Summer surface water chemistry dynamics in different landscape units from Yedoma Ice Complex to the Lena River

• Main Authors: Polakowski, Lydia, Morgenstern, Anne, Boike, Julia, Bornemann, Niko, Overduin, Paul
• Format: Conference Object
• Language: unknown
• Published: Bibliothek Wissenschaftspark Albert Einstein 2016
• Subjects: Arctic; Arctic Ocean; Relict Lake; Weir; Ice; lena river; permafrost; Thermokarst
• Online Access: https://epic.awi.de/id/eprint/43291/; https://epic.awi.de/id/eprint/43291/1/ICOP_2016_Book-of-Abstracts_793.pdf; https://hdl.handle.net/10013/epic.49765; https://hdl.handle.net/10013/epic.49765.d001

The effect of climate warming on the degradation of permafrost in Arctic coastal lowlands and associated hydrological and biogeochemical processes varies between different types of permafrost deposits. The Lena River Delta consists of three geomorphological main terraces that differ in their genesis and stratigraphic, cryological, geomorphological and hydrological characteristics. The third terrace was formed during the late Pleistocene and consists mainly of Yedoma-type Ice Complex deposits, whereas the first terrace has formed during the Holocene by deltaic processes. Permafrost degradation on both terraces releases dissolved organic carbon (DOC) to thermokarst lakes and via streams DOC gets transported to the Lena River channels and the Arctic Ocean. This presentation shows 1. differences in the surface water chemistry between the first terrace and the Yedoma Ice Complex and their landforms, 2. analyses of the temporal variability of DOC during the summer, and 3. an estimation of summer DOC flux for the considered catchment of about 6.45 km2. Between June and September 2013 and 2014, respectively summer surface water and soil water samples were collected in a small catchment in the south of Kurungnakh Island in the central Lena River Delta. This catchment covers the first terrace as well as the Yedoma Ice Complex and is characterized by thermokarst lakes and streams on both terraces. Two weirs were installed in the main stream along the drainage flow path to continuously measure discharge during summer 2013. We divided the study area into landscape units and compared pH, electrical conductivity, stable isotopic composition and DOC concentrations between units and between terraces. The considered landscape units are streams and thermokarst lakes on Yedoma Ice Complex and on the first terrace, Yedoma uplands, streams, which are fed by the Ice Complex, a relict lake on the first terrace and the Olenyokskaya Channel, a main branch of the Lena River. DOC concentrations in the landscape units on Yedoma Ice Complex ranged between 3.5 mg L-1 (streams) and 52.5 mg L−1 (soilwater of Yedoma uplands) and on the first terrace between 2.8 mg L−1 (streams) and 15.6 mg L−1 (relict lake). The electrical conductivity on Yedoma Ice Complex ranged between 35 μS cm-1 (soilwater of Yedoma uplands) and 151 μS cm−1 (streams) and on the first terrace between 54 μS cm−1 (streams and relict lake) and 140 μS cm−1 (streams). δ18O values on Yedoma Ice Complex and first terrace ranged between -22.4 ‰ (soilwater of Yedoma uplands) and -16.4 ‰ (streams) and between -20.4 ‰and -14.7 ‰ (streams), respectively. δD ranged between -165.6 ‰ (soilwater of Yedoma uplands) and 125.5 ‰ (streams, which are fed by the Ice Complex) and between -160.8 ‰ and -119.4 ‰ (streams). Source waters on the Yedoma Ice Complex had higher DOC concentrations and lower electrical conductivity than Yedoma Ice Complex thermokarst lakes and the drainage flow path. This suggests that more labile organic carbon, perhaps derived from permafrost degradation on the Yedoma Ice Complex, enriches the lake but is removed from the lake, for example, by mineralization in the water column. Along the drainage flow path no further decrease of DOC concentration was observed, despite increasing discharge from weir 1 at the beginning of the flow path to almost two and a half times at weir 2 at the end of the flow path, and despite decreasing discharge during the measuring period from 1814 m3 d−1 in the end of July to 199 m3 d−1 in the end of August for weir 1 and from 2819 m3 d−1 in the end of July to 567 m3 d−1 in the end of August for weir 2. The temporal variability of DOC concentration during the sampling periods was low. In 2013 one sample site of soil water collection fluctuated slightly in August between 10.5 mg L−1 and 13.3 mg L−1, whereas the remaining landscape units showed no temporal variability. In 2014 the DOC concentration of the relict lake on the first terrace decreased from July (13.5 mg L−1) to September (11.1 mg L−1). Otherwise there were no changes in DOC concentration in the remaining landscape units. DOC measurements of the Olenyokskaya Channel show a decrease in DOC concentration from 12.4 mg L−1 in June to 7.6 mg L−1 in September. Using discharge data of 2013 a summer DOC flux of about 220 kg in 29 days for the study site above weir 2 with an area of 6.45 km2 was calculated.