Mayorga Emilio, Aufdenkampe Anthony K, Masiello Caroline A, Krusche Alex V, Hedges John I, Quay Paul D, Richey Jeffrey E, Brown Thomas A
School of Oceanography, University of Washington, Seattle, Washington 98195, USA.
Nature. 2005 Jul 28;436(7050):538-41. doi: 10.1038/nature03880.
Rivers are generally supersaturated with respect to carbon dioxide, resulting in large gas evasion fluxes that can be a significant component of regional net carbon budgets. Amazonian rivers were recently shown to outgas more than ten times the amount of carbon exported to the ocean in the form of total organic carbon or dissolved inorganic carbon. High carbon dioxide concentrations in rivers originate largely from in situ respiration of organic carbon, but little agreement exists about the sources or turnover times of this carbon. Here we present results of an extensive survey of the carbon isotope composition (13C and 14C) of dissolved inorganic carbon and three size-fractions of organic carbon across the Amazonian river system. We find that respiration of contemporary organic matter (less than five years old) originating on land and near rivers is the dominant source of excess carbon dioxide that drives outgassing in medium to large rivers, although we find that bulk organic carbon fractions transported by these rivers range from tens to thousands of years in age. We therefore suggest that a small, rapidly cycling pool of organic carbon is responsible for the large carbon fluxes from land to water to atmosphere in the humid tropics.
河流中的二氧化碳通常处于过饱和状态，导致大量的气体逸出通量，这可能是区域净碳收支的一个重要组成部分。最近有研究表明，亚马逊河的二氧化碳逸出量是其以总有机碳或溶解无机碳形式输送到海洋的碳量的十倍以上。河流中高浓度的二氧化碳主要源于有机碳的原位呼吸作用，但对于这种碳的来源或周转时间，目前尚无定论。在此，我们展示了对亚马逊河系中溶解无机碳以及有机碳三个粒径级分的碳同位素组成（13C和14C）进行广泛调查的结果。我们发现，源自陆地和河流附近的现代有机物质（年龄小于五年）的呼吸作用是导致中大型河流二氧化碳逸出的过量二氧化碳的主要来源，尽管我们发现这些河流输送的总有机碳组分的年龄范围从数十年到数千年不等。因此，我们认为，一小部分快速循环的有机碳库是造成潮湿热带地区从陆地到水体再到大气的大量碳通量的原因。
