High methane emissions from a littoral zone on the Qinghai-Tibetan Plateau

The littoral zones of lakes have been regarded as hotspots of methane (CH₄) fluxes through several studies. In the present study, we measured CH₄ fluxes in six kinds of littoral zones of Huahu Lake on the Qinghai-Tibetan Plateau in the peak growing season of 2006 and 2007. We found that CH₄ efflux (ranging from −0.1 to 90 mg CH₄ m⁻² h⁻¹) from the littoral zones of this lake was relatively high among those of boreal and temperate lakes. Our results also showed that emergent plant zones (Hippuris vulgaris and Glyceria maxima stands) recorded the highest CH₄ flux rate. The CH₄ flux in the floating mat zone of Carex muliensis was significantly lower than those of the emergent plant zones. CH₄ fluxes in the floating-leaved zone of Polygonum amphibium and bare lakeshore showed no significant difference and ranked last but one, only higher than that of the littoral meadow (Kobresia tibetica). Plant biomass and standing water depths were important factors to explain such spatial variations in CH₄ fluxes. No significant temporal variations in CH₄ fluxes were found due to the insignificant variations of physical factors in the peak growing season. These results may help in our understanding of the importance of the littoral zone of lakes, especially the emergent plant zone, as a hotspot of CH₄ emission.     

湖泊沉积物-水界面微量重金属扩散作用及其水质影响研究

通过对云南泸沽湖、洱海沉积物孔隙水微量重金属剖面特征及界面扩散通量的研究,定量评估了微量重金属界面扩散作用对上覆湖水水质的影响,并探讨了春季节性变化规律,结果表明,孔隙水微量重金属浓度面均呈典型的峰形分布,界面氧化还原状况的变化是影响这种分布的主要因素;微量重金属界面扩散通量在夏季明显大于冬季,深水区大于浅水区;这种擅长 用作用对湖水中微量重金属含量的变化影响较大,尤其对深度较小,水体寄宿时间长、     

Carbon exchange between ecosystems and atmosphere in the Czech Republic is affected by climate factors

By comparing five ecosystem types in the Czech Republic over several years, we recorded the highest carbon sequestration potential in an evergreen Norway spruce forest (100%) and an agroecosystem (65%), followed by European beech forest (25%) and a wetland ecosystem (20%). Because of a massive ecosystem respiration, the final carbon gain of the grassland was negative. Climate was shown to be an important factor of carbon uptake by ecosystems: by varying the growing season length (a 22-d longer season in 2005 than in 2007 increased carbon sink by 13%) or by the effect of short- term synoptic situations (e.g. summer hot and dry days reduced net carbon storage by 58% relative to hot and wet days). Carbon uptake is strongly affected by the ontogeny and a production strategy which is demonstrated by the comparison of seasonal course of carbon uptake between coniferous (Norway spruce) and deciduous (European beech) stands.     

Blue carbon in human-dominated estuarine and shallow coastal systems

Estuarine and shallow coastal systems (ESCS) are recognized as not only significant organic carbon reservoirs but also emitters of CO₂ to the atmosphere through air–sea CO₂ gas exchange, thus posing a dilemma on ESCS’s role in climate change mitigation measures. However, some studies have shown that coastal waters take up atmospheric CO₂ (C_atm), although the magnitude and determinants remain unclear. We argue that the phenomenon of net uptake of C_atm by ESCS is not unusual under a given set of terrestrial inputs and geophysical conditions. We assessed the key properties of systems that show the net C_atm uptake and found that they are often characteristic of human-dominated systems: (1) input of high terrestrial nutrients, (2) input of treated wastewater in which labile carbon is highly removed, and (3) presence of hypoxia. We propose that human-dominated ESCS are worthy of investigation as a contributor to climate change mitigation.     

A Budget Model to Scale Nutrient Biogeochemical Cycles in Two Semienclosed Gulfs

The nutrient dynamics of the Strymonikos and Ierissos Gulfs, two semienclosed coastal water bodies, are studied using a simple steady-state budget model, according to the Land–Ocean Interaction in the Coastal Zone modeling guidelines. Strymon river plume dynamics prevailed in the area of the Inner and Outer Srymonikos Gulfs, comprising two layers, while the Ierissos Gulf was defined as a one-box system. Seasonal and mean annual model input data for river discharge, precipitation, evaporation, and concentrations of salt, phosphorus, and nitrogen were obtained during four field campaigns. Results from the nitrogen and phosphorus cycling revealed the importance of river discharge in the horizontal and vertical transport of these substances within the system. Furthermore, it occurred that the major biogeochemical transformation of nitrogen and phosphorus takes place in the immediate nearshore zone (Inner Strymonikos Gulf), while the outer system sustains its nutrient dependence on oceanic exchanges. Therefore, under the summer low flow conditions, the river-influenced inner system acts as a net source of nitrogen and phosphorus, while under increased Strymon River discharge, phosphorus is transferred to the biological material (and the sediments), and the system moves to an autotrophic state. The outer system showed an opposite behavior being autotrophic throughout the year and heterotrophic in February. The Ierissos Gulf, a system not directly influenced by significant river discharge, experienced a seasonally independent behavior with net heterotrophic and denitrification processes prevailing. Model scenarios demonstrated that phosphate concentration increases, even under low river flow conditions and stimulates primary production in excess of respiration, resulting in nitrogen fixation prevalence in the Inner Strymonikos Gulf.     

Distribution of Ultraviolet solar Radiation at Riyadh Region, Saudi Arabia

The ultraviolet UV solar radiation flux is monitored over a fixed time interval to study the daily, monthly and annual variations for a nearly one decade in Riyadh. Mathematical expressions will be presented based on a comparison between theoretical and experimental values. It is believed that the present analysis of UV radiation suggest that the environmental effects led to a better understanding of UV scattering, UV reflection, ozone and clouds layers in Riyadh and other selected areas in the mid-east region.     

Fluxes of NH3 and HNO3 over heathland in the Netherlands:implications for chemical interactions

The surface exchange of NH₃ and HNO₃ gases over heathland was measured with the aerodynamic gradient method in Leende,the Netherlands during April 25 and May 9,1991.Due to reactions in the system NH₃,HNO₃ and NH₄NO₃,the NH₃ deposition flux is overestimated,while HNO₃ shows apparent emission fluxes mostly during the field experiment.Results reveal that NH₃ gradients are influenced slightly by HNO₃ and the HNO₃ gradients are strongly controlled by the NH₃.A clear relationship between NH₃ and HNO₃ gradient is suggested by the Leende experiment. Before the late afternoon,NH₃ deposition gradients will cause HNO₃ upward gradients,meanwhile the NH₃ gradients themselves will become smaller.After the HNO₃ upward gradient reaches maximum,the NH₃ deposition gradients will be enlarged or the emission gradients depressed,while the HNO₃ upward gradients become smaller.     

长江口潮滩湿地-大气界面碳通量特征

选择长江河口崇明东滩为典型研究区域,使用原位静态箱-气相色谱法,对长江河口潮滩湿地-大气界面碳通量(CH4和CO2)进行了为期一年的现场观测实验.结果表明,观测期内,崇明东滩低潮滩(CM-3)表现为碳的吸收汇,平均碳通量为-13.23 mg·m-2·h-4,且有明显的变化特征,8月为碳吸收的高峰期,2月碳的通量值最低;虽然低潮滩CH4年平均排放通量仅为0.04mg·m-2·h-1,在碳通量中所占比例很小,但却是大气CH4的持续排放源.中潮滩(CM-2)为大气CH4的排放源,在7月达到排放高峰;对CO2而言,光照条件下(明箱)以吸收为主,而无光照时(暗箱)中潮滩是CO2的排放源.中潮滩湿地-大气界面碳的年平均交换通量为51.79 mg·m-2·h-1,显著高于低潮滩,植被和有机质含量的不同是导致两者差异的主要原因.温度和光照是影响碳通量及其季节变化的重要因素.海三棱藨草植株和中、低潮滩藻类的光合作用均显著促进了潮滩对大气碳的吸收.     

Distributions of dimethylsulfide in the Bohai sea and Yellow Sea of China

IntroductionDimethylsulfide(CH3SCH3,DMS)isbelievedasthemostimportantvolatilesulfurcompoundreleasedfromtheseawater(Turner,1 988;Andreae ,1 990 ) .ThelatestestimationofDMSfluxfromtheoceantotheatmosphereis 2 0 7± 5 2Tg a ,accountingfor 85%ofglobalDMSsources(Watts,2 0 0 0 ) .AtmosphericDMSisinitiallyoxidizedbyOHinthedaytimeandnitrateradical(NO3)atnightasmajorsinksofDMSintheatmosphere(Andreae ,1 986;Yin ,1 990a ;Barnes ,1 996) .TheoxidationofatmosphericDMSseemstocontributelargelytot…     

Concentration field and turbulent fluxes during the mixing of two buoyant plumes

In this work an experimental study of mixing of two identical plumes, carried out in a turbulent neutral boundary layer generated in a wind tunnel, is presented. Measurements have been performed with fast flame ionisation detectors (FFIDs) and a two-component Laser-Doppler Anemometer system. Results allow the study of both the average and the fluctuating concentration field, including the turbulent vertical and longitudinal mass fluxes, in single plumes and during the interaction of two identical plumes. This information gives insight into the details of the mixing phase of the two plumes. Results of trajectories and additional rise (due to plume interactions) have been compared with previous measurements carried out in laminar cross-flows, showing similar behaviour. Concentration distributions in plume cross-sections in turbulent cross-flows differ from those measured in laminar cross-flows. Average vertical and longitudinal velocity measurements into the plume core show the strength of the shielding effect of the upwind plume and some details of interaction between the counter-rotating vortex pairs (CVPs). For large values of the alignment angle φ, between the line joining the stacks and the cross-flow, an average negative vertical velocity is measured in the middle of the plume even if its centre of mass is rising. This downward velocity is induced by the slow interaction of the CVPs and generates a vertical stretching of the plume and negative rise enhancement. Vertical turbulent fluxes change sign on the plume centreline and are of opposite sign with respect to the longitudinal turbulent fluxes. Results indicate a good linearity between vertical turbulent fluxes and concentration gradients, with different proportionality for the top and bottom parts of the plume (especially in the near field) indicating that dispersion could be described by a gradient-transfer model.