Dissolved organic carbon, major and trace element in peat pore water of sporadic, discontinuous and continuous permafrost zone of Western Siberia

Abstract. Mobilization of dissolved organic carbon (DOC) and related trace elements (TE) from the frozen peat to surface waters in the permafrost zone is one the major consequence of on-going permafrost thaw and active layer thickness (ALT) rise in high latitude regions. The interstitial soil solutions are efficient tracers of on-going bio-geochemical processes in the critical zone and can help to decipher the intensity of carbon and metals migration from the soil to the rivers and further to the ocean. To this end, we collected, across a 640 km latitudinal transect of sporadic to continuous permafrost zone of western Siberia peatlands, soil porewaters from 30 cm depth using suction cups and we analyzed DOC, DIC and 40 major and TE in 0.45 µm filtered fraction of 80 soil porewaters. Despite an expected decrease of the intensity of DOC and TE mobilization from the soil and vegetation litter to the interstitial fluids with the increase of the permafrost coverage, decrease in the annual temperature and ALT, the DOC and many major and trace element did not exhibit any distinct decrease in concentration along the latitudinal transect from 62.2° N to 67.4° N. The DOC demonstrated a maximum of concentration at 66° N, on the border of discontinuous/continuous permafrost zone, whereas the DOC concentration in peat soil solutions from continuous permafrost zone was equal or higher than that in sporadic/discontinuous permafrost zone. Moreover, a number of major (Ca, Mg) and trace (Al, Ti, Sr, Ga, REEs, Zr, Hf, Th) elements exhibited an increasing, not decreasing northward concentration trend. We hypothesize that the effect of temperature and thickness of the ALT are of secondary importance relative to the leaching capacity of peat which is in turn controlled by the water saturation of the peat core. The water residence time in peat pores also plays a role in enriching the fluids in some elements: the DOC, V, Cu, Pb, REE, Th were a factor of 1.5 to 2.0 higher in mounds relative to hollows. As such, it is possible that the time of reaction between the peat and downward infiltrating waters essentially controls the degree of peat pore-water enrichments in DOC and other solutes. A two-degree northward shift in the position of the permafrost boundaries may bring about a factor of 1.3 decrease in Ca, Mg, Sr, Al, Fe, Ti, Mn, Ni, Co, V, Zr, Hf, Th and REE porewater concentration in continuous and discontinuous permafrost zones, and a possible decrease in DOC, SUVA, Ca, Mg, Fe and Sr will not exceed 20 % of their actual values. The projected increase of ALT and vegetation density, northward migration of the permafrost boundary, or the change of hydrological regime are unlikely to modify chemical composition of peat pore water fluids larger than their natural variations within different micro-landscapes, i.e., within a factor of 2.

Download Full-text

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

Biogeosciences ◽

10.5194/bg-14-3561-2017 ◽

2017 ◽

Vol 14 (14) ◽

pp. 3561-3584 ◽

Cited By ~ 31

Author(s):

Tatiana V. Raudina ◽

Sergey V. Loiko ◽

Artyom G. Lim ◽

Ivan V. Krickov ◽

Liudmila S. Shirokova ◽

...

Keyword(s):

Trace Elements ◽

Organic Carbon ◽

Western Siberia ◽

Peat Soil ◽

Major And Trace Elements ◽

Permafrost Zone ◽

Discontinuous Permafrost ◽

Latitudinal Transect ◽

Soil Solutions ◽

Continuous Permafrost

Abstract. Mobilization of dissolved organic carbon (DOC) and related trace elements (TEs) from the frozen peat to surface waters in the permafrost zone is expected to enhance under ongoing permafrost thaw and active layer thickness (ALT) deepening in high-latitude regions. The interstitial soil solutions are efficient tracers of ongoing bio-geochemical processes in the critical zone and can help to decipher the intensity of carbon and metals migration from the soil to the rivers and further to the ocean. To this end, we collected, across a 640 km latitudinal transect of the sporadic to continuous permafrost zone of western Siberia peatlands, soil porewaters from 30 cm depth using suction cups and we analyzed DOC, dissolved inorganic carbon (DIC), and 40 major elements and TEs in 0.45 µm filtered fraction of 80 soil porewaters. Despite an expected decrease in the intensity of DOC and TE mobilization from the soil and vegetation litter to the interstitial fluids with the increase in the permafrost coverage and a decrease in the annual temperature and ALT, the DOC and many major and trace elements did not exhibit any distinct decrease in concentration along the latitudinal transect from 62.2 to 67.4° N. The DOC demonstrated a maximum of concentration at 66° N, on the border of the discontinuous/continuous permafrost zone, whereas the DOC concentration in peat soil solutions from the continuous permafrost zone was equal to or higher than that in the sporadic/discontinuous permafrost zone. Moreover, a number of major (Ca, Mg) and trace (Al, Ti, Sr, Ga, rare earth elements (REEs), Zr, Hf, Th) elements exhibited an increasing, not decreasing, northward concentration trend. We hypothesize that the effects of temperature and thickness of the ALT are of secondary importance relative to the leaching capacity of peat, which is in turn controlled by the water saturation of the peat core. The water residence time in peat pores also plays a role in enriching the fluids in some elements: the DOC, V, Cu, Pb, REEs, and Th were a factor of 1.5 to 2.0 higher in mounds relative to hollows. As such, it is possible that the time of reaction between the peat and downward infiltrating waters essentially controls the degree of peat porewater enrichments in DOC and other solutes. A 2° northward shift in the position of the permafrost boundaries may bring about a factor of 1.3 ± 0.2 decrease in Ca, Mg, Sr, Al, Fe, Ti, Mn, Ni, Co, V, Zr, Hf, Th, and REE porewater concentration in continuous and discontinuous permafrost zones, and a possible decrease in DOC, specific ultraviolet absorbency (SUVA), Ca, Mg, Fe, and Sr will not exceed 20 % of their current values. The projected increase in ALT and vegetation density, northward migration of the permafrost boundary, or the change of hydrological regime is unlikely to modify chemical composition of peat porewater fluids larger than their natural variations within different micro-landscapes, i.e., within a factor of 2. The decrease in DOC and metal delivery to small rivers and lakes by peat soil leachate may also decrease the overall export of dissolved components from the continuous permafrost zone to the Arctic Ocean. This challenges the current paradigm on the increase in DOC export from the land to the ocean under climate warming in high latitudes.

Download Full-text

Supplementary material to "Dissolved organic carbon, major and trace element in peat pore water of sporadic, discontinuous and continuous permafrost zone of Western Siberia"

10.5194/bg-2017-24-supplement ◽

2017 ◽

Author(s):

Tatiana V. Raudina ◽

Sergey V. Loiko ◽

Artyom Lim ◽

Ivan V. Krickov ◽

Liudmila S. Shirokova ◽

...

Keyword(s):

Organic Carbon ◽

Dissolved Organic Carbon ◽

Trace Element ◽

Pore Water ◽

Western Siberia ◽

Permafrost Zone ◽

Peat Pore Water ◽

Continuous Permafrost ◽

Supplementary Material

Download Full-text

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

Biogeosciences ◽

10.5194/bg-12-6915-2015 ◽

2015 ◽

Vol 12 (23) ◽

pp. 6915-6930 ◽

Cited By ~ 84

Author(s):

J. E. Vonk ◽

S. E. Tank ◽

P. J. Mann ◽

R. G. M. Spencer ◽

C. C. Treat ◽

...

Keyword(s):

Organic Carbon ◽

Dissolved Organic Carbon ◽

Aquatic Systems ◽

The Arctic ◽

Permafrost Region ◽

Soil Leachate ◽

Discontinuous Permafrost ◽

Spatial Coverage ◽

Continuous Permafrost ◽

Permafrost Regions

Abstract. As 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 Arctic.

Download Full-text

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

Biogeosciences Discussions ◽

10.5194/bgd-12-8353-2015 ◽

2015 ◽

Vol 12 (11) ◽

pp. 8353-8393 ◽

Cited By ~ 5

Author(s):

J. E. Vonk ◽

S. E. Tank ◽

P. J. Mann ◽

R. G. M. Spencer ◽

C. C. Treat ◽

...

Keyword(s):

Organic Carbon ◽

Dissolved Organic Carbon ◽

Aquatic Ecosystems ◽

The Arctic ◽

Permafrost Region ◽

Soil Leachate ◽

Discontinuous Permafrost ◽

Spatial Coverage ◽

Continuous Permafrost ◽

Permafrost Regions

Abstract. As Arctic regions warm, the large organic carbon pool stored in permafrost becomes increasingly vulnerable to thaw and decomposition. The transfer of newly mobilized carbon to the atmosphere and its potential influence upon climate change will largely depend on the reactivity and subsequent fate of carbon delivered to aquatic ecosystems. Dissolved organic carbon (DOC) is a key regulator of aquatic metabolism and its biodegradability will determine the extent and rate of carbon release from aquatic ecosystems to the atmosphere. Knowledge of the mechanistic controls on DOC biodegradability is however 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 used as common practice in the literature. We further 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 BDOC losses in both soil and aquatic systems. We hypothesize that the unique composition of permafrost-derived DOC combined with limited prior microbial processing due to low soil temperature and relatively shorter flow path lengths and transport times, resulted in higher overall terrestrial and freshwater BDOC 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 losses in large streams and rivers, but no apparent change in smaller streams and 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 seasons progress. 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 as well as its variability throughout the Arctic summer. We lastly present a recommended standardized BDOC protocol to facilitate the comparison of future work and improve our knowledge of processing and transport of DOC in a changing Arctic.

Download Full-text

Permafrost coverage, watershed area and season control of dissolved carbon and major elements in western Siberian rivers

Biogeosciences Discussions ◽

10.5194/bgd-12-10621-2015 ◽

2015 ◽

Vol 12 (13) ◽

pp. 10621-10677 ◽

Cited By ~ 2

Author(s):

O. S. Pokrovsky ◽

R. M. Manasypov ◽

S. Loiko ◽

L. S. Shirokova ◽

I. A. Krivtzov ◽

...

Keyword(s):

Environmental Factors ◽

Western Siberia ◽

Biomass Productivity ◽

Major Elements ◽

Permafrost Zone ◽

Spring Flood ◽

Free Zone ◽

Discontinuous Permafrost ◽

Continuous Permafrost

Abstract. Analysis of dissolved organic and inorganic carbon (DOC and DIC, respectively), pH, Na, K, Ca, Mg, Cl, SO4 and Si in ~ 100 large and small rivers (< 100 to ≤ 150 000 km2) of western Siberia sampled in winter, spring, summer and autumn over a more than 1500 km latitudinal gradient allowed for establishing the main environmental factors controlling the transport of dissolved river components in this environmentally important region, comprising continuous, discontinuous, sporadic and permafrost-free zones. There was significant latitudinal trend consisting in general decrease of DOC, DIC, SO4, and major cation (Ca, Mg, Na, K) concentrations northward, reflecting the interplay between groundwater feeding (detectable mostly in the permafrost-free zone, south of 60° N) and surface flux (in the permafrost-bearing zone). The trend of inorganic components was mostly pronounced in winter and less visible in spring, whereas for DOC, the trend of concentration decrease with latitude was absent in winter, and less pronounced in the spring flood than in the summer baseflow. The latitudinal trends persisted over all river watershed sizes, from < 100 to > 10 000 km2. This suggested that in addition to groundwater feeding of the river, there was a significant role of surface and shallow subsurface flow linked to plant litter degradation and peat leaching. Environmental factors are ranked by their increasing effect on DOC, DIC, δ13CDIC, and major elements in western Siberian rivers as the following: watershed area < season < latitude. Seasonal fluxes of dissolved components did not significantly depend on the river size and as such could be calculated as a~function of watershed latitude. Unexpectedly, the DOC flux remained stable around 3 t km−2 yr−1 until 61° N, decreased two-fold in the discontinuous permafrost zone (62–66° N), and increased again to 3 t km−2 yr−1 in the continuous permafrost zone (67° N). The DIC, Mg, K and Ca followed this pattern. The total dissolved cation flux (TDS_c) ranged from 1.5 to 5.5 t km−2 yr−1, similar to that in central Siberian rivers of the continuous permafrost region. While Si concentration was almost unaffected by the latitude over all seasons, the Si flux systematically increased northward, suggesting a decreasing role of secondary mineral formation in soil and of vegetation uptake. The dominating effect of latitude cannot however be interpreted solely in terms of permafrost abundance and water flow path (deep vs. surface) but has to be considered in the context of different climate, plant biomass productivity, unfrozen peat thickness and peat chemical composition. It can be anticipated that, under climate warming in western Siberia, the maximal change will occur in small (< 1000 km2 watershed) rivers DOC, DIC and ionic composition, and this change will be mostly pronounced in summer and autumn. The wintertime concentrations and spring flood fluxes and concentrations are unlikely to be appreciably affected by the change of the active layer depth and terrestrial biomass productivity. Assuming a conservative precipitation scenario and rising temperature over next few centuries, the annual fluxes of DOC and K in the discontinuous permafrost zone may see a maximum increase by a factor of 2, whereas for DIC and Mg, this increase may achieve a factor of 3. The fluxes of Ca and TDS_c may increase by a factor of 5. At the same time, Si fluxes will either remain constant or decrease two-fold in the permafrost-bearing zone relative to the permafrost-free zone of western Siberia.

Download Full-text

Dynamics and chemistry of dissolved organic carbon in Precambrian Shield catchments and an impounded wetland

Canadian Journal of Fisheries and Aquatic Sciences ◽

10.1139/f03-050 ◽

2003 ◽

Vol 60 (5) ◽

pp. 612-623 ◽

Cited By ~ 24

Author(s):

T R Moore ◽

L Matos ◽

N T Roulet

Keyword(s):

Organic Matter ◽

Organic Carbon ◽

Dissolved Organic Carbon ◽

Pore Water ◽

Neutral Fraction ◽

Plant Tissues ◽

Pore Waters ◽

Experimental Lakes Area ◽

Peat Pore Water ◽

Doc Export

We examined the sources, sinks, and fluxes of dissolved organic carbon (DOC) and its chemical fractions over a 4-year period in upland and wetland catchments in the Experimental Lakes Area, Ontario. In an upland catchment, the major sources of DOC were precipitation, vegetation, and soil organic matter, resulting in a summer (June to October) export of 2.1 g·m2. DOC concentrations in peat pore water ranged from 20 to 60 mg·L1 and were related to hydrologic pathways. DOC export from catchments containing wetlands ranged from 0.8 to 5.7 g·m2 and export from the peatland portion of the catchment was estimated to be 2830 g·m2. Flooding to a depth of 1.2 m in the peatland section of one catchment resulted in an increase in pore-water and pond DOC concentrations, attributed to the decomposition of plant tissues and peat. Because only 14% of the catchment was flooded, impoundment did not result in a significant increase in DOC export. Between 85 and 93% of DOC was contained in the acid fractions, with small amounts in the neutral fractions. Flooding increased the proportion of the hydrophilic neutral fraction in peat pore waters for 2 years after flooding.

Download Full-text