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Ecological Engineering 51 (2013) 104– 116

Contents lists available at SciVerse ScienceDirect

Ecological Engineering

j o ur nal homep age : www.elsev ier .com/ locate /eco leng

mproved Yangtze River Diversions: Are they helping to solve algal bloomroblems in Lake Taihu, China?

iping Lia,b, Chunyan Tanga,b, Chao Wanga,b,∗, Desmond O. Anima,e, Zhongbo Yuc,f, Kumud Acharyad

Key Laboratory of Integrated Regulation and Resource Development on Shallow Lakes Ministry of Education, Nanjing 210098, ChinaCollege of Environment, Hohai University, Nanjing 210098, ChinaDepartment of Geoscience, University of Nevada, Las Vegas, NV 89119, USADesert Research Institute, Las Vegas, NV 89119, USACollege of Engineering, Kwame Nkrumah University of Science and Technology, Kumasi, GhanaState Key Laboratory of Hydrology Water Resources and Hydraulic Engineering, Nanjing, 210098, China

r t i c l e i n f o

rticle history:eceived 19 September 2012eceived in revised form 4 December 2012ccepted 7 December 2012vailable online 3 January 2013

eywords:FDCutrophicationulti-objective optimization method

hallow lakeater ageater transfer

a b s t r a c t

To mitigate eutrophication by enhancing water exchange in Lake Taihu, the third largest freshwater lakein China, a water transfer project was initiated in 2002. The project was designed to flush pollutants out ofthe lake by transferring water from the Yangtze River. However, the original Yangtze River Diversion didnot significantly enhance water exchange in the Meiliang Bay, the most polluted area of Lake Taihu. Toovercome this deficiency, the improved Yangtze River Diversions have been designed recently by addingtwo new pump stations named Meiliang and Xingou around Meiliang Bay. Effectiveness of water transferprojects was investigated in this study by using a three-dimensional hydrodynamic model, EnvironmentalFluid Dynamics Code (EFDC), based on the concept of water age. Model results showed that adding newpump stations significantly improved the effectiveness of Yangtze River Diversion in Meiliang Bay. Successof water transfer is also strongly associated with the inflow or outflow rate of water transfer projectsand wind conditions. Southeastern winds which dominate in summer increase performance of watertransfer and improve water exchanges in Meiliang Bay. Considering water age and cost, an economicallyeffective influent flow rate from Wangyu River (the original Yangtze River Diversion) was predicted to

3

be 120 m /s, and the corresponding appropriate outflow rate from the Meiliang pump station was about15–20 m3/s on the basis of multi-objective optimization method, which decreased the average water agein Meiliang Bay by 24.32% of the original Yangtze River Diversion. Adding Xingou pump station had thesimilar contribution to reducing the water age in Meiliang Bay as the Meiliang pump station. In general, theimproved Yangtze River Diversions played a supplementary role for the original Yangtze River Diversionin solving algal bloom problems in Meiliang Bay.

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. Introduction

Inter-basin water transfer engineering, conveying water arti-cially from present surplus to deficit catchment/river foredistributing much needed water supplies, changing living con-itions and ecological environment, has been successfully used inany places in the world (Davies et al., 1992). Over 160 large-scale

nter-basin water transfer projects have been built in 24 countries

specially in Canada, the United States, former Soviet Union andndia etc. (Wang, 2004). For example, the Snowy Mountain Scheme,he first inner-basin water transfer project in southeast Australia

∗ Corresponding author at: College of Environment, Hohai University, Nanjing10098, China. Tel.: +86 25 83787330.

E-mail address: cwang@hhu.edu.cn (C. Wang).

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925-8574/$ – see front matter © 2012 Elsevier B.V. All rights reserved.ttp://dx.doi.org/10.1016/j.ecoleng.2012.12.077

© 2012 Elsevier B.V. All rights reserved.

as completed in 1974 for the dual purpose of irrigation of theoutheast inland and the largest power generation supply for Can-erra, Melbourne and Sydney with a gap of 740 m along the wayPigram, 2000). The California State Water Project was built inhe 1960s and 1970s to transfer water from Northern to aridouthern California to address water supply and hydropower withroville Dam, San Luis Reservoir and the California Aqueduct pri-ary projects (Davies et al., 1992). In China, inter-basin water

ransfer projects have boomed in recent decades. The famous Greatanal with a total length of 1794 km from Beijing to Hangzhouity is the longest and first manual-canal in the world mainly foravigation (Yao, 1998). Also, the South-to-North Water Diversion

roject is another well-known water transfer project in China.t is regarded as a strategic and ambitious approach to resolve

ater shortage problems in the north with three transfer routeselivering water from a different reach of Yangtze River to the north

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Y. Li et al. / Ecological En

f China facing water shortage (Liu and Zheng, 2002). These histor-cal inter-basin water transfer projects have traditionally helpedavigation, irrigation, water supply, hydropower, flood control etc.,nd rarely been used for water quality improvement and ecologicalestoration.

However, with economic and population growth in recentecades, water quality degradation and frequent occurrence ofutrophication events have become ubiquitous in many lakes,eservoirs and other freshwater bodies affected by anthropogenicutrient inputs (Paerl and Huisman, 2008; Qin et al., 2010). Amongumerous efforts, water transfer has become a new remedy inhort terms by diluting the polluted water with fresh water, andlleviating eutrophication problems in many lakes, such as Greenake and Moses Lake in USA, Lake Xuanwu and Lake Taihu inhina, etc. (Hua et al., 2008; Hu et al., 2008; Oglesby, 1968;elch and Patmont, 1980). Long term ecological and engineering

mpacts of these water transfer projects are not clearly under-tood, especially when ecological system becomes a little unstablefter implementing water transfer such as in Lake Taihu, ChinaZhai et al., 2010). Therefore, attention should be paid to inves-igate and assess impacts of water transfer on socioeconomics,tructural integrity and ecological environment of the receivingystem.

Lake Taihu, the third largest freshwater lake in China, hasxperienced severe eutrophication problems over the past severalecades. Water quality in Lake Taihu is deteriorating and often doesot meet the quality level to provide potable drinking water orerve as habitats for aquatics (Hu et al., 2008). For example, thelgal bloom events that occurred during the summer of 2007 ledo a crisis of water supplies for approximately four million resi-ents in Wuxi city (CD, 2007). Water transfer from the Yangtzeiver was initiated in 2002 to dilute polluted water and to accel-rate flushing pollutants and algae out of the lake (Hu et al., 2008,010; Qin et al., 2010; Zhai et al., 2010). The main route of the orig-

nal water transfer is bringing fresh water from the Yangtze Rivernto Lake Taihu via the Wangyu River and taking water out of theake through the Taipu River (Fig. 1). Due to its importance to theegion and uniqueness, this project has caught much attention inhe past few years. Jia et al. (2008) and Wu (2008) concluded thathe original Yangtze River Diversion could improve water quality ofake Taihu based on a short-term monitoring data of water qual-ty parameters before and after transfer. On the other hand, Zhait al. (2010) disclosed that the original Yangtze River Diversionad positive effect on water quality only in parts of the lake, suchs Gonghu Bay, Northwest Zone, Southwest Zone and Central Zone,ut had no significant effect on Meiliang Bay based on a regressionnalysis of long-term data. Hu et al. (2008, 2010) found that con-entration of phytoplankton decreases, while the water transferctually increases the concentrations of phosphorus and nitrogenn areas of the lake where nutrient concentrations are lower thanhe influent water. Li et al. (2011) used the concept of water age, anndicator for reflecting mass exchange and transport process, andhowed that water ages were spatiotemporally heterogeneous inature due to the original Yangtze River Diversion. Therefore, theriginal Yangtze River Diversion may alleviate the eutrophicationssue in parts of the lake, but could not substantially enhance waterxchanges in the Meiliang and Zhushan Bays, where the most pol-uted areas and the drinking water intakes are located.Later, themproved Yangtze River Diversions are implemented or plannedo combat with severe ecological and environmental health riskssociated with hyper eutrophication in Meiliang Bay of Lake Taihu

y adding two pump stations named Meiliang and Xingou aroundeiliang Bay (Fig. 1). They are aiming to pump water out of Meil-

ang Bay and accelerate water exchange in the most polluted areasZheng et al., 2009). However, several key issues about how best to

eiaM

ing 51 (2013) 104– 116 105

anage the operations of Yangtze River Diversions remain unclear.or example, what is environmental and ecological impact on bothreceiving” (Lake Taihu) and “donating” (Yangtze River) systems ofater transfer? What is the appropriate inflow rate from Yangtzeiver and outflow rate from the pump stations to maximize theenefit for improving lake’s water exchange with a minimum costrom an economic point of view? To answer these questions, a

ulti-objective optimization method is required to obtain a rea-onable tradeoff between the environmental benefit and economicost during water transfer. Currently, this method has been widelysed in environmental/economic multicriterion decision-makingor water distribution network design and water management, etc.Farmani et al., 2005; Xevi and Khan, 2005). However, the methodas not been applied in obtaining the optimization for the environ-ental benefit and economic cost of water transfer in Lake Taihu

et.In addition, selecting a suitable parameter for describing envi-

onmental benefit is critical to assess the impact of water transfern migrating algal bloom in the lake. Since water age reflectshe time elapsed for dissolved substances to be transported fromne point to another, making it a useful timescale for describinghe complex hydrodynamic and biogeochemical processes in largehallow lakes such as Lake Taihu (Shen and Wang, 2007). Li et al.2011) demonstrated that water age can be successfully used inake Taihu and found that water age also could be used as an indica-or of spatial pattern of phytoplankton distribution. Therefore, thehange rate of water age induced by the water transfer engineer-ng has been chosen as the indicator for describing environmentalenefit in this study.

The objectives of this study were to: (1) understand the contrib-tions of winds and transferred inflow rate from Yangtze River onhe environmental benefit of Lake Taihu by using three dimensionalumerical model Environmental Fluid Dynamic Code (EFDC); (2)uantify the optimal transferred inflow rate from the originalangtze River Diversion considering both environmental benefitnd economic cost using the multi-objective optimization method;3) estimate the optimal discharge of two newly designed pumptations for the improved Yangtze River Diversions by the multi-bjective optimization method; and (4) assess the impacts of bothriginal and improved Yangtze River Diversions on the migratinglgal bloom in Lake Taihu.

. Study area

Lake Taihu is located in the lower Yangtze River delta, with aotal water surface area of 2338 km2 and an average water depthf 1.9 m (Qin et al., 2010). Lake Taihu is frequently influencedy winds and therefore has wind-induced currents to transportissolved matters and exchange water. The dominant wind direc-ion on the lake is southeast in the summer and northwest inhe winter, with a mean wind speed of 3.5–5 m/s (Hu et al.,006).

The river network around Lake Taihu is very complicated with river density of 3.24 km/km2 (Qin et al., 2007). Lake Taihu isivided into eight subareas: Zhushan Bay, Meiliang Bay, Gonghuay, Northwest Zone, Southwest Zone, Central Zone, East Epigealone, and Dongtaihu Bay according to their hydrological charac-eristics, aquatic plant distributions, water quality conditions andopographies (Hu et al., 2008). Special location of the influent and

ffluent rivers in Lake Taihu results in much better water qualityn the southeast of the lake than in the northwest. Water intakesre mainly concentrated in the eastern part of Lake Taihu (Fig. 1).eiliang Bay located in the northern part of Lake Taihu, where algal

106 Y. Li et al. / Ecological Engineering 51 (2013) 104– 116

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ig. 1. The location of Taihu watershed and the main tributaries, and the newly buater transfer routes. (Eight subareas of Lake Taihu: 1-Gonghu Bay, 2-Meiliang Bay

one, 8-Central Zone.)

loom occurs frequently, resulting in severe water crisis for theearby Wuxi city.

Existing route of the original Yangtze River Diversion into Lakeaihu is via Wangyu River to Gonghu Bay, and flowing out via theaipu River at Dongtaihu Bay (Fig. 1). This project has been car-ied out since 2002. The actual influent rate from Wangyu Riveranges from 20 to 240 m3/s (Jia et al., 2008). However, the orig-nal Yangtze River Diversion did not significantly enhance waterxchange in the Meiliang Bay, the most polluted area of Lakeaihu. To overcome this deficiency, the improved Yangtze Riveriversions have been designed recently by adding two new pump

tations named Meiliang and Xingou around Meiliang Bay. Meiliangump station, located at the confluence of Meiliang Bay, Wuli Baynd Liangxi River (Fig. 1), was built in March 2004 with the designedaximal operation flow rate of 50 m3/s, and put into test run in

006 (JWRA, 2006). Local route for water movement driven byeiliang pump station is from Meiliang Bay to Wuli Bay, and even-

ually flowing into the center of Wuxi City via Liangxi, Caowangnd Changguang rivers (Fig. 1). Xingou pump station, located nearangtze River, is planned to take polluted water out from Meil-

ang Bay to Yangtze River through Zhihu,Wujin and Xingou riversFig. 1). Its designed maximum pumping rate is about 50 m3/s. Thewo pump stations operate alternatively or conjunctively wheneeded.

. Methods

.1. Numerical model description

EFDC, a three dimensional numerical model, initially developed

y United States Environmental Protection Agency (USEPA), wassed to simulate hydrodynamics of Lake Taihu including water

evel, current and water age. EFDC has been successfully appliedo a wide range of environmental studies simulating circulation,

a

m

raulic projects (i.e. Meiliang and Xingou pump stations). The bold lines representushan Bay, 4-Northwest Zone, 5-Southwest Zone, 6-Dongtaihu Bay; 7-East Epigeal

hermal stratification, sediment transport, water quality, tracersnd eutrophication in lakes, rivers, estuaries, reservoirs, wetlands,nd coastal regions (Gong et al., 2009; Li et al., 2010, 2011). Detailsf EFDC are documented by Hamrick (1992) and Craig (2011).

.2. Age calculation

Water age is defined as “the time that has elapsed since thearticle under consideration left the region in which its age is pre-cribed as being zero” (Delhez et al., 1999) in this paper. Morepecifically, the age is zero at the entrance of the tributaries tohe lake and the age at any specified location stands for the timelapsed for a water particle to be transported from its boundary tohat location (Shen and Wang, 2007). The water age distributionsary spatiotemporally (Delhez et al., 1999). In this study, assum-ng that there was only one tracer discharged into the lake withoutther sources and sinks, water age was computed based on tracernd age concentrations (Delhez et al., 1999; Shen and Wang, 2007)s follows:

∂c(

t, �x)

∂t+ ∇ (

uc(

t, �x)

− K∇c(

t, �x))

= 0 (1)

∂˛(

t, �x)

∂t+ ∇ (

u˛(

t, �x)

− K∇˛(

t, �x))

= c(

t, �x)

(2)

here c is the tracer concentration, is the age concentration, u ishe velocity field, K is the diffusivity tensor, t is time, �x is coordinate.he mean water age “a” then can be calculated as follows:

( �) ˛(

t, �x)

t, x =c(

t, �x) (3)

Eqs. (1)–(3) were used to calculate the water age using the EFDCodel with specified initial and boundary conditions.

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.3. Multi-objective optimization method for water transfer inake Taihu

To decrease the water age in Lake Taihu, especially in Meiliangay and reduce the economic cost, the multi-objective optimizationethod was used to obtain an optimal inflow rate from Yangtze

iver and outflow rate for the adding pump stations. The functions shown as below (Eq. (4)):

Minimize y(Qi) = WA(Qi) − WA

SWA+ M(Qi) − M

SM

Subject to Qi ∈ [q1, q2]

(4)

here y(Qi) is the objective function. When y(Qi) reaches the min-mum value, the combinations of water ages and correspondingnflow or outflow rate (Q) reach the minimum values, which meanshat the environmental benefit gets its maximum values and at the

ean time the economic cost takes a relative small values. WA(Qi),¯ A and SWA are water age in Lake Taihu changing with transferredow, the mean and standard deviation of water age, respectively.imilarly, M(Qi), M and SM are the economic cost of transferredater in Lake Taihu, the mean and standard deviation of economic

ost, respectively. (WA(Qi) − WA)/SWA and (M(Qi) − M)/SM are thetandardized dimensionless objective with mean of zero and vari-nce of one. The smaller value of the standardized dimensionlessbjective means the smaller water age and less economic cost. Thenflow or outflow rate is in the feasible range of q1 to q2 accordingo the model simulated scenarios.

.4. Change rate of water age

Effectiveness of the improved Yangtze River Diversions (i.e.,eiliang and Xingou pump station) on mitigating eutrophication

n Lake Taihu, were measured by the change rate of water age inhis study. Larger the change rate of water age, better the waterxchange the lake achieves. The equation is shown as below (Eq.5)):

hange rate of water age% = WA − WAnew

WA× 100% (5)

here WA is the water age (day) for the original Yangtze Riveriversion; WAnew is the water age for the improved Yangtze Riveriversions.

.5. Model setup

Rectangular grids were used with 4465 active cells and a uni-orm cell size 750 m in both x and y directions. Three evenlyistributed sigma layers were adopted in vertical dimension. Theottom topography data was obtained from Taihu Basin Author-

ty (TBA) and interpolated into the model grids. A typical initialverage water depth in each grid ranged from 0.5 m in the lit-oral areas to 2.5 m in the central lake regions. Average maximumlopes of water depth were less than 0.33, meeting the conditionf hydrostatic consistency and avoiding a pressure gradient errorrom sigma transformation (Mellor et al., 1994; Li et al., 2011).

The model was driven by atmospheric forcing, surface windtress, and inflow/outflow tributaries. The lake is a typical shallowake with wind-driven currents and a lack of thermal stratifica-ion. Therefore, temperature was treated as constant due to its littleffect on the results. Details of inflow/outflow tributaries are foundn Li et al. (2011). Daily precipitation data were obtained by averag-

ng data from 8 monitoring stations in the vicinity of the lake (TBA,009a). Daily wind data were obtained from the weather station ofaihu Laboratory for Lake Ecosystem Research, Chinese Academyf Sciences near the Meiliang Bay.

3eWs

ing 51 (2013) 104– 116 107

The model’s initial conditions were set for surface elevation,ow velocity and water age. The initial surface elevation was set ashe average value of the first day of the simulation period with anssumption that the lake surface was leveled. The age concentra-ion was set to zero. A 100-second time step was used to make the

odel run quickly and stably. Additionally, the sensitivity analysisesults explained that inflow/outflow tributaries play a minor rolen the velocity profiles in the lake, while wind strongly affects theelocity fields. Wind drag coefficient and bottom roughness heights set as a typical value of 0.0013 (Pang et al., 1994) and 0.02 m (Lit al., 2011) for water level calibration, respectively. The detailedodel calibrations and verification can be found in Li et al. (2011).

.6. Model application

The effect of the improved Yangtze River Diversions on waterxchanges of Lake Taihu were estimated by the validated EFDCodel. During the simulation, impacts of other tributaries around

he lake were ignored due to a limited impact on the hydrodynamicrocess. As Lake Taihu is large and shallow, hydrodynamic pro-esses are highly associated with the freshwater from Wangyuiver and wind-induced lake circulation. Therefore, the most effi-ient flow discharge from the original Yangtze River Diversion inhe entire lake should be investigated prior to studying the appro-riate outflow discharge from Meiliang and Xingou pump stationsor the improved Yangtze River Diversions. Three groups of sce-arios were set in this study including a series of wind conditionsnd flow discharges for Wangyu River, Taipu River, Meiliang andingou pump stations (Table 1). Group one aimed to obtain theost economically efficient influent flow via Wangyu River for

he entire lake under different flow discharges between 50 and00 m3/s with an increment of 5 m3/s, and nine wind forcing con-itions (wind speed of 5 m/s, wind directions N, NE, E, SE, S, SW,, NW and no wind). The objective of Group two investigated

he appropriate outflow discharge of Meiliang pump station underhe optimal influent discharge from Wangyu River obtained fromroup one conditions. Group two included 10 cases in which thenfluent discharge from Wangyu River was set to constant (opti-

al inflow obtained by group one) and the outflow from Meiliangump station increased from 5 to 50 m3/s at every 5 m3/s inter-al. Meanwhile the sum of outflow from Taipu River and Meiliangump station were always equal to inflow from Wangyu River toeep the water balance consistent. In additional, eight wind direc-ions were considered in group two. Group three investigated theffect of improved Yangtze River Diversions based on the resultsrom Group two. Only southeast wind, the dominate wind directionn summer was considered.

For all the cases, the model configurations and parameters,xcept the driving factors shown in Table 1, were kept the sames mentioned in Section 3.5. Each model was run for 365 days withonstant time step of 100 s.

. Results

.1. Influence of the transferred water from the original Yangtzeiver and winds on water ages in Lake Taihu

In order to assess the impact from wind-driven force andhe original Yangtze River Diversion, the results from group oneTable 1) were selected for further analysis. The water age on Julian

65 (the last day of simulation) was selected to reflect the timelapsed for transferred water to be transported from the inlet ofangyu River to any given location in the lake. To illustrate the

patial heterogeneity of water ages caused by the transferred water

108 Y. Li et al. / Ecological Engineering 51 (2013) 104– 116

Table 1Model simulation scenarios.

Model scenarios Winds Flow discharge (unit: m3/s)

Wangyu River (inflow) Taipu river (outflow) Meiliang pump station(outflow)

Xingou pumpstation (outflow)

Group one No windWind speed 5 m/s, wind directions areN, NE, E, SE, S, SW, W, NW, respectively.

From 50 to 200 increasedby 5

From 50 to 200 increased by 5 – –

Group two Wind speed 5 m/s, wind directions areN, NE, E, SE, S, SW, W, NW, respectively.

Optimal inflow obtainedfrom Group one

Keep water balance: outflowfrom Taipu River = inflow fromWangyu River – outflow fromMeiliang pump station

From 5 to 50 increasedby 5

–

Group three Wind speed 5 m/s, wind direction is SE Optimal inflow obtainedfrom Group one

Keep water balance: outflowfrom Taipu River = inflow fromWangyu River – outflow fromMeiliang pump station –outflow from Xingou pump

Optimal inflowobtained from Grouptwo

20

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ote: “–” means no flow discharge.

nd winds, change in water age for the entire lake and each speci-ed lake regions were provided below.

.1.1. Change in water age in the whole lake by original Yangtzeiver Diversion

Averaged water ages in Lake Taihu were calculated taking theeights of water age in every lake regions into consideration,

ccording to the targeted water quality i.e., total nitrogen (TN) andotal photosphere (TP) and water volume in each lake region (Qint al., 2010).

The averaged water age in the entire lake gradually decreasedith increasing transferred water from Yangtze River, and the

hange rate highly depended on the magnitude of the transferrednfluent flow rate (Fig. 2a). Taking southeast wind scenario as anxample, water age substantially decreased from 301 to 179 dayss inflows increased from 50 to 200 m3/s. When the transferrednfluent flow rate was low, the change rate of averaged water agen the bay was relatively high. For instance, when the transferrednflow increased from 50 to 100 m3/s, 100 to 150 m3/s, 150 to00 m3/s, the averaged water age in the lake decreased by 26.14%,6.20% and 15.44% respectively under the southeast wind, suggest-

ng that there is little improvement in water exchanges from 150o 200 m3/s in Lake Taihu induced by the original Yangtze Riveriversion.

Wind direction was a major driving factor for changing waterge in the lake. For the entire lake, the averaged water age showedhe similar pattern in most wind directions (i.e. no wind, south-ast, southwest, northeast, northwest, west and east wind) withhe exception of north and south wind (Fig. 2a). The change inater ages were less than 13 days under most wind directions,

ut more than 50 days under north and south wind. In addition,or specific inflows from Wangyu River, water age in north windcenario had the maximum values, followed by south wind andhen other wind directions having a minimum. For example, whenransferred inflow rate was set to 200 m3/s, water age is about 255,27 and 173 days in south, north and other winds, respectively. Ituggested that north and south wind does not help to improve theerformance of water transfer.

Considering a combined impact of water transfer and winds, theuctuation in water age was much smaller in lower flow rates ofransferred water than in higher flow rates under different wind

irections (Fig. 2a). More specifically, the averaged water age inhe lake was equal to 300 days with 50 m3/s inflow in all windirections. However, the water age ranged from 150 to 280 days

n the higher flow rate of 200 m3/s. Therefore, wind directions had

tZtw

station

arkedly impact on the averaged water age in high flow dischagesrom the Yangtze River.

.1.2. Change in water age in specific lake regions by the originalangtze River Diversion

In order to identify the major impact factor in each lake region,he maximum contribution of inflows and winds in different lakeegions were investigated since both the transferred inflow andinds could alter water age in the lake. The results showed that the

hange of water age exhibited great spatial variability, and the con-ribution of winds and transferred inflow on water age in each lakeegion were different. For Meiliang Bay, the maximum contributionn water age caused by winds was almost twice as much as that ofhe transferred water (Fig. 2b). The maximal change in water ageeached 122 days when the transferred inflow increased from 50o 200 m3/s, however the number was 228 days when wind direc-ion changed from north to southeast. Hence, water age in Meiliangay highly depended on wind directions. In addition, water ages inhe northwest of the lake (i.e., Zhushan Bay, Northwest and South-est zones) were also contributed more by winds than transferred

nflows. The ratio of wind versus inflow contributions on water ageere about 1.2, 1.4 and 1.3 in Zhushan Bay, Northwest and South-est zones, respectively (Fig. 2c–e). In the contrary, for Gonghu Bay,

ast Epigeal Zone and Central Zone where the route of water trans-er passed by, the maximum contribution of transferred inflows60%) were larger than that of wind (40%) (Fig. 2f, g, i). For Dong-aihu Bay, location of the outlet of water transfer (Taipu River), thenfluent flow rate and wind played an equal role on the change in

ater age (Fig. 2h).Our results also suggested that each lake region had its own

avorite wind direction to accelerate water transfer and enhanceater exchange capacity. For Meiliang Bay, southeast and north-est winds help to enhance the transferred water from Yangtzeiver to transport into this bay and decrease its water age, whileortheast wind hindered this process. For example, when the trans-

erred inflow from Yangtze River was 100 m3/s, the averaged waterges in Meiliang Bay were 142 and 166 days under the southeast-rly and northwesterly wind, much smaller than 334 days underhe northeasterly wind (Fig. 2b). For other heavily polluted zonesi.e. Zhushan Bay, Northwest Zone and Southeast Zone), the mostuitable wind directions to accelerate water movement were east-rly, westerly and northeasterly, respectively (Fig. 2c–e). In reverse,

he undesirable wind directions for Zhushan Bay and Northwestone for water exchange were both north and south winds. Forhe Southeast Zone, they were southeast and northwest windshich were just the opposite to Meiliang Bay (Fig. 2e). The water

Y. Li et al. / Ecological Engineering 51 (2013) 104– 116 109

Fig. 2. Water age on Julian day 365 in eight lake zones under eight different wind direction and four flow discharges (i.e. 50 m3/s-black line, 100 m3/s-red line, 150 m3/s-blueline, 200 m3/s-yellow line). (a) the entire lake considering the weights of each lake region; (b)Meiliang Bay; (c) Zhushan Bay; (d) Northwest Zone; (e) Southwest Zone; (f)G tationo

adNdmGhwowatt(RG

als

aptei

4R

onghu Bay; (g) East Epigeal Zone; (h) Dongtaihu Bay; (i) Central Zone. (For interpref the article.)

ges ranged between 160 and 240, 98 and 290 and 157 and 284ays for desirable winds with increasing inflows for Zhushan Bay,orthwest Zone and Southwest Zone, respectively. For some windirections such as north and south winds, there was no improve-ent in water age no matter how large the inflow discharge was.onghu Bay where the transferred water entered into the lakead the youngest water age (∼80 days), and was independent ofind direction (Fig. 2f). East Epigeal Zone and Dongtaihu Bay were

bviously fond of north wind to enhance water exchange, whichas opposite to the influence of winds on the entire lake (Fig. 2g

nd h). The water age for Central Zone under desirable wind direc-ions (easterly and westerly winds) was about 132–300 days when

ransferred inflows from Wangyu River varied from 50 to 200 m3/sFig. 2i). Generally, water ages in the lake regions close to Wangyuiver and the route of the original Yangtze River Diversion (e.g.,onghu Bay) were younger than those lake regions away from this

il

of the references to color in figure legend, the reader is referred to the web version

rea (e.g., Southwest Zone). However, water ages in the heavily pol-uted lake regions such as Meiliang Bay and Zhushan Bay did nothow much change caused by the original Yangtze River Diversion.

In general, the impact and contributions of transferred waternd winds on water age varied in different lakes, while the generalattern was similar. Each lake region had its favorite winds andransferred inflow rate for reducing water age and enhancing waterxchange, hence it is essential to consider those differences whenmplementing the original Yangtze River Diversion.

.2. Optimal transferred inflow rate from the original Yangtzeiver Diversion for the entire lake

Water age was getting younger with an increase in transferrednflow rate from Yangtze River via the Wangyu River for the entireake, it is necessary to optimize inflow rate for maximizing the

110 Y. Li et al. / Ecological Engineer

Fig. 3. The averaged water age (WA, unit: day) in response to transferred inflowrate (Q, unit: m3/s) via Wangyu River under different wind direction in Lake Taihu.(w

eac

TWfwddwf(

s

W

W

W

wtgacm

cs(itb

M

tg

ps

atosamwsa(

4R

eabMioro(wcHr

MwewssWoitanawuif3rt(age dropped to the lowest point (107 days in southeast wind and

WA1, WA2, WA3, Q1, Q2 and Q3 represent water age and inflow rate in three groupsith different wind directions, respectively. R2 is the coefficient of determination.)

ffect of water transfer at a minimal cost. Specific relationshipsmong transferred inflow rate (Q), averaged water age (WA), andost of water transfer (M) were quantified and studied.

A series of flow discharges from the Wangyu River (Group one inable 1) were conducted to obtain the relationship between Q andA in Lake Taihu. The results showed that water age in the lake

ollowed power function with the transferred inflow rate, whichere obviously clustered into three functions depending on windirections (Fig. 3). The first function was suitable for most windirections (i.e. no wind, southeast, southwest, northeast, north-est, west and east wind), and the other two functions were fitted

or north and south wind, respectively. The three functions of WAdays) and Q (m3/s) for different wind directions were given below:

Function one for most wind directions (i.e. no wind, southeast,outhwest, northeast, northwest, west and east wind):

A1 = 1793.5Q−0.441 , R2 = 0.98, P < 0.05 (6)

Function two for north wind

A2 = 534.26Q−0.142 , R2 = 0.99, P < 0.05 (7)

Function three for south wind

A3 = 739.63Q−0.223 , R2 = 0.97, P < 0.05 (8)

where WA1, WA2, WA3, Q1, Q2 and Q3 stand for averagedater age and inflow rate in three functions, respectively. R2 is

he coefficient of determination, larger than 0.97 for the threeroups, suggesting that the power regression analysis was gener-lly reliable. P less than 0.05 in three cases suggested significantorrelations. Function one was chosen for multi-objective opti-ization method since it covered most wind scenarios.Meanwhile, the economic cost of water transferred (M)

hanging with transferred inflow rate (Q) was studied. In thistudy, only the energy power cost about 4000 RMB/million m3

634 dollars/million m3) was considered as the economic expensen complementing water transfer process (TBA, 2009b). The rela-ionship between Q (m3/s) and M (million RMB/year) were givenelow:

= 0.004 × 365 × 86400 × 10−6Q = 0.126Q (9)

According to Eqs. (4), (6) and (9), the multi-objective optimiza-ion method for water transfer in Lake Taihu was established toain the optimal inflow rate from Wangyu River and provide a best

1Iy

ing 51 (2013) 104– 116

ossible solution to satisfy environmental and economic benefitsimultaneously (Eqs. (10)):

Minimize y (Qi) = WA(Qi) − WA

SWA+ M(Qi) − M

SM

Subject to

⎧⎪⎨⎪⎩

WA = 1793.5Q−0.44

M = 0.126Q

Qi ∈ [50, 200]

(10)

The result showed that the optimal transferred water inflow wasbout 120 m3/s from Wangyu River and the corresponding objec-ive function (the solid blue line, Fig. 4) value reached the minimumf 0.13 (point B, Fig. 4). The intersection (point A in Fig. 4) of thetandardized relationship among water age, cost of water transfernd inflows was the best solution for tradeoff between environ-ental and economic benefits and gain the maximum efficiency ofater transfer. In optimal transferred water inflow rate of 120 m3/s

cenario, the averaged water age of Lake Taihu was about 218 daysnd the cost of energy power was approximately 14.12 million RMB2.24 million dollars).

.3. Appropriate pumping flow rate for the improved Yangtzeiver Diversions

As the original Yangtze River Diversion did not significantlynhance water exchange in the Meiliang Bay, the most pollutedreas of Lake Taihu, the improved Yangtze River Diversions haveeen planned recently by adding two new pump stations namedeiliang and Xingou around Meiliang Bay. The effectiveness of

mproved Yangtze River Diversions was investigated by a seriesf numerical experiments (Group two), and the transferred inflowate from the original Yangtze River Diversion was kept constantf 120 m3/s. The change rate of water age was calculated by Eq.5). The result showed that Meiliang pump station could reduceater age in Meiliang Bay, and its change rate was highly asso-

iated with the wind directions and pumping flow rates (Fig. 5).owever, there was only slight effect on water age for other lake

egions (Figs. 6 and 7).Winds and pumping flow rate largely affected the efficiency of

eiliang pump station which showed three trends depending onind scenarios. The first one was clustered by north, south, north-

ast and southwest winds, which was a vertical angle area in theind rose. The second was west and east winds. The last case was

outheast and northwest winds (Fig. 5). Water age reduced in verymall magnitude with increased pumping flows in the first trend.

ater age was worse than other wind scenarios and the change ratef water age was relatively less as well although the change ratemproved with the increasing of pumping rates. For example, forhe pumping flow rate of 50 m3/s scenario, the change rate of waterge reached the maximum about 12.4%, 2.55%, 10.16% and 20.58% inorth, south, northeast and southwest wind, respectively. For westnd east wind direction (2nd trend), the change rate of water ageas particularly obvious in the early stage with increased pumpingntil the rate reached 30 m3/s which stabilized thereafter. Specif-

cally, taking east wind case as an example, water age decreasedrom 230 to 105 days when pumping rate increased from zero to0 m3/s and remained at 105 days after that. The maximum changeate of water age was about 54% when pumping rate was largerhan 30 m3/s. For the case of the southeast and northwest winds3rd trend) water age first decreased and then increased. Water

30 days in northwest wind) when pumping rate was 20 m3/s.n general, water age in the southeast and northwest winds wasounger than other wind directions. Thus, Meiliang pump station

Y. Li et al. / Ecological Engineering 51 (2013) 104– 116 111

Fig. 4. The relationship for transferred inflow rate (Q) and standardized water age (WA), and standardized cost of water transfer (M); and the milti-objective programmingfor water transfer in Lake Taihu. (Note: standardized water age and standardized cost of water transfer using principal coordinate, the objective function curve using vicecoordinates.)

ater a

iwefw

NoMtsmMwco

itsa

mSitnHe

Fig. 5. The impact of pumping rate from Meiliang Pumping Station on w

n conjunction with the Yangtze River Diversion provided enhancedater exchanges in Meiliang Bay. In terms of environmental ben-

fit, the pumping flow rate of 20 m3/s appears to be a good choiceor implementing the Meiliang Bay in summer with the dominantind (southeast wind) when algae are in high-incidence season.

For areas neighboring to Meiliang Bay (i.e. Zhushan Bay,orthwest Zone), the result showed that there was no obvi-us improvement and even may be worse caused by additionaleiliang pump station in most wind scenarios (Fig. 6). Most impor-

antly, no improvement for the two polluted regions was found inummer with the southeast wind when it was most likely to imple-ent Meiliang pump station. Besides, the larger pumping rate via

eiliang pump station caused stronger effect on polluted zoneshether good or bad (Fig. 6). More specifically, for Zhushan Bay,

ompared with no Meiliang pump station scenario, the change ratef water age was in the range of −20 to 10% and had a maximum

o

wt

Fig. 6. The change rate of water age in Zhushan Bay (a) and Northwest Zone (

ge distribution (a) and its change rate of water age in Meiliang Bay (b).

mprovement in southwest wind (Fig. 6a). Similarly, water age inhe Northwest Zone was only beneficial from the pumping withouthwest and northeast wind and the improved efficiency wasbout 8–15% (Fig. 6b).

The Meiliang pump station only had slight impact on the perfor-ance of water exchange in other lake regions (e.g. Central Zone,

outhwest Zone et al.) away from the two water outlets (i.e., Meil-ang pump station and Taipu River). For example, by comparinghe changes caused by Meiliang pump station in southeast wind,o obvious variation of water age existed in those areas (Fig. 7).owever, for Dongtaihu Bay connecting with Taipu River (anotherxit of water transfer) water age worsened from 313 to 333 because

f operation of the Meiliang pump station (Fig. 7).

Our results suggested that Meiliang pump station mainlyorked on the water exchange in Meiliang Bay. Only the rela-

ionships for pumping rate (Q), water age in Meiliang Bay (WA),

b) under different winds and pumping rate via Meiliang pump station.

112 Y. Li et al. / Ecological Engineering 51 (2013) 104– 116

F from Wa

aoosiMls

rpmm

Bsd(e

f1ssl1oRd

4

FM

ig. 7. The spatial distribution of water age in Lake Taihu under the optimal inflow

nd (b) represent 0 and 20 m3/s outflow via Meiliang pump station, respectively.

nd cost of pumping water (M) were considered to obtain theptimal pumping rate via Meiliang pump station using multi-bjective optimization method, while the corresponding mostuitable inflow rate was 120 m3/s from the Yangtze River. Accord-ng to the function between Q and WA in southeast wind (Fig. 5), and

(Eq. (9)), the multi-objective optimization method was estab-ished to gain the appropriate pump-out flows from Meiliang pumptation (Eq. (11)):

Minimize y(Qi) = WA(Qi) − WA

SWA+ M(Qi) − M

SM

Subject to

⎧⎪⎨⎪⎩

WA = 0.043Q 2 − 2.294Q + 137.7

M = 0.126Q

Qi ∈ [5, 50]

(11)

The result (Fig. 8) showed that the objective function y(Qi)

eached minimum at point C (15, −1.65), suggesting that the appro-riate pumping flow rate equals to15 m3/s for reaching the maxi-um environmental benefit (indicated by water age) at the mini-um economical cost. More specifically, the water age in Meiliang

w

i

ig. 8. The relationship between the pumping rate (Q) from Meiliang pump station and ceiliang Bay.

angyu River of 120 m3/s with or without outflow thru Meiliang pump station. (a)

ay was about 110 days and the economical cost for Meiliang pumptation was approximately 1.89 million RMB (about 0.3 millionollars). Another intersection with the pumping rate of 48 m3/spoint C (48, 1.36)), not an ideal situation, which represented lessnvironmental alleviation and more economic cost (Fig. 8).

Considering the youngest water age, pumping rate of 20 m3/sor an emergency case and the most cost-effective outflow rate of5 m3/s for a regular case seem to be appropriate. Xingou pumptation on water age had a similar effect with Meiliang pumptation on water ages not only in Meiliang Bay but also in otherake regions. The appropriate pumping rate in summer was also5–20 m3/s. Therefore, a case can be made that the most suitableutflow rate from the pump stations for the improved Yangtzeiver Diversions would be between 15 and 20 m3/s in summeruring the algae bloom season.

.4. Effect of combination of two Yangtze River Diversions on

ater ages

In order to evaluate a combined effect of the original andmproved Yangtze River Diversion, the results from group three

orresponding normalized cost of water transfer (M), averaged water ages (WA) in

Y. Li et al. / Ecological Engineer

Fig. 9. Time series of water ages for different hydraulic projects. (the blue line (A)represent the original Yangtze River Diversion; the red line (B) represent conjunc-tion the original Yangtze River Diversion and Meiliang pump station; the green line(tr

(Mla(oBtppbb

5

5

pfpdWfcawf

teawcpaat

tataDai

tYaNfthtlfe

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iteraisticanwo

3

C) represent conjunction Yangtze River Diversion, Meiliang and Xingou pump sta-ions.). (For interpretation of the references to color in figure legend, the reader iseferred to the web version of the article.)

Table 1) were selected (Fig. 9). The results showed that water age ineiliang Bay varied with time. Water age gradually tended to stabi-

ize after 100 days and after that only depended on inflows/outflownd wind conditions. On Julian 365, water age in Meiliang Bay∼107 days) was the youngest under the case of conjunction theriginal Yangtze River Diversion with Meiliang pump station (line). The oldest water age in Meiliang Bay (∼142 days) occurred inhe case of water transfer engineering without any other assistedrojects (line A). However, together with Meiliang and Xingouump stations simultaneously, water age (∼127 days) did not getetter as expected, indicating that the two pump stations wereetter to be operated alternatively than running together(line C).

. Discussion

.1. Effect of water transfer projects on water age in Lake Taihu

Water age reflects the time elapsed for the material to be trans-orted from one point to another, which is a useful timescaleor describing the complex hydrodynamic and biogeochemicalrocesses and to interpret the spatial patterns of phytoplanktonistribution in large shallow lakes such as Lake Taihu (Shen andang, 2007; Li et al., 2011). The young water age is beneficial

or water exchange, diluting nutrient load and removing algae byurrents. A relatively old age tends to provide viable condition forlgae bloom in Lake Taihu. In this study, the results suggested thatater age in Lake Taihu was influenced by the amount of the trans-

erred water and winds due to its largeness and shallowness.For the entire lake, the southeast wind, dominating wind direc-

ion in summer, was the most suitable wind to enhance waterxchange in the lake, suggesting that the wind should be taken intoccount when implementing the water transfer projects. Besides,ater age in Lake Taihu and inflows from Wangyu River in spe-

ific winds could be explained by power equation, which not onlyrovide a quick and low-cost preliminary estimation of the waterge in the lake according to specific inflow and wind scenarios, butlso provide a vital basis for gaining the optimal inflow rates fromhe Yangtze River via Wangyu River into Lake Taihu.

For specific lake regions, inflow rates and winds during waterransfer process play diverse roles due to the water transfer routend the characteristics of lake regions such as the shoreline andopography. The degree of effects depended on transferred water

nd winds in each lake region. In general, the original Yangtze Riveriversion might preferentially enhance water exchange in somereas of the lake such as Gonghu Bay, Central and East Epigeal Zonesn most wind scenarios, suggesting that those lake regions near

5ita

ing 51 (2013) 104– 116 113

he water transferred path were impacted more by inflows fromangtze River than by winds. However, the distribution of waterge in the most polluted areas (i.e., Meiliang and Zhushan Bay,orthwest and Southwest Zones), which are away from the trans-

erred water path, were mostly impacted by wind directions ratherhan the amount of transferred water from Yangtze River. Theseeterogeneous impact caused by water transfer in Lake Taihu, aypical large shallow lake, is different from that found in other smallakes such as Moses and Green Lakes in Washington with more uni-orm and good exchange rate in the entire lake (Welch, 1981; Hiltt al., 2011).

The improved Yangtze River Diversion including Meiliang andingou pump stations help by providing better water exchanges toombat with a severe ecological and environmental health risk ineiliang Bay. Owing to the implementation of these new pump sta-

ions, algal blooms in Meiliang Bay decreased directly with youngerater ages. From the numerical results, southeast wind direction

ould enhance the performance of water transfer projects andccelerate water exchange (increased by 24.32%), suggesting thatlthough algae might be gathered and driven into Meiliang Bay anded to excessive accumulation by southeast wind, the new pumptations could help by pumping polluted water fast and loweringotential for algal accumulation. Hence, from hydrodynamics andiogeochemical processes perspective, these additional pump sta-ions enhance water exchange capacity and reduce time for algaerowth in the lake, especially in Meiliang Bay.

.2. The optimal transferred inflow/outflow rates for originaliversion

In comprehensive analysis of the water age and economic ben-fits, our results showed that the optimal transferred inflow rateas 120 m3/s from original Yangtze River via Wangyu River for

mproving the water exchange in the entire lake, and the appropri-te pumping rate was 15–20 m3/s from the Meiliang and Xingouump stations. This suggests that application of those flow ratesould maximize effect at a minimal cost. Li et al. (2011) foundut that the optimal transferred inflow rate was 100 m3/s fromangtze River via Wangyu River only by comparing water age

mprovement under four influent flow conditions (50, 100, 150,nd 200 m3/s). Li et al.’s study did not consider economical cost. Inhis study, 30 different influent flow conditions of Wangyu Riverrom 50 to 200 m3/s with an increment of 5 m3/s, and nine windorcing conditions were considered by comparing both the waterge improvement and economic cost based on multi-objective opti-ization method.Usually, the water age improvement effectiveness in a lake will

ncrease with the increase in the amount of transferred water andhis was so for the original Yangtze River Diversion to improve thentire lake. Instead, it is not the case for Meiliang pump station toeduce the water age in Meiliang Bay. Generally, the averaged waterge in Meiliang Bay firstly decreased and then increased with thencrease of pumping rate. Additionally, the water age in the bay alsohowed high heterogeneity, with the younger water ages located inhe nearby area of Meiliang pump station and the older water agesn the southwestern part of Meiliang Bay (Fig. 10). Furthermore, thehanging trend of water ages showed various pattern in differentrea in Meiliang Bay. In the northeast part of Meiliang Bay con-ecting with Meiliang pump station, water ages decreased greatlyith pumping rate increasing from 0 to 20 m3/s (Fig. 10a–c), while

nly slightly declined when pumping rate increased from 20 to

0 m /s (Fig. 10c–f). On the contrary, in the southwest part of Meil-

ang Bay, water age increased as the pumping rate increased, andhe area with large water ages expanded obviously as well (Fig. 10),ccounting for approximately 40% of Meiliang Bay when pumping

114 Y. Li et al. / Ecological Engineering 51 (2013) 104– 116

F ping r4

rdSiletzmwaatp

damafoi

asiittce

5a

wsbss

ig. 10. The spatial distribution of water ages in Meiliang Bay under different pum0 m3/s; (d) 50 m3/s.

ate was equal to 50 m3/s (Fig. 10f). This phenomenon is perhapsue to the lake bottom topography and lake’s circulation (Fig. 11).ince the bottom elevation in the middle of southern area in Meil-ang Bay (<0.7 m) are relatively lower compared to the neighboringittoral zone (1.2–1.8 m) (Fig. 11a), the deeper water depth accel-rated the faster water movement. The circulation pattern showedhat water moved from Gonghu Bay along with southeast littoralone to the north part of Meiliang Bay, and then flowed back to theouth of Meiliang Bay along the deeper areas in the bay. Mean-hile, some part of water left the bay thru Meiliang pump station. In

ddition, two distinct vortexes were found located at the northeastnd southwest of Meiliang Bay, hindering the water exchange inhose places (Fig. 11b). This phenomenon was more obvious whenumping rate was greater than 20 m3/s under southeast wind.

Different multi-objective optimization methods are used iniverse fields of water management problems. For example, Rajnd Kumar (1999) adopted a ranking method for group decisionaking using maximizing and minimizing sets by fuzzy weights

nd employed the method in ranking different projects proposedor Krishna basin in India. Zarghami et al. (2009) investigatedn water transfer projects using multiple attribute decision mak-ng. However, in terms of two essential objectives (water age

tewg

ates via Meiliang pump station. (a) 0 m3/s;(b) 10 m3/s; (c) 20 m3/s; (d) 30 m3/s; (e)

nd economic index) of water transfer projects, our method oftandardizing the two objectives into dimensionless is more intu-tionistic, easy and feasible. Multi-objective optimization methods an effective method to guide practical management of waterransfer project in Lake Taihu. This study presents the first stepoward implementation of an integrated lake system managementombining comprehensive relationship between water age andconomic index based on multi-objective concept in Lake Taihu.

.3. Influence of inter-basin water transfer on surroundingquatic ecosystem

The major ecological problems of inter-basin water transferere the change of water quality, eutrophication, algae bloom,

pecies invasion, etc. (Fornarell and Antenucci, 2011). As discussedefore, positive effects of water diversion included the water agehortening, in generally speaking, elevated water level which madeediment less resuspension and less internal loading release, dilu-

ion of nutrient concentration of water column. However, negativeffects were obvious, including amplifying the heterogeneity ofater age in spatial distribution which would deteriorate the algal

rowth and outbreaks; pollutants were transferred from one place

Y. Li et al. / Ecological Engineering 51 (2013) 104– 116 115

and ci

twwwiittttMwcpwttsmrttnwYbBgGcZsTrc

rotfws

aobbirirbafioasbc

6

ipr

Fig. 11. Bottom elevation (a)

o another without withdrawal from the system, which wouldorsen the water quality of receiving water bodies. Yangtze Riverater transfer projects could be a typical example for inter-basinater transfer. Much attention has been paid on investigating the

nteraction between the “donating” (Yangtze River) and “receiv-ng” (Lake Taihu) ecosystem. The concentrations of TN and TP inhe transferred water from Yangtze River were slightly higher thanhe averaged TN and TP concentration in the lake, and lower thanhat in part of lake, such as Meiliang Bay. Li et al. (2011) concludedhat some lake regions have higher nutrient concentrations (e.g.,

eiliang and Zhushan Bays) than inflows and may benefit fromater transfer directly, but lake regions with lower nutrient con-

entrations (e.g., eastern parts in Lake Taihu) may suffer from moreollution from the water transfer. Besides, the new aquatic speciesould be brought from Yangtze River to Lake Taihu and might dis-

urb the original species. Zhai et al. (2010) found that the waterransfer projects generally had a positive effect on Lake Taihu in ahort term. Thus, the decrease in Chl-a concentration and improve-ent of water quality in some degree would only be a short-term

eaction caused by water transfer if the nutrient concentration inhe transferred water were not reduced to a reasonable level.Theransferred effluent water from the lake by the Taipu River andew pump stations has a high nutrient and algal concentration,hich may impact the surrounding aquatic ecosystem includingangtze River. The polluted pumped out water from Meiliang Bayy Meiliang pump staion transferred into Liangxi River and Wuliay (connecting with Caowang and Changguang Rivers) eventuallyo back into the river network around the center of Wuxi City andreat Canal (Fig. 1). Part of the polluted water from Meiliang Bayould also go back to Yangtze River by Xingou pump station throughhihu, Wujin and Xingou Rivers (Fig. 1). During the algal bloom sea-

on, the effluent water with high algal concentration from the Lakeaihu may result in the decline of the water quality in the nearbyiver network and Yangtze River (TBA, 2009c). Hu et al. (2010) dis-losed that water transfer caused a net increase of nutrient in the

tweo

rculation (b) in Meiliang Bay.

iver system close to Taipu River, since the nutrient concentrationf transferred water was higher than that in the river network. Sincehere are many factors affecting the performance of water trans-er, whether Yangtze River Diversion and additional pump stationsill be an ecological disaster for the rivers in the basin needs to be

tudied further.The impact of inter-basin water transfer on the surrounding

quatic ecosystem has been investigated for similar projects inther parts of the world. Snowy Mountain Scheme, the first inter-asin water transfer project in southeast Australia, was completedefore environmental impact assessments, and now some studies

ndicate that possible ecological impacts exist on the donor andecipient systems, such as flow reductions and the salt wedgingn the donor (the Snowy River), significantly decreasing in annualunoff, changes in sediment transport and aquatic systems of theasin (Davies et al., 1992). South-to-North Water Diversion Projectlso caused some ecological and environment problems disturbingragile ecological balance of the North China, such as seasonal dry-ng of river courses, sedimentation in river mouths, developmentf groundwater depression cones, and severe land subsidence (Liund Zheng, 2002). Therefore, at the planning stage of those mas-ive inter-basin water transfer projects, not only the techniquesut also their potential ecological impacts should be well studied byonsidering comprehensive social, economic and ecological effects.

. Conclusion

A series of three-dimensional numerical model (EFDC) exper-ments were conducted to evaluate the effect of water transferrojects on alleviating eutrophication problem in Lake Taihu. Theesults showed that both transferred water and wind strongly con-

ribute to the effectiveness of such projects in Lake Taihu. Southeastind, the dominant wind in summer, was beneficial for water

xchange when combined with water transfer in Lake Taihu. Theptimal transferred inflow rate was 120 m3/s from the original

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16 Y. Li et al. / Ecological En

angtze River via Wangyu River for improving water exchange inhe entire lake, and the appropriate pumping rate was 15 to 20 m3/srom Meiliang pump station for improving the water exchange in

eiliang Bay. Xingou pump station could contribute to improv-ng the water exchange in Meiliang Bay and it was more efficiento operate alternatively with Meiliang pump station when needed.owever, there was no obvious improvement caused by additionalump stations for other polluted zones (Zhushan Bay, Northwestnd Southwest zone). In general, water transfer projects couldrovide some relief for serious water supply crises as an emergencyeasure if well managed. The improved Yangtze River Diversion

nly played a complementary role in mitigating eutrophication inake Taihu. Careful consideration is essential for ecological impactf water transfer projects in future.

cknowledgments

The research was supported by Grant # 2010 CB429003,010CB951101 and Chinese National Science Foundation51009049, 51179053, 50979022); The research was also sup-orted by Program for Excellent Talents in Hohai University, Qingan Project, Grant # 40911130507, 2012ZX07506-002, IRT0717,069-50986312. We would like to thank the Taihu Basin Authorityf Ministry of Water Resources, Shanghai, China, and Taihu Labo-atory for Lake Ecosystem Research, Chinese Academy of Sciences,or providing monitoring data.

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