氮和硫在人为扰动的青藏高原高寒森林中的分布特征

青藏高原海拔高、降水少、气温低、生态系统脆弱,其中高寒森林面积占青藏高原总面积的12.1%,是该地区具有代表性的生态系统。高寒森林气温低、海拔高、氮硫生物化学反应速率低,导致其氮硫沉降临界负荷低于热带和亚热带森林,对大气氮硫沉降增加敏感。增加的氮硫沉降可能对高寒森林土壤和地表水化学产生负面影响,进而破坏森林生态系统的生态平衡和健康。选取人为扰动地区的青藏高原高寒森林(大通和湟源站点)为研究对象,分析氮硫在穿透水、表层土壤水和地表水中的分布特征,为中国制定大气污染综合防治政策和青藏高原生态保护政策提供区域实例。大通和湟源高寒森林的穿透水、表层土壤水和地表水pH均位于6-8之间。Ca2+是穿透水、表层土壤水和地表水的主要盐基阳离子,SO4^(2-)和NO3-是主要阴离子。湟源高寒森林站点硫沉降量(0.48 keq·hm^(-2)·a^(-1))高于高寒森林最小硫沉降临界负荷0.22 keq·hm^(-2)·a^(-1)。两处高寒森林的氮沉降量(大通为0.22 keq·hm^(-2)·a^(-1),湟源为0.30 keq·hm^(-2)·a^(-1))均超过青藏高原平均氮沉降量0.21 keq·hm^(-2)·a^(-1),但低于高寒森林最小氮沉降临界负荷0.71 keq·hm^(-2)·a^(-1)。因此,硫沉降对该地区高寒森林的潜在威胁大于氮沉降。高寒森林的穿透水氮硫通量均高于表层土壤水(氮0.16 keq·hm^(-2)·a^(-1)、硫0.21 keq·hm^(-2)·a^(-1))和地表水氮硫通量(氮8.37×10^(-3)keq·hm^(-2)·a^(-1)、硫0.13 keq·hm^(-2)·a^(-1)),因此高寒森林枯落物层和高寒森林小流域均表现为氮汇和硫汇。尽管高寒森林地表水几乎没有氮硫输出,但是氮硫沉降的增加会导致表层土壤水和地表水中氮硫通量的升高,因此,持续增加的氮、硫污染物排放量加剧了对青藏高原高寒森林的生态威胁。

澳洲南部海域二甲基硫海气通量的分布及预测

海洋生物二甲基硫(DMS)的海气通量能改变云层的变化和区域的太阳辐射量,降低地球表面的温度,而极地的大量融冰导致DMS海气通量(DMSflux)对气候的影响更明显。文章中研究了2012—2014年亚南极几乎无冰的澳洲南部海域(40°S—60°S, 110°E—140°E)环境数据(包括:风速、云盖、海表温度、叶绿素、冰盖和混合层深度)的区域分布和年际变化。继而用遗传算法校准DMS模型的参数,得到DMS浓度和DMSflux在研究区域的分布。最后用耦合模型相互比较项目(CMIP5)试验预测未来(大约2100年)在四倍二氧化碳环境下的DMSflux,并与当代(2012—2014年)一倍二氧化碳的情形作比较。研究结果显示:四倍二氧化碳情形下的海表温度、云盖和风速分别上升了0.9%、5.6%和12.3%,混合层深度下降了41.0%;海气传输速度的增加率为58.8%,由于很少的融冰, DMS flux只增加了9.4%,因此, DMS flux的增加速度远比不上南北极。研究结果表明,亚南极几乎无冰的澳洲南部海域的DMS对减弱温室效应的作用不明显。

重庆地区硫平衡估算

本文根据实测重庆地区的SO_2和SO_4^(2-)的混合沉降速度,计算了硫干沉降通量。重庆硫干沉降密度大于湿沉降。区域内硫沉降密度为11.6g(s)m^(-2)·a(-1)。四面山硫沉降有70%来自重庆区域硫的传输。

The Relationship of Sulfate-methane Interface,the Methane Flux and the Underlying Gas Hydrate

The sulfate-methane interface is an important biogeochemical identification interface for the areas with high methane flux and containing gas hydrate. Above the sulfate-methane interface, the sulfate concentration in the sediment is consumed progressively for the decomposition of the organic matter and anaerobic methane oxidation. Below the sulfate-methane interface, the methane concentration increases continuously with the depth. Based on the variation characters of the sulfate and methane concentration around the sulfate-methane interface, it is feasible to estimate the intensity of the methane flux, and thereafter to infer the possible occurrence of gas hydrate. The geochemical data of the pore water taken from the northern slope of the South China Sea show the sulfate-methane interface is relatively shallow, which indicates that this area has the high methane flux. It is considered that the high methane flux is most probably caused by the occurrence of underlying gas hydrate in the northern slope of the South China Sea.

Methane Dynamics in Northern Peatlands: A Review

Northern peatlands store a large amount of carbon and play a significant role in the global carbon cycle. Owing to the presence of waterlogged and anaerobic conditions, peatlands are typically a source of methane (CH4), a very potent greenhouse gas. This paper reviews the key mechanisms of peatland CH4 production, consumption and transport and the major environmental and biotic controls on peatland CH4 emissions. The advantages and disadvantages of micrometeorological and chamber methods in measuring CH4 fluxes from northern peatlands are also discussed. The magnitude of CH4 flux varies considerably among peatland types (bogs and fens) and microtopographic locations (hummocks and hollows). Some anthropogenic activities including forestry, peat harvesting and industrial emission of sulphur dioxide can cause a reduction in CH4 release from northern peatlands. Further research should be conducted to investigate the in fluence of plant growth forms on CH4 flux from northern peatlands, determine the water table threshold at which plant production in peatlands enhances CH4 release, and quantify peatland CH4 exchange at plant community level with a higher temporal resolution using automatic chambers.