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Nitrogen transport by rivers of south Asia

机译：南亚河流的氮素运输

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The South Asian rivers show a discharge weighted average NOd3-N of 2 mg/l and average sediment-bound N, that is mostly organic, of 0.2%. The reported global average for the uncontaminated river system is of the order of about 0.028 mg/l (NOd3-N). Hence, our freshwater aquatic systems can no longer be considered natural, at least with respect to nitrogen transport. The average is still below the WHO limit of 100 1 mg/ NOd3-N for drinking water, but there are extreme variations in different rivers (Ganges, Krishna, etc. (India)) and at different locations (Cauvery at Tiruchirapalli 29 mg/l, Ganges at Patna, 140 mg/l, etc.). Sediment-bound N is generally less than 1%, but values as high as about 3% have been reported for some rivers indicating rapid transfer of soil organic matter to rivers as particulate organic nitrogen. While the nitrogen story for various groundwater regions is well understood as representing fertilizer run-off, the riverine N is yet to be studied in detail; the link between river processes and global climate change would warrant urgent study of the river system of South Asia, that carries an annual water flux of about 2100 kmu3 (about 6% of global run-off) and an annual sediment flux of over one billion tons (about 10% of global flux). Rough calculations of available data indicate that the total N flux from rivers to oceans in South Asia is likely to be several factors higher than that indicated by some representative contaminated rivers of the world.
机译：南亚河流域的排放加权平均NOd3-N为2 mg / l，平均沉积物结合氮（主要为有机物）为0.2％。据报告，未受污染的河流系统的全球平均值约为0.028 mg / l（NOd3-N）。因此，至少在氮运输方面，我们的淡水水生系统不再被认为是天然的。平均值仍然低于WHO的饮用水极限100 1 mg / NOd3-N，但是不同河流（甘格斯，克里希纳等（印度））和不同地点（蒂鲁吉拉伯利的农耕地29 mg / l，巴特那的恒河，140 mg / l等）。沉积物结合的氮通常小于1％，但是据报道，某些河流的氮含量高达3％，表明土壤有机质以颗粒状有机氮的形式迅速转移到河流中。人们已经很好地理解了各个地下水区域的氮含量代表着肥料的径流，但仍需对河流氮进行详细研究。河流过程与全球气候变化之间的联系将需要对南亚河流系统进行紧急研究，该系统的年水通量约为2100 kmu3（约占全球径流量的6％），年沉积物通量超过10亿吨（约占全球通量的10％）。对现有数据的粗略计算表明，南亚从河流到海洋的总氮通量可能要比世界上一些受污染的典型河流所表明的高。

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