# Solving Nuisance Cyanobacteria Eutrophication Through Biotechnology
## 1 Introduction  
The use of fertilisers in agriculture [1] and the atmospheric precipitations [2] have increased nitrate and phosphate concentrations in rivers, lakes, and coastal lagoons in the last decades [3]. As a result, undesirable algal growth (bloom), frequently cyanobacteria have been observed [4; 5], a phenomenon that may further be promoted by global warming [6; 7]. The algal blooms often cover the surface and increase the turbidity of waters, inhibiting the solar irradiance from supplying energy to the benthic zone and the primary producers of photosynthesis, which then disappear [8; 9]. When the algal material dies and the decomposition process starts to induce oxygen depletion (anoxia), and in turn may lead to the death of aquatic lives and to a range of other effects that reduces biodiversity [10]. Excessive algal growth (blooms) in several coastal lagoons due to an excess of nutrient loads is seen as a problem by many stakeholders, such as fisheries, municipal administration, and nature conservationists [11; 12]. Although efforts should be undertaken in reducing nutrient loads, to avoid long recovery periods the floating algal biomass should be harvested [13]; it could also help to reduce nutrient water concentration, especially phosphate and nitrogen, which in turn, would improve water quality and minimize eutrophication [10; 14; 15]. The control of algal blooms could help to ensure adequate oxygen levels for the water fauna and maintain biodiversity and fish production, thereby keeping the ecosystem functioning and productive [16]. As far as is concerned, the harvested algal biomass is important to further explore the existing technologies as for example composite [17], bioethanol [18] and biomethane [19] production which economic feasibility has not yet been confirmed [20]. The third generation of biofuels, based on improvements in the production of biomass, is taking advantage of specially engineered energy crops such as algae which are harvested or cultivated to act as a low-cost, high-energy and entirely renewable feedstock. They have been successfully used as feedstock in biohydrogen (H\({}_{2}\)) production recently, because of their rich carbohydrate content [21; 22; 23]. Algae can fix CO\({}_{2}\) in the form of carbohydrates in the cytoplasm and in the form of lipids in cell membranes [24]. Carbohydrates are stored in the form of glycogen in cyanobacteria, starch in green and red algae, and \(\beta\)-glucans in brown algae [25; 26]. The use of algae could help to reduce the dependency on ground-based biomass, especially energy crops, and help diversify the possible input materials for bioenergy production [27; 28]. It is known that molecular hydrogen will be the optimal energy carrier of the future and contribute to the growth of the world's economy by facilitating a stable supply of energy. Hydrogen combustion yields only water thus reducing emissions of carbon dioxide in the atmosphere [29]. At present, most of the world's hydrogen is produced by reforming fossil fuels, which is accompanied by the release of carbon into the environment. However, hydrogen might be produced from non-fossil renewable resources. In this respect, the light-induced conversion of water into hydrogen and oxygen is preferable. One of the prospective ways of obtaining hydrogen from water at the expense of solar energy is to use photosynthetic microorganisms capable of hydrogen production, such as cyanobacteria and green algae [21; 30; 31; 32]. The aim of this paper was to study the species' composition, photosynthetic pigments (Chl-a and Chl-c) and performance (OJIP-kinetics and JIP-test parameters), biochemistry (lipids and carbohydrates composition), and hydrogen production potential of _Limmoraphis_ (_Lyngbya_) biomass collected from a hyper-europhicated lagoon belonging in the Porto-Lagos Lagoon and Vistonis Lake complex, Thrace Region, in Greece.