Remote Sensing of the Aquatic Environments

The book highlights recent research efforts in the monitoring of aquatic districts with remote sensing observations and proximal sensing technology integrated with laboratory measurements. Optical satellite imagery gathered at spatial resolutions down to few meters has been used for quantitative estimations of harmful algal bloom extent and Chl-a mapping, as well as winds and currents from SAR acquisitions. The knowledge and understanding gained from this book can be used for the sustainable management of bodies of water across our planet

The dynamics of biological nitrogen fixation in prairie lakes

Nutrient-rich lakes are highly susceptible to cyanobacterial blooms. Nutrient pollution can lead to worsening blooms and the loss of important ecosystem services. A key approach to managing aquatic health has been nutrient control. Although current technologies can remove a large proportion of nutrients from wastewater prior to discharge, agricultural nutrients are difficult to control, as are in-lake sources of nutrients, such as biological nitrogen fixation. The consumption of dissolved inorganic nutrients can be rapid and potentially lead to the depletion of nitrogen stores in highly productive lakes. Reductions in nitrogen loads can be compensated for through nitrogen fixation by select cyanobacteria (diazotrophic taxa) to a variable extent. The goal of this work is to support a better understanding of potential management options for eutrophication and for blooms by better understanding the uniquity of cyanobacterial blooms and the associated roles of nitrogen fixation in time and space. This study is the first to use 15N2-calibrated acetylene reduction bottle assays to measure gross rates of nitrogen fixation in lakes located in southern Saskatchewan, Canada. Nutrient-rich lakes with differing nutrient sources were sampled over the course of one summer. Results indicated that upstream lakes receiving nutrients pulses from land-surface runoff and internal cycling experienced fluctuations in total biomass, predominantly cyanobacteria, and a mid-bloom shift in taxa dominance from diazotrophic to non-diazotrophic taxa. Meanwhile, downstream wastewater-impacted lakes receiving more constant nutrient supplies (in addition to nutrient pulses) were able to maintain more consistent levels of biomass, which were dominated by diazotrophic cyanobacteria. Nitrogen fixation rates were greatest in lakes with fluctuations in biomass, while the lakes with more consistent biomass dominated by diazotrophs actually exhibited relatively low rates of nitrogen fixation. A more intensive study of one upstream lake found that cyanobacteria rapidly increased with elevated water temperatures and increasing PAR. At the onset of the bloom, key nitrogen fixation events co-occurred with transient stratification in limnetic zones. Interestingly, some of the highest seasonal rates of nitrogen fixation occurred in surface scum formations, which were consistently dominated by diazotrophs, suggesting that fixation is important to scums. Although existing work in the region found that nitrogen fixation provides a relatively small proportion nitrogen compared to external and internal cycling, this thesis work shows that diazotrophic cyanobacteria may provide short-term relief from nitrogen depletion. Nitrogen fixation can help support high densities of cyanobacteria, and potentially toxin-producing taxa

Effects of Drinking Water Treatment Processes on Removal of Algal Matter and Subsequent Water Quality

Seasonal algal blooms in drinking water sources have increased significantly over the recent past as a result of increased temperature and nutrient loading in surface water due to agricultural and surface runoff. More than 95% of algal cells can be removed by coagulation and flocculation processes. However, algal organic matter (AOM) is not removed well during coagulation, thus causes several operational challenges in drinking water treatment. This research was conducted to investigate the effectiveness of coagulation, granular activated carbon adsorption, and filtration processes on AOM removal and to evaluate disinfection by-products formation potential with/without UV irradiation. Initially, coagulation performance for the treatment of algae-laden raw water was investigated systematically by central composite design using response surface methodology. The main mechanism of algae and AOM removal was charge neutralization at an optimum pH of around 6.0. Thereafter, the optimum coagulation conditions using alum for AOM of six different algal and cyanobacterial species were determined. The AOM removal by coagulation correlated well with the hydrophobicity of the AOM solution. The disinfection by-product formation potential of the AOM due to chlorination was determined after coagulation. The efficiency and mechanism of AOM removal by granular activated carbon (GAC) adsorption were determined by batch adsorption experiments. The adsorption equilibrium data followed both Langmuir and Freundlich models. The adsorption process followed a pseudo-second-order kinetic model, and the calculated thermodynamic parameters indicated that GAC adsorption for AOM removal was spontaneous and endothermic in nature. The fouling behavior of the microfiltration membranes after GAC adsorption pre-treatment was investigated and the filtration resistance and AOM removal efficiency were determined. The GAC adsorption increased the removal of AOM, decreased membrane fouling, and identified intermediate blocking as the major fouling mechanism of the membrane. The effects of combined low-pressure ultraviolet (LPUV) irradiation and chlorination on the disinfection byproducts (DBPs) formation from AOM was investigated for common algae existed in surface water, AOM degradation was likely promoted by photodegradation of aromatics, and chlorine oxidation/substitution. Insights obtained of this work will help in properly designing and operating the AOM removal and reducing DBPs formation during water treatment of algae-laden source water