水-气界面CO_2通量监测的静态箱法与薄边界层模型估算法比较

模型估算法与静态箱法是水-气界面气体通量监测的主要方法,因原理不同监测结果通常存在一定差异.目前对引起上述差异的主要环境因素仍不清晰.本研究使用自行设计的静态箱对三峡支流澎溪河水-气界面CO2通量进行监测,并与同步开展的CO2通量薄边界层模型估算法结果相比较,探讨该水域引起这两种监测方法结果产生差异的主要环境因素.结果表明,瞬时风速、水汽温差及水深均会对静态箱法及模型估算法的监测结果产生影响.风速越强、水汽温差越大、水深越大,这两种方法监测结果的差异就越小;而水域面积对两种方法的差异没有影响.比较发现,两种方法所获通量数据呈显著正相关,但静态箱法所获通量数据离散性显著高于薄边界层模型估算法.从方法的稳定性角度,在峡谷河道型水库水体温室气体监测中薄边界层模型估算法可能更为适宜.     

三峡澎溪河水-气界面温室气体模型估算及其敏感性分析

模型估算法是水-气界面温室气体通量监测的主要方法,所得成果也不胜枚举.然而监测过程中诸多环境因素会对最终结果产生不确定的影响.结合三峡库区澎溪河背景条件,利用模型估算法进行水-气界面温室气体通量(以CO_2为例)估算,并且采用修正Morris筛选法尝试分析模型估算法中各个参数对温室气体扩散通量(以CO_2为例)的局部敏感性.研究结果表明:利用模型估算法计算三峡澎溪河流域水-气界面温室气体通量具有较高的可行性和可靠性;风速、水温以及pH值会对监测结果产生影响,且风速越强、水温越高、pH值越小,CO_2扩散通量就越大;pH值是高灵敏参数,风速和水温是灵敏参数.在三峡库区澎溪河监测过程中更应注意pH值的精确性,每次采样前需校正仪器.     

西洞庭湖季节性淹水和植被类型对温室气体排放通量的影响

植被类型及淹水带来的干湿交替过程是影响温室气体排放的重要因素.本文通过原状土柱模拟实验,模拟西洞庭湖水文节律变化对不同土壤—植被系统温室气体排放的影响.利用静态箱—气相色谱法研究不同植被—土壤类型(芦苇湿地、灰化苔草湿地和刚砍伐的杨树林湿地)在季节性淹水条件下的CO_2、CH_4和N_2O的排放通量变化,并探讨了在水位变化的情况下,不同植被—土壤类型对全球增温潜势的贡献.结果表明:在不同的水文条件下,芦苇湿地的CO_2排放通量均显著高于苔草和杨树林湿地;淹水过程导致3种植被类型覆盖湿地CO_2排放通量显著降低,甲烷排放通量升高,其中芦苇湿地CH_4排放通量升高显著,苔草和杨树林湿地CH_4排放通量升高不明显;水文变化及植被类型对N_2O排放通量的影响不显著;不同植被类型湿地对全球增温潜势的贡献为:芦苇杨树林苔草,分别为16191.3、3405.6和1883.1 kg/hm~2.本研究结果表明在西洞庭湖湿地恢复过程中,不再人为增大芦苇湿地面积,将杨树林湿地恢复为苔草湿地,更有利于降低湿地恢复过程中温室气体的排放.     

水库温室气体净通量评估模型(G-res Tool)及在长江上游典型水库初步应用

目前准确量化温室气体排放量已成为气候变化研究和政策制定的关键.在IPCC水库温室气体净通量的概念性框架下,国际水电协会汇总分析了全球223座水库的CO₂和CH₄研究成果,构建了G-res Tool,其可以用于评估已建或待建水库在长时间尺度下的温室气体净通量.本文介绍了G-res Tool模型的基本原理与模型框架,利用模型内置数据库中所涉及的中国长江上游12座典型水库数据进行初步应用分析,12座水库温室气体净通量平均值为88.17 g CO₂e/（m²·a）,在全球约7000座水库中所处水平为11.67%,处于低阈值范围.在水库温室气体净通量分析结果中,其他非相关人类活动产生的水库温室气体通量（UAS）在蓄水后总通量（Post）中所占比重远高于蓄水前温室气体通量（Pre）.长江上游水库蓄水后的CH₄和CO₂通量对于温室效应的贡献量相当.通过将G-res Tool模型蓄水后的温室气体通量评估结果和所涉及到的12座水库中已发表的数据对比分析发现,G-res Tool具有简便、适用面广等特点.但G-res Tool毕竟仍为经验性模型,其基本原理和模块设计上的内在缺陷在很大程度上限制了其应用范围并造成了一定的不确定性.对个案水库而言,长期跟踪观测与机理研究仍是未来减少水库温室气体净通量不确定性的关键.     

亚热带城市湖泊与河流CO2气体通量特征及其影响因素

湖泊、河流等内陆水体是连接陆地生态系统和海洋的“长程碳环路”的重要节点,也是温室气体二氧化碳(CO₂)排放源,在调节陆地、海洋间的碳迁移转换中发挥着重要作用。相对于自然水体,城市水体因面积小、水深浅且受监测方法限制,水-气界面碳通量经常被忽略。为探讨我国亚热带城市水体温室气体排放特征,本研究以湖南省长沙市典型城市水体,包括洋湖、西湖、松雅湖、月湖4个湖泊和湘江长沙段为研究对象,分别于2022年4和10月采用光化学反馈-腔增强吸收光谱法(OF-CEAS)和扩散模型法对水-气界面CO₂通量进行对比测定。结果表明,长沙城市湖泊与河流春季为CO₂排放源,秋季为吸收汇,河流水-气界面CO₂通量呈显著季节差异。河湖之间CO₂通量在春季表现为显著差异,秋季差异不显著。CO₂通量与水体溶解氧、水体总氮浓度等呈显著正相关。2种方法的CO₂通量对比测定在湖泊上显著相关,但对河流而言相关性不显著。研究揭示的城市湖泊与河流CO₂气体的排放特征有利于深入探究城市水体碳的迁移转化,可对全面了解全球气候变化过程和河湖湿地温室气体减排和调控提供科学支撑。     

一种基于土壤温湿资料计算地表土壤热通量的温度预报校正法

分析大气边界层观测站地表能量平衡需要估计其地表土壤热通量。发展了一种由多层土壤温度和湿度观测资料估算土壤热通量的新方法。该方法首先求解一维热扩散方程得到土壤温度的基本廓线,然后校正所求温度廓线与观测值的偏差,最后积分温度廓线得到土壤各层的热通量。与众多的方法不同,该方法不需要事先给定不易准确测量和推求的热传导（或热扩散）系数值。通过与实测资料对比、模型合成数据试验、以及敏感性分析等,表明该方法的计算结果稳定可靠,对土壤表层数厘米深度内有无观测资料也不敏感。此外,指出热流板可准确测量热通量的方向和相位,但所测通量值的误差常较大。     

三峡水库CO2、CH4通量监测分析研究

自成库以来,三峡水库CO₂、CH₄等温室气体通量较蓄水前发生明显改变。如何科学认识和客观评估三峡水库修建及运行对其CO₂、CH₄等温室气体通量的影响备受关注。本文简要回顾了自2009年以来在三峡水库开展CO₂、CH₄等温室气体通量监测与分析工作,综述认为,现阶段三峡水库温室气体排放以水-气界面扩散释放为主要途径。陆源输入的有机碳是主导三峡水库CO₂、CH₄产生的主要碳源,但在局部区段或时段自源性有机碳的贡献亦十分显著。同蓄水前相比,三峡水库碳排放量呈现为净增加,淹没效应约占水库C净增量的20%,库区内点面源污染负荷并未对CO₂排放的净增量产生显著贡献,阻隔效应和生态系统重建效应对三峡水库碳排放的净增量产生显著贡献。近10年来,监测方法比对、监测点位优化等工作在一定程度上完善了三峡水库温室气体通量监测体系。新方法、新技术的引入也为三峡水库温室气体通量监测分析提供了有利支撑和保障,但复杂水文环境...     

大型水库分层期和混合期溶存温室气体空间变化及排放通量

水库作为温室气体的重要来源,对区域气候变化有不可忽略的影响。然而,目前对水库溶存温室气体的空间异质性及垂向特征的认知仍然欠缺。为了揭示水库分层期和混合期溶存温室气体空间特征及排放通量,也为厘清水库温室气体产生和排放的关键过程提供重要支撑。研究选择东北地区大型水库——汤河水库为对象,于2021年7—9月和10月(分别代表水库分层期和混合期)对水库不同位置(坝前、库中和库尾)开展溶存温室气体垂向分层监测。研究结果显示,水库CH₄排放通量变化范围为0.018～0.174 mmol/(m²·d),是大气CH₄的源,空间分布为库尾>库中>坝前;CO₂通量为-4.91～58.77 mmol/(m²·d),除分层期东支库尾,其余点位均表现为大气CO₂的源,空间分布为坝前>库中>库尾。时间上,分层期CH₄排放通量(0.071±0.044 mmol/(m²·d))高于混合期((0.027±0.008) mm...     

湖、库水体CH4冒泡排放研究进展

冒泡排放是湖、库水体CH₄排放的主要方式之一,其排放通量和占CH₄总排放量比例均具有极其显著的时空差异性,是当前水体CH₄排放估算不确定性的主要来源之一。然而,目前关于湖、库水体CH₄冒泡排放通量监测、时空分布规律、过程机制和模型模拟的系统梳理鲜有报道。本研究对比了目前水体CH₄冒泡的监测方法技术的适用性及优缺点,分析总结湖、库水体CH₄冒泡排放及通量的时空分布特征,梳理CH₄气泡在沉积物-水体中的产生-成长-迁移-释放的过程、影响因素及模型,并提出了水体CH₄冒泡过程模型框架。最后,本研究提出未来研究应基于湖、库水体分类、设备开发和改进来构建适应性的湖、库水体CH₄冒泡排放监测标准体系,开发基于过程的CH₄冒泡机理模型,为认识变化环境下湖、库水体CH₄冒泡过程和准确估算CH₄排放量提供支撑。     

城市景观湖泊不同时间尺度CH4通量特征及影响因素分析——以南京市莫愁湖为例

城市景观湖泊对温室气体的收支发挥着重要作用。本文以南京市莫愁湖为研究对象,采用静态箱-温室气体分析仪法实时监测湖泊水-气界面CH₄通量,分析湖泊主要温室气体CH₄在日尺度和季节尺度上因冒泡和扩散排放方式不同对其通量的影响,探究影响湖泊CH₄通量的因素。结果表明:(1)在日尺度上,四季24 h内CH₄均呈排放状态,受白天冒泡影响,四季CH₄总通量均存在白天高于夜间的日变化特征。(2)在季节尺度上,莫愁湖CH₄排放通量呈现显著的时空异质性,受冒泡通量的影响夏季CH₄通量明显高于春、秋、冬三季;B区的CH₄总通量(6.04 nmol/(m²·s))显著高于A区(3.82 nmol/(m²·s)),水体的营养化程度和离岸距离是空间变化的主要影响因素。A、B两区CH₄排放夏季以冒泡排放为主,春、秋、冬以扩散排放为主。(3)在日尺度上,CH₄通量受气温、水温、辐射和风速等气象要素影响,与水质参数间的关系不显著;在季节尺度上,CH₄通量与温度(气温、水温)、水体营养盐水平、叶绿素a浓度及富营养化程度的时间变化相一致,也随着水体透明度、pH和氧化还原电位的减小而呈增加的趋势。本研究为准确估算城市湖泊CH₄排放量提供重要的数据基础。     

Entrainment of meltwaters in hyperpycnal flows during deglaciation superfloods in the Gulf of Mexico

Northern Gulf of Mexico is a key archival site of the Laurentide Ice Sheet melting history and the only margins containing evidence of meltwater outflows contemporaneous with global meltwater pulse mwp-1A. Inconsistencies between these meltwater floods and the absence of strong climate responses to large freshwater fluxes predicted by climate models raised questions concerning the validity of planktonic foraminiferal δ¹⁸O record in the Gulf of Mexico as a reliable index of freshwater fluxes. Isotope records of depth-stratified foraminifera document unusual trends compatible with entrainment of ¹⁸O-depleted freshwaters in hyperpycnal flows reaching the seafloor and rising to the surface as buoyant plumes. These exceptionally large outbursts of floodwaters, coeval with a prominent erosion intensity peak in continental paleohydrology, were catastrophically released in a rapid succession over a period of ca. 500 yr (14.7–14.2 kyr). Correspondence in time and magnitude between the torrential floods and the mwp-1A event supports the view that LIS was likely a substantial freshwater source. Drainage of meltwaters through torrential hyperpycnal flows that underwent substantial mixing with seawater may resolve the problem with ocean modeling results that predict a much stronger climate response to large freshwater hypopycnal fluxes into the ocean.     

我国流域水生态监测与评价体系研究进展及发展对策

水生态监测与评价是水生态系统管理、保护和可持续利用的基础。20世纪80年代开始,欧美发达国家水环境管理政策开始强调生态保护,重视流域水生态质量,先后开展了以水生生物为核心的河流水生态监测与评价研究计划。然而我国目前流域水环境监测与评价的指标主要以传统的理化监测指标为主,缺乏指示水生态变化的水生生物指标,单一的水质改善无法反映水生态环境好转这一长远目标,不能满足“十四五”水生态环境管理由以水污染防治为主向水环境、水生态、水资源“三水”统筹转变的总体要求。本研究系统分析发达国家和地区(如美国、欧盟、澳大利亚等)水生态监测与评价技术体系与业务化运行方面的先进经验,总结梳理我国水生态监测与评价试点已有的工作基础,分析制约我国当前流域水生态监测与评价的关键问题,从保护目标、管理模式、监测网络、科学研究和公众参与五个方面,提出开展我国流域水生态监测与评价体系构建和业务化运行的有关建议,为准确评估和预测流域水生态质量状况的变化、开展保护修复成效评估提供决策支持和重要参考。     

Informing policy to protect coastal coral reefs: Insight from a global review of reducing agricultural pollution to coastal ecosystems

The continuing degradation of coral reefs has serious consequences for the provision of ecosystem goods and services to local and regional communities. While climate change is considered the most serious risk to coral reefs, agricultural pollution threatens approximately 25% of the total global reef area with further increases in sediment and nutrient fluxes projected over the next 50 years. Here, we aim to inform coral reef management using insights learned from management examples that were successful in reducing agricultural pollution to coastal ecosystems. We identify multiple examples reporting reduced fluxes of sediment and nutrients at end-of-river, and associated declines in nutrient concentrations and algal biomass in receiving coastal waters. Based on the insights obtained, we recommend that future protection of coral reef ecosystems demands policy focused on desired ecosystem outcomes, targeted regulatory approaches, up-scaling of watershed management, and long-term maintenance of scientifically robust monitoring programs linked with adaptive management.     

Quantifying CO2 fluxes from soil surfaces to the atmosphere

Measurements of CO₂ fluxes from ground surface of the atmosphere (soil respiration) are needed to quantify biotic and abiotic reaction rates in unsaturated zones and to gain insight into the importance of these processes on global warming. The use of three techniques (dynamic closed chambers, static chambers, and gradient calculations) to determine soil respiration was assessed by measuring fluxes of microbially produced CO₂ from an unsaturated mesocosm (2.4 m dia.×3.2 m thick) and two unsaturated minicosms (0.58 m dia.×1.2 m thick), one maintained at 18–23 °C (HT) and the other at 5 °C (LT). By injecting known and constant CO₂ fluxes into the bottom of the HT minicosm and measuring the resulting fluxes, it was shown that the dynamic closed chamber (DCCS) technique yielded accurate measurements of fluxes over the range observed from natural unsaturated media. Over this same range, results showed that the concentration gradient method yielded reasonable estimates of fluxes but its accuracy was limited by uncertainties in both the concentration gradient and the gaseous diffusion coefficient in the soil atmosphere. The static chamber method underestimated the actual flux at higher CO₂ fluxes and when adsorption times of >24 h were used.     

Exchange flux of total gaseous mercury between air and natural water surfaces in summer season

The exchanges of mercury between surface and air are of significance in the biogeochemical cycling of Hg in the environment, but there are still few reliable data on air/surface exchange in aquatic systems. Field measurement campaigns over seawater surface at Kristineberg Marine Research Station (KMRS) and over Hovg?rds?n River surface at Knobesholm in southwestern Sweden were conducted to measure mercury flux using a dynamic flux chamber technique coupled with automatic mercury vapor-phase analyzers. Both sites show net emissions during summer time. Mercury fluxes measured over both river and seawater surfaces exhibit a consistently diurnal pattern with maximum fluxes during the daytime period and minimum fluxes during the nighttime period. At freshwater site, mercury flux is strongly correlated with the intensity of net solar radiation, and negatively correlated with relative humidity. A typical exponential relationship between mercury flux and water temperature was observed at freshwater measurement site. At seawater site, a strong correlation between mercury flux and intensity of solar radiation was obtained. The driving force of mercury emission from water surface to air is the super-saturation of dissolved gaseous mercury in aqueous phase.     

Degassing of stratified magma by compositional convection

A new model is proposed for passive degassing from sub-volcanic magma chambers. The water content in stably stratified shallow magma chamber will be equated to its solubility at the upper boundary by convection. Water from a lower layer high in water content can enrich the contact zone of the upper layer and lead to further convective overturn of this boundary layer. A complete set of equations describing convection with bubble formation and dissolution is reduced to a simplified form by assuming a small bubble content. The development and pattern of flow driven by vesiculation is modeled numerically in a 2D magma chamber for relatively low Raleigh numbers (5×10⁵). Bubbles rising from the magma will collect near the roof in a layer of 8–10 vol% and then escape upward to fumaroles. The Stokes flux of bubbles escaping from an andesitic magma with viscosity 10⁴ P and a top surface of about 500×500 m corresponds with observed total magmatic water fluxes of 35 kg/s. Pressure within the chamber is buffered by elastic (and local visco-elastic) deformations in the solid rocks bounding the chamber to the range between ambient and close to lithostatic values. In a chamber closed to fresh magma inputs, the decrease in volume due to such gentle volatile escape lowers the reference pressure. Bubbles flux from the lower layer induced by variation of the saturation level around stratification boundary may be efficient mechanism for the water transport between layers.     

Defensive reactions of freshwater ecosystems against external influences

Eutrophication and toxic loading of freshwater occurred even in early geological epochs as a result of natural factors (e.g., large animals, volcanism), and nutrients and xenobiotics are more quickly integrated in material cycling in aquatic than in terrestrial systems. Therefore, aquatic ecosystems show many defensive mechanisms against organic and toxic loading. Many other defensive reactions can be described in addition to the well-known example of microbial self-purification.Freshwater ecosystems possess compartments which cooperate towards the function and protection of the whole system but, in opposition to these “euoecisms”, there are also “dysoecisms”. The defensive reactions of an ecosystem are founded largely on species-egoistic adaptations that have an (accidental) system-altruistic effect. The whole ecosystem reacts only seldom, and it is not clear whether there are selection processes which favour water bodies with a slow eutrophication and therefore slow silting-up, because the freshwaters are important for the global water balance.It is possible to compare organismic with ecosystemic defensive reactions but the origin of both reactions is very different.     

近地层能量闭合度对陆面过程模式影响

大量近地层观测试验表明,利用涡动相关法观测的湍流通量小于近地层可利用能量,即近地层能量是不闭合的,这种不闭合度一般为20%甚至更高.而陆面过程模式是基于地气间能量平衡建立,并且模式中的湍流边界层参数化方案通常根据实际观测的湍流通量来确定,因此能量不闭合必将对陆面过程模式造成一定的影响.本文利用2007年春季SACOL站的近地层观测资料,依据能量守恒将能量不闭合中的残余能量通过波文比分配到观测的湍流通量中,即修正涡动相关法观测的湍流通量使得近地层能量达到平衡;之后分别利用观测和修正的湍流通量,建立了能量不闭合和闭合情形下的湍流参数化方案,借助陆面过程模式SHAW,通过数值模拟和对比分析方法考察近地层能量闭合度对陆面过程模式的影响.研究结果表明近地层能量闭合对陆面过程模式有显著的影响:在陆面过程数值模拟中,当应用近地层能量不闭合的湍流通量形成的湍流参数化方案时,陆面过程模式会明显高估地表长波辐射及土壤温度;但当应用修正湍流通量使得近地层能量达到闭合形成的湍流参数化方案后,在不改变任何地表土壤物理生化属性的情况下,陆面过程模式能较好地模拟地表长波辐射和土壤温度.