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Terrestrial organic matter characterization in Arctic River through molecular and isotopic analyses

Final Report Summary - TOMCAR-PERMAFROST (Terrestrial organic matter characterization in Arctic River through molecular and isotopic analyses)

The Terrestrial Organic Matter Characterization in Arctic River (TOMCAR-Permafrost) project, led by Dr. Roman Teisserenc, focused on the comprehension of organic matter (OM) and contaminant dynamics within two arctic rivers (Great Whale River in Canada and Yenisei River in Russia). Developed within the framework of global carbon cycle modification due to global warming, the project objectives were to assess the quality and quantity of organic carbon fluxes and associate contaminants (such as mercury) to the Arctic Ocean.
Indeed, this ocean is the one that receive the most terrestrial inputs relative to its volume. Arctic terrestrial ecosystem has also the particularity to host the largest permafrost area and the largest soil organic carbon stock with half of world soil organic carbon. It is also an area that record the greatest warming and future scenario suggest that this warming will be disproportionally higher in this area. In brief, we have a huge stock of organic carbon, stored in a frozen ground that started to thaw at an unprecedented rate but we still have little information about the fate of this carbon. Will it produce atmospheric CO2, CH4? Will it be predominantly transferred to deeper soil horizons or transferred to the aquatic ecosystem? This project is focusing on this last point. As several contaminants are found associated with organic matter in natural environment, we also track their dynamics within this project.
In order to achieve these goals, we implemented field-based laboratories at each river outlet in order to integrate a whole watershed dynamic. While we monitored the Great Whale River only during a spring flood, we monitored the Yenisei River during 2 years. For each sampling day, we took more than 150 variables and parameters (from hydrology to organic matter molecular level analysis).
For the Great Whale River, we can highlight several results:
- During this period, the Great Whale River has exported between 200 and 700 tons of dissolved organic carbon (DOC) per day
- Molecular characteristics of this DOC is extremely variable during the flood event, ranging from old, altered DOC to fresh, labile DOC.
- We observe a partition of this quality between DOC and particulate organic carbon (POC), with fresher DOC coming mostly from the leaching of softwoods.
- Snow cover is variable along the period and unfrozen part of the watershed composition directly influence DOC composition within the river.
- Mercury concentrations ([Hg]), both in particulate and dissolved phase, increase during the flood event and [Hg] recorded are among the highest recorded for Arctic rivers
For the Yenisei River, main results to date are the following:
- Thanks to our high resolution sampling, DOC export from the Yenisei basin was estimated to be the largest of all arctic rivers with more than 5 Tg.yr-1. Quality of this DOC is highly variable trough time with “fresher” organic carbon during the spring flood.
- We measured the highest level of Hg in an Arctic river during the 2014 spring freshet providing key results for our comprehension of Arctic Hg budget.
- Remote sensing showed promising results in order to monitor organic carbon dynamics at the Yenisei river outlet.

In conclusion, these results collected within the TOMCAR-Permafrost project bring new information about the fate of DOC and POC in Arctic rivers and will help to understand the Hg cycle in the Arctic Ocean.
Our approach has numerous advantages with respect to previous biogeochemical studies of Arctic rivers. Isotopic and molecular level analyses of dissolved and particulate organic carbon are increasingly used in freshwater ecosystems. To the best of our knowledge, no study has reported their combined use in Arctic rivers along with spatial analysis. Within the theoretical frame of global change, much needed scientific results could be expected from such a study. For the first time we were able to generate new knowledge on the quality of organic matter and its potential implication for the local and global carbon cycle (old and young carbon during spring freshet).
As interest in Polar environments among the research community has increased, our project fits completely into the next step of understanding the organic carbon cycle in these environments. This new knowledge can be use both in the understanding of greenhouses gas emissions and the fate of contaminants. Furthermore it will help modeller to precise the carbon cycle and potential retroaction from terrestrial and aquatic ecosystems.
Taking into consideration the role of Europe within the sustainable development frame and as a world leader on environmental issues, there is no doubt that this research will participate to this leadership. Strategically, Europe should care about this ecosystem and the anthropogenic pressure it undergoes. Currently very coveted, the Arctic region needs particular scientific, environmental and political consideration. Climate change is global so the positive or negative feedbacks of permafrost thawing on climate has a significant impact for European countries. Furthermore, the release of contaminants associated with organic matter into the Arctic Ocean is becoming a considerable environmental health concern for northern European populations.
Documentary film:
In order to promote the research done under TOMCAR-Permafrost project, with a particular focus on sampling mission in remote area, Franco-Russian collaboration set up and logistical challenge raised by arctic fieldwork, we produced a film that can be watch here: