U.S. Geological Survey, Denver Federal Center, Denver, CO 80225, USA; Department of Geography University of California, Santa Barbara, CA 93106-4060, USA.
Department of Geography University of California, Santa Barbara, CA 93106-4060, USA.
Sci Total Environ. 2015 May 1;514:250-60. doi: 10.1016/j.scitotenv.2015.02.001. Epub 2015 Feb 7.
Sulfur, a nutrient required by terrestrial ecosystems, is likely to be regulated by atmospheric processes in well-drained, upland settings because of its low concentration in most bedrock and generally poor retention by inorganic reactions within soils. Environmental controls on sulfur sources in unpolluted ecosystems have seldom been investigated in detail, even though the possibility of sulfur limiting primary production is much greater where atmospheric deposition of anthropogenic sulfur is low. Here we measure sulfur isotopic compositions of soils, vegetation and bulk atmospheric deposition from the Hawaiian Islands for the purpose of tracing sources of ecosystem sulfur. Hawaiian lava has a mantle-derived sulfur isotopic composition (δ(34)S VCDT) of -0.8‰. Bulk deposition on the island of Maui had a δ(34)S VCDT that varied temporally, spanned a range from +8.2 to +19.7‰, and reflected isotopic mixing from three sources: sea-salt (+21.1‰), marine biogenic emissions (+15.6‰), and volcanic emissions from active vents on Kilauea Volcano (+0.8‰). A straightforward, weathering-driven transition in ecosystem sulfur sources could be interpreted in the shift from relatively low (0.0 to +2.7‰) to relatively high (+17.8 to +19.3‰) soil δ(34)S values along a 0.3 to 4100 ka soil age-gradient, and similar patterns in associated vegetation. However, sub-kilometer scale spatial variation in soil sulfur isotopic composition was found along soil transects assumed by age and mass balance to be dominated by atmospheric sulfur inputs. Soil sulfur isotopic compositions ranged from +8.1 to +20.3‰ and generally decreased with increasing elevation (0-2000 m), distance from the coast (0-12 km), and annual rainfall (180-5000 mm). Such trends reflect the spatial variation in marine versus volcanic inputs from atmospheric deposition. Broadly, these results illustrate how the sources and magnitude of atmospheric deposition can exert controls over ecosystem sulfur biogeochemistry across relatively small spatial scales.
硫是陆地生态系统所需的营养物质，但由于其在大多数基岩中的浓度较低，且在土壤中的无机反应中通常保留较差，因此在排水良好的高地环境中，它很可能受到大气过程的调节。即使在人为硫的大气沉降较低的情况下，大气硫源对未污染生态系统的控制作用也很少被详细研究过。在这里，我们测量了夏威夷群岛的土壤、植被和大气总沉降物中的硫同位素组成，目的是追踪生态系统硫的来源。夏威夷熔岩的地幔衍生硫同位素组成（δ(34)S VCDT）为-0.8‰。毛伊岛的总沉降物在时间上有变化，δ(34)S VCDT 范围从+8.2 到+19.7‰，反映了三种来源的同位素混合：海水盐（+21.1‰）、海洋生物源排放（+15.6‰）和基拉韦厄火山活跃喷口的火山排放（-0.8‰）。可以从相对较低（0.0 到+2.7‰）到相对较高（+17.8 到+19.3‰）的土壤 δ(34)S 值沿 0.3 到 4100 ka 的土壤年龄梯度的转变，以及在相关植被中的类似模式，来解释生态系统硫源的直接、风化驱动的转变。然而，在假定由大气硫输入主导的土壤年龄和质量平衡的土壤横切线上，发现了土壤硫同位素组成的亚公里尺度空间变化。土壤硫同位素组成范围从+8.1 到+20.3‰，通常随海拔（0-2000 米）、离海岸的距离（0-12 公里）和年降雨量（180-5000 毫米）的增加而降低。这些趋势反映了大气沉降中海洋与火山输入的空间变化。总的来说，这些结果说明了大气沉降的来源和数量如何在相对较小的空间尺度上对生态系统硫生物地球化学产生控制作用。
