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首页> 外文期刊>Journal of Geophysical Research. Biogeosciences >Spatial patterns of soil nitrification and nitrate export from forested headwaters in the northeastern United States
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Spatial patterns of soil nitrification and nitrate export from forested headwaters in the northeastern United States

机译：美国东北部森林水源地土壤硝化和硝态氮输出的空间格局

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摘要

Nitrogen export from small forested watersheds is known to be affected by N deposition but with high regional variability. We studied 10 headwater catchments in the northeastern United States across a gradient of N deposition (5.4 - 9.4 kg ha ~(-1) yr ~(-1)) to determine if soil nitrification rates could explain differences in stream water NO _3 ~- export. Average annual export of two years (October 2002 through September 2004) varied from 0.1 kg NO _3 ~--N ha ~(-1) yr ~(-1) at Cone Pond watershed in New Hampshire to 5.1 kg ha ~(-1)) yr ~(-1) at Buck Creek South in the western Adirondack Mountains of New York. Potential net nitrification rates and relative nitrification (fraction of inorganic N as NO _3 ~-) were measured in Oa or A soil horizons at 21-130 sampling points throughout each watershed. Stream NO _3 ~- export was positively related to nitrification rates (r ~2 = 0.34, p = 0.04) and the relative nitrification (r ~2 = 0.37, p = 0.04). These relationships were much improved by restricting consideration to the 6 watersheds with a higher number of rate measurements (59-130) taken in transects parallel to the streams (r ~2 of 0.84 and 0.70 for the nitrification rate and relative nitrification, respectively). Potential nitrification rates were also a better predictor of NO _3 ~- export when data were limited to either the 6 sampling points closest to the watershed outlet (r ~2 = 0.75) or sampling points <250 m from the watershed outlet (r ~2 = 0.68). The basal area of conifer species at the sampling plots was negatively related to NO _3 ~- export. These spatial relationships found here suggest a strong influence of near-stream and near-watershed-outlet soils on measured stream NO _3 ~- export.
机译：众所周知，森林小流域的氮输出受氮沉降的影响，但区域差异很大。我们研究了美国东北部10个上游水源地的氮沉降梯度（5.4-9.4 kg ha〜（-1）yr〜（-1）），以确定土壤硝化速率是否可以解释溪流水NO _3〜-的差异。出口。两年（2002年10月至2004年9月）的年平均出口量从新罕布什尔州锥塘流域的0.1 kg NO _3〜--N ha〜（-1）yr〜（-1）到5.1 kg ha〜（-1 ））〜（-1）在纽约西部阿迪朗达克山脉的Buck Creek South。在整个流域的21-130个采样点的Oa或A土壤层中，测量了潜在的净硝化速率和相对硝化作用（无机N的含量为NO _3〜-的分数）。流NO_3〜-的出口与硝化率（r〜2 = 0.34，p = 0.04）和相对硝化（r〜2 = 0.37，p = 0.04）成正相关。通过在平行于河流的样带中进行较高的速率测量（59-130），将考虑因素限制在6个流域上，可以大大改善这些关系（硝化速率和相对硝化的r〜2分别为0.84和0.70）。当数据仅限于最接近流域出口的6个采样点（r〜2 = 0.75）或距流域出口<250 m的采样点（r〜2）时，潜在的硝化速率也是NO _3〜-出口的较好预测指标。 = 0.68）。采样区针叶树种的基础面积与NO _3〜-出口呈负相关。在此发现的这些空间关系表明，近溪流域和近流域出口土壤对测得的溪流NO _3〜-的出口影响很大。

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