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Almost invariably, higher nutrient concentrations are found at the lowermost sites along large rivers, due to a variety of human activities. Nitrate values typically are elevated by runoff of agricultural fertilizer, and phosphorus values by sewage effluent. However, changing geological conditions along a river’s length may also contribute to longitudinal trends. Lowlands are more heavily farmed and settled than upland regions because they are more suitable for agriculture, and so the relative importance of human influence versus underlying conditions is difficult to separate. The strong influence of human presence is unmistakable, however. Long-term data from the Mississippi River establish that nitrate concentrations changed little from the turn of the century until the 1950s and then roughly doubled in the following 35 years, coincident with a steady rise in fertilizer application of the same time period (Turner and Rabalais, 1991). Human population density in the watersheds of 42 major rivers of the world was found to explain 76﹪of the variation in average annual nitrate concentration (Peierls et al.,1991).





2 Answers

  • Vic
    Lv 6
    1 decade ago
    Favorite Answer

    幾乎不變的是,由於種種的人類活動,沿著大河的最低處被發現了較高的營養濃度。硝酸鹽的數值典型地因為農業肥料的流出而升高,而磷的數值則是由於污水的排放。然而,沿著一條河的全程來改變地質條件也可能促成縱趨勢。低地比高地區域被更高度的耕作與殖民,因為它們更適合農耕,所以相對情況下的人類影響的相對重要性並不容易去分割。然而,人類存在的強烈影響是明顯的。來自密西西比河的長期資料證實了從20世紀開始直到50年代期間內硝酸鹽濃度有少量的改變,然後在接下來的35年內大概增加了一倍,與相同時期內肥料運用的穩定增加相吻合(Turner and Rabalais, 1991)。世界42條主要河流流域的人口密度被發現用以解釋了平均每年硝酸鹽濃度變化量的76%(Peierls et al.,1991).。

    Source(s): mE
  • ?
    Lv 7
    1 decade ago

    幾乎不變,高營養集中在最下站點沿著大的河發現,由於多種人活動。 硝酸鹽估價通常農業肥料的決賽,和磷價值以滲漏污水舉起。 不過,兌換沿著一河長度的地質狀況可能也為長度趨勢做貢獻。 與高地地區相比較,低地被更重耕種並且解決,因為他們更適於農業, 因此人影響與為條件的基礎的相對的重要性難分開。 但是,人出席的強大的影響是明顯的。 來自密西西比河的長期的數據確定硝酸鹽集中從世紀之交改變得很少, 直到20世紀50年代然後粗略在以下的35 年加倍, 用在相同的時間段(特納和Rabalais,1991)的肥料應用方面的一次穩定的升高一致 . 在世界的42條主要的河的流域的人人口密度被發現解釋76 ﹪年平均硝酸鹽集中那些變化(Peierls et al.,1991).

    Source(s): 天之心
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