Quantifying Ecological Stability: From Community to the Lake Ecosystem

We performed a methodological study aimed at extending our previously developed approach to quantify the ecological stability of biotic communities and an entire ecosystem, using Lake Kinneret as a case study. The ecological stability of the biotic communities (phytoplankton and zooplankton) of Lake Kinneret was estimated using two different aggregating schemes. The first scheme used the combined stability index, based on the combined indices of the individual phytoplankton (SI[Comb]_P) and zooplankton (SI[Comb]_Z) taxonomic groups. The total community stability index was calculated based on the total abundances of these communities. The stability of the entire ecosystem was estimated for two sets of ecosystem state variables, a lake “trophic state” set and a “water quality” set, which provided considerably different estimates of the lake ecosystem stability. Good agreement between the results of this study and qualitative estimates of Lake Kinneret stability validates the suitability of this approach to estimate the stability of different ecological units.     

Quantifying the ecological stability of a phytoplankton community: The Lake Kinneret case study

The widely used term “stability” has multiple meanings and is rarely quantified in limnological studies. The main objective of this study was to develop an approach for quantifying the stability of a phytoplankton community using Lake Kinneret as a case study. It is a first attempt of calculating an index of stability for each of the five main taxonomic groups of the Kinneret phytoplankton (Bacillariophyta, Chlorophyta, Cryptophyta, Cyanophyta and Dinophyta), and for the entire community. A simple statistical approach to calculate the stability index was devised, using phytoplankton wet-weight biomass as the parameter being manipulated. The period 1970–1979 was selected as a reference period. The following stability indices were established and applied (each at three time scales): (1) a stability index for each of five main taxonomic groups; (2) a combined index of the stability, aggregating the stabilities of the individual taxonomic groups and (3) a stability index of entire community based on total phytoplankton biomass. The dynamics of these indices during 1969–2011 were examined. Destabilization of the community structure was triggered by an increase in the variability of Bacillariophyta biomass shortly after the reference period, in 1981–1983. Only 10 years later, the community destabilization become associated with progressively increasing biomass of Cyanobacteria. Dinophyta were the last to destabilize in the mid 1990s. Despite notable changes in the community structure, the total phytoplankton biomass remained relatively stable. Therefore, in 1969–2011 the stability index based on total phytoplankton biomass was higher than the combined index based on the stabilities of the individual taxonomic groups. Only weak relationships were found between the stability index values and potential driving forces (lake water level fluctuations and nutrient loads). While this approach was applied to Lake Kinneret, the concept presented is not lake specific and could be applied to other lakes.     

井冈山地区莲鱼复合种养模式效益评价

为研究莲鱼复合种养生态系统中的浮游植物群落特征, 及该养殖模式的经济和生态效益, 2019年春季至秋季, 对江西井冈山地区莲鱼种养、莲单种和鱼单养3种种养模式的水质及浮游生物开展了季节调查, 结合当地生产经营, 分析了不同种养模式的经济效益及生态足迹。研究表明, (1)共鉴定出浮游植物7门103种,其中绿藻56种, 蓝藻21种, 硅藻16种, 裸藻3种, 隐藻4种, 金藻2种, 黄藻1种。复合种养模式水体的水质均处于轻污染-无污染状态, 优于单种和单养模式, 且优势种存在季节性差异。(2)冗余分析表明, 水温和溶解氧是影响莲鱼复合种养生态系统浮游植物群落结构的关键环境因子, 总磷(鱼单养模式的主要影响因子)和硝酸氮(莲单养模式的主要影响因子)并不是影响该复合种养模式中浮游植物群落的主要环境因子。(3)莲鱼复合种养经济效益为25200元/公顷, 介于鱼单养和莲单种模式之间, 但其产生每万元利润的生态足迹最低, 为4.48 hm2, 是鱼单养模式的80.9%, 莲单种的33.2%。江西井冈山地区的莲鱼复合种养模式是一种高效益、低生态负荷的综合种养模式, 适宜在当地大面积推广。     

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.     

A comparative study of the impact of species composition on a freshwater phytoplankton community using two contrasting biotic indices

Biodiversity index based on species richness and evenness has been a frequently used measure to describe phytoplankton community composition and the impact of water pollution on biotic components, despite it could not reflect clearly the impact of a particular species on the structure and function of phytoplankton community. On the contrary, an index based on the niche theory has been developed and used to elucidate the changes of phytoplankton community with the alteration of species composition under various levels of water quality. Through comparison on the Shannon–Wiener biodiversity index (H′) and the community pollution value (CPV), this paper depicted the algal species composition change along the gradation of water quality and quantified the impact of species composition on the structure and function of a freshwater phytoplankton community in four urban lakes in central China. This study found that not only CPV could indicate water pollution status but also the fluctuation of CPV along water pollution gradient could show the influence of dominant species composition on community function. The comparison between Shannon–Wiener biodiversity index and CPV shows that the presence of dominant species sustains the stability and the succession of phytoplankton community under the changing water environments. The results of this study indicate that the combination of biodiversity index and CPV can provide a systematic way to understand biotic interactions and species responses to altered habitats at the community level. Most importantly, these indicators will provide valuable information for lake management and restoration practices.     

Coherence of phytoplankton and attached diatom-based ecological status assessment in Lake Balaton

Coherence between ecological status assessment by phytoplankton and attached diatoms was analyzed in the littoral zone of Lake Balaton. Sampling of periphytic diatoms, phytoplankton, and water were carried out at ten different littoral sites in the northern and southern shores of the lake for a year. Phytoplankton species were sorted into functional groups and ecological status was assessed by means of the phytoplankton assemblage Q index. The index TDIL was calculated using quantitative attached diatom data. Significant differences were found between the ecological assessments based on phytoplankton and phytobenthos metrics, both seasonally and spatially. The Q index indicated ecological states varying from bad to good, while the average of diatom indices varied from moderate to high conditions. The Q index provided more realistic ecological status of Lake Balaton, compared with trophic status based on TP values, especially in the summer period. Differences in the response-time indication of phytoplankton and attached diatoms suggest that lack of coherence should also be expected between the responses of other BQEs.     

Phytoplankton structure and dynamics in a volcanic lake in Deception Island (South Shetland Islands,Antarctica)

This work constitutes the first floristic and ecological analysis of the phytoplankton community of a volcanic freshwater lake in Deception Island (62°57′S, 60°38′W, South Shetland Islands, Antarctica). The main limnological features and phytoplankton size fractions were analyzed. Samples were taken during the austral summer of 2002 at two opposite sites. According to ANOVA results performed with abiotic variables, no significant differences between sites were found. The phytoplankton community showed low algal species richness, with an important contribution of the tychoplanktonic taxa. In terms of species number, Bacillariophyceae was the dominant class. Autotrophic picoplankton registered the highest densities from the second sampling date onwards. Nanophytoplankton was represented by unidentified chrysophycean organisms, which showed different distribution patterns between sites. The net phytoplankton abundance remained low during the sampling period and was strongly correlated with chlorophyll a concentration. Both nutrient concentrations and chlorophyll a values indicated oligotrophic conditions.     

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。     

Water Quality Quantification: Basics and Implementation

Quantitative estimation of water quality and its relationships with management activities is a necessary step in efficient water resources management. However, water quality is typically defined in abstract terms and management activities are rarely quantified with respect to their impact on lake water quality. Here we show by demonstration of systems for Lake Kinneret, Israel and the Naroch Lakes of Belarus how water quality can be quantified in relation to lake management activities to be a part of sustainable management.     

Comparative responses of phytoplankton during chemical recovery in atmospherically and experimentally acidified lakes1

Twenty lakes recovering from a century of atmospheric acid deposition over Northeastern Ontario were resurveyed for phytoplankton following a 20‐year period and were compared with a 23‐year study of an experimentally acidified lake, L302S (Experimental Lakes Area, ON, Canada). Phytoplankton species significantly tracked abiotic changes during both acidification and chemical recovery in all lakes based on concordance testing. However, ordination analyses showed that many phytoplankton communities had not returned to their preacidification state. Significant explanatory variables of taxonomic responses were pH, dissolved organic carbon (DOC), and inorganic nutrients (N, P), based on canonical correspondence analysis (CCA). Increases in DOC and pH influenced a significant taxonomic shift from acid‐tolerant dinoflagellates to a diverse assemblage of cyanobacteria, chlorophytes, and diatoms. Declining nitrogen levels defined a secondary environmental gradient, which was characterized by a decrease in filamentous green algal abundance. L302S remained remote in ordination space from the more chronically and heavily polluted lakes in Northeastern Ontario, indicating that experimental acidification provided a conservative estimate of the true damage to atmospherically polluted lakes. However, L302S did increasingly resemble lakes in Northeastern Ontario, suggesting that experimental acidification simulated the impacts of moderate levels of atmospheric pollution. Our findings demonstrate the importance of ecological history in understanding the responses by boreal lake ecosystems to environmental change.     

Spatiotemporal and long-term variation in phytoplankton communities in the oligotrophic Lake Pyhäjärvi on the Finnish-Russian border

As part of the joint Finnish-Russian research and development project “Assessment of the ecological state of the transboundary waters”, seasonal and spatial variations in the phytoplankton communities of Lake Pyhäjärvi were studied in order to identify possible long-term (1963–2002) changes and to present recent data (since 2002) on phytoplankton biomass and species composition. Some changes in both phytoplankton biomass and species composition, particularly in the littoral zone and northern basins of the lake, were obvious at the end of the 1980s; in particular, the density of blue-greens increased during that period. Biomasses increased five-fold in 1980, decreased after 1990 and have remained low (0.14 mg l^?l) to the present time. The effective water protection measures applied, especially reducing the phosphorus load from municipal wastewaters and airborne pollution, can now be seen to have improved the water quality. Although no significant temporal differences were found in phytoplankton biomass during the intensive biweekly sampling in 2002, considerable spatial variation was seen within the lake. An obvious change in the species composition of phytoplankton and an increase in biomass were seen even in the loaded parts of the lake. Despite the spatial differences in phytoplankton biomass and community structure, the changed species composition in the northern part of the lake indicated a clear recovery from the blue-green and Chrysophyceae dominated high biomass of the 1980s.     

COMBINATION OF FLOW CYTOMETRY AND SINGLE CELL ABSORPTION SPECTROSCOPY TO STUDY THE PHYTOPLANKTON STRUCTURE AND TO CALCULATE THE CHL A SPECIFIC ABSORPTION COEFFICIENTS AT THE TAXON LEVEL1

The phytoplankton community structure of a hypertrophic lake was quantitatively determined with the aid of flow cytometry. The flow cytometry signals were calibrated to obtain cell‐specific information, such as the chl a content and the biovolume per cell. The reliability of this method was tested with laboratory cultures. The results of the phytoplankton structure in a hypertrophic lake with respect to chl distribution in the different algal groups obtained by flow cytometry were compared with the results from HPLC pigment fingerprinting. Both methods yield the percentage contribution of the different algal groups to total chl a. The chl a specific absorption coefficient of the phytoplankton (a^*_Phy) was determined via visible (VIS) spectroscopy of samples taken from a hypertrophic lake (Auensee) in 2003. The results indicated that a^*_Phy of the total cell suspension is dependent on the phytoplankton structure as well as on environmental factors. The linear relationship between a^*_Phy at 675 nm and the product of the chl a content per cell and the biovolume offered the possibility to normalize phytoplankton absorption spectra to acquire the taxon‐specific a^*_Phy. The estimated a^*_Phy (675 nm) values were used to normalize single cell absorption spectra at this wavelength to obtain the a^*_Phy between 400 and 750 nm for representatives of the major algal groups. Our measurements show that the absorption coefficient for the whole phytoplankton community varies within the season. Finally, we used the a^*_Phy and the chl a distribution to calculate the light absorption of each algal group in the hypertrophic lake.     

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.     

Field estimates of zooplankton community grazing in the limed Lago d'Orta (Italy) by the use of a radioisotope-free technique

Grazing experiments were carried out in a limed lake (Lago d'Orta) during the periods, 23–24 March and 28–29 June 1990. A simple in situ technique based on cell counts before and after incubation was used in order to evaluate the impact of the natural zooplankton community on the lake phytoplankton. An estimation of the daily consumption by the natural zooplankton community showed that about 4.6% and 1.04% of the standing algal biomass was removed during March and June respectively. The differences in grazing activities were likely due to the difference in zooplankton community structure and to the surrounding environmental conditions, mainly influenced by the liming intervention, started in the lake water since 1989.     

The structure and dynamics of the phytoplankton assemblages in Lake Kinneret, Israel

The phytoplankton of Lake Kinneret, a warm monomictic lake,is dominated by a Pyrrhophyta-Chlorophyta assemblage. Four stagesof succession of planktonic algae occur in the lake, startingwith thermal and chemical destratification and ending with stratification. The index of diversity of the phytoplankton communities is highduring the destratification and mixed periods. The index reachesminimal values during late summer, when the ecosystem is subjectto strong physical, chemical and biological stresses. The diversityin Lake Kinneret increases with the increase in nutrients andnot with the increase in temperature. During most of the year, the nanoplanktonic forms are in greaternumbers than the netplankton species. This fact is correlatedwith the amounts of available nutrients in the lake. The annual averages of the wet autotrophic biomass in Lake Kinneretare very high in comparison with other warm lakes. The contributionof the nanoplanktonic species to the total algal biomass isvery small during the Peridinium bloom, but represents approximatelyhalf of the total algal biomass during the rest of the year. The concentration of nutrients in the water, together with theadverse competitive effect of Peridinium on other algae, areto a large extent responsible for the composition, successionand abundance of the phytoplankton assemblages in Lake Kinneret.     

COMPARISON OF IN SITU PHOTOSYNTHETIC ACTIVITY OF EPIPHYTIC,EPIPELIC AND PLANKTONIC ALGAL COMMUNITIES IN AN OLIGOTROPHIC LAKE,SOUTHERN FINLAND1

The photosynthetic activity of different algal communities at the outer edge of an Equisetum fluviatile L. stand in an oligotrophic lake (Pääjärvi, in southern Finland) was investigated. Production by the algal communities was measured simultaneously using a modified ¹⁴C-method, and the results were related to the volume of algae and the available irradiance. The relative production rate (P/B quotient) of phytoplankton was ca. 3 × that of epiphyton and ca. 20 × that of epipelon. Epiphyton productivity remained almost constant although the algal volume varied greatly, suggesting that the surface layer of the algal community was mainly responsible for the photosynthetic activity. In the littoral area (at 1 m depth) primary production/m² of lake surface by phytoplankton, epiphyton and epipelon was similar but in the littoriprofundal area (2–4 m) phytoplankton production was twice that of epipelon. Primary productivity of epiphyton and epipelon/m² of substratum was about equal to phytoplankton productivity/m³ of water at the same irradiance. This relation provided a means of estimating the relative contributions of the different algal communities to the total algal production in the lake.     

Resistance to drought affects persistence of alternative regimes in shallow lakes of the Boreal Plains (Alberta,Canada)

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Planktonic food chains of a highly humic lake

The development and metabolism of the plankton of a highly humic lake were followed over the vernal primary production maximum. The study was made in a mesocosm in which large filter feeders, typical of this lake in summer, were absent. During the rising phase of phytoplankton, the community was predominantly autotrophic. The most important constituents in the algal biomass were a dinoflagellate, Gymnodinium sp. (40–50%), and a prasinophycean, Scourfieldia cordiformis (7%). The biomasses of Chlamydomonas spp. and Chrysococcus spp. reached their maxima a few days later and Cryptomonas sp. became most abundant at the end of the experiment. After the phytoplankton maximum, about one week from the beginning ofthe experiment, grazing of algae by phagotrophic protozoans and phosphate depletion led to a rapid decrease of algal biomass and the community became predominantly heterotrophic. In spite of a large variation in algal biomass and primary production, the biomass of bacteria remained of the same order of magnitude as in algae both before and after the algal maximum. Bacteria were mostly responsible for the plankton respiration, which also showed no dependence on primary production. Since exudation by phytoplankton was also low, the nutrition of bacterioplankton was probably mainly based on allochthonous dissolved organic matter rather than or primary production. Thus the production of bacteria was an additional food source for higher trophic levels along with phytoplankton. Because filter feeding zooplankton was absent in the experiment, protozoans were the only grazers utilizing algae and bacteria. Essentially all growth of bacteria was used by bacterivores.     

Disturbance events affecting phytoplankton biomass,composition and species diversity in a shallow,eutrophic, temperate lake

The seasonal changes in phytoplankton biomass and species diversity in a shallow, eutrophic Danish lake are described and related to different disturbance events acting on the phytoplankton community.Both the spring diatom maximum and the summer bloom of the filamentous blue-green alga, Aphanizomenon flos-aquae (L.) Ralfs, coincided with low values of phytoplankton species diversity and equitability. Diatom collapse was mainly due to internal modifications as nutrient depletion (Si, P) caused by rapid growth of phytoplankton, and increased grazing activity from zooplankton. A large population of Daphnia longispina O.F. Müller in June effectively removed smaller algal competitors, thus favouring the development of a huge summer bloom (140 mm³ l^–1) of Aphanizomenon flos-aquae. Heavy rainfall and storms in late July increased the loss of Apahnizomenon by out-flow and disturbed the stratification of the lake. These events caused a marked decline in phytoplankton biomass but had no effect on species diversity. A second storm period in late August circulated the lake completely and was followed by a rapid increase in phytoplankton diversity, and a change in the phytoplankton community structure from dominance of large, slow-growing K-selected species (Aphanizomenon) to small, fast-growing r-selected species (cryptomonads).