The relationship between phytoplankton composition and physical–chemical variables: a comparison of taxonomic and morphological–functional descriptors in six temperate lakes

1. The relationship between phytoplankton composition and physical–chemical variables was studied in six temperate lakes, characterizing the phytoplankton taxonomically or by a rarely used morphological–functional approach (m/f approach) developed by Reynolds (1997) . This approach divides phytoplankton into three groups (C-, S- and R-strategists) by morphological characters thought to be related to light and nutrient acquisition. 2. The lakes ranged from oligotrophic to moderately eutrophic and exhibited both polymictic and dimictic patterns of mixing. Across the trophic gradient total phytoplankton biomass ranged from 0.3 to 4.8 mg (wet weight) L^–1 and total phosphorus (TP) from 0.19 to 1.07 μm . 3. The taxonomic groups predominantly represented were cyanobacteria, diatoms, dinoflagellates, chrysophytes and chlorophytes. The m/f group that was dominant (> 50% of total biomass) in five of the six lakes was composed of S-strategists. In four of the six lakes the second most abundant group comprised R-strategists. In only one lake was biomass dominated by C-strategists. 4. Within-lake seasonal variations in taxonomic and m/f groups were not predicted well from physical or chemical variables. This lack of predictability is probably caused, in part, by the problem of rapid seasonal variation in environmental conditions as compared to the replacement time of phytoplankton. Considering the data as a whole, however, several physical and chemical variables were significantly related to taxonomic and m/f groups. Some correlations agreed with expectations from the literature and some did not. 5. For taxonomic groups, as expected, cyanobacteria were positively associated with temperature, pH and TP and negatively with light and NO₃ : TP ratios. Chrysophytes were negatively related to temperature, pH, soluble reactive phosphorus and TP. No other division showed a substantial correspondence to literature expectations. 6. For m/f groups: R-strategists were correlated with high dissolved nutrients (both N and P) and low light; S-strategists were correlated with low dissolved N. C-strategists were generally in low abundance in the study lakes, as might be expected from the generally low nutrients in the six lakes. Opposite to expectations, however, their abundance in the study lakes was negatively correlated to dissolved P. 7. Despite a lack of complete predictive ability, the m/f approach performed better than the taxonomic approach. This suggests that size and shape of phytoplankton may predict their response to physical and chemical conditions better than taxonomy at the division level.     

Steady state phytoplankton assemblages during thermal stratification in deep alpine lakes. Do they occur?

Phytoplankton seasonal and long-term succession can be described and functionally classified by associations similar as in terrestrial vegetation studies. Such a concept has to include 'climax' into pelagic succession which in turn leads to the question to what extent steady state assemblages occur and if during periods of dynamic equilibrium can be identified. Here we explore the situation with respect to the above question for deep, nutrient poor, alpine lakes in Austria. We first track the long-term development of phytoplankton biomass, their taxonomic structure and their relation to total phosphorus and chlorophyll-a as predictors of trophic state over the past 35 years. We then analyse this data set for coherent algal associations which can be ascribed to trait separated functional groups according to Reynolds et al. (2002). A three year period of stable environmental conditions has then be extracted from the progression of trophic state indices, having similar dominating species each year. These years were finally analysed for steady state conditions according to definitions given in Sommer et al. (1993). During thermal stratification, achievement of an equilibrium could be ruled out although coexistence of several dominating species lasted for several weeks. Habitat templates were constructed from environmental variables prior to biomass peaks for two species important in summer assemblages, the dinoflagellate Ceratium hirundinella and the diatom Fragilaria crotonensis. In summary, functional groups proved to be a valid and useful concept to describe species succession of phytoplankton in deep alpine lakes while pelagic climax is much less clear and steady state conditions were never met.     

Coupling dissolved organic carbon,CO2 and productivity in boreal lakes

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Higher temperatures enhance the effects of invasive sportfish on mountain zooplankton communities

1. Decades of introductions of exotic sportfish to mountain lakes around the world have impoverished them biologically, and this may be exacerbated by global warming. We assessed the current status of invasive salmonids and native zooplankton communities in 34 naturally fishless lakes along an elevational gradient, which served as an environmental proxy for the expected effects of climate change. 2. Our main goal was to explore how climate‐related variables influence the effects of stocked salmonids on the total biomass, species richness and taxonomic composition of zooplankton. We predicted that warmer conditions would dampen the negative predatory effects of exotic brook trout (Salvelinus fontinalis) on zooplankton communities because more temperate lakes contain a greater diversity of potentially tolerant species. 3. Instead, we discovered that the persistence of stocked brook trout in the warmer lakes significantly amplified total zooplankton biomass and species richness. In colder and deeper lakes, zooplankton were relatively unaffected by S. fontinalis, which however persisted better in alpine lakes than at lower elevations after stocking practices were halted over two decades ago. Warmer lake conditions and higher concentrations of dissolved organic carbon (DOC) were significant primary drivers of zooplankton species turnover, both favouring greater species diversity. 4. Our findings of an ecological surprise involving potential synergistic positive effects of climate warming and exotic trout on native zooplankton communities presents a conundrum for managers of certain national mountain parks. Present mandates to eradicate non‐native trout and return the mountain lakes to their naturally fishless state may conflict with efforts to conserve biodiversity under a rapidly changing climate.     

Structure, biomass, production and depth distribution of periphyton on artificial substratum in shallow lakes with contrasting nutrient concentrations

1. To examine how the vertical distribution of periphytic biomass and primary production in the upper 0–1 m of the water column changes along an inter‐lake eutrophication gradient, artificial substrata (plastic strips) were introduced into the littoral zones of 13 lakes covering a total phosphorus (TP) summer mean range from 11 to 536 μg L^?1. Periphyton was measured in July (after 8 weeks) and September (after 15 weeks) at three water depths (0.1, 0.5 and 0.9 m). 2. Periphyton chlorophyll a concentration and dry weight generally increased with time and the communities became more heterotrophic. Mean periphytic biomass was unimodally related to TP, reaching a peak between 60 and 200 μg L^?1. 3. The proportion of diatoms in the periphyton decreased from July to September. A taxonomic shift occurred from dominance (by biovolume) of diatoms and cyanobacteria at low TP to dominance of chlorophytes at intermediate TP and of diatoms (Epithemia sp.) in the two most TP‐rich lakes. 4. The grazer community in most lakes was dominated by chironomid larvae and the total biomass of grazers increased with periphyton biomass. 5. Community respiration (R), maximum light‐saturated photosynthetic rate (P_max), primary production and the biomass of macrograzers associated with periphyton were more closely related to periphyton biomass than to TP. Biomass‐specific rates of R, P_max and production declined with increasing biomass. 6. Mean net periphyton production (24 h) was positive in most lakes in July and negative in all lakes in September. Net production was not related to the TP gradient in July, but decreased in September with increasing TP. 7. The results indicate that nutrient concentrations alone are poor predictors of the standing biomass and production of periphyton in shallow lakes. However, because periphyton biomass reaches a peak in the range of phosphorus concentration in which alternative states occur in shallow lakes, recolonisation by submerged macrophytes after nutrient reduction may potentially be suppressed by periphyton growth.     

Warmer climates boost cyanobacterial dominance in shallow lakes

Dominance by cyanobacteria hampers human use of lakes and reservoirs worldwide. Previous studies indicate that excessive nutrient loading and warmer conditions promote dominance by cyanobacteria, but evidence from global scale field data has so far been scarce. Our analysis, based on a study of 143 lakes along a latitudinal transect ranging from subarctic Europe to southern South America, shows that although warmer climates do not result in higher overall phytoplankton biomass, the percentage of the total phytoplankton biovolume attributable to cyanobacteria increases steeply with temperature. Our results also reveal that the percent cyanobacteria is greater in lakes with high rates of light absorption. This points to a positive feedback because restriction of light availability is often a consequence of high phytoplankton biovolume, which in turn may be driven by nutrient loading. Our results indicate a synergistic effect of nutrients and climate. The implications are that in a future warmer climate, nutrient concentrations may have to be reduced substantially from present values in many lakes if cyanobacterial dominance is to be controlled.     

Effects of drought and pluvial periods on fish and zooplankton communities in prairie lakes: systematic and asystematic responses

The anticipated impacts of climate change on aquatic biota are difficult to evaluate because of potentially contrasting effects of temperature and hydrology on lake ecosystems, particularly those closed‐basin lakes within semiarid regions. To address this shortfall, we quantified decade‐scale changes in chemical and biological properties of 20 endorheic lakes in central North America in response to a pronounced transition from a drought to a pluvial period during the early 21st century. Lakes exhibited marked temporal changes in chemical characteristics and formed two discrete clusters corresponding to periods of substantially different effective moisture (as Palmer Drought Severity Index, PDSI). Discriminant function analysis (DFA) explained 90% of variability in fish assemblage composition and showed that fish communities were predicted best by environmental conditions during the arid interval (PDSI 相似文献   

Distribution of planktonic ciliates in highly coloured subtropical lakes: comparison with clearwater ciliate communities and the contribution of myxotrophic taxa to total autotrophic biomass

SUMMARY 1. The planktonic ciliate communities of eleven organically coloured north and central Florida lakes representing a variety of trophic conditions were examined during 1979–80. The total abundance and biomass of ciliates were not significantly different from comparable clearwater lakes and only minor taxonomic replacements were noted at the order level.
2. Timing of population peaks of oligotrophic lakes was dissimilar to clearwater lakes of the same trophic state, but seasonality in meso-trophic and eutrophic lakes resembled patterns described for comparable clearwater lakes.
3. Various ciliate components were strongly correlated with chlorophyll a concentrations, but only moderately correlated to dominant phytoplankton groups. No significant correlations were found between ciliate components and bacterial abundance.
4. Myxotrophic taxa numerically dominated oligotrophic systems, particularly during midsummer, and accounted for a large percentage of the total ciliate biomass. Estimates of the ciliate contribution to total autotrophic biomass indicate that these zoochlorellae-bearing protozoa may account for much of the autotrophic biomass during midsummer periods in coloured lakes, and thus may lead to an overestimation of phytoplankton standing crops available to zooplankton grazers if chlorophyll a is used as a surrogate measure of algal biomass.     

Resource Ratios and Phytoplankton Species Composition in a Strongly Stratified Lake

The epilimnetic phytoplankton and its relations to nutrient content in Lake Verevi through the whole vegetation period in 2000 were studied. Lake Verevi (surface 12.6 ha, mean depth 3.6 m, maximum depth 11 m) is a hypertrophic hard-water lake, where the so-called spring meromixis occurs due to an extremely warm spring. Most dissolved nutrients in the epilimnion were low already in spring, and their concentrations were quite stable during the study period. The concentration of total silicon was very low in spring but increased rapidly in summer. Total phosphorus followed the pattern for stratified eutrophic lakes, and total nitrogen was quite high. The stoichiometric N:P ratio fluctuated between 25 and 81. The dynamics of phytoplankton biomass with a spring peak from April to May and a late summer peak from July to August is typical of Estonian eutrophic lakes. Green algae and chrysophytes occurred in the phytoplankton throughout the vegetation period. The spring peak was dominated by diatoms (Synedra ulna and Synedra acus var. angustissima) and the summer peak was caused by Aphanizomenon klebahnii and Ceratium hirundinella. The study showed that in physically stratified systems, the total concentration of limiting resources and plain physical factors (light and temperature) may be more important in the determination of phytoplankton dominants than different resource ratios. A combination of light and temperature optimum, along with nutrient utilization and transport capacity, effectively segregates phytoplankton species and can be used for the explanation of seasonal succession pattern.     

Composition,dynamics and production of Rotatoria in the plankton of some lakes of the Danube Delta

The Rosu, Puiu and Porcu lakes from the Danube Delta are lacustrine ecosystems characterized by a particularly great variation of the biotic and abiotic factors. This variation causes the development of a zooplankton reduced from the point of view of number and biomass, but rich from the taxonomic point of view. Its monthly and annual fluctuations can hardly be correlated to the rest of the plankton fauna and microflora. Rotifer production is low, turnover at the level of plankton rotifers being relatively uniform and dependent on water temperature.     

Long‐term effects of climate change on carbon flows through benthic secondary production in small lakes

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Inorganic carbon promotes photosynthesis,growth, and maximum biomass of phytoplankton in eutrophic water bodies

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Periphyton-macroinvertebrate interactions in light and fish manipulated enclosures in a clear and a turbid shallow lake

In a clear and a turbid freshwater lake the biomasses of phytoplankton, periphytic algae and periphytonassociated macrograzers were followed in enclosures with and without fish (Rutilus rutilus) and four light levels (100%, 55%, 7% and < 1% of incoming light), respectively. Fish and light affected the biomass of primary producers and the benthic grazers in both lakes. The biomass of primary producers was generally higher in the turbid than the clear lake, and in both lakes fish positively affected the biomass, while shading reduced it. Total biomass of benthic grazing invertebrates was higher in the clear than in the turbid lake and the lakes were dominated by snails and chironomids + ostracods, respectively. While light had no effect on the biomass of grazers in the clear lake, snail breeding was delayed in the most shaded enclosures and presence of fish reduced the number of snails and the total biomass of grazers. In the turbid lake ostracod abundance was not influenced by light, but was higher in fish-free enclosures. Density of chironomids correlated positively with periphyton biomass in summer, while fish had no effect. Generally, light-mediated regulation of primary producers was stronger in the turbid than in the clear lake, but the regulation did not nambiguously influence the primary consumers. However, regulation by fish of the benthic grazer community was stronger in the clear than in the turbid lake, and in both lakes strong top-down effects on periphyton were seen. The results indicate that if present-day climate in Denmark in the future is found in coastal areas at higher latitudes, the effect of lower light during winter in such areas will be highest in clear lakes, with typically lower fish biomass and higher invertebrate grazer density.     

Winter ecology of shallow lakes: strongest effect of fish on water clarity at high nutrient levels

While the structuring role of fish in lakes is well studied for the summer season in North temperate lakes, little is known about their role in winter when fish activity and light irradiance potentially are lower. This is unfortunate as the progressing climate change may have strong effects on lake winter temperature and possibly on trophic dynamics too. We conducted an enclosure experiment with and without the presence of fish throughout winter in two shallow lakes with contrasting phosphorus concentrations. In hypertrophic Lake Søbygård, absence of fish led to higher biomass of zooplankton, higher grazing potential (zooplankton:phytoplankton ratio) and, accordingly, lower biomass of phytoplankton and chlorophyll a (Chl a), while the concentrations of total nitrogen (TN), total phosphorus (TP), oxygen and pH decreased. The average size of egg-bearing Daphnia and Bosmina and the minimum size of egg-bearing specimens of the two genera rose. In the less eutrophic Lake Stigsholm, zooplankton and their grazing potential were also markedly affected by fish. However, the decrease in Chl a was slight, and phytoplankton biovolume, pH and the oxygen concentration were not affected. TN was higher when fish were absent. Our results indicate that: (i) there is a notable effect of fish on zooplankton community structure and size during winter in both eutrophic and hypertrophic North temperate lakes, (ii) Chl a can be high in winter in such lakes, despite low light irradiance, if fish are abundant, and (iii) the cascading effects on phytoplankton and nutrients in winter may be more pronounced in hypertrophic lakes. Climate warming supposedly leading to reduced winter mortality and dominance of small fish may enhance the risk of turbid state conditions in nutrient-enriched shallow lakes, not only during the summer season, but also during winter.     

Littoral benthic macroinvertebrates of alpine lakes (Tatra Mts) along an altitudinal gradient: a basis for climate change assessment

Littoral benthic macroinvertebrates were studied in three alpine lakes in the High Tatra Mountains (Slovakia) located at different elevations: 2157, 1940 (alpine zone) and 1725 m (sub-alpine zone). The study sites were selected in order to obtain a gradient in thermal regimes and particular organic matter (POM). Differences in the faunal composition of lakes were tested for the ability of these differences to indicate climatic changes, and species/taxa were identified that could be used for the purposes of monitoring and climate change assessment. Macroinvertebrates were sampled quantitatively during the ice-free seasons of 2000 and 2001, and lake surface water temperature (LSWT) and POM were measured. LSWT and POM were negatively correlated with elevation, whereas ice cover was positively correlated with elevation. A total of 60 oligostenothermic macroinvertebrate species/taxa were collected belonging to ten higher taxonomic groups. Statistical analysis showed trends in several biotic metrics with altitude. More specifically, there was a clear increase in the number of species/taxa, genera, and higher taxonomic groups, as well as an increase in the Shannon–Wiener diversity with decreasing altitude. On the contrary, evenness and density of benthic macroinvertebrates did not show any clear relationship with altitude. Gatherers of detrital particles dominated the assemblages’ trophic structures, but no distinct changes in the proportion of functional feeding groups along the altitudinal gradient were found. While the non-insect fauna of the lakes was rather uniform across the elevational gradient, the insect fauna composition was highly correlated with altitude, as confirmed by Detrended Correspondence Analysis. Aquatic insects, in particular chironomids and caddisflies, can therefore be used as good indicators of temperature changes. Our results suggest that under warmer conditions, non-insect benthic macroinvertebrates will remain more or less stable, while aquatic insects will undergo an increase in the number of thermophilic species typical for lower altitudes. These colonizers will increase the diversity of alpine lakes, while the extinction of cold stenothermal species will lead to impoverishment of the native fauna. An indirect impact on benthic macroinvertebrates through changes in food sources is likely, and changes in trophic structure of the littoral assemblages can be expected.     

淡水湖泊浮游藻类对富营养化和气候变暖的响应

水体富营养化和气候变暖是淡水生态系统面临的两大威胁。文章分别阐述了富营养化和气候变暖对淡水湖泊浮游藻类直接和间接效应, 并总结气候变暖可能通过影响水体理化性质、水生植物组成、食物链结构从而直接或间接改变浮游藻类生物量或群落结构。作者重点分析了气候变暖下湖泊生态系统蓝藻水华暴发机制, 比较了不同湖泊蓝藻对气候变暖和富营养化响应的异同点, 发现气候变暖和富营养化对湖泊生态系统影响存在相似性, 表现在均促进湖泊由清水-浊水稳态转变、增加蓝藻水华发生频率和强度。然而二者对湖泊浮游藻类影响的相对重要性取决于分层型湖泊和混合型湖泊的差异性、不同营养型湖泊和不同类群蓝藻组成差异性。作者认为, 开展气候变暖和富营养化下, 湖泊浮游藻类功能群响应研究亟待进行。     

Relations between production and biomass of phytoplankton in four Swedish lakes of different trophic status and humic content

Production and biomass values from phytoplankton populations in four different Swedish lakes were analysed. The production in all lakes was directly proportional to biomass during homothermal periods. When the lakes were stratified there was a strong negative relation between specific growth rate and biomass. The data fitted to a logistic density dependent growth equation of the form: dB/ dt = µ_mB(1-B · K^–1) where B is the biomass, µ_m the maximum specific growth rate and K the carrying capacity. The equation was used to derive the parameters µ · µ_m ^–1 and carrying capacity (the maximum possible biomass). These parameters were then discussed in relation to light climate, phosphorus concentration and humic content.     

Shifts in fish communities along the productivity gradient of temperate lakes—patterns and the importance of size-structured interactions

Species biomass and size composition of fish faunas along a productivity gradient were studied in south Swedish lakes. Generally, with increasing productivity (measured as chlorophyll content), Salmoniformes were replaced by percids, which in turn were replaced by cyprinids, as suggested in previous studies. However, percids showed two peaks in biomass, one in medium productive lakes due to perch and one in highly productive lakes due to zander. Benthic piscivores were present in all lakes, whereas pelagic piscivores were absent in the least productive lakes. The proportion of piscivores in the total fish biomass showed a peak in medium productive lakes, largely reflecting the importance of piscivorous perch. The median size of the dominant cyprinids (roach) in the systems studied increased as the importance of piscivores increased, which was interpreted as a size refuge response to increased predation pressure. The same pattern was present for the dominant planktivore, vendace, in low productive systems. Although a predictable pattern of change in the fish fauna was found along the productivity gradient, other environmental factors such as structural complexity may be the ultimate cause of the observed succession pattern.     

Analysis of environmental drivers influencing interspecific variations and associations among bloom-forming cyanobacteria in large,shallow eutrophic lakes

Non-diazotrophic Microcystis and filamentous N₂-fixing Aphanizomenon and Dolichospermum (formerly Anabaena) co-occur or successively dominate freshwaters globally. Previous studies indicate that dual nitrogen (N) and phosphorus (P) reduction is needed to control cyanobacterial blooms; however, N limitation may cause replacement of non-N₂-fixing by N₂-fixing taxa. To evaluate potentially counterproductive scenarios, the effects of temperature, nutrients, and zooplankton on the spatio-temporal variations of cyanobacteria were investigated in three large, shallow eutrophic lakes in China. The results illustrate that the community composition of cyanobacteria is primarily driven by physical factors and the zooplankton community, and their interactions. Niche differentiation between Microcystis and two N₂-fixing taxa in Lake Taihu and Lake Chaohu was observed, whereas small temperature fluctuations in Lake Dianchi supported co-dominance. Through structural equation modelling, predictor variables were aggregated into ‘composites’ representing their combined effects on species-specific biomass. The model results showed that Microcystis biomass was affected by water temperature and P concentrations across the studied lakes. The biomass of two filamentous taxa, by contrast, exhibited lake-specific responses. Understanding of driving forces of the succession and competition among bloom-forming cyanobacteria will help to guide lake restoration in the context of climate warming and N:P stoichiometry imbalances.