NWT RESEARCH DATABASE

Tags: physical sciences, soil, vegetation, climate change, environmental change, snow depth, tundra ecosystems, nutrient levels, biogeochemistry, nitrogen

Objective(s): To substantially advance our understanding of how Canadian arctic tundra ecosystems function, and therefore how they are likely to be affected by perturbations such as climate change, resource development and extraction, and atmospheric pollution.

Project Description: The goal of this research over the next five years is to substantially advance our understanding of how Canadian arctic tundra ecosystems function, and therefore how they are likely to be affected by perturbations such as climate change, resource development and extraction, and atmospheric pollution. Specifically, the researchers will focus on the impacts on vegetation due to warmer summer temperatures, deeper winter snow, increased nutrient availability and changes in herbivory. This research will involve sampling of small pieces of soil and vegetation from an area within a 5 km radius of the Daring Lake Research Station, as well as from the small experimental manipulations (fertilizer plots (5 x 7 m), snow fences (15 m), greenhouses (~2 x 5 m) and fenced enclosures (20 x 20m)) that have been set up within an approximate 3 km area close to the station. Question 1) What is the significance of biogeochemical processes during winter and spring-thaw to overall annual nitrogen cycling in tundra ecosystems? This question will be addressed through long-term manipulations of snow depth (fences) and nitrogen availability (using additions of the stable isotopic tracer 15N in late Fall) at Daring Lake. The effects of deepened snow on winter and springtime nitrogen availability to plants will be studied, as well as soil solution and microbial pools, and run-off/leachates in the subsequent spring and summer seasons. Relative partitioning amongst microbial and vegetation components including shrubs will be determined using the 15N label. Question 2) What are the principal controls on the functioning of common tundra ecosystem types, and how are they likely to be affected directly and indirectly by climate change? As indicated in previous Aurora Research Permits (e.g. #14124R; #14277), the researcher has initiated and now maintain a series of strategic long-term experiments in birch hummock tundra at Daring to investigate the response dynamics and interactions between various factors that are expected to be altered by future climate (e.g. snow accumulation, vegetation distributions). These experiments will provide the essential foundation to characterize many of the major controls on the functioning of an ecosystem-type that extends across a large section of the Canadian low Arctic, and to contrast our findings with those from other major arctic research sites (e.g. Toolik Lake in Alaska, and Abisko in Sweden). Question 3) Are shrubs becoming more abundant in the Canadian low arctic? Although recent shrub density increases and expansion have been well characterized in Alaskan tundra, we currently know very little about corresponding vegetation change in northern Canada. Ten longterm shrub monitoring plots have been established (100 m2) at Daring in 2006 and detailed maps were made indicating shrub density, height, and branching architecture. These measures will be repeated in 2011. In addition, at a larger scale, the research team will compare and ground-truth IKONOS high resolution satellite images of the Daring region from 2000 with 2010. Question 4) What is the outcome of tundra plant-soil microbial competition for nitrogen over the 5-10 year time scale? When nitrogen is added to tundra, soil microbes tend to accumulate most of it within days to weeks. Over five year and longer time scales, continued large nutrient additions result in enhanced plant uptake, presumably because microbes are ‘saturated’ and no longer competing. Although these studies have been interpreted as indicators of potential impacts of increased nutrient availability associated with faster decomposition due to climate warming, actual rates of increase are likely to be much lower. If so, will plants gain access to the enhanced Nitrogen, or will they be outcompeted by ‘hungry’ (i.e. unsaturated) microbes? To investigate the medium term temporal dynamics of plant-microbial competition for moderately enhanced nitrogen availability, the researchers have three experiments (single large additions; ongoing low level additions; and 15N additions) and will monitor the plots over the next five years. Question 5) What are the impacts of herbivory on vegetation production and composition, and how might these impacts be altered as a result of climate change. The exclosure plots will be used described above to investigate how herbivory from caribou and small mammals interacts with vegetation growth and composition. Specifically, plant growth, leaf tissue chemistry inside and outside the exclosures will be measured to characterize the effects of herbivores, and to investigate if plant leaf chemistry (secondary metabolites) alters when herbivory is excluded. The research team is in close interaction with staff at the Department of Environment and Natural Resources. The researchers plan on giving a public talk in Yellowknife summarizing the current state of knowledge and hopefully getting some feedback which can be incorporated into future research plans. Copies of the publications achieved through this research will be forwarded to the Aurora Research Institute, and the Division of Environment and Natural Resources, Government of NWT for distribution to the communities. The research team participates in the Daring Lake Science Camp each year. Just as in 2007 and 2008, the researchers will try to recruit at least one local student from the science camp or locally from Yellowknife to stay on and help with vegetation and soil sampling. The research team will actively participate (i.e. present and discuss) at local science and public meetings that are feasible for the researchers to attend. The fieldwork for this study will be conducted from July 14, 2011 to September 9, 2011.