Article: Tundra wildfire triggers sustained lateral nutrient loss in Alaskan Arctic by Abbott and colleagues (2021)
Background: Wildfires are constantly in the news. For some that might not be a surprise-- global climate change increases the frequency of extreme environments which results in many areas experiencing high temperatures and dry conditions. As such, these environments become more susceptible to wildfires, which then promote even more drastic changes in ecosystem health. The Arctic is the last place one would expect a wildfire; however, they are expected to increase in frequency by 4- to 11-fold by 2100. Because wildfires directly influence stream nutrient input (i.e., lateral nutrient flux) via the melting of soil permafrost (frozen layer of soil that contains large carbon/nutrient stocks), Abbott and colleagues use stream and soil nutrient concentrations as indicators of terrestrial ecosystem health post-wildfire. In order to predict the effects of future wildfires on ecosystem health and the global carbon budget, it is important to study the effects of rare wildfire events on the Arctic ecosystem now.
Methods: Abbott and colleagues’ study area was along the Anaktuvauk River in the North Slope of Alaska (150km south of the Arctic Ocean). In 2007, a lightning strike caused a wildfire that burned 1039km2 of Arctic tundra which resulted in a loss of 7700g (~17lbs) of organic carbon per m2 of land. To measure large-scale ecosystem characteristics, water samples were collected from a helicopter at 42 tributaries (adjacent to burned and unburned areas) covering a 110km range. As with the water samples, soil samples were collected at unburned, moderately burned, and severely burned sites to determine carbon, nitrogen, and other nutrient stocks.
Findings: Carbon and nitrogen stocks in plants were similar in both burned and unburned sites-- showing that the plant community had recovered from fire. However, carbon and nitrogen stocks within the active layer of soil (belowground) were 22-85% lower at burned sites compared to unburned sites. Organic nutrient (carbon, nitrogen, phosphorus, sulfur) movement from terrestrial soils to stream water (i.e., lateral nutrient flux) was 25-65% greater in burned areas compared to unburned areas. Therefore, streams adjacent to more severely burned areas contained higher concentrations of organic matter.
Conclusions: For terrestrial Arctic ecosystems, nutrient loss to adjacent stream networks is devastating when considering that the soils are nutrient limited to begin with. Since the samples were collected 10 years post-wildfire, the findings represent a lingering nutrient composition deficit.This can severely inhibit this ecosystem’s ability to recover from increased wildfire frequency. Further, permafrost in the Arctic has historically been able to offset much of the greenhouse gasses that humans emit. As permafrost continues to melt and wildfires become more common, permafrost will be less available to buffer us from more extreme climate change. Previously it was believed that burned terrestrial environments in the Arctic caused nutrient loss to adjacent streams to decrease; however, Abbott and colleagues have found the opposite to be true. These important findings will allow us to adjust our future predictions of how wildfires will impact the Arctic plant community, permafrost structure, and adjacent stream health.
Figure: Study site which includes the 2007 Anaktuvuk River wildfire area and surrounding wastersheds.
Reference:
Abbott, B.W., et al. “Tundra wildfire triggers sustained lateral nutrient loss in Alaskan Arctic.” Global Change Biology (2020).
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