Impact of water quality on macroinvertebrate assemblages along a tropical stream in Kenya

Prudent management of lotic systems requires information on their ecological status that can be estimated by monitoring water quality and biodiversity attributes. To understand environmental conditions in Gatharaini drainage basin in Central Kenya, a study was carried out to establish the relationship between water quality and macroinvertebrate assemblages between the months of March and September 1996. Six sampling sites, each 25 m long were selected along a 24‐km stretch of the stream, which drained land under agricultural, residential and industrial use. Water physico‐chemical data was explored using multivariate analysis of Principal Component Analysis to detect environmental trends downstream. Both macroinvertebrates and water physico‐chemical data of suggested trends were analysed for variations and correlations. Temperatures and invertebrate densities changed significantly between the dry and wet season (P < 0.01) but the fluctuations were not evident downstream. Water physico‐chemical characteristics (total dissolved solids (TDS), pH, turbidity, dissolved oxygen) and biodiversity indices (species richness, diversity, dominance, evenness) changed markedly downstream (P < 0.01). Biodiversity indices correlated inversely with TDS, pH and turbidity but positively with dissolved O₂. It was evident macroinvertebrate assemblages changed significantly downstream as opposed to functional feeding groups. Diptera was important in most sites whilst Oligochaeta dominance increased downstream corresponding to the deterioration in water quality. Collectors/browsers were the dominant functional feeding groups at most sites. This study showed that significant changes in aquatic macroinvertebrate assemblages were primarily due to water quality rather than prevailing climatic conditions.     

安宁河中游底栖动物群落结构及其与环境因子的关系

为了解安宁河底栖动物群落结构及其影响因素, 分别于丰水期(2015年7、8月)和枯水期(2016年1、2月)开展了安宁河中游干支流底栖动物的2次调查, 并于2015年7月至2016年6月进行安宁河支流的周年调查。共检出底栖动物5门115属122种, 其中水生昆虫居多(109种)。干流丰、枯水期底栖动物的密度和生物量都明显低于支流, 丰水期干支流底栖动物的密度和生物量都明显低于枯水期。安宁河支流全年优势种为四节蜉(Baetis sp.)、蚋(Simulium sp.)、高翔蜉(Epeorus sp.)、花翅蜉(Baetiella sp.)、扁襀(Peltoperlidae spp.)和小蜉(Ephemerella sp.)。安宁河支流底栖动物密度以12月最高, 7月最低; 生物量以1月最高, 7月最低。典范对应分析(CCA)分析结果显示, 影响丰水期安宁河底栖动物分布的关键环境因子为底质类型和海拔, 影响枯水期底栖动物分布的主要环境因子为流速、海拔和水温; 影响安宁河支流底栖动物群落结构周年变化的主要环境因子为水温与电导。研究为高海拔地区河流生物多样性研究和保护提供科学参考。     

Effects of Mediterranean climate annual variability on stream biological quality assessment using macroinvertebrate communities

Data on macroinvertebrates of selected reference sites were compiled from a long-term monitoring programme carried out in the Mediterranean Catalan Basins (NE Spain) that permitted analysis for nine years, from 1996 to 2004, using a homogeneous data collection procedure. This study aims to analyse the differences in composition and structure of macroinvertebrate communities at family level in five Mediterranean river types, and the values of biological quality metrics (IBMWP and IASPT indices, taxon richness and EPT) in reference conditions. Also differences between seasons (spring vs. summer) and between dry and wet periods were analysed. The dry and wet periods were determined using the Standardised Precipitation Index (SPI). A total of 29 reference sites were selected out of 184 sampling sites analysed, and 171 reference samples were available (from 1996 to 2004), of which 88 were sampled in dry periods, whereas 83 correspond to wet periods. Differences on community composition at family level were appreciated, clustering the rivers in three different groups: (1) rivers with a continuous flow regime located in siliceous zones; (2) rivers with a continuous flow regime located in calcareous zones; and (3) temporary rivers regardless of geology. Moreover, our results explain that the characteristics of hydrological periods (dry and wet) characterize the differences between communities better than just the season. The analysis of four biological quality metrics reveals clear differences between values obtained from dry and wet periods concerning taxon richness, EPT values and IBMWP biological indices, whereas the IASPT index does not show significant differences. The median taxonomic richness in wet periods is 32 macroinvertebrate families per sample while in dry periods this value falls to 22. Reference values of IBMWP index, the total number of taxa, and EPT metric are different between dry and wet periods in spring samples, while these differences are not relevant for IASPT index except for temporary streams. Hydrological specific conditions should additionally be considered in order to better calculate biological reference conditions, and to properly apply biological quality metrics used to establish the ecological status in Mediterranean rivers, especially in temporary ones. The use of the dry–wet period classification according to the climate characteristic results is a more accurate application of the Water Framework Directive in Mediterranean rivers. Implications of future climate change should be also considered from our results.     

鄱阳湖不同水文期浮游生物群落结构特征和影响因素及水质评价

为阐明鄱阳湖不同水文期浮游生物群落结构特征及其影响因素,研究于2017年8月(丰水期)和12月(枯水期)在鄱阳湖湖区典型水域设置5个采样点进行浮游生物采样调查。研究期间共鉴定浮游植物8门75属186种,丰水期与枯水期均以硅藻门和绿藻门为主。共鉴定浮游动物4类76种,丰水期与枯水期均以原生动物和轮虫为主。方差分析显示:浮游植物密度与生物量在不同水文期之间的差异均为极显著(P<0.01),浮游动物丰水期密度高于枯水期,但无显著差异(P>0.05),浮游动物生物量(P<0.05)在不同水文期差异显著。冗余分析(RDA)显示:丰水期透明度和浮游生物呈显著负相关关系,电导率和浮游生物呈显著正相关。透明度、电导率与营养盐是影响丰水期浮游生物群落结构的主要环境因素,枯水期水温和溶解氧是驱动鄱阳湖浮游生物群落生态分布的主要环境因素。基于Shannon-Wiener(H′)、Margalef(d)和Pielou(J)等生物多样性指数的水质评价结果表明:鄱阳湖研究区域水质状态处于寡污-中污之间。研究揭示了2个水文期对通江湖泊浮游生物的影响:季节变化不改变湖泊浮游生物的物种组成及优势种,但...     

Sampling variation in macroinvertebrate data and implications for river quality indices

SUMMARY 1. The EC Water Framework Directive (2000/60/EC) recognises the need for biological monitoring. Indices derived from standard samples of macroinvertebrates are frequently used for the appraisal of the ecological quality of rivers. However, information on the errors or chance variation that can influence the value of an index is also important. 2. This paper describes a study to quantify the observed sampling variation in three ecological indices based on the Biological Monitoring Working Party (BMWP) score system across a wide range of river types and qualities. The indices are number of BMWP taxa, BMWP score and Average Score Per Taxon (ASPT). 3. The study sites were selected to encompass the four major groups within the River InVertebrate Prediction And Classification System (RIVPACS) site classification for Britain. Within each group, four sites which differed in ecological quality grade were chosen (total of 16 sites). At each site three standard RIVPACS samples were taken in each of spring, summer and autumn by trained staff. In each season, two samples were taken by one biologist and the third by a different individual to allow for within and between‐operator variation. 4. The effects of sampling variation within a season on the number of taxa, BMWP score and ASPT across all sites, irrespective of operator, could be represented by some simple parameters. We found that the sampling SD of the square root of the number of taxa, square root of BMWP score and the untransformed ASPT were roughly constant in each case, irrespective of site type or quality. For each index, SD for two and three seasons combined samples were smaller than for single season samples. 5. Inter‐operator influences on sample values were negligible (4–12% of total sampling SD) in this study. This underlines the importance of adequate training for all staff involved in extensive monitoring programmes which use standard procedures from one year to the next, but may involve different staff. 6. Indices for number of taxa, BMWP score and ASPT were all estimated with greater precision from combined season samples than from the averages of two or three seasons' samples. 7. This study enables us to estimate confidence intervals for the values of the number of taxa, BMWP score and ASPT based on single season, two or three season combined samples collected using standard RIVPACS procedures for any river site in Britain. The results can also be used in simulation models which incorporate the effects of sampling variation into assessments of the ecological quality of river sites based on the ratio of observed to RIVPACS expected values of these BMWP indices.     

Transitional and coastal waters ecological status assessment: advances and challenges resulting from implementing the European Water Framework Directive

The derivation, performance, sensitivity and inherent uncertainty of ecological quality indicators have become major topics in developing tools for the management of marine, transitional and coastal waters. In reviewing the advances in these waters, related to an ecological status assessment, we show the future challenges to be addressed within the European Water Framework Directive (WFD). Using new analyses carried out under the research project ‘Water Bodies in Europe: Integrative Systems to Assess Ecological status and Recovery’, we provide a complete set of assessments for the biological quality elements (BQEs) (phytoplankton, macroalgae-seagrasses, macroinvertebrates and fish) to be assessed, as well as the validation of existing indicators and multimetric indices and, in some cases, the development of new assessment indices. We show that these indices respond differently to different human pressures and they each have challenges in defining reference conditions against which future changes are judged. In investigating good ecological potential, as the response to heavily modified water bodies, we show that there are flaws in the Directive, not least in its definitions. Our analyses have also focussed on uncertainty in using the indices and we emphasise the problems of defining ecological class boundaries based on indices which themselves may be combined indices (multimetrics). The analysis shows that some of those multimetrics are redundant and/or are inter-correlated and thus may reduce the sensitivity in defining ecological class boundaries. If this is related to the drivers-pressures-state change-impacts-response approach then there are lessons for management measures aimed at achieving good ecological status and even the potential for legal challenges to decisions based on uncertain indices under the WFD. Hence, we conclude the continued need for advances in assessing pressures and gradients, and defining reference conditions for state change, index development, impact assessment and the validation of indices for each BQE.     

Critical influence of seasonal sampling on the ecological quality assessment of small headwater streams

Variability in the ecological quality assessment of reference sites was tested on small headwater streams in Ireland. Although headwater streams constitute a large portion of the river channel network, they are not routinely monitored for water quality. Various metrics were used including the Irish Q-value and the newly developed Small Streams Risk Score (SSRS), and metrics applied elsewhere in the Atlantic biogeographic region in Europe, including the Biological Monitoring Working Party score (BMWP), the Average Score per Taxon (ASPT), the Ephemeroptera, Plecoptera and Trichoptera taxa (EPT), the Belgium Biotic Index (BBI) and the Danish Stream Fauna Index (DSFI). The AQEM (version 2.5a) assessment software was used to apply some of these metrics. The spring and summer datasets are used to test the performance of biotic metrics with respect to season, and the applicability of their use to assess the ecological quality of wadeable streams. The quality status of most sites assigned by the various metrics was high using the spring invertebrate data, and an apparent considerable deviation in quality status occurred when the summer data was applied. Seasonal differences were noted using all the biotic indices and are attributed to the absence of pollution-sensitive groups in summer. Seasonal variability in the water quality status was particularly evident in acidic streams draining non-calcareous geologies with peaty soils that had relatively lower numbers of taxa. Some indices applied reflect a greater seasonal difference in the quality category assigned. The least amount of variability between seasons was obtained using the ASPT and the SSRS risk assessment system. Results suggest that reference status is reliably reflected in spring when more pollution-sensitive taxa were present, and that a new ecological quality assessment tool is required for application in summer when impacts may be most severe. This highly heterogeneous freshwater habitat seems to have too few taxa present in the summer to reliably determine the ecological quality of the stream using the available indices. Handling editor: R. Bailey     

Potential sources of bacteriological pollution for two bays with marinas in Trinidad

Welcome Bay and Chaguaramas Bay in the northwest peninsula of Trinidad contain large marinas and smaller sections of bathing beaches. Bacteriological surveys were conducted at both bays to assess water quality and to determine potential sources of pollution. These surveys were conducted during the wet season of 1996 and the dry season of 1997. Eleven sample stations were established at Welcome Bay and 12 at Chaguaramas Bay. Freshwater samples were collected from rivers and drains within the survey area. Marine water samples were collected from marinas, bathing beaches and inshore and outer areas at both bays. Five water samples were collected from each sampling station during the wet season of 1996 and six during the dry season of 1997. The membrane filter technique was used to determine faecal coliform and Escherichia coli levels in all samples. There was a seasonal effect on water quality, with significantly higher faecal coliform levels in the wet season, when water quality was not in compliance with international standards. This represents a potential health risk in bathing areas. Water quality was better at the outer area of both bays. Water quality at the inner bay areas was most likely adversely affected by land-based sources of pollution identified in this study. These sources include three drains and two rivers, which discharged into the bays. Yachts were apparently not a source of sewage pollution: there was no significant relationship between yacht number and faecal coliform levels.     

Taxon-specific physico-chemical change points for stream benthic invertebrates

Freshwater organisms face numerous stressors, such as nutrient enrichment, contaminant pollution, sedimentation and alterations in stream hydrology and habitat structure. One of the most significant and widespread stressors in European freshwaters is expected to be water pollution from intensive land use. However, the information on critical threshold concentrations at which taxa decline or increase in frequency and abundance is missing for the large majority of river benthic invertebrate taxa. The main aim was to determine ecological change points for benthic invertebrate taxa at which rapid alterations in species frequency and abundance occur as a consequence of relatively small changes in the environmental gradient. These change points can be interpreted as critical threshold concentrations. A total of 468 river benthic invertebrate taxa and nine physico-chemical variables describing the daytime dissolved oxygen, chloride, nutrient concentrations and organic load were analyzed. We selected 751 river sites from a nationwide range of locations in Germany for this investigation. Depending on the physico-chemical variable, between 20.6% and 48.8% of the total number of tested taxa were assigned with a valid change point. All taxa were assigned to negative or positive response groups depending on the response direction. Except for daytime dissolved oxygen, negative responding taxa are referred to as decreasers and positive responding taxa as increasers, respectively. In total, 25.8–100% of the decreasers’ change points were below (and above in the case of daytime dissolved oxygen) the background values defined as quality criteria for German rivers by the water authorities. This indicates that stricter quality criteria may need to be set to reach the good ecological status according to the European Water Framework Directive. The calculated daytime dissolved oxygen change points were essentially in line with the species saprobic values and taxon-specific change points for physico-chemical variables fit well with the data provided in other international studies. We deliver valuable knowledge about the sensitivities and response schemes of river benthic invertebrate species. This information is especially useful for the development of efficient management and policy tools to predict the likelihood of occurrence of individual species under different levels of anthropogenic impact.     

拉萨河河流健康评价指标体系构建及应用

为全面反映拉萨河干流生态环境现状,基于拉萨河特征和国内外研究构建了包含水文、水质、生物、生境、服务功能5个要素12个指标的河流健康评价指标体系,提出了赋值标准,并在拉萨干流进行了应用。评价所用数据来自资料收集、文献调研、现场监测和调查。评价结果显示拉萨河干流整体处于较为健康状态,且上游健康状况优于中下游。上游河段枯水期水质达到I类水功能区水质目标,丰水期氨氮含量未达到I类水功能区水质目标,总达标率为50%,赋50分,其余指标赋值大于75分;中游河段受水电站运行和灌溉引水影响,流量过程变异程度、河流连通阻隔状况、大型底栖无脊椎动物科级耐污指数赋值较低,分别为0分、25分和45分,生态基流保障度、外来鱼类入侵率、河道稳定性指标较上游变差,赋值在50—75分之间,其余指标赋值大于75分;下游河段流量过程变异程度、外来鱼类入侵情况赋值为0分,河流连通阻隔状况与中游相同为25分,大型底栖无脊椎动物科级耐污指数赋45分,河道稳定性赋68分,其余指标赋值大于75分。从河流健康角度分析,未来拉萨河流域管理应重点关注上游湿地面源问题、中下游水利水电工程的综合效应、人类聚集区鱼类入侵等问题。     

珠江三角洲河网浮游轮虫的群落结构

通过2012年4次对珠江三角洲河网浮游动物的生态调查,研究该水域浮游轮虫的群落结构,包括种类组成、优势种、生物量及多样性等的时空分布,探讨了浮游轮虫群落结构与环境因子的相关关系,并阐析了浮游轮虫的聚群结构.结果表明： 共检出53种浮游轮虫.优势种类的季节演替及空间变化明显,针簇多肢轮虫占有较大优势.从季节变化来看,枯水期密度及生物量均大于丰水期,丰水期的生物多样性指数和均匀度要高于枯水期,浮游轮虫生物量和多样性的季节间差异显著;从空间分布来看,平均密度及平均生物量均呈现自西南向东北升高的趋势,最大密度及生物量均出现在市桥,而生物多样性指数和均匀度指数的空间变化趋势则相反,最高值均出现在青岐,浮游轮虫密度在各调查站位间差异显著,生物量及多样性在各调查站位间的差异不显著.浮游轮虫的密度与生物量、生物多样性指数与均匀度指数呈显著正相关,多样性与生物量呈显著负相关,生物多样性指数和均匀度指数随着生物量的增加显著降低.在不同季节,浮游轮虫密度与水温、pH、溶解氧、叶绿素a含量及总磷、总氮等环境因子密切相关.根据浮游轮虫密度对调查站位进行聚群分析得出5种聚群结构,说明相应调查站位的水质状况有显著差异.     

Structure and dynamics of zooplankton communities,Alligator Rivers Region,N.T., Australia

Biological monitoring in the Alligator Rivers region, northern Australia, provides baseline ecological information to assess the impact of uranium mining and milling and settlement in the area. Spatial and temporal variations 1978–1980 in zooplankton communities of the Magela Creek, a tributary of the East Alligator River, are described. Extremely diverse plankton assemblages occur late in the wet season (Dec.–May), with up to 80 taxa of rotifers and microcrustacea in some billabongs (= ox-bows), while there is a decrease in diversity but increase in population density as the dry season progresses. Natural fluctuations in water quality may be extreme, and limiting to plankters common elsewhere in the tropics. The plankton is composed largely of littoral or epiphytic taxa, with endemic species in all groups.     

A comparative assessment of the status of Surajkund and Rani Pond,Aurangabad, Bihar,India using overall Index of Pollution and Water Quality Index

The Water Quality Index is one of the most effective tools to communicate information on the quality of water to the people. An attempt was made to assess the annual and seasonal status of Surajkund and Rani Pond, Aurangabad, Bihar, India using the overall Index of Pollution and Water Quality Index from November 2017 to October 2019. The values of eleven parameters namely water temperature, pH, electrical conductivity, dissolved oxygen, biochemical oxygen demand, total alkalinity, hardness, total dissolved solids, chloride, nitrate and fluoride were calculated following standard methodology. A statistically significant difference was found among these parameters. The values were compared with the standard to determine the overall Index of Pollution and Water Quality Index. Results indicated that electrical conductivity, total alkalinity and total dissolved solid were higher than prescribed limits. The values 1.5–3.50 of the overall Index of Pollution estimated that the average status of water of Surajkund was acceptable (C2) but Rani Pond and Surajkund during the summer season were slightly polluted (C3). The values 74.18–233.89 of the Water Quality Index inferred that the average status of water of Surajkund and Rani Pond was slightly polluted (C3). However, on a seasonal basis, the water quality of Surajkund was acceptable (C2) but Rani Pond was slightly polluted (C3) to polluted (C4). The results revealed anthropogenic activity and entry of untreated sewage in these water bodies. The water quality felt the necessity to adopt proper management policy and conservation efforts to these water bodies.     

Validation of daily surface water depth model of the Greater Everglades based on real-time stage monitoring and aerial ground elevation survey

As part of the Everglades Depth Estimation Network (EDEN) project, this paper describes validation of raster-based daily surface water depth models of the Greater Everglades in Florida developed using real-time stage data and elevation data obtained from a survey with an aerial height finder. Daily median stage data obtained at over 200 locations were interpolated using the multiquadric radial basis function. Surface water depth was obtained by subtracting a digital elevation model from the interpolated stage raster. The model was validated with 751 independent field measurements of surface water depth between 1999 and 2004. Correlations between prediction error and both density of the monitoring gages and distance from a major linear geographic feature, such as a canal, were weak, suggesting that the error does not depend on these features. South Florida has distinct dry and wet seasons and the study area is dominated by sawgrass and wet prairie. Seasonality and ground vegetation type significantly affect prediction error. Correlation between observed and predicted water depth was high for all combination of season and vegetation type (0.83–0.96). Model validation using an equivalence test provided evidence of equivalence between predicted and observed water depths in dry season prairie-dominated and wet season sawgrass-dominated areas with the strict test and in dry season sawgrass-dominated areas with the liberal test, but not in wet season prairie-dominated areas. Equivalence between observed and predicted water depth for both dry season sawgrass- and wet season prairie-dominated areas were confirmed with the strict test after further model calibrations using linear regressions.     

Water use patterns of estuarine vegetation in a tidal creek system

Water availability is a key determinant of the zonation patterns in estuarine vegetation, but water availability and the use of different water sources over space and time are not well understood. We have determined the seasonal water use patterns of riparian vegetation over an estuarine ecotone. Our aim was to investigate how the water use patterns of estuarine vegetation respond to variations in the availability of tidal creek water and rain-derived freshwater. The levels of natural stable isotopes of oxygen and hydrogen were assessed in the stem of the mangrove Avicennia marina (tall and scrub growth forms), Casuarina glauca and Melaleuca quinquenervia that were distributed along transects from river/creek-front towards inland habitats. The isotopic composition of plant tissues and the potential water sources were assessed in both the wet season, when freshwater from rainfall is present, and the dry season, when mangrove trees are expected to be more dependent on tidal water, and when Casuarina and Melaleuca are expected to be dependent on groundwater. Our results indicate that rainwater during the wet season contributes significantly to estuarine vegetation, even to creek-side mangroves which are inundated by tidal creek water daily, and that estuarine vegetation depends primarily on freshwater throughout the year. In contrast, high intertidal scrub mangroves were found to use the greatest proportion of tidal creek water, supplemented by groundwater in the dry season. Contrary to prediction, inland trees C. glauca and M. quinquenervia were found also to rely predominantly on rainwater—even in the dry season. The results of this study reveal a high level of complexity in vegetation water use in estuarine settings.     

Development of a macroinvertebrate multimetric index for the assessment of low-land streams in the neotropics

The water and habitat quality in Panamanian streams and rivers are being degraded by agriculture, urbanization, industrial activities, mining, and other forms of development. Thus, the need for standards, especially those examining the biological attributes of lotic systems, are urgently required. We describe the development of a multimetric index based on macroinvertebrates collected in low-land streams in the Panama Canal Watershed (PCW), which differed in their levels of human impacts. The index was developed using 12 streams and validated using a further three, all of which were sampled on four occasions, in the dry and wet seasons of 2007 and 2008. We examined 42 metrics related to macroinvertebrate community structure, composition, and function. Based on their ability to distinguish reference from moderately or severely impacted streams, and on their independence, we selected seven metrics (Margalef's index (taxa), Shannon's evenness index (taxa), number of EPT (taxa), % of Trichoptera, ratio of Chironomidae/Diptera individuals, % of scrapers, and % of shredders). These metrics were then standardized and developed into the Neotropical Low-land Stream Multimetric Index (NLSMI). Overall, the NLSMI distinguished well among the different levels of impairment (Reference, Moderate impact, and Severe impact) and showed a strong, significant correlation with principal component analysis (PCA) axis one values, with the PCA based on a set of physico-chemical variables indicative of stream quality. The wet season generally resulted in lower NLSMI values, leading us to suggest that sampling for biomonitoring be carried out in the dry season. Overall, this preliminary macroinvertebrate NLSMI shows promise for developing a biomonitoring programme to assess the ecological integrity of streams, to aid with management, restoration, and conservation, and to serve as a basis to develop a more geographically extensive multimetric index.     

A list of macroinvertebrates in Dutch water types: A first step towards an ecological classification of surface waters based on key factors

An ecological classification of surface waters in the Netherlands is presented. This classification is based on literature data and the authors opinions concerning the habitat range of macroinvertebrate taxa. Water types were defined by key factors. Taxa were assigned to these water types and provided with a characterizing weight. The list may be a useful tool in the ecological management of waters.     

南水北调中线水源区浮游植物与水质评价

通过2003年3月至2005年8月对南水北调中线水源区水体浮游植物的调查,结果表明:该水域共有浮游植物8门63属96种及变种,其中以硅藻的种类最多,其次是绿藻和蓝藻。藻类的细胞密度表现出明显的季节变化,夏季最高冬季最低。从近3年的浮游生物检测结果可知,整个水源区年平均藻类细胞密度为109.33×10⁴ cells·L^-1,处于较低的水平,而且未检出水体重污染指示种,充分说明南水北调中线水源区富营养化程度较低。运用Margalef和Menkinick多样性指数对该水域的水质进行评价,数据显示2003~2005年该水源区的d值和α值,各采样点之间的差异并不显著,说明各采样点的水质营养状况虽有差异,但总体水平基本相当。水质评价结果:水体为寡污型,基本处于中营养状态。通过水生生物资源的调查,做好水源区的长期生态监测,可为建立中线水源区长期生态研究数据信息库及库区生态环境保护政策制定提供理论依据,对保证中线水质质量十分重要。     

Investigation of ecological factors controlling quality of flue-cured tobacco (Nicotiana tabacum L.) using classification methods

The growth and quality of tobacco are associated with ecological conditions, such as soil, climate or weather, and geographical attributes. Tobacco, especially flue-cured tobacco, is an important cash crop and widely cultivated in southwestern China. However, knowledge about critical ecological indicators affecting quality of flue-cured tobacco is limited in this region. In the current study, two well-known clustering algorithms, i.e., k-means and classification and regression trees (CART), were applied to investigate the critical ecological indicators controlling quality of flue-cured tobacco. On the basis of six quality indices and Davis–Bouldin index, a total of 142 flue-cured tobacco leaf samples were classified into three groups with low, medium, and high quality using k-means algorithm. The results obtained by CART model showed that geographical attributes (altitude, latitude, and longitude) and weather indicators had high effects on the quality of flue-cured tobacco followed by soil properties and varieties. Flue-cured tobacco plants with high quality preferred to be grown in areas with low values of altitude, rainfall and relative humidity, high values of latitude, longitude, sunshine hours, and temperature-related indices (mean, maximum and minimum temperatures and their difference), and low concentrations of soil nutrients in this study area. Nevertheless, further study should be conducted to understand the interaction among the ecological variables.     

The role of wetlands in wildlife migration in the Tarangire ecosystem,Tanzania

Twenty-two years of rainfall data from six sites, 5 years of animal migration data and 2 years of water quality at 13 sites were explored to quantify the role of water in the Tarangire ecosystem. Inter-annual fluctuations in rainfall were large and not predictable solely from the Southern Oscillation Index. Seasonal fluctuations of rainfall were pronounced, with marked wet and dry seasons. In the dry season, the only drinking water available for wildlife was the Tarangire River and a number of small, scattered wetland-fringed water holes. Their salinity was often high (>8 ppt) and was higher in dry years than in wet years, as well as at the start of the wet season. Water quantity and quality may control the annual migration of wildebeest, zebra, elephants and buffaloes. These animals aggregate in the dry season in areas with the least salty water. The timing of seasonal variations in rainfall is largely predictable and controls annual migration. All wildebeest and most zebras migrated out of Tarangire National Park and into the wider Tarangire ecosystem at the start of the wet season, and they returned into the park in the dry season. Some elephants and buffaloes also migrated in out of the park and a larger resident population remained, whose size may vary inter-annually depending on surface water quantity and quality. The extent of the migration zone may also vary inter-annually.This revised version wa published online in March 2005 with corrections to the issue cover date.