Macrozooplankton and the persistence of the deep chlorophyll maximum in a stratified lake

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Light and nutrient control phytoplankton biomass responses to global change in northern lakes

Global change affects terrestrial loadings of colored dissolved organic carbon (DOC) and nutrients to northern lakes. Still, little is known about how phytoplankton respond to changes in light and nutrient availability across gradients in lake DOC. In this study, we used results from whole‐lake studies in northern Sweden to show that annual mean phytoplankton biomass expressed unimodal curved relationships across lake DOC gradients, peaking at threshold DOC levels of around 11 mg/L. Whole‐lake single nutrient enrichment in selected lakes caused elevated biomass, with most pronounced effect at the threshold DOC level. These patterns give support to the suggested dual control by DOC on phytoplankton via nutrient (positively) and light (negatively) availability and imply that the lakes' location along the DOC axis is critical in determining to what extent phytoplankton respond to changes in DOC and/or nutrient loadings. By using data from the large Swedish Lake Monitoring Survey, we further estimated that 80% of northern Swedish lakes are below the DOC threshold, potentially experiencing increased phytoplankton biomass with browning alone, and/or combined with nutrient enrichment. The results support the previous model results on effects of browning and eutrophication on lake phytoplankton, and provide important understanding of how northern lakes may respond to future global changes.     

Effects of sediment resuspension on phytoplankton production: teasing apart the influences of light, nutrients and algal entrainment

1. Wind‐induced sediment resuspension can affect planktonic primary productivity by influencing light penetration and nutrient availability, and by contributing meroplankton (algae resuspended from the lake bed) to the water column. We established relationships between sediment resuspension, light and nutrient availability to phytoplankton in a shallow lake on four occasions. 2. The effects of additions of surficial sediments and nutrients on the productivity of phytoplankton communities were measured in 300 mL gas‐tight bottles attached to rotating plankton wheels and exposed to a light gradient, in 24 h incubations at in situ temperatures. 3. While sediment resuspension always increased primary productivity, resuspension released phytoplankton from nutrient limitation in only two of the four experiments because the amount of available nitrogen and phosphorus entrained from the sediments was small compared with typical baseline levels in the water column. In contrast, chlorophyll a entrainment was substantial compared with baseline water column concentrations and the contribution of meroplankton to primary production was important at times, especially when seasonal irradiance in the lake was high. 4. Comparison of the in situ light climate with the threshold of light‐limitation of the phytoplankton indicated that phytoplankton in the lake were only likely to be light‐limited at times of extreme turbidity (e.g. >200 nephelometric turbidity units), particularly when these occur in winter. Therefore, resuspension influenced phytoplankton production mainly via effects on available nutrients and by entraining algae. The importance of each of these varied in time. 5. The partitioning of primary productivity between the water column and sediments in shallow lakes greatly influences the outcome of resuspension events for water column primary productivity.     

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.     

河口浮游植物生态学研究进展

综述了河口浮游植物种类组成、时空分布、初级生态及其影响因素等方面的主要研究进展,同时,对河口浮游植物在水环境监测中的作用以及河口浮游植物多样性与边缘效应进行了初步探讨。研究表明,通常河口区重要的浮游植物有硅藻、甲藻等,微型、超微型浮游植物在河口生态系统中占有重要地位。河口浮游植物种类组成、初级生产的时空变化明显,并受到光、温度、营养盐、动物摄食以及径流等因素的影响。     

Spatial distribution of chlorophyll a and its relationship with the environment during summer in Lake Poyang: a Yangtze-connected lake

Lake Poyang, a Yangtze-connected lake that is the largest freshwater lake in China, was studied in summer from 2009 to 2012. The primary objective was to investigate the spatial variability of chlorophyll a (chl a) on a whole-lake scale and to identify the key factors affecting phytoplankton growth. Stepwise multiple linear regression and Spearman’s rank correlation analyses showed that the shade index is the major factor determining the spatial distribution of chl a; nutrients don’t explain much variation in chl a, except in the east. The relationships between shade index and chl a varied regionally. Chl a varied inversely with the variation of the shade index, especially in the north and south, reflecting light limitation. However, the correlation was positive in the east due to high chl a concentration negatively affecting light availability, which was promoted by sufficient nutrients. In the center, no factor was found to have an obvious effect on phytoplankton growth, most likely because of human activities and high heterogeneity. These new data on the spatial variability of chl a and its relationship with light availability in Lake Poyang will be crucial to understand chl a regulation and contribute to the knowledge regarding phytoplankton in the Yangtze Basin.     

Long-term dynamics of phytoplankton assemblages: Microcystis-domination in Lake Taihu, a large shallow lake in China

Long-term phytoplankton assemblages in a large shallow Chineselake, Lake Taihu, were presented using the monthly monitoringdata from October 1991 to December 1999. Earlier research results(1960, 1981 and 1988) were applied to discuss the differenttrophic stages of the lake. The species composition in the lakewas more closely related to eutrophication level than to lake-size,shallowness, or turbidity. Each summer, a single peak of phytoplanktonbiovolume appeared in Meiliang Bay. The results of principalcomponents analysis showed a distinct temporal shift in speciescomposition between summer and winter. A clear spatial differencein phytoplankton occurred between Meiliang Bay and the lakecentre. Wind speed and direction affected the horizontal distributionof phytoplankton, especially Microcystis, in the lake. Temperature,underwater light climate, nutrients and grazing by zooplanktonand by fish were discussed to explain the overwhelming dominanceof Microcystis. Four nutrient-phytoplankton stages were identifiedin the lake: an oligo-mesotrophic stage with low algal biomassuntil 1981, a eutrophic situation with blooms of Microcystisduring 1988–1995, hypertrophic conditions with the dominanceof Planctonema and total phosphorus up to 200 mg m^-3 from 1996to 1997 and the restoration period after 1997. The wax and waneof the phytoplankton assemblages were mainly controlled by temperature,wind and turbidity while long-term biomass dynamics were influencedby the level of nutrients.     

Phytoplankton growth and stoichiometric responses to warming,nutrient addition and grazing depend on lake productivity and cell size

Global change involves shifts in multiple environmental factors that act in concert to shape ecological systems in ways that depend on local biotic and abiotic conditions. Little is known about the effects of combined global change stressors on phytoplankton communities, and particularly how these are mediated by distinct community properties such as productivity, grazing pressure and size distribution. Here, we tested for the effects of warming and eutrophication on phytoplankton net growth rate and C:N:P stoichiometry in two phytoplankton cell size fractions (<30 µm and >30 µm) in the presence and absence of grazing in microcosm experiments. Because effects may also depend on lake productivity, we used phytoplankton communities from three Dutch lakes spanning a trophic gradient. We measured the response of each community to multifactorial combinations of temperature, nutrient, and grazing treatments and found that nutrients elevated net growth rates and reduced carbon:nutrient ratios of all three phytoplankton communities. Warming effects on growth and stoichiometry depended on nutrient supply and lake productivity, with enhanced growth in the most productive community dominated by cyanobacteria, and strongest stoichiometric responses in the most oligotrophic community at ambient nutrient levels. Grazing effects were also most evident in the most oligotrophic community, with reduced net growth rates and phytoplankton C:P stoichiometry that suggests consumer‐driven nutrient recycling. Our experiments indicate that stoichiometric responses to warming and interactions with nutrient addition and grazing are not universal but depend on lake productivity and cell size distribution.     

The vertical distribution of phytoplankton in stratified water columns

What determines the vertical distribution of phytoplankton in different aquatic environments remains an open question. To address this question, we develop a model to explore how phytoplankton respond through growth and movement to opposing resource gradients and different mixing conditions. We assume stratification creates a well-mixed surface layer on top of a poorly mixed deep layer and nutrients are supplied from multiple depth-dependent sources. Intraspecific competition leads to a unique strategic equilibrium for phytoplankton, which allows us to classify the distinct vertical distributions that can exist. Biomass can occur as a benthic layer (BL), a deep chlorophyll maximum (DCM), or in the mixed layer (ML), or as a combination of BL+ML or DCM+ML. The ML biomass can be limited by nutrients, light, or both. We predict how the vertical distribution, relative resource limitation, and biomass of phytoplankton will change across environmental gradients. We parameterized our model to represent potentially light and phosphorus limited freshwater lakes, but the model is applicable to a broad range of vertically stratified systems. Increasing nutrient input from the sediments or to the mixed layer increases light limitation, shifts phytoplankton towards the surface, and increases total biomass. Increasing background light attenuation increases light limitation, shifts the phytoplankton towards the surface, and generally decreases total biomass. Increasing mixed layer depth increases, decreases, or has no effect on light limitation and total biomass. Our model is able to replicate the diverse vertical distributions observed in nature and explain what underlying mechanisms drive these distributions.     

Occurrence of mixotrophic flagellates in relation to bacterioplankton production, light regime and availability of inorganic nutrients in unproductive lakes with differing humic contents

1. Field data from five unproductive Swedish lakes were used to investigate the occurrence of mixotrophic flagellates in relation to bacterioplankton, autotrophic phytoplankton, heterotrophic flagellates and abiotic environmental factors. Three different sources of data were used: (i) a 3‐year study (1995–97) of the humic Lake Örträsket, (ii) seasonal measurements from five lakes with widely varying dissolved organic carbon (DOC) concentrations, and (iii) whole lake enrichment experiments with inorganic nutrients and organic carbon. 2. Mixotrophic flagellates usually dominated over autotrophic phytoplankton in Lake Örträsket in early summer, when both bacterial production and light levels were high. Comparative data from the five lakes demonstrated that the ratio between the biomasses of mixotrophic flagellates and autotrophic phytoplankton (the M/A‐ratio) was positively correlated to bacterioplankton production, but not to the light regime. Whole lake carbon addition (white sugar) increased bacterial biomass, and production, reduced the biomass of autotrophs by a factor of 16, and increased the M/A‐ratio from 0.03 to 3.4. Collectively, the results indicate that the dominance of mixotrophs among phytoplankton was positively related to bacterioplankton production. 3. Whole lake fertilisation with nitrogen (N) and phosphorus (P) demonstrated that the obligate autotrophic phytoplankton was limited by N. N‐addition increased the biomass of the autotrophic phytoplankton but had no effect on mixotrophic flagellates or bacteria, and the M/A‐ratio decreased from 1.2 to 0.6 after N‐enrichment. Therefore, we suggest that bacteria under natural conditions, by utilising allochthonous DOC as an energy and carbon source, are able to outcompete autotrophs for available inorganic nutrients. Consequently, mixotrophic flagellates can become the dominant phytoplankters when phagotrophy permits them to use nutrients stored in bacterial biomass. 4. In Lake Örträsket, the biomass of mixotrophs was usually higher than the biomass of heterotrophs during the summer. This dominance could not be explained by higher grazing rates among the mixotrophs. Instead, ratios between mixotrophic and heterotrophic biomass (the M/H‐ratio) were positively related to light availability. Therefore, we suggest that photosynthesis can enable mixotrophic flagellates to outcompete heterotrophic flagellates.     

Weedbeds and big bugs: the importance of scale in detecting the influence of nutrients and predation on macroinvertebrates in plant‐dominated shallow lakes

1. The scale of investigations influences the interpretation of results. Here, we investigate the influence of fish and nutrients on biotic communities in shallow lakes, using studies at two different scales: (i) within‐lake experimental manipulation and (ii) comparative, among‐lake relationships. 2. At both scales, fish predation had an overriding influence on macroinvertebrates; fish reduced macroinvertebrate biomass and altered community composition. Prey selection appeared to be size based. Fish influenced zooplankton abundance and light penetration through the water column also, but there was no indication that fish caused increased resuspension of sediment. 3. There were effects of nutrients at both scales, but these effects differed with the scale of the investigation. Nutrients increased phytoplankton and periphyton at the within‐lake scale, and were associated with increased periphyton at the among‐lake scale. No significant effect of nutrients on macroinvertebrates was observed at the within‐lake scale. However, at the among‐lake scale, nutrients positively influenced the biomass and density of macroinvertebrates, and ameliorated the effect of fish on macroinvertebrates. 4. Increased prey availability at higher nutrient concentrations would be expected to cause changes in the fish community. However, at the among‐lake scale, differences were not apparent in fish biomass among lakes with different nutrient conditions, suggesting that stochastic events influence the fish community in these small and relatively isolated shallow lakes. 5. The intensity of predation by fish significantly influences macroinvertebrate community structure of shallow lakes, but nutrients also play a role. The scale of investigation influences the ability to detect the influence of nutrients on the different components of shallow lake communities, particularly for longer lived organisms such as macroinvertebrates, where the response takes longer to manifest.     

闽南-台湾浅滩近岸上升流区浮游植物碳同化速率的研究

本文采用~(14)C同位素示踪法,测定了浮游植物光合作用速率,结合浮游植物细胞含碳量,计算了不同季节、不同深度下浮游植物碳同化速率常数,讨论了不同环境条件对浮游植物碳同化速率常数的影响。结果表明,闽南-台湾浅滩近岸上升流的形成,是该海域高生产力的主要原因,上升流期间浮游植物复制时间要比非上升流期间浮游植物复制时间缩短1.8倍。同时还表明,温度,光照强度、营养盐是控制浮游植物生长的主要因子。上升流期间营养盐始终保持在较高的水平。是上升流区具有较大的浮游植物碳同化速率常数(3.3d~(-1))的原因之一。适宜该海域浮游植物生长的光照强度在3 000—15 000lx之间,温度的影响可用Goldman和Carpenter模式近似表示。     

Relationships between phytoplankton dynamics and the availability of light and nutrients in a shallow sub-tropical lake

The role of light and nutrient availability in controlling theabundance and structure of phytoplankton populations was studiedin Lake Okeechobee, a large eutrophic lake in south florida,USA. Measurement of selected environmental parameters at samplingsites within four ecologically distinct regions of the lakewere combined with direct experimental determinations of limitinglevels of light and nutrients for phytoplankton growth to determinespatial and temporal variations in the relative roles of theselimiting factors. Estimated mean light availability in the mixedlayer, I_m, was significantly lower in the turbid central regionof the lake than in other regions. Correlations between I_m andphytoplankton standing crops led to the conclusion that lowlight availability in the central region of the lake, and toa lesser extent in other areas, restricts phytoplankton standingcrops to levels below the potential provided by the nutrientsavailable. The results of the irradiance-growth experimentsconfirmed the conclusions of the correlation analyses that phytoplanktongrowth is restricted by the levels of light availability experiencedduring the winter and spring in the central region of the lake.Bioassays indicated that nitrogen was the most frequently limitingnutrient for phytoplankton growth. High rates of nitrogen fixationwere frequently observed in the lake, along with correspondinglyhigh abundances of nitrogen-fixing cyanobacteria and nitrogenfixation activity. Elevated concentrations of soluble inorganicnitrogen appeared to suppress both nitrogen fixation and therelative abundance of nitrogen-fixing cyanobacteria.     

Temperature modulated effects of nutrients on phytoplankton changes in a mountain lake

Piburger See, a dimictic mountain lake in Austria, experienced moderate cultural eutrophication in the 1950s. Lake restoration led to a re-oligotrophication in the 1990s with a decrease in seasonal phytoplankton biovolume until the late 1990s, but a reversed trend from the early 2000s onwards. We hypothesize that recent changes in phytoplankton biomass and functional structure are triggered by changes in lake nitrogen and silica concentrations, and we expect climate-related factors to modulate the trophic status of Piburger See. Phytoplankton data were analyzed by non-metric multidimensional scaling (NMDS) applied on biovolume of morpho-functional groups, combined with correlation analyses of environmental variables. Since the 2000s, short-term changes in phytoplankton of Piburger See were explained by varying concentrations and ratios of nitrogen and silica, while the inter-annual variability in phytoplankton species composition was rather attributed to superimposed rising water temperature and lake thermal stability. Our results underline the co-dominant role of phosphorus and nitrogen as phytoplankton drivers in lakes that experience periods of nitrogen limitation. The combined impact of nutrients and climate on phytoplankton development can thus mimic short-term increases in the trophic level of less productive lakes.     

The phytoplankton of Great Bitter Lake,Egypt, including the impacts of nutrient-laden and heated effluents

A year-long survey of the phytoplankton and nutrients in Great Bitter Lake indicates that this is a severely eutrophic lake. Chlorophyll levels were consistently high (>30μg/l), especially in summer (>90μg/l). The phytoplankton community comprised mostly diatoms and blue-green algae, although dinoflagellates and green algae were important at times. Local effects of effluent from a drain coming from the city of Ismailia were evident, although the effect of tourist hotels at Palma Beach was not detectable. The discharge of heated water from a thermal power plant raised the water temperature in the impacted area by 13°C in autumn and 22°C in summer and also caused decreases in chlorophyll and phytoplankton abundance. Dissolved nutrient levels were high and, especially at the offshore station, had a rather constant ratio of dissolved inorganic nitrogen to phosphate. The distribution of phytoplankton and chlorophyll were related more to temporal, presumably seasonal, variation than proximity to point sources of pollution.     

Role of atelomixis in replacement of phytoplankton assemblages in Dom Helvécio Lake, South-East Brazil

Scale and frequency of changes in a lake’s physical structure, light dynamics, and availability of nutrients are closely related to phytoplankton ecology. Since phytoplankton assemblages were first described, phytoplankton ecologists concluded that these assemblages provide insight into phytoplankton responses to environmental changes. Objectives of this study were to investigate ecology of phytoplankton during a complete hydrological cycle in the deepest natural lake in Brazil, Dom Helvécio, and to sort species into the list of assemblages, checking its accordance with environmental changes in a tropical system within the middle Rio Doce Lake district, South-East Brazil. Canonical Correspondence Analysis, t-test, Mann–Whitney U-test, and Kruskal–Wallis test were used to analyze climatological, environmental, and plankton data, which were obtained monthly in 2002. A new phytoplankton assemblage, N_A (atelomixis-dependent desmids), is suggested because atelomixis (robust movement of water occurring once a day) contributed to replacement of species in Dom Helvécio Lake. Stability of stratification, water chemistry, and composition of phytoplankton assemblages characterized two periods. The first period occurred in six rainy months (Jan–Mar and Oct–Dec) when the lake was stratified and phytoplankton was dominated by two assemblages: N_A and F. The second period occurred in six dry months (Apr–Sep) when the lake was nonstratified and phytoplankton was dominated by four assemblages: S2, X1, A, and L_O. Results suggest that phytoplankton in Dom Helvécio Lake was shaped by seasonal and daily changes of water temperature, even with its lower amplitude of variation within 2002 (El Niño year). These changes promoted water column stratification or mixing, reduced light, and increased nutrient availability. Temperature, therefore, is similarly important to phytoplankton ecology in tropical regions as it is in temperate ones. Sorting phytoplankton species into assemblages matched well with environmental changes and periods identified so it is also suggested that this can be further used as an appropriate tool to manage water quality when evaluating tropical lakes.     

Vertical partitioning of the phytoplankton assemblage in ultraoligotrophic Crater Lake, Oregon, U.S.A.

SUMMARY 1. The summertime phytoplankton assemblage in abysmally deep (Z_max: 589 m) Crater Lake, Oregon, consists of over 100 species, which are variously distributed in the upper 200 m of the vertical water column. The depth distribution of the lake's three most prevalent species follows a predictabk pattern: Nitzschia gracilis in the 0–20 m stratum, Tribonema sp. at mid–depth (80–20 m), and Stephanodiscus hantzschii in the lowermost stratum (160–200 m). These major species, which account for approximately 80% or more of the lake's total phytoplankton biomass and primary production, exist under atypical temperature, light, and nutrient conditions.
2. The spatial distribution of phytoplankton in Crater Lake resembles a three-tier structure. Unlike most lakes, where the entire phytoplankton communities exist in less disparate environmental conditions, or are vertically mixed periodically by storm events and seasonal lake turnover. the Crater Lake community is partitioned into stratified environments.
5. The disparate and unusual characteristics of these environments, and the hydrological and limnological stability of the lake basin, are perhaps important factors regulating the diversity, dominance. and partitioning of the lake's phytoplankton populations.     

Functional approach based on morphology as a model of phytoplankton variability in a subtropical floodplain lake: a long-term study

Long-term phytoplankton dynamics in a floodplain lake, between periods of limnophase and potamophase was studied using the morphology-based functional classification (MBFG). The work was carried out to test the hypothesis that the temporal distribution of MBFGs is influenced by the hydrosedimentological regime of the Paraná River, and that these differences can be registered by analyzing the dominant MBFGs in the two periods. Samples were taken in an isolated floodplain lake on the Upper Paraná River floodplain, Brazil, from 2000 to 2012, and water level, water temperature, conductivity, pH, dissolved-oxygen, euphotic zone, maximum depth, and nutrients were used to explain the distribution of MBFGs. 478 taxa were identified and distributed in seven MBFGs (I–VII). MBFG V (flagellates algae) and VI (diatoms) showed 100% frequency of occurrence. MBFG II was associated exclusively with the limnophase; MBFG IV and VII were associated with limnophase periods with higher pH and dissolved-oxygen content; and MBFG I, III, V, and VI were associated with limnophase and potamophase, mainly associated with transparency, nutrients, and conductivity. The MBFG approach represented the trends of each group in terms of its occurrence and biovolume, according to the hydrosedimentological regime, providing broad-scale information on changes in the phytoplankton.     

The influence of light and nutrient addition upon the sediment chemistry of iron in an arctic lake

The geochemical response of sediments to increased nutrient input to an Alaskan, arctic lake was examined using direct measurements of sediment-water chemical fluxes. An unexpected increase in Fe flux occurred when sediments were exposed to high incident radiation and nutrient concentrations. Correlation between light and acid-soluble Fe concentrations suggests that photoreduction of Fe(III) oxides may occur, but nutrient addition enhanced the effect indicating that primary productivity was also important. The processes controlling the flux of Fe from sediments in this lake were complex and included the redox potential (dissolved oxygen concentration) of the water, quality of organic matter present in the sediment, light, and nutrients supplied from the sediments and/or water column. These four factors together with the possibility of direct uptake of Fe by phytoplankton and the possible release of algal reductants may contribute to Fe cycling in this lake.     

Comparative limnology of a deep-discharge reservoir and a surface-discharge lake on the Madison River, Montana

SUMMARY. Phytoplankton standing crop, primary production, light penetration, temperature, and various chemical concentrations were measured in a man-made, deep-discharge, reservoir and in a natural, surface-discharge, lake in order to relate limnological conditions in the two bodies of water to their depth of outflow. The quantity and depth distribution of heat stored during the summer varied markedly. The reservoir functioned as a heat trap, whereas heat was readily dissipated from the lake. Salinity increased more in the lower layer of the lake. Throughout the summer, nutrient-rich water was discharged from the reservoir whereas nutrient-poor water was discharged from the lake. Phytoplankton standing crops were greater in the lake and were dominated by flagellates and diatoms. In the reservoir, blue-green algae were predominant. Rates of primary production and respiration were higher in the lake, but estimated algal turnover times were faster in the reservoir. It was concluded that depth of outflow has a direct and predictable effect on certain physical and chemical conditions within these two bodies of water; but effects of discharge depth on phytoplankton were secondary and thus difficult to ascertain.