Showing papers by "Anas Ghadouani published in 2008"

Application of Hydrogen Peroxide for the Removal of Toxic Cyanobacteria and Other Phytoplankton from Wastewater

Abstract: Phytoplankton blooms containing elevated levels of cyanobacteria are common in wastewatertreatment plants. Microcystis aeruginosa, the most common freshwater cyanobacterial species, produces the hepatotoxin microcystin, which is a threat to human and environmental health. Blooms also affect the viability of treating and reusing water and cause problems when detritus accumulates in pipe and pumping delivery infrastructure. We proposed the application of hydrogen peroxide (H2O2) to induce cyanobacterial cell death. Spectral fingerprinting of phytoplankton into four groups (cyanobacteria, chlorophyta, diatoms, and cryptophyta) allowed for determination of equivalent chlorophyll-a (chl-a) concentrations contributed by photosynthetic pigments, an indicative measure of the photosynthetic activity of each phytoplankton group. This was used to establish the effect of H2O2 addition on phytoplankton in wastewater samples. The lowest H2O2 dose that caused statistically significant exponential decay of phytoplankton groups was approximately 3.0 x 10(-3) g H2O2/microg phytoplankton chl-a. At this dose, cyanobacteria and total phytoplankton exhibited a half-life of 2.3 and 4.5 h, respectively. Cyanobacteria decayed at a rate approximately twice that of chlorophyta and diatoms, and the combined chl-a of all phytoplankton groups decreased to negligible levels within 48 h of H202 application.

Development and persistence of deep chlorophyll maxima in oligotrophic lakes over the summer season

Abstract: Deep chlorophyll maxima (DCM) are common features in temperate and tropical oligo-mesotrophic stratified lakes, where they can account for an important part of the primary production (FEE 1976, CuLLEN 1982, PICK et al. 1984, PEDROSAuo et al. 1987, PADISÁK et al. 2003). However, the mechanisms that lead to the development and persistence of DCMs remain to be fully understood (PEREZ et al. 2002, BuRNETT et al. 2006, SAWATZKY et al. 2006). A number ofhypotheses have been proposed to explain the development an d persistence of DCMs in lakes: (l) the limiting resource hypothesis, stating that DCM is due to in silu algal productivity in the metalimnion, where nutrient supply comes from mineralisation of sinking epilimnetic particles and zooplankton excretion (CARMACHO et al. 2000); (2) the behavioural hypothesis, stating that only mobile or mixotrophic algae species adapted to low light develop in DCM layers (FAHNENSTIEL & GLIME 1983, PEDRos-Auó et al. 1987); (3) the sedimentation hypothesis, stating that sinking of epilimnetic algae over depth along the density gradient generates DCM in the metalimnion (CuLLEN 1982); and (4) the depth-specific zooplankton grazing hypothesis, stating that lower grazing rate in the metalimnion lead to the maintenance ofDCM (PILATI & WuRTSBAUGH 2003). In fact, several ofthese processes may interact to control the development and persistence of DCMs in lakes (RICHERSON et al. 1978, PADISÁK et al. 2003, BURNETT et al. 2006). W e describe the development and persistence of DCMs using high resolution in silu fluorometry in 3 Laurentian lakes (Québec, Canada) during summer 2002. The objective of this study was to evaluate how DCM patterns were related to environmental factors such as photosynthetic active radiation, nutrients, and crustacean zooplankton community.