including shifts in carbon source, changing DOC residence time related to increasing thaw-depth, increasing water temperatures later in the summer, as well as decreasing hydrologic connectivity between soils and surface water as the thaw season progresses. Our results suggest that future climate warming-induced shifts of continuous permafrost into discontinuous permafrost regions could affect the degradation potential of thaw-released DOC, the amount of BDOC, as well as its variability throughout the Arctic summer. We lastly recommend a standardized BDOC protocol to facilitate the comparison of future work and improve our knowledge of processing and transport of DOC in a changing Arcti

Reviews and syntheses: Effects of permafrost thaw on Arctic aquatic ecosystems

“…The biodegradability of DOC in various Arctic systems is dependent on several factors including DOC source and chemical character (Michaelson et al, 1998;Wickland et al, 2007Wickland et al, , 2012Balcarczyk et al, 2009;Mann et al, 2012;Olefeldt et al, 2013;Abbott et al, 2014), nutrient availability (Holmes et al, 2008;Mann et al, 2012;Wickland et al, 2012;Abbott et al, 2014), water temperature (Wickland et al, 2012), and prior processing (Michaelson et al, 1998;Wickland et al, 2007;Spencer et al, 2015). There are strong seasonal patterns in DOC biodegradability in large Arctic rivers, where the relative amount of biodegradable DOC (BDOC) is greatest in winter and spring, and generally declines through the summer and autumn (Holmes et al, 2008;Mann et al, 2012;Wickland et al, 2012;Vonk et al, 2015), reflecting the influences of seasonal thaw depth on DOC sources and hydrologic connectivity. Soil BDOC does not show a strong seasonality (Wickland et al, 2007;Vonk et al, 2015), supporting the notion that changes in DOC residence time and processing in soils prior to delivery to surface waters is a primary control on aquatic BDOC (Striegl et al, 2005;Vonk et al, 2015).…”

“…There are strong seasonal patterns in DOC biodegradability in large Arctic rivers, where the relative amount of biodegradable DOC (BDOC) is greatest in winter and spring, and generally declines through the summer and autumn (Holmes et al, 2008;Mann et al, 2012;Wickland et al, 2012;Vonk et al, 2015), reflecting the influences of seasonal thaw depth on DOC sources and hydrologic connectivity. Soil BDOC does not show a strong seasonality (Wickland et al, 2007;Vonk et al, 2015), supporting the notion that changes in DOC residence time and processing in soils prior to delivery to surface waters is a primary control on aquatic BDOC (Striegl et al, 2005;Vonk et al, 2015).…”

“…Newly thawed soils are potential DOC sources that can exceed DOC released from seasonally thawed active layer soils (sub-Arctic Sweden, Roehm et al, 2009;Alaska, Waldrop et al, 2010). Studies of distinct DOC sources suggest that non-permafrost-derived soil pore water DOC is moderately biodegradable (Wickland et al, 2007;Roehm et al, 2009;Vonk et al, 2015), whereas certain permafrost soilderived DOC can be highly biodegradable, particularly Pleistocene yedoma DOC in NE Siberia and Alaska (Vonk et al, 2013;Abbott et al, 2014;Spencer et al, 2015). These studies point to a high susceptibility of permafrost DOC to degradation during transport from soils, and within surface waters, compared to non-permafrost DOC, with aliphatic DOC originating in permafrost being preferentially degraded (NE Siberia, Spencer et al, 2015).…”

Dissolved organic carbon and nitrogen release from boreal Holocene permafrost and seasonally frozen soils of Alaska

“…However, systematic comparative examination of potential DOC and TDN release, dissolved organic matter (DOM) properties, and biodegradability of DOC from permafrost and active-layer soils across a wide range of soil types is needed to more definitively understand how observed patterns in surface water chemistry are related to changing terrestrial sources. Studies of soil leachates in circumpolar regions have focused primarily on potential DOC release from active-layer soils (Neff and Hooper 2002, Michaelson and Ping 2003, Guo et al 2007, Vonk et al 2015, O'Donnell et al 2016 and from deep Pleistocene yedoma soils (Dutta et al 2006, Drake et al 2015, Ewing et al 2015. Only a small number of studies have compared solute leachate chemistry and/or biodegradability from paired active-layer and shallow permafrost soils (Ward and Cory 2015, Reyes and Lougheed 2015, Selvam et al 2017 and those studies are limited to soils collected from a single location.…”

Dissolved organic carbon and major and trace elements in peat porewater of sporadic, discontinuous, and continuous permafrost zones of western Siberia

“…The majority of available studies addressed the carbon and element transformation in the permafrost regions via analysis of rivers (Lobbes et al, 2000;Striegl et al, 2005;Spencer et al, 2008Holmes et al, 2012;Wickland et al, 2012;Giesler et al, 2014;Mann et al, 2015), lakes (Kokelj et al, 2005(Kokelj et al, , 2009Guo et al, 2007;Laurion et al, 2010;Tank et al, 2009), mires (Olefeldt and Roulet, 2012;Olefeldt et al, 2013Olefeldt et al, , 2014 or soil organic matter (SOM) from various depth and soil aqueous leachate (Swindles et al, 2015;Hodgkins et al, 2014Hodgkins et al, , 2016Drake et al, 2015;Vonk et al, 2015a;Yang et al, 2016) and largely ignored soil porewater chemistry. At the same time, interstitial soil solutions are known to be efficient tracers of ongoing bio-geochemical processes in the critical zone (Hendershot et al, 1992;Stutter and Billett, 2003;Quinton and Pomeroy, 2006;Karavanova and Malinina, 2007;Gangloff et al, 2016) and can help to decipher the intensity of carbon and metals migration from the soil to the rivers and further to the ocean.…”