Regional nitrogen budgets and riverine N&P fluxes for the drainages to the North Atlantic Ocean: Natural and human influences
Regional nitrogen budgets and riverine N&P fluxes for the drainages to the North Atlantic Ocean: Natural and human influences
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DOI：
10.1007/bf02179825
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发表时间：
1996-10-01
期刊：
影响因子：
4
通讯作者：
Zhu, ZL
中科院分区：
文献类型：
--
作者：
Howarth, RW;Billen, G;Zhu, ZL
我们提出了从北美、南美、欧洲和非洲的14个地区流向北大西洋的河流总氮和总磷通量的估计，这些地区共同构成了通往北大西洋的流域。亚马孙盆地是总磷通量的主导区域，单位面积磷通量最高。来自亚马逊的总氮通量也很大，在整个北大西洋地区13.1Tg年(-1)的总氮通量中贡献了3.3Tg年(-1)。然而，在单位面积上，最大的氮通量出现在北海周围高度扰动的流域、欧洲西北部和美国东北部，所有这些流域的河流氮通量都超过1,000公斤N公里(-2)年(-1)。在所有区域，非点源氮源主导着流向沿海的河流氮通量。北大西洋盆地温带地区的河流总氮通量与人口密度有关，正如以前在世界主要河流中观察到的硝酸盐通量一样。然而，更引人注目的是，河流总氮通量与温带地区人类活动产生的氮输入总量(化肥使用、人类导致大气中氮氧化物的沉积增加、豆类作物的固定以及农产品中氮的进出口)之间存在很强的线性相关性。平均而言，河流中的区域氮通量只占这些人类活动产生的氮素输入的25%。湿地和水生生态系统中的反硝化作用可能是主要的汇，森林中的储存可能也很重要。地下水中的氮素储存虽然在一些地方很重要，但在所有地区都是一个非常小的氮素输入汇。农业氮源在许多地区，特别是密西西比盆地和北海流域的投入中占主导地位。在一些地区，如美国东北部，氧化氮沉积是河流氮素出口的主要控制因素。使用来自相对原始地区的数据作为变化指数，我们估计，许多温带地区的河流氮通量比工业化前增加了2到20倍，尽管一些地区，如加拿大北部，相对没有变化。来自受干扰最严重的北海流域的通量增加了6到20倍。来自亚马逊盆地的通量也至少是来自未受干扰的温带地区的估计通量的2至5倍，尽管该区域的人口密度和人为氮输入都很少。这表明热带地区的天然河流氮素通量可能显著大于温带地区。然而，森林砍伐可能是造成热带通量的原因之一。无论是哪种情况，预计未来几十年化肥使用量和大气沉降量的增加都可能导致许多热带河流系统的氮素负荷大幅增加。
We present estimates of total nitrogen and total phosphorus fluxes in rivers to the North Atlantic Ocean from 14 regions in North America, South America, Europe, and Africa which collectively comprise the drainage basins to the North Atlantic. The Amazon basin dominates the overall phosphorus flux and has the highest phosphorus flux per area. The total nitrogen flux from the Amazon is also large, contributing 3.3 Tg yr(-1) out of a total for the entire North Atlantic region of 13.1 Tg yr(-1). On a per area basis, however, the largest nitrogen fluxes are found in the highly disturbed watersheds around the North Sea, in northwestern Europe, and in the northeastern U.S., all of which have riverine nitrogen fluxes greater than 1,000 kg N km(-2) yr(-1).Non-point sources of nitrogen dominate riverine fluxes to the coast in all regions. River fluxes of total nitrogen from the temperate regions of the North Atlantic basin are correlated with population density, as has been observed previously for fluxes of nitrate in the world's major rivers. However, more striking is a strong linear correlation between river fluxes of total nitrogen and the sum of anthropogenically-derived nitrogen inputs to the temperate regions (fertilizer application, human-induced increases in atmospheric deposition of oxidized forms of nitrogen, fixation by leguminous crops, and the import/export of nitrogen in agricultural products). On average, regional nitrogen fluxes in rivers are only 25% of these anthropogenically derived nitrogen inputs. Denitrification in wetlands and aquatic ecosystems is probably the dominant sink, with storage in forests perhaps also of importance. Storage of nitrogen in groundwater, although of importance in some localities, is a very small sink for nitrogen inputs in all regions. Agricultural sources of nitrogen dominate inputs in many regions, particularly the Mississippi basin and the North Sea drainages. Deposition of oxidized nitrogen, primarily of industrial origin, is the major control over river nitrogen export in some regions such as the northeastern U.S.Using data from relatively pristine areas as an index of change, we estimate that riverine nitrogen fluxes in many of the temperate regions have increased from pre-industrial times by 2 to 20 fold, although some regions such as northern Canada are relatively unchanged. Fluxes from the most disturbed region, the North Sea drainages, have increased by 6 to 20 fold. Fluxes from the Amazon basin are also at least 2 to 5 fold greater than estimated fluxes from undisturbed temperate-zone regions, despite low population density and low inputs of anthropogenic nitrogen to the region. This suggests that natural riverine nitrogen fluxes in the tropics may be significantly greater than in the temperate zone. However, deforestation may be contributing to the tropical fluxes. In either case, projected increases in fertilizer use and atmospheric deposition in the coming decades are likely to cause dramatic increases in nitrogen loading to many tropical river systems.