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53-476: Lake Ledro is reputed to be one of the cleanest lakes in Trentino, and during the summer it reaches a temperature of 24 °C (75 °F), attracting tourists with its four bathing banks. In 2009 and 2011, the lake suffered from algal blooms , caused by Planktothrix . Lake Ledro originates from the deposition of a morainal bank during the fourth glacial era. Since 1929, the lake level has been regulated to suit

106-521: A dive light. Water in the open ocean appears clear and blue because it contains much less particulate matter , such as phytoplankton or other suspended particles, and the clearer the water, the deeper the light penetration. Blue light penetrates deeply and is scattered by the water molecules, while all other colours are absorbed; thus the water appears blue. On the other hand, coastal water often appears greenish. Coastal water contains much more suspended silt and algae and microscopic organisms than

159-424: A fast rate. In fact, ninety five percent of photosynthesis in the ocean occurs in the photic zone. Therefore, if we go deeper, beyond the photic zone, such as into the compensation point , there is little to no phytoplankton, because of insufficient sunlight. The zone which extends from the base of the euphotic zone to the aphotic zone is sometimes called the dysphotic zone. Ninety percent of marine life lives in

212-406: A food source. Detritivores and scavengers are rare in the photic zone. Microbial decomposition of dead organisms begins here and continues once the bodies sink to the aphotic zone where they form the most important source of nutrients for deep sea organisms. The depth of the photic zone depends on the transparency of the water. If the water is very clear, the photic zone can become very deep. If it

265-456: A large impact on those who reside in it. The depth is, by definition, where radiation is degraded down to 1% of its surface strength. Accordingly, its thickness depends on the extent of light attenuation in the water column. As incoming light at the surface can vary widely, this says little about the net growth of phytoplankton. Typical euphotic depths vary from only a few centimetres in highly turbid eutrophic lakes, to around 200 meters in

318-492: A luciferin-luciferase reaction to create a blue light emission glow. There are seventeen major types of dinoflagellate toxins, in which the strains, Saxitoxin and Yessotoxin, are both bioluminescent and toxic. These two strains are found to have similar niches in coastal areas. A surplus of Dinoflagellates in the night time creates a blue-green glow, however, in the day, it presents as a red brown color which names algal blooms, Red Tides. Dinoflagellates have been reported to be

371-515: Is left at 100 metres. No light penetrates beyond 1000 metres. In addition to overall attenuation, the oceans absorb the different wavelengths of light at different rates. The wavelengths at the extreme ends of the visible spectrum are attenuated faster than those wavelengths in the middle. Longer wavelengths are absorbed first; red is absorbed in the upper 10 metres, orange by about 40 metres, and yellow disappears before 100 metres. Shorter wavelengths penetrate further, with blue and green light reaching

424-648: Is one of the most important in Europe for evidencing the extent and wealth of the manufactures of its time. Algal blooms An algal bloom or algae bloom is a rapid increase or accumulation in the population of algae in fresh water or marine water systems. It is often recognized by the discoloration in the water from the algae's pigments. The term algae encompasses many types of aquatic photosynthetic organisms, both macroscopic multicellular organisms like seaweed and microscopic unicellular organisms like cyanobacteria .   Algal bloom commonly refers to

477-485: Is the aphotic (or midnight) zone, where no light penetrates. This region includes the majority of the ocean volume, which exists in complete darkness. Phytoplankton are unicellular microorganisms which form the base of the ocean food chains . They are dominated by diatoms , which grow silicate shells called frustules . When diatoms die their shells can settle on the seafloor and become microfossils . Over time, these microfossils become buried as opal deposits in

530-430: Is the uppermost layer of a body of water that receives sunlight , allowing phytoplankton to perform photosynthesis . It undergoes a series of physical, chemical, and biological processes that supply nutrients into the upper water column . The photic zone is home to the majority of aquatic life due to the activity ( primary production ) of the phytoplankton. The thicknesses of the photic and euphotic zones vary with

583-563: Is very common from the exposure of algal blooms. Water-borne diseases are also present as our drinking waters can be contaminated by cyanotoxins. If the HAB event results in a high enough concentration of algae the water may become discoloured or murky, varying in colour from purple to almost pink, normally being red or green. Not all algal blooms are dense enough to cause water discolouration. Dinoflagellate s are microbial eukaryotes that link bioluminesce and toxin production in algal blooms. They use

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636-431: Is very murky, it can be only fifty feet (fifteen meters) deep. Animals within the photic zone use the cycle of light and dark as an important environmental signal, migration is directly linked to this fact, fishes use the concept of dusk and dawn when its time to migrate, the photic zone resembles this concept providing a sense of time. These animals can be herrings and sardines and other fishes that consistently live within

689-595: The marine sediment . Paleoclimatology is the study of past climates. Proxy data is used in order to relate elements collected in modern-day sedimentary samples to climatic and oceanic conditions in the past. Paleoclimate proxies refer to preserved or fossilized physical markers which serve as substitutes for direct meteorological or ocean measurements. An example of proxies is the use of diatom isotope records of δ13C , δ18O , δ30Si (δ13C diatom , δ18O diatom , and δ30Si diatom ). In 2015, Swann and Snelling used these isotope records to document historic changes in

742-428: The photic , or sunlit zone of the ocean. Along coastal regions and in freshwater systems, agricultural, city, and sewage runoff can cause algal blooms. Algal blooms, especially large algal bloom events, can reduce the transparency of the water and can discolor the water. The photosynthetic pigments in the algal cells, like chlorophyll and photoprotective pigments, determine the color of the algal bloom. Depending on

795-584: The Northern corner at the West end of the lake)), although these are dry for most of the year. At Lake Ledro is the site of an archaeological area with an associated museum and botanical garden situated on the River Ponale flowing out of the lake to the east. The area was discovered in the 1920s when the level of the lake was lowered to supply the hydroelectric plant being built at Riva del Garda. This archaeological site

848-472: The air that contain toxins. Because human exposure can take place by consuming seafood products that contain the toxins expelled by HAB algae, food-borne diseases are present and can affect the nervous, digestive, respiratory, hepatic, dermatological, and cardiac systems in the body. Beach users have often experienced upper respiratory diseases, eye and nose irritation, fever, and have often needed medical care in order to be treated. Ciguatera fish poisoning (CFP)

901-506: The algae species concentration simply deviates from its normal growth. Blooms are the result of a nutrient needed by the particular algae being introduced to the local aquatic system. This growth-limiting nutrient is typically nitrogen or phosphorus, but can also be iron, vitamins, or amino acids. There are several mechanisms for the addition of these nutrients in water. In the open ocean and along coastlines, upwelling from both winds and topographical ocean floor features can draw nutrients to

954-478: The amount of light penetration, as discussed in pelagic zone . The upper 200 metres is referred to as the photic or euphotic zone. This represents the region where enough light can penetrate to support photosynthesis, and it corresponds to the epipelagic zone. From 200 to 1000 metres lies the dysphotic zone, or the twilight zone (corresponding with the mesopelagic zone). There is still some light at these depths, but not enough to support photosynthesis. Below 1000 metres

1007-523: The benign feeding of higher trophic levels to more harmful effects like blocking sunlight from reaching other organisms, causing a depletion of oxygen levels in the water, and, depending on the organism, secreting toxins into the water. Blooms that can injure animals or the ecology, especially those blooms where toxins are secreted by the algae, are usually called " harmful algal blooms " (HAB), and can lead to fish die-offs, cities cutting off water to residents, or states having to close fisheries. The process of

1060-413: The cause of seafood poisoning from the neurotoxins. There are three major categories for management of algal blooms consisting of mitigation, prevention, and control. Within mitigation, routine monitoring programs are implemented for toxins in shellfish and an overall surveillance of the area. The HAB levels of the shellfish will be determined and can manage restrictions to keep contaminated shellfish off

1113-445: The concentration of photosynthetic pigment, quantification of the bloom's negative effect, or relative concentration of the algae compared to the rest of the microbial community. For example, definitions of blooms have included when the concentration of chlorophyll exceeds 100 ug/L, when the concentration of chlorophyll exceeds 5 ug/L, when the species considered to be blooming exceeds concentrations of 1000 cells/mL, and when

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1166-421: The deepest depths. This is why things appear blue underwater. How colours are perceived by the eye depends on the wavelengths of light that are received by the eye. An object appears red to the eye because it reflects red light and absorbs other colours. So the only colour reaching the eye is red. Blue is the only colour of light available at depth underwater, so it is the only colour that can be reflected back to

1219-573: The energy requirements of the hydroelectric power station of Riva del Garda , which uses the water of the lake to produce electricity on a pumped-storage basis . The Lake's water sources are mainly underneath the lake. There are also tributaries (Massangla (at the West end of the lake, joined by the Torrente Assat of Pieve), Assat of Pur (from the South, at the East end of the lake), and Rio di Val Molini (at

1272-526: The establishment of globally cooler conditions and the expansion of glaciers across the Northern Hemisphere from 2.73 Ma. While the halocline appears to have prevailed through the late Pliocene and early Quaternary glacial–interglacial cycles , other studies have shown that the stratification boundary may have broken down in the late Quaternary at glacial terminations and during the early part of interglacials. Phytoplankton are restricted to

1325-400: The eye, and everything has a blue tinge under water. A red object at depth will not appear red to us because there is no red light available to reflect off of the object. Objects in water will only appear as their real colours near the surface where all wavelengths of light are still available, or if the other wavelengths of light are provided artificially, such as by illuminating the object with

1378-405: The familiar “ROYGBIV”; red, orange, yellow, green, blue, indigo, and violet. Water is very effective at absorbing incoming light, so the amount of light penetrating the ocean declines rapidly (is attenuated) with depth. At one metre depth only 45% of the solar energy that falls on the ocean surface remains. At 10 metres depth only 16% of the light is still present, and only 1% of the original light

1431-427: The food market. Moving fish pens away from algal blooms is also another form of mitigation. Within prevention, this category is less known but policy changes are implemented to control sewage and waste. Within control, there are mechanical, biological, chemical, genetic and environmental controls. Mechanical control involves dispersing clay into the water to aggregate with the HAB leading to less of these HAB to go through

1484-578: The intensity of sunlight as a function of season and latitude and with the degree of water turbidity. The bottommost, or aphotic, zone is the region of perpetual darkness that lies beneath the photic zone and includes most of the ocean waters. In the photic zone, the photosynthesis rate exceeds the respiration rate. This is due to the abundant solar energy which is used as an energy source for photosynthesis by primary producers such as phytoplankton. These phytoplankton grow extremely quickly because of sunlight's heavy influence, enabling it to be produced at

1537-689: The location and abundance of phytoplankton by detecting the amount of chlorophyll present in coastal and open waters—the higher the concentration, the larger the bloom. Observations show blooms typically last until late spring or early summer, when nutrient stocks are in decline and predatory zooplankton start to graze. The visualization on the left immediately below uses NASA SeaWiFS data to map bloom populations. The NAAMES study conducted between 2015 and 2019 investigated aspects of phytoplankton dynamics in ocean ecosystems, and how such dynamics influence atmospheric aerosols , clouds, and climate. In France, citizens are requested to report coloured waters through

1590-430: The nutricline. Chemical factors include oxygen and trace elements. Biological factors include grazing and migrations. Upwelling carries nutrients from the deep waters into the photic zone, strengthening phytoplankton growth. The remixing and upwelling eventually bring nutrient-rich wastes back into the photic zone. The Ekman transport additionally brings more nutrients to the photic zone. Nutrient pulse frequency affects

1643-448: The open ocean . It also varies with seasonal changes in turbidity, which can be strongly driven by phytoplankton concentrations, such that the depth of the photic zone often decreases as primary production increases. Moreover, the respiration rate is actually greater than the photosynthesis rate. The reason why phytoplankton production is so important is because it plays a prominent role when interwoven with other food webs . Most of

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1696-508: The open ocean. Many of these organisms, such as phytoplankton, absorb light in the blue and red range through their photosynthetic pigments, leaving green as the dominant wavelength of reflected light. Therefore the higher the phytoplankton concentration in water, the greener it appears. Small silt particles may also absorb blue light, further shifting the colour of water away from blue when there are high concentrations of suspended particles. The ocean can be divided into depth layers depending on

1749-427: The organism, its pigments, and the depth in the water column, algal blooms can be green, red, brown, golden, and purple. Bright green blooms in freshwater systems are frequently a result of cyanobacteria (colloquially known as "blue-green algae") such as Microcystis . Blooms may also consist of macroalgal (non- phytoplanktonic ) species. These blooms are recognizable by large blades of algae that may wash up onto

1802-429: The oversupply of nutrients leading to algae growth and oxygen depletion is called eutrophication . Algal and bacterial blooms have persistently contributed to mass extinctions driven by global warming in the geologic past, such as during the end-Permian extinction driven by Siberian Traps volcanism and the biotic recovery following the mass extinction. The term algal bloom is defined inconsistently depending on

1855-417: The photic zone conditions of the north-west Pacific Ocean , including nutrient supply and the efficiency of the soft-tissue biological pump , from the modern day back to marine isotope stage 5e , which coincides with the last interglacial period . Peaks in opal productivity in the marine isotope stage are associated with the breakdown of the regional halocline stratification and increased nutrient supply to

1908-404: The photic zone, which is approximately two hundred meters deep. This includes phytoplankton (plants), including dinoflagellates , diatoms , cyanobacteria , coccolithophores , and cryptomonads . It also includes zooplankton , the consumers in the photic zone. There are carnivorous meat eaters and herbivorous plant eaters. Next, copepods are the small crustaceans distributed everywhere in

1961-414: The photic zone. The initial development of the halocline and stratified water column has been attributed to the onset of major Northern Hemisphere glaciation at 2.73 Ma, which increased the flux of freshwater to the region, via increased monsoonal rainfall and/or glacial meltwater, and sea surface temperatures . The decrease of abyssal water upwelling associated with this may have contributed to

2014-444: The photic zone. Due to biological uptake, the photic zone has relatively low levels of nutrient concentrations. As a result, phytoplankton doesn't receive enough nutrients when there is high water-column stability. The spatial distribution of organisms can be controlled by a number of factors. Physical factors include: temperature, hydrostatic pressure, turbulent mixing such as the upward turbulent flux of inorganic nitrogen across

2067-409: The photic zone. Finally, there are nekton (animals that can propel themselves, like fish, squids, and crabs), which are the largest and the most obvious animals in the photic zone, but their quantity is the smallest among all the groups. Phytoplankton are microscopic plants living suspended in the water column that have little or no means of motility. They are primary producers that use solar energy as

2120-420: The photo zone only. As its growth is completely dependent upon photosynthesis. This results in the 50–100 m water level inside the ocean. Growth can also come from land factors, for example minerals that are dissolved from rocks, mineral nutrients from generations of plants and animals ,that made its way into the photic zone. An increase in the amount of phytoplankton also creates an increase in zooplankton,

2173-407: The phytoplankton competition. Photosynthesis produces more of it. Being the first link in the food chain, what happens to phytoplankton creates a rippling effect for other species. Besides phytoplankton, many other animals also live in this zone and utilize these nutrients. The majority of ocean life occurs in the photic zone, the smallest ocean zone by water volume. The photic zone, although small, has

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2226-444: The presence of nutrients. When phosphates are introduced into water systems, higher concentrations cause increased growth of algae and plants. Algae tend to grow very quickly under high nutrient availability, but each alga is short-lived, and the result is a high concentration of dead organic matter which starts to decompose. Natural decomposers present in the water begin decomposing the dead algae, consuming dissolved oxygen present in

2279-623: The process of sedimentation. Biological control varies largely and can be used through pheromones or releasing sterile males to reduce reproduction. Chemical control uses toxic chemical release. However, it may cause problems of mortality of other non targeted organisms. Genetic control involves genetically engineering species in their environmental tolerances and reproduction processes. However, there are problems of harming indigenous organisms. For environmental control, it can use water circulation and aeration. Photic zone The photic zone (or euphotic zone , epipelagic zone , or sunlight zone )

2332-917: The project PHENOMER. This helps to understand the occurrence of marine blooms. Wildfires can cause phytoplankton blooms via oceanic deposition of wildfire aerosols. A harmful algal bloom (HAB) is an algal bloom that causes negative impacts to other organisms via production of natural toxins, mechanical damage to other organisms, or by other means. The diversity of these HABs make them even harder to manage, and present many issues, especially to threatened coastal areas. HABs are often associated with large-scale marine mortality events and have been associated with various types of shellfish poisonings . Due to their negative economic and health impacts, HABs are often carefully monitored. HAB has been proved to be harmful to humans. Humans may be exposed to toxic algae by direct consuming seafood containing toxins, swimming or other activities in water, and breathing tiny droplets in

2385-446: The rapid growth of microscopic unicellular algae, not macroscopic algae. An example of a macroscopic algal bloom is a kelp forest . Algal blooms are the result of a nutrient, like nitrogen or phosphorus from various sources (for example fertilizer runoff or other forms of nutrient pollution ), entering the aquatic system and causing excessive growth of algae. An algal bloom affects the whole ecosystem . Consequences range from

2438-399: The result of an excess of nutrients , particularly some phosphates . Excess nutrients may originate from fertilizers that are applied to land for agricultural or recreational purposes and may also originate from household cleaning products containing phosphorus . The reduction of phosphorus inputs is required to mitigate blooms that contain cyanobacteria. In lakes that are stratified in

2491-443: The scientific field and can range from a "minibloom" of harmless algae to a large, harmful bloom event. Since algae is a broad term including organisms of widely varying sizes, growth rates, and nutrient requirements, there is no officially recognized threshold level as to what is defined as a bloom. Because there is no scientific consensus, blooms can be characterized and quantified in several ways: measurements of new algal biomass,

2544-760: The shoreline. Once the nutrient is present in the water, the algae begin to grow at a much faster rate than usual. In a mini bloom, this fast growth benefits the whole ecosystem by providing food and nutrients for other organisms. Of particular note are the harmful algal blooms (HABs), which are algal bloom events involving toxic or otherwise harmful phytoplankton. Many species can cause harmful algal blooms. For example, Gymnodinium nagasakiense can cause harmful red tides , dinoflagellates Gonyaulax polygramma can cause oxygen depletion and result in large fish kills, cyanobacteria Microcystis aeruginosa can make poisonous toxins, and diatom Chaetoceros convolutus can damage fish gills. Freshwater algal blooms are

2597-620: The situation can be corrected by changing the water in the tank and then reducing the amount of food given. Turbulent storms churn the ocean in summer, adding nutrients to sunlit waters near the surface. This sparks a feeding frenzy each spring that gives rise to massive blooms of phytoplankton. Tiny molecules found inside these microscopic plants harvest vital energy from sunlight through photosynthesis. The natural pigments, called chlorophyll, allow phytoplankton to thrive in Earth's oceans and enable scientists to monitor blooms from space. Satellites reveal

2650-405: The solar energy reaching the Earth is in the range of visible light, with wavelengths between about 400-700 nm. Each colour of visible light has a unique wavelength, and together they make up white light. The shortest wavelengths are on the violet and ultraviolet end of the spectrum, while the longest wavelengths are at the red and infrared end. In between, the colours of the visible spectrum comprise

2703-463: The summer, autumn turnover can release substantial quantities of bio-available phosphorus potentially triggering algal blooms as soon as sufficient photosynthetic light is available. Excess nutrients can enter watersheds through water runoff. Excess carbon and nitrogen have also been suspected as causes. Presence of residual sodium carbonate acts as catalyst for the algae to bloom by providing dissolved carbon dioxide for enhanced photosynthesis in

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2756-424: The water during the process. This can result in a sharp decrease in available dissolved oxygen for other aquatic life. Without sufficient dissolved oxygen in the water, animals and plants may die off in large numbers. This may also be known as a dead zone . Blooms may be observed in freshwater aquariums when fish are overfed and excess nutrients are not absorbed by plants. These are generally harmful for fish, and

2809-410: The zooplankton feeds on the phytoplankton as they are at the bottom of the food chain. Dimethylsulfide loss within the photic zone is controlled by microbial uptake and photochemical degradation. But what exactly is dimethylsulfide and why is it important? This compound (see the photo) helps regulate sulfur cycle and ecology within the ocean. Marine bacteria, algae, coral and most other organisms within

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