Going down to the river to sample

One week has passed and we still have not experienced any rain. The dry season is going on, the Zackenberg river level and speed are decreasing, the small streams are drying up.

Aiming at investigate and characterize the mobilization of mineral and organic compounds, we have dedicated our second week to collect water samples along the Zackenberg river and its main tributaries. For each sampling location, we collect 7 litters of water in order to have enough material for all our analyses (DOC, POC, biomarkers, DOM optical properties, 14C, minerals,…). We targeted sites before and after the main confluences in order to assess the different tributary contributions in dissolved and particulate export.

After sampling in the delta following a decreasing degree of salinity using our robust and loyal electric conductivity sensor, we walked upstream to sample the Aucella, Lindeman and Palnatoke rivers (map below).

Simplified geological map of the Zackenberg catchment area (Hasholt and Hagedorn, 2000; modified from Koch and Haller, 1965)

The Zackenberg river displays a typical cloudy look with a quite low electric conductivity (~44 µS cm-1) illustrating an important load of fine sediments but a low concentration in total dissolved solutes. Interestingly, within the delta, just before reaching the Young sound, a small and clear stream flows into the Zackenberg displaying a higher electric conductivity (picture in the right corner, ~200 µS cm-1). While no source of water is visible in the surroundings, we assume some subsurface flows coming from the deltaic sediments and enriched in dissolved solutes sustain the Zackenberg discharge.

Upstream, the three main streams – Aucella, Lindeman and Palnatoke – which flow into the Zackenberg river, also show higher electric conductivity values (from ~115 to 370 µS cm-1). The Lindeman and Palnatoke rivers display a great discharge of clear water and their influence in the main channel is clearly visible along tens of meters.

Gathering our courage, we hiked up to the lake in Store Sodal located at ~13 km far from the station. The full day journey was beautiful, tough on the way back with our 25 kg of load on our backs but the glacial valley hosting the lake offers a splendid view on the spikes of the Zackenberg and the mountains supporting glaciers. After 3h30 walking in landscapes as hospitable as the Mordor or squishy as peatlands, we discovered a long lake (6.5 km) of the same blurry water as the Zackenberg river but displaying a very low conductivity (~17 µS cm-1). Retracing our steps and loaded with heavy water, we observed the same water properties downstream until the confluence with Lindeman. Interestingly and as expected, while the cloudy appearance of the Zackenberg river remains all along, its electric conductivity significantly increases after meeting Aucella, Lindeman and Palnatoke and keeps high values until the outlet.

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