Biogeochemistry

Biogeochemistry is the study of the cycles of chemical elements, such as carbon and nitrogen, and their interactions with and incorporation into living things transported through earth scale biological systems in space through time. Biochemical cycle: biogeochemical cycle or substance turnover or cycling of substances is a pathway by which a chemical substance moves through biotic (biosphere) and abiotic (lithosphere, atmosphere, and hydrosphere) compartments of Earth. Marine biogeochemistry and historical background Biogeochemistry is the scientific discipline that deals with the biological controls on environmental chemistry and with the geochemical controls on the structure and function of ecosystems. The discipline has a long history. The term biogeochemistry was first coined by the Russian scientist Vladimir Vernadsky in 1926. Historical Development of Biogeochemistry (Gorham) 1) Photosynthesis and respiration 2) Decomposition 3) Metabolism of nitrogen and sulfur 4) Mineral nutrition of plants 5) Weathering of rocks and soils. Vernadsky (1863-1945) Biosphere term originated by the Austrian geologist Eduard Suess (1831-1914) in early 1900's and developed further by the Russian, Vladimir Vernadsky. Suess also coined the term hydrosphere and lithosphere to correspond with the term atmosphere. 2 principle: of vegetation” (1630-1750) Lord Bacon (philosopher and scientist) thought that water was the "principal nourishment" of plants. Recent advancement and Scope of marine biogeochemistry 2: biogeochemical circle, process Nitrogen cycle : The nitrogen cycle is the biogeochemical cycle by which nitrogen is converted into multiple chemical forms as it circulates among the atmosphere, terrestrial, and marine ecosystems. Steps of nitrogen cycle Nitrogen fixation Nitrogen assimilation Nitrogen regeneration Decomposition of organic nitrogen (to ammonia) Nitrification Denitrification Nitrogen (N) is an essential nutrient for all organisms, and it is a critical element of protein, vitamins and DNA, and is important in biochemical structures and process that define life. 1: Nitrogen fixation The biological fixation of nitrogen can be synthetically represented by the following global formula: N2 + 8H+ + 6e- → 2NH4+ Nitrogen assimilation Nitrogen assimilated in the form of nitrate or nitrite by the plankton should be converted to ammonia before it can be converted into amino acids for protein synthesis. NO3 - + 2H+ + 2 e- = NO2- +H2O NO2 -+H+ + e- = N2O22- +H2 N2022- +6H+ +e-= NH2OH NH2OH + 2H+ +2e-= NH3 NH3 to amino acids to protein Nitrification: The biological conversion of ammonium to nitrate nitrogen is called Nitrification. Nitrification occurs in two distinct stages: oxidation of ammonium to nitrite (nitrosation) and Oxidation of nitrite to nitrate (nitration). 1) Nitrosation: in the first stage, ammonium ion is oxidized to nitrite in two steps: The first step is catalyzed by the enzyme, monooxygenase which forms the hydroxylamine by using O2 as oxidant:  2NH4+ + O2 → 2NH2OH + 2H+ In the second step, hydroxylamine is oxidized to nitrite by the enzyme hydroxylamine-dehydrogenase:  2NH2OH + 2O2 → 2H+ + 2H2O + 2NO2- 2)   Nitration:  the oxidation of nitrite to nitrate, which occurs through the activity of the nitrite oxidase enzyme, completes the process of nitrification: 2NO2- + O2 → 2NO3- Denitrification : Denitrification is a microbially facilitated process where nitrate is reduced and ultimately produces molecular nitrogen (N2) through a series reactions NO3- + H+ → N2O N2O →N2 Diagram of nitrogen cycle in marine environment Sources of nitrogen in marine environment: Rock weathering River run off Domestic sewage Industrial effluents Agricultural activities Atmospheric inputs Marine organisms Different forms NO3- (Nitrate) NO2-(nitrite) NH4+ (ammonium ion) N2O(nitrous oxide) Role of microbes in the transformation of different nitrogenous compounds 1: fixation N2+8H =NH3+H2 ( Cynobacteria) 2: nitrification NH4+=NO2-(nitrosomonas) NO2-=NO3- (nitrobactor) 3: ammonification N2=NH3+ (rhizobium) 5: Denitrification NO3-=N2 (bacillus, prococus, pseudomonas) Major sources and importance of phosphate, carbon, silicon Sources of phosphorus Agricultural manure Municipal wastewater Industrial wastewater Urban and suburban runoff and in stream sediment Natural sources (chemical weathering , volcanic eruption etc.) Seawater and ocean crust interaction and decomposed burial on seabed Source of carbon: Active uptake: - dissolve in seawater. such CH4 , CFCs ,CO2 Respiration: organisms release carbon di oxide. Volcanic eruption Upwelling Sediment of seabed Major sources of carbon in Karnafully River Mainly anthropogenic source Decomposition Plants Organic matters Major carbon sinks: A carbon sink is a natural or artificial reservoir that accumulates and stores some carbon-containing chemical compound for an indefinite period. The process by which carbon sinks remove carbon dioxide (CO2) from the atmosphere is known as carbon sequestration. Carbon sinks can be natural or man-made. They absorb more carbon than they release whereas carbon source is anything that releases more carbon than they absorb. Terrestrial Tropical rainforest, Forest and plants Earth crust Agricultural lands Fresh water lakes and wetlands Marine Coastal ecosystems Open ocean Coral reefs Weathering Carbon sources 1. Atmosphere: A major source of atmospheric CO2 is degassing from volcanic activity which acts as a release of carbon dioxide 2. Volcanic activity: the process of subduction of crust provides a sink for CO2. 3. decomposition of organic material. 4. Major carbon species Reservoirs of carbon on the earth: Carbon is found in several areas: 1. Atmosphere ( CH4 and CO2) 2. Biosphere (living and dead organisms) 3. Lithosphere (soil an rocks) 5. Hydrosphere (oceans, rivers and lakes) Carbon cycle, diagram The carbon cycle is the biogeochemical cycle by which carbon is exchanged among the biosphere, pedosphere, geosphere, hydrosphere, and atmosphere of the Earth. The carbon cycle is one of the major biogeochemical cycles describing the flow of essential elements from the environment to living organisms and back to the environment again. This process is required for the building of all organic compounds and involves the participation of many of the earth's key forces. The carbon cycle has affected the earth throughout its history; it has contributed to major climatic changes, and it has helped facilitate the evolution of life. The complexities of the carbon cycle are depicted in the diagram below The carbon cycle passes through three main stages: reservoirs, assimilation, and release. Much of the earth's carbon is contained in the atmosphere which serves as a reservoir. Atmospheric carbon consists mostly of carbon dioxide and has two major sinks: terrestrial ecosystems and marine ecosystems, both of which deal with photosynthesis as a part of assimilation and respiration as a part of release. Terrestrial ecosystems draw carbon dioxide from the atmosphere and use it in photosynthesis. The equation, C02 + H20 + light => C6H12O6 + O2 + energy, shows how carbon dioxide is broken down and used to produce glucose for the plants and oxygen as a byproduct. All plants act as a sink for carbon dioxide because it is a necessary gas for photosynthesis. Of the terrestrial ecosystems, forests have the highest rates of productivity, thus utilizing carbon at a higher rate compared to oceans. Marine ecosystems are separated into two areas: coastal ecosystems and the open ocean. Coastal ecosystems include estuaries, wetlands, and continental shelves. Open oceans are considered all areas beyond the shelves. Both have the capacity to store significant amounts of carbon in sediments and also are able to sequester carbon in photosynthesis or chemosynthesis through phytoplankton, seaweeds, and other marine algae. Most storage of carbon is in marine sediments and rocks, although some carbon is used by marine life in the formation of calcium carbonate. Three main processes (or pumps) that make up the marine carbon cycle bring atmospheric carbon dioxide (CO2) into the ocean interior and distribute it through the oceans. These three pumps are: (1) the solubility pump, (2) the carbonate pump, and (3) the biological pump. Another carbon sink is the weathering of mountains and other rock formations formed by plate tectonics, mainly silicate weathering. Carbon dioxide is consumed from silicate weathering as seen in this equation: CaSiO3 + 2CO2 + 2H2O => CaCO3 + SiO2 + CO2 + 2H2O Distribution or movement of carbon Carbon fluxes and stocks Carbon flux: Transfer of carbon from one carbon pool to another in units of measurement of mass per unit area and time. Carbon stocks: The absolute quantity of carbon held within a pool at a specified time. Basic steps of phosphorus cycle: Phosphorus (P) is an essential element to all life, being a structural and functional component of all organisms.P provides the phosphate-ester backbone of DNA and RNA, and it is crucial in the transmission of chemical energy through the ATP molecule .P is also a structural constituent in many cell components such as phosphoproteins, and phospholipids in cell membranes, teeth, and bones. Phosphorus, in the form of orthophosphate, plays a key role in photosynthesis (i.e., primary productivity). The phosphorus cycle is the movement of phosphorus from the environment to organisms and then back to the environment Phosphorus moves in a cycle through rocks, water, soil and sediments and organisms. Here are the key steps of the phosphorus cycle Over time, rain and weathering cause rocks to release phosphate ions and other minerals. This inorganic phosphate is then distributed in soils and water. Plants take up inorganic phosphate from the soil. The plants may then be consumed by animals. Once in the plant or animal, the phosphate is incorporated into organic molecules such as DNA . When the plant or animal dies, it decays, and the organic phosphate is returned to the soil. Within the soil, organic forms of phosphate can be made available to plants by bacteria that break down organic matter to inorganic forms of phosphorus. This process is known as mineralization. Phosphorus in soil can end up in waterways and eventually oceans. Once there, it can be incorporated into sediments over time. Role of microbes in the phosphorus cycle : Microbes play an important role in the remineralization of organic phosphorus compounds. Prokaryotic microorganisms and the lower eukaryotes (e.g., E. Coli, Pseudomonas sp., and Candida maltosa, a yeast) have been recognized as being capable of phosphonate remineralization and they can do so via a wide range of pathways. Microbes in the marine environment can also create new pathways for the uptake of phosphorus by zooplankton. Phosphorus transformations at the sediment/water interface are generally considered to be governed by abiotic processes and bacteria were assumed to play only an indirect role. However, recent findings by Gachter and Meyersuggest that not only bacteria in sediments regenerate phosphate but that they also do contribute to the production of refractory organic P compounds. Thus, such bacteria may regulate the flux of P across the sediment/water interface and contribute to its terminal burial by the production of refractory organic P compounds and biogenic apatite. Major active species (compounds) of phosphorus: P is the eleventh most abundant element in the Earth’s crust, comprising approximately 0.1% by mass. It occurs in the form of inorganic phosphate minerals and organic phosphate derivatives in rocks and soil. Apatite [Ca5(PO4)3- (F,Cl,OH)] is the most common naturally occurring P containing mineral in the Earth’s crust (over 95% of P); however, approximately 300 additional minerals that contain phosphate (PO43-).The organic phosphorus derivatives in soils and sediments include orthophosphate monoesters, orthophosphate diesters, phosphonates, and phosphorus anhydrides. Role of phosphorus in marine productivity Major Sources of sulphur Earth crust is the largest reservoir of sulphur Sulfate anions , dissolved H2S, DMS (dimethyl sulfide) Biological source (microbial) Fossil fuel Sulfuric acid rain Volcanic eruption Major Sources and sinks of phosphorus Phosphorus is primarily delivered to the ocean via continental weathering .This P is transported to the ocean primarily in the dissolved and particulate phases via riverine influx. However, atmospheric deposition through aerosols, volcanic ash, and mineral dust is also important. Rock weathering Anthropogenic (sewage, human waste, agricultural waste ,fertilizer , soil erosion, livestock, paper pulp manufacturing) Hydrothermal vent Biogenic production Atmospheric Deposition(Aerosols associated with eolian dust particles ) volcanic ash The dominant sink for oceanic P is deposition and burial in marine sediment (after transformation from dissolved to particulate forms). A minor sink for P is uptake through seawater-oceanic crust interactions associated with hydrothermal activity on the ocean’s floor. total P burial in open ocean marine sediments range from 9.3 × 1010 mol/year 71 to 34 × 1010 mol/year.The major component of this burial flux is reactive P, with most of the nonreactive P having been deposited in the continental shelves. Phosphorite deposits are authigenic formations derived from the microbial hydrolysis and release of organic. Marine sediments primarily as sinking particulate matter. Figure : oceanic /marine phosphorus cycle transformations between P pools in the water column and sediments. (PIP, particulate inorganic phosphorus; POP, particulate organic phosphorus; DIP, dissolved inorgranic phosphorus; DOP, dissolved organic phosphorus. Particulate phosphorus forms can undergo transformations throughout the water column and within the sedimentary record. Particulate phosphorus forms may also undergo regeneration into dissolved forms. Particulate phosphorus is lost from surface waters via sinking. Biological cycling and remineralization are the primary Mechanisms of transformations of the dissolved phases and are dominant in surface waters, though microbial remineralization continues at depth. Dissolved phosphorus forms are lost from surface waters via downwelling and biological uptake (into POP) and are returned to surface waters via upwelling Trace element in ocean The trace metals can be classified into one of the following types: (1) nutrient, (2) conservative, and (3) scavenged, with some elements exhibiting a mixture of these types. Various forms of iron and silicon Fe(OH)2+ H3SiO4 Effects of trace element on biological organisms in the ocean, Trace elements concentrated in the soft parts of organisms and skeletal material. Trace elements affect behavior of marine biological systems They control uptaking process of some organisms They are dietary requirement for various organisms Primary productivity: Primary productivity is the rate at which energy is converted by photosynthetic and chemosynthetic autotrophs to organic substances. The total amount of productivity in a region or system is gross primary productivity. 2H2O + CO2 + light → (CH2O) + H2O + O2 Name of primary producer: Photosynthetic bacteria ,cyanobacteria Plants (seagrass) , saltmarsh Algae (seaweed and kelp) Phytoplankton: Phytoplankton fall into a number of major categories including diatoms, dinoflagellates, coccolithophores and picoplankton or cyanobacteria. Factors affecting primary production Sunlight: The sunlit (euphotic) zone has enough light for plants to carry out photosynthesis, so food is more abundant, and most of marine life is found there. The depth of this zone varies. Temperature : there is an optimal temperature for primary production. Primary production in tropical zone is larger than polar zone. Nutrient : nutrients play am important role in marine primary production . the water is enriched with mostly nutrients (estuarine water , upwelling zone ) in which primary production is relatively high. Soil Water: sunlight easily penetrate clear water, so primary production in clear water is greater than turbid water. Depth: beyond a depth of 200 meters that photosynthesis is no longer possible. Major nutrients in ocean Macronutrients micronutrients 1 Nitrogen (N)= NO3- NO2- NH4+ Phosphorous (P)= H2PO4- HPO4- PO43- Potassium (K) Carbon(C) Iron (Fe) Silica (Si)= SiO2 , Si(OH)4 Impact of excessive nutrients in the ocean Nutrient pollution (algal bloom), a form of water pollution, refers to contamination by excessive inputs of nutrients. It is a primary cause of eutrophication of surface waters, in which excess nutrients, usually nitrogen or phosphorus, stimulate algal growth. Sources of nutrient pollution include surface runoff from farm fields and pastures, discharges from septic tanks and feedlots, and emissions from combustion. Excess nutrients have been summarized as potentially leading to: Population effects: excess growth of algae (blooms Community effects: species composition shifts (dominant taxa); Ecological effects: food web changes, light limitation; Biogeochemical effects: excess organic carbon (eutrophication); dissolved oxygen deficits (environmental hypoxia); toxin production Human health effects: excess nitrate in drinking water (blue baby syndrome); disinfection by-products in drinking water Biodiversity effects: excessive algae blooms (biodiversity loss). Significance nutrients in oceanic productivity Primary productivity is defined as the amount of carbon fixed by autotrophic organisms through the synthesis of organic matter from inorganic compounds such as CO2 and H2O using energy derived from solar radiation or chemical reactions. The major process through which primary productivity occurs is thought to be photosynthesis. The reaction of this process is as follow- Light nCO2 + nH2O → (CH2O) n + nO2 Chlorophyll Primary producers are organisms, like plants, that can take inorganic molecules such as Carbon Dioxide and solar light’s energy and convert them into organic molecules such as carbohydrates. They are essential for marine plants and animals growth and maintenance of life in the sea. Silicon is also essential for plant growth They are important part marine organism’s body parts They are essential part of marine biogeochemical process. Large quantities of nutrients are taken up during the active growth of phytoplankton for the building up of their cellular protoplasm. nitrogen is a constituent of all proteins and nucleic acids. Plants consists of approximately 7.5% nitrogen (dry mass) Silicon cycle and major sources Silicon, the seventh-most-abundant element in the universe, is a key nutrient element in the ocean, required for the growth of diatoms and some sponges and utilized by radiolarians, silicoflagellates, several species of choanoflagellates, and potentially some picocyanobacteria. Four pathways serve as external sources of silicic acid (also called DSi) to the ocean, all of which ultimately derive from the weathering of Earth’s crust. Rivers also transport significant quantities of particulate amorphous silica that may dissolve, as may dust deposited on the ocean’s surface. Lastly, terrigenous silicates in sediments of continental margins may dissolve, and submarine basalts react with high- and low-temperature hydrothermal fluids, releasing DSi. 1: river fluxes: Rivers are responsible for almost 80 percent of the Si entering the global ocean 2: submarine water discharge : Submarine groundwater discharge (SGD) is a potentially important but poorly quantified source of nutrients to the coastal ocean. DSi input via submarine groundwater (SGW) influx to the ocean was not considered in the previous budget but may be considerable, and is similar in some places to surface river inputs (e). For instance, DSi input to the Bay of Bengal via SGW of 0.093 Tmol Si year−1 (Georg et al. 2009) is equivalent to 66% of the Ganges-Brahmaputra river flux of DSi to the ocean. 3: volcanic activity 4 : atmospheric inputs: 5: oceanic inputs: 6: Aeolian inputs. Estimation of aeolian inputs of DSi to the ocean (FA) requires knowledge of dust fluxes and dissolution rates. Dry deposition of particulate lithogenic silica onto the ocean ranges from 2.8 to 4.6 Tmol Si year-1. 7: hydrothermal vent inputs: They are inherently different because reactions at high temperatures leach silicon from the oceanic crust, resulting in high-DSi hydrothermal fluids, whereas cooling of these fluids before they exit from the seabed removes DSi through precipitation of clays like smectite Silicon is one of the most abundant elements on Earth. Hence it is also found universally in organisms. the minute oceanic algae, diatoms, and zooplanktons called radioralia, are the most important in terms of silicon biogeochemical cycling. The major inputs of silicon to the ocean are river runoff (at a rate of 4.2 x 1012 kg /y total), upwelling, and transportation of dust by wind. The particulate materials transported by rivers and wind form clastic rocks such as sandstone, or mud (clays that contains silicates) turns into shale. The major chemical species in the ocean is silicic acid (HSiO(OH)3 and its dissociated form SiO(OH)3–). The total amount of dissolved silicon in the ocean can beestimated at 3 x 1015 kg, assuming a concentration of 2 μg/ g. The growth and number of diatoms, however, are regulated by the availability of silicon in the ocean surface. Role of diatoms in silicon cycling and coastal marine food web Diatoms are major contributors of phytoplankton in the coastal zone and support major fisheries. Average silica production has been estimated at 6 Tmol Si year-1 in the major upwelling zones of the ocean and at 74 Tmol Si year-1 for eastern boundary coastal regions outside of the major upwelling zones The importance of studying the marine biogeochemical cycle of Si arises from both an ecological and a biogeochemical perspective and is related to the importance of diatoms in the global C cycle. Diatoms form the basis of the food web that characterizes the most productive regions and sustains the most important fisheries on the planet and play a fundamental role in the export of C to higher trophic levels. Diatoms are the best food for grazers. Seasonally sedimented phytoplankton blooms are a major source of nutrients that are processed rapidly through the benthic system in open coastal areas. Benthic suspension feeders are among the main contributors to the biomass of benthic communities of coastal and estuarine ecosystems worldwide . they benefit directly from pelagic primary production in the overlying water column and are responsible for a large share of the energy flow from the pelagic to the benthic system (Figure 11.3), in addition to secondary production in benthic environments. Important of diatoms in pelagic and benthic food web : a diatom is important because it represents a pool of energy with the appropriate size. diatoms are essential simply because they are often there. They tend to dominate whenever conditions become optimal for phytoplankton growth. These conditions are met in spring blooms, coastal upwelling plumes, river plumes, macrotidal coastal ecosystems and transient open ocean blooms triggered by wind-mixing events, decay of ocean eddies and atmospheric dust inputs . diatoms and dinoflagellates) generally have a low surface to volume ratio, which leads to a need for a nutrient-rich habitat .Diatoms dominate in a number of regimes that offer high-nutrient. Stoichiometry Stoichiometry is a section of chemistry that involves using relationships between reactants and/or products in a chemical reaction to determine desired quantitative data. In Greek, stoikhein means element and metron means measure, so stoichiometry literally translated means the measure of elements. Stoichiometric Coefficients: In a balanced reaction, both sides of the equation have the same number of elements. The stoichiometric coefficient is the number written in front of atoms, ion and molecules in a chemical reaction to balance the number of each element on both the reactant and product sides of the equation. Though the stoichiometric coefficients can be fractions, whole numbers are frequently used and often preferred. This stoichiometric coefficients are useful since they establish the mole ratio between reactants and products. In the balanced equation: 2Na(s)+2HCl(aq)→2NaCl(aq)+H2(g) we can determine that 2 moles of HCl will react with 2 moles of Na(s) to form 2 moles of NaCl(aq) and 1 mole of H2(g). If we know how many moles of Na we start out with, we can use the ratio of 2 moles of NaCl to 2 moles of Na to determine how many moles of NaCl were produced or we can use the ration of 1 mole of H2 to 2 moles of Na to convert to NaCl. This is known as the coefficient factor. Law of Conservation of Mass: According to this law, during any physical or chemical change, the total mass of the products remains equal to the total mass of the reactants. Stoichiometry allows us to make predictions about the outcomes of chemical reactions. Making useful predictions is one of the main goals of science. Here are some examples: Predict the mass of a product of a chemical reaction if given the starting masses of reactants. Predict the volume of a gas which will be produced by a reaction if given the starting amounts of reactants. Determine the optimal ratio of reactants for a chemical reaction so that all reactants are fully used. Redfield ratio or Redfield stoichiometry is the atomic ratio of carbon, nitrogen and phosphorus found in phytoplankton and throughout the deep oceans. Alfred Redfield analyzed thousands of samples of marine biomass across all of the ocean regions. From this research he found that globally the elemental composition of marine organic matter (dead and living) was remarkably constant across all of the regions. The stoichiometric ratios of carbon, nitrogen, phosphorus remain relatively consistent from both the coastal to open ocean regions. Some feel that there are other elements, such as potassium, sulfur, zinc, copper, and iron are also important in the ocean chemistry. As a result an extended Redfield ratio was developed to include this as part of this balance. This new stoichiometric ratio states that the ratio should be 106 C:16 N:1 P:0.1-0.001 Fe. Uses of red field ratio 1: The research that resulted in this ratio has become a fundamental feature in the understanding of the biogeochemical cycles of the oceans. 2: The Redfield ratio is instrumental in estimating carbon and nutrient fluxes in global circulation models. 3: They also help in determining which nutrients are limiting in a localized system, if there is a limiting nutrient. 4 :The ratio can also be used to understand the formation of phytoplankton blooms and subsequently hypoxia by comparing the ratio between different regions. Mass balance is the mass that enters a system must, by conservation of mass, either leave the system or accumulate within the system. Input=output + accumulation .if this balance equation is to be applied to an individual species and then the entire process. Input+ generation =output+consumption + accumulation Most oceanographers construct simple models to test their understanding of the essential elements of the system and to predict the response of a system to perturbations and forcing. The two main types of models used. These are: Box (or reservoir) Models and Continuous Transport-Reaction Models. The Change in Mass with Time = Sum of all Input Sources + Sum of Internal Sources –Sum of Outputs – Sum of all Internal Sinks Such box models are used to determine the rates of transfer between reservoirs and transformations within a reservoir. Advantages are: 1. It is easy to conceptualize where material is coming from and where it is going. 2. Provide an overview of fluxes, reservoir sizes, and turnover or residence times ). 3. They provide the basis for more detailed quantitative models. 4. They help identify gaps in knowledge. Disadvantages are: 1. The analysis is superficial and over-simplified. 2. Little or no insight is gained into what goes on inside the reservoirs or into the nature of the fluxes between them. 3. They usually assumes homogeneous average distributions within reservoirs 4. They can easily give a false impression of certainty, even if all the individual fluxes have solid estimates. Remember, a model is an imitation of reality Residence Time (τ The residence time (also called turnover time) is defined as the ratio of the dissolved mass in a reservoir divided by the mass flux in or out of the reservoir. For example, using a simple model with one source and one sink, τcan be thought of as the time it would take to fill the reservoir if the source (Q) remained constant and the sink was zero (or vice-versa). τ= mass / input or removal flux = M / Q = M / S and turbulent conditions Importance of primary producer for recycling nutrients in the ocean Role of primary producer in the utilization c, n ,p and si in the ocean Certain blue green algae (trichodesium spp.) fixes nitrogen on large scale in tropical and subtropical water using solar energy. Soluble nitrogen compounds of dead organism are broken down by proteolytic bacteria Plants(Diatoms and some chlorophyta) and animals(radiolarians) are silicified structured. Phytoplankton and marine plants take inorganic molecules such as Carbon Dioxide and solar light’s energy and convert them into organic molecules. Ocean acidification refers to a reduction in the pH of the ocean over an extended period of time, caused primarily by uptake of carbon dioxide (CO2) from the atmosphere. Process CO2 (aq) + H2O {\displaystyle \leftrightarrow } H2CO3 {\displaystyle \leftrightarrow } HCO3− + H+ {\displaystyle \leftrightarrow } CO32− + 2 H+. Impacts Hydrothermal vent Primary productivity is the rate at which energy is converted by photosynthetic and chemosynthetic autotrophs to organic substances. 15