Cyanobacteria Biovolume Research Articles

Influence of fisheries and shoreline management on limnological characteristics of three Missouri reservoirs

ABSTRACT Landscape-level analyses based on land cover, morphology, and hydrology account for most of the cross-system variation in pelagic nutrients and suspended solids in Missouri reservoirs. They are based on geometric means, which reduce the influence of extreme temporal variation measured in individual reservoirs. This analysis of 3 conservation reservoirs, managed to benefit recreational fisheries, details how internal processes can alter nutrients, chlorophyll, mineral turbidity, and transparency in long-term (21–42 year) datasets, which contribute to temporal variation. Management practices include the addition of grass carp and herbicides to control nuisance macrophytes and shoreline stabilization with rock and water willow. Among these reservoirs, there is strong evidence that macrophyte removal can increase pelagic nutrients by >90%, resulting in a switch to plankton-dominated conditions (alternative states). In one case, eradication of aquatic vegetation increased mineral turbidity by >60%, which was reversed by reestablishing macrophytes and stabilizing the shoreline. This temporal series supports the modifications of phytoplankton–nutrient relations by mineral turbidity shown in state-wide analyses. Collectively, the long-term data show a significant increase in cyanobacteria biovolume and cyanotoxins, with maximum microcystin concentrations increasing as much as 20 times. Actively flipping lakes to plankton-dominated systems via fisheries management and shoreline stabilization practices has negative impacts on overall water quality, with implications for human and wildlife health.

Cyanobacteria species dominance and diversity in three Australian drinking water reservoirs

The objective of this study was to identify correlations between environmental variables and cyanobacterial diversity, succession and dominance in three Australian water supply reservoirs. We assessed up to 15 years of in-lake water quality monitoring data from Lake Wivenhoe and Lake Tingalpa (Queensland), and Lake Myponga (South Australia). Lakes Wivenhoe and Tingalpa, subject to a subtropical climate, had higher cyanobacterial richness than Lake Myponga in temperate South Australia. Richness in the subtropical lakes was positively correlated (P < 0.05) with total cyanobacteria biomass, and cyanobacteria biovolume > 0.03 mm3/l (Alert level 1; World Health Organization) was often composed of multiple cyanobacteria species. Peaks in total cyanobacteria biomass and diversity occurred in all three lakes from late spring to early autumn. Unicellular picocyanobacterial dominance was negatively correlated (P < 0.05) with total nitrogen while dominance of colonial and filamentous species with larger cells (e.g. Microcystis spp., Raphidiopsis spp., Dolichospermum circinale) was positively correlated (P < 0.05) with total phosphorus. Among the species with larger cells, diazotrophic D. circinale often dominated when total nitrogen was at low concentrations. Our results support decision making for selecting cyanoHAB control strategies based on single- or multi-species dominance and reinforce that new monitoring technologies could support species-level assessments.

Evaluation of indicators for cyanobacterial risk in 108 temperate lakes using 23\xa0years of environmental monitoring data

BackgroundCyanobacterial blooms are of increasing concern for drinking water supply. In Sweden, a survey among drinking water producers showed that the sense of urgency was little. At 60% of the Swedish drinking water treatment plants, operators lacked monitoring strategies. To get a picture of the size of the problem the presence of cyanobacterial risk in 108 Swedish lakes was evaluated from 23 years of environmental monitoring data. The drivers and indicators for cyanobacterial growth were investigated by analyzing water quality in 9 lakes that have more frequent cyanobacteria bio-volume above the WHO drinking water alert level 1: 0.2 mm3L−1.ResultsThe study shows that the most common species in those lakes are Anabaena/Dolichospermum and Aphanizomenon followed by Microcystis, Woronichinia and Planktothrix, which can produce a variety of toxins such as anatoxins, cylindrospermopsins, microcystins and saxitoxins, supported by literature study. Our results show that cyanobacterial risk in those problematic 9 lakes are mainly nutrients driven with possibly contribution of increased organic matter. By applying non-linear quantile regression with total phosphorus (TP) as an example, we demonstrated that certain drivers such as TP can be useful for cyanobacterial risk assessment and provide control measures by setting nutrients targets. We also evidenced that cyanobacterial peaks presented at low TN:TP ratio while not necessarily vice versa. We also further evaluated that chlorophyll-a and transparency might be suitable as indicators for cyanobacterial blooms in certain lakes, while for most of the lakes, their connection is low.ConclusionNutrients are main drivers for higher cyanobacterial occurrence in the 9 lakes. We suggest TP concentrations should be investigated thoroughly to provide important knowledge which can be used to set nutrient targets to sustain safe drinking water supply and recreational services. The complexity of indicating cyanobacterial risk in a local condition was also highlighted in this study and future study is suggested. To classify different types of lake and identify their drivers and the similarities of species composition changes in those lakes will be future studied.

The Occurrence of Potential Harmful Cyanobacteria and Cyanotoxins in the Obrzyca River (Poland), a Source of Drinking Water.

Harmful cyanobacteria and their cyanotoxins may contaminate drinking water resources and their effective control remains challenging. The present study reports on cyanobacterial blooms and associated cyanotoxins in the Obrzyca River, a source of drinking water in Poland. The river was examined from July to October 2019 and concentrations of microcystins, anatoxin-a, and cylindrospermopsin were monitored. The toxicity of water samples was also tested using an ecotoxicological assay. All studied cyanotoxins were detected with microcystins revealing the highest levels. Maximal microcystin concentrations (3.97 μg/L) were determined in September at Uście point, exceeding the provisional guideline. Extracts from Uście point, where the dominant species were Dolichospermum flos-aquae (August), Microcystis aeruginosa (September), and Planktothrix agardhii (October), were toxic for Dugesia tigrina Girard. Microcystin concentrations (MC-LR and MC-RR) were positively correlated with cyanobacteria biovolume. Analysis of the chemical indicators of water quality has shown relationships between them and microcystins as well as cyanobacteria abundance.

High growth rates of a dominant calanoid copepod in the northern San Francisco Estuary

ABSTRACTWe measured growth rates of the copepod Pseudodiaptomus forbesi in relation to food, environmental conditions and hydrology in the northern San Francisco Estuary, California, USA. We conducted 38 copepod growth-rate experiments during summers 2015–2017 at four sites in a tidal, freshwater channel that had strong gradients in environmental conditions. Copepod growth rates were measured using the artificial cohort method with an image analysis technique, and seston attributes were measured to investigate the effects of food quantity and quality on copepod growth rates. Growth rates ranging from 0.03 to 0.47 day−1 (median 0.30 day−1) and growth rates, chlorophyll, turbidity and total lipids in the channel decreased with distance downstream. Growth rates had a saturating response to chlorophyll and were generally higher than rates previously measured in larger estuarine channels, presumably because of higher chlorophyll and temperature in our study area. Growth rate was positively associated with biovolume of cyanobacteria but not with that of other major phytoplankton groups, which is consistent with a recent finding of high feeding of P. forbesi on cyanobacteria. This adds to the small but growing literature suggesting that crustacean planktons are able to overcome the nutritional deficiencies of cyanobacteria to grow and reproduce.

Spatio-temporal variation of cyanobacteria and cyanotoxins in public supply reservoirs of the semi-arid region of Brazil

Cyanobacteria harmful algal blooms (CyanoHABs) have become increasingly frequent and intense in public supply reservoirs as a result of eutrophication and global climate change. The semi-arid region of Brazil has a well documented history of CyanoHABs but the underlying factors that control the excessive proliferation of these organisms and the production of their bioactive secondary metabolites are not comprehensively understood. This study aimed to identify the environmental factors that explain the spatial and temporal variations in the abundance of cyanobacteria and the concentration of cyanotoxins (microcystins, saxitoxins, and cylindrospermopsin) in semi-arid reservoirs. The following hypotheses were tested: (a) the largest biovolumes of potential toxin producing cyanobacteria occur when cyanotoxin concentrations are highest; and (b) the environmental factors that explain variations in biovolume of cyanobacteria also explain changes in cyanotoxins concentrations. Samples were taken from four reservoirs located in the Northeast region of Brazil, over a three-month period (October 2016 and February and June 2017). Of the 24 species of cyanobacteria identified, 13 were potentially toxin-producing. Physicochemical variables such as water volume of the reservoir, water transparency, soluble reactive phosphorus, and total phosphorus explained the abundance of cyanobacteria and the levels of cyanotoxins. These results corroborate the hypothesis that similar physicochemical conditions influence the abundance and diversity of cyanobacteria and cyanotoxins. Cyanobacterial blooms composed of more than one potential toxin producing species were observed in the studied reservoirs, where potential microcystin-producing species were the most common. Microcystins and saxitoxins were detected in all the reservoirs studied, while cylindrospermopsin and the cyanobacterium Cylindrospermopsis raciborskii were simultaneously recorded in only one reservoir (Camalaú Reservoir). Cylindrospermopsin was only detected in a reservoir for the first time in the State of Paraíba. Canonical redundancy analysis showed that the cyanotoxins were related to potential toxin producing species. These results corroborate the proposed hypothesis that there is a correlation between cyanotoxins and the biomass of potential producers. Also, there were situations where cyanotoxins were detected without the presence of potential producers. These results demonstrate the need for reassessment of potential toxin producing species of cyanobacteria in semi-arid reservoirs. This may lead to the identification and characterization of novel producers of these bioactive secondary metabolites.

Comparison of Microphototrophic Communities Living in Different Soil Environments in the High Arctic

The Arctic region undergoes rapid climate change resulting in soil warming with consequent changes in microbial community structure. Therefore, it is important to gain more knowledge on the pioneer photosynthetic microorganisms and their relations to environmental factors. Here we provide a description of the community composition of microbial phototrophs in three different types of soils in the High Arctic (Svalbard): vegetated soil at a raised marine terrace, biological soil crust (BSC) at high elevation, and poorly-developed BSC in a glacier foreland. The studied sites differed from each other in microclimatic conditions (soil temperature and soil water content), soil chemistry and altitude. Combining morphological (cell biovolume) and molecular methods (NGS amplicon sequencing of cyanobacterial 16S rRNA and eukaryotic 18S rRNA sequences of isolates), we studied the diversity and biovolume of cyanobacteria and eukaryotic microalgae. The results showed that cyanobacteria prevailed in the high altitude BSC as well as in pioneering BSC samples in glacier foreland though with lower biomass. More specifically, filamentous cyanobacteria, mainly Leptolyngbya spp., dominated the BSCs from these two localities. In contrast, coccoid microalgae (green and yellow-green algae) had higher biovolume in low altitude vegetated soils. Thus, the results of this study contribute to a better understanding of microphototrophic communities in different types of Arctic soil environments.

Spatial variability and temporal dynamics of cyanobacteria blooms and water quality parameters in Missisquoi Bay (Lake Champlain)

Abstract Cyanobacteria bloom events have been associated with eutrophication processes, along with hydrologic and climate factors. Missisquoi Bay is a portion of Lake Champlain (USA–Canada) that is highly eutrophic and prone to cyanobacteria blooms and cyanotoxins. This study assessed the spatial–temporal influence of nutrients, turbidity and temperature in cyanobacteria distributions during a bloom event in the summer of 2006. Correlations, generalized linear models (GLMs), geostatistics and local indications of spatial association (LISA) autocorrelation analysis tested the influence of nutrient and non-nutrient explanatory variables in cyanobacteria biovolume. Total phosphorus exhibited a high direct correlation with cyanobacteria biovolume. The best performing GLMs included total phosphorus, total nitrogen, Secchi depth (as turbidity) and temperature as explanatory variables of cyanobacteria biovolume. Variogram analysis of those variables resulted in a better understanding of the underlying spatial variation process of the cyanobacteria bloom event. The LISA test revealed a moderate but stable autocorrelation between cyanobacteria biovolume and total phosphorus from 180 to 1,000 m of weight distance, suggesting the possibility of up-scaling the current results to coarse-resolution satellite imagery for more frequent monitoring of bloom events. The LISA test also revealed the spatial–temporal dynamic (movement of cyanobacteria scums) of high cyanobacteria blooms with high total phosphorus concentration.

Decreased nitrogen loading controls summer cyanobacterial blooms without promoting nitrogen‐fixing taxa: Long‐term response of a shallow lake

AbstractThe effectiveness of controlling nitrogen (N) to manage lake eutrophication is debated. Long‐term, whole‐lake case studies are required to determine whether diazotrophic cyanobacteria can fix sufficient N to offset a reduction of N‐inputs. We document the recovery of shallow, productive Lake Müggelsee (Germany) over 37 yr (sampling interval 1–2 weeks) during a decrease of N and phosphorus (P) loading of 79% and 69%, respectively. Nitrogen concentrations in the lake responded immediately to loading reduction whereas P concentrations remained elevated for about 20 yr. Total nitrogen (TN) in the lake was always lower than TN in the inflow. Accordingly, estimated denitrification and N‐burial rates substantially exceeded N2 fixation rates in the long term. Phosphorus was growth limiting in spring whereas N was clearly limiting in summer due to high sediment P‐release. TN : TP ratios, normalized to phytoplankton biovolume by regression, were 25.5 (weight) in spring and 3.3 in summer. During the study period, dissolved inorganic N (DIN) concentrations in summer decreased and the duration of low DIN concentrations increased by ca. 100 d. The biovolume of cyanobacteria and total phytoplankton decreased by 89% and 76%, respectively. The proportion of N2‐fixing cyanobacteria during summer decreased from 36% to 14% of the total phytoplankton biovolume. The total concentration of heterocysts and estimated total N2 fixation did not change over time. In the long term, decreasing N‐inputs effectively controlled summer cyanobacteria including N2‐fixing taxa, which did not compensate for the N‐deficit. A P‐only control strategy would not have been as successful.

Seasonal changes in peryphytic microbial metabolism determining mercury methylation in a tropical wetland

Mercury (Hg) methylation, a key process in the biogeochemical cycle of Hg, is mainly attributed to sulfate-reducing bacteria and methanogenic Archaea. However, environmental regulation by these groups has not yet been ascertained in tropical environments, especially in respect to the seasonal flood flooding. This work evaluated the variation of net methylmercury production potential in relation to biological characteristics of the periphyton, environmental factors, and flood pulse seasons. Our results indicate that there is a seasonal change between metabolic groups as main Hg methylators, sulfate-reducing bacteria in the dry season and methanogenic Archaea in the flood season. In addition, there was a positive relationship between dissolved organic carbon (DOC), phosphorus, cyanobacteria biovolume, and periphytic Hg methylation potential. These results shed a new light on MeHg production plasticity, mediated by landscape and flood pulses in tropical wetlands, as well as on ecological relationships within the periphyton.

Forecasting cyanobacteria dominance in Canadian temperate lakes

Predictive models based on broad scale, spatial surveys typically identify nutrients and climate as the most important predictors of cyanobacteria abundance; however these models generally have low predictive power because at smaller geographic scales numerous other factors may be equally or more important. At the lake level, for example, the ability to forecast cyanobacteria dominance is of tremendous value to lake managers as they can use such models to communicate exposure risks associated with recreational and drinking water use, and possible exposure to algal toxins, in advance of bloom occurrence. We used detailed algal, limnological and meteorological data from two temperate lakes in south-central Ontario, Canada to determine the factors that are closely linked to cyanobacteria dominance, and to develop easy to use models to forecast cyanobacteria biovolume. For Brandy Lake (BL), the strongest and most parsimonious model for forecasting % cyanobacteria biovolume (% CB) included water column stability, hypolimnetic TP, and % cyanobacteria biovolume two weeks prior. For Three Mile Lake (TML), the best model for forecasting % CB included water column stability, hypolimnetic TP concentration, and 7-d mean wind speed. The models for forecasting % CB in BL and TML are fundamentally different in their lag periods (BL = lag 1 model and TML = lag 2 model) and in some predictor variables despite the close proximity of the study lakes. We speculate that three main factors (nutrient concentrations, water transparency and lake morphometry) may have contributed to differences in the models developed, and may account for variation observed in models derived from large spatial surveys. Our results illustrate that while forecast models can be developed to determine when cyanobacteria will dominate within two temperate lakes, the models require detailed, lake-specific calibration to be effective as risk-management tools.

Multispectral remote sensing of harmful algal blooms in Lake Champlain, USA.

This study developed satellite remote sensing models to detect cyanobacterial blooms via chlorophyll a in Lake Champlain. Landsat Enhanced Thematic Mapper Plus data was used to retrieve chlorophyll a concentrations, phytoplankton, and cyanobacteria biovolume by calibrating and validating with coincident observation data. Correlation analysis results showed that band 2 (green band) and the band ratio of 2/1 (green/blue) were most highly correlated to chlorophyll a concentration (r = 0.76 and 0.82, respectively). Multiple regression results identified band 2 and 3 (red), and band ratio of 2/1 and 3/1 (red/blue) as critical information to estimate chlorophyll a concentrations. The regression models accounted for 72 to 83% of the variability in chlorophyll a observations, allowing for estimates of phytoplankton and cyanobacteria levels in the lake. Satellite image processing results successfully showed the temporal and spatial distribution of chlorophyll a, phytoplankton, and cyanobacteria in the lake. This information can be used to evaluate the effect of pollution sources and weather conditions, and assist decision making for water management.

Biovolume de cianobactérias e algas de reservatórios tropicais do Brasil com diferentes estados tróficos

O presente estudo visou apresentar o biovolume de cianobactérias e algas fitoplanctônicas e perifíticas de reservatórios com diferentes estados tróficos do Parque Estadual das Fontes do Ipiranga, São Paulo, SP, Brasil. O estudo inclui uma proposta para determinação do biovolume de formas coloniais de Cyanobacteria como, por exemplo, Microcystis e Sphaerocavum. A lista de biovolume auxiliará os estudos sobre ecologia de algas, permitindo a aplicação dessa informação em trabalhos nessa área de estudo, além de servir de modelo comparativo em outros ecossistemas de região tropical. A lista inclui o biovolume de 568 táxons, incluindo informações sobre suas respectivas classes taxonômicas, máxima dimensão linear e razão superfície/volume.

The role of environmental parameters in the structure of phytoplankton assemblages and cyanobacteria toxins in two hypereutrophic lakes

We evaluated the variability of cyanotoxins, water chemistry, and cyanobacteria communities in two hypereutrophic drowned river mouth lakes (Spring Lake and Mona Lake; summer 2006) in west Michigan, USA. Even with considerable geographical and watershed similarity, local variations in nutrient concentrations and environmental factors were found to influence the differences observed in cyanobacteria assemblages and cyanotoxins levels between the two lakes. Limnothrix sp. dominated the phytoplankton community in Spring Lake (82% of biovolume) and was negatively correlated with total phosphorus (TP) concentrations. Although Spring Lake was treated with alum during the previous year, Limnothrix sp. was able to bloom in the lower P environment. In contrast, the N2-fixing cyanobacterium, Anabaena flos-aquae, dominated the phytoplankton in Mona Lake (64% of biovolume). N2-fixing cyanobacteria dominance in Mona Lake was correlated with higher TP lower dissolved nitrogen levels. Cylindrospermopsis raciborskii was found in both systems; however, the toxin-producing polyketide synthetase gene was not present in either population. The higher TP in Mona Lake appeared to account for the 3-fold increase in cyanobacteria biovolume. Restoration plans for both lakes should include assessments of internal loading and continued phytoplankton monitoring to track the temporal distribution of cyanobacteria species and cyanotoxin concentrations.

Multispectral Remote Sensing of Harmful Algal Blooms in Lake Champlain, USA

ABSTRACT This study developed satellite remote sensing models to detect cyanobacterial blooms via chlorophyll a in Lake Champlain. Landsat Enhanced Thematic Mapper Plus data was used to retrieve chlorophyll a concentrations, phytoplankton, and cyanobacteria biovolume by calibrating and validating with coincident observation data. Correlation analysis results showed that band 2 (green band) and the band ratio of 2/1 (green/blue) were most highly correlated to chlorophyll a concentration (r = 0.76 and 0.82, respectively). Multiple regression results identified band 2 and 3 (red), and band ratio of 2/1 and 3/1 (red/blue) as critical information to estimate chlorophyll a concentrations. The regression models accounted for 72 to 83% of the variability in chlorophyll a observations, allowing for estimates of phytoplankton and cyanobacteria levels in the lake. Satellite image processing results successfully showed the temporal and spatial distribution of chlorophyll a, phytoplankton, and cyanobacteria in the lake. This information can be used to evaluate the effect of pollution sources and weather conditions, and assist decision making for water management.

The influence of environmental conditions and hydrologic connectivity on cyanobacteria assemblages in two drowned river mouth lakes

We evaluated the temporal and spatial variability of cyanotoxins, water chemistry, and cyanobacteria communities in two lakes of different trophic status. Bear Lake is a hypereutrophic system that flows into mesotrophic Muskegon Lake. Total microcystins (MC) in Bear Lake (mean, 1.66 μg/L) were composed of multiple structural analogs: 43% MC-LR, 50% MC-RR, and 7% MC-YR. Total microcystins in Muskegon Lake (mean, 0.52 μg/L) consisted of MC-LR (76%), MC-RR (14%), MC-YR (6%), and MC-LA (3%). The lakes were dominated by the cyanobacteria Microcystis spp., which accounted for 75% of phytoplankton biovolume in Bear Lake and > 90% in Muskegon Lake. Total microcystin concentration was positively correlated with cyanobacteria biovolume and turbidity (Muskegon Lake) and total phosphorus (Bear Lake), while negatively correlated with ammonia (Bear Lake) and nitrate (both lakes). The relationships between microcystins and environmental factors differed between lakes, despite hydrologic connectivity, suggesting that local conditions have a greater influence on toxin production than regional effects. Cylindrospermopsis raciborskii was found in both systems; however, the assemblage does not appear to be capable of producing cylindrospermopsin due to the absence of the PKS gene. Although the Bear Lake discharge appears to be the source of C. raciborskii, the physical/chemical properties of Muskegon Lake (lower turbidity and temperature, higher nitrate) may constrain the growth of this invasive species. Thus, local conditions in each lake are important in determining which species are capable of maintaining a viable population.

Warm spring and summer water temperatures in small eutrophic lakes of the Canadian prairies: potential implications for phytoplankton and zooplankton

Shallow, polymictic lakes with low heat storage capacity are especially susceptible to warmer spring conditions, predicted for a changing climate. In these lakes, atmosphere to water mass heat transfer is efficient as a result of high wind exposures and large surface areas relative to volumes. We examined effects of warmer water temperatures on phytoplankton and zooplankton abundance and species composition in three small eutrophic lakes (5.2‐14.9 ha) of the Canadian prairies in Winnipeg, Manitoba, Canada, over two open-water seasons with contrasting spring weather conditions, i.e. 2005-a “normal” spring and 2006-a warm spring. Warmer spring and summer water temperatures were associated with decreased water transparency, increased phytoplankton biomass, increased relative filamentous cyanobacteria biomass and shifts in dominant genera from Aphanizomenon to Anabaena and Planktothrix. Zooplankton responded strongly; abundance of Daphnia (D. pulicaria, D. ambigua and D. parvula) decreased while rotifers, Skistodiaptomus oregonensis and Bosmina longirostris increased in abundance. Of several factors influencing phytoplankton dynamics, total dissolved nutrients [nitrogen (N), phosphorus (P) and N:P] and water column stability did not show important changes between years. In contrast, water temperature [described as the metric degree-days (8C day)] was related to changes in phytoplankton and % cyanobacteria biovolume. Daphniid abundance showed a significant negative relationship with an increase in filamentous cyanobacteria biomass and, thus we suggest, was indirectly associated with increased water temperatures.

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

Summary1. 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 (Pmax), 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, Pmax 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.

Effects of fomesafen, alone and in combination with an adjuvant, on plankton communities in freshwater outdoor pond mesocosms

Ecotoxicological effects of the diphenyl ether herbicide fomesafen, applied alone or in combination with the adjuvant Agral 90 (mixture of polyethoxylated derivatives of nonylphenol), were assessed on planktonic communities in 18-m3 outdoor mesocosms during a nine-month study. Four mesocosms were treated with fomesafen only (nominal concentration: 40 microg/L), four were treated with the mixture fomesafen-Agral 90 (nominal concentration: 40 microg/L and 90 microg/L, respectively), and four were kept as the controls. Five treatments were performed every three weeks from April 18, 2000. Mean (+/- standard error [SE]) values of fomesafen concentration in water of 62.5 (+/-5.3) and 19.4 (+/-7.6) microg/L were measured at the end of the treatment period in fomesafen- and mixture-treated mesocosms, respectively. Fomesafen, either alone or in mixture with Agral 90, had a significant positive effect on the abundance and biovolume of Cyanobacteria, Cryptophyceae, Dinophyceae, and Bacillariophyceae. Chlorophyceae were inhibited by the herbicide and laboratory toxicity tests confirmed that green algae were more sensitive toward fomesafen than other algal classes. A positive effect of treatments on phytoplankton taxonomic diversity also was observed, indicating that, like natural disturbances of intermediate strength, xenobiotics sometimes may enhance the diversity of algal communities. Fomesafen alone did not have any clear effect on zooplankton. Abundance of calanoid copepods was reduced significantly in the mixture-treated ponds, suggesting either a direct effect of the adjuvant and/or an enhancement of herbicide toxicity by Agral 90. The abundance of other zooplanktonic herbivorous groups increased due to a reduced competition for food for herbivorous species and a higher availability of preys for predators. No algal bloom was observed in the treated ponds, presumably because of grazing pressure and the low availability of nutrients.

Testing predictions of the lake food web theory on pelagic communities of Australian reservoirs

Several predictions of the theory developed for pelagic food webs of the Northern Hemisphere were tested on water bodies of Eastern Australia. Eleven reservoirs, representing trophic and latitudinal gradients were sampled for nutrients, phytoplankton, zooplankton and pelagic fish. Two models of regression analysis, which analysed possible interactions between trophic levels were based on different sets of data. In one, each reservoir was represented by only one pair of observations – annual mean or single observation (“regional model”). In the other, seasonal means of four frequently sampled reservoirs similar in productivity were used (“temporal model”). Significant variation in total phytoplankton biovolume (TPB) was predicted by total phosphorus concentration (TP), total nitrogen concentration (TN), mean crustacean length and acoustic biomass of planktivorous fish in both models. This suggested that nutrient limitation, zooplankton grazing and positive effects of fish were probably important in controlling the biomass of primary producers at both regional and temporal scales. In the regional model, the biomass of fish was also negatively correlated with Daphnia biomass and mean crustacean length, suggesting that the trophic cascade hypothesis may be applicable to Eastern Australia for the considered range of reservoir productivities.The biovolume of cyanobacteria was not correlated to any variables tested in the regional model. In contrast, nutrient and food web variables had significant effects on cyanobacterial biovolume in the temporal model. This suggested that factors governing seasonal succession were probably more important for cyanobacteria than variation in reservoir productivity or location.Contrary to previous views, no negative relationship between total biomass of zooplankton and TPB was found in both models, suggesting that the community structure of zooplankton rather than its total biomass mediates top‐down effects. Many predictions of the food web theory remained robust in spite of substantial differences in animal taxonomy and physical environment of Australian ecosystems.