泽雅水库混合深度的年内变化及其对藻类生消影响

就水库藻类水华的发生机制而言,近年来值得关注的研究动向是,一些研究者开始认识到光照和混合的交互作用可能对藻类水华生消过程起到了关键作用,即认为水体混合深度的变化直接影响着可获得光强,从而决定着藻类生物量的时空分布。在这些研究中,混合层深度的确定是探讨藻类生消过程影响的前提。然而已有的研究大都只进行粗略的估计。本文提出采取系统聚类分析的方法确定泽雅水库不同时期的混合深度。在具体分析过程中,将测得的某一天某一深度处的pH,DO,温度,电导率,氧化还原电位等5个参数结果看成一类,采用类间平均连接法,间隔尺度变量为欧氏距离的平方进行聚类。对采用系统聚类分析法和已有的"1°C"法计算得的全年的混合深度的变化趋势进行比较,认为系统聚类分析法可以更为准确地反应水体混合的实际情况。依据混合深度的不同特征,在年内水库水体可划分为热成层时期,全混时期和两者之间的过渡期,藻类生物量与混合深度呈负相关。在热成层期间,藻类生物量都超过了13mm³L^-1。而到了9月份,当混合层深度扩展到15m以上时,藻类生物量明显下降,此后水体处于全混时期,藻类生物量较低,在9-20mm³/L^-1波动。基于稳态假设的前提下,发现随着混合深度增加,稳态藻类生物量呈单峰变化,在混合深度2m处达到最大值,即在混合深度为0-2m之间时,藻类沉降作用是藻类生物量的主要影响因素,随着深度增加,沉降作用下降,因此藻类生物量增加;当混合深度超过2m之后,光限制作用占主导因素,藻类生物量随混合深度增加而下降。这一结果为 Diehl的假说提供了水库现场的实证。     

Pelagic zonation of water quality and phytoplankton in the Great Lakes

Analysis of aquatic ecosystem data collected from large water bodies must consider spatial variations. A suite of pelagic survey stations exists for the Laurentian Great Lakes, but little is known about their redundancy. We present a strategy to delineate the lakes into zones based on water quality and phytoplankton biovolume. Water samples were collected from 72 sites in two seasons (spring and summer) from 2007 to 2010 in all five lakes. Integrated samples were analyzed for phytoplankton biovolume and nine water quality parameters. We conducted cluster analysis, principal components analysis and non-metric multidimensional scaling methods for water quality and phytoplankton taxon-specific biovolume for the Great Lakes basin and for each lake separately. There were significant lake-to-lake differences, and based on lake-specific analyses, Lake Superior, Lake Michigan and Lake Erie were each divided into three zones; Lake Huron and Lake Ontario were each grouped into two zones. The zones identified by water quality and phytoplankton provide an understanding of spatial distributions for evaluating monitoring data.     

Classification and ordination of profundal macroinvertebrate communities in nutrient poor, oligo-mesohumic lakes in relation to environmental data

SUMMARY. 1. Profundal macroinvertebrates and water chemistry of sixty-eight nutrient poor, poorly buffered lakes were sampled in 1983 or 1986. Assemblages of profundal zoobenthos were classified using two-way indicator species analysis (TWINSPAN), ordinated by canonical correspondence analysis (CCA), and related to physico-chemical factors using CCA. discriminant analysis, and regression.
2. 90% of zoobenthos (TWINSPAN) groups were classified correctly using discriminant analysis. Depth (Function 1), soluble reactive Si(OH)₄ and HCO₃, -(2), and phytoplankton biovolume and pH (3) were the strongest correlates with the three discriminant functions.
3. Regression analysis showed that depth, KmnO₄, consumption, and phytoplankton biovolume were the best estimators of zoobenthos biomass in the profundal.
4. Multivariate analyses showed species assemblages amongst the profundal zoobenthos to be good indicators of lake type, particularly depth, pH, and phytoplankton biovolume.     

The relationship between phytoplankton biovolume and chlorophyll in a deep oligotrophic lake: decoupling in their spatial and temporal maxima

The seasonal distributions of phytoplankton biovolume and chlorophylla content were monitored for 14 months in a deep oligotrophic,high mountain lake (Redó, Pyrenees). An allometric relationshipof chlorophyll with biovolume was found throughout the periodstudied, with a correlation coefficient of 0.66. However, therelationship changed with season and the taxonomic compositionof the phytoplankton. Both parameters showed a similar seasonalpattern, but differences in space and time were observed. Thechlorophyll maximum was recorded deeper and later than thatof phytoplankton biovolume. While the biovolume maximum wasrelated to an improvement in conditions for growth (nutrientinput during column mixing periods), and reflected an increasein biomass, the chlorophyll maximum was related to changes incell pigment content, and to spatial or successional trendsin species dominance. Flagellated chrysophytes predominatedat the chlorophyll maxima. Chlorophyll content per unit of phytoplanktonbiovolume fluctuated greatly throughout the year, dependingon light intensity, temperature and phytoplankton composition.Of the main groups of phytoplankton in the lake, the dinoflagellates,which dominated the summer epilimnion phytoplankton community,recorded the lowest pigment content per biovolume (which isconsistent with their size). Higher chlorophyll contents perbiovolume were found in the deep hypolimnion and during thewinter cover period associated with small cells such as somespecies of chlorococcales chlorophytes. When flagellated chrysophyteswere predominant, a broad range of chlorophyll values per biovolumewas found and there was no significant correlation between thetwo biomass indices. These findings reaffirm the need to treatphytoplankton biomass estimates with caution, in particularwhen conducting primary production studies. While our resultsshow that changes in chlorophyll content per cell occur as aphotoacclimation response along a vertical profile, they alsopoint out a component of the successional trends which appearin a phytoplankton growth phase in a lake.     

Seasonal variation of mixing depth and its influence on phytoplankton dynamics in the Zeya reservoir, China

In reservoirs or lakes, mixing depth affects growth and loss rates of phytoplankton populations. Based on 1-year data from the Zeya reservoir, China, we scaled the mixing depth throughout a whole year by utilizing cluster analysis, and then investigated its influence on phytoplankton dynamics and other physical and chemical parameters. Over the whole year, all physical and chemical parameters except TN and temperature had significant correlations with mixing depth, indicating that mixing depth is one of the important driving factors influencing water environment. According to mixing depth, a year can be divided into three different periods, including the thermally stratified period, isothermally mixed period, and transition period between them. When considering the former two different periods separately, mixing depth had no correlation with the phytoplankton biovolume. However, over the whole year a significant correlation was observed, which indicated that the influence of mixing depth on phytoplankton growth in the Zeya reservoir still followed Diehl’s theory. Furthermore, according to the steady-state assumption, a unimodal curve (mixing depth—phytoplankton biovolume) with a significant peak appearing at a mixing depth of 2 m was observed, closely agreeing with Diehl’ prediction.     

Do phytoplankton communities correctly track trophic changes? An assessment using directly measured and palaeolimnological data

1. Measurements of total phosphorus (TP) concentrations since 1975 and a 50‐year time series of phytoplankton biovolume and species composition from Lake Mondsee (Austria) were combined with palaeolimnological information on diatom composition and reconstructed TP‐levels to describe the response of phytoplankton communities to changing nutrient conditions. 2. Four phases were identified in the long‐term record. Phase I was the pre‐eutrophication period characterised by TP‐levels of about 6 μg L^?1 and diatom dominance. Phase II began in 1966 with an increase in TP concentration followed by the invasion of Planktothrix rubescens in 1968, characterising mesotrophic conditions. Phase III, from 1976 to 1979, had the highest annual mean TP concentrations (up to 36 μg L^?1) and phytoplankton biovolumes (3.57 mm³ L^?1), although reductions in external nutrient loading started in 1974. Phases II and III saw an expansion of species characteristic of higher nutrient levels as reflected in the diatom stratigraphy. Oligotrophication (phase IV) began in 1980 when annual average TP concentration, Secchi depth and algal biovolume began to decline, accompanied by increasing concentrations of soluble reactive silica. 3. The period from 1981 to 1986 was characterised by asynchronous trends. Annual mean and maximum total phytoplankton biovolume initially continued to increase after TP concentration began to decline. Reductions in phytoplankton biovolume were delayed by about 5 years. Several phytoplankton species differed in the timing of their responses to changing nutrient conditions. For example, while P. rubescens declined concomitantly with the decline in TP concentration, other species indicative of higher phosphorus concentrations, such as Tabellaria flocculosa var. asterionelloides, tended to increase further. 4. These data therefore do not support the hypotheses that a reduction in TP concentration is accompanied by (i) an immediate decline in total phytoplankton biovolume and (ii) persistence of the species composition characterising the phytoplankton community before nutrient reduction.     

Effects of zebra mussels on phytoplankton and ciliates: a field mesocosm experiment

Many observational studies in North American lakes have documenteddecreases in phytoplankton abundance after the invasion of thezebra mussel (Dreissena polymorpha). However, few field experimentshave examined in detail the effect of zebra mussels on phytoplanktonabundance and species composition over an extended period. Replicatedin situ mesocosms were used to evaluate the impact of naturaldensities of zebra mussels on phytoplankton and ciliate biovolume,and algal species composition over a 5-week period in a habitatthat lacked extant mussel populations. Mussel biomass used inthe experiment was determined using a regression model basedon a data analysis that predicts zebra mussel biomass from totalphosphorus concentration. Within 1 week, zebra mussels decreasedphytoplankton biovolume by 53% and ciliate biovolume by 71%.The effect of zebra mussels on ciliate biovolume was sustainedthroughout the study. However, the effect of zebra mussels onphytoplankton abundance gradually waned over the remaining 4weeks of the experiment, such that the declining effect of zebramussels could not be explained by a shift towards less edibleand/or faster growing algal species. The mussels’ decliningcondition could help to explain the effect observed over thecourse of the experiment.     

Analysis of long-term variation in phytoplankton biovolume in the northern basin of Lake Biwa

The long-term variation in phytoplankton biovolume in the northern basin of Lake Biwa was analyzed using periodic phytoplankton census data from January 1979 to December 2009. Population densities obtained from census data were transformed into biovolumes, and phytoplankton species were categorized into three size fractions: net phytoplankton (≥4,000 μm³ cell^?1, ≥ca. 20 μm in diameter), large nanophytoplankton (100–4,000 μm³ cell^?1, ca. 6–20 μm in diameter), and small nanophytoplankton (<100 μm³ cell^?1, <ca. 6 μm in diameter). Although the annual total biovolume gradually decreased over time, the total biovolumes in winter and spring were found to increase. Furthermore, a decrease in the biovolume of net phytoplankton and an increase in that of small nanophytoplankton were observed. Because of succession in the phytoplankton community, the average cell volume of the phytoplankton community decreased from 269 μm³ cell^?1 in the 1980s to 56 μm³ cell^?1 in the 2000s. Lake warming accompanied with the intensification of thermal stratification and the augmentation of wind speed were observed at Lake Biwa over the study period. Serial analysis correcting for autocorrelation revealed that oligotrophication in the epilimnion, induced by lake warming and limitation of light available for phytoplankton growth by wind-induced water mixing, was a potential factor in the succession of the phytoplankton community.     

Grazer control and nutrient limitation of phytoplankton biomass in two Australian reservoirs

1. Grazer and nutrient controls of phytoplankton biomass were tested on two reservoirs of different productivity to assess the potential for zooplankton grazing to affect chlorophyll/phosphorus regression models under Australian conditions. Experiments with zooplankton and nutrients manipulated in enclosures, laboratory feeding trials, and the analysis of in-lake plankton time series were performed. 2. Enclosures with water from the more productive Lake Hume (chlorophyll a = 3–17.5 μg l^–1), revealed significant zooplankton effects on chlorophyll a in 3/6, phosphorus limitation in 4/6 and nitrogen limitation in 1/6 of experiments conducted throughout the year. Enclosures with water from the less productive Lake Dartmouth (chlorophyll a = 0.8–3.5 μg l^–1), revealed significant zooplankton effects in 5/6, phosphorus limitation in 5/6 and nitrogen limitation in 2/6 of experiments. 3. While Lake Hume enclosure manipulations of the biomass of cladocerans (Daphnia and Diaphanosoma) and large copepods (Boeckella) had negative effects, small copepods (Mesocyclops and Calamoecia) could have positive effects on chlorophyll a. 4. In Lake Hume, total phytoplankton biovolume was negatively correlated with cladoceran biomass, positively with copepod biomass and was uncorrelated with total crustacean biomass. In Lake Dartmouth, total phytoplankton biovolume was negatively correlated with cladoceran biomass, copepod biomass and total crustacean biomass. 5. In both reservoirs, temporal variation in the biomass of Daphnia carinata alone could explain more than 50% of the observed variance in total phytoplankton biovolume. 6. During a period of low phytoplankton biovolume in Lake Hume in spring–summer 1993–94, a conservative estimate of cladoceran community grazing reached a maximum of 0.80 day^–1, suggesting that Cladocera made an important contribution to the development of the observed clear-water phase. 7. Enclosure experiments predicted significant grazing when the Cladocera/Phytoplankton biomass ratio was greater than 0.1; this threshold was consistently exceeded during clear water phase in Lake Hume. 8. Crustacean length had a significant effect on individual grazing rates in bottle experiments, with large Daphnia having highest rates. In both reservoirs, mean crustacean length was negatively correlated with phytoplankton biovolume. The observed upper limit of its variation was nearly twice as high compared to other world lakes.     

Development of a phytoplankton indicator system for the ecological assessment of brackish coastal waters (German Baltic Sea coast)

The implementation of the European Water Framework Directive (WFD) requires the development of ecologically-based classification systems for anthropogenically-induced eutrophication in all types of water bodies. Due to the inherent high temporal and spatial variability of hydrological and geochemical parameters of the coastal waters of the southern Baltic Sea, discrimination between anthropogenic impact and natural variability is necessary. The development of statistical methods for this discrimination was the main aim of this study. These methods were used to derive indicative phytoplankton parameters for different stages of eutrophication for the investigation area. For this purpose, a long-term phytoplankton data series was analysed, which covered a broad salinity and eutrophication gradient. In order to detect eutrophication effects, the analysis was restricted to phytoplankton spring bloom events and to the salinity range between 5 and 10 psu, i.e. superimposing seasonal and hydrodynamic effects were eliminated. An artificial abiotic degradation vector was developed based on four typical water quality parameters. A total of 11 potentially indicative phytoplankton parameters on different taxonomical levels arose from a correlation analysis with this degradation vector. These indicators were then tested for their ability to discriminate between three eutrophication levels. Finally, seven phytoplankton indices could be proposed: total phytoplankton biovolume, the percentage of diatoms and the biovolume of different size ranges of diatoms and one indicative species (Woronichinia compacta). Guest editors: A. Razinkovas, Z. R. Gasiūnaitė, J. M. Zaldivar & P. Viaroli European Lagoons and their Watersheds: Function and Biodiversity     

Nutrient addition effects on chlorophyll a,phytoplankton biomass,and heterocyte formation in Lake Erie’s central basin during 2014–2017: Insights into diazotrophic blooms in high nitrogen water

1. Phosphorus (P) usually is the primary limiting nutrient of phytoplankton biomass, but attention towards nitrogen (N) and trace nutrients, such as iron (Fe), has surfaced. Additionally, N-fixing cyanobacterial blooms have been documented to occur in N-rich, P-poor waters, which is counterintuitive from the paradigm that low N and high P promotes blooms. For example, Lake Erie's central basin has Dolichospermum blooms when nitrate concentrations are high, which raises questions about which nutrient(s) are selecting for Dolichospermum over other phytoplankton and why an N-fixer is present in high N waters?
2. We conducted a 4-year (2014–2017) study in Lake Erie's central basin to determine which nutrient (P, N, or trace nutrients such as Fe, molybdenum [Mo], and boron [B]) constrained chlorophyll concentration, phytoplankton biovolume, and nitrate assimilation using nutrient enrichment bioassays. The enriched lake water was incubated in 1-L bottles in a growth chamber programmed at light and temperatures of in situ conditions for 4–7 days. We also quantified heterocytes when N-fixing cyanobacteria were present.
3. Compared to the non-enriched control, the P-enriched (+P) treatment had significantly higher chlorophyll and phytoplankton biovolume in c. 75% of experiments. Combination enrichments of P with ammonium-N, nitrate-N, Fe, Mo, and B were compared to the +P treatment to determine secondary limitations. +P and ammonium-N and +P nitrate-N resulted in higher chlorophyll in 50% of experiments but higher phytoplankton biovolume in only 25% of experiments. These results show that P was the primary limiting nutrient, but there were times when N was secondarily limiting.
4. Chlorophyll concentration indicated N secondary limitation in half of the experiments, but biovolume indicated only N secondary limitation in 25% of the experiments. To make robust conclusions from nutrient enrichment bioassays, both chlorophyll and phytoplankton biovolume should be measured.
5. The secondary effects of Fe, Mo, and B on chlorophyll were low (<26% of experiments), and no secondary effects were observed on phytoplankton biovolume and nitrate assimilation. However, +P and Fe resulted in more chlorophyll than +P in experiments conducted during Dolichospermum blooms, and +P and B significantly increased the number of heterocytes in Dolichospermum. These results indicate that low Fe availability might select for Dolichospermum, and low B constrains heterocyte formation in the central basin of Lake Erie. Furthermore, these results could apply to other lakes with high N and low P where diazotrophic cyanobacterial blooms occur.

     

Structure of the Phytoplankton Community and Its Relationship to Water Quality in Donghu Lake, Wuhan, China

The phytoplankton community structure, in terms of species composition, total standing crop,and abundance of the dominant algal species, at four stations in Donghu Lake, Wuhan, China, was investigated monthly from January 1994 to December 1996. A total of 260 taxa was observed, of which Chlorophyta (106 taxa) contributed the highest portion of the total number of taxa, followed by Bacillariophyta (82 taxa)and Cyanophyta (32 taxa). The total standing crop measured by means of chlorophyll a content, cell density,and cell biovolume, as well as the abundance of the dominant species, declined in the order of Station I to Station Ⅳ. Seasonal changes of the standing crop varied greatly among the four stations. Although the cell density at the four stations showed a single peak within a year, the peak density varied from July to November, dependent on the sampling year and the station. For chlorophyll a content and cell biovolume,multiple peaks were observed at Stations Ⅰ and Ⅱ, but a single peak was found at Stations Ⅲ and Ⅳ. The phytoplankton community structure indicated that the trophic status was the highest at Station Ⅰ (most eutrophic), followed by Station Ⅱ; Stations Ⅲ and Ⅳ were the least trophic areas. The long-term changes in phytoplankton community structure further suggested that changes in phytoplankton community structure were correlated with water quality, and eutrophication of Donghu Lake had been aggravated since the 1950s.     

Structure of the Phytoplankton Community and Its Relationship to Water Quality in Donghu Lake, Wuhan, China

The phytoplankton community structure, in terms of species composition, total standing crop,and abundance of the dominant algal species, at four stations in Donghu Lake, Wuhan, China, was investigated monthly from January 1994 to December 1996. A total of 260 taxa was observed, of which Chlorophyta (106 taxa) contributed the highest portion of the total number of taxa, followed by Bacillariophyta (82 taxa) and Cyanophyta (32 taxa). The total standing crop measured by means of chlorophyll a content, cell density,and cell biovolume, as well as the abundance of the dominant species, declined in the order of Station I to Station IV. Seasonal changes of the standing crop varied greatly among the four stations. Although the cell density at the four stations showed a single peak within a year, the peak density varied from July to November, dependent on the sampling year and the station. For chlorophyll a content and cell biovolume,multiple peaks were observed at Stations I and II, but a single peak was found at Stations III and IV. The phytoplankton community structure indicated that the trophic status was the highest at Station I (most eutrophic), followed by Station II; Stations III and IV were the least trophic areas. The long-term changes in phytoplankton community structure further suggested that changes in phytoplankton community structure were correlated with water quality, and eutrophication of Donghu Lake had been aggravated since the 1950s.     

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.     

Diatoms and biomonitoring: should cell size be accounted for?

Despite the fact that biovolume calculation is a common procedure in most phytoplankton and periphyton studies, diatom community analyses are usually based on relative abundance data. In a biomonitoring context, a community metric that accounts for cell size could be of interest due to the potential differences that might exist in nutrient uptake between large and small-sized species. This paper addresses the question of whether diatom community analysis should be based on relative abundance, biovolume or cell surface. The results show that although community structure expressed as relative proportion of taxa varied according to the metric used, the ordinations conducted with each metric were similar. The explained percentage of species variance was slightly higher with the relative abundance metric compared to the metrics based on relative biovolume or cell surface area. Partial CCAs showed that each water chemistry variable generally explained a higher portion of species variance when the relative abundance was used. The analyses conducted with two size groups (small and large taxa) expressed as relative abundance and relative biovolume showed similar results. Moreover, our data showed that there is no significant relationship between diatom size and total phosphorus. According to these results, it seems that relative abundance would be the most appropriate metric to use for biomonitoring purposes. The biovolume and cell surface area calculations added substantially to the total analysis time due to the numerous measurements required, but did not improve the variance explained in community structure, and site ordinations were not significantly different. Electronic supplementary material Electronic supplementary material is available for this article at and accessible for authorised users.     

Phytoplankton responses to grazing by Daphnia galeata in the biomanipulated Bautzen reservoir

We studied the response of phytoplankton to grazing by Daphnia galeata in the hypertrophic Bautzen reservoir (Dresden, Germany) from January 1995 to May 1996 during a long-term whole-lake biomanipulation experiment. The correlation between clearance rate of D. galeata and total phytoplankton biomass was negative only if biomass of Microcystis aeruginosa was excluded. This suggests that M. aeruginosa is the main grazing resistant phytoplankton species in the Bautzen reservoir. Except for M. aeruginosa and grazing-resistant Staurastrum quadridentatum spec. nov. (Scharf, 1995) no other phytoplankton species was able to reach a biovolume above 1 mm3 L-1 when the clearance rate of Daphnia exceeded 0.1 L L-1 d-1. There was significant positive correlation between mean cell or colony size of phytoplankters and clearance rate of D. galeata, showing an advantage of bigger cells or colonies at high grazing pressure. Cross-correlation indicated a time lag of about one month between changes in grazing pressure and a change in phytoplankton mean size. The phytoplankton species were divided into edible and inedible fractions, depending on their width and length. No edible species were able to reach high biovolumes during high biomasses of D. galeata but a positive correlation was found between the edible fraction of phytoplankton biovolume and the clearance rate of D. galeata. However, this relationship disappeared when the ‘ingestible edible’ fraction of M. aeruginosa was excluded, suggesting a rejection of ‘edible’ Microcystis colonies by D. galeata. A negative correlation was found between the inedible fraction of phytoplankton biovolume without M. aeruginosa and the clearance rate of D. galeata which might be due to superior competition of M. aeruginosa. We could clearly show that biomanipulation might not work well with respect to the reduction of total phytoplankton biomass under hypertrophic conditions and finally discuss a theoretical threshold of phosphorus (probably around 80 μg L-1), below which biomanipulation should become effective. This revised version was published online in July 2006 with corrections to the Cover Date.     

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.     

Comparisons of zooplankton and phytoplankton in created shallow water habitats of the lower Missouri River: implications for native fish

Shallow water habitat (SWH) is important for riverine fish and their invertebrate prey, yet the availability of SWH has declined in many systems due to human impacts. We evaluated the potential ecological benefits of restoring SWH by comparing zooplankton and phytoplankton from created backwaters (a floodplain feature connected to the river on the downstream end but disconnected at the upstream end) and chutes (a side channel of the river that diverts flow from the main channel through the chute and back into the main channel) on the lower Missouri River. We tested the hypothesis that backwaters support higher abundances of zooplankton and phytoplankton than chutes using data that were collected during the summer of 2010. As predicted, backwaters had more diverse cladoceran communities and greater abundances of rotifers, copepod nauplii, adult copepods, and cladocerans than chutes. Total algal biovolume was the same in chutes and backwaters; however, phytoplankton taxa richness was higher in backwaters, and there was a greater biovolume of green algae (Chlorophyta), Crypotophyta, cyanobacteria, and Euglenophyta in backwaters than in chutes. Differences in zooplankton and phytoplankton between backwaters and chutes appeared to be related to slower current velocities, longer retention times, and lower levels of turbidity and total suspended solids in backwaters. While chutes have the potential to provide greater habitat diversity than the mainstem, there were no differences in water quality or phytoplankton abundance, community structure, or diversity between these two habitats. Combined, our results suggest that created backwaters initially provide a greater potential food resource for native fishes. However, additional research is needed to determine whether chutes can also develop beneficial shallow water features over a longer period of time.     

Spatial–temporal patterns of methane dynamics in Lake Taihu

Many European lakes are monitored according to the EU Water Framework Directive (WFD), with focus on phytoplankton biomass and species composition. However, the low-frequency WFD monitoring may miss short-term phytoplankton changes. This is an important issue because short-term extreme meteorological events (heat waves and heavy rain) are predicted to increase in frequency and intensity with climate change. We used records from Lake Mondsee (Austria) from 2009 to 2015 to test if a reduction from monthly to seasonal sampling affected the average annual phytoplankton biovolume. Furthermore, we combined inverted light microscopy, FlowCAM and flow cytometry to estimate the effect of sampling during extreme events on average phytoplankton biovolume. Relative to monthly sampling, seasonal sampling significantly overestimated phytoplankton biomass. A heat wave in 2015 and two episodes of heavy rain in 2015 and 2016 caused species-specific changes; biovolumes of chlorophytes and the filamentous cyanobacterium Planktothrix rubescens (De Candolle ex Gomont) Anagnostidis & Komárek increased significantly during the heat wave. Using live material with FlowCAM and flow cytometry, we detected small and fragile cells and colonies that were either ignored or underrepresented by analysing fixed samples with light microscopy. We suggest a modified sampling and analysis strategy to capture short-term changes within the phytoplankton community.     

Change in cyanobacterial biovolume due to preservation by Lugol's Iodine

Cyanobacterial biovolume is used as a guide to the public health risk from these organisms for users of potable and recreational waters. Most routine surveillance programs preserve phytoplankton samples before analysis. We tested the effect of Lugol's Iodine, a common preservative, on the cell biovolume of four common freshwater cyanobacteria, Microcystis aeruginosa, Anabaena circinalis, Cylindrospermopsis raciborskii and Aphanocapsa incerta. Linear dimensions and cell area were measured with an image analyser. All four species shrank after preservation. The magnitude of shrinkage varied with species and preservation time but was not affected by Lugol's concentration. The maximum shrinkage in each species was a 30–40% reduction compared to the live cell biovolume. These results suggest shrinkage can be a greater source of uncertainty in estimating the biovolume of toxigenic cyanobacteria in aquatic environments than natural variability in the cell dimensions, instrument precision or cell counting. Standardised cyanobacterial biovolume lists based on agreed geometric shapes and formulae would improve the value of this information for public health risk assessment.