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Phosphorus output and confluence in the alpine forest streams of the upper reach of Yangtze River

基金项目：国家自然科学基金项目(No. 31170423,31270498,31200474);国家"十二五"科技支撑计划(No. 2011BAC09B05);四川杰出青年学术与技术带头人培育项目(No. 2012JQ0008,2012JQ0059)

摘要：长江上游水源涵养地高山森林溪流磷输出不仅是森林生态系统磷输出的主要形式,而且与下游水域环境密切相关,但对此人们一直缺乏必要的关注.因此,为了解森林溪流磷的最大输出潜力,于2013年8月中旬溪流流量较大的季节,调查了海拔3600~3700 m的高山森林18条溪流的磷输出及其从源头到尽头的变化特征.结果表明:在所选样地内,溪流中总磷储量为8120.1 mg,单位水体面积储量为5.4 mg · m^-2,单位水体面积总输出量为150.3 kg · km^-2 · d^-1,单位集水区面积总输出量为0.2 kg · km^-2 · d^-1,集水区潜在年输出总量约为67.7 kg · km^-2.溪流中总磷含量维持在检出限0.01~0.6 mg · L^-1之间,所有溪流上游总磷含量和储量均明显高于下游;溪流尽头总磷储量仅为源头总储量的29.2%,尽头平均浓度为源头平均浓度的30.9%.这些结果表明,高山森林溪流具有明显的磷输出特征,但从源头到尽头的汇流过程中,溪流水体能显著降低总磷含量及储量,表现出明显的自净能力,这也是高山森林生态系统养分传输纽带的重要体现.

Abstract：Phosphorus output from forest streams is not only the main phosphorus loss way in the water conservation areas of the upper Yangtze River, but also plays an important role in downstream waters environment. In order to understand the potential maximum phosphorus loss from forest streams, phosphorus output and content variations from source to end were investigated in 18 streams in an alpine forest (altitude 3600~3700 m) in mid August 2013. The results indicated that total phosphorus (TP) pool was 8120.1 mg in the sampling streams, and the unit water area of TP pool was 5.4 mg · m^-2. The phosphorus output of unit water area was 150.3 kg · km^-2 · d^-1 and that of the unit catchment area was 0.2 kg · km^-2 · d^-1. The estimated annual maximum phosphorus output was 67.7 kg · km^-2. TP content remained in 0~0.5 mg · L^-1 in the sampling streams. Additionally, TP content and pool upstream were higher than those downstream regardless of sampling streams, respectively. Total TP pool upstream was 29.2% of downstream and mean TP concentration upstream was 30.9% of downstream. These results suggested that a number of phosphorus lost from the alpine forest streams, but these streams with obvious self-purification ability could significantly reduce the output of TP as the streams flowing from up to downstream. The observations demonstrate that the streams act as important nutrition transport lines in the alpine forest.