A tracer approach to investigation of the nitrogen (N) cycle of streams, first developed at the Arctic LTER, has transformed scientific understanding of the nitrogen cycle and food web structure in flowing waters.
Research at the Arctic LTER site is transforming scientific understanding of how the arctic landscape will respond to climate change. Warming of the Arctic is thawing previously frozen ground (permafrost) and in some places, especially where there is buried ice, the thawed soil forms sinks and slumps called thermokarst terrain. In extreme cases this thermokarst terrain leads to complete failures of hillslopes in which tons of soil, organic matter, and associated nutrients are redistributed downslope and downstream. ARC LTER investigators have observed unequivocal evidence of accelerated rate of thermokarst formation in regions of arctic Alaska where permafrost warming is well advanced. For example, Gooseff et al. (2010) used aerial photographs to determine that the rate of thermokarst formation in this region of the Arctic was greater now than at any time over the past 20 to 30 years.
The addition of large amounts of soil to streams and rivers decreases light penetration through the water column and smothers the stream bed, both of which disrupt primary production at the benthic level (very bottom of the stream or lake) and the higher foodwebs in stream and lake ecosystems (Bowden et al. 2008). ARC LTER’s long-term experiments on the effect of small increases in phosphate concentrations suggest that nutrient additions such as these could shift the base of the stream’s primary productivity from algal diatoms attached to the surface of rocks to aquatic mosses. This shift could completely change the stream insect community, the primary food for stream fish. In addition to the direct effects on the ecology of streams, thermokarst terrain affects the broader landscape, altering the local soil nutrient and water conditions affecting microbial activity and soil biogeochemical dynamics. These changes in turn promote the development of different plant communities, primarily shrubs, which then alter the dynamics of snow accumulation during the winter and thaw during the spring. These altered characteristics of the landscape likely will have important influences on herbivores and the predators that depend on them, including humans. Finally, when permafrost thaws the massive store of carbon it contains is released and some is decomposed, releasing carbon dioxide and methane to the atmosphere. This release leads to the potential for a positive feedback loop of increased warming, increased thawing, and further carbon emissions that will have global, and not just local, impacts (Schuur et al. 2008).
Nobody knows exactly how much of the carbon in permafrost will eventually make its way to the atmosphere or what the long-term effects of thermokarst development will be on the arctic landscape. However, ARC LTER has developed information that has transformed scientific understanding of what happens to the chemistry and biology of terrestrial and aquatic habitats in the Arctic when permafrost thaws. This information is essential for managers and policymakers worldwide, who must make recommendations about how to react and adapt to future change in the arctic environment.
Bowden, W. B., M. N. Gooseff, A. Balser, A. Green, B. J. Peterson, and J. Bradford. 2008. Sediment and nutrient delivery from thermokarst features in the foothills of the North Slope, Alaska: Potential impacts on headwater stream ecosystems. Journal of Geophysical Research-Biogeosciences 113, G02026; doi:10.1029/2007JG000470.