Lars Kutzbach

Spatial and seasonal variability of polygonal tundra water balance: Lena River Delta, northern Siberia (Russia)

The summer water balance of a typical Siberian polygonal tundra catchment is investigated in order to identify the spatial and temporal dynamics of its main hydrological processes. The results show that, besides precipitation and evapotranspiration, lateral flow considerably influences the site-specific hydrological conditions. The prominent microtopography of the polygonal tundra strongly controls lateral flow and storage behaviour of the investigated catchment. Intact rims of low-centred polygons build hydrological barriers, which release storage water later in summer than polygons with degraded rims and troughs above degraded ice wedges. The barrier function of rims is strongly controlled by soil thaw, which opens new subsurface flow paths and increases subsurface hydrological connectivity. Therefore, soil thaw dynamics determine the magnitude and timing of subsurface outflow and the redistribution of storage within the catchment. Hydraulic conductivities in the elevated polygonal rims sharply decrease with the transition from organic to mineral layers. This interface causes a rapid shallow subsurface drainage of rainwater towards the depressed polygon centres and troughs. The re-release of storage water from the centres through deeper and less conductive layers helps maintain a high water table in the surface drainage network of troughs throughout the summer.RésuméLe bilan d’eau estival d’un bassin d’alimentation typique de la toundra polygonale sibérienne a fait l’objet d’investigations afin d’identifier la dynamique spatio-temporelle des ses principaux processus hydrologiques. Les résultats montrent que, à côté de la précipitation et de l’évapotranspiration, un flux latéral influence considérablement les conditions hydrogéologiques spécifiques du site. La microtopographie marquée de la toundra polygonale contrôle fortement l’écoulement latéral et la modalité d’emmagasinement du bassin objet de l’investigation. Les bords intacts des polygones centrés bas constituent des barrières hydrologiques, qui libèrent l’eau accumulée en été plus tard que les polygones à bords dégradés et dépressions au dessus des biseaux glacées dégradées. La fonction barrière des bordures est fortement contrôlée par le dégel du sol, qui ouvre de nouveaux chenaux d’écoulement en subsurface et en accroît la connectivité hydrologique. C’est pourquoi, la dynamique du dégel détermine l’instant et le volume d’émission d’eau en subsurface et la redistribution de la réserve dans le bassin versant. Les conductivités hydrauliques des bordures polygonales élevées diminuent brusquement avec la transition d’horizons organiques à des horizons minéraux. Ceci cause un drainage superficiel rapide de l’eau de précipitation vers les centres déprimés des polygones et goulottes. Le relargage de l’eau en réserve depuis les centres à travers des couches plus profondes et moins conductrices aide à maintenir élevée la surface libre de l’aquifère sous le réseau de drainage superficiel des goulottes durant tout l’été.ResumenSe investiga el balance de agua de verano en una típica cuenca siberiana de polígonos de tundra para identificar la dinámica espacial y temporal de sus principales procesos hidrológicos. Los resultados muestran que, además de la precipitación y evapotranspiración, el flujo lateral influye considerablemente las condiciones hidrológicas del sitio específico. La destacada microtopografía de los polígonos de tundra controla fuertemente el comportamiento del flujo lateral y almacenamiento de la cuenca investigada. Los bordes intactos de los polígonos bajos centrados constituyen barreras hidrológicas, que liberan el agua de almacenamiento del verano después que los polígonos con bordes degradados y canales por encima de cuñas degradadas del hielo. La función de barrera de los bordes está controlada fuertemente por el deshielo del suelo, que abre nuevas trayectorias al flujo subsuperficial y aumenta la conectividad hidrológica subsuperficial. Además, la dinámica de deshielo del suelo determina la magnitud y el tiempo de la salida subsuperficial y la redistribución del almacenamiento dentro de la cuenca. Las conductividades hidráulicas en los bordes elevados del polígono disminuyen drásticamente con la transición de capas orgánicas a minerales. Esto causa un rápido drenaje subsuperficial somero del agua de lluvia hacia el centro de los polígonos deprimidos y canales. La reliberación del agua del almacenamiento desde el centro a través de capas menos conductivas y más profundas ayuda a mantener un nivel freático alto en la red de drenaje superficial de canales durante todo el verano.摘要为确定它的主要水文过程的时空动态,本文研究了一个典型的西伯利亚多边形冻原流域在夏季的水均衡。结果显示,除了降水和蒸发蒸腾,侧向流在相当程度上影响着特定场地的水文条件。多边形冻原主要的微地形特征强烈控制着研究流域的侧向流和储存行为。在中心偏低的多边形的完整边缘上建造水文屏障,以此可利用退化冰楔之上退化的边缘和凹槽在夏天释放储存的水。边缘上屏障的作用受到土壤解冻强烈的控制,解冻作用打开了地下水流的流径,提高了地下的水文连通性。因此,土壤解冻的动态决定了流出的地下水的规模和时间,以及流域内所储存水量的重新分配。升高的多边形边缘从有机层过渡到矿物层,渗透系数急剧减小。这造成了浅部雨水向凹陷的多边形中心和洼地迅速排水。所储存的水通过更深部的低渗透岩层从中心重新释放,这有助于夏季在地表凹槽排水系统中保持一个较高的水位。ResumoÉ investigado o balanço hídrico estival de uma típica bacia hidrográfica de tundra poligonal para identificar as dinâmicas espaciais e temporais dos seus principais processos hidrológicos. Os resultados mostram que, para além da precipitação e da evapotranspiração, o escoamento lateral influencia consideravelmente as condições hidrológicas em cada local. A característica microtopografia da tundra poligonal controla fortemente o escoamento lateral e o comportamento do armazenamento na bacia investigada. Os bordos intactos dos polígonos com centro deprimido constituem barreiras hidrológicas que libertam a água armazenada mais tarde no verão do que nos polígonos com bordos degradados e fendas situadas acima das cunhas de gelo degradadas. A função de barreira dos bordos é fortemente controlada pelo descongelamento do solo que abre novos percursos de escoamento subterrâneo e incrementa a conectividade hidrológica subsuperficial. Consequentemente, a dinâmica do descongelamento do solo determina a magnitude e a temporização do escoamento e a redistribuição do armazenamento dentro da bacia. A condutividade hidráulica nos bordos poligonais elevados diminui drasticamente com a transição entre as camadas orgânicas a as camadas minerais. Isto provoca uma rápida drenagem subsuperficial pouco profunda da água de chuva em direção aos centros deprimidos e às fendas. A re-libertação da água armazenada a partir dos centros através de camadas mais profundas e menos condutivas ajudam a manter ao longo do verão um nível de água elevado na rede de drenagem superficial formada pelas fendas.

Diurnal dynamics of CH4 from a boreal peatland during snowmelt

Peatlands are one of the major natural sources of methane (CH4), but the quantification of efflux is uncertain especially during winter, fall and the highly dynamic spring thaw period. Here, we report pronounced diurnal variations in CH4 fluxes (FCH4), measured using the eddy-covariance technique during the snow-thawing period at a boreal peatland in north-western Russia. Following the background winter emission of ∼0.5mgm−2 h−1, strong diurnal variability in CH4 fluxes from 21 April to 3 May was apparently controlled by changes in surface temperature (Tsur) and near-surface turbulence as indicated by the friction velocity (u*).CH4 fluxeswere∼0.8mgm−2 h−1 during night and∼3mgm−2 h−1 during peak efflux. Primarily, the freeze-thaw cycle of an ice layer observed at the wet peatland microforms due to surface temperatures oscillating between 0◦C during the days and 0◦C during the nights appeared to strongly influence diurnal variability. Once the ice layer was melted, increases in wind speed seemed to enhance CH4 efflux, possibly by increased mixing of the water surface. Apparently, a combination of physical factors is influencing the gas transport processes of CH4 efflux during the highly dynamic spring thaw period.

Permafrost-Affected Soils of the Russian Arctic and their Carbon Pools

Permafrost-affected soils have accumulated enormous pools of organic matter during the Quaternary period. The area occupied by these soils amounts to more than 8.6 million km2, which is about 27 % of all land areas north of 50 ◦ N. Therefore, permafrost-affected soils are considered to be one of the important cryosphere elements within the climate system. Due to the cryopedogenic processes that form these particular soils and the overlying vegetation that is adapted to the arctic climate, organic matter has accumulated to the present extent of up to 1024 Pg (1 Pg = 1015 g = 1 Gt) of soil organic carbon stored within the uppermost 3 m of ground. Considering the observed progressive climate change and the projected polar amplification, permafrost-affected soils will undergo fundamental property changes. Higher turnover and mineralisation rates of the organic matter are consequences of these changes, which are expected to result in an increased release of climate-relevant trace gases into the atmosphere. The controversy of whether permafrost regions continue accumulating carbon or already function as a carbon source remains open until today. An increased focus on this subject matter, especially in underrepresented Siberian regions, could contribute to a more robust estimation of the soil organic carbon pool of permafrost regions and at the same time improve the understanding of the carbon sink and source functions of permafrost-affected soils.

Carbon dioxide exchange fluxes of a boreal peatland over a complete growing season, Komi Republic, NW Russia

The carbon pool of peatlands has been considered as potentially unstable in a changing climate. This study is the first presenting carbon dioxide (CO2) net ecosystem exchange, CO2 efflux due to ecosystem respiration and CO2 uptake by gross primary production over a complete growing season for different microforms of a boreal peatland in Russia (61°56′N, 50°13′E). CO2 fluxes were measured using the closed chamber technique from the 25th April in the period of snow melt until the end of the vegetation period and the first frost on the 20th October 2008 at seven different microform types: minerogenous and ombrogenous hollows, lawns and hummocks, respectively, and Carex lawns situated in a transition zone between minerogenous and ombrogenous mire parts. The total number of chamber flux measurements was 5,517. Ombrogenous hummocks and lawns were sources of CO2 over the investigation period whereas hollows and minerogenous lawns were CO2 sinks. Some plots of Carex lawns and minerogenous hummocks were sinks while other plots of these microform types were sources. The CO2 fluxes were characterised by large variability not only between the microform types but also within the respective microform types. Of all microform types, the Carex, ombrogenous, and minerogenous lawns showed the highest variability in CO2 fluxes, which is probably related to a stronger within-microform heterogeneity in vegetation composition and coverage as well as in the water table level. Air temperature was one of the dominant controls on the CO2 flux dynamics. Water table and green area index were found to have strong influence on CO2 fluxes both within different patches of the same microform type as well as between different microforms.

Attenuation Correction Procedures for Water Vapour Fluxes from Closed-Path Eddy-Covariance Systems

Evapotranspiration is a source of water vapour to the atmosphere, and as a crucial indicator of landscape behaviour its accurate measurement has widespread implications. Here we investigate errors that are prevalent and systematic in the closed-path eddy-covariance measurement of latent heat flux: the attenuation of fluxes through dampened cospectral power at high frequencies. This process is especially pronounced during periods of high relative humidity through the adsorption and desorption of water vapour along the tube walls. These effects are additionally amplified during lower air temperature conditions. Here, we quantify the underestimation of evapotranspiration by a closed-path system by comparing its flux estimate to simultaneous and adjacent measurements from an open-path sensor. We apply models relating flux loss to relative humidity itself, to the lag time of the cross-correlation peak between the water vapour and vertical wind velocity signals, and to models of cospectral attenuation relative to the cospectral power of simultaneous sensible heat-flux measurements. We find that including the role of temperature in modifying the attenuation–humidity relationship is essential for unbiased flux correction, and that physically based cospectral attenuation methods are effective characterizers of closed-path instrument signal loss relative to the unattenuated flux value.

Hydrology-driven ecosystem respiration determines the carbon balance of a boreal peatland☆

The carbon (C) balance of boreal peatlands is mainly the sum of three different C fluxes: carbon dioxide (CO2), methane (CH4) and dissolved organic carbon (DOC). Intra- and inter-annual dynamics of these fluxes are differentially controlled by similar factors, such as temperature and water-table. Different climatic conditions within and between years might thus result in varying absolute and relative contributions of each flux to net ecosystem productivity (NEP). In this study CO2 fluxes were measured at a boreal peatland in eastern Finland during a dry year (2006) and a wet year (2007) and combined with DOC and CH4 fluxes from the same site. CO2 uptake in the wet year was 65% higher than in the dry year, caused by higher water table (WT) and subsequently reduced rates of soil respiration. Two to three-fold increases in DOC and CH4 fluxes in the wet year did not completely offset the higher CO2 uptake in that year, resulting in NEP of -83.7±14 g C m(-2) in the dry and -134.5±21 g C m(-2) in the wet year. Thus, in our study, WT was identified as the most important factor responsible for variations in the C balance between the observed years.

Russian boreal peatlands dominate the natural European methane budget

About 60% of the European wetlands are located in the European part of Russia. Nevertheless, data on methane emissions from wetlands of that area are absent. Here we present results of methane emission measurements for two climatically different years from a boreal peatland complex in European Russia. Winter fluxes were well within the range of what has been reported for the peatlands of other boreal regions before, but summer fluxes greatly exceeded the average range of 5–80 mg CH4 m−2 d−1 for the circumpolar boreal zone. Half of the measured fluxes ranged between 150 and 450 mg CH4 m−2 d−1. Extrapolation of our data to the whole boreal zone of European Russia shows that theses emissions could amount to up to 2.7 ± 1.1 Tg CH4 a−1, corresponding to 69% of the annual emissions from European wetlands or 33% of the total annual natural European methane emission. In 2008, climatic conditions corresponded to the long term mean, whereas the summer of 2011 was warmer and noticeably drier. Counterintuitively, these conditions led to even higher CH4 emissions, with peaks up to two times higher than the values measured in 2008. As Russian peatlands dominate the areal extend of wetlands in Europe and are characterized by very high methane fluxes to the atmosphere, it is evident, that sound European methane budgeting will only be achieved with more insight into Russian peatlands.

Environmental impacts – Terrestrial ecosystems

The chapter starts with a discussion of general patterns and processes in terrestrial ecosystems, including the impacts of climate change in relation to productivity, phenology, trophic matches and mismatches, range shifts and biodiversity. Climate impacts on specific ecosystem types—forests, grasslands, heathlands, and mires and peatlands—are then discussed in detail. The chapter concludes by discussing links between changes in inland ecosystems and the wider North Sea system. Future climate change is likely to increase net primary productivity in the North Sea region due to warmer conditions and longer growing seasons, at least if summer precipitation does not decrease as strongly as projected in some of the more extreme climate scenarios. The effects of total carbon storage in terrestrial ecosystems are highly uncertain, due to the inherent complexity of the processes involved. For moderate climate change, land use effects are often more important drivers of total ecosystem carbon accumulation than climate change. Across a wide range of organism groups, range expansions to higher latitudes and altitudes and changes in phenology have occurred in response to recent climate change. For the range expansions, some studies suggest substantial differences between organism groups. Habitat specialists with restricted ranges have generally responded very little or even shown range contractions. Many of already threatened species could be particularly vulnerable to climate change. Overall, effects of recent climate change on terrestrial ecosystems within the North Sea region are still limited.

A long-term (2002 to 2017) record of closed-path and open-patheddy covariance CO 2 net ecosystem exchange fluxes from theSiberian Arctic

Ground-based observations of land–atmosphere fluxes are necessary to progressively improve global climate models. Observed data can be used for model evaluation and to develop or tune process models. In arctic permafrost regions, climate–carbon feedbacks are amplified. Therefore, increased efforts to better represent these regions in global climate models have been made in recent years. We present a multi-annual time series of land–atmosphere carbon dioxide fluxes measured in situ with the eddy covariance technique in the Siberian Arctic (7222 N, 12630 E). The site is part of the international network of eddy covariance flux observation stations (FLUXNET; site ID: Ru-Sam). The data set includes consistently processed fluxes based on concentration measurements of closed-path and open-path gas analyzers. With parallel records from both sensor types, we were able to apply a site-specific correction to open-path fluxes. This correction is necessary due to a deterioration of data, caused by heat generated by the electronics of open-path gas analyzers. Parameterizing this correction for subperiods of distinct sensor setups yielded good agreement between openand closed-path fluxes. We compiled a long-term (2002 to 2017) carbon dioxide flux time series that we additionally gap-filled with a standardized approach. The data set was uploaded to the Pangaea database and can be accessed through https://doi.org/10.1594/PANGAEA.892751. Published by Copernicus Publications. 222 D. Holl et al.: Long-term eddy covariance CO2 fluxes from the Siberian Arctic