Mechanisms and assessment of water eutrophication

Yang et al. 1J Zhejiang Univ Sci B 2008 9(3):197-20997Journal of Zhejang University SCIENCE BISSN 1673-1581 (Pnnt); ISSN 1862-1783 ((Online)www.zu.du.cnjzus; ww.springrdink.comE-mail jzus@zju.edu.cnJZuSReview:Mechanisms and assessment of water eutrophicationXiao-e YANG', Xiang wul2, Hu-lin HAO', Zhen-li HE'3(MOE Key Laboratory of Pllued Environment Remediation and Ecological Health, Zhejiang Universiny, Hangzhou 310029, China)(Zhejiang Provincial Key Laboratory of Subtropic Soil and Plant Nurition, Zhejiang Univeriy, Hangzhou 310029, China)(Institute of Food and Agriculural Sciences, Indian River Research and Education Center, University ofFlorida, Fort Pierce, FL 34945, USA)tE-mail: xyang@zju.edu.cnReceived Dec. 24, 2007; revision accepted Jan.28, 2008Abstract:Water eutrophication has become a worldwide environmental problem in recent years, and understanding themechanisms of water eutrophication will help for prevention and remediation of water eutrophication. In this paper, recent ad-vances in current status and major mechanisms of water eutrophication, assessment and evaluation criteria, and the influencingfactors were reviewed. Water eutrophication in lakes, reservoirs, estuaries and rivers is widespread all over the world and theseverity is increasing, especially in the developing countries like China. The asessment of water eutrophication has been ad-vanced from simple individual parameters like total phosphorus, total nitrogen, etc, to comprehensive indexes like total nutrientstatus index. The major influencing factors on water eutrophication include nutrient enrichment, hydrodynamics, environmentalfactors such as temperature, salinity, carbon dioxide, element balance, etc, and microbial and biodiversity. The occurrence ofwater eutrophication is actually a complex function of all the possible influencing factors. The mechanisms of algal blooming arenot fully understood and need to be futher invetigated.Key words: Eutrophication mechanisms, Influencing factors, Nutrient enrichment, Assessment criterion, Water qualitydoi: 10.1631/jzus.B0710626Document code: ACLC number: X52INTRODUCTIONconsidered as a major threat to the health of coastalmarine waters (Andersen et al, 2004). Once a waterWater eutrophication is one of the most chal-body is eutrophicated, it will lose its primary functionslenging environmental problems in the world. Theand subsequently influence sustainable developmentincreasing severity of water eutrophication has beenof economy and society. Therefore, nowadays thebrought to the attention of both the govermments andsolution of water eutrophication and recovery of thethe public in recent years. The mechanisms of water multiple functions of the water system have becomeeutrophication are not fully understood, but excessivethe key issues for environmental biologists. The mainnutrient loading into surface water system is consid- purpose of this paper is to provide a brief review onered to be one of the major factors (Fang et al, 2004;.recent advances on understanding the mechanisms ofTong et al, 2003). The nutrient level of many lakes water eutrophication and progresses in identifying theand rivers has increased dramatically over the past 50influence factors inducing water eutrophication.years in response to increased discharge of domesticwastes and non-point pollution from agriculturalpractices and urban development (Mainstone and Parr，DEFINITION AND OCCURRENCE OF WATER2002). For more than 30 years, nutrient enrichment,EUTROPHICATIONespecially phosphorus (P) and nitrogen (N), has beenDefinil中国煤化工" Project supported by the Key Project from the Ministry of Education ofB large amountsChina (No. 705824), the Project from Science and Technology Bureauof plaYHCN M H Shie (fom theof Zhejiang Province No.2006C13059), and a grant from the St. LucieRiver Water litiaive (SFWMD contract No. OT060162), USA, in partGreek words eu meaning“well" and trophe meaning19Yang etal./J Zhejang Univ Sci B 2008 9(3):197-209"nourishment"). Eutrophication can be defined as thespite the use of over 17000 ha of stormwater treatmentsum of the effects of the excessive growth of phyto-areas (Richardson et al, 2007).planktons leading to imbalanced primary and secon-Assessment of water eutrophicationdary productivity and a faster rate of succession fromSurface water quality guidelines have been im-existence to higher serial stage, as caused by nutrientproved in recent years. The parameters to assess theenrichment through runoffs that carry down overusedfertilizers from agroecosystems and/or dischargedambient surface water quality have been increased. Inhuman waste from settlements (Khan and Ansari,China, the parameters for assessing environmental2005). Water eutrophication can be greatly acceler-quality of surface water have been increased to overated by human activities that increase the rate of nu-30 (CNEPA, 2002). Five classes of surface watertrient input in a water body, due to rapid urbanization,quality have been set up, and some selected parame-industrialization and intensifying agricultural pro-ters for assessing water quality of lakes or reservoirsduction. For lake aquatic ecosystems, buman activi-are shown in Table 1. However, there are no perfectties in the watershed can lead to loss of dominantevaluation criteria for assessing water eutrophication.species and functional groups, high nutrient tumover,Generally, the physical and chemical evaluation pa-low resistance, high porosity of nutrients and sedi-rameters were used to assess water eutrophication,ments, and the loss of productivity (Liu and Qiu,mainly nutrient concentration (N and P), algal chlo-2007). For example, aquaculture is one of many hu-rophyll, water transparency and dissolved oxygen.man activities contributing to the environmental de-Although there are many different assessment pacline of coastal waters and the collapse of fisheriesrameters, the concentrations of total nitrogen andstocks worldwide (Alongi et al, 2003). Because thephosphorus are the two basic ones. Cheng and Liinfluence of the human activities, excessive nitrogen,(2006) used total nutrient status index (TNI) to assessphosphorus and other nutrients are loaded into watereutrophication status of lakes. The calculation of totalbodies like lake, reservoirs, embouchure and bay,nutrient status index is as follows:which could cause negative ecological consequencesTNI= SW,TNI, w,=引/2q,on aquatic ecosystem structures, processes and func-tions, result in the fast growth of algae and otherwhere, TNI is the sum of indexes of all nutrient pa-plankton, and deteriorate water quality (Western,rameters, TNI; is the TNI of j parameter, W; is the2001). Generally speaking, water eutrophication isproportion of j parameter in the TNI, and rgj is thecaused by the autotrophy algae blooming in water,relation of chlorophyll a (Chla) to other parameters.which composes its bioplasm by sunlight energy andThe available parameters concerned include total ni-inorganic substances through photosynthesis- -thetrogen (TN), total phosphorus (TP), Chla, dissolvedprocess of eutrophication is described as follows:oxygen (DO), chemical oxygen demand by K2MnO4oxidation method (CODMn), biological oxygen de-106CO2+ 16NO; + HPO? +122H20+18H*mand (BODs), etc, and TN, TP and Chla are selectedEnergy+microelement' C1o6H26O11oNi6P (bioplasm for calculaing the TNI (Cheng and Li, 2006). Table 2of algae)+138O2.shows the burthen values of TN, TP and TNI in vari-ous eutrophicated water. It has been shown that theAccording to above equation, it can be concludedeutrophication or red tide occurs when N concentra-that inorganic nitrogen and phosphorus are the major tion in water reaches 300 ug/L and P concentrationcontrol factors for the propagation of algae, especially reaches 20 ug/L. Richardson et al.(2007) reported thatphosphorus. The Florida Everglades, a wetland of exceeding a surface water mean TP threshold con-intemnational importance, has been undergoing a sig- centration of 15 ug/L causes an ecological imbalancenificant shift in its native flora and fauna due to ex- in algal, macrophyte and macroinvertebrate assem-cessive total phosphorus (TP) loadings (an average of blage中国煤化工Y structure in the147 ton per anum from 1995 to 2004) and an elevated Everg:onsidered that amean TP concentration (69 μgL of TP in 2004) from threshHcNMHGmaybemoreeagricultural runoff and Lake Okeechobee outflow de- alistic and protective for all trophic levels.Yang et al.1Jhejang Univ SciB 2008 9(3):197-209199Table 1 The criteria of surface water quality for lakes or reservoir (CNEPA, 2002)Surface water quality classificationClass IClass IIClass IVClass VWater temperature (°C)Maximum week increasesl; maximum week decreases2H6-9DO (mg/L)Saturation290%≥52:CODma(mg/L)<4≤6s10≤I5CODcr (mgL)S20s30≤40BODs (mg/L)≤3≤4≤10TN (mg/L)S0.2s0.5S1.0S1.5S2.0NH-N (mg/L)s0.15NO2-N (mgL)<0.06<0.1c0.15Sl.0≤1.0TP (mg/L)≤0.025g0.05s0.1s0.2Chlorophyll as0.001s0.004≤0.01s0.03s0.065Transparency (m)≥1:4>2.521.520.5Escherichia coli(Lh)S200S2000≤10000S20000≤40000DO: dissolved-oxygen; CODhma: Chemical oxygen demand by KzMnO4 oxidation method; CODc: Chemical oxygen demand by chro-mium oxidation metbod; BODs: Biological oxygen demand; TN: Total nitogen; TP: Total phosphonusTable 2 The burden values of N and P in various eutrophicated waterEutrophic statusTP(ugL)TN (ugL)Primary productivityTNIReferencesOligotropic water5~10250-6005~300 mg C/m20~30 Likens et al.(1977)Moderately eutrophic10-30500~11001000 mg C(m2d)31-60 Cheng and Li(2006Richardson et al.(2007)Eutrophic30~1001000-200061~100Hypereutropic>100>2000TN: Total nitrogen; TP: Total phospborus, TNI: Total nutrient status indexInglett and Reddy (2006) reported evidences tonitrogen by phytoplankton grown under eutrophicationsupport the use of stable C (delta C-13) and N (deltaand subsequent OM decomposition and denitrificationN-15) isotopic ratios as indicators for eutrophicationin surface sediments, indicating that the lake has suf-and shifts between N and P limitation. Lin et al.(2006) fered from progressive eutrophication since 1990.compared the stable isotopes from dissolved nutrientsMore sensitive biological indicators for assess-and plants and water column nutrient parameters and ing water eutrophication are needed to further study.integration of multiple proxies in a sediment coreWater eutrophication caused a degradation of healthyfrom Meiliang Bay of Taihu Lake, and found thataquatic ecosystem, so the assessment methods anddifferences in aquatic plant species and trophic statusparameters should reflect the extents of aquatic eco-between East Taihu Bay and Meiliang Bay are indi-system health. A set of ecological indicators includingcated by their variations in delta C-13 and delta N-15structural, functional and system-level aspects wereof aquatic plants and delta N-15 of NHt -N. A sig-proposed for a lake ecosystem health assessment,nificant influence of external nutrient inputs on wateraccording to the structural, functional and sys-quality of Meiliang Bay is reflected in temporal tem-level responses of lake ecosystems to chemicalchanges in delta N-15 of NHt -N and hy-stresses including acidification, eutrophication, anddro-environmental parameters. The synchronouscopper, oil and pesticide contamination. The struc-change between delta C-13 and delta N-15 values oftural indicators included phytoplankton cell size andsedimented organic matter (OM) has been atributedbiomass, zooplankton body size and biomass, speciesto elevated primary production at the beginning ofdiversitv macro- and micro-7oonlankton biomass, theeutrophication between 1950 and 1990, and then zooplan中国煤化工the macrozoo-recent inverse correlation between them has beenplanktd!YH. CNMH Ghe functionalcaused by the uptake of N- l5-enriched inorganic indicators encompassea une aigal i assimilation ratio,200Yang et al. 1J Zhejang Unv SciB 2008 9(3):197-209resource use eficiency, community production, gross and river in the world. Erie Lake is excessively rich inproduction/respiration (i.e, P/R) ratio, gross produc- nutrients (Reutter, 1989), which has resulted in hugetion/standing crop biomass (i.e, P/B) ratio, and blooms of floating blue green algae and the atchedstanding crop biomass/unit energy flow (i.e, B/E) green alga, Cladophora spp. These blooms haveratio. The ecosystem-level indicators consisted of rolled onto beaches in large mats resembling greenecological buffer capacities, energy, and structural steel wool. Water eutrophication has been reported inenergy. Based on these indicators, a direct measure- USA for Washington Lake (Welch and Crooke, 1987),ment method (DMM) and an ecological modelingOkeechobee Lake (Schelske, 1989), City Park Lakemethod (EMM) for lake ecosystem health ssessment (Ruley and Rusch, 2002), etc. In Lugano Lake, be-were developed (Xu et al, 2001). The results of a casetween Italy and Switzerland, a faster rate of eutro-study demonstrate that both methods provided similar phication was reported due to excessive dischargesresults which corresponded with the lake's actualfrom human settlements around the lake, owing totrophic state.population increase and immigration (Barbieri andSimona, 2001). The majority of Danish lakes areOccurrence of water eutrophicationhighly eutrophic due to high nutrient input from do-The investigation from the UNEP (United Nationmestic sources and agricultural activities (Jeppesen etEnvironmental Protection) indicates that about al, 1999). Garg et al.(2002) studied three lakes of30%~ 40% of the lakes and reservoirs have been af-Bhopal (Upper Lake, Lower Lake and Mansarovarfected more or less by water eutrophication all over Lake) in India, to assess the potential fertility of lenticthe world. Table 3 cites selected samples of water waters and analyze the floral ecology. The highesteutrophication occurrence in lake, reservoir, estuary level of eutrophication was found in MansarovarTable 3 Selected samples of water eutrophication occurrence in lake, reservoir, estuary and river in the worldNutrient N, P)PhytoplanktonWater bodyHistory of eutrophicationReferencesconcentrationsbiomassErie Lake, USA TP: 115 ugLChlorophyll 2:Blu-green algae bloomReutter, 1989;58 g/Lbetween 1965 and 1979Maggie, 2004Declined quality from 1995lkeechobee Lake, TP: 50~100 ug/LN and P are limitors Eutrophic at presentSchelske, 1989Florida, USAfor phytoplanktonCity Park Lake, TN: 682 ug/LChlorophyll a:Eutrophic (000-20)Ruley and Rusch,Louisiana, USA TP: 330 ug/L35.1 ug/L2002Lugano LakeTP: 140 ug/LPhytoplankton dry. Strongly eutrophic from 1960s Barbieni and Simona,weight: 7~16 g/m22001Danish lakesTN: 2.4 mg/LHighly eutrophicJeppesen et al, 1999TP: 0.37 mg/L73 ug/LPamvotis Lake,TP: 0.11 ug[L,Cultural eutrophication over Romero et al, 2002NorthwestNH; : 0.25 mg N/L,the past 40 years;GreeceEutrophication at presentNO; : 0.56 mg N/LBerg River, South TN: 217 mg/L,Hypertrophicde Vlliers, 2007AfricaTP: 70 mg/LChivero Lake,TN: 0.3~8.4 mg/L Chlorophyll a:Highly eutrophic since 1980s Nhapi, 2004ZimbabweTP: 1.01~5.01 mg/L18.02-22.48 g/LNdebele and Magadza,2006Taihu Lake, China TN: 2.56~ 4.5 mg/LAlgae biomass:Class I/I in the early 1960s; Ye et al, 2007TP: 0.25-0.35 g/L2.7-6.4 mg/LClass IV in the mid-1990s;Jin et al, 2006Now, inferior Class VSonghua Lake,TN: 1.14-1.98 mg/L Algae density:中国煤化工时a,2004ChinaTP: 0.038~0.102 mg/L 210.84x10*-432.68x10* cl/LYHCNMH GDianchi Lake,TN: 2.13- 8.27 mg/LClass I11 In tne early 1Y/US;Guo and Sun, 2002_ChinaTP: 0.33-0.59 mg/LYang et al.1JZhejiang Univ Scl B 2008 9(3):197-209201Lake. The nutrient loading into the lake initiallytreatment rate is 60% in 2030, approximately 30 bil-promoted the growth of phytoplanktons. Eutrophica-lion ton of polluted water would still be dischargedtion constitutes a serious threat to many Europeandirectly into the lakes. Therefore, by 2030, all thelakes (Sendergaard et al, 2007), such as Pamvotisurban lakes and most of the medium sized lakes at theLake in Northwest Greece (Romero et al, 2002),urban-rural fringe areas in China may be eutrophi-which has undergone cultural eutrophication over thecated or bypertrophicated.past 40 years and is currently eutrophic. In SouthIn the region of Yangtze River delta, 80% of theAfrica, de Villiers (2007) reported that hypertrophicrivers have been polluted and the water quality cannotconditions indicated by TP levels prevail at leastmeet the standards of drinking water source. Theepisodically at all of the Berg River monitoring sta-degraded water quality mainly due to eutrophicationtions; additionally, river water phosphate levels showin this region has resulted in extremely serious prob-a dramatic increase by a factor of more than 10 overlems for drinking water supply. In Zhejiang Provincethe past 20 years, mainly due to anthropogenic inputs.about 36 out of 88 counties are suffering from theChivero Lake, Zimbabwe was reported to be hyper-short supply of good drinkable water sources. In 2004,trophic and not sustainable (Nhapi, 2004). Sewagewater eutrophication and algae blooming even OC-effluent is the major source of nutrients in the lake.curred in the Qiantang River, which has the highestIn China, water eutrophication occurred in 67water flow velocity in China. High concentration oflakes (51.2% of the total lakes). Although the Boy-phosphorus and nitrogen is gradually causinganghu Lake and the Dongtinghu Lake are still eutrophication.mesotrophic at present, Dianchi Lake in Yunnan isWater eutrophication in rivers occurs worldwide.possibly the most hypertropic lake in the world. In theDuring the past several decades, catastrophic losses inearly 1970s the water of Dianchi Lake was graded asseagrass meadows have occurred worldwide, espe-Class II, now declined to the more inferior Class V cially in flushed estuaries, coastal embayments and(Lu et al, 2005). Taihu Lake, in China, has similarlagoons where nutrient loads are both large and fre-eutrophication ise. It is the third largest freshwater quent (Burkholder et al, 2007; Ralph et al, 2006).lake in China, located in the Yangtze River delta, oneCoastal marine ecosystems of Northem Europe areof the more developed areas of eastem China. In re-under pressure from global change (e.g， nutrientcent decades, because of severe pollution, waterenrichment), which threatens these resources (Gowenquality in Taihu Lake degraded ftom Class /II in theand Stewart, 2005). There are many statutory obliga-early 1960s to Class I1/II1 in the early 1980s and thentions and strong political pressures for greatly in-to Class IV by the mid- 1990s. At present, 83.5% ofcreased emphasis on the control of nutrients levels inthe lake area is eutrophic with an inferior Class V UK rivers because of serious problem of water eu-ranking (Liu and Qiu, 2007). The increasingly widertrophication (Mainstone and Parr, 2002). Withinoccurence of excessive algae growth also beginsEurope, many national and intermnational initiativesearlier and lasts longer each year in Taihu Lake, andhave been implemented in order to reduce the inputsin the summer of 2007 an outbreak of blue algaland effects of nutrients in waters, e.g., the Europeanbloom caused many drinking water treatment plantsUnion's Water Framework Directive (Andersen et al.,shut down and created a severe“water crisis event" in 2004).Wuxi City. Chaohu Lake is the fifth largest lake inChina, located in central Anhui Province, and has a Harmfulness of water eutrophicationpopulation of 2.3 million and more than 3000 facto-Generally speaking, the main harmfulness ofries in its basin. Since the 1990s, massive and rapidwater eutrophication is that it can break out the in-nutrient loading has made it one of the most eutrophictrinsic equilibrium of the aquatic ecosystem and leadfreshwater lakes in China. Jin et al.(2005) reported to the damage of the water ecosystem and the gradualthat eutrophic trend of Taihu Lake, Chaohu Lake anddegeneratinnofits. finetinng As a result, it can affectXuanwu Lake in the region of the middle and lower water q中国煤化工of water becomevalleys of Yangtze River was predicated using theworse|YHC N M H Gt can penetrateecological stress model. Provided the pollution water water boay ana photosyninesis oI plants under the202 .Yang et al./J Zhejiang Unv Sci B 2008 9(3):197-209water will be weakened or even stopped. Water eu- farmland, etc. Increased nutrient load to water body istrophication can also cause the supersaturation or lacknow recognized as a major threat to the structure andof dissolved oxygen in water, which will be danger- functions of near shore coastal ecosystems, and se-ous to aquatic animals and cause great death to them.vere eutrophication problems associated with harmfulEutrophic systems tend to accumulate large amounts algal blom is a major manifestation. Although re-of organic carbon causing a shift in organic matterlated to nutrient enrichment in general, the basicbiochemical composition (Dell'Anno et al, 2002).cause of water eutrophication is more connected to anMeanwhile, because of water eutrophication, a massimbalance in the load of nitrogen and phosphorusof algae, mainly Cyanophyta and green algae, bloomwith respect to silica (Dauvin et al, 2007). At present,and formm a thick layer of“green scum” on waterexcessive TN and TP in water are considered as thesurface. Algae can release toxins and render the or-only factors inducing water eutrophication, but nu-ganic matters in water to be decomposed into harmfultrient enrichment is only the necessary but not thegases, which will poison the fish and seashell.sufficient condition for algal boom. Eutrophication isThe harmfulness of eutrophication also includesnot likely to occur if both TN and TP in water are low,causing the shortage supply of drinking water sourcebut eutrophication may not occur in water high in TNby degrading water quality. When the blooming algaeand TP if other conditions such as temperature anddie, they can produce lots of algae's toxin which iscurrent speed are not favorable. The influencing fac~harmful to human health. Cyanobacteria toxinstors of water eutrophication include: (1) excessive TN(cyanotoxins) including cytotoxins and biotoxins areand TP, (2) slow current velocity, (3) adequate tem-responsible for acute lethal, acute, chronic andperature and favorable other environmental factors,sub-chronic poisonings of wild/domestic animals andand (4) microbial activity and biodiversity (Li andhumans. The biotoxins include the neurotoxins; ana-Liao, 2002). Water eutrophication may occur rapidlytoxin-a, anatoxin-a(s) and saxitoxins plus the hepa- when all of these conditions are favorable.totoxins; microcystins, nodularins and cylindros-permopsins (Carmichael, 2001). Recent investigation Nutrient enrichmentshowed that the algae produced toxins, which are theThere is clear evidence that nutrient loading tometabolized production of Cyanotoxins, were de- lakes, estuaries and coastal oceans has greatly in-tected in the Yangtze River, as well as many reser-creased through human activities over the past fewvoirs and lakes of Yellow River vlleys, apart fom decades and that this has caused or enhanced many ofDianchi Lake, Taihu Lake and Chaohu Lakes (Yu andthe symptoms of the aquatic ecosystem transformationLen, 2004). Besides, increased ntrte concentation in known as eutrophication (Bishop et al, 2006). Therethe eutrophic water will be dangerous to human health,are diferent opinions on the relationship of nutrienttoo, as products of nitrite nitifcation process is a enrichment to water eutrophication and algal bloom:strong carcinogen. Thus, the exacerbation of water (1) When P concentration in water is low, it may beeutrophication with the increased severity of algae the limitig facor for inducing water eutrophicationblooming in surface water system has atracted great and algal bloom; (2) When P concentration in waterattention of both public and private sections.increases rapidly, other may become a new limitingfactor, such as pH, water depth, temperature, light,wave, wind or other biological factors; (3) The influ-FACTORS INFLUENCING WATER EUTRO- ence of N and P sill lasts for a longer time because ofPHICATIONthe high development level of our society (Zhao,2004).Water eutrophication is mainly caused by ex-N and P input and enrichment in water are thecessive loading of nutrients into water bodies like N most primary factors to induce water eutrophication.and P. Excessive nutrients come from both point The'a”of alga is aspolltion such as waste water from industry and mu-“CrosH中国煤化工hemieal componicipal sewage, and non point pollution like irigationnents ,YHC N M H G elements whichwater, surface run water containing fertilizer fromaccount for least proportion in the molecular formulaYang et al.1J Zhejiang Univ Sci B 2008 9(3):197-209203of algae, especially P, it is the main limiting factor to graphical and periodic distribution of phytoplankton.control the growth of alga in water Mainstone and It has been considered that the growth of phyto-Parr, 2002). It was reported that 80% lake and reser-plankton is influenced by dissolved silicate-Si (DSi)voir eutrophication is restricted by phosphorus, about concentration in water and its ratio to nitrate. When10% lake and reservoir eutrophication is relative tothe DSinitrate-N atomic ratio is near 1:1, aquaticnitrogen, and the rest 10% lake and reservoir eutro-food webs leading from diatoms which require sili-phication is relative to other factors (Zhao, 2004). In cate to fish may be compromised and the frequency ormany ecosystems, phytoplankton biomass is corre-size of harmful or noxious algal blooms may increase.lated with the availability ofN or P (Cloem 2001; Used together, the DSinitrate-N ratio and nitrate-NBledsoe et al, 2004). The composition of phyto-concentration are the robust comparative indicators ofplankton species is also affected by the concentrations eutrophication in large rivers (Turner et al, 2003).of N and P (Reynolds, 2006). The ratio of N:P in thewater body (referred to as the“Redfield ratio") is anHydrodynamicsimportant indicator of which nutrient is limiting eu-There is no relationship between water distur-trophication. If the Redfield ratio is 16:1, P is most bance and diatom alga occurrence or its scale, butlikely the limiting factor for algal growth; lower ratioswater disturbing can influence the growth of Pyrro-indicate that N is of great importance (Redfield et al, phyta alga because Pyrrophyta alga blooms when it is1963; Hodgkiss and Lu, 2004). P has been shown to grown in relatively stable water. Cai et al.(2007)be the principal limiting nutrient for primary produc- found that when there is no water to dilute, disturbingtion of phytoplankton in many freshwater environ-water itself can influence the process of eutrophica-ments (Phlips, 2002), while N is commonly limiting tion and species succession, which, however, is notin marine ecosystems (Cloerm, 2001). However, thererelated to disturbing water itself but is influencedare many exceptions to this general pattern. In some indirectly by changing light and nutrient status. Infreshwater environments, particularly in the tropicsshallow water, increased frequency of disturbanceand subtropics, N has been found to be the primarycould increased the P release from the sediment, es-limiting nutrient for phytoplankton production, due inpecially at high temperature (Cai et al, 2007). This islarge part to excessive P load and long growing sea-an instructional point to maintain beneficial alga insons. For instances, in the Ten Mile Creek of Indian water. Also, tide not only can urge alga assemblingRiver Lagoon, where TP is >0.2 mg/L, chlorophyll abut can also influence the multiplication of algaand turbidity sharply increased with addition of bloom through changing the concentration of nutri-available N (0.2~6.0 mg/L), but not affected by addi-tion in water. Zhu et al.(2007) studied the effects oftion of reactive P (Lin et al, 2008). The results indi- hydrodynamics on phosphorus concentrations in wa-cate that available N is the limiting nutrient for theter of Taihu Lake, a large, shallow and eutrophic lakegrowth of phytoplankton at water bodies with bigh P. of China. They found that hydrodynamical distur-In phosphate-deficient water bodies or those havingbance had no significant relationship with waterreasonably good growth of blue-green algae, which quality at the top layer when significant wave heightfix enough of the atmospheric nitrogen, phosphoruswas smaller than 30 cm, but it significantly increasedbecomes the limiting element, because a portion ofP suspended solids (SS) concentration of the bottomis used to counterbalance high nitrate content (Rey-water layer. Concentrations of nutrients showed nonolds, 2006). Such circumstances can be seen that no positive correlation with SS concentration in the wa-paroxysmal algal boom may break out in heavilyter body. Intensive sediment resuspension may noteutrophicated water bodies with both high N and P. have occurred when the hydrodynamic stress onThus, it is the key point to control the concentrationssediment was only a litle higher than the criticalof both N and P reasonably for solving the problem of stress for sediment resuspension. A new method forwater eutrophication.confirming the critical stress for intensive sedimentThe variations in the chemical composition of resuspe中国煤化工ill needs to benatural waters are believed to be an important factordevelo|Y台CNMHG,(99)studiedin regulating the abundance, composition and geo- hydrodyuanu ycVcuuUu ui curuphication in the04Yang et al.1J Zhejang Univ SciB 2008 9(3):197-209Brest Bay (France). The Brest Bay is a semi-enclosed highly relative with the beginning growth time ofcoatal ecosystem where primary production is nu- Gymnodinium, but whether it has universality to alltrient-limited, even if huge nutrients loading ftom algae still needs to be studied. In the Vistula Lagoon,tributaries are present. The most striking feature of salinity gradient was determined as an importantthe bay is the semi- diumal tidal influence, resulting in factor (along with water temperature and predation byarge water exchange with the continental shelf. A young herring) that defined the dynamics of z00-historical study of the available data has shown the plankton abundance and biomass in this estuarysteadiness of this ecosystem during the last two dec- (Telesh, 2004).ades inspite of increasing eutrophic conditions.2. Carbon dioxide level is one of major factorscontrolling water eutrophication. Cyanophytes areEnvironmental factorsmore capable of utilizing low levels of carbon dioxideA range of factors are related to water eutfo- and become more buoyant at low levels of carbonphication, but the mechanisms of their influencingdioxide and high pH. It keeps them in the upper layersalgal bloom are not fully understood. In many mod-of the water column with abundant sunlight. In addi-erately eutrophicated water bodies, algal bloom 0C-tion, some species produce dense mats of vegetation,curs in some seasons or some years, when the envi-inhibit the growth of other phytoplankton, and alsoronmental conditions are favorable. The algal bloomlimit the swimming of zooplankton. These factorscaused by phosphorus inputs also modifies severaltogether mean that a slow-moving freshwater eco-abiotic factors of the water body. These factors di-system can rapidly become dominated by blue-greenrectly govern the growth, diversity and density of thealgae, displacing not only members of the phyto-biotic components. The impact of algal bloom on anyplankton but some of the animal community as well.one or some of these factors indirectly influences theThe reduction of light reaching the lake floor alsostructure and characteristics of the water bodies. Theinhibits submerged and rooted macrophytes, andinfluence of nutrient inputs on some of these factors issediments become anoxic as large amounts ofdiscussed as follows:1. Temperature and salinity are the two impor-planktonic biomass are added to them (Kant andtant factors to induce alga bloom. Alga bloom alwaysRaina, 1990). The fluctuations in free carbon dioxideoccurs at temperature between 23 °C and 28。C, sa-values correspond directly with the fluctuation in thelinity between 23% and 28%. The variation of tem-standing crop of phytoplankton. As the diversity andperature and salinity also affect algal bloom, and andensity of phytoplanktons increase through variousimportant condition for algal bloom is that tempera-months, the amount of free carbon dioxide for pho-ture increases and salinity decreases faster than evertosynthetic activity becomes limiting. The pHin short time. From the conception of ecology, ex-changes in these ponds are govermed by the amount ofquisite change of temperature may cause the subro-free carbon dioxide, carbon trioxide, and bicartbonategation of biological communities, thus leading to(Kant and Raina, 1990). Inflow nutrient concentration,algal bloom when other environment conditions areinflow volume and inflow water temperature showadequate (Wang et al, 1996). Statistical analysisvery regular and reasonable impacts on the quality ofshows that the influence of temperature on algallake water (lmteaz et al, 2003). Yin (2002) reportedgrowth rate is the largest, followed by salinity andthat monsoons served as a flushing mechanism in twotheir iteraction. The proces of sporangium pull ways: (1) They reduced seasonal eutrophication bylating is hypersensitive to temperature. When undernutrient enrichment in summer, and (2) they pre-adequate temperature, it can bourgen largely and vented long-term (nnua) accumulation of organicalga boom will form very fast. Change of sliy is matler in the sediments due to nurient enichmentinalso influenced by the concentration of nutrition.the region. Because of the monsoon-influencedResearch shows that salinity is negatively related withprocesses and low phosphorus in the Pearl River es-NO:-N, and PO,; -P, but positively related with中国煤化工waters of HongKongto enrichment ofNH;-N, and however, it is not very related with nitrogHCNMHGNO2 -N. In addition, average temperature in winter is3. Light plays an important role in the growth,Yang et al.1J Zhejiang Univ Sci B 2008 9(3):197-20905diversity and density of aquatic flora. Algal growthalga bloom (Paerl, 1998; Paerl et al, 2003). It canhas been reported to increase with light intensity, and enhance abundant breeding of alga bloom. Nutri-luminescence of 4000 lux was found most favorableent-enhanced microbial production of organic matter,(Shen, 2002). As eutrophication progresses, a decline or eutrophication, is frequently accompanied by al-of submerged macrophytes occurs in many shallowtered microbial community structure and functionwater bodies, probably due to low light intensity(Paerl, 1998). The amount of microbial biomass iscaused by algal blooming. It is suggested that thepositively related to the content of organic matter andadaptation strategy of Potamogeton maackianus un- the amount of plankton in eutrophicated water. Thereder a certain range of low light stress is to accelerateexists certain intrinsic relationship between thethe elongation of the main and lateral shoots and toamount of bacteria and the occurrence of eutrophica-increase their density (Ni et al, 1999). The light has tion. The decomposition of organic matter by bacteriabeen almost completely absorbed by the plankton ofactivities can produce nutrients and organic sub-the top few meters, so that too lttle light penetrates tostances, which may promote algal bloom breaking out.the thermocline and beyond to support photosynthesis.Of course, it may also produce some toxic substances,However, there is a rain of corpses into the deep water, which are harmful to other algal species, so that it willwhose decomposition requires oxygen. Since theselectively enhance the bloom of some algae to be-deep water is cut off from the air until fall overtum, ancome preponderant species and subsequently eutro-oxygen deficit develops in the deep water, and thephication will occur. It may be relative with the de-bottom mud is reduced. Eutrophication in an estuary composing of bacteria biomass, which can promoteis a complex process, and climate change is likely toeffective circulation of nutrients when alga bloom andaffect each estuary differently due to interactions witheutrophication occur under lower concentrations ofnutrient loading and physical circulation. Hence, it isnutrients. Chang et al.(2005) demonstrated that im-essential to consider the effects of climate change onpose of submerged macrophyte in combination ofthe context of individual estuarine function to suc-immobilized nitrogen cycling bacteria could effec-cesfully manage eutrophication (Howarth et al, tively reduce chlorophyll a concentration and increase2000).water transparency. Marshland drainage channelsThere are other factors like pH and dissolved(=ditches) in the UK are relicts of a once extensiveoxygen affecting water eutrophication (Khan andhabitat whose management requires quantitative inAnsari, 2005). The minima and maxima in the con-formation on the ecology of marshland organisms.centration of dissolved oxygen are found to be di-Distribution of these organisms in wetlands world-rectly related to the maxima and minima of thewide can reflect natural water quality, vegetation andphytoplankton，The direct relationship betweenanthropogenic factors (Watson and Omerod, 2004).phytoplankton and dissolved oxygen content haAcrophyte-specific richness and abundance increasedbeen observed by a number of researchers (Khan andalong an upstream-to-downstream zonation, whichAnsari, 2005). pH is a plant growth limiting factor.vas characterized by an increase in mineralizationThe change in pH is directly related to the availabilityand nutrient level (Thiebaut and Muller, 1998). Inand absorption of nutrients from solution. lonizationhyper-eutrophicated water body, remarkable im-of electrolytes or the valence numbers of dfferent ion provement in water quality and inhibition on algalspecies are influenced by changes in pH. An acidicgrowth was obtained by introducing nutrient cyclingpH has been reported to promote growth of Spi- bacteria in proper combination with floating hydro-rodelapolyrrhiza at a faster rate, but high pH values phyte (Chang et al, 2006).promote the growth of phytoplankton and result inA comparison of aquatic macrophyte diversity ofbloom. It must be pointed out that many factors in-two streams reflected the impact of human-inducedfluencing eutrophication are relative and affect eachperturbations (fish farms, domestic sewage) in suchother.weakly. mineralized and poorlv buffered waters.Disturb中国煤化工nt loading wereMicrobial and biodiversitycharact|Y. CN MH Gichness and byMicrobial activity is the inducement factor to the absenue ur nranenus algac ( imebaut and Mul-206Yang et al.1J Zhejiang Univ SciB 2008 9(3):197-209ler, 1998). Vadineanu et al.(1992) studied the phyto-release of the contaminants in sediments should beplankton and submerged macrophytes in the aquaticclarified, which named inner pollution converging inecosystems of the Danube Delta and found that thewater bodies, especially the absorption and release ofspecies changes were linked to accelerated eutrophi-P in sediments; the mechanism of the excessive pro-cation of the lakes, with increased phosphorus loadingduction of algae and Cyanobacteria, especially ex-and a reduction in the N/P ratio. Distinct changescessive production of blue-green algae in waterwere observed in the macrophyte species compositionshould be further studied, which is the key for thein response to phosphorus enrichment (Vaithiyana-prevention of algae and Cyanobacteria growth. Also,than and Richardson, 1999). Marshes in the unen-the guidelines for estimating eutrophication are stillriched and enriched areas were dominated by Ladi-very incomplete. Comprehensive guidelines for as-umjamaicense and Typha domingensis, respectively.sessing eutrophication should be established by con-Open-water areas were characterized by Eleocharissidering various factors in combination with the de-spp, Utricularia spp, Chara zeylanica and Nym-velopment of economy and society, especially inphaea odorata in ligotrophic areas and by floatingmodem society ecology and health are paid more andplants and Polygonum spp. in eutrophic areas. A shiftmore attention in order to avoid adverse influence onin primary producers from eelgrass to macroalgae inhe sustainable ecological development and humanresponse to increased nutrient loading altered thehealth to the best of our abilities. In view of the highhabitat, physicochemical structure and food webs.level of nutrients already polluted into lakes, reser-The nitrogen decreased shoot density and biomass ofvoirs, estuaries, etc, understanding the functions ofthe eelgrass and promoted a record increase in thethe factors influencing algal growth and bloom willalgal biomass (Deegan et al, 2002). Enhanced nu-certainly help contrlling algal bloom even at hightrient concentrations and loading have been observednutrient burden in surface water bodies.in several coastal areas of the North Sea, resulting inincreased production and changes in the speciesReferencescomposition of phytoplankton (Colijn et al, 2002).Alongi, D.M., Chong, v.C, Dixon, P.,, Sasekumar, A., Tirendi,F, 2003. The infuence of fish cage aquaculture on pe-Garg et al.(2002) studied aquatic flora in three lakeslagic carbon flow and water chemistry in tidally domi-of Bhopal (Upper Lake, Lower Lake and Mansarovarnated mangrove estuaries of peninsular Malaysia. MarineLake) in India and assessed the potential fertility ofEnvironmental Research, 55(4);313-333. (doi:10. 1016/the lentic water and its aquatic flora. EutrophicationS0141-1136(02)00276-3]was highest in Mansarovar Lake. The observations ofAndersen, J.H, Conley, D.J, Hedal, S., 2004. Palaeoecology,reference conditions and classification of ecologicalGarg et al.(2002) indicated that different species ofstatus: The EU Water Framework Directive in practice.phytoplankton could subsist up to a certain nutrientMarine Pollution Buletin, 49(4):283 290. (doi:10.1016/level, beyond which competition between cyano-j.marpolbul.2004.04.014]pbytes and other algae enhanced and eliminated theBarbieri, A., Simona, M, 2001. Trophic evolution of Lakesensitive plankton flora.Lugano related to extermal load reduction: Changes inphosphorus and nitrogen as well as oxygen balance andbiological parameters. Lakes and Reservoirs Researchand Managemen, 6():37-47. [dol:10.1046/. 1440-1770.RESEARCH PERSPECTIVES2001.0020.x]Bishop, M.J, Powers, S.P, Porter, HJ, Peterson, C.H, 2006.Benthic biological efects of seasonal hypoxia in a eu-The problem of water eutrophication has becometrophic estuary predate rapid coastal development. Es-more and more severe worldwide, but the mechanismtuarine Coastal and ShelfScience, 70(3):415-422. [oi:10.of its occurrence has not been fully understood. The1016/j. ecss 2006.06.031]limited knowledge of water eutrophication processes Bledsoe, E.L, Phips, EJ, Jett, C.E, Donelly, K.A., 2004.will add difficulties for the prevention and remedia-The relationships among 336 phytoplankton biomass,tion of water eutrophication. Therefore, more re-中国煤化工in an inner-shelfsearches should be turmed to the mechanisms ofwater Burkheutrophication under different watershed conditions.CNMH(:ette, B.W, 2007..nal of ExperimentalFor example, the mechanisms of the adsorption andMarine Biology and Ecology, 350(1-2):46-72. (doi:10.Yang et el./J Zhejang Univ SciB 2008 9():197-2092071016/jembe .2007 ,06.024]consequences in a lake ecosystem. Tropical Ecology,Cai, J.B., Ding, X.F, Peng, HY, Chang, H.Q,, Yang, X.E,43(2);355-358.2007. Effects of environmental factors and submergedGowen, T.R.J, Stewart, B.M, 2005. The Irish Sea: Nutrientaquatic plants on phosphorus release from the sediment.status and phytoplankton. Journal of Sea Research,Journal of Soil and Water Conservation, 21(2):151-15454();:36- 50. (doi:10. 1016/.seares.2005.02.03](in Chinese).Guo, H.C, Sun, Y.F, 2002. Characteristic analysis and controlCarmichael, w.W, 2001. Health effects. toxin-producingstrategies for the eutrophicated problem of the Lake Di-Cyanobacteria:“The CyanoHABs". Human and Eco-anchi. Progress in Geography, 21(5):500-506 (in Chi-logical Risk Assment, 7(5):1393-1407. [doi:10.nese).1080/20018091095087]Hodgkiss, 1.J, Lu, S.H, 2004. 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BYERSISSN 1673-1581 (Print); ISSN 1862-1783 (Ontine), monthlyJournal of Zhejiang UniversitySCIENCE Bwww.zju.edu.cnjzus; www.springerlink.comjzus@zju.edu.cnJZUS-B focuses on“Biomedicine, Biochemistry & Biotechnology"Online submission: htp://ww.editorialmanager.com/zusb/mainpage.htmlJZUS-B is covered by SCI-E in 2008Welcome Contributions to JZUS-BJZUS-B warmly and sincerely welcome scientists all over the world to contribute Reviews, Ar-ticles and Science Letters focused on Biomedicine, Biochemistry and Biotechnology. Especially,Science Letters (3~4 pages) would be published as soon as about 30 davs Nnte: detailed researcharticles can still be published in the professional jourmals i中国煤化Iers is pub-lished by JZUS-B).TYHCNMHG