成都市水资源承载力评价及差异分析

以成都市及其各区县为研究对象,评估成都市水资源承载力及其利用水平,并探究其内部区域差异。评价结果表明:从成都市总体情况来看,成都市实际经济规模超过水资源系统最大承载力,而实际人口规模小于水资源系统最大承载力,其承载力指数和协调指数分别为1.734 9,0.672 4,水资源的开发利用略有超载,可持续性不高;从区域内区县来看,其水资源可支撑的经济规模、人口规模,承载力指数和协调指数上呈现出较大差异。西部区县的承载力指数低于东部区县,水资源系统受到的压力较小,承载能力较强;西部区县协调指数同样低于东部区县,说明西部区县水资源利用方式有待改善,利用效率有待提高。     

Squaring the circle: reconciling fishing and conservation of aquatic ecosystems

Size‐at‐entry regulations in fisheries cause major disruption to aquatic ecosystems, including truncation of age‐ and size‐structures, destabilization of fish stocks, directional selection on phenotypic traits and a by‐catch of unwanted species and sizes. Here, we use simple dynamic models of size‐spectra to examine an alternative, so‐called balanced harvesting. Balanced harvesting helps in retaining the approximate power‐law size‐structure of natural ecosystems, whereas size‐at‐entry regulations do not. Balanced harvesting is less likely to destabilize steady states than size‐at‐entry regulations set close to the size at maturation. Surprisingly, our numerical results suggest that steady‐state biomass yield can be substantially increased by switching from size‐at‐entry to balanced harvesting. On the basis of these results, we argue that the goals of conservation and of greater yields seem less difficult to reconcile than have previously been thought. However, to work towards these goals require a change in our approach to fishing.     

基于生态足迹理论浅析三亚生态城市发展

基于生态足迹理论,对三亚生物资源及能源资源消耗进行汇总计算,并对得出的三亚生态足迹与生态承载力数值分析对比,结果表明三亚处于生态负载。鉴于三亚生态不可持续,三亚在推进城市建设时,要树立生态发展理念,加强三亚城市布局优化,进一步转化资源利用方式,提升生态效益,以实现三亚绿色发展。     

Effects of gravel mulch on aeolian transport:a field wind tunnel simulation

The shape,size and coverage of gravels have significant impacts on aeolian sand transport.This study provided an understanding of aeolian transport over the gravel mulching surfaces at different wind velocities by means of a mobile wind tunnel simulation.The tested gravel coverage increased from 5% to 80%,with a progressive increment of 5%.The gravels used in the experiments have three sizes in diameter.Wind velocities were measured using 10 sand-proof pitot-static probes,and mean velocity fields were obtained and discussed.The results showed that mean velocity fields obtained over different gravel mulches were similar.The analysis of wind speed patterns revealed an inherent link between gravel mulches and mean airflow characteristics on the gravel surfaces.The optimal gravel coverage is considered to be the critical level above or below which aeolian transport characteristics differ strongly.According to the present study,the optimal gravel coverage was found to be around 30% or 40%.Threshold velocity linearly increased with gravel coverage.Sand transport rate first increased with height above the wind tunnel floor(Hf),reaching a peak at some midpoint,and then decreased.     

Biomass management targets and the conservation and economic benefits of marine reserves

The establishment of no‐take marine reserves has been increasingly promoted as a key measure to achieve conservation and sustainability goals in fisheries. Regardless of the wide range of benefits cited, the effectiveness of reserve establishment depends critically on fisheries management outside the reserves. We construct a bioeconomic model of a fishery that allows for the establishment of a no‐take marine reserve and evaluate how the choice of the off‐reserve management target influences the effectiveness of reserve establishment. We evaluate two biomass targets: (i) B_MSY or the biomass that produces the maximum sustainable yield (MSY) and (ii) B_MEY or the biomass that maximizes the net present value of the returns to fishing. The parameterized model shows that, for a wide range of scenarios, the fishery will be better off in terms of both conservation and economic objectives when the no‐take reserve is established in conjunction with the B_MEY target rather than with the B_MSY target. Model results further show that the opportunity cost of securing additional fish biomass, in both deterministic and stochastic environments, is lower when the reserve size is increased under the B_MEY target. This finding is important because marine reserves have been established as a key measure to restore depleted fish stocks, and the results suggest that this objective can be achieved with lower economic costs in a B_MEY managed fishery.     

海南南繁区水稻基因飘流的最大阈值距离及其时空分布特征

【目的】陵水、三亚、乐东三县（市）是各类水稻（包括转基因水稻）冬季南繁的主要基地或中心。计算并绘制海南南繁区乡镇尺度水稻基因飘流的最大阈值距离图,为南繁水稻育种设置合理的隔离距离提供参考。【方法】采用已建立的水稻基因飘流模型和阈值分析方法,依托南繁区自动气象站资料,计算了该区域乡、镇尺度向不育系和栽培稻基因飘流的最大阈值距离（the maximum threshold distances of gene flow,MTDs）,分析其时、空分布特征和影响因子。参照中国农业部有关水稻种子生产的质量标准,阈值分别设为1%和0.1%。【结果】南繁区向不育系的MTD_1%平均值为（110±31）m,最短为53 m,最长为195 m。向不育系的MTD_0.1%平均值为（169±44）m,最短为75 m,最长为271 m。向栽培稻的MTD_1%均小于1 m;MTD_0.1%平均值为（3.4±1.1）m,最短为0.6 m,最长为5.8 m。向不育系和栽培稻的MTD_0.1%两者相差近50倍。南繁区MTDs有2个高值区和4个高值点,3个低值区和5个低值点。以陵水、三亚、乐东为主体的南繁区,地处热带,三面临海,北面有五指山为屏障。冬季盛行东北季风,春季和初夏盛行南太平洋的东南季风和印度洋的西南季风。因此,南繁区的沿海陆地平原大都风速较大;沿海陆地与五指山区之间为中、低山丘陵地带,丘陵的走向和高度决定了该区的风向和风速;五指山南坡附近的丘陵地区,风速会因屏障效应而明显减小。【结论】地形特征和大气环流影响风向和风速,决定了南繁区MTDs空间分布的基本格局：高值区主要分布在该地区的东翼、西翼和南部沿海平原;低值区主要分布在五指山南麓的屏障区域。     

西藏色季拉山急尖长苞冷杉林下苔藓持水性能研究

西藏色季拉山为典型的高原山地原始暗针叶林,面积较大的急尖长苞冷杉林为原始暗针叶林的主体。其林分生长良好,林下植被丰富,特别是林下苔藓层发育很好。采用野外观测法和室内浸泡法对西藏色季拉山不同坡向不同海拔急尖长苞冷杉林下的苔藓进行种类鉴定并进行持水能力研究。结果表明:调查地内共有苔藓9科13属14种,其中羽藓科锦丝藓属锦丝种为优势种,各海拔段均有分布;色季拉山阴坡各海拔段苔藓厚度均要高于阳坡;无论是天然持水量还是最大持水量,阴坡均要高于阳坡,两个坡向的3 800 m海拔段持水量最大;苔藓在浸水后0.5～1 h内持水量迅速上升,1 h后慢慢增加并稳定。结果表明苔藓在降雨1 h内对降雨的吸持有重要作用;苔藓持水量与浸泡时间可用对数函数拟合。     

齿墩状内消能工的消能及压力特性

输水管道或泄洪洞常见的内消能方式为孔板和洞塞,结合明渠水流中的消能工形式提出了齿墩状内消能工,并通过物理模型试验对不同面积收缩比的齿墩状内消能工进行了研究,分析了它们的过流能力、消能率、压强沿程变化及脉动压强特性.结果表明:齿墩状内消能工的过流能力主要是由消能工的体型及尺寸决定的,其面积收缩比越大,消能率越低,过流能力就越强;齿墩状内消能工的时均压强在收缩段骤降,在其后部逐渐上升,而后恢复至稳定,其恢复长度基本相同;齿墩状内消能工的脉动压强最大点均出现在收缩段后1倍圆管直径范围内,随后迅速减小,逐渐趋于平稳;面积收缩比为0.471 2的齿墩状消能工的脉动强度最小,因而其抗空化性能优于其他情况,且脉动压强最大点的压强概率密度分布接近正态分布.     

汉江水源地土地资源承载力时空格局研究

从粮食、耕地、人口的角度出发,利用土地承载模型、土地承载指数和趋势分析法,借助GIS技术,研究了汉中市县域尺度土地承载力的时空变化特征,并预测了该市2020年耕地资源承载潜力。结果表明:（1）从时间上来看,20世纪90年代汉中市土地承载处于人粮基本平衡状态,2000年以后土地承载指数开始上升,人粮关系出现紧张,截至2010年表现为土地过载现象。（2）空间来看,宁强、略阳、西乡自20世纪90年代始人口就略显超载,山区县由农业生产粗放的经营转为多种因素综合作用下的区域粮食安全隐患。（3）对比2020年全国粮食作物单产为5 370~5 810 kg/hm²,加快农业内部结构调整,加强农业科技投入力度,可在区域范围内保证粮食安全。     

基于生态足迹的海南省自然生态承载力研究

以海南省为例,基于生态足迹模型,计算海南省2012年生态足迹与生态承载力,分析其生态足迹和生态承载力的关系,力求为处理海南省的经济发展与生态环境保护的关系提供科学依据。分析表明:海南省2012年人均生态足迹为1.574 7 hm²/人,人均生态承载力为1.153 6 hm²,生态足迹是其生态承载力的1.37倍左右。对区域生态供需平衡关系进行分析,生态承载力供需平衡指数处于1.1～1.5区间,存在赤字问题,生态承载状况超载,并提出了海南省可持续发展过程中应采取的对策措施。