# Solving Nuisance Cyanobacteria Eutrophication Through Biotechnology
## 5 Discussion  
Intensive algal blooms in coastal lagoons are indicative of the eutrophication phenomenon, which is related to water nutrient levels. The most cases of eutrophication in coastal lagoons are the result of cyanobacteria blooms, like our paradigm in the Lafri Lagoon. These cyanobacterial blooms seem to prevent optimal ecosystem function, as indicated by water quality assessments [44] and the relatively low fish production [45]. The cyanobacterial biomass tolerates high light intensities and performs photoadaptation to high light conditions [46]. The variability of the fluorescence induction measurements showed a physiologically heterogeneous or differently stressed material possibly because of the onset of decomposition procedure and sedimentation. This is also in agreement with relatively low values of maximum quantum yield (Fv/Fm = 0.42) and of photosynthetic performance indices (PI\({}_{\text{abc}}\) = 0.32, PI\({}_{\text{total}}\) = 2.67) of algal biomass in the Lafri lagoon (Figure 2). The sedimentation of the algae may enhance the establishment of anoxic conditions in the lagoon water; this may also be because of the high H\({}_{2}\) production, which expels the rest of oxygen from the water phase [47]. Our results in Figures 5 and 6 indicate that the cyanobacterial bloom biomass had the ability to establish hypoxic conditions and to produce H\({}_{2}\) in a closed illuminated system that mimics natural conditions. Two mechanisms have been proposed in green algae for H\({}_{2}\) production. The first is the photosystem II (PSII) dependent pathway, which under anoxic conditions transfers electrons from water through photosystem II (PSII) and photosystem I (PSI) to ferredoxin (Fd), and at the end to hydrogenase that reduces protons to H\({}_{2}\)[30; 48]. The second pathway is the PSII independent pathway that depends on the metabolic oxidation of organic compounds (glucose and other carbohydrates) coupled to PSI through the plastoquinone (PQ) pool and results in H\({}_{2}\) production [49]. Except for the above photobiological hydrogen production pathways, there is also another known as dark fermentation. The majority of microbial hydrogen production through dark fermentation is driven by the anaerobic metabolism of pyruvate, formed during the catabolism of various organic substances [50; 51]. In cyanobacteria, three different hydrogenase enzymes have been identified: a nitrogenase, a reversible bidirectional hydrogenase, and an uptake hydrogenase [31; 52]. Nitrogenase produces hydrogen as a side reaction while fixing N\({}_{2}\). Our results (Figure 6) clearly show that the increase in H\({}_{2}\) production is combined with N\({}_{2}\) fixation, which confirms (in our paradigm) the participation also of nitrogenases in the procedure of H\({}_{2}\) production from the particular algal bloom biomass. Reprogramming of the above eutrophication procedure could be a biotechnological application schematically presented in Figure 7. The absolute negative impact of eutrophication consists of different steps, some of which, if we observe them individually, have a positive impact and could be important for biotechnological applications: 1) The excess amount of nutrients and fertilizers that flush from land to lagoon will be transformed by the algae into massive algal biomass that biofilers and improves the water quality of the lagoon [15; 53]. 2) Because of the hypertrophication, there is no limitation of nutrients that lead to a high production of organic matter in algal biomass in the form of carbohydrates (sugars) and lipids (Figures 4 and 5) that could be easily converted into biofuels. These two steps of the eutrophication procedure are very important for the water quality but also for biotechnological applications, especially for the production of 3 rd generation biofuels, without any cost. The last step of algal blooms is the decomposition and sedimentation of the algal material.