Prevention of Harmful Algal Blooms by Control of Growth Parameters

Harmful Algal Blooms (HAB) were investigated to prevent the outbreak of HAB in both freshwater and seawater. Parameters inducing HAB were volcanic eruption, sunlight, aeolian dust, environmental factors (current, pH, dissolved oxygen, food web, turbulence, growth phase), enzyme, iron, nutrients (carbon, nitrogen, phosphorus, sulfur, silicon, minerals) while the critical growth parameter for the outbreak of HAB was iron (Fe). HAB development was halted in freshwater and seawater due to the sulfur compounds (H2S, sulfates) inducing the deficiency of the dissolved Fe in the water. The atomic ratio of N/P is commonly known to be 16/1 in freshwater and 176/1 in seawater for HAB. Therefore, nitrogen can be a relatively limiting factor in seawater while phosphorus in freshwater. HAB could be prevented by control of growth parameters such as pH, temperature, sunlight, turbulence, nitrogen, phosphorus, iron, and sulfur compounds prior to reaching the early exponential phase of algal growth.


Introduction
Harmful algae have been the subjects of scientific and societal interest for centuries. There are harmful algal blooms (HAB) in both freshwater and seawater. This is because blooms of toxic dinoflagellates, which are known as "red tides", cause a variety of deleterious effects on aquatic ecosystems. These include negative aesthetic effects such as beach fouling, oxygen deficiency, clogging of fish gills, or poisoning of various organisms [1], as observed recently in Florida [2]. Red tides of Chattonella causing massive fish kills have been recorded in Japan, China, USA (Florida), and South Australia. Chattonella spp. has also been observed T.-J. Kim in Southeast Asia, New Zealand, Brazil, and Europe (North Sea). Red tides of H. akashiwo accompanied by fish kills of salmon and yellowtail have occurred in Japan, Canada (British Columbia), New Zealand, Chile, and Scotland. The mechanism by which Chattonella spp. kill fish remains unclear, but suffocation due to gill tissue damage was the ultimate cause of fish death [3]. Kim [4] postulated that HAB occur only if the environmental factors such as light, nutrients, calm water surface layer, temperature, and pH could be simultaneously satisfied with the requirements of the mineral ions supplied by the Asian dust as enzymatic cofactors for the rapid bio-synthesis of the macromolecules during HAB within limited area. The present study examined the prevention of HAB by control of growth parameters including the iron (Fe) in global aeolian dust and water as the key initiator for HAB while sulfur compounds (S) (H 2 S, sulfates) induced Fe deficiency in the water due to a chemical reaction as sedimentary insoluble FeS/FeS 2 for prevention of HAB.

Distribution of Fe and Chlorophyll-a in Freshwater
Samples of the Asian dust were collected at Anmyon Island (36˚34'3"N, 126˚19'45.6"E) nearby Seoul in South Korea by an air pollution monitoring equipment (Tisch Environmental Inc.). Figure 1 showed the weekly distribution of Fe concentration in the Asian dust (red color) and chlorophyll-a in Daechung Lake (blue color) in South Korea from January 2006 to December 2012. Climate condition was clear along the west coast of the Korean Peninsula. Iron was measured by ICP at Korean Basic Science Support Center while chlorophyll-a was determined by method of the standard process test for water contamination. The mean lag times each year between the peak of the Fe concentration and the peak of the chlorophyll-a concentration were shown as follows: 2006 (1. The cumulative concentration of Fe in the Asian dust was determined each year by the integration between weekly time intervals defined as below. ( ) ( ) 11 1 Fe Fe = ( ) ( ) ( ) 12 1 2 Fe Fe Fe = + ( ) ( ) ( ) ( )   freshwater and seawater so long as the weekly distribution of Fe concentration in the desert dust was available in advance.

Determination of On-Line Cell Concentration of Cochlonidium polykrikoides
Indonesia is a good reservoir for the growth of Cochlonidium polykrikoides, as shown in Figure 3, due to the following reasons; 1) Many volcanoes (127) to supply nutrients during volcanic eruptions.
3) Many islands (18,000) to grow at each seashore.   Korea and Japan during summer, as shown in Figure 3.
The scanning data (250 -350 nm) of optical density for Cochlonidium polykrikoides [6] at cell concentration of 1000, 3000, and 6000 cells⁄ml (Figure 4(a)) were plotted to obtain the first derivatives for searching the optimal optical density, which suggested 300 nm as the optimal optical density for the measurement of Cochlonidium polykrikoides, as shown in Figure 4(b). Figure 4(c) showed that the cell concentrations of Cochlonium polykrikoides were linearly (R 2 = 0.9972) proportional to the optical densities at 300 nm, which could be caused by its preference for ultraviolet band with high energy in accordance with Einstein-Planck relation. It was thus possible to determine the cell concentration of Cochlonidium polykrikoides via an on-line method at 300 nm instead of the present tedious method of cell number counting by microscope after off-line sampling. It was postulated that on-line real-time monitoring of Cochlonidium polykrikoides could be possible for the early warning of HAB in conjunction with a smart phone system so long as a portable detector was available at 300 nm. Figure 5 showed that iron deficiency (−Fe) inhibited the algal growth while iron enrichment (+Fe) enhanced the phytoplankton productivity. However, fresh 100% Japanese Ontake volcanic ash with enriched sulfur compounds (V100) showed reduced algal-growth.
Standard H 2 S gas with 50 ppm (RIGAS in Korea) with a flow rate of 2 L/min Figure 5. Growth curve of Chlorella vulgaris with various JM media; with its own Fe (+Fe, -+-), fresh 100% volcanic ash (V100, -▲-), without its own Fe (Fe, -•-). Standard deviation was expressed by each error bar for three measurements with excellent reproducibility, modified from Kim [7].
T.-J. Kim for 10 minutes was bubbled into 1 liter of the algal freshwater dissolved 25 g FeSO 4 ·7H 2 O. Algae were sedimented due to lack of Fe in freshwater induced by H 2 S bubbling. The sedimentary materials were filtered to analyze by X-ray diffractometer (XRD) (Model Dmax2500/PC) for the presence of iron sulfides in the form of Greigite-Fe 3 S 4 among sulfur and iron oxide, as shown in Figure 6.
Quantitative analysis of Figure 6 implied that the crystallinity of Fe 3 S 4 constituted 4.06 wt% of total sedimentary materials among amorphous peaks. It was thus evident that sulfur compounds bind Fe to sediment in black iron sulfide and deprive Fe from the growth of phytoplankton. Decomposed microorganism produced H 2 S as high as 0.122% [9] or 1220 ppm while the safe level is below 10 ppm [10]. Therefore, the disposable Biogas with H 2 S of 0.2% -3.5% [10] could be bubbled into both of freshwater and seawater cautiously to prevent HAB typically in Florida [2] during the early algal growth phase.

Volcanic Eruption
Volcanic gases are commonly composed in the order of H 2 O (37% -97.1%), Figure 6. Distribution of X-ray diffractometer (XRD) pattern for the sedimentary materials induced by the chemical reaction between dissolved FeSO [12]. The primary producers in the ocean that absorb iron (Fe) are phytoplankton or cyanobacteria, while hematite (Fe 2 O 3 ) and geothite (FeOOH) in the aeolian dust are associated with fine (0.3 -1 μm) particles with long residence times (days) in the atmosphere and thus potentially long transport paths [13]. Fe is essentially required during photosynthesis, electron transport, energy transfer, N (nitrate and nitrite) assimilation, and cyanobacteria N 2 -fixation by nitrogenase complex with 32 to 36 Fe atoms [14]. Under aerobic conditions typifying surface waters, Fe Increases of reductant under anoxic conditions [15], NADPH-oxidoreductase/ ferric reductase [13], iron-reducing bacteria [16], photochemical, superoxide, humic acid and fulvic acid in peat [17], reduce Fe , to be transferred into the algal cytosol by Fe permease [13] for the biosynthesis of macromolecules while excess Fe is stored in ferritin or cellular Fe pool [18]. The only missing ingredient after phytoplankton blooms is the dissolved Fe in HNLC (High Nutrient, Low Chlorophyll) regions unless there are further Fe inputs from aeolian dust or volcanic ash.
The more H 2 S available from either the volcanic gas and sulfur oxidation, or soluble sulfates through sulfate reducing bacteria, the more sedimentation occurs in the forms of FeS and FeS 2 . Therefore, it can be seen that the volcanic eruption enhances the formation of FeS and FeS 2 , which induces less and less Fe available to algae to be the Fe limited condition of LC (Low-Chlorophyll). On the other hand, nutrients such as nitrate, phosphate and silicate are fairly soluble and utilized by algae. However, since Fe was limited, the growth of algae was reduced [19] and thus nutrients were less utilized and further enriched to be HN (High-Nutrient).

Sunlight with Algae Size
Photosynthesis is the process by which sunlight energy is transformed into chemical energy to produce organic compounds that serve as cellular building   Table 1 shows the seasonal HAB with various algae sizes. Anabaena can bloom during early winter due to its small surface area, requiring small amount of light energy flux (low light intensity and short radiation period). Microcystis has a relatively large surface area, requiring a large amount of light energy flux (strong light intensity and long radiation period). As for cyanobacteria, the order of large surface area in Table 1 is Microcystis > Aphanizomenon > Oscillatoria > Anabaena. Since more energy is required for a large surface area, diatoms of Cyclotella and Stephanodicus have relatively small surface areas for blooming in spring. As for Cochlonidium polykrikoides, they form several cells connected together to get more solar energy during summer and early fall with a preference for the highest energy band at 300 nm, as verified in Figure 4  polykrikoides has a diameter of 35 μm with several cells connected together.
Therefore, any cloth around the fish farmery with pore diameter less than 35 μm may block the penetration of Cochlonidium polykrikoides into the fish farmery.
Since traffic signal yellow (590 nm) shows the least absorption (%) for chlorophyll-a, artificial LEDs with 590 nm could be installed in the fish farmery to repel Cochlonidium polykrikoides, requiring the highest solar energy at 300 nm ( Figure 4(b)).

Desert Dust
Major aeolian dust events arise from the Sahara and Sahel deserts ("African dust"), the Australian deserts ("Australian dust"), and the Taklamakan and Gobi deserts and the Loess plateau ("Asian dust") [21]. Tanaka and Chiba [22] com-  blooms appeared on the basis of peak-to-peak value as shown in Figure 8(c), whereas dry dust deposition was obtained by modeling [25]. During the last decade there has been a significant rise in observations of blooms of the toxic cyanobacterium Lyngbya majuscula along the east coast of Queensland, Australia. L. majuscula productivity was significantly (p < 0.05) stimulated by soil extracts, which were high in phosphorus, Fe and organic carbon [15]. It is well-known that Asian desert dust particles can be transported long distances and reach the North American Continent, and oceanic deposition encourages phytoplankton growth in the North Pacific Ocean by natural Fe fertilization [26]. The contributions of Fe, nitrogen, and phosphate by the dust deposition from Asian dust storms promoted the growth of cyanobacterium Synechococcus in the Kuroshio Current [27], which is the common prey of red-tide dinoflagellates and heterotropic nanoflagellates [28]. Asian dust particles were confirmed to be carriers of bacteria such as Antinobacteria, Bacilli, Sphingobacteria [21].   Table 2 shows the necessary elements for algal growth compared correspondingly with components of wind carried particles of Asian dust. HAB could be thus prevented by blocking the deposition of desert dust.

Iron
Iron (Fe) is the second most abundant metal and the fourth most abundant element by weight in the earth's crust while Asian dust contain iron commonly expressed in iron oxides [31] ranging from 4 to 6 weight percent depending upon different sources [13]. Fe is typically released into the soil or into the ocean through the weathering of rocks or through volcanic eruptions. Fe is an important limiting nutrient for HAB, which is used to produce chlorophyll and protein, as shown in Figure 9.
Photosynthesis depends on adequate Fe supply, whose concentration in water is quite low because of low solubility (<1 mg·L −1 in freshwater). The primary producers in the ocean that absorb Fe are typically phytoplankton or cyanobacteria. Fe is then assimilated by consumers when they eat the bacteria or plankton, the latter providing a crucial source of food to many large aquatic organisms such as fish and whales. When animals, fishes and plankton die, decomposing As shown in Figure 11, algae utilize the dissolved iron, Fe in competition with insoluble FeS/FeS 2 , the latter being significant if the volcanic activity is stronger for the sulfur compounds (S) than the desert contribution for iron (Fe).
Photosynthesis takes place in chloroplast to capture light energy, whose principal photoreceptor is chlorophyll-a with molecular formula of C 55   containing 10 -20 thylakoid and thylakoid membrane is covered with 300 chlorophylls [37]. It is expected that each photosynthetic cell contains 1.2 × 10 5 -1.2 × 10 6 chlorophylls to be approximated that each photosynthetic cell of algae requires Fe atoms as much as: (88 -92 Fe atoms/chlorophyll-a) × (1.2 × 10 5 -1.2 × 10 6 chlorophyll-a/algae cell) = 1 × 10 7 -1 × 10 8 Fe atoms/algae cell, which can be close to experimental observation of intracellular Fe quota for Synechococcus spp of ~10 −18 mol/cell [38] (~1 × 10 6 Fe atoms/cell). Since the algal concentration is in the range of 10 6 cells/ml during algal blooms [39], the resultant Fe atom concentration (atoms/ml) can be 1 × 10 13 -1 × 10 14 (Fe atoms/ml). If the blooming patch is assumed to be 100 meter long, 100 meter wide and 1 meter deep during photosynthesis, its volume can be 10 4 m 3 or 10 7 liter. Thus, Fe atoms in such a volume can be 1 × 10 23 -1 × 10 24 Fe atoms during HAB. Besides, one mole of iron is 55.8 g with 6 × 10 23  PO − ) where dissolved Fe is received from river discharges. In addition, Fe released from the sediments may rise to the surface, along with other minerals. Also, winds carry Fe-rich dust into the oceans from continental land masses, and this dust provides a source of Fe to algae. For example, the cyanobacterium Trichodesmium is abundant in the Arabian and Caribbean seas and the Indian Ocean because it is able to capture Fe from dust entering such waters. When Fe is relatively abundant, some algae can store it in ferritin, an Fe-storage protein with 1800 Fe and 640 P per molecule [41]. Kawaguchi [42] have proposed bioavailable Fe as an indicator of ecosystem health in the southeastern USA. Ingle [43] predicted the Florida red tide (dinoflagellate blooms) by means of the Fe index. Alderkamp [44] showed that Fe from melting glaciers fueled phytoplankton blooms in the Antarctic. Langroudi [45] cultured algae of Tetraselmis suecica to see that the amount of Fe for its maximum growth was 0.3 ppm while less than 1% of soluble Fe (0.05 ppm) was observed in a Australian creek out of total Fe (43 ppm) [15].
Since the structural formula of chlorophyll-a is C 55 H 68 O 5 N 4 Mg, the most limiting nutrient out of C, H, O, N can be the nitrogen while the oxygen is abundant in the water. However, since algal N 2 fixation and N (specifically nitrate and nitrite) require an abundant supply of Fe 2+ (Figure 12), HAB can occur only if Fe in Fe 2+ is fully available for the abrupt cell growth, expressed by the spontaneous increase of the concentration of chlorophyll-a during the exponential growth phase of the algae. In many cases, estuarine HAB have been linked to terrestrial run-off, following periods of heavy rainfall [15].
Since dissolved Fe levels decreased by six to seven orders of magnitude due to the formation of low-soluble FeS and FePO 4 in waters, most of the delivered Fe by the Asian dust (60,000 -120,000 ppm) can be mainly precipitated to the sediments, since Fe in freshwater is only 0.3 ppm and Fe in seawater is barely 0.0034 ppm. Therefore, it can be expected that Fe utilization rate by algae is regulated by the release of Fe 2+ from Fe complex by reduction, whose reaction is the function of the equilibrium constant and thus the absolute temperature of the freshwater and the seawater. This temperature dependence may be the reason why there is no HAB during the cold season of winter. Table 3 implied that HAB occurred in August after 4 to 5 weeks of heavy rainfall, exceeding the average 103 mm rainfall on one day in July. Since the cyanobacterial growth in the middle of water was commonly observed a week earlier than the onset of HAB, it could be postulated that the algal growth took about 4 weeks during the lag phase of growth while about one week for the late log phase of growth, after which it reached the stationary phase forming large surface algal aggregations of HAB. It was known that the required time for the algal reproduction was 6 hours for diatom under no turbulence. Since the bacterial conversion of Fe 3+ to Fe 2+ took 15 hours [16] and the photosynthesis was maximized during the 6 hours from dawn (6 AM) to midday (12 PM) [4], the resultant summation (6 + 15 + 6) hours were 27 hours for HAB by diatom, which was in accordance with other studies [24] indicating HAB by diatoms after strong winds of a day or two in the sunlit surface waters.

Nutrients
The fundamental solution for the demise of HAB was to reduce the nutrients in the form of organic materials. Perhaps the most contentious explanation has been the idea that run-off from land was a major contributor to HAB. When managers released water from the massive inland reservoir as a flood-control measure during heavy rains, the nutrient-rich water has been diverted to the river and on to the sea, laden with nutrient pollution from the cities and farms  Nitrogen: Algae require combined nitrogen to synthesize amino acids, nucleic acids, chlorophyll, and toxins [45]. Nitrogen sources commonly used by cyanobacteria include ammonium, nitrate, nitrite, urea and atmospheric N 2 , as summarized in . DIN is actively transported across the cell membrane via "uptake sites" and metabolised within the cell to form chlorophyll and amino acids and, in turn, proteins and nucleotides [47].
Since uptake mechanism of DIN across the cell membrane is "active transport", it requires external energy such as ATP or NAD(P)H. The conversion of 1 mole nitrogen to 2 mole ammonia requires 25 moles ATP. Therefore, the nitrogen uptake should be followed by ATP synthesis. The atomic ratio of N/P is commonly known to be 16/1 in freshwater and 176/1 in seawater for HAB. Therefore, nitrogen can be the limiting factor relatively in seawater while phosphorus is the limiting factor in freshwater. This may be why cyanobacterial blooms of N 2 -fixing Anabaena and Aphanizomenon are common in freshwaters rich in phosphate. Surplus nitrogen is known to be stored in cyanophycin granules and phycobiliproteins [48]. Dinoflagellates might store their N in the form of uric acid crystals within the cytosol [46]. Although algae typically take up ammo- Phosphorus (P) in inorganic phosphate is required during the photosynthesis, as illustrated in Figure 9. Energy stored in the phosphate bonds of ATP generated from photosynthesis is mobilized in the form of biomolecules such as polysaccharides, porphyrins, cellulose, proteins, lipids, RNA, and DNA. These macromolecules biosynthesize cell wall (mucopeptides) and membrane (proteins).
Inorganic P is found in the soil or water. Plants and algae assimilate inorganic P into their cells, and transfer it to other animals that consume them. When organisms die, their P is released by decomposer bacteria, which convert organic P to inorganic P. Aquatic P follows a seasonal cycle, while inorganic P peaks in the spring causing rapid algae and plant growth, and then declines. As plants and animals die, organic P is re-released into the water. P based fertilizers can cause excessive algae growth in aquatic systems, which can have negative impacts on the environment [22]. In oligotrophic freshwaters, the mineral nutrient that most commonly limits algal growth is P. Blooms of the toxic cyanobacterium Microcystis are common events globally, whose intracellular P pool showed a percentage of total cell-associated P (50% -90%) similar to what has been reported for actively growing algae in marine systems [49]. Surplus phosphate is known to be stored in polyphosphate bodies of cyanobacterial cells [48]. Phosphate levels are usually low in oligotrophic freshwater because this ion readily binds Al 3+ , Fe 3+ , and Ca 2+ , forming highly insoluble complexes in soils and lake sediments. Schindler [50] showed that eutrophication of lakes was not controlled by reducing nitrogen input but limited by phosphorus input. However, where there is sufficient phosphorus available, biologically available Fe becomes a significant limiting factor of biological growth in oceanic systems as well as coastal and estuarine ecosystems [15]. Jun [51] showed that there were four chemically defined sediment P such as adsorbed P, non apatite inorganic P(NAI-P), apatite P and residual P while the release of sediment P was apparent in the NAI-P rich sediments. The phosphorus in calcium phosphate of apatite P was released if pH was low while the phosphorus in (Fe + Al) complexed NAI-P was released if pH was high due to the preferred formation of (Fe + Al) hydroxides. Typically phosphate was decreased if the temperature of freshwater was below 15˚C [52], as shown in Figure 13(b). It was therefore expected that there could be HAB if freshwater temperature was above 15˚C.
The discharge allowance of phosphorus from the wastewater treatment plant is 0.2 ppm in Korea. In order to reduce the hazard of HAB in the river, one suggestion is to recycle the wastewater for further removal of phosphorus from the discharge water.
When phosphorus becomes so abundant that it no longer limits algal growth in eutrophic lakes, another nutrient (usually nitrogen, though sometimes Fe) becomes limiting. Moisander [53] reviewed that phosphorus availability might determine the times and locations for blooms of N 2 -fixing harmful cyanobacterium Nodularia in the Baltic Sea, Australia, United States, South Africa, and New Zealand although they acknowledged the possibility of other controlling factors such as trace element limitations. Figure 13(a) showed that dissolved phosphate could be kept minimal if pH was maintained below 6. Since phosphate is used as the energy source during biosynthesis of HAB as shown in Figure 9, HAB can be prevented by keeping pH below 6 ( Figure 13(a)) and temperature below 15˚C (Figure 13   SO − ). Sulfate-reducing bacteria convert sulfate to sulfide ion (S 2− ), which readily combines with Fe to form an insoluble precipitate, FeS. As a result, less dissolved Fe is available to react with phosphate, so dissolved phosphate levels remain relatively high (0.088 ppm) in marine waters [40]. Decomposed microorganisms from foodstuff disposal produced H 2 S gas [9], which could be applied to both of freshwater and seawater to sediment the dissolved Fe as insoluble FeS and FeS 2 for prevention of HAB in Florida's lake and coast, as shown in Figure 14  are on the trajectories of the Asian dust [26]. Unlike the majority of other phytoplankton, diatoms utilize silicic acid Si(OH) 4 , to construct their cell walls and are controlled by its availability and distribution. The ratio of Si/Fe in Asian dust [29] was approximately 7 while 182 -526 in algal cell. Limitation of diatom metabolism by the supply rate of silicic acid results in a physiological cascade that affects diatom primary productivity and nitrogen use, potentially altering regional nitrogen and carbon cycling. Diatoms using silicon to make their shells are important bloom-forming phytoplankton that contribute ~40% of global ocean productivity [55]. Lippermeier [56] observed that both diatom cell numbers and chlorophyll-a concentration were increased after the addition of Na 2 SiF 6 , which showed the importance of silicate for the photosynthetic performance similar to that of other nutrients like nitrogen, phosphate and iron.
Healey [57] found that chlorophyll-a synthesis of diatom Navicula pelliculosa ceased in 5 to 7 h of silicon (Si) starvation while Kong [58] observed 6 hours for diatom doubling time. Under ammonium limitation the ratio of silica to chlorophyll-a was 22.7 -21.0 in Skeletonema costatum [59]. The Weddell Sea has been deemed by scientists to have the clearest water of any sea with a Secchi disc visible at a depth of 79.86 meters (Weddell Sea-Wikipedia, https://en.m.wikipedia.org). The Weddell Sea showed the lowest biogenic silica accumulation rates in the Southern Ocean [60]. Therefore, the clearest water of the Weddell Sea could be induced by the high content of silica. It was thus recommended to spread the silica powder (~74% Si) over the water surface prior to the early exponential phase of algal growth for prevention of HAB in freshwater or in seawater.

Minerals:
Algal growth requires the assimilation of mineral nutrient from the water. and Fe/N (1/600 -1/3000 in Synechococcus) [65]. Thus, Fe and molybdenum can be limiting factors for algal growth. In order to prevent HAB, it is important to limit mineral ions as primary sources and not secondary ones.

Environmental Factor
Water quality parameters and meteorological conditions influencing HAB, have been extensively studied by many investigators [4] [33] [53]. Growth factors for HAB are summarized in Table 4 while important parameters were stepwise discussed as below.

Current
Currents are unidirectional water flows that are strongly influenced by winds and coastal topography, which bring a constant supply of inorganic nutrients to algae. Figure 15 shows is not inwards to the land but outwards to the coast. It is important to consider the facts that major aeolian dust events arise from the Sahara and Sahel deserts ("African dust"), the Australian deserts ("Australian dust") and the Taklamakan and Gobi deserts, the Loess plateau, and the northern India and Bangladesh   ("Asian dust"). Figure 15(a) (Global red tide occurrence region) and Figure   15(b) (Global harmful cyanobacterial blooms occurrence country) show that aeolian dusts carry the micronutrients in the atmosphere or by oceanic currents to cause global HAB in both on the coast (Figure 15(a)) and in-land ( Figure   15(b)).

pH
Abundance of cyanobacteria as a function of pH was shown in various rice soils from India [68] in Figure 16. Cyanobacteria had the maximal growth at a pH of 7.15. Therefore, cyanobacteria growth can be retarded if pH < 5 or pH > 10 as less as 1000 folds from 10 8 units/g soil to 10 Figure 16. Abundance of cyanobacteria as a function of pH in various rice soils from India (redrawn and correlated from Nayak [68]).
(NaOH) with dilution of more than 1000 folds. Since algal growth is strongly dependent upon pH, it is possible to prevent HAB in the freshwater by pH adjustment, especially during the early growth phase with a small blooming area. Figure 17 showed the algal growth curves in the seawater with various pH in the bench scale. The least cell growth was observed at pH of 5 and 6 although it was impossible to adjust the pH of seawater in the field.

Temperature and Salinity
Since temperature promotes the enzymatic activity of algal, temperature is an important parameter to prevent HAB in freshwater and seawater. From 2010 to 2012 the Han River in Korea showed HAB when water temperature was greater than 25˚C. On the other hand HAB induced by C. polykrikoides showed the reduced cell growth curve when the seawater temperature was less than 10˚C, as seen in Figure 18 & Figure 19. Stable stratification with thermocline induced HAB in the seawater [58]. Low salinity did not extensively decrease the growth of C. polykrikoides. HAB in the seawater after the heavy rainfall (Table 2) could be associated with bulk inputs of nutrient, iron, nitrogen, and minerals, run-off from land by heavy rainfall into the sea. Diluted salinity of seawater after the heavy rainfall might not be the main reason of HAB in the seawater.

Dissolved Oxygen
In aquatic systemes, the concentration of dissolved oxygen (DO) is related to water temperature and the speed at which the water moves. Mass balance DO in the water is given by,     Water mills and boat turbulence for the enhanced DO can inhibit HAB in freshwater and in seawater.

Food Web
Algae play an important role in the aquatic food web, as shown in Figure 20.
Algae growth and reproduction decreased so long as their preys of the particulate or dissolved in organic materials in aquatic system are limited. One of the best ways to prevent HAB is thus to increase their grazer, lytic bacteria, and virus [28].

Turbulence
HAB was inhibited by shear in the freshwater and in the seawater. Therefore, suitable nutrient, temperature, light, and shear are the initial growth requirements to prevent HAB [70]. Boat turbulence and water mills on the surfaces of the freshwater (river, lake, reservoir) and the seawater (fish farmery) disturb the water surfaces for turbulence to prevent HAB. Long hydraulic retention time without turbulence or shear induce HAB in the waters.  . Conceptual diagram of aquatic food webs with algae (redrawn from Graham [14]).

Enzyme
Enzymes as protein molecules possess complex structures with a variety of reactive amino acid side chains in enzyme active sites to provide many kinds of catalytic activities. Especially, metal ion requirements for an enzyme are usually specific, with little or no enzyme activity observed if the specified metal ion is absent or if another metal ion is substituted for the natural one. Metal ions such as Fe, magnesium, manganese, cobalt, copper, nickel, molybdenum, zinc, and others are required for enzyme catalytic action. As with the organic cofactors, metal ions are required in only very small amounts, so they are considered essential trace elements or micronutrients. It can be seen that all the biological processes including HAB can be manipulated by their relevant enzymatic activities with micronutrients of metal ions. Figure 21 shows the schematic flow diagram of HAB with enzymes. Since enzymes accelerate specifically the biosynthesis of macromolecules such as polysaccharides, lipids, and proteins to be made as algal membrane, cell wall, DNA, and RNA, only if the cofactors of mineral ions are available, the initial step of algal growth is fully dependent upon the availability of metal ions. It is thus necessary to keep certain levels of minerals free of aeolian desert dust not only for proper enzymatic reaction at an optimal temperature and pH but also for algal growth and reproduction during HAB.

Growth Phase
The algal growth curve is typically shown in Figure 22(a). It is difficult to determine the timing of the onset of logarithmic growth phase (Figure 22(b)) to prevent HAB.
An index (θ ) was proposed as control parameter of HAB defined as,      Table 4. Therefore, HAB can be prevented if the algal growth is limited by the key parameters prior to reaching the early exponential growth phase, after which the algal toxins are produced to be superior to other competing species and reaching the exponential growth phase and the stationary phase where no further prevention tool is possible and we can only observe the resultant damage of HAB.

Conclusion
Harmful algal blooms (HAB) were initiated by the iron (Fe) from volcanic ash, river, bottom sediment, and desert dust to be converted as