| Abstrakt: |
Climate change in the Arctic leads to permafrost degradation and to associated changes in freshwater geochemistry. There is a limited understanding of how disturbances such as active layer detachments or retrogressive thaw slumps impact water quality on a catchment scale. This study investigates how permafrost degradation affects concentrations of dissolved organic carbon (DOC), total dissolved solids (TDS), suspended sediment, and stable water isotopes in adjacent Low Arctic watersheds. We incorporated data on disturbance between 1952 and 2015, as well as sporadic runoff and geochemistry data of streams nearby. Our results show that the total disturbed area decreased by 41% between 1952 and 2015, whereas the total number of disturbances increased by 66% in all six catchments. The spatial variability of hydrochemical parameters is linked to catchment properties and not necessarily reflected at the outflow. Degrading ice‐wedge polygons were found to increase DOC concentrations upstream in Ice Creek West, whereas hydrologically connected disturbances were linked to increases in TDS and suspended sediment. Although we found a great spatial variability of hydrochemical concentrations along the paired watershed, there was a linear relationship between catchment size and daily DOC, total dissolved nitrogen, and TDS fluxes for all six streams. Suspended sediment flux on the contrary did not show a clear relationship as one hydrologically connected retrogressive thaw slump impacted the overall flux in one of the streams. Understanding the spatial variability of water quality will help to model the lateral geochemical fluxes from Arctic catchments. Plain Language Summary: One effect climate change has in the Arctic is the thawing of permafrost. Permafrost is defined as ground that remains below 0 °C for at least two consecutive years. The low temperatures in the High North lead to very slow decomposition rates of organic material from plants and animals. A lot of this material has accumulated over thousands of years. As air temperatures in the Arctic are rising, permafrost is thawing. This is also termed permafrost degradation. It can occur in two forms: (1) The gradual deeper thawing of permafrost is called thermal perturbation. It might lead to a subsidence (sinking) of the ground, because water that was previously frozen runs off. (2) Thawing of the ground may lead to a destabilization of the ground and connected landslides. This is termed physical or surface disturbance. These two forms of permafrost degradation have an impact on the water quality of rivers flowing through the terrain. In this study, we investigated the impacts of permafrost degradation on stream hydrochemistry on Herschel Island, Yukon Territory, Canada. We identified active physical disturbances in the past using aerial photographs from 1952 and 1970 and satellites images from 2011 and 2015. This was done for the areas from which rainwater flows into the same river (catchment area) of six streams named Water Creek, Beach Creek, Fox Creek, Ice Creek West, Ice Creek East, and Eastern Gully. In 2016, we collected water samples along two neighboring streams (Ice Creek West and Ice Creek East) to compare the impacts of local physical disturbances on the hydrochemistry. In these two streams, we also measured water flow (discharge) during the monitoring season. We further collected samples at the outflow of the other four streams nearby. Water samples were analyzed in the laboratory for different chemical properties that help us to understand the influence of permafrost degradation. For the six streams, we found that the total disturbed area decreased by 41% between 1952 and 2015, whereas the total number of disturbances increased by 66%. We were able to link permafrost degradation to changes in chemical water composition within the two neighboring streams. It is important that disturbances are "hydrologically connected" to impact concentrations of inorganic compounds (total dissolved solids) and mud (suspended sediment) in the streams. Essentially, this means that water needs to flow through these disturbances to mobilize the material and influence the concentration in the stream. Taking all studied streams together, the overall flux of dissolved organic carbon, total dissolved solids, and total dissolved nitrogen (i.e., the amount of chemical compound [in kg] transported away in every liter of river water) depends on catchment size. The larger the catchment, the more of this material is transported away. This relationship could not be confirmed for suspended sediment, because a hydrologically connected retrogressive thaw slump heavily impacted the flux in one of the streams. This study is important because the river water ultimately drains into the Arctic Ocean and might change the water quality there. This may have consequences for the animals and plants living in the ocean. We need to understand the influence of permafrost degradation on stream water quality to assess future changes of the Arctic Ocean. Key Points: Between 1952 and 2015, the total disturbed area decreased by 41%, and the number of disturbances increased by 66%Hydrological connectivity of permafrost disturbances is essential to impact suspended sediment and solute concentrations in the streamThere is a linear relationship between catchment size and daily flux of dissolved organic carbon, total dissolved nitrogen, and solutes [ABSTRACT FROM AUTHOR] |
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