Effects of long-term nitrogen addition and precipitation changes on CH4 flux in an alpine steppe北大核心CSCD

土壤是甲烷(CH4)重要的源和汇.氮沉降和降水格局变化正在急剧改变土壤碳循环,进而可能对土壤CH4通量造成深刻影响.高寒生态系统是巨大的碳库,对氮沉降和降水变化十分敏感.然而,目前多数研究集中在短期实验上,缺乏对长期氮沉降和降水变化背景下CH4通量的响应及其调控因素的认识.以青藏高原高寒草原为研究对象,在2013年搭建模拟氮沉降和降水格局改变实验平台.基于静态箱–气相色谱法测定2020年生长季(5-10月)土壤CH4通量.结果显示,高寒草原土壤呈CH4的汇.氮添加没有显著改变生长季和植物生长高峰CH4通量.然而,降水变化显著改变了生长季和植物生长高峰CH4通量,其中降水增加(+50%降水)降低了CH4的吸收(分别为–16%和–45%),降水减少(–50%降水)增强了CH4的吸收(分别为+73%和+33%).进一步研究发现,与植物属性和功能基因丰度相比,土壤环境因子主导了CH4通量变化(解释率>90%).其中CH4通量与土壤含水量和温度显著正相关,与土壤pH显著负相关.综上所述,在未来全球变化情景下,降水格局改变更能调节青藏高原高寒草原CH4通量的变化.(图6表1参37)     

区域土地利用变化对生态环境影响定量评估——以铜川市城郊区为例

区域土地利用变化对生态环境的影响,是地理学全球变化研究的重要内容,而生态服务价值则是目前生态学、生态经济学研究的热点问题。研究利用研究区地形、土壤、植被数据和近10年来每年的气候、土地利用数据,运用生态服务价值测算模型,计算了1994~2003年铜川市城郊区历年的生态服务价值,并模拟了无土地利用变化情景下的生态服务价值,提出了土地利用变化环境效应指数,并尝试性地运用该指数定量评价了城郊区土地利用变化对生态环境的影响。结果表明:①由于气候变化、人类活动尤其是土地利用变化等原因的影响,城郊区生态服务价值年际间变化很大,1994~2003年期间,在不考虑水域生态服务功能情况下（基于水域面积年际变化极小考虑）,城郊区生态服务价值在4.77×108~1.56×10⁹元间波动;②模拟了无土地利用变化情景下的生态服务价值,结果表明每年基于无土地利用变化情景下的生态服务价值明显低于基于土地利用变化情景下的生态服务价值;③运用土地利用变化环境效应指数计算模型计算了土地利用变化环境效应指数,结果表明都大于1,从1994年到2003年期间,土地利用变化环境效应指数除个别年份略有波动外,整体呈增加趋势,反映了土地利用变化对城郊区生态环境的影响是积极的。     

长江流域农业区非点源氮的平衡变化及其区域性差异

建立长江流域农业区氮平衡变化模型,并在该模型的基础上,计算长江流域各县1990和2000年的氮平衡变化,然后汇总出全流域氮的输入、输出及剩余量. 计算结果显示,全流域农业区1990年氮的输入量为7.65×106 t/a,输出量为4.23×106 t/a,剩余量为3.42×106 t/a(其中进入水体2.05×106 t/a,残留在土壤中1.37×106 t/a);2000年全流域农业区氮的输入量为10.22×106 t/a,输出量为5.44×106 t/a,剩余量为4.78×106 t/a(其中进入水体2.65×106 t/a,残留在土壤中2.13×106 t/a);1990—2000年长江流域农业区氮输入量增加2.57×106 t/a,氮输出量增加1.21×106 t/a,剩余量增加1.36×106 t/a(其中进入水体氮变化量为0.60×106 t/a,残留在土壤中氮变化量为0.76×106 t/a). 重庆、上海、武汉、无锡、南昌、成都等地区氮进入水体的量变化较大,为今后长江流域农业区水体氮污染重点防治区.      

珠江三角洲耕地土壤质量演化及其机制

通过对代表性区域的调查研究,探讨了珠江三角洲耕地土壤质量演化的趋势及其形成机制.结果表明,与第二次土壤普查时期(1980)比较,珠江三角洲耕地土壤有机质全氮稳中有降,土壤速效氮(NO_3~--N)、速效磷含量显著增加,已达丰富水平,土壤速效钾含量有所增加、但仍偏低,土壤有效镁、硼、钼仍严重缺乏,部分土壤有效硅、锰缺乏;伴随大量水田改种蔬菜、水果等经济作物而产生的耕作制度变化、利用强度增加以及相应的化学氮、磷肥料过量投入、蔬菜地施用石灰等管理措施等,是导致珠江三角洲耕地土壤有机质下降和产生新的养分非均衡化的主要影响因素.     

Linking species- and ecosystem-level impacts of climate change in lakes with a complex and a minimal model

To study the interaction between species- and ecosystem-level impacts of climate change, we focus on the question of how climate-induced shifts in key species affect the positive feedback loops that lock shallow lakes either in a transparent, macrophyte-dominated state or, alternatively, in a turbid, phytoplankton-dominated state. We hypothesize that climate warming will weaken the resilience of the macrophyte-dominated clear state. For the turbid state, we hypothesize that climate warming and climate-induced eutrophication will increase the dominance of cyanobacteria. Climate change will also affect shallow lakes through a changing hydrology and through climate change-induced eutrophication. We study these phenomena using two models, the full ecosystem model PCLake and a minimal dynamic model of lake phosphorus dynamics. Quantitative predictions with the complex model show that changes in nutrient loading, hydraulic loading and climate warming can all lead to shifts in ecosystem state. The minimal model helped in interpreting the non-linear behaviour of the complex model. The main output parameters of interest for water quality managers are the critical nutrient loading at which the system will switch from clear to turbid and the much lower critical nutrient loading – due to hysteresis – at which the system switches back. Another important output parameter is the chlorophyll-a level in the turbid state. For each of these three output parameters we performed a sensitivity analysis to further understand the dynamics of the complex model PCLake. This analysis showed that our model results are most sensitive to changes in temperature-dependence of cyanobacteria, planktivorous fish and zooplankton. We argue that by combining models at various levels of complexity and looking at multiple aspects of climate changes simultaneously we can develop an integrated view of the potential impact of climate change on freshwater ecosystems.     

Combining a generic process-based productivity model and a statistical classification method to predict the presence and absence of tree species in the Pacific Northwest,U.S.A.

Although long-lived tree species experience considerable environmental variation over their life spans, their geographical distributions reflect sensitivity mainly to mean monthly climatic conditions. We introduce an approach that incorporates a physiologically based growth model to illustrate how a half-dozen tree species differ in their responses to monthly variation in four climatic-related variables: water availability, deviations from an optimum temperature, atmospheric humidity deficits, and the frequency of frost. Rather than use climatic data directly to correlate with a species’ distribution, we assess the relative constraints of each of the four variables as they affect predicted monthly photosynthesis for Douglas-fir, the most widely distributed species in the region. We apply an automated regression-tree analysis to create a suite of rules, which differentially rank the relative importance of the four climatic modifiers for each species, and provide a basis for predicting a species’ presence or absence on 3737 uniformly distributed U.S. Forest Services’ Forest Inventory and Analysis (FIA) field survey plots. Results of this generalized rule-based approach were encouraging, with weighted accuracy, which combines the correct prediction of both presence and absence on FIA survey plots, averaging 87%. A wider sampling of climatic conditions throughout the full range of a species’ distribution should improve the basis for creating rules and the possibility of predicting future shifts in the geographic distribution of species.     

泥炭沼泽土壤酶活性对水热条件变化的响应及其与CO_2释放通量的关系——以小兴安岭地区为例

采用实验室培养的方法,研究了小兴安岭地区两类典型的泥炭沼泽:苔草型泥炭沼泽和泥炭藓型泥炭沼泽中几种水解酶活性(β-葡萄糖苷酶、酚氧化酶)对不同温度和水位变化的响应,以及与CO_2释放通量的相瓦关系.结果表明:β-葡萄糖苷酶活性在两类泥炭沼泽中受多种因素制约,在一定湿度范围内受水位控制较明显,当土壤湿度降低到一定程度时,温度对土壤酶活性影响增强.酚氧化酶活性与温度密切相关,但对温度变化的响应存在明显的季节性差异.相对而言,苔草型泥炭沼泽中β-葡萄糖苷酶和酚氧化酶活性显著高于相同培养条件下泥炭藓型泥炭沼泽.总体上,苔草型泥炭沼泽中水解酶活性较泥炭藓型泥炭沼泽中高,但是其CO_2释放通量却低于泥炭鲜型泥炭沼泽,表明与有机碳分解有关的水解酶的活性高低不能作为解释泥炭沼泽CO_2释放通量大小的唯一指标.     

大气颗粒物“二重源解析”技术的误差分析

"二重源解析"模型计算结果的误差是采样误差、样品处理误差、化学组分分析误差、数据处理误差以及数学模型误差等所有误差的积累。提出了"二重源解析"解析结果的相对误差和标准偏差表达式,并用之计算了某市利用"二重源解析"模型计算的源贡献值的相对误差和标准偏差,还针对从源排放出来的初始态颗粒物在传输过程中发生的扬尘态变化提出了扬尘转化率的概念和计算方法。     

IMPACTS OF CLIMATE CHANGE ON MISSOURI RWER BASIN WATER YIELD1

ABSTRACT: Water from the Missouri River Basin is used for multiple purposes. The climatic change of doubling the atmospheric carbon dioxide may produce dramatic water yield changes across the basin. Estimated changes in basin water yield from doubled CO₂ climate were simulated using a Regional Climate Model (RegCM) and a physically based rainfall‐runoff model. RegCM output from a five‐year, equilibrium climate simulation at twice present CO₂ levels was compared to a similar present‐day climate run to extract monthly changes in meteorologic variables needed by the hydrologic model. These changes, simulated on a 50‐km grid, were matched at a commensurate scale to the 310 subbasin in the rainfall‐runoff model climate change impact analysis. The Soil and Water Assessment Tool (SWAT) rainfall‐runoff model was used in this study. The climate changes were applied to the 1965 to 1989 historic period. Overall water yield at the mouth of the Basin decreased by 10 to 20 percent during spring and summer months, but increased during fall and winter. Yields generally decreased in the southern portions of the basin but increased in the northern reaches. Northern subbasin yields increased up to 80 percent: equivalent to 1.3 cm of runoff on an annual basis.     

A COMPARISON OF DELTA CHANGE AND DOWNSCALED GCM SCENARIOS FOR THREE MOUNTAINOUS BASINS IN THE UNITED STATES1

ABSTRACT: Simulated daily precipitation, temperature, and runoff time series were compared in three mountainous basins in the United States: (1) the Animas River basin in Colorado, (2) the East Fork of the Carson River basin in Nevada and California, and (3) the Cle Elum River basin in Washington State. Two methods of climate scenario generation were compared: delta change and statistical downscaling. The delta change method uses differences between simulated current and future climate conditions from the Hadley Centre for Climate Prediction and Research (HadCM2) General Circulation Model (GCM) added to observed time series of climate variables. A statistical downscaling (SDS) model was developed for each basin using station data and output from the National Center for Environmental Prediction/National Center for Atmospheric Research (NCEPINCAR) reanalysis regridded to the scale of HadCM2. The SDS model was then used to simulate local climate variables using HadCM2 output for current and future conditions. Surface climate variables from each scenario were used in a precipitation‐runoff model. Results from this study show that, in the basins tested, a precipitation‐runoff model can simulate realistic runoff series for current conditions using statistically down‐scaled NCEP output. But, use of downscaled HadCM2 output for current or future climate assessments are questionable because the GCM does not produce accurate estimates of the surface variables needed for runoff in these regions. Given the uncertainties in the GCMs ability to simulate current conditions based on either the delta change or downscaling approaches, future climate assessments based on either of these approaches must be treated with caution.