Templer Pamela H, Weathers Kathleen C, Lindsey Amanda, Lenoir Katherine, Scott Lindsay
Department of Biology, Boston University, Boston, MA, 02215, USA,
Oecologia. 2015 Jan;177(1):5-15. doi: 10.1007/s00442-014-3121-5. Epub 2014 Nov 19.
Atmospheric inputs of N and S in bulk deposition (open collectors) and throughfall (beneath canopy collectors) were measured in and adjacent to two Class 1 wilderness areas of the northeastern US. In general, atmospheric S inputs followed our expectations with throughfall S fluxes increasing with elevation in the White Mountains, New Hampshire and throughfall S fluxes being greater in coniferous than deciduous stands in both sites. In contrast, throughfall N fluxes decreased significantly with elevation. Throughfall NO3 (-) fluxes were greater in coniferous than deciduous stands of Lye Brook, Vermont, but were greater in deciduous than coniferous stands of the White Mountains. We found overlap in the range of values for atmospheric N inputs between our measurements and monitoring data [National Atmospheric Deposition Program (NADP) and Clean Air Status and Trends Network (CASTNET)] for wet and total (wet + dry) deposition at Lye Brook. However, our measurements of total S deposition in the White Mountains and bulk (wet) deposition at both Lye Brook and the White Mountains were significantly lower than NADP plus CASTNET, and NADP data, respectively. Natural abundance (18)O in throughfall and bulk deposition were not significantly different, suggesting that there was no significant biological production of [Formula: see text] via nitrification in the canopy. NO3 (-) concentrations in streams were low and had natural abundance (18)O values consistent with microbial production, demonstrating that atmospheric N is being biologically transformed while moving through these watersheds and that these forested watersheds are unlikely to be N saturated.
在美国东北部的两个一类荒野地区及其附近，对大气中氮和硫在大气沉降（开放式收集器）和穿透雨中（树冠层下方收集器）的输入量进行了测量。总体而言，大气硫输入量符合我们的预期，在新罕布什尔州怀特山脉，穿透雨中的硫通量随海拔升高而增加，且在两个地点，针叶林林分中的穿透雨硫通量均高于落叶林林分。相比之下，穿透雨氮通量随海拔显著降低。在佛蒙特州莱布鲁克，针叶林林分中的穿透雨硝酸根通量高于落叶林林分，但在怀特山脉，落叶林林分中的穿透雨硝酸根通量高于针叶林林分。我们发现，在莱布鲁克，我们对大气氮输入量的测量值与监测数据[国家大气沉降计划（NADP）和清洁空气状况与趋势网络（CASTNET）]中湿沉降和总沉降（湿沉降 + 干沉降）的氮输入量范围存在重叠。然而，我们对怀特山脉总硫沉降以及莱布鲁克和怀特山脉的大气湿沉降的测量值分别显著低于NADP加CASTNET和NADP数据。穿透雨和大气沉降中的天然丰度氧-18没有显著差异，这表明树冠层中通过硝化作用产生[化学式：见原文]的量不显著。溪流中的硝酸根浓度较低，其天然丰度氧-18值与微生物产生一致，这表明大气氮在流经这些流域时正在进行生物转化，并且这些森林流域不太可能处于氮饱和状态。
