The role of watershed characteristics, permafrost thaw, and wildfire on dissolved organic carbon biodegradability and water chemistry in Arctic headwater streams

[摘要] In the Alaskan Arctic, rapid climate change is increasing the frequency ofdisturbance including wildfire and permafrost collapse. These pulsedisturbances may influence the delivery of dissolved organic carbon (DOC) toaquatic ecosystems, however the magnitude of these effects compared to thenatural background variability of DOC at the watershed scale is not wellknown. We measured DOC quantity, composition, and biodegradability from 14river and stream reaches (watershed sizes ranging from 1.5–167 km²)some of which were impacted by permafrost collapse (thermokarst) and fire.We found that region had a significant impact on quantity andbiodegradability of DOC, likely driven by landscape and watershedcharacteristics such as lithology, soil and vegetation type, elevation, andglacial age. However, contrary to our hypothesis, we found that streamsdisturbed by thermokarst and fire did not contain significantly alteredlabile DOC fractions compared to adjacent reference waters, potentially dueto rapid ecosystem recovery after fire and thermokarst as well as thelimited spatial extent of thermokarst. Overall, biodegradable DOC rangedfrom 4 to 46 % and contrary to patterns of DOC biodegradability in largeArctic rivers, seasonal variation in DOC biodegradability showed no clearpattern between sites, potentially related to stream geomorphology andposition along the river network. While thermokarst and fire can alter DOCquantity and biodegradability at the scale of the feature, we conclude thattundra ecosystems are resilient to these types of disturbance.

[学科分类] 地球化学与岩石