Christensen T R, Johansson T, Olsrud M, Ström L, Lindroth A, Mastepanov M, Malmer N, Friborg T, Crill P, Callaghan T V
GeoBiosphere Science Centre, Physical Geography and Ecosystems Analysis, Lund University, Lund, Sweden.
Philos Trans A Math Phys Eng Sci. 2007 Jul 15;365(1856):1643-56. doi: 10.1098/rsta.2007.2035.
This is the first attempt to budget average current annual carbon (C) and associated greenhouse gas (GHG) exchanges and transfers in a subarctic landscape, the Lake Torneträsk catchment in northern Sweden. This is a heterogeneous area consisting of almost 4000 km2 of mixed heath, birch and pine forest, and mires, lakes and alpine ecosystems. The magnitudes of atmospheric exchange of carbon in the form of the GHGs, CO2 and CH4 in these various ecosystems differ significantly, ranging from little or no flux in barren ecosystems over a small CO2 sink function and low rates of CH4 exchange in the heaths to significant CO2 uptake in the forests and also large emissions of CH4 from the mires and small lakes. The overall catchment budget, given the size distribution of the individual ecosystem types and a first approximation of run-off as dissolved organic carbon, reveals a landscape currently with a significant sink capacity for atmospheric CO2. This sink capacity is, however, extremely sensitive to environmental changes, particularly those that affect the birch forest ecosystem. Climatic drying or wetting and episodic events such as insect outbreaks may cause significant changes in the sink function. Changes in the sources of CH4 through increased permafrost melting may also easily change the sign of the current radiative forcing, due to the stronger impact per gram of CH4 relative to CO2. Hence, to access impacts on climate, the atmospheric C balance alone has to be weighed in a radiative forcing perspective. When considering the emissions of CH4 from the mires and lakes as CO2 equivalents, the Torneträsk catchment is currently a smaller sink of radiative forcing, but it can still be estimated as representing the equivalent of approximately 14000 average Swedish inhabitants' emissions of CO2. This can be compared with the carbon emissions of less than 200 people who live permanently in the catchment, although this comparison disregards substantial emissions from the non-Swedish tourism and transportation activities.
这是首次尝试对亚北极地区景观（瑞典北部的托内湖流域）的年均碳（C）及相关温室气体（GHG）交换与转移进行预算。该地区情况复杂，包含近4000平方公里的混合石南荒原、桦木林、松林以及泥潭、湖泊和高山生态系统。这些不同生态系统中，以温室气体二氧化碳（CO₂）和甲烷（CH₄）形式存在的碳的大气交换量差异显著，从贫瘠生态系统中几乎没有通量，到石南荒原中少量的CO₂汇功能和较低的CH₄交换率，再到森林中显著的CO₂吸收以及泥潭和小湖泊中大量的CH₄排放。考虑到各个生态系统类型的面积分布以及将径流作为溶解有机碳的初步估算，整个流域的预算显示该地区目前对大气CO₂具有显著的汇能力。然而，这种汇能力对环境变化极为敏感，尤其是那些影响桦木林生态系统的变化。气候变干或变湿以及诸如昆虫爆发等偶发事件可能导致汇功能发生显著变化。由于每克CH₄相对于CO₂具有更强的影响，永久冻土融化增加导致的CH₄源变化也可能轻易改变当前辐射强迫的符号。因此，要评估对气候的影响，必须从辐射强迫的角度权衡单独的大气碳平衡。当将泥潭和湖泊中CH₄的排放换算为CO₂当量时，托内湖流域目前是一个较小的辐射强迫汇，但仍可估计相当于约14000名瑞典居民的平均CO₂排放量。这可以与该流域内永久居住的不到200人的碳排放进行比较，不过这种比较忽略了非瑞典旅游和交通活动的大量排放。
