Anas Ghadouani
Anas is a Professor of Environmental Engineering at the University of Western Australia and is the leader of the Aquatic Ecology and Ecosystem Studies Group. His research interest include limnology and ecosystem studies, Ecological Engineering, Wastewater management, algal blooms and cyanobacterial toxins.
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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.""
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."
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.
Simple hydrograph analysis could not separate treatment effects on the water table response. Subsequent statistical analysis revealed that 20-30% of the variability in the water table data over the 12 year study period was attributable to the alley farming experiment. To futher investigate the effect of the experiment on groundwater response, additional hydrograph analysis was conducted to compare the trends in the control piezometers in relation to those located within the belts. A difference of 0.9 m was observed between the mean groundwater levels in the control piezometers and the mean levels in the perennial belt piezometers. For a mean specific yield of 0.03 m(3) m(-3) (standard deviation of 0.03 m(3) m(-3)) this equates to an additional average annual water use of 27 mm yr(-1) (standard deviation of 33 mm yr(-1)) by the perennial agroforestry system. It is concluded that declining annual rainfall is the principal control on hydrograph response at the site, whilst perennial biomass development has a lesser impact on water table depth.
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.""
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."
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.
Simple hydrograph analysis could not separate treatment effects on the water table response. Subsequent statistical analysis revealed that 20-30% of the variability in the water table data over the 12 year study period was attributable to the alley farming experiment. To futher investigate the effect of the experiment on groundwater response, additional hydrograph analysis was conducted to compare the trends in the control piezometers in relation to those located within the belts. A difference of 0.9 m was observed between the mean groundwater levels in the control piezometers and the mean levels in the perennial belt piezometers. For a mean specific yield of 0.03 m(3) m(-3) (standard deviation of 0.03 m(3) m(-3)) this equates to an additional average annual water use of 27 mm yr(-1) (standard deviation of 33 mm yr(-1)) by the perennial agroforestry system. It is concluded that declining annual rainfall is the principal control on hydrograph response at the site, whilst perennial biomass development has a lesser impact on water table depth.