不同水文情景下洪泽湖二氧化碳排放通量特征及影响因素

内陆水域二氧化碳(CO₂)排放是全球碳平衡的重要组成部分,全球CO₂排放通量估算通常有很大不确定性,一方面源于CO₂排放数据观测的时空离散性,另一方面也是缺少水文情景与CO₂排放通量关联性的研究.本文观测了2018年洪泽湖不同水文情景表层水体CO₂排放通量特征,并探讨其影响因素.结果表明,洪泽湖CO₂排放通量为丰水期((106.9±73.4) mmol/(m²·d))>枯水期((18.7±13.6) mmol/(m²·d))>平水期((5.2±15.5) mmol/(m²·d)),且碳通量由丰(310.2~32.0 mmol/(m²·d))、枯(50.8~2.2 mmol/(m²·d))、平(-17.3~39.8 mmol/(m²·d))3种水文情景的交替表现出湖泊碳源到弱碳汇的转变,空间上CO₂排放通量总体呈现北部成子湖区低、南部过水湖区高的分布趋势.洪泽湖CO₂排放对水文情景响应敏感,特别是上游淮河流域来水量的改变,是主导该湖CO₂排放时空分异的重要因子.丰水期湖泊接纳了淮河更多有机和无机碳的输入,外源碳基质的降解和矿化显著促进了水体CO₂的生产与排放,同时氮、磷等营养物质的大量输入,加剧了水体营养化程度,进一步提高CO₂排放量,间接反映出人类活动对洪泽湖CO₂变化的深刻影响.平、枯水期随着上游淮河来水量的减少,驱动水体CO₂排放的因素逐渐由外源输入转变为水体有机质的呼吸降解.此外,上游河口区DOM中陆源类腐殖质的累积与矿化能够促进CO₂的排放,而内源有机质组分似乎并没有直接参与CO₂的排放过程.研究结果揭示了水文情景交替对湖库CO₂排放的重要影响,同时有必要进行高频观测以进一步明晰湖泊的碳通量变化及其控制因素.     

Simulated response of an intermittent stream to rainfall frequency patterns

The response of intermittent catchments to rainfall is complex and difficult to model. This study uses the spatially distributed CATchment HYdrology (CATHY) model to explore how the frequency of daily rainfall (λ) can affect the hydrologic regime of intermittent catchments. After a multi-objective calibration and validation of CATHY against experimental measurements of streamflow and groundwater levels in a catchment used as a pasture, the role of λ in affecting streamflow characteristics was explored using different scenarios. With different values of λ for the dry and wet periods of the year, CATHY showed that a series of frequent rainfall events was often associated with incipient streamflow, independent of the season. Activation of streamflow during the wet season was related to multiple factors and was not often associated with the shallow groundwater levels near the outlet of the catchment. The interplay between rainfall depth and intensity acted as the most important factor for the generation of streamflow. Using the difference between accumulated rainfall and evapotranspiration as a measure of wetness, saturated subsurface flow mechanism generated streamflow in simulations with wetness at least three times larger than mean wetness of other simulations. Although groundwater uprise near the outlet did not effectively contribute to streamflow in the initial days of flow, it strongly correlated with the magnitude of the runoff coefficient. Values of λ close or equal to the maximum value in the wet season can sustain the connectivity between groundwater and streamflow in the riparian zone. This connectivity increases the catchment wetness, which consequently results in an increase of the generated streamflow. Our study showed that rainfall regimes characterized by different λ were able to identify distinct flow regimes typical of either intermittent, ephemeral, or nonflowing catchments. Decrease of λ in the wet season is likely associated with a reduction of streamflow, with a shift of flow regime from intermittent to ephemeral or no-flow.     

Exploring sustainable aquaculture development using a nutrition-sensitive approach

Micronutrient deficiencies constitute a pressing public health concern, especially in developing countries. As a dense source of bioavailable nutrients, aquatic foods can help alleviate such deficiencies. Developing aquaculture that provides critical micronutrients without sacrificing the underlying environmental resources that support these food production systems is therefore essential. Here, we address these dual challenges by optimizing nutrient supply while constraining the environmental impacts from aquaculture. Using life cycle assessment and nutritional data from Indonesia, a top aquaculture producer, we sought to identify aquaculture systems that increase micronutrient supplies and reduce environmental impacts (e.g., habitat destruction, freshwater pollution, and greenhouse gas emissions). Aquaculture systems in Indonesia vary more by environmental impacts (e.g. three order of magnitude for fresh water usage) than by nutritional differences (approximately ± 50% differences from mean relative nutritional score). Nutritional-environmental tradeoffs exist, with no single system offering a complete nutrition-environment win–win. We also find that previously proposed future aquaculture paths suboptimally balance nutritional and environmental impacts. Instead, we identify optimized aquaculture production scenarios for 2030 with nutrient per gram densities 105–320% that of business-as-usual production and with environmental impacts as low as 25% of those of business-as-usual. In these scenarios Pangasius fish (Pangasius hypophthalmus) ponds prove desirable due to their low environmental impacts, but average relative nutrient score. While the environmental impacts of the three analyzed brackish water systems range from average to high compared to other aquaculture systems, their nutritional attributes render them necessary when maximizing all nutrients except vitamin A. Common carp (Cyprinus carpio) ponds also proved essential in maximizing zinc and omega n-3, while Tilapia (Oreochromis niloticus) cages were necessary in optimizing the production of calcium and vitamin A. These optimal aquaculture strategies also reduce business-as-usual demand for wild fish-based feed by 0–30% and mangrove expansion by 0–75% with no additional expansion into inland open waters and freshwater ponds. As aquaculture production expands globally, optimization presents a powerful opportunity to reduce malnutrition rates at reduced environmental impacts. The proposed reorientation promotes UN sustainable development goals 2 (zero hunger), 3 (health), 13 (climate action) and 14 (life under water) and requires concerted and targeted policy changes.     

Effects of land-based sources on water quality in the Omerli reservoir (Istanbul,Turkey)

The Omerli reservoir is located on the northeastern side of the Istanbul City. It is one of the most important sources of drinking water with a surface area of 23.1 km² and a volume of 220 × 10⁶ m³ in the Marmara Region. Water quality characteristics of the lake investigated from May 2002 to April 2003 enabled us to identify the effect of waste loads on water quality of Omerli Lake. The following parameters were measured in the lake water: temperature (16.1°C), conductivity (250 μS/cm), secchi disk depth (1.9 m), dissolved oxygen (DO) (9.36 mg/L), nutrients [ortho-phosphate (78.9 μg/L), nitrate + nitrite (707.5 μg/L) and ammonia-nitrogen (264 μg/L)], chlorophyll a (9.43 μg/L), total organic carbon (3.33 mg/L), total suspended solids (4.54 mg/L), total poly aromatic hydrocarbon (t-PAH) (0.69 μg/L) and copper (24.5 μg/L). T-PAH (16.5 mg/g-dry-w), Cu (96.5 μg/g-dry-w), organic carbon (org-C) (2.0%) and N (0.44%) were determined in the surface sediment. The values of chlorophyll a and DO in the upper layer were relatively high and low secchi disk depths indicates eutrophic state. There are five channels discharging water, including waste water, into the lake. All channels were sampled during six occasions in order to cover variations between seasons. The following parameters were measured: total organic carbon, total phosphorus, total kjeldahl nitrogen, ammonia and total suspended solids with the flow rates. The Göçbeyli stream has the highest flow into the lake (1.5 × 10⁸ m³/year) but most of the nutrients were discharged from the Pa?aköy channel. It is accounting for 81% of ammonia and 80% of total phosphorus into the lake. Three scenarios were run using AQUATOX model: (1) all existing inflows are discharging into the lake (present situation); (2) none is discharging; (3) all are discharging except the Pa?aköy channel. The first scenario produced concentrations consistent with measurements in the lake. In all stations, a phytoplankton peak value was predicted during November and December 2002, and January 2003. In the second scenario, as expected, a significant decrease in the concentrations was predicted. In the third scenario, a small improvement in the water quality was obtained. To significantly improve the state of the lake, instead of entering Pa?aköy channel, wastewater should bypass the lake.     

中国2050年的能源需求与CO2排放情景

 利用国家发展和改革委员会能源研究所能源环境综合政策评价模型（IPAC模型）,对中国未来中长期的能源需求与CO2排放情景进行了分析,对该情景的主要参数和结果进行了介绍,并对模型中的政策评价进行了介绍。同时报告了实现减排所需的技术。结果显示：未来中国经济将快速增长,能源需求和相应的CO2排放也将明显快速增加,与2005年相比,2030年能源需求可能增加1.4倍,2050年可能增加1.9倍。但中国也有较大的机会在2020年之后将能源需求量的增加幅度明显减小,将CO2排放控制住,使之不再出现明显增长,甚至有可能在2030年之后下降。     

CO2 threshold for millennial-scale oscillations in the climate system: implications for global warming scenarios

We present several equilibrium runs under varying atmospheric CO₂ concentrations using the University of Victoria Earth System Climate Model (UVic ESCM). The model shows two very different responses: for CO₂ concentrations of 400 ppm or lower, the system evolves into an equilibrium state. For CO₂ concentrations of 440 ppm or higher, the system starts oscillating between a state with vigorous deep water formation in the Southern Ocean and a state with no deep water formation in the Southern Ocean. The flushing events result in a rapid increase in atmospheric temperatures, degassing of CO₂ and therefore an increase in atmospheric CO₂ concentrations, and a reduction of sea ice cover in the Southern Ocean. They also cool the deep ocean worldwide. After the flush, the deep ocean warms slowly again and CO₂ is taken up by the ocean until the stratification becomes unstable again at high latitudes thousands of years later. The existence of a threshold in CO₂ concentration which places the UVic ESCM in either an oscillating or non-oscillating state makes our results intriguing. If the UVic ESCM captures a mechanism that is present and important in the real climate system, the consequences would comprise a rapid increase in atmospheric carbon dioxide concentrations of several tens of ppm, an increase in global surface temperature of the order of 1–2°C, local temperature changes of the order of 6°C and a profound change in ocean stratification, deep water temperature and sea ice cover.     

Evaluating the reliability of global historical land use scenarios for forest data in China

Global historical land use scenarios are widely used to simulate the climatic and ecological effects of changes in land cover; however, reliability evaluation of these scenarios for data on China's forests is missing. By using a historical document-derived Chinese forest dataset(CHFD) for the years 1700–2000, we evaluated the reliability of data on forests in China over three global scenarios—SAGE(Center for Sustainability and the Global Environment), PJ(Pongratz Julia), and KK10(Kaplan and Krumhardt 2010)—through trend-related, quantitative, and spatial comparisons. The results show the following:(1) Although the area occupied by forests in China in the SAGE, PJ, KK10, and CHFD datasets decreased over the past 300 years, there were large differences between global scenarios and CHFD. The area occupied by forests in China in the SAGE scenario for 1700–1990 was 20%–40% more than that according to CHFD, and that occupied by forests in the KK10 from 1700 to 1850 was 32%–46% greater than that in CHFD. The difference between the PJ and CHFD was lower than 20% for most years.(2) Large differences were detected at the provincial and grid cell scales, where the PJ scenario was closer to CHFD in terms of total forested area. Provinces with large differences in terms of trend and quantity were 84% and 92% of all provinces, respectively. Grid cells with relative differences greater than 70% accounted for 60%–80% of all grids.(3) These global historical land use scenarios do not accurately reveal the spatiotemporal pattern of Chinese forests due to differences in the data sources, methods of reconstruction, and spatial scales.     

Extreme Waves and Wave Run-up in Halifax Harbour under Climate Change Scenarios

The tendency for rising sea levels, combined with changes in the frequency and intensity of extreme storm events raises the potential for flooding and inundation of coastal locations such as Halifax Harbour, in the context of climate change. In this study, we consider three scenarios for extreme high water levels based on climate change scenarios and estimates for land subsidence, rising mean sea levels, and return period analysis for extreme events (from previous studies). We also investigate the effect of ocean waves on these estimates for extreme high water levels. Because the most damaging storm to make landfall in Nova Scotia over the last century was Hurricane Juan (2003), it was chosen to simulate the extreme case of storm-generated waves and wave run-up in Halifax Harbour. To simulate waves generated by Hurricane Juan, a nested-grid system consisting of two modern state-of-the-art operational wave models was used. High quality winds were used to drive the wave models, and the simulations used recently updated high resolution coastal bathymetry. Observed water elevation changes in Halifax Harbour were used in wave model simulations of Hurricane Juan. The Federal Emergency Management Agency's (FEMA) run-up model is used to estimate wave run-up elevation, which is validated with recorded high water observations along the coastline. Simulated waves and wave run-up elevations for Hurricane Juan suggest that the maximum significant wave heights at the mouth of the Harbour were 9.0 m, and the wave run-up was as high as 2.0 m along the shoreline of Halifax Harbour. In this way, we estimated the impact of waves and wave run-up on extreme high water elevations for three climate change scenarios in Halifax Harbour, under worst-case conditions. The sensitivity of these estimates is analyzed for different water level variations, wave propagation directions and shore slope profiles.

[Traduit par la rédaction] La tendance à la hausse du niveau de la mer de pair avec les changements dans la fréquence et l'intensité des événements de tempêtes extrêmes augmentent le risque d'inondation et de submersion à des emplacements côtiers comme le port d'Halifax dans le contexte du changement climatique. Dans cette étude, nous examinons trois scénarios de niveaux de hautes eaux extrêmes basés sur des scénarios de changement climatique et estimations de subsidence du terrain, l’élévation du niveau moyen de la mer ainsi que l'analyse de la période de retour d’événements extrêmes (faite lors d’études antérieures). Nous examinons aussi les effets des vagues de l'océan sur ces estimations de niveaux de hautes eaux extrêmes. Étant donné que la tempête la plus dévastatrice à avoir touché terre en Nouvelle–Écosse au cours du dernier siècle a été l'ouragan Juan (2003), c'est celle-ci que nous avons choisie pour simuler le cas extrême de vagues produites par une tempête et de remontée de vagues dans le port d'Halifax. Pour simuler les vagues produites par Juan, nous nous sommes servis d'un système à grilles imbriquées consistant en deux modèles de vagues opérationnels à la fine pointe de la technologie. Les modèles de vagues étaient pilotés par des données de vent de haute qualité et les simulations disposaient d'une bathymétrie côtière à haute résolution récemment mise à jour. Les changements observés d’élévation de l'eau dans le port d'Halifax ont été utilisés dans les simulations de l'ouragan Juan par les modèles de vagues. Nous utilisons le modèle de remontée des vagues de la Federal Emergency Management Agency (FEMA) pour estimer la hauteur des remontées, qui est validée par rapport aux observations de hautes eaux enregistrées le long de la côte. Les vagues et les hauteurs de remontée des vagues simulées pour l'ouragan Juan suggèrent que la hauteur significative maximale des vagues à l'entrée du port était de 9,0 m et la remontée des vagues atteignait 2,0 m le long de la côte du port d'Halifax. Nous avons de cette manière estimé l'impact des vagues et de la remontée des vagues sur l’élévation des hautes eaux extrêmes pour trois scénarios de changement climatique dans le port d'Halifax dans les conditions les plus défavorables. Nous analysons la sensibilité de ces estimations à divers changements de niveau d'eau, directions de propagation et profils de pente côtière.     

The use of PPP or MER in the construction of emission scenarios is more than a question of ‘metrics’

Abstract

The Intergovernmental Panel on Climate Change (IPCC)'s Special Report on Emissions Scenarios (SRES, IPCC, 2000) has been a matter of debate since Ian Castles and David Henderson claimed that the scenarios were based on unsound economics, giving rise to improbably high emission growth. A main point in their critique was that the scenario-makers converted national gross domestic product (GDP) data to a common measure using market exchange rates (MER) rather than purchasing power parity (PPP) rates. The IPCC responded to the critique by claiming that the use of PPP- or MER-based measures is just a question of ‘metrics’, as important as the ‘switch from degrees Celsius to Fahrenheit’. This paper addresses both the critique from Castles and Henderson and the response from the IPCC. It builds on our earlier argument that the use of MER-based measures, although misleading in some respects, probably has not given rise to seriously exaggerated emission forecasts because comparing regional income levels by the use of MER has two types of implications that draw in different directions and effectively neutralize one another. Nevertheless, we argue that the choice between MER and PPP in the construction of emission scenarios is far more than just a question of metrics. Finally, we discuss whether the SRES scenario with the lowest cumulative emissions is a reasonable lower limit with respect to global emission growth.