Dynamics and limitations of phytoplankton biomass along a gradient in Mwanza Gulf,southern Lake Victoria (Tanzania)

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Factors affecting the seasonality and distribution of cyanobacteria and chlorophytes: a case study from the large lakes south of the Alps,with special reference to Lake Garda

Chlorophytes and cyanobacteria are among the most typical algal groups, contributing to the aesthetic appearance and quality of the epilimnetic waters of the deep (251–410 m) and large (6.5–49×10⁹ m³) lakes located on the southern edge of the Alps (from oligo-mesotrophy to meso-eutrophy: Maggiore, Garda, Como, Iseo and Lugano). The results obtained from monthly surveys carried out in the largest of these lakes (Garda) have been reported in detail. The thermal stability of the water column and silica depletion were the main factors responsible for the decline of the great spring diatoms. The successive growth of Mougeotia sp. was favoured by its lower sinking velocity and resistance to the increasing grazing pressure. During summer, the maximum stability of the water column, with high vertical nutrient concentration gradients, determined a major algal differentiation with a typical increase, among others, of Chlorococcales at the surface and metalimnetic stratification of various Oscillatoriales. The development of oligotrophic blooms, caused by a rapid thickening at the surface of Anabaena in the eastern, sheltered basin, was also discussed in light of the trophic characterisation of Lake Garda. From autumn to spring, the decreasing light, the increasing mixing depth and nutrient availability favoured a progressive dominance of vertical homogeneous populations of Planktothrix (autumn) and colonial diatoms. The same functional groups of chlorophytes and cyanobacteria have been recognised in the studies published so far on the phytoplankton of deep southern subalpine lakes. In this respect, their morphometric and physical properties appear to constitute a sort of standardising factor, reducing the range of possible dominants. With increasing TP concentrations and biomass, filaments of Planktothrix and Planktolyngbya, along with the Chlorococcales, became important. The dominance of Mougeotia (one of the most characteristic features of these large lakes) appears restricted to a medium trophic range, whereas the distribution of the Chroococcales and other filaments ascribed to Pseudanabaena and/or Limnothrix is more irregular. The conspicuous presence of Aphanizomenon in Lake Lugano is typical and characteristic of a more productive lake. Among the Nostocales, a clear interpretation of the Anabaena blooms in lakes Garda and Iseo is complicated by the peculiar behaviour of filaments concentrating at the surface, which is apparently restricted, within the medium trophic range, to stable water columns.     

Effect of anthocyanins, carotenoids, and flavonols on chlorophyll fluorescence excitation spectra in apple fruit: signature analysis, assessment, modelling, and relevance to photoprotection

Whole apple fruit (Malus domestica Borkh.) widely differing in pigment content and composition has been examined by recording its chlorophyll fluorescence excitation and diffuse reflection spectra in the visible and near UV regions. Spectral bands sensitive to the pigment concentration have been identified, and linear models for non-destructive assessment of anthocyanins, carotenoids, and flavonols via chlorophyll fluorescence measurements are put forward. The adaptation of apple fruit to high light stress involves accumulation of these protective pigments, which absorb solar radiation in broad spectral ranges extending from UV to the green and, in anthocyanin-containing cultivars, to the red regions of the spectrum. In ripening apples the protective effect in the blue region could be attributed to extrathylakoid carotenoids. A simple model, which allows the simulation of chlorophyll fluorescence excitation spectra in the visible range and a quantitative evaluation of competitive absorption by anthocyanins, carotenoids, and flavonols, is described. Evidence is presented to support the view that anthocyanins, carotenoids, and flavonols play, in fruit with low-to-moderate pigment content, the role of internal traps (insofar as they compete with chlorophylls for the absorption of incident light in specific spectral bands), affecting thereby the shape of the chlorophyll fluorescence excitation spectrum.     

基于空间主成分和最小累积阻力模型的内陆河景观生态安全评价与格局优化——以张掖市甘州区为例

以干旱内陆河主要生态环境问题为出发点,利用景观生态学方法、空间主成分分析和GIS技术,获取甘州区生态安全格局的分布状况.选取海拔、坡度、自然和文化景观保护区、土壤类型、土壤侵蚀量、植被覆盖度、距道路距离、距工业用地距离、距居民点距离以及距水体距离等10个要素作为约束条件,并采用景观最小累积阻力模型构建生态廊道和生态节点来优化生态功能网络的结构及功能.结果表明： 甘州区生态安全综合状况一般,以中等安全水平为主,面积为1318.7 km²,占研究区总面积的36.7%.低度安全水平的区域主要位于研究区北部,占研究区总面积的19.9%.构建了由6条生态廊道、14个生态节点、1个较大的生态源区和若干个小面积源区组成的点、线、面交织的区域生态网络格局,将有效改善研究区的生态安全水平.
     

基于浮游植物生物完整性指数的湖泊生态系统评价——以2012年冬季太湖为例

依据2012年12月对太湖29个样点和同一地理区划4个湖、库的浮游植物和环境变量的监测结果,应用生物完整性理论和方法,构建冬季太湖浮游植物生物完整性指数,评价冬季太湖水生态健康质量。采用干扰程度最小系统法定义筛选确定参照点,对51个候选参数进行分布范围筛选、判别能力分析、参数间相关性分析,获得了太湖枯水期P-IBI指数的6个构成参数:总分类单元数、硅藻门分类单元%、细胞Simpson指数、细胞密度、硅藻门细胞密度%和绿藻门个体密度%。采用比值法统一各参数的量纲,累加后得到枯水期太湖P-IBI分值,并划分健康评价标准。应用P-IBI对冬季太湖水生态进行评价,8个参照点中1个点位评价结果为健康其余7个为亚健康;25个受损点中,2个点位为亚健康,9个点位为一般,12个点位为差,2个点位为极差。太湖总体受到了不同程度的人为干扰,东太湖湖区水生态状况最好,评价结果多为亚健康或一般;竺山湖、贡湖、东部沿岸和西部沿岸次之;南部沿岸和湖心区最差,湖心区有2个点位评价结果为极差。与冬季太湖P-IBI指数显著相关的水化学因子是氨氮和总磷含量。     

典型移民城市食物氮足迹估算分析——以深圳市为例

城市食物源氮消费产生的环境排放是全国氮污染的重要源头,城市食物氮足迹评估可反映维持城市人口基本食物需求的活性氮排放以及对周边环境的潜在影响。以典型移民城市深圳市为例,基于改进N-Calculator模型的基础上,估算了2010-2015年间因城市人口流动导致的城市食物氮足迹变化,并分析其时空异质性及其与城市化间的关系。结果表明：深圳市不同类型城市居民食物氮足迹不一致,其中常住户籍居民人均食物氮足迹从14.63 kg N a^-1增加至15.17 kg N a^-1,高于非户籍居民食物氮足迹13.09 kg N a^-1,其主要体现在瓜果、肉类、水产品等食物消费上。总体上,深圳城市食物氮足迹呈增长趋势,5年增幅11.50%,增幅最大为常住户籍居民食物氮足迹,但目前深圳非户籍居民的食物消费主导着城市食物氮足迹。深圳城市内部区域食物氮足迹呈高度空间异质性与聚集性,各区域增长量差异明显,街道尺度城市食物氮足迹增长热点主要分布在城市的西部沿海区域,部分热点区域单位增长量数量级比肩区级尺度单位的增长量,城市区域食物氮足迹与人口城市化的关联性不明显,但与经济城市化存在一定的关联性。当前城市移民落户趋势及居民高氮饮食倾向不利于城市氮足迹的削减,减少食物生产上游活性氮流失为深圳市贯彻粤港澳大湾区协同可持续发展的关键。     

恢复力视角下生态型城市植被恢复空间分异及其影响因素——以陕南商洛市为例

植被恢复是建设生态型城市的重要途径,通过明晰植被恢复空间分异与潜在的植被恢复力,有助于指导可持续性生态城市的建设。以商洛市为例,基于MODIS归一化植被指数(NDVI)数据,利用Sen+Mann-Kendall模型和Hurst模型研究2000—2013年商洛市植被恢复趋势及未来持续能力,并采用地理加权回归模型(GWR)分析市域尺度内植被恢复空间分布的影响因素。结果表明:(1)2000—2013年商洛市的植被恢复效果明显,植被覆盖增大的区域占总面积的82.5%,减小的区域占总面积的9.4%;(2)2000—2013年,受城镇的距离及土地集约程度等人文因素的影响,西北部植被恢复略好于东南部。(3)Hurst指数显示,商洛市未来植被恢复的持续性不强。48.0%的区域未来植被覆盖可能会呈现由改善变退化的现象,而持续增大的区域仅占36.7%,植被恢复力仍有待加强。(4)市域尺度上,植被恢复趋势空间差异形成的自然因素包括高程、坡度、坡向、与水体的距离,而人文因素则由距离城镇的距离和土地利用集约度所主导。地理加权回归显示各区县植被恢复趋势的空间影响因素及其强度并不一致,充分说明人地关系变化对植被恢复作用机理的复杂性。     

Assessment of rates of deformity in wild frog populations using in situ cages: a case study of Leopard Frogs (Rana pipiens) in Ontario, Canada

High rates of deformity in wild amphibian populations from north-eastern North America have been increasingly reported since 1995. In the St Lawrence River basin (Canada) elevated frequencies of limb and eye deformities in mudpuppies (Necturus maculosus) and leopard frogs (Rana pipiens) were recorded in the early 1990s. A caging study was conducted during 1998 to verify the rates recorded in leopard frogs and pursue the potential causes of deformities seen in juveniles and adults. Week-old leopard frog tadpoles were collected from a reference wetland and maintained through to metamorphosis in cages in previously identified high risk wetlands. Deformity frequencies were measured and compared with frequencies measured in wild populations of leopard frogs inhabiting the same wetlands. The results of caging studies and sampling of wild populations were also compared with corresponding data collected from a reference wetland. No deformities were observed in caged or wild reference animals. Very low deformity frequencies (up to 2.2%) were observed in frogs caged in high risk wetlands, but greater frequencies (3.4-10%) were observed in wild young-of-the-year frogs captured at the same sites. The types of deformities were similar among groups; they included fused, missing or extra digits and disproportionate hindlimb length or eye pupil size. In addition, mortality rates were elevated in two cages in high risk wetlands. In general, the caging procedure was effective in establishing the potential for production of deformities in the waters of a given wetland, but tended to underestimate the rates calculated for samples of wild populations. The ramifications of the first-year findings for similar assessments of amphibian deformity rates and establishment of cause-effect linkages are discussed.     

Quantitative comparison of taxa and taxon concepts in the diatom genus Fragilariopsis: a case study on using slide scanning,multiexpert image annotation,and image analysis in taxonomy1

Semiautomated methods for microscopic image acquisition, image analysis, and taxonomic identification have repeatedly received attention in diatom analysis. Less well studied is the question whether and how such methods might prove useful for clarifying the delimitation of species that are difficult to separate for human taxonomists. To try to answer this question, three very similar Fragilariopsis species endemic to the Southern Ocean were targeted in this study: F. obliquecostata, F. ritscheri, and F. sublinearis. A set of 501 extended focus depth specimen images were obtained using a standardized, semiautomated microscopic procedure. Twelve diatomists independently identified these specimen images in order to reconcile taxonomic opinions and agree upon a taxonomic gold standard. Using image analyses, we then extracted morphometric features representing taxonomic characters of the target taxa. The discriminating ability of individual morphometric features was tested visually and statistically, and multivariate classification experiments were performed to test the agreement of the quantitatively defined taxa assignments with expert consensus opinion. Beyond an updated differential diagnosis of the studied taxa, our study also shows that automated imaging and image analysis procedures for diatoms are coming close to reaching a broad applicability for routine use.