Hydro-geochemical characteristics and transformation processes of the Lena River Delta branches

Previous studies have shown that arctic river delta systems are areas of accumulation of geochemical substances at the sea-river mixing zone. In the Lena River Delta our previous work shows the tendencies of water runoff redistribution changes and heterogeneity of suspended supply distribution along the delta branches, accumulation and erosion zone in the different parts of the delta. Nevertheless, the processes of geochemical flow transformation in the subaerial deltas are so far underestimated. In order to close this gap, we sampled water, suspended and bottom sediments in the Lena River Delta in the summer seasons of 2010 and 2014. Most of the sampling points were tight to the profiles of hydrological measurements held in the delta and highlighted in Fedorova et al. [2015]. The results show that geochemical transformation of the Lena River runoff is taking place in the delta. The most active time for the transformation is the summer season due to the activity of sediment accumulation and biogeochemical processes. Hydrological conditions in the delta affect also its hydrogeochemical characteristics. Furcation of the delta branches affects the hydrodynamic conditions of different delta areas. The factors influencing the geochemical characteristics of the delta were identified on the base of geochemical indexes approach applied to sediments and statistical factor analysis. Based on geochemical indexes (Al/Na, Si/Al, Fe/Mn and Fe/Al ratios) similar conditions were determined for the main branch of the Lena, the upstream parts of Bykovskaya and Tumatskaya branches and in Olenekskaya branch near Chay-Tumus. Despite of high runoff the branches are characterized by element accumulation, which can be explained by decreasing of flow turbulence and specificity redox conditions in these areas. Bottom sediments are one of the most important indicators of geochemical transformation processes. The results of statistical factor analysis show three main factors for formation of the these geochemical conditions in the delta: 1. the general water flow of the Lena River, which is influenced by the lithogenous base of the river catchment, 2. the cryogenic condition of the Lena Delta (permafrost degradation processes and cryogenic weathering) and 3. biogeochemical transformation during redistribution of chemical water components , suspended matter and bottom sediments. Acknowledgements The research was supported by grant No. 14-05-00787 A of Russian Foundation for Basic Research References Fedorova, I.; Chetverova, A.; Bolshiyanov, D.; Makarov, A.; Boike, J.; Heim, B.; Morgenstern, A.; Overduin, P. P.; Wegner, C.; Kashina, V.; Eulenburg, A.; Dobrotina, E. and Sidorina, I. [2015]: Lena Delta hydrology and geochemistry: long-term hydrological data and recent field observations. Biogeosciences, 12(2):345–363, doi:10.5194/bg-12-345-2015

Spatial-temporal coherence of different scale hydrological processes in the Lena River delta

The Lena River delta is one of the hydrologically entertaining objects. Hundreds channels and thousands lakes as well as thawing ice complex and permafrost active layer dynamic allow to investigate spatial-temporal coherence of different scale hydrological processes. During 15 years Russian-German scientific collaboration on hydrological, hydrochemical and hydrobiological studies have been operated on different water objects for cause-effect relation of large and specific micro processes indication. Transient liquid-frozen water phase change is significant not only for active layer runoff forming but also for hydrochemical and biological specific. Thus, maximum of DOC is in the overlaying soil layer than permafrost border [Bobrova et al., 2013]. It could be used for modeling of runoff forming and biological activity estimation. Measured temperature of lacustrine bottom sediment of one thermokarst lake on Samoylov Island shows maximal volume 3,7 °C on 1,75 cm beneath water-sediment border [Skorospekhova, 2015]. It is also can be interpreted as biological processes activity, for example, organic material destruction with additional heating. It could be observed more detail and can be used for modeling of a lake thermic regime. Hydrobiological specificity shows similarity of species in the channels and lakes, poorness of biodiversity, especially in big channel; only stagnant in summer season Bulkurskaya channel has more zooplankton species in four times than the main river channel [Nigamatzyanova et al., 2015]. Decline of water turbidity from the delta top to channel edges is about 5-8 times [Charkin et al., 2009]. Considerable turbidity increase is formed according to permafrost thawing and can reach 500 g l-1 including high concentration of carbon and biogenic elements. Thermokarst lake degradation [Morgenstern et al., 2011] plays also an important role for permafrost hydrology in the delta. Outflow from an ice complex forms a high local suspended supply in adjacent river branches and influences on biological processes consequently [Dubinenkov et al., 2015]. Underestimated effect of water and sediment discharge increase in the middle part of river branches had been marked [Fedorova et al., 2015]. Head flux of the large Lena River forms taliks under channels with more sophisticated affect in the shoreline zone of the Laptev Sea due to aquifer dynamic and mixing of fresh and salt water. Talik effect on hydrology and sedimentation (and suspended material transformation) in the central part of the delta is currently carried out according to geophysical and hydrogeological methods. First field measurements are planned to be done in April 2016 and results will be presented in the ICOP 2016. The studies have been done with support of RFBR grant 14-05-00787 and 15-35-50949, in the framework of Russian-German projects “ CarboPerm” and “Scientific station “Samoylov Island”. The project for both SPBU and DFG funding had also applied for field and scientific investigation as well. References Bobrova, O.; Fedorova, I.; Chetverova, A.; Runkle, B. and Potapova, T. Input of Dissolved Organic Carbon for Typical Lakes in Tundra Based on Field Data of the Expedition Lena–2012. In Proceedings of the 19th International Northern Research Basins Symposium and Workshop, Southcentral Alaska, USA – August 11–17, 2013, 2013. Charkin, A.N.; Dudarev, O.V.; Semiletov, I.P.; Fedorova, I.; Chetverova, A.A.; J., Vonk; Sanchez- Garcia, L.; Gustafsson, ö. and Andersson, P. edimentation in the System of the Delta Lena River - the South Western Part of Buor-Haya Gulf (the Laptev Sea). In The 16th International Symposium on Polar Sciences. Incheon, Korea. 2009, 2009. Dubinenkov, I.; Flerus, R.; Schmitt-Kopplin, P.; Kattner, G. and Koch, B.P. [2015]: Origin-specific molecular signatures of dissolved organic matter in the Lena Delta. Biogeochemistry, 123(1):1–14, doi:10.1007/s10533-014-0049-0. Fedorova, I.; Chetverova, A.; Bolshiyanov, D.; Makarov, A.; Boike, J.; Heim, B.; Morgenstern, A.; Overduin, P. P.; Wegner, C.; Kashina, V.; Eulenburg, A.; Dobrotina, E. and Sidorina, I. [2015]: Lena delta hydrology and geochemistry: long-term hydrological data and recent field observations. Biogeosciences, 12(2):345–363, doi:10.5194/bg-12-345-2015. Morgenstern, A.; Grosse, G.; Günther, F.; Fedorova, I. and Schirrmeister, L. [2011]: Spatial analyses of thermokarst lakes and basins in Yedoma landscapes of the Lena Delta. The Cryosphere, 5(4):849–867, doi:10.5194/tc-5-849-2011. Nigamatzyanova, G.; Frolova, L.; Chetverova, A. and Fedorova, I. Hydrobiological investigation of branches of the Lena River edge zone. In Uchenye Zapiski Kazanskogo Universiteta, Seriya Estestvennye Nauki. 2015. in Russian. Skorospekhova, T. Report of a spring campaign of the expedition “Lena 2015”. AARI’s library stock, 2015

Contribution of permafrost degradation landforms to summer export of DOC from Yedoma-type Ice Complex

Thermo-erosional landforms (valleys, gullies) and their associated streams are the main connecting pathways between inland permafrost areas and rivers and coasts. Surface and ground waters are routed along these streams, which transport particulate and dissolved matter from the catchments to the rivers and coastal waters. Regions of ice-rich permafrost, such as the Yedoma-type Ice Complex, are not only characterized by a high abundance of thermo-erosional landforms, which formed during the Holocene, but are subject to extensive degradation under current arctic warming by processes such as thermal erosion, thermokarst, and active layer deepening. In the Siberian Lena River Delta Yedoma-type Ice Complex deposits occur on insular remnants of a Late-Pleistocene accumulation plain that has been dissected by Lena River branches and degraded by thermal erosion and thermokarst during the Holocene. This region serves as suitable exemplary study area for estimating the contribution of 1) different permafrost degradation landforms to the export of water and dissolved matter from Yedoma-type Ice Complex to the river and 2) active degradation of old permafrost versus seasonal runoff from the surface and active layer. In the summers of 2013 and 2014 we sampled surface and soil waters from streams and their watersheds in Yedomatype Ice Complex landscapes of the Lena River Delta and analyzed them for a range of hydrogeochemical parameters including electrical conductivity (EC), dissolved organic carbon (DOC) and stable isotopic composition.\ud The sampling sites were spread over an E-W-extent of about 150 km and are characterized by very diverse geomorphological and hydrological situations in terms of distance to the river branches, catchment size, discharge, degree of thermo-erosional activity, and connection to other permafrost degradation landforms (thermokarst lakes and basins). Three key sites were sampled three and four times from June to September 2013 and 2014, respectively, in order to analyze intra-seasonal changes. The results show large variances in EC (25 to 1205 μS/cm), DOC concentrations (2.9 to 119.0 mg/l), �18O (-29.8 to -14.6 ‰ vs. SMOW), and �D (-228.9 to -117.9‰ vs. SMOW) over the whole dataset, with distinct characteristics in the parameter combination for different degradation landform and water types. The temporal variability at the repeatedly sampled sites is low, which implies that there is not much change in the processes that determine the water composition throughout the summer season. By comparing differences in surface water chemistry between flow path systems that tap into varying amounts of source water (precipitation, surface and ground water, ground ice) and have differing residence times and extents, we explore the effect of future changes in thermokarst and thermo-erosional intensity and resulting changes in flow path hydrogeochemistry for thermoerosional features draining ice-rich permafrost

Colored dissolved organic matter in thermokarst lakes of Yamal peninsula: sources, annual variations and connection to lake and catchment properties

Ongoing Arctic warming changes arctic landscapes in various ways. It potentially alters the organic matter supply to lakes in the Arctic. Arctic warming may increase vegetation density in the catchments of lakes and thus increase of the organic matter supply to the lakes can be expected. Furthermore, warming may cause an increase of ground temperature and deepening of the active layer in permafrost soils, and thus activate various cryogenic processes including thermodenudation (Leibman et al. 2015). We present results of study of colored dissolved organic matter (CDOM) in thermokarst lakes of the central Yamal peninsula (Western Siberia, Russia) and the interconnection of CDOM with lake and catchment characteristics. We used a complex approach including field observations, laboratory measurements, and high spatial resolution optical and synthetic aperture radar (SAR) remote sensing and geographical information system (GIS) data analysis. CDOM absorption and spectral slope values, and suspended particulate matter concentrations (SPM) in several thermokarst lakes were obtained during 2011 – 2015 field campaigns. Availability of very high spatial resolution (GeoEye-1, WorldView-2) and high spatial resolution (SPOT5) optical satellite images as well as high resolution TanDEM-X DEM data, TSX and ALOS PALSAR SAR satellite images for the study area allowed to produce a large dataset of lake and catchment-related parameters (n=18). CDOM absorption at 440 nm in 363 lakes was retrieved from optical satellite images (correlation with in-situ data: R^2=0.68, n=24) using the band ratio method of Kutser et al. (2005). We also detected that increased turbidity in some of the lakes due to wind events in some of the optical satellite acquisitions affect the accuracy of retrieved CDOM values. The statistical analysis “boosted regression tree” was applied in order to find the most important variables controlling the CDOM concentration in central Yamal thermokarst lakes. The results show the following most important variables: the lake area/lake catchment area ratio, the elevation of the lake (i.e., floodplain or non-floodplain lake), median value of the Normalized Difference Vegetation Index (NDVI) of the lake catchment, activity of thermodenudation (thermocirques above the shore line) and total snow water equivalent (SWE) in the lake catchment. In this analysis we used a representative data of approximately 350 square kilometers including all geomorphic terrace levels and the floodplains of Se-Yakha and Mordy-Yakha rivers. Annual concentrations of CDOM in Yamal thermokarst lakes also differed. We found the clear relation of CDOM absorption values to climatic controls (summer air temperature and atmospheric precipitation) and recent activation of thermocirque in the study region. The enhanced erosion of the lake cliffs and enhanced atmospheric precipitation may increase the inflow of fresh terrestrial organic matter into the lakes from the surrounding catchments. Activation of thermocirques controls the additional input of SPM and CDOM into the lake water influencing also the lake color. References: Kutser T, Pierson DC, Kallio K, Reinart A, Sobek S. 2005. Mapping lake CDOM by satellite remote sensing. Remote Sensing of Environment 94: 535–540 DOI:10.1016/j.rse.2004.11.009 Leibman MO, Khomutov AV, Gubarkov AA, Mullanurov DR, Dvornikov YA. 2015. The research station “Vaskiny Dachi”, Central Yamal, West Siberia, Russia – A review of 25 years of permafrost studies. Fennia 193: 3–30

Degradation of Lena Delta Ice Complex by thermokarst and thermal erosion

During the past decade, we have studied thermokarst and thermo-erosional processes and landforms in Ice Complex deposits of the Lena Delta. Ice Complex deposits are very ice-rich permafrost up to tens of meters thick. They are widespread in the Arctic and have attracted raising attention due to their vulnerability to thaw under climatic warming. In the Lena Delta they occur on the third geomorphological main terrace, which is distributed as several islands in the southern delta. Degradation processes throughout the Holocene have affected these late Pleistocene deposits. Rapid permafrost thaw underneath ponding water (thermokarst) has created thermokarst lakes; when these lakes drain, thermokarst basins remain that can be several kilometers wide and up to twenty meters deep. Rapid permafrost thaw by running water (thermal erosion) has created gullies, valleys and valley networks that are also deeply incised into the terrain surface. All these landforms and associated processes play an important role for the landscape’s hydrology, energy budget and carbon cycle. Our investigations have aimed at 1) understanding the evolution of thermokarst and thermal erosion in the Lena Delta Ice Complex throughout the Holocene, 2) quantifying current terrain changes (permafrost degradation and aggradation) as well as the contribution of different landform types to organic matter export from the Ice Complex to the Lena River, and 3) deducing potential future thermokarst and thermo-erosional activity. Our methodological approach has been a combination of geomorphological analyses in the field and based on satellite imagery and digital elevation models (DEM), sediment and water sampling. As main results we would like to highlight the following: - Thermokarst development started during the transition from Pleistocene to Holocene and has evolved throughout the Holocene. - Only a minor part of the third terrace in the Lena Delta provides the conditions for the future formation of thermokarst and thermo-erosional landforms, because a large area has already been degraded by thermokarst and thermal erosion during the Holocene. - Newly developing thermokarst landforms will not be able to grow to such large sizes as the existing Holocene thermokarst landforms. - The existing landforms vary much in their activity: some thermokarst lakes and thermo-erosional valleys are expanding and actively erode the Ice Complex deposits, many have been stable over the last decades and some lakes have shrunk or drained thereby giving way for permafrost to reestablish. - This variation of erosion activity is also reflected in different hydrogeochemical compositions of the waters in thermokarst lakes and streams in thermo-erosional valleys: water samples from eroding sites have higher concentrations of dissolved organic carbon (DOC) than stable sites, while thermokarst lakes in the drainage pathway act as DOC-reducing landscape components along the transport route. Acknowledgments. We wish to thank all colleagues who supported our field work in the Lena Delta during the past ten years and helped with sample processing in the lab. A. Morgenstern was supported by the German Academic Scholarship Foundation and by the Helmholtz Association (grant PD-003)