Yale School of Forestry and Environmental Studies, 210 Prospect Street, New Haven, Connecticut 06511, USA.
Ecol Appl. 2010 Oct;20(7):1820-37. doi: 10.1890/09-1125.1.
In tropical regions, the effects of land-cover change on nutrient and pollutant inputs to ecosystems remain poorly documented and may be pronounced, especially in montane areas exposed to elevated atmospheric deposition. We examined atmospheric deposition and canopy interactions of sulfate-sulfur (SO4(2-)-S), chloride (Cl-), and nitrate-nitrogen (NO(3-)-N) in three extensive tropical montane land-cover types: clearings, forest, and coffee agroforest. Bulk and fog deposition to clearings was measured as well as throughfall (water that falls through plant canopies) ion fluxes in seven forest and five coffee sites. Sampling was conducted from 2005 to 2008 across two regions in the Sierra Madre Oriental, Veracruz, Mexico. Annual throughfall fluxes to forest and coffee sites ranged over 6-27 kg SO4(2-)-S/ha, 12-69 kg Cl-/ha, and 2-6 kg NO(3-)-N/ha. Sulfate-S in forest and coffee throughfall was higher or similar to bulk S deposition measured in clearings. Throughfall Cl- inputs, however, were consistently higher than Cl- amounts deposited to cleared areas, with net Cl- fluxes enhanced in evergreen coffee relative to semi-deciduous forest plots. Compared to bulk nitrate-N deposition, forest and coffee canopies retained 1-4 kg NO(3-)-N/ha annually, reducing NO(3-)-N inputs to soils. Overall, throughfall fluxes were similar to values reported for Neotropical sites influenced by anthropogenic emissions, while bulk S and N deposition were nine- and eightfold greater, respectively, than background wet deposition rates for remote tropical areas. Our results demonstrate that land-cover type significantly alters the magnitude and spatial distribution of atmospheric inputs to tropical ecosystems, primarily through canopy-induced changes in fog and dry deposition. However, we found that land cover interacts with topography and climate in significant ways to produce spatially heterogeneous patterns of anion fluxes, and that these factors can converge to create deposition hotspots. For land managers, this finding suggests that there is potential to identify species and ecosystems at risk of excess and increasing deposition in montane watersheds undergoing rapid transformation. Our data further indicate that montane ecosystems are vulnerable to air pollution impacts in this and similar tropical regions downwind of urban, industrial, and agricultural emission sources.
在热带地区，土地覆盖变化对生态系统养分和污染物输入的影响记录甚少，而且可能非常显著，尤其是在高山地区，那里更容易受到大气沉降的影响。我们研究了三种广泛的热带山地土地覆盖类型（空地、森林和咖啡农林）中的硫酸盐硫（SO4(2-)-S）、氯（Cl-）和硝酸盐氮（NO(3-)-N）的大气沉降和冠层相互作用。在墨西哥东马德雷山脉的两个地区的七个森林和五个咖啡站点测量了对空地的总沉降和雾沉降以及穿透雨（穿过植物冠层的水）离子通量。采样时间为 2005 年至 2008 年。森林和咖啡站点的年穿透雨通量范围为 6-27kg SO4(2-)-S/ha、12-69kg Cl-/ha 和 2-6kg NO(3-)-N/ha。森林和咖啡穿透雨中的硫酸盐-S 高于或与空地测量的总 S 沉降量相似。然而，穿透雨 Cl-输入量始终高于清除区的 Cl-沉降量，与半落叶森林相比，常绿咖啡增强了净 Cl-通量。与总硝酸盐-N 沉降相比，森林和咖啡冠层每年保留 1-4kg NO(3-)-N/ha，减少了 NO(3-)-N 对土壤的输入。总的来说，穿透雨通量与受人为排放影响的新热带地区的报告值相似，而总 S 和 N 沉降量分别是远程热带地区背景湿沉降率的九倍和八倍。我们的结果表明，土地覆盖类型显著改变了大气输入到热带生态系统的大小和空间分布，主要是通过雾和干沉降引起的冠层变化。然而，我们发现，土地覆盖与地形和气候以显著的方式相互作用，产生阴离子通量的空间异质模式，这些因素可以汇聚形成沉积热点。对于土地管理者来说，这一发现表明，有可能识别出在经历快速转型的山地流域中，面临过量和不断增加的沉积风险的物种和生态系统。我们的数据进一步表明，在顺风的城市、工业和农业排放源下风的类似热带地区，山地生态系统容易受到空气污染的影响。
