Dynamics of phytoplankton in Finnish lakes

The studies on lake phytoplankton in Finland are reviewed and the major aspects of the phytoplankton dynamics are discussed. Special attention has been paid to the factors limiting productivity and species succession in different communities. After the early mainly taxonomical and floristic publications on phytoplankton at the end of last century, phytoplankton studies in lakes have proceeded along two different lines: 1) the species composition of communities and taxonomy, and 2) their production ecology or dynamics. Recently, both approaches have been combined, resulting in some profound ecological studies. In many lakes, phosphorus has been shown to be a limiting factor for phytoplankton productivity. However, it has also been shown that the irradiance and water temperature may effectively regulate the seasonal trend of phytoplankton productivity. This is the case especially in polyhumic forest lakes, where allochthonous material seems to play a major role also in primary production ecology.     

Biological indicators track differential responses of pelagic and littoral areas to nutrient load reductions in German lakes

External nutrient loading was reduced over the past decades as a measure for improving the water quality of eutrophic lakes in western Europe, and has since been accelerated by the adoption of the European Water Framework Directive (WFD) in 2000 (EC, 2000). A variety of eutrophication-related metrics have indicated that the response of biological communities to this decreased nutrient loading has been diverse. Phytoplankton, a major component of the pelagic community, often responded rapidly, whereas a significant delay was observed for submerged macrophytes colonizing littoral areas. In this study we tested whether assessment methods developed for phytoplankton and macrophytes in lakes during Germany's implementation of the WFD reflect this differential response. An assessment of 263 German lakes confirmed that a lower ecological state was recorded when based on the biological quality element (BQE) for macrophytes than the BQE for phytoplankton during the investigated period (2003–2012). On average, lakes had a moderate ecological status for both phytoplankton and macrophyte BQEs, but differences of up to three classes were observed in single cases. Long-term data were available for five lowland lakes subject to strong reductions in phosphorus loading. Their phytoplankton-based assessments indicated a constant improvement of the ecological status in parallel to decreasing water phosphorus concentrations. In contrast, macrophyte-based assessments indicated a 10–20 year delay in their ecological recovery following nutrient load reduction. This delay was confirmed by detailed data on the temporal development of macrophyte species diversity and maximum colonization depths of two lakes after nutrient load reduction. We conclude that the available WFD assessment methods for phytoplankton and macrophyte BQEs are suitable to track the differential response of pelagic and littoral areas to nutrient load reductions in German lakes.     

Use of marker pigments and functional groups for assessing the status of phytoplankton assemblages in lakes

Phytoplankton is a key biological quality element for the establishment of the Water Framework Directive (WFD) ecological status in reservoirs and lakes. In freshwaters, inverted microscope examination is the traditional standard method for estimating phytoplankton and assessing taxonomic composition. Based on the enumeration of algal units and measurements for biovolume calculation, this technique is cumbersome and time-consuming. In large monitoring programmes, such as the application of the WFD in lakes and reservoirs, chemotaxonomy (HPLC pigment analysis and CHEMTAX treatment) is ideally suited as an alternative method because it allows the rapid processing of large numbers of samples from numerous locations and depths, thereby providing ideal temporal and spatial resolution. The low taxonomical detail obtained by HPLC and CHEMTAX (phytoplankton classes or phyla) can easily be overcome by a rapid inverted microscope screening with identification of the dominant species. Combining HPLC and microscopy provides a useful method for monitoring phytoplankton assemblages, which can be used to implement the WFD with respect to phytoplankton. Here, we present the application of a method combining marker pigments and microscopy to phytoplankton samples from 12 Belgian reservoirs. This method substantially reduced the workload and enabled us to assess the status of the phytoplankton assemblage in these lakes. The method complies with the WFD, as it takes into account taxonomic composition, assesses abundance and biomass of the phytoplankton taxa, and easily detects blooms. Additionally, a set of templates of probability of occurrence of phytoplankton functional groups at the maximal ecological potential for reservoirs from the Central/Baltic region is presented, based on reference conditions defined for natural lakes from other regions.     

Quantifying uncertainties in biologically-based water quality assessment: A pan-European analysis of lake phytoplankton community metrics

Lake phytoplankton are adopted world-wide as a sensitive indicator of water quality. European environmental legislation, the EU Water Framework Directive (WFD), formalises this, requiring the use of phytoplankton to assess the ecological status of lakes and coastal waters. Here we provide a rigorous assessment of a number of proposed phytoplankton metrics for assessing the ecological quality of European lakes, specifically in response to nutrient enrichment, or eutrophication, the most widespread pressure affecting lakes. To be useful indicators, metrics must have a small measurement error relative to the eutrophication signal we want them to represent among lakes of different nutrient status. An understanding of variability in metric scores among different locations around a lake, or due to sampling and analytical variability can also identify how best this measurement error is minimised.To quantify metric variability, we analyse data from a multi-scale field campaign of 32 European lakes, resolving the extent to which seven phytoplankton metrics (including chlorophyll a, the most widely used metric of lake quality) vary among lakes, among sampling locations within a lake and through sample replication and processing. We also relate these metrics to environmental variables, including total phosphorus concentration as an indicator of eutrophication.For all seven metrics, 65–96% of the variance in metric scores was among lakes, much higher than variability occurring due to sampling/sample processing. Using multi-model inference, there was strong support for relationships between among-lake variation in three metrics and differences in total phosphorus concentrations. Three of the metrics were also related to mean lake depth. Variability among locations within a lake was minimal (<4%), with sub-samples and analysts accounting for much of the within-lake metric variance. This indicates that a single sampling location is representative and suggests that sub-sample replication and standardisation of analyst procedures should result in increased precision of ecological assessments based upon these metrics.For three phytoplankton metrics being used in the WFD: chlorophyll a concentration, the Phytoplankton Trophic Index (PTI) and cyanobacterial biovolume, >85% of the variance in metric scores was among-lakes and total phosphorus concentration was well supported as a predictor of this variation. Based upon this study, we can recommend that these three proposed metrics can be considered sufficiently robust for the ecological status assessment of European lakes in WFD monitoring schemes.     

Planktonic indices in the evaluation of the ecological status and the trophic state of the longest lake in Poland

Due to the intensive mixing polymictic lakes should be homogenous. However, morphometric diversity and high water dynamics contribute to the differentiation of many parameters in various areas of the lakes. This study analyzes both phytoplankton and zooplankton to assess differences in water quality along the north–south axis of the longest lake in Poland. New phytoplankton indicators were applied for determining the lake's ecological status: the Q index based on functional groups and the PMPL (Phytoplankton Metric for Polish Lakes) index based on phytoplankton biomass. TSI_ROT index (Rotifer Trophic State Index), which comprises the percentage of species indicating a high trophic state in the indicatory group and the percentage of bacteriovorus in the Rotifera population, was used for zooplankton analysis.TP content was different at different sites – we observed its gradual increase from the south to the north. Spatial variation of phosphorus did not considerably affect plankton diversity. The phytoplankton was dominated by Oscillatoriales, typical of shallow, well-mixed eutrophic lakes. The ecological status of the lake based on the EQR (Ecological Quality Ratio) was poor or moderate. The zooplankton was dominated by rotifers (at almost all sites), which indicates a eutrophic state of the lake. The values of phytoplankton indices at the studied sites did not differ considerably; the differences resulted more from local conditions such as the contaminant inflow and the macrophyte development than water dynamics.We have demonstrated that in the lake dominated by filamentous Cyanobacteria the ecological status should be determined according to the PMPL index or other indices dependent on the dominant Cyanobacteria species. Since the Q index does not include the functional group S1, the results can lead to the false conclusion that water quality improves with an increased amount of phytoplankton. The high abundance of Cyanobacteria in the lake may have contributed to the poor growth of rotifers.     

Lake‐type‐specific seasonal patterns of nutrient limitation in German lakes,with target nitrogen and phosphorus concentrations for good ecological status

相似文献   

Zooplankton as indicators in lakes: a scientific-based plea for including zooplankton in the ecological quality assessment of lakes according to the European Water Framework Directive (WFD)

With the implementation of the EU Water Framework Directive (WFD), the member states have to classify the ecological status of surface waters following standardised procedures. It was a matter of some surprise to lake ecologists that zooplankton were not included as a biological quality element (BQE) despite their being considered to be an important and integrated component of the pelagic food web. To the best of our knowledge, the decision of omitting zooplankton is not wise, and it has resulted in the withdrawal of zooplankton from many so-far-solid monitoring programmes. Using examples from particularly Danish, Estonian, and the UK lakes, we show that zooplankton (sampled from the water and the sediment) have a strong indicator value, which cannot be covered by sampling fish and phytoplankton without a very comprehensive and costly effort. When selecting the right metrics, zooplankton are cost-efficient indicators of the trophic state and ecological quality of lakes. Moreover, they are important indicators of the success/failure of measures taken to bring the lakes to at least good ecological status. Therefore, we strongly recommend the EU to include zooplankton as a central BQE in the WFD assessments, and undertake similar regional calibration exercises to obtain relevant and robust metrics also for zooplankton as is being done at present in the cases of fish, phytoplankton, macrophytes and benthic invertebrates.     

基于因子分析的南湾水库水源地浮游植物生物完整性评价

于2016年在淮河流域饮用水源地水库-南湾水库,开展了3次浮游植物调查,在分析南湾水库浮游植物群落结构的基础上,依据生物完整性理论,采用因子分析方法对南湾水库开展了生态完整性评价。研究结果显示:3次调查中浮游植物种类数变化较小,但所属种类存在明显的季节差异;浮游植物密度9月份最高,3月密度最低,而生物量则正好相反,3月最高而9月最低。进一步采用因子分析对群落数据进行分析,筛选确定了4个公因子。其中,因子1反映了群落的耐污特征与能力;因子2表征了群落的多样性特征;因子3表征了群落丰富度状况;因子4表征了水体富营养状况。因子分析得分表明:从时间上来看,南湾水库9月水生态状况最差,从空间上看,则人口密度大的库湾区域水生态状况较差。因子得分较好地反映了水库不同时间与地点水生态状况的相对大小,表明基于因子分析生物完整性评价能够较地应用于南湾水库,也适合推广应用于其他水体的生态评价工作中。     

Site-specific chlorophyll reference conditions for lakes in Northern and Western Europe

The Water Framework Directive (WFD) requires EU Member States to assess the “ecological status” of surface waters. As a component of ecological status, many European countries are developing a classification scheme for chlorophyll concentrations as a measure of phytoplankton biomass. The chlorophyll classification must be based on the degree of divergence of a water body from an appropriate baseline or ‘reference condition’. This article describes the development of a series of regression models for predicting reference chlorophyll concentrations on a site-specific basis. For model development, a large dataset of European lakes considered to be in reference condition, 466 lakes in total, was assembled. Data were included from 12 European countries, but lakes from Northern and Western Europe dominated and made up 92% of all reference lakes. Data have been collated on chlorophyll concentration, altitude, mean depth, alkalinity, humic type, surface area and geographical region. Regression models were developed for estimating site-specific reference chlorophyll concentrations from significant predictor ‘typology’ variables. Reference chlorophyll concentrations were found to vary along a number of environmental gradients. Concentrations increased with colour and alkalinity and decreased with lake depth and altitude. Forward selection was used to identify independent explanatory variables in regression models for predicting site-specific reference chlorophyll concentrations. Depth was selected as an explanatory variable in all models. Alkalinity was included in models for low colour and humic lakes and altitude was included in models for low colour and very humic lakes. Uncertainty in the models was quite high and arises from errors in the data used to develop the models (including natural temporal and spatial variability in data) and also from additional explanatory variables not considered in the models, particularly nutrient concentrations, retention time and grazing. Despite these uncertainties, site-specific reference conditions are still recommended in preference to type-specific reference conditions, as they use the individual characteristics of a site known to influence phytoplankton biomass, rather than adopt standards set to generally represent a large population of lakes of a particular type. For this reason, site-specific reference conditions should result in reduced error in ecological status classifications, particularly for lakes close to typology boundaries.     

Some aspects of the seasonal distribution of flagellates in mountain lakes

In a larger regional survey in Tyrol, phytoplankton species composition and biovolume of mid-altitude and high-mountain lakes was studied. Results from eight lakes showed that flagellates (mainly Chrysophyceae, Dinophyceae, and Cryptophyceae) are important components of the phytoplankton.In the mid-altitude lakes a spring and an autumn maximum of Chrysophyceae as well as a summer maximum of large dinoflagellates are observed, whereas Cryptophyceae and Dinophyceae show irregular distributions. In the high-mountain lakes the seasonal variations of phytoplankton, including flagellates, are limited by the long duration of the winter situation. However similar sequences of phytoplankton assemblages as in the midaltitude lakes can be observed. Flagellates in high-mountain lakes are important to sustain phytoplankton standing crop under the winter snow and ice cover.In order to show similarities and differences of high-mountain and mid-altitude lakes, vertical profiles of phytoplankton from three lakes and seasonal patterns of Gymnodinium uberrimum from two lakes are compared. In addition the patterns of cryptomonads differing in their ecological requirements (Cryptomonas spp. and Rhodomonas minuta) are shown for a meromictic mid-altitude lake.     

天津市典型湖库湿地生态完整性评价

对湖库湿地进行生态健康评价,可为湖库湿地生态系统修复和管理提供决策依据。本文以天津市为例,选取20个典型的湖库湿地采样点,基于2018年8—9月期间调查获取的物理、化学和生物群落指标(浮游动物、浮游植物、底栖动物、鱼类、水生大型植物、河岸带植物)数据,构建包含物理完整性、化学完整性和生物完整性在内的生态完整性指数(IEI)对采样点生态健康状况进行评价。根据栖息地环境质量(QHEI)、水质状况和人类活动干扰3方面选取参照点,采用标准化方法筛选候选指标,应用层次分析法计算各指标权重,最终得出天津市典型湖库湿地生态完整性评价结果。结果表明: 1)所有样点中,“健康”点位占5.0%,“较好”点位占20.0%,“一般”点位占35.0%,“较差”点位占30.0%,“差”点位占10.0%。天津市典型湖库湿地生态健康状况整体处于一般水平,呈现出西部优于东部的趋势,空间差异显著;2)基于栖息地评分、水质状况与人类活动干扰相结合选取参照点是可行的,依据水质指标可降低选择参照点时的主观性;3)适用性验证结果表明,IEI可较好表征各点位的健康状况,区分效率明显,适用于评价研究区湖库湿地生态健康状况。     

Taxa-specific eco-sensitivity in relation to phytoplankton bloom stability and ecologically relevant lake state

Phytoplankton (including plant-like, animal-like algae and Cyanobacteria) blooms have recently become a serious global threat to the sustenance of ecosystems, to human and animal health and to economy. This study focused on the composition and stability of blooms as well as their taxa-specific ecological sensitivity to the main causal factors (especially phosphorus and nitrogen) in degraded urban lakes. The analyzed lakes were assessed with respect to the trophic state as well as ecological status. Total phytoplankton biomass (ranging from 1.5 to 181.3 mg dm⁻³) was typical of blooms of different intensity, which can appear during a whole growing season but are the most severe in early or late summer. Our results suggested that steady-state and non-steady-state bloom assemblages including mono-, bi- and multi-species or heterogeneous blooms may occur in urban lakes. The most intense blooms were formed by the genera of Cyanobacteria: Microcystis, Limnothrix, Pseudanabaena, Planktothrix, Bacillariophyta: Cyclotella and Dinophyta mainly Ceratium and Peridinium. Considering the sensitivity of phytoplankton assemblages, a new eco-sensitivity factor was proposed (E-SF), based on the concept of Phytoplankton Trophic Index composed of trophic scores of phytoplankton taxa along the eutrophication gradient. The E-SF values of 0.5, 1.3, 6.7 and 15.1 were recognized in lakes having a high, good, moderate or poor ecological status, respectively. For lake restoration, each type of bloom should be considered separately because of different sensitivities of taxa and relationships with environmental variables. Proper recognition of the taxa-specific response to abiotic (especially to N and P enrichment) and biotic factors could have significant implications for further water protection and management.     

Catchment land use and trophic state impacts on phytoplankton composition: a case study from the Rotorua lakes’ district, New Zealand

Trophic state of lakes has been related to catchment land use, but direct links between phytoplankton taxa and land use are limited. Phytoplankton composition, represented by relative cell abundance of phyla, was measured over a period of 4 years in 11 lakes in the Rotorua region, New Zealand. The lakes differed in morphometry, trophic state and land use (as percentage catchment area). We tested whether relative proportion of land uses, indirectly representing relative nutrient loading, was the overarching driver of phytoplankton composition. Trophic state was correlated negatively with native forest and positively with pasture and urban area. Cyanoprokaryota were correlated negatively with native forest and positively with pasture and trophic state, Chlorophyta were correlated positively with native forest and urban land use and negatively with pasture and trophic state, and Bacillariophyta were positively correlated with dissolved reactive silica to dissolved inorganic nitrogen (Si:DIN) and Si to dissolved reactive phosphorus (Si:DRP) ratios. Lakes with higher nutrient loads had higher trophic state and Cyanoprokaryota dominance. Chlorophyta were negatively correlated with Cyanoprokaryota and Bacillariophyta, suggesting competition amongst these groups. Our results apply to lakes potentially subject to changes in catchment land use, which may have implications for trophic state, phytoplankton composition and Cyanoprokaryota blooms.     

Biological assessment of European lakes: ecological rationale and human impacts

相似文献   

A phytoplankton trophic index to assess the status of lakes for the Water Framework Directive

Despite improvements in wastewater treatment systems, the impact of anthropogenic nutrient sources remains a key issue for the management of European lakes. The Water Framework Directive (WFD) provides a mechanism through which progress can be made on this issue. The Directive requires a classification of the ecological status of phytoplankton, which includes an assessment of taxonomic composition. In this paper, we present a composition metric, the plankton trophic index, that was developed in the WISER EU FP7 project and demonstrate how it has been used to compare national phytoplankton classification systems in Northern and Central Europe. The metric was derived from summer phytoplankton data summarised by genus from 1,795 lakes, covering 20 European countries. We show that it is significantly related to total phosphorus concentrations, but that it is also sensitive to alkalinity, lake size and climatic variables. Through the use of country-specific reference values for the index, we demonstrate that it is significantly related to other national phytoplankton assessment systems and illustrate for a single European (intercalibration) lake type how it was used to intercalibrate WFD boundaries from different countries.     

Ecological status assessment of European lakes: a comparison of metrics for phytoplankton, macrophytes, benthic invertebrates and fish

Data on phytoplankton, macrophytes, benthic invertebrates and fish from more than 2000 lakes in 22 European countries were used to develop and test metrics for assessing the ecological status of European lakes as required by the Water Framework Directive. The strongest and most sensitive of the 11 metrics responding to eutrophication pressure were phytoplankton chlorophyll a, a taxonomic composition trophic index and a functional traits index, the macrophyte intercalibration taxonomic composition metric and a Nordic lake fish index. Intermediate response was found for a cyanobacterial bloom intensity index (Cyano), the Ellenberg macrophyte index and a multimetric index for benthic invertebrates. The latter also responded to hydromorphological pressure. The metrics provide information on primary and secondary impacts of eutrophication in the pelagic and the littoral zone of lakes. Several of these metrics were used as common metrics in the intercalibration of national assessment systems or have been incorporated directly into the national systems. New biological metrics have been developed to assess hydromorphological pressures, based on aquatic macrophyte responses to water level fluctuations, and on macroinvertebrate responses to morphological modifications of lake shorelines. These metrics thus enable the quantification of biological impacts of hydromorphological pressures in lakes.     

Increased nutrient loading and rapid changes in phytoplankton expected with climate change in stratified South European lakes: sensitivity of lakes with different trophic state and catchment properties

We hypothesised that increasing winter affluence and summer temperatures, anticipated in southern Europe with climate change, will deteriorate the ecological status of lakes, especially in those with shorter retention time. We tested these hypotheses analysing weekly phytoplankton and chemistry data collected over 2 years of contrasting weather from two adjacent stratified lakes in North Italy, differing from each other by trophic state and water retention time. Dissolved oxygen concentrations were higher in colder hypolimnia of both lakes in the second year following the cold winter, despite the second summer was warmer and the lakes more strongly stratified. Higher loading during the rainy winter and spring increased nutrient (N, P, Si) concentrations, and a phytoplankton based trophic state index, whilst the N/P ratio decreased in both lakes. The weakened Si limitation in the second year enabled an increase of diatom biovolumes in spring in both lakes. Chlorophyll a concentration increased in the oligo-mesotrophic lake, but dropped markedly in the eutrophic lake where the series of commonly occurring cyanobacteria blooms was interrupted. The projected increase of winter precipitation in southern Europe is likely to increase the nutrient loadings to lakes and contribute to their eutrophication. The impact is proportional to the runoff/in-lake concentration ratio of nutrients rather than to the retention time, and is more pronounced in lakes with lower trophy.     

The habitat template of phytoplankton morphology-based functional groups

The identification of the main factors driving phytoplankton community structure is essential to understand and adequately manage freshwater ecosystems. We hypothesize that differences in morphological traits reflect phytoplankton functional properties that will be selected under particular environmental conditions, namely their habitat template. We apply a morphology-based functional groups (MBFG) approach to classify phytoplankton organisms and define each group template. We use machine learning techniques to classify a large number of phytoplankton communities and environmental variables from different climate zones and continents. Random forest analysis explained well the distribution of most groups’ biovolume and the selected variables reflected ecological preferences according to morphology. By means of a classification tree it was also possible to identify thresholds of the environmental variables promoting groups dominance in different lakes. For example group III (filaments with aerotopes and high surface/volume including potentially toxic species) was dominant when light attenuation coefficient was >3.9 m⁻¹ and total nitrogen was >2,800 μg l⁻¹. We demonstrate that morphology captures ecological preferences of phytoplankton groups and provides empirical values to describe their habitat template.     

Cyanophytes and chlorophytes versus raphidophytes in humic lakes with different catchment basins

The aim of the study was to evaluate the effects of coniferous forest cover in the catchment basin and relative catchment area (catchment area to lake volume ratio) on phytoplankton composition in humic lakes. The study was carried out in 11 small and shallow lakes situated in the West Polesie region (Eastern Poland). The lakes were divided with respect to forest cover in their catchment basins into two groups: high forest cover — HFC (more than 60%) and low forest cover — LFC (less than 60%). The study showed that both, land use in the catchments (proportion of forests) and the relative catchment area determined physicochemical and biological parameters in the lakes. The high relative catchment area affects their high productivity expressed by high chlorophyll a concentration and low water visibility. The lakes of the LFC group had low water colour as well as high concentration of total phosphorus (P_tot), reaction (pH), and conductivity of water and a large number of cyanophytes and chlorophytes. The dominant species, e.g., Planktolyngbya limnetica, Limnothrix planctonica, Planktothrix agardhii, Coenococcus planctonicus, were characteristic of high trophic status. In the lakes of the HFC group, P_tot, pH, conductivity of water and the contribution of cyanophytes and chlorophytes was considerably lower, whereas the water colour and the number of raphidophytes represented by Gonyostomum semen was high. The large number of raphidophytes and the small amount of chlorophytes and cyanophytes in the lakes of the HFC group indicated the lake naturalness.     

Deterministic diversity changes in freshwater phytoplankton in the Yunnan–Guizhou Plateau lakes in China

Diversity measures reflect different aspects of a community, which are determined by different ecological processes. However, information is still limited on the ecological processes that are represented by different measures of species diversity. In this study, the primary driving factors for richness and diversity indices were tested. The possible ecological processes represented by each index were analyzed. First, the type of ecological process that governed the phytoplankton community in the Yunnan–Guizhou Plateau lakes, either deterministic or stochastic, was identified by Caswell's neutral model. The results indicate that a deterministic process governs the phytoplankton community. Second, the driving factors of richness and diversity indices were screened with mixed models. The results suggest that the variation of phytoplankton richness in different lakes or sites was primarily related to bottom-up factors. The variations in evenness and other measures based on the relative abundance were driven by both top-down and bottom-up factors, such as zooplankton biomass, and pH and mean light, respectively. Finally, although the different measures of diversity may respond to specific bottom-up or top-down processes, the responses to the two processes were not independent of each other. These findings will increase our understanding of the relationships between ecological processes and diversity measures for freshwater phytoplankton.