Shantou University
Department of Science
The Yalgorup lakes, a groundwater-fed system in south-western Australia recognized as a Ramsar wetland, hold significant scientific and conservation value due to the presence of a unique range of lake systems, resident waterfowl and, on... more
The Yalgorup lakes, a groundwater-fed system in south-western Australia recognized as a Ramsar wetland, hold significant scientific and conservation value due to the presence of a unique range of lake systems, resident waterfowl and, on the eastern shore of Lake Clifton, the presence of the only thrombolite reef in the southern hemisphere. Recent concern over changing physico-chemical conditions in the lakes, particularly an increase in salinity, prompted this study: the current status of the inherent thrombolite community is unknown. Salinity, total phosphorous (TP), phosphate, total nitrogen (TN), nitrate, chlorophyll-a and relative abundance of the thrombolite microflora were measured in Lake Clifton to analyse changing conditions in this lake and to determine the effect of these water parameters on the thrombolite community. Comparisons with historical data revealed a significant increase in salinity since 1985 and a possible increase in phosphorus concentrations in the lake in the recent decade, although historical nutrient data are rather sparse. The increased salinity may be due to concentration of lake water through a combination of high evaporation, long-term reduction in rainfall and increased groundwater abstraction. Comparison of the composition of the thrombolite community with historical data indicates a large reduction in relative abundance of Scytonema sp. and other filamentous cyanobacterial species, which are believed to be fundamental for the thrombolite structure. It is concluded the changing physico-chemical environment of the Yalgorup Lakes may have led to the decline in important genera in the thrombolite community; however, the mechanisms underlying this change remain unknown.
In many lakes, zooplankton show a distinct diel vertical migration (DVM) behavior, especially during periods of stratification. Excretion products of these zooplankton could potentially cause an upward nutrient transport and consequent... more
In many lakes, zooplankton show a distinct diel vertical migration (DVM) behavior, especially during periods
of stratification. Excretion products of these zooplankton could potentially cause an upward nutrient transport and consequent nutrient enrichment for phytoplankton in the epilimnion. We quantified the upward transport of phosphorus by the cladoceran Daphnia DVM experimentally by adding a radioactive tracer (33P) to the hypolimnion of large indoor mesocosms and measuring tracer accumulation in the epilimnion over time. During the daytime, when all Daphnia were found in the hypolimnion, no phosphorus transport from the hypolimnion into the epilimnion took place. As soon as the Daphnia started their upward migration, around dusk, we observed a continuous increase in phosphorus concentration in the epilimnion. The amount of phosphorus transported was in a biologically meaningful range. Our results strongly suggest that Daphnia vertical migration presents a continuous nutrient supply for the epilimnion.
of stratification. Excretion products of these zooplankton could potentially cause an upward nutrient transport and consequent nutrient enrichment for phytoplankton in the epilimnion. We quantified the upward transport of phosphorus by the cladoceran Daphnia DVM experimentally by adding a radioactive tracer (33P) to the hypolimnion of large indoor mesocosms and measuring tracer accumulation in the epilimnion over time. During the daytime, when all Daphnia were found in the hypolimnion, no phosphorus transport from the hypolimnion into the epilimnion took place. As soon as the Daphnia started their upward migration, around dusk, we observed a continuous increase in phosphorus concentration in the epilimnion. The amount of phosphorus transported was in a biologically meaningful range. Our results strongly suggest that Daphnia vertical migration presents a continuous nutrient supply for the epilimnion.
1. The vertical distribution of Daphnia in stratified lakes strongly depends on the depth profiles of temperature and food resources. However, ecological requirements for these factors are slightly different for juvenile and adult... more
1. The vertical distribution of Daphnia in stratified lakes strongly depends on the depth profiles of temperature and food resources. However, ecological requirements for these factors are slightly different for juvenile and adult Daphnia.2. Here, I investigated whether food quality influences the habitat selection of Daphnia pulicaria at night and whether the habitat selection of juvenile and adult D. pulicaria is different. Daphnia were allowed to choose their optimal habitat in large, stratified water columns (plankton towers, Plön) that held either the green alga Scenedesmus obliquus (high quality) in the cold hypolimnion (Hypo-treatment) or S. obliquus in the warm epi- and cold hypolimnion (SCEN-treatment) or the non-toxic cyanobacterium Synechococcus elongatus (low quality) in the warm epilimnion and S. obliquus in the cold hypolimnion (SYN treatment).3. When food (S. obliquus) was present only in the hypolimnion (Hypo-treatment), juveniles and adults distributed similarly in the water column and spent most of their time in the interface between the warm and the food rich layer.4. When food was present in the epilimnion and hypolimnion (SCEN- and SYN-treatments), juvenile and adult D. pulicaria moved into the warm and now also food-rich epilimnion, however, the magnitude of this shift depended on the food type and age class of Daphnia. Adult and juvenile D. pulicaria spent most of their time in the epilimnion when food there was of a high quality (S. obliquus; SCEN-treatment). However, compared to the juveniles, adult Daphnia spent significantly more time in the colder hypolimnion when epilimnetic food was of a low quality (S. elongatus; SYN-treament).5. Therefore, habitat selection of adult D. pulicaria was affected by food quality whereas the habitat selection of juveniles was not.6. Additional growth and reproduction experiments show that the food quality is likely to be responsible for the different habitat selection of juveniles and adults in the SYN-treatment.7. In conclusion, my experiments show that D. pulicaria behaviourally reacts to the quality of its food source.
We studied the habitat choice of juvenile and adult Daphnia pulicaria in thermally stratified water columns ( plankton towers) with a deep water algal maximum (DCM). The DCM consisted of either filamentous cyanobacteria (Planktothrix... more
We studied the habitat choice of juvenile and adult Daphnia pulicaria in thermally stratified water columns ( plankton towers) with a deep water algal maximum (DCM). The DCM consisted of either filamentous cyanobacteria (Planktothrix agardhii), non-filamentous Chlorophyceae (Scenedesmus obliquus) or a mixture of both. Adult D. pulicaria spent more time at colder temperatures in the presence of P. agardhii than in the presence of S. obliquus, either as the sole food source or when mixed with P. agardhii. Juvenile D. pulicaria did not show a different habitat choice in the three food treatments. In a fourth treatment, we also determined Daphnia distribution in the absence of food. Comparing the habitat choice of juveniles and adults in each of the four treatments, the latter spent more time at colder temperatures when food was absent or when in the sole presence of P. agardhii. Additional grazing and stable isotopic marker experiments showed that D. pulicaria ingested and assimilated Planktothrix filaments. The results suggest that the differences in habitat choice between adult D. pulicaria in the presence of different food types were influenced by food quality effects: adult Daphnia which move to colder waters in the presence of low quality P. agardhii decrease their metabolic rate and might thus be able to invest more resources into reproduction when environmental conditions improve.
Many freshwater zooplankton species perform a diel vertical migration (DVM) and spend the day within the lower, colder hypolimnion of stratified lakes. Trade-offs that arise from this migration have already attracted much attention and... more
Many freshwater zooplankton species perform a diel vertical migration (DVM) and spend the day within the lower, colder hypolimnion of stratified lakes. Trade-offs that arise from this migration have already attracted much attention and the cold temperature in the hypolimnion is thought to be the main cost of this behaviour. In this study we additionally looked at the extra costs daphnids have from being exposed to a fluctuating temperature regime (cold during the day and warm during the night) which is less well studied until today. In our experiment Daphnia hyalina Leydig and Daphnia magna Straus either spent 24 h in constant warm water (19 °C), 24 h in constant cold water (12 °C), or spent 12 h in warm and 12 h in cold water in an alternating way (fluctuating temperature regime). We expected the values of the life history parameters of Daphnia in the fluctuating temperature regime to be exactly halfway between the values of the life history parameters in the warm and cold treatments because the daphnids spent exactly half of the time in warm water, and half of the time in cold water. Concordant with earlier studies our results showed that age at first reproduction and egg development time were reduced at higher temperatures. In the fluctuating temperature regime the values of both parameters were exactly halfway between the values at permanently warm and cold temperature regimes. In contrast, somatic growth was higher at higher temperatures but was lower in the fluctuating temperature regime than expected from the mean somatic growth rate. This suggests that a fluctuating temperature regime experienced by migrating daphnids in stratified lakes involves additional costs for the daphnids.
Diel vertical migration (DVM) of large zooplankton is a very common phenomenon in the pelagic zone of lakes and oceans. Although the underlying mechanisms of DVM are well understood, we lack experimental studies on the consequences of... more
Diel vertical migration (DVM) of large zooplankton is a very common phenomenon in the pelagic zone of lakes and oceans. Although the underlying mechanisms of DVM are well understood, we lack experimental studies on the consequences of this behaviour for the zooplankton’s food resource—the phytoplankton. As large zooplankton species or individuals migrate downwards into lower and darker water strata by day and upwards into surface layers by night, a huge amount of herbivorous biomass moves through the water column twice a day. This migration must have profound consequences for the phytoplankton. It is generally assumed that migration supports an enhanced phytoplankton biomass and a change in the composition of the phytoplankton community towards smaller, edible algae in the epilimnion of a lake. We tested this assumption for the first time in field experiments by comparing phytoplankton biomass and community assemblage in mesocosms with and without artificially migrating natural stocks of Daphnia hyalina. We show that DVM can enhance phytoplankton biomass in the epilimnion and that it has a strong impact on the composition of a phytoplankton community leading to an advantage for small, edible algae. Our results support the idea that DVM of Daphnia can have strong effects on phytoplankton dynamics in a lake.
Diel vertical migration (DVM) of herbivorous zooplankton is a widespread behavioural phenomenon in freshwater ecosystems. So far only little attention has been paid to the impact of DVM on the phytoplankton community in the epilimnion.... more
Diel vertical migration (DVM) of herbivorous zooplankton is a widespread behavioural phenomenon in freshwater ecosystems. So far only little attention has been paid to the impact of DVM on the phytoplankton community in the epilimnion. Some theoretical models predict that algal population growth in the epilimnion should depend on the herbivores’ migration and grazing patterns: even if migrating zooplankton consume the same total amount of algae per day in the epilimnion as non-migrating zooplankton, nocturnal grazing should result in enhanced algal growth and favour algal species with high intrinsic growth rates over species with lower intrinsic growth rates. To test these hypotheses we performed experiments in which several algal species were confronted with different feeding regimes of Daphnia. In the experiments algal growth did not only depend on the absolute time of grazing but was comparatively higher when grazing took place only during the night, even when the grazing pressure was the same. Furthermore, algal species with higher intrinsic growth rates had higher advantages when being grazed upon only discontinuously during the night than algal species with a smaller intrinsic growth rate. The grazing pattern itself was an important factor for relative algal performance.
Despite substantial divergence, the European toads Bombina bombina and Bombina variegata (Anura: Discoglossidae) interbreed freely wherever their parapatric distributions adjoin. Natural selection that stabilizes the resulting hybrid... more
Despite substantial divergence, the European toads Bombina bombina and Bombina variegata (Anura: Discoglossidae) interbreed freely wherever their parapatric distributions adjoin. Natural selection that stabilizes the resulting hybrid zones should rest in part on the adaptation to different breeding habitat of the pure taxa. While B. bombina lays its eggs in semipermanent ponds, B. variegata is a typical puddle breeder. Here, we investigate whether selection for rapid larval development in B. variegata has resulted in the loss of effective antipredator defenses, thus excluding this species from predator-rich ponds. We collected adults from four populations in Romania (two for each taxon) and reared the offspring from four crosses per population in the laboratory either in the presence or in the absence of caged odonate predators (Aeshna cyanea). In predation trials, we found no taxon difference in mortality rate among tadpoles that had been reared with predators.
The resilience of B. variegata tadpoles may have been due to their remarkable phenotypic plasticity. In both taxa, predator presence led to the development of a higher tail fin, which has been shown to reduce predation rates in other amphibians. This response was much stronger in B. variegata than in B. bombina. Moreover, differences between the two B. variegata populations in terms of laboratory predation rates and levels of plasticity correlated with predator abundance at the collection sites so as to suggest local adaptation in predator defenses. Finally, delayed metamorphosis in the predator-induced morphs of both taxa implies a cost to the defense. Given the heterogeneity of temporary habitat in terms of desiccation rate and predator occurrence, the greater amount of phenotypic plasticity in B. variegata fits predictions of life history theory. At the same time, our results leave the question unresolved as to why this species avoids ponds.
The resilience of B. variegata tadpoles may have been due to their remarkable phenotypic plasticity. In both taxa, predator presence led to the development of a higher tail fin, which has been shown to reduce predation rates in other amphibians. This response was much stronger in B. variegata than in B. bombina. Moreover, differences between the two B. variegata populations in terms of laboratory predation rates and levels of plasticity correlated with predator abundance at the collection sites so as to suggest local adaptation in predator defenses. Finally, delayed metamorphosis in the predator-induced morphs of both taxa implies a cost to the defense. Given the heterogeneity of temporary habitat in terms of desiccation rate and predator occurrence, the greater amount of phenotypic plasticity in B. variegata fits predictions of life history theory. At the same time, our results leave the question unresolved as to why this species avoids ponds.
Toxic cyanobacterial blooms represent a serious hazard to environmental and human health, and the management and restoration of affected waterbodies can be challenging. While cyanobacterial blooms are already a frequent occurrence, in the... more
Toxic cyanobacterial blooms represent a serious hazard to environmental and human health, and the management and restoration of affected waterbodies can be challenging. While cyanobacterial blooms are already a frequent occurrence, in the future their incidence and severity are predicted to increase due to climate change. Climate change is predicted to lead to increased temperature and changes in rainfall patterns, which will both have a significant impact on inland water resources. While many studies indicate that a higher temperature will favour cyanobacterial bloom occurrences, the impact of changed rainfall patterns is widely under-researched and therefore less understood.This review synthesizes the predicted changes in rainfall patterns and their potential impact on inland waterbodies, and identifies mechanisms that influence the occurrence and severity of toxic cyanobacterial blooms.It is predicted that there will be a higher frequency and intensity of rainfall events with longer drought periods in between. Such changes in the rainfall patterns will lead to favourable conditions for cyanobacterial growth due to a greater nutrient input into waterbodies during heavy rainfall events, combined with potentially longer periods of high evaporation and stratification. These conditions are likely to lead to an acceleration of the eutrophication process and prolonged warm periods without mixing of the water column. However, the frequent occurrence of heavy rain events can also lead to a temporary disruption of cyanobacterial blooms due to flushing and de-stratification, and large storm events have been shown to have a long-term negative effect on cyanobacterial blooms. In contrast, a higher number of small rainfall events or wet days can lead to proliferation of cyanobacteria, as they can rapidly use nutrients that are added during rainfall events, especially if stratification remains unchanged.With rainfall patterns changing, cyanobacterial toxin concentration in waterbodies is expected to increase. Firstly, this is due to accelerated eutrophication which supports higher cyanobacterial biomass. Secondly, predicted changes in rainfall patterns produce more favourable growth conditions for cyanobacteria, which is likely to increase the toxin production rate. However, the toxin concentration in inland waterbodies will also depend on the effect of rainfall events on cyanobacterial strain succession, a process that is still little understood. Low light conditions after heavy rainfall events might favour non-toxic strains, whilst inorganic nutrient input might promote the dominance of toxic strains in blooms. This review emphasizes that the impact of changes in rainfall patterns is very complex and will strongly depend on the site-specific dynamics, cyanobacterial species composition and cyanobacterial strain succession. More effort is needed to understand the relationship between rainfall patterns and cyanobacterial bloom dynamics, and in particular toxin production, to be able to assess and mediate the significant threat cyanobacterial blooms pose to our water resources.► Rainfall characteristics are important determinants for bloom occurrence. ► High intensity rainfall events and droughts will increase bloom occurrences. ► Higher frequency of events that disrupt stratification will reduce toxic bloom occurrence. ► Predictive ability of future toxin concentrations in the water is limited. ► Effect of rainfall on food web structures that control blooms is little understood.
- by Anas Ghadouani and +1
- •
- Cyanobacteria, Review, Rainfall
Determining the trophic niche width of an animal population and the relative degree to which a generalist population consists of dietary specialists are long-standing problems of ecology. It has been proposed that the variance of stable... more
Determining the trophic niche width of an animal population and the relative degree to which a generalist population consists of dietary specialists are long-standing problems of ecology. It has been proposed that the variance of stable isotope values in consumer tissues could be used to quantify trophic niche width of consumer populations. However, this promising idea has not yet been rigorously tested. By conducting controlled laboratory experiments using model consumer populations (Daphnia sp., Crustacea) with controlled diets, we investigated the effect of individual- and population-level specialisation and generalism on consumer d13C mean and variance values. While our experimental data follow general expectations, we extend current qualitative models to quantitative predictions of the dependence of isotopic variance on dietary correlation time, a measure for the typical time over which a consumer changes its diet. This quantitative approach allows us to pinpoint possible procedural pitfalls and critical sources of measurement uncertainty. Our results show that the stable isotope approach represents a powerful method for estimating trophic niche widths, especially when taking the quantitative concept of dietary correlation time into account.
"Cyanobacteria and their toxins (e.g., microcystins) commonly occur in waste stabilization ponds (WSPs), and are a risk to human and ecological health. Although many studies have investigated their removal from batch cultures and drinking... more
"Cyanobacteria and their toxins (e.g., microcystins) commonly occur in waste stabilization ponds (WSPs), and are a risk to human and ecological health. Although many studies have investigated their removal from batch cultures and drinking water reservoirs, few have been conducted into their removal from WSPs. Hydrogen peroxide (H2O2) has been reported as a benign chemical to decrease cyanobacteria. This study reports on the applicability of the use of H2O2 for the removal of cyanobacteria and microcystins from wastewater. An approach is described which presents an economical and rapid method for determining
the appropriate dosage for full-scale application to WSPs. Evidence is presented from full-scale trials that indicate that where H2O2 is added upwind, wind-induced mixing during application is sufficient for treatment of an entire WSP. However, our data also shows that reduction of cyanobacteria is higher
in the upper layer of WSPs. This may potentially lead to an overestimation of the overall reduction if only surface samples are considered. As H2O2 significantly decreased the cyanobacterial fraction and microcystin concentrations within days of application, and growth of eukaryote phytoplankton increased, we suggest that H2O2 may be an efficient algicide treatment in WSPs. The longevity of this effect was in the order of three weeks, indicating that repeated application might be necessary to avoid the development of renewed dominance of cyanobacteria. However, such a repeated application needs close monitoring, as, at this stage, the information on the effect on other organisms in full-trials at WSPs is limited. For instance, although recent laboratory experiments suggest that the average doses used in experiments could lead to death of zooplankton within 24 h, this is unlikely to happen in WSPs due to the zooplanktons’ ability to actively avoid unfavourable conditions. In summary, this paper offers WSP operators the possibility to assess the benefit of using H2O2 to rapidly suppress cyanobacterial and microcystin concentrations and hence prevent them from entering the environment."
the appropriate dosage for full-scale application to WSPs. Evidence is presented from full-scale trials that indicate that where H2O2 is added upwind, wind-induced mixing during application is sufficient for treatment of an entire WSP. However, our data also shows that reduction of cyanobacteria is higher
in the upper layer of WSPs. This may potentially lead to an overestimation of the overall reduction if only surface samples are considered. As H2O2 significantly decreased the cyanobacterial fraction and microcystin concentrations within days of application, and growth of eukaryote phytoplankton increased, we suggest that H2O2 may be an efficient algicide treatment in WSPs. The longevity of this effect was in the order of three weeks, indicating that repeated application might be necessary to avoid the development of renewed dominance of cyanobacteria. However, such a repeated application needs close monitoring, as, at this stage, the information on the effect on other organisms in full-trials at WSPs is limited. For instance, although recent laboratory experiments suggest that the average doses used in experiments could lead to death of zooplankton within 24 h, this is unlikely to happen in WSPs due to the zooplanktons’ ability to actively avoid unfavourable conditions. In summary, this paper offers WSP operators the possibility to assess the benefit of using H2O2 to rapidly suppress cyanobacterial and microcystin concentrations and hence prevent them from entering the environment."
""The increasing incidence of toxic cyanobacterial blooms, together with the difficulties to reliably predict cyanobacterial toxin (e.g. microcystins) concentration, has created the need to assess the predictive ability and variability of... more
""The increasing incidence of toxic cyanobacterial blooms, together with the difficulties to reliably predict cyanobacterial toxin (e.g. microcystins) concentration, has created the need to assess the predictive ability and variability of the cyanobacterial biomass– microcystin relationship, which is currently used to assess the risk to human and ecosystems health. To achieve this aim, we assessed the relationship between cyanobacterial biomass and microcystin concentration on a spatiotemporal scale by quantifying the concentration of cyanobacterial biomass and microcystin in eight lakes over 9 months. On both a temporal and spatial scale, the variability of microcystin concentration
exceeded that of cyanobacterial biomass by up to four times. The relationship between cyanobacterial biomass and microcystin was weak and site specific. The variability of cyanobacterial biomass only explained 25 % of the variability in total microcystin concentration and 7 % of the variability of cellular microcystin concentration. Although a significant correlation does not always
imply real cause, the results of multiple linear regression analysis suggest that the variability of cyanobacterial biomass and cellular microcystin concentration is influenced by salinity and total phosphorus, respectively. The weak cyanobacterial biomass–microcystin relationship, coupled with the fact that microcystin was present in concentrations exceeding the WHO drinking water
guidelines (1 μgL−1) in most of the collected samples, emphasizes the high risk of error connected to the traditional indirect microcystin risk assessment method.""
exceeded that of cyanobacterial biomass by up to four times. The relationship between cyanobacterial biomass and microcystin was weak and site specific. The variability of cyanobacterial biomass only explained 25 % of the variability in total microcystin concentration and 7 % of the variability of cellular microcystin concentration. Although a significant correlation does not always
imply real cause, the results of multiple linear regression analysis suggest that the variability of cyanobacterial biomass and cellular microcystin concentration is influenced by salinity and total phosphorus, respectively. The weak cyanobacterial biomass–microcystin relationship, coupled with the fact that microcystin was present in concentrations exceeding the WHO drinking water
guidelines (1 μgL−1) in most of the collected samples, emphasizes the high risk of error connected to the traditional indirect microcystin risk assessment method.""
- by Anas Ghadouani and +1
- •
Toxic cyanobacterial blooms can strongly affect freshwater food web structures. However, little is known about how the patchy occurrence of blooms within systems affects the spatial distribution of zooplankton communities. We studied this... more
Toxic cyanobacterial blooms can strongly affect freshwater food web structures. However, little is known about how the patchy occurrence of blooms within systems affects the spatial distribution of zooplankton communities. We studied this by analysing zooplankton community structures in comparison with the spatially distinct distribution of a toxic Microcystis bloom in a small, shallow, eutrophic lake. While toxic Microcystis was present at all sites, there were large spatial differences in the level of cyanobacterial biomass and in the zooplankton communities; sites with persistently low cyanobacterial biomass displayed a higher biomass of adult Daphnia and higher zooplankton diversity than sites with persistently high cyanobacterial biomass. While wind was the most likely reason for the spatially distinct occurrence of the bloom, our data indicate that it was the differences in cyanobacterial biomass that caused spatial differences in the zooplankton community structures. Overall, our study suggests that even in small systems with extensive blooms ‘refuge sites’ exist that allow large grazers to persist, which can be an important mechanism for a successful re-establishment of the biodiversity in an ecosystem after periods of cyanobacterial blooms.
- by Elke S Reichwaldt and +1
- •
""Microcystins are produced by several species of cyanobacteria and can harm aquatic organisms and human beings. Sediments have the potential to contribute to the removal of dissolved microcystins from the water body through either... more
""Microcystins are produced by several species of cyanobacteria and can harm aquatic organisms and human beings. Sediments have the potential to contribute to the removal of dissolved microcystins from the water body through either adsorption to sediment particles or biodegradation by the sediment’s bacterial community. However, the relative contribution of these two removal processes remains unclear and little is known about the significance of sediment’s overall contribution. To study this, changes in the concentration of microcystin-LR (MCLR) in the presence of sediment, sediment with microbial inhibitor, and non-sterile lake water were quantified in a laboratory experiment. Our results show that, in the presence of sediment, MCLR concentration decreased significantly in an exponential way without a lag phase, with an average degradation rate of 9 mg d-1 in the first 24 h. This indicates that sediment can contribute to the removal of MCLR from the water immediately and effectively. Whilst both, the biodegradation and adsorption ability of the sediment contributed significantly to the removal of MCLR from the water body, biodegradation was shown to be the dominant removal process. Also, the sediment’s ability to degrade MCLR from the water was shown to be faster than the biodegradation through the bacterial community in the water. The present study emphasizes the importance of sediments for the removal of microcystins from a water body. This will be especially relevant in shallow systems where the interaction between the water and the sediment is naturally high. Our results are also useful for the application of sediments to remove microcystins at water treatment facilities.""
- by Haihong Song and +2
- •
- Adsorption, Biodegradation, Cyanobacterial Toxins, Microcystin
Microcystins are toxins produced by cyanobacteria. They occur in aquatic systems across the world and their occurrence is expected to increase in frequency and magnitude. As microcystins are hazardous to humans and animals, it is... more
Microcystins are toxins produced by cyanobacteria. They occur in aquatic systems across the world and their occurrence is expected to increase in frequency and magnitude. As microcystins are hazardous to humans and animals, it is essential to understand their fate in aquatic systems in order to control health risks. While the occurrence of microcystins in sediments has been widely reported, the factors influencing their occurrence, variability, and spatial distribution are not yet well understood. Especially in shallow lakes, which often develop large cyanobacterial blooms, the spatial variability of toxins in the sediments is a complex interplay between the spatial distribution of toxin producing cyanobacteria, local biological, physical and chemical processes, and the re-distribution of toxins in sediments through wind mixing. In this study, microcystin occurrence in lake sediment, and their relationship with biological and physicochemical variables were investigated in a shallow, eutrophic lake over five months. We found no significant difference in cyanobacterial biomass, temperature, pH, and salinity between the surface water and the water directly overlying the sediment (hereafter ‘overlying water’), indicating that the water column was well mixed. Microcystins were detected in all sediment samples, with concentrations ranging from 0.06 to 0.78 µg equivalent microcystin-LR/g sediments (dry mass). Microcystin concentration and cyanobacterial biomass in the sediment was different between sites in three out of five months, indicating that the spatial distribution was a complex interaction between local and mixing processes. A combination of total microcystins in the water, depth integrated cyanobacterial biomass in the water, cyanobacterial biomass in the sediment, and pH explained only 21.1% of the spatial variability of microcystins in the sediments. A more in-depth analysis that included variables representative of processes on smaller vertical or local scales, such as cyanobacterial biomass in the different layers and the two fractions of microcystins, increased the explained variability to 51.7%. This highlights that even in a well-mixed lake, local processes are important drivers of toxin variability. The present study emphasises the role of the interaction between water and sediments in the distribution of microcystins in aquatic systems as an important pathway which deserves further consideration.
Toxic cyanobacterial blooms in urban lakes present serious health hazards to humans and animals and require effective management strategies. Managing such blooms requires a sufficient understanding of the controlling environmental... more
Toxic cyanobacterial blooms in urban lakes present serious health hazards to humans and animals and require effective management strategies. Managing such blooms requires a sufficient understanding of the controlling environmental factors. A range of them has been proposed in the literature as potential triggers for cyanobacterial biomass development and cyanotoxin (e.g. microcystin) production in freshwater systems. However, the environmental triggers of cyanobacteria and microcystin variability remain a subject of debate due to contrasting findings. This issue has raised the question of whether the relevance of environmental triggers may depend on site-specific combinations of environmental factors. In this study, we investigated the site-specificity of environmental triggers for cyanobacterial bloom and microcystin dynamics in three urban lakes in Western Australia. Our study suggests that cyanobacterial biomass, cyanobacterial dominance and cyanobacterial microcystin content variability were significantly correlated to phosphorus and iron concentrations. However, the correlations were different between lakes, thus suggesting a site specific effect of these environmental factors. The discrepancies in the correlations could be explained by differences in local nutrient concentration. For instance, we found no correlation between cyanobacterial fraction and total phosphorous (TP) in the lake with the highest TP concentration, while correlations were significant and negative in the other two lakes. In addition, our study indicates that the difference of the correlation between total iron (TFe) and the cyanobacterial fraction between lakes might have been a consequence of differences in the cyanobacterial community structure, specifically the presence or absence of nitrogen-fixing species. In conclusion, our study suggests that identification of significant environmental factors under site-specific conditions is an important
strategy to enhance successful outcomes in cyanobacterial
bloom control measures.
strategy to enhance successful outcomes in cyanobacterial
bloom control measures.
The occurrence of cyanobacteria and microcystin is highly dynamic in natural environments and poses one of the biggest challenges to water resource management. While a number of drivers are known to be responsible for the occurrence... more
The occurrence of cyanobacteria and
microcystin is highly dynamic in natural environments
and poses one of the biggest challenges to water resource
management. While a number of drivers are known to be
responsible for the occurrence of cyanobacterial blooms,
the drivers of microcystin production are not adequately
known. This study aims to quantify the effects of the
changes in the structures of phytoplankton and
cyanobacterial communities on the dynamics of
microcystin production under highly variable nutrient concentration.
In our study, nutrient variability could explain
64 % of the variability in microcystin production. When
changes in the fractions of non-cyanobacteria versus
cyanobacteria genera were additionally included, 80 %
of the variability in microcystin production could be explained;
under high nutrient concentrations, noncyanobacterial
phytoplankton groups were dominant over
cyanobacteria and cyanobacteria produced more toxins. In
contrast, changes in the cyanobacterial community structures
could only explain a further 4 % of the dynamics of
microcystin production. As such, the dominance of noncyanobacterial
groups appears to be a useful factor to
explain microcystin occurrence in addition to traditionally
used factors such as absolute cyanobacterial cell numbers,
especially when the nutrient regime is taken into account.
This information could help to further refine the risk
assessment frameworks which are currently used to manage
the risk posed by cyanobacterial blooms.
microcystin is highly dynamic in natural environments
and poses one of the biggest challenges to water resource
management. While a number of drivers are known to be
responsible for the occurrence of cyanobacterial blooms,
the drivers of microcystin production are not adequately
known. This study aims to quantify the effects of the
changes in the structures of phytoplankton and
cyanobacterial communities on the dynamics of
microcystin production under highly variable nutrient concentration.
In our study, nutrient variability could explain
64 % of the variability in microcystin production. When
changes in the fractions of non-cyanobacteria versus
cyanobacteria genera were additionally included, 80 %
of the variability in microcystin production could be explained;
under high nutrient concentrations, noncyanobacterial
phytoplankton groups were dominant over
cyanobacteria and cyanobacteria produced more toxins. In
contrast, changes in the cyanobacterial community structures
could only explain a further 4 % of the dynamics of
microcystin production. As such, the dominance of noncyanobacterial
groups appears to be a useful factor to
explain microcystin occurrence in addition to traditionally
used factors such as absolute cyanobacterial cell numbers,
especially when the nutrient regime is taken into account.
This information could help to further refine the risk
assessment frameworks which are currently used to manage
the risk posed by cyanobacterial blooms.
- by Elke S Reichwaldt and +1
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- Cyanobacteria, Allelopathy, Public Health, Phytoplankton
Urbanization strongly impacts aquatic ecosystems by decreasing water quality and altering water cycles. Today, much effort is put towards the restoration and conservation of urban waterbodies to enhance ecosystem service provision,... more
Urbanization strongly impacts aquatic ecosystems by decreasing water quality and altering water cycles. Today, much effort is put towards the restoration and conservation of urban waterbodies to enhance ecosystem service provision, leading to liveable and sustainable cities. To enable a sustainable management of waterbodies, the quantification of the temporal and spatial variability of pollution levels and biogeochemical processes is essential. Stable isotopes have widely been used to identify sources of pollution in ecosystems. For example, increased nitrogen levels in waterbodies are often accompanied with a higher nitrogen stable isotope signature (δ15N), which can then be detected in higher trophic levels such as mussels. The main aim of this study was to assess the suitability of nitrogen stable isotopes as measured in mussels (Mytilus edulis), as an indicator able to resolve spatial and temporal variability of nitrogen pollution in an urban, tidally influenced estuary (Swan River estuary in Western Australia). Nitrogen concentrations were generally low and nitrogen stable isotope values of nitrate throughout the estuary were well within natural values of uncontaminated groundwater, organic nitrate from soils, or marine-derived sources, indicating groundwater inflow rather than pollution by human activity was responsible for differences between sites. The δ15N signature in mussels was very stable over time within each site which indicated that mussels can be used as time-integrated sentinel organisms in urban systems. In addition, our study shows that the nature of the relationship between δ15N in the mussels and the nitrate in the water can provide insights into site-specific biogeochemical transformation of nutrients. We suggest that mussels and other sentinel organisms can become a robust tool for the detection and characterization of the dynamics of a number of emerging anthropogenic pollutants of concern in urban water systems.