VNU University Of Science - 334 Nguyen Trai –Thanh Xuan – Hanoi Faculty of EnvironmentEnvironmental Technology Environmental Chemistry REPORT Eutrophication on natural water Group Students: Dang Minh Son, Cu Thi Hien, Le Nam Thanh, Nguyen Ngoc Khanh, Phan Lam Tung, andNguyen Quang Van Class:K55 TT KHMT, Faculty of Environmental Science, VNU University of Science Instructor: Assoc Prof Nguyen Thi Ha Hanoi, 14thMay 2013 Abstract Eutrophication in natural water systems The paper is about eutrophication on natural water systems Eutrophication is water pollution as the result of the excess of one or more nutrient(s) in a water-body Eutrophication promote excessive plants growth leading to many effects on water quality such as increased biomass of phytoplankton, increases in blooms of gelatinous zooplankton, decreases in water transparency (increased turbidity), color, smell, and water treatment problems, dissolved oxygen depletion, loss of desirable fish species…Eutrophication can be human-caused or natural Untreated sewage effluent and agricultural run-off carrying fertilizers are examples of human-caused eutrophication However, it also occurs naturally in situations where nutrients accumulate (e.g depositional environments), or where they flow into systems on an ephemeral basis Nitrogen is one of two main agents that causes almost eutrophication Nitrogen pollution has increased remarkably over the past several decades as a result of increased creation of reactive N for fertilizer use and, inadvertently, from combustion of fossil fuels The paper makes clear of the sources where nitrogen (N) came from; its transformation, transportation and conversion processes in the system; the impacts of eutrophication on systems purposes One of the most dominant Introduction During the last four decades, eutrophication has undoubtedly been the most challenging threat to the quality of our freshwater resources Survey of the International Lake Environmental Committee has indicated in the early 1990s that some 40-50% of lakes and reservoirs are eutrophicated Many of these water bodies are extremely important for drinking water supply, substances causing Nitrogen (N2) recognition eutrophication Therefore, of is early eutrophication, understanding all processes relating to transformation of nitrogen in natural water during occurring eutrophication processes and impacts of it are so important to manage and minimize nutrient enrichment in almost water bodies This paper will give more knowledge for eutrophication in recreation, fishery, and other economic Eutrophication in natural water systems natural water, especially nitrogen that cause this phenomenon ensue, promoting growth of bacteria such Definition of eutrophication In the most basic terms, eutrophication is nutrient pollution When an ecosystem experiences an increase in nutrients, primary producers reap the benefits first In aquatic ecosystems, species such as algae experience a population increase (called an algal bloom) Algal blooms limit the sunlight available to bottomdwelling organisms and cause wide swings in the amount of dissolved oxygen in the water Oxygen is required by all aerobically respiring plants and animals and it is replenished in daylight by photosynthesizing plants and algae Under eutrophic conditions, dissolved oxygen greatly increases during the day, but is greatly reduced after dark by the respiring algae and by microorganisms that feed on the increasing mass of dead algae When dissolved oxygen levels decline to as Clostridium botulinum that produces toxins deadly to birds and mammals Zones where this occurs are known as dead zones Sources Eutrophication can be human-caused or natural Untreated sewage effluent and agricultural run-off carrying fertilizers are examples of human-caused eutrophication However, it also occurs naturally in situations where nutrients accumulate (e.g depositional environments), or where they flow into systems on an ephemeral Eutrophication generally excessive growth plant basis promotes and decay, favoring simple algae and plankton over other more complicated plants, and causes a severe reduction in water quality hypoxic levels, fish and other marine Eutrophication was recognized as a water animals suffocate As a result, creatures pollution problem in European and North such as fish, shrimp, and especially American lakes and reservoirs in the mid- immobile bottom dwellers die off In 20th century Since then, it has become extreme more widespread Surveys showed that cases, anaerobic conditions Eutrophication in natural water systems 54% of lakes in Asia are eutrophic; in fertilizer and livestock manure to provide Europe, 53%; in North America, 48%; in and South America, 41%; and in Africa, 28% crops.Mineral fertilizers are the major [1] Many ecological effects can arise source of nitrogen input in agriculture from stimulating primary production, but However, we cannot know exactly the there are three particularly troubling amount of nitrogen which crops need and ecological impacts: decreased we use fertilizer based on estimation So, biodiversity, changes species it is easy to make excessive nitrogen in supplement Nitrogen for composition and dominance, and toxicity Nitrogen effects particularly soluble to facilitate uptake by For further understanding about eutrophication, let us consider one case of eutrophication which is cause by the excess of nitrogen in the system in commercial fertilizer is crops Nitrogen which is not taken up by plants may be metabolized by microorganisms in the soil to improve soil fertility This is a slow process however, and the major risk is that nutrients, Nitrogen is one of two main agents (the particularly nitrate which is very soluble, other is Phosphorus) that causes almost will run off into surface water or percolate eutrophication ecosystems (N and P for saltwater into groundwater Livestock manure is the for freshwater second most important source of nutrient has inputs to agricultural land Not all the increased remarkably over the past several nitrogen contained in excreted manure is decades as a result of increased creation of spread on the land A certain amount is reactive and, lost through volatilization of ammonia inadvertently, from combustion of fossil from stables and during storage This fuels [2] There are many sources where N ammonia is a contributor to acidification can come from including the following Acid rain Concentration of nitrogen five sources [3] [4] dioxide in the air rises more and more AgricultureNitrogen is essential for crop because growth and human usually use mineral deforestation, transportation, agricultural ecosystems) N Nitrogen for pollution fertilizer use of burning fossil fuel, and industrial activities It combines with Eutrophication in natural water systems water vapor to create nitric acid which Chemical forms of nitrogen are most often soluble into the rain water to make acid of concern with regard to eutrophication, rain It is also cause the rise in nitrogen because concentration in natural water requirements so that additions of nitrogen Wastewater Untreated wastewater and wastewater treated by mechanical- biological methods contain about 32mg/L nitrogen So, waste water is a source of nitrogen which causes of nitrogen eutrophication in natural water plants have high nitrogen compounds will stimulate plant growth Nitrogen is not readily available in soil because N2, a gaseous form of nitrogen, is very stable and unavailable directly to higher plants Terrestrial ecosystems rely on microbial nitrogen fixation to convert N2 into other forms such as nitrates Aquaculture In aquaculture, excess fish However, there is a limit to how much food pollutes the water as complete use of nitrogen can be utilized Ecosystems the food cannot be achieved Nitrogen receiving more nitrogen than the plants present in the excess food is dissolved or require suspended in the water This process also Saturated terrestrial ecosystems then can effect to the amount of nitrogen in natural contribute both inorganic and organic water nitrogen to freshwater, coastal, and marine The sediment of water bodies like rivers, eutrophication, where nitrogen is also lakes, marshes -its muddy bottom layer typically -contains relatively high concentrations of following nitrogen These can be released to water, transformation of nitrogen in the system are called a nitrogen-saturated limiting part nutrient shows fate The and particularly under conditions of low oxygen concentrations The nutrients in State the sediment come from the past settling Nitrogen in water can take several forms of algae and dead organic matter The dominant combined N species in water are: dissolved inorganic N:NH 4+, State and transformation NO3-, NO2-; dissolved organic N; particulate N, which is usually organic but can contain inorganic N Eutrophication in natural water systems Transformation In normal its bioplasm by sunlight energy and condition, transformation inorganic substances through process depending on water properties, photosynthesis—the process of various inorganic nitrogen compounds eutrophication is described as follows: may be found In aerobic waters nitrogen is mainly present as N2 and NO3- and depending on environmental conditions it According to above equation, it can be may also occur as N2O, NH3, NH4+, HNO2, concluded that inorganic nitrogen and NO2- or HNO3 phosphorus are the major control factors Nitrification and de-nitrification processes carried out by various microorganisms Nitrification means ammonium oxidation from protein decomposition processes by bacteria, and subsequent conversion to nitrates This requires oxygen, which is added by aeration The water must be aerated for a sufficient period of time Ammonium is converted to nitrite, and subsequently to nitrate The reaction mechanism is a follows: for the propagation of algae, especially phosphorus Generally, the physical and chemical evaluation parameters were used to assess water eutrophication, mainly nutrient concentration (N and P), algal chlorophyll, water transparency and dissolved oxygen The eutrophication or red tide occurs when N concentration in water reaches concentration 300 reaches μg/L and 20 P μg/L Richardson et al (2007) reported that exceeding a surface water mean TP threshold concentration of 15 μg/L causes During the de-nitrification bacteria an ecological imbalance in algal, macro- decompose nitrates to nitrogen This does phyte and macro-invertebrate assemblages not require aeration, as it is an anaerobic as well as slough community structure in process Nitrogen is eventually released the Everglades areas [6] into air [5] In excess nutrient contents, water eutrophication is caused by the autotrophy algae blooming in water, which composes To further understand the fate of nitrogen in the system and how it transform, let us take the look deeper in the process Eutrophication in natural water systems Nitrogen cycling generally has reactions Assimilation, as shown in the following figure: Fixation, Ammonification, and Denitrifilication [7] Nitrogen bacterially demonstrate in Belham Tarm in English mediated, exergonic reduction process Lake District The author founded that which convert molecular N to ammona: added N-enriched sodium nitrate was fixation is a Nitrification, removed from water within 14days The added In general, N fixation adenosine N accumulated in resulting Microcytis bloom These result suggested triphosphate (ATP) which is generated by that photosynthesis, is producers maybe important mechanism However for removal of nitrate, although this Anabeana, depends on the ultimate fate of nitrogen Aphanizomenon, Gloeotrichia) can fix once it reach the sediment because of N nitrogen directly maybe available for re-release Assimilation of nitrogenThe importance Ammonification Ammonium production of plankton assimilation of nitrate was occur both in the water column of rivers inefficient so at cyanobacteria this night (primary process Nitrogen stripping by primary Eutrophication in natural water systems and lakes and their sediment Microbial nitrite is rarely present in appreciable decomposition convert organic nitrogen to concentration in fresh water Nitrate, the ammonia trial form This process is end product is highly oxidized, soluble oxygen-demanding regenerates and biologically available.Nitrification is available nitrogen for re-assimilation by oxygen demanding and can, in some primary producer Ammonification can aquatic systems, create anoxic conditions result rapid in nitrogen cycling between This is because of Nitrosomonas and the sediment and the water column nitrobacter are strict aerobes, requiring Ammonia can exist as the ammonium minimum oxygen concentration around cation (NH4+) or as the un-ionied ammonia 2mg/l to function efficiently and molecule (NH3) High temperature and high pH encourage the conversion of ammonium to ammonia High concentration of ammonia areusually only associated with wastewater discharge where biological treatment is minimum Denitrification Loss of nitrate can occur through denitrification or dissimilatory nitrate reduction Denitrification is quantitative more important, particularly in lake sediment and is high in summer month The rate and extent of Nitrification is a two stage oxidation denitrification is controlled by the oxygen process mediated be chemoautotrophic supply and available energy provided by general organic matter It is seen as an important Nitrosomas (NH3 to NO2-) and nitrobacter (NO2- to NO3-) The net reaction mechanism in the reduction of nitrate concentration in reservoirs, but it is limited be the requirement for anaerobic condition and fixed bacterial carbon The oxidation of ammonia to nitrite by supply nitrosomonas is usually rate-limiting, so Eutrophication in natural water systems Table 1: FACTORS RELATE TO EACH PROCESS OF NITROGEN Process Nitrogen fixation Mineralization Nitrification Denitrification Assimilation Factor Cyanobacteria at lake surface Photosynthesis bacteria at anoxic zone N fixation when soluble N concentration is low More important in lake sediment Rapid mineralization when plankton biomass dominate lake Autotrophic in NH4+ and O2 dependent Seasonal, affected by NO3-supply general occur in sediment-water interface Phytoplankton, varies with NO3concentration + NH4 can be assimilated if available As mention in the previous part of the paper, many ecological effects can arise from stimulating primary production including the decreased biodiversity, changes in species composition and dominance, and toxicity effects Rather than impacts of nitrogen eutrophication, the below effects will give the whole picture of eutrophication in general to ecosystem [8] Effects of eutrophication Effect on water chemistry Dissolved Oxygen (DO) Nutrient enrichment leads to excessive growth of primary Eutrophication in natural water systems producers as well as heterotrophic bacteria and fungi, which increases the metabolic activities of natural water and may lead to a depletion of dissolved oxygen (Mallin et al 2006) During the day, photosynthesis by primary producers provides a large amount of oxygen to the water At night, photosynthesis stops and elevated respiration by algae and bacteria continues to consume dissolved oxygen, which can deplete DO Furthermore, as primary producers die, they are decomposed by bacteria that consume oxygen Large populations of decomposers consume more dissolved oxygen, which increases the severity of DO depletion For example, daily oxygen fluctuations in enriched streams at low flow were reported to range from a high of approximately 25 mg/L at noon to a low of approximately mg/L at night (Wong and Clark 1976) pH During photosynthesis, carbon dioxide (CO2) and water are converted by sunlight into oxygen and carbohydrate Hydroxyl ions (OH-) are produced, raising the water column pH In addition, plants use a large amount of dissolved CO2 for photosynthesis, resulting in lower levels of carbonic acid (H2CO3) in the water column Thus, photosynthesis increases water column pH At night, increased respiration from biota increases the release of CO2 into the water, increasing the production of carbonic acid and hydroxyl ions, which, in turn, increases the acidity Other chemicals Toxic effects of chemicals released from certain cyanobacteria have been reported in lakes; very few studies have found cyanotoxins in streams Pfiesteria, a toxic substance produced by dinoflagellates that cause fish kills, has also been reported in coastal rivers associated with nutrient enrichment (Burkholder 1999) A relatively new golden alga, Prymnesium parvum, has been reported to be toxic in Texas The toxin prymnesin affects gill-breathing organisms including fish, tadpoles, and clams (Rhodes and Hubbs 1992) and has been responsible for an estimated 2.5 million dead fish and millions of dead clams in the Pecos, the Colorado, and Brazos river basins in Texas 10 Eutrophication in natural water systems Other chemicals can taint drinking water supplies and recreational waters 2methylisoborneol and geosmin are two chemicals produced by cyanobacteria that can cause taste and odor problems in drinking water Livestock that drink water contaminated with cyanobacteria have died (Dodds and Welch 2000) Humans who drink or swim in water that contains high concentrations of toxins from cyanobacteria may experience gastroenteritis, skin irritation, allergic responses, or liver damage (CDC 2004) Direct biological responses of streams to eutrophication: primary producers Responses of algal biomass to nutrient enrichment A number of authors have documented the positive relationship between benthic algal biomass and nutrient concentrations (see reviews by ENSR 2001, Virginia WRRC 2006, Dodds 2002, 2006) These studies established that total N and total P in the water column are significantly related to benthic algal biomass that the more nutrient enrichment is, the more algal biomass has Responses of algal species composition to nutrient enrichment Algal species composition changes with elevated nutrient concentrations (Stevenson 1996, Pan et al 1996, Stevenson and Smol 2001) Because of their small scale, periphytic algae composition receives less public attention, while problematic macroalgae (e.g., Cladophora) and cyanobacteria receive more Under most circumstances, a diatom dominated algal community represents healthy, non-enriched stream water quality, while a predominance of filamentous algae may indicate problems with nutrient enrichment Since algae are often the problem associated with enrichment, a change of taxonomic composition in a stream can show whether nuisance algae are present and can indicate long or short-term changes in point and nonpoint source pollution (Lowe and Pan 1996) that cannot be detected by a onetime sampling of water chemistry Thus, algal species composition could be considered an important indicator of nutrient pollution Responses of macrophytes to nutrient enrichment Nutrient effects on macrophytes are poorly studied (Chambers et al 1999) However, nutrient supply can affect plant attributes Nutrient enrichment in streams and rivers leads to increasing plant biomass (Chambers and 11 Eutrophication in natural water systems Prepas 1994, Gucker et al 2006), declines in plant richness (Thiebaut and Muller 1998, San- Jensen et al 2000) For example, reduction of nutrient (particularly N) input from municipal wastewater sources led to macrophyte biomass declines in the Bow River (Alberta) (Sosiak 2002) Indirect biological responses of streams to eutrophication: microbial cycling The organisms are important components of water food webs and play a key role in carbon cycling Bacteria -Similar to algae, bacteria are also limited by nutrients in aquatic systems, especially in planktonic forms (Cole 1982) Bacteria can outcompete algae for nutrients because of their higher surface area to volume ratio - Bacteria can either inhibit algae by outcompeting it when nutrients are limited, or they may interact positively with algae by using its photosynthetic products and decomposing dead plant and algal biomass and recycling nutrients - Nutrient enrichment tends to increase both algal and bacteria biomass (Carr et al 2005) Sobczak (1996) found that interactions between bacteria and algae are weakened in the presence of a labile source of allochthonous DOC, under extreme light limitation, or under extremely oligotrophic conditions where algae are severely nutrient limited Fungi Similar to bacteria, fungi also play an important role in detrital decomposition in water Fungal communities in many water bodies are also limited by nutrients (Grattan and Suberkropp 2001, Tank and Dodds 2003) This limitation can be released by nutrient additions that lead to significantly higher fungal biomass Bacteria and fungi also compete with each other for nutrients (Gulis and Suberkropp 2003b) Gulis and Suberkropp (2003b) found that fungi inhibit bacterial growth and reduce bacterial biomass by 2-fold at low nutrient concentrations, suggesting that nutrient availability may modify microbial interactions Fungi seem to be a superior competitor than bacteria on leaves Fungal biomass can be one or two order of magnitudes higher than bacterial biomass in polluted water 12 Eutrophication in natural water systems Indirect biological responses to eutrophication: herbivores Nutrient enrichment accelerates autotrophic production and algal biomass in water, and consequently changes ecosystem structure at other trophic levels Invertebrates - Changes in macroinvertebrate composition with nutrient enrichment are more complicated than changes of abundance Mayflies, a group of invertebrates that are considered sensitive to environmental pollutants, show highest relative abundance when algal biomass is at intermediate levels (Miltner and Rankin 1998) The abundance of scrapers, a functional group that is closely related to grazers, is highest when nutrient levels are elevated, indicating positive effects from increased algal availability Similarly, scrapers and detritivores (e.g., Oligochaeta, Lumbriculidae) have shown significant increases in density or biomass on certain substrata with enrichment even while total macroinvertebrate density or biomass did not (Sabater et al 2005) - Enrichment may also alter benthic habitat for macroinvertebrates In addition to food sources for invertebrates, benthic algae, especially macroalgae, are important habitat for macroinvertebrates Some algal species or growth forms are grazer- resistant (e.g., Oedogonium spp.) and are good habitat for many invertebrates Fish - Fish may benefit from increases in food availability when nutrient additions increase primary and secondary production Enrichment of oligotrophic streams and rivers may result in increased algal biomass, increased benthic invertebrates, and fishes - One of the consequences of nutrient enrichment may be loss of sensitive fish taxa and increases in tolerant taxa The strong correlation between fish metrics and nutrient pollution indicates that nutrient enrichment has contributed to changes in the structure of fish assemblages While nutrient enrichment could potentially benefit fish production in the short term, the ecological consequence of nutrient addition could have severe impacts on water ecosystems (Stockner et al 2000) In addition, excess algal growth would eliminate important feeding and respiration habitat, further reducing survivorship While it is evident that some nutrient subsidy benefits the growth of select species, the overall impact is negative, especially at stressful nutrient levels 13 Eutrophication in natural water systems Effect on food web structure As we know that each trophic level is controlled by both predators (top-down control) and resources (bottom-up control) Changes at one trophic level would alter material cycling and other trophic levels in the food web (trophic cascading) Long-term fertilization studies have demonstrated the cascading effect of nutrient enrichment at several trophic levels Huntsman (1948) first recognized that fertilizers stimulate downstream algal growth, and lead to increased insect and fish densities Since then, more quantitative studies (Peterson et al 1993, Slaney and Ashley 1998) have shown that nutrient additions increase algal biomass at least at the beginning of the enrichment Later, top-down forces take effect to control primary consumers and consequently algal biomass Generally, grazing has demonstrated a larger effect than resource limitation in influencing algal biomass and composition (Steiman 1996, Lamberti 1996, Flecker et al 2002) While nutrient additions affect higher trophic levels, predators also play an important role in influencing nutrient demand and nutrient supply Nutrient limitation in the presence and absence of fishes and the response to nitrogen enrichment is significantly greater on substrates accessible to natural fish assemblages compared to substrates where grazing fishes are excluded Many experiments demonstrate simultaneous and interactive effects of top- down and bottom-up factors in limiting primary producers in water Conclusion Today there is a scientific consensus, which has emerged from research at several spatial and temporal scales that N represents the largest pollution problem in coastal waters and one of the greatest threats to the ecological functioning of these ecosystems (Nixon 1995; Howarth et al 2000b; NRC 2000) [2] Along with this is the widespread of eutrophication in many water systems leading to water pollution in many regions Human activities can accelerate the rate at which nutrients enter ecosystems Runoff from agriculture and development, pollution from septic systems and sewers, and other human-related activities increase the flow of both inorganic nutrients and organic substances into ecosystems 14 Eutrophication in natural water systems Eutrophication poses a problem not only to ecosystems, but to humans as well Reducing eutrophication should be a key concern when considering future policy, and a sustainable solution for everyone, including farmers and ranchers, seems feasible While eutrophication does pose problems, humans should be aware that natural runoff (which causes algal blooms in the wild) is common in ecosystems and should thus not reverse nutrient concentrations beyond normal levels Cleanup measures have been mostly, but not completely, successful but still, some targeted point sources did not show a decrease in runoff despite reduction efforts The knowledge given by this paper will provide basic information about eutrophication relate to nitrogen, in order to find solutions to treat, manage, minimize this polluted phenomenon Because this paper just focus on the sources, fate, transformation, and impacts of Nitrogen in eutrophication , if needing more information relating to eutrophication, the following references will provide for more understanding References [1] Lake Biwa Research Institute, "Survey of the State of the World's Lakes," Lake Biwa Research Institute, 1993 [2] Robert W Howarth and Roxanne Marino, "Nitrogen as the limiting nutrient for eutrophication in coastal marine ecosystems: Evolving views over three decades," American Society of Limnology and Oceanography, Inc, 2006 [3] Donald M Anderson, Patricia M Glibert, Joann M , "Harmful algal blooms and eutrophication: Nutrient sources, composition, and consequences," Estuaries, vol 25, no 4, pp 704-726, 2002 [4] "Division of Technology, Industry and Economics," United Nations Environment Programme UNEP, 14 May 2013 [Online] Available: http://www.unep.or.jp/ietc/publications/short_series/lakereservoirs-3/3.asp [5] Xiao-e YANG, Xiang WU, Hu-lin HAO, Zhen-li HE, "Mechanisms and assessment 15 Eutrophication in natural water systems of water eutrophication," Journal of Zhejiang University Science B, vol 3, no 9, pp 197-209, 2008 [6] David W Bressler and Michael J Paul, PhD, "Effect of eutrophication on wetland ecosystems," Tetra Tech, Inc [7] A Heathwaite, "Nitrogen cycling in surface waters and lakes," in Nitrogen cycle Surface water, 1993 [8] Lei Zheng, PhD and Michael J Paul, PhD, "Effects of eutrophication on stream ecosystems," Tetra Tech, Inc 16 [...].. .Eutrophication in natural water systems Other chemicals can taint drinking water supplies and recreational waters 2methylisoborneol and geosmin are two chemicals produced by cyanobacteria that can cause taste and odor problems in drinking water Livestock that drink water contaminated with cyanobacteria have died (Dodds and Welch 2000) Humans who drink or swim in water that contains high concentrations... Fungi seem to be a superior competitor than bacteria on leaves Fungal biomass can be one or two order of magnitudes higher than bacterial biomass in polluted water 12 Eutrophication in natural water systems Indirect biological responses to eutrophication: herbivores Nutrient enrichment accelerates autotrophic production and algal biomass in water, and consequently changes ecosystem structure at other trophic... producers in water 6 Conclusion Today there is a scientific consensus, which has emerged from research at several spatial and temporal scales that N represents the largest pollution problem in coastal waters and one of the greatest threats to the ecological functioning of these ecosystems (Nixon 1995; Howarth et al 2000b; NRC 2000) [2] Along with this is the widespread of eutrophication in many water systems... humans as well Reducing eutrophication should be a key concern when considering future policy, and a sustainable solution for everyone, including farmers and ranchers, seems feasible While eutrophication does pose problems, humans should be aware that natural runoff (which causes algal blooms in the wild) is common in ecosystems and should thus not reverse nutrient concentrations beyond normal levels Cleanup... runoff despite reduction efforts The knowledge given by this paper will provide basic information about eutrophication relate to nitrogen, in order to find solutions to treat, manage, minimize this polluted phenomenon Because this paper just focus on the sources, fate, transformation, and impacts of Nitrogen in eutrophication , if needing more information relating to eutrophication, the following references... stressful nutrient levels 13 Eutrophication in natural water systems Effect on food web structure As we know that each trophic level is controlled by both predators (top-down control) and resources (bottom-up control) Changes at one trophic level would alter material cycling and other trophic levels in the food web (trophic cascading) Long-term fertilization studies have demonstrated the cascading effect... eutrophication in coastal marine ecosystems: Evolving views over three decades," American Society of Limnology and Oceanography, Inc, 2006 [3] Donald M Anderson, Patricia M Glibert, Joann M , "Harmful algal blooms and eutrophication: Nutrient sources, composition, and consequences," Estuaries, vol 25, no 4, pp 704-726, 2002 [4] "Division of Technology, Industry and Economics," United Nations Environment... May 2013 [Online] Available: http://www.unep.or.jp/ietc/publications/short_series/lakereservoirs-3/3.asp [5] Xiao-e YANG, Xiang WU, Hu-lin HAO, Zhen-li HE, "Mechanisms and assessment 15 Eutrophication in natural water systems of water eutrophication, " Journal of Zhejiang University Science B, vol 3, no 9, pp 197-209, 2008 [6] David W Bressler and Michael J Paul, PhD, "Effect of eutrophication on wetland... leading to water pollution in many regions Human activities can accelerate the rate at which nutrients enter ecosystems Runoff from agriculture and development, pollution from septic systems and sewers, and other human-related activities increase the flow of both inorganic nutrients and organic substances into ecosystems 14 Eutrophication in natural water systems Eutrophication poses a problem not only to... high concentrations of toxins from cyanobacteria may experience gastroenteritis, skin irritation, allergic responses, or liver damage (CDC 2004) Direct biological responses of streams to eutrophication: primary producers Responses of algal biomass to nutrient enrichment A number of authors have documented the positive relationship between benthic algal biomass and nutrient concentrations (see reviews