Assessing the reliability of δ15N as a proxy for atmospheric reactive N deposition in remote Arctic lakes: an integrated study of the biogeochemistry of δ15N in snowpack and lake sediments along a precipitation gradient in south-west Greenland

Chris J. Curtis1, N. John Anderson2, Gavin L. Simpson3, Vivienne J. Jones4, Jan Kaiser5, Erika Whiteford2, Suzanne McGowan6
1 School of Geography, Archaeology & Environmental Studies, University of the Witwatersrand
2 Dept of Geography, Loughborough University, Leicestershire, LE11 3TU, UK.
3 Dept of Biology, University of Regina, Saskatchewan, Canada
4 ECRC, University College London, Gower Street, London WC1E 6BT, UK.
5 School of Environmental Sciences, University of East Anglia, Norwich, NR4 7TJ, UK.
6 School of Geography, University of Nottingham Malaysia Campus, Jalan Broga 43500, Semenyih, Selangor Darul Ehsan, Malaysia.

O 3.3 in Fluxes between the atmosphere and ecosystems

17.07.2014, 11:40-12:00, H17

The relative impacts of anthropogenic nitrogen deposition and global climate change on remote Arctic and alpine lakes have been the subject of much debate in the recent literature. Some studies have attributed recent changes in diatom assemblages in lake sediment records to the effects of climate warming on ice-cover duration and increased growing season length, or associated impacts of warming on catchment mineralisation and fluxes of nutrients. Other studies have attributed similar changes to increased inputs of anthropogenic nitrogen deposition, even at extremely low levels, as such changes have been widely observed in alpine lakes in various regions of North America. However, there is generally a strong temporal association between trends in anthropogenic N deposition due to fossil fuel combustion and climate change indicators, due to their common source. Furthermore, diatoms are known to respond to both drivers and so the separation of the relative importance of nitrogen and climate impacts is a major challenge. The stable isotope of nitrogen 15N has been widely used as an indicator of anthropogenic N deposition impact on lake biogeochemistry on the premise that a recent depletion in d15N of bulk lake sediments may be due to increased inputs of N from anthropogenic sources assumed to be depleted in 15N. However, such studies often lack co-located measurements of both deposition and lake sediment d15N, and in reality the palaeolimnological d15N record may show differing, even opposing, patterns in spatially co-located sites. Here we combine stable isotope and chemical analyses of precipitation and snowpack combined with d15N analyses of 210Pb-dated sediment cores from three contrasting groups of Arctic lakes to elucidate the dominate controls and constraints on sediment records of altered N biogeochemistry in lakes. The study groups are located in west Greenland, a region which had showed a cooling rather than a warming signal until recently but importantly contains some lakes showing the classic d15N depletion in their sediment records. We compare three groups of lakes with contrasting limnologies across an inferred spatial gradient in N deposition, corresponding to a gradient in precipitation, from the relatively arid interior adjacent to the Greenland ice sheet to the much wetter coastal zone. We demonstrate that limnology, catchment attributes and other factors may break down the link between precipitation d15N and what is recorded in lake sediments.

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Letzte Änderung 19.06.2014