A continuing 30-year decline in water quality of Jiaojiang Estuary，China

Chun-yeWang，Bin Zhou*，Bei HuangCollege of Marine Siene，Shanghai Oean University，Shanghai 201306，PR ChinaCollege of Siene，Hangzhou Normal University，Hangzhou 311121，PR ChinaZhejiang Provinial Zhoushan Oean Eologil EnvironmentMonitoring Station，Zhoushan 316000，PRChina Reeived 21 August 2014；aepted 5 January 2015Availale online 7 Feruary 2015

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A continuing 30-year decline in water quality of Jiaojiang Estuary，China

Chun-yeWanga，b，Bin Zhoub，*，Bei HuangcaCollege of Marine Science，Shanghai Ocean University，Shanghai 201306，PR China
bCollege of Science，Hangzhou Normal University，Hangzhou 311121，PR China
cZhejiang Provincial Zhoushan Ocean Ecological EnvironmentMonitoring Station，Zhoushan 316000，PRChina Received 21 August 2014；accepted 5 January 2015
Available online 7 February 2015

Abstract

A quantitative description of a long-term seriesof aquatic environmental factorsand their spatialdistributionswas generated usingmeasured data from the Jiaojiang Estuary from 1982 to 2011.Theaquatic environmental factors included suspendedmatter，salinity，and nutrients.Based on these factors，the aquatic ecosystem health in the Jiaojiang Estuary over the last 30 years was analyzed.The results indicated that the suspended matter concentration in the estuary wasmainly affected by the amounts of suspended sediment and solid waste，w ith the value fluctuating over a long period，and the range of high concentration expanded continually；the salinity w asmainly affected by precipitation and surfacewater resources，showing an overalldecreasing trend，and the region with low salinitymoved seaward and toward the reclamation areas；and the nutritionalstatus，mainly affected by discharge of industrialwastewater and domestic sewage，was satisfactory in the 1980s and 1990s，but the status became severe in recent years.Reclamation had a great influence on these three factors:high reclamation strength led to a significant increase in the suspendedmatter concentration and a deterioration of the nutritional status，and the reclamation ratewas negatively relatedw ith thesalinity in theestuary.Therewasa significantpositive correlation betw een thehealth statusof the aquatic ecosystem and salinity，w ith a correlation coefficientof 0.93.The correlation coefficientbetw een the health statusand nutritionalstatuswas-0.71，w hile the correlation between the suspendedmatter concentration and health statuswasnotassignificantas thatof theother two factors.The dynamicsof theaquatic environment could be divided into four stages:sustainable health from the 1980s to the 1990s，continued deterioration from 2000 to 2003，improvement from 2004 to 2005，and secondary deterioration from 2006 to 2011.The Jiaojiang Estuary is faced w ith imm inentenvironmental pressure at present.

?2015 Hohai University.Production and hosting by Elsevier B.V.This is an open access article under the CC BY-NC-ND license（http:// creativecommons.org/licenses/by-nc-nd/4.0/）.

Water quality decline；Aquatic ecosystem health；Aquatic environmental factor；Suspendedmatter concentration；Salinity；Nutritional status；Jiaojiang Estuary

1.In troduction

W ith the acceleration of econom ic development and human activities，the destruction of the integrity of water sourceshas become more serious，requiring intervention（Steinemann， 2000；Dante et al.，2005；Yang et al.，2007）.An estuary is the ecological convergence zone of freshwater and m arine system s，which exhibitsunique physical，chem ical，and biological properties and high productivity.

Sim ilar to many estuaries worldw ide，the watershed upstream of the Jiaojiang Estuary is characterized by a high population density and developed socialeconomy.The critical water environmental problems in this area result from the discharge of industrialwastewater and domestic sewage from numerous outfalls into the adjacentwaters.Industrial effluent has been discharged into local water bodies and has further entered the Jiaojiang Estuary，leading to water quality deterioration.Tide cycles have further caused the w idespread deathof shellfish in offshore aquaculture（Wang et al.，2005）. M oreover，human activities have altered the natural conditions and created significant pressure on the aquatic environment in the Jiaojiang Estuary.

Research on the aquatic ecosystem of the Jiaojiang Estuary by Du etal.（2011）has indicated that thewater quality of this area was worse than Grade IV according to the Sea Water Quality Standard（GB 3097-1997），and runoff and pollutant emissions were themain factors leading to thewater quality deterioration.Zhang et al.（2013）showed that dissolved inorganic nitrogen（DIN），dissolved inorganic phosphate（DIP），and oil were the prim ary substances，exceeding their control standards in the Jiaojiang Estuary.Jiang et al.（2006）surveyed the concentrations of typical organic contam inants，indicating thatwastewater from the chemical industry was the main source of aniline and nitrobenzene in seawater and sediment.PAHs were found from the combustion of fossil fuels at the Taizhou Power Plant，and PCBs from the translocation of waste emission from thewaste electronicmachine recycling industry.Based on an investigation of the concentrations of DIN，DIP，Hg，Pb，dissolved oxygen（DO），and chemical oxygen demand（COD）in the Jiaojiang Estuary，Wang et al.（2005）concluded that the estuary was in a state of serious pollution.The average eutrophication index there was very high，w ith a value reaching 288，and the biodiversity and biomass of the system were quite low，demonstrating the frangibility of the Jiaojiang Estuary.

Guo and Chen（2007）demonstrated that sedimentation at harbors isan emergent problem for some coastal cities in this area.These researchersobtained distribution characteristicsof suspended matter in the Jiaojiang Estuary and Taizhou Gulf，and found that the oil concentration was high in the Jiaojiang Estuary，and that the water quality at 83.40%of the stations was worse than Grade I.Li et al.（1999）showed that suspended matter（SM）mainly included suspended sediment，inorganic and organic materials，and clay，which are waterinsoluble，and the suspended sedimentmainly came from sea transport.Because of the reduction of sea transport in recent years，the suspended sediment concentration in the Jiaojiang Estuary has decreased.

Some contaminants come from ocean engineering projects，such as land reclamation.The Jiaojiang Estuary reclamation has a long history，which can be dated back to the year 1145. By 1949，an area of 307 km2had been reclaimed，w ith seven seawalls constructed on the south bank of the estuary.A fter that，the Jiaojiang Estuary underwent additional reclamation projects，and theseawallnumber increased to 10.From 2000 to 2013，the number of seawalls increased to 12，w ith two other seawallsconstructed in 2001 and 2009，respectively.Atpresent，the total area of reclamation has reached about 450 km2.

Although investigations of the water quality have been conducted in the Jiaojiang Estuary，this research was focused either on singular aquatic environmental factors or aquatic organisms.Results that profiled the aquatic environmental quality more holistically were ephem eral and covered only one season or one year.The dynam ics of the aquatic environment over long periods of time need to be analyzedmore com pletely，especially for parameters regarding industrial wastewater，domestic sewage，hydrodynam ics，and so on.

For the purpose of identifying the reasons for the water quality decline in the Jiaojiang Estuary，the aquatic environmental factors and the aquatic ecosystem health over the last 30 years were analyzed based on the historical data.Natural and human factorswere also explored.It isexpected that this study w ill provide theoretical support to environmental protection in the Jiaojiang Estuary.

2.M ethodology

2.1.Study area

The Jiaojiang Watershed encompasses an area of 6 603 km2.Approximately 0.53 million people lived there in 2013.It is located on the central coastof Zhejiang Province，at the confluence of the Lingjiang and Yongningjiang rivers.The coastline is 51.4 km.The area ismainly covered w ith water，w ith land predominantly in agriculture and construction.The average runoff is 163 m3/s，the annual river discharge is 6.6 km3，and the rainy season is from April to September.

The Jiaojiang Estuary is located in them iddle of Zhejiang Province，which opens outward like themouth of a horn.The depth of most of the area is less than 10 m，and there are shallow regionsw ith a depth less than 2m outside themouth（Guo and Chen，2007）.The average tidal range in the Jiaojiang Estuary is 4.01 m，and the maximum tidal range is 6.30 m. With abundantnatural resources，theeconomic development is rapid in this region.Marine aquaculture hasbeen developed in this region，and fish，shrimp，and crab farms have been established（Sun et al.，2012）.Industrial development is quite intense on both banks of the Jiaojiang River，and construction and operation have greatly threatened the ad jacent intertidal and coastal waters（Zhao et al.，2009）.

2.2.Station setting

Water sampleswere collected in summer，and the sampling rangewas28°37′N to 28°41′N and 121°26′E to 121°37′E.This study wasonly concerned w ith coastalwaters in the Jiaojiang Estuary，and fivemarine ecologicalmonitoring stationswere setalong the river-to-sea direction，denoted as S0，S1，S2，S3，and S4 in Fig.1.

2.3.Data collecting methods

The sample collection，pretreatment，and analysis were conducted according to the procedures described in Specifications for Marine Monitoring（GB17378.3-1998 and GB17378.4-1998）.The reclamation dynamics in the Jiaojiang Estuary were extracted using remote sensing images on the ArcGIS platform based on color，shade，size，shape，texture，pattern，location，and other combinations.The concentrations of suspended matter，salinity，DO，COD，active phosphate），D IN，and oilwere obtained from the investigation by the Zhejiang Provincial Zhoushan Ocean EcologicalEnvironm ent M onitoring Station.Inform ation on precipitation，surfacewater resources，industrial wastewater，and domestic sewagewasobtained from the EnvironmentBulletin of Taizhou Cit y issued by the Taizhou Environmental Protection Bureau at http://www.zjtz.gov.cn/.

Fig.1.M arine ecological monitoring stations in offshore area in Jiaojiang Estuary.

2.4.Evaluation methods

2.4.1.Evaluation of eutrophication

The eutrophication index E was calculated as follow s（Lan，2011）:

The values of E in the ranges of E<0.5，0.5≤E<1.0，1.0≤E<3.0，and E≥3.0 correspond to poor，moderate，rich，and high rich nutritional status，respectively.A higher value of E indicatesamore seriouspollution status.

2.4.3.Evaluation of water environment health

This paper refers to the ecosystem health assessm ent m ethod for Queensland waters（Longstaff and Sm ith，2004）. The water quality standard score of each indicator was calculated as follows: where Siis the standard score of indicator i w ith a range of 0-1，and a greater value of Sicorresponds to a healthier ecosystem；Xiis themeasured value of indicator i；Giis the guidelinevalueof indicator i，which is the reference value；and Wiis theworst value of indicator i thatmight occur.

The standard score of each indicator reflects the degree of itsmeasured value deviating from the reference value.If the measured data is close to the reference value，the standard score w ill be close to 1.The comprehensive score of aquatic ecosystem health S can be obtained by taking the average of all indicators.Values of S in the ranges of 0.75

Because there has been no systematic research on the criteria formarine aquatic environments in China，this study utilized the Sea Water Quality Standards（GB 3097-1997）as the reference.The criteria forwater quality of Grade I，suitable for marine fisheries，marine nature reserves，and endangered marine species reserves，were taken as the guideline values. The theoreticalm inimum of indicatorsor lower quartile of all datawas taken as theworst value.Two special circumstances were considered in this study:when Xiis superior to Gi，the standard scoreof indicator i is1，and when Xiis inferior to Wi，the standard score of indicator i is 0.The reference values of the indicators are shown in Table 1.

3.Resu lts and d iscussion

2.4.2.Evaluation of organic pollution

The organic pollution index A was calculated as follows（Lan，2011）:

whereρ（DIP）andρ（DO）are the concentrations of dissolved inorganic phosphate and oxygen in mg/L，respectively；and ρ0（COD），ρ0（DIP），ρ0（DIN），andρ0（DO）are the criteria of each indicator，w ith valuesof 3.00，0.30，0.03，and 5.00mg/L，respectively，forwater quality of Grade IIaccording to the Sea Water Quality Standard（GB 3097-1997）.

When A≤1，thewater quality is considered to be in a good condition；when 1

3.1.Suspended matter and its impact factors in Jiaojiang Estuary

The suspended matter concentration in the Jiaojiang Estuary from 1982 to 2011 displayed an M-shaped fluctuation，as shown in Table 2.The averagesuspendedmatter concentration in the 1980swas50mg/L，and the highest values occurred in 2003 and 2008.As shown in Fig.2，the suspended matter concentration decreased seaward from the estuary.

As shown in Fig.3，the contour for the suspended matter concentration of 203mg/Lmoved seaward from 2005 to 2008，indicating that the range of high concentration expanded continually.It was considered that an aquatic environment w ith a suspended matter concentration greater than 203mg/L was unhealthy.The vertex positions of the contour for the suspended matter concentration of 203 mg/L were（28°40′48′N，121°34′12′E），（28°40′12′N，121°27′00′E），（28°40′12′′N，121°33′36′′E），and（28°40′48′′N，121°34′48′′E）in the years 2003，2005，2007，and 2008，respectively.In comparison to 2003，the vertex position of the contourmoved 11.73 km toward the estuary in 2005.It moved 10.77 km seaward from 2005 to 2007 and then 2.38 km in 2008.

There are many factors affecting the suspended matter concentration in the estuary，and the amount of suspended sediment isa critical factor.Both the Jiaojiang and Lingjiang rivers had little sediment，w ith an average am ount of 1.22×106t per year，and the sediment transport was measured in nearly flood conditions（Chi，2010；Li et al.，1999）.According to the observed data，the annual average amount of sediment transport from the Yangtze River into the seadecreased from 4.68×108t in the1980s to 3.52×108t in the 1990s.Thus，the reduction of the suspended matter concentration from the 1980s to the 1990s was related to the reduction of sediment transport.

Table 1 Criteria for aquatic environmental indicators in Jiaojiang Estuary.

Table 2 M easured data of some aquatic environmental factors in Jiaojiang Estuary.

Fig.2.Horizontal distributions of suspended matter concentration in Jiaojiang Estuary in different years.

Fig.3.Change of contour for suspended matter concentration of 203mg/L in Jiaojiang Estuary.

The water-insoluble debris generated in the Jiaojiang Estuary，such as industrial solid waste，domestic garbage，inorganic and organic m atter，and clay，has inevitably led to an increase in the suspended matter concentration.The amounts of solid waste em ission were 1.6×105t，6.16×104t，and 4.45×104t in 2008，2009，and 2011，respectively，and the amounts of sludge emission were 1.00×103t，1.08×104t，and 1.54×104t，respectively.Solid waste is treated near the Jiaojiang Estuary，and the generated waste has been discharged into the sea，resulting in increasing suspendedmatter concentration.The greatest amount of solid waste emission occurred in 2008，corresponding to the highestmeasured value of the suspended matter concentration in this year.

Reclamation isanother human factor causing an increase in the suspended m atter concentration.Reclam ation history stretchesback for nearly am illennium，w ithmostdikeshaving been built recently，in the early 2000s.The average reclamation rates were 0.38，2.47，2.08，1.00，1.19，22.88，and 44.99 km2/year during the periods of 1145 to 1949，1950 to 1969，1970 to 1979，2000 to 2003，2007，2008，and 2009，respectively.During the periods of 1980 to 1999 and 2004 to 2006，therewasnotany reclamation activity in thisarea.Asa resultof reclamation，sediment flowed outw ithwater from the cofferdam into the sea，disrupting the sediment distribution at the bottom，producing more suspended sediment，and increasing the water turbidity.Furthermore，the changes of tidal power induced by reclamation altered the suspended matter concentration（Liu，2007；Wang et al.，2009）.This result is consistentwith Zeng（2012）.

Fig.4.Horizontal distributions of salinity in Jiaojiang Estuary in different years.

3.2.Salinity and its impact factors in Jiaojiang Estuary

The variation of the sea surface salinity in the Jiaojiang Estuary since the 1980s is shown in Table 2，demonstrating an overall downward trend w ithin a range of 28.50‰-21.15‰. The salinity rem ained around 28‰from the 1980s to the 1990s，and decreased to its lowest value of 21.15‰in 2010. The horizontal distribution of sea surface salinity is shown in Fig.4.Therewasa significant increase in the salinity gradient seaward from the estuary，which was in linew ith the general trend.

The value of 21.90‰is the standard of salinity for the healthy aquatic ecosystem in the Jiaojiang Estuary，as shown in Table1.Fig.5 indicates theexpanding rangeof low salinity；the range moved toward the reclamation areas in 2011.The vertex positionsof the contour fora salinity of 21.90‰wereat（28°40′48′′N，121°28′12′′E），（28°40′12′′N，121°30′36′E），（28°40′12′′N，121°33′36′′E），（28°40′12′′N，121°33′00′′E），and（28°36′00′′N，121°36′06′′E）in the years 2003，2005，2007，2008，and 2011，respectively.The distribution of salinity contours for values lower than 21.90‰shows that the region of low salinity moved seaward and toward the reclamation areasoverall.In comparison to 2003，thevertex position of the contour for a salinity of 21.90‰moved 3.89，4.01，0.77，and 9.01 km seaward from the estuary，respectively，in 2005，2007，2008，and 2011.

Salinity is affected by river runoff，precipitation，surface water，groundwater，evaporation，and exchange of water from inside and outside of the estuary（Zhao etal.，2010）.As shown in Table 3，relatively high average precipitation occurred in 2010 and the minimum occurred in 2003，while opposite trends in salinity weremeasured in those years，with a correlation coefficientof-0.56.Asevidenced by thesedynamics，precipitation can reducesalinity，and can be an inducement for salinity change in the Jiaojiang Estuary.The distribution of surface water resources was consistent w ith precipitation，indicating that both played a role in salinity reduction.

Tidal processes influence the exchange ofwater from inside and outside the estuary，and reclamation has been thought to reduce the m ineralization of groundwater and salinity of seawater.This study demonstrated that the salinity remained at about28‰from the 1980s to the 1990s because of little reclamation activity during this period.With the advent of new reclamation projects in the 21st Century，there has been an obviously decreasing trend in salinity.However，the salinity increased from 2004 to 2006，which could be attributed to no reclamation activity during this period.The salinity further decreased from 2007 to 2010，w ith the lowestvalue of 21.15‰occurring in 2010，during theperiod when large-scale reclamation eventswereinitiated.Thesalinityand reclamation ratewere negatively correlated，w ith a correlation coefficientof-0.8.

Fig.5.Change of contour for salinity of 21.90‰in Jiaojiang Estuary.

Table 3 Measured precipitation and surfacewater resources data in Jiaojiang Estuary.

Table 4 Nutritional status indexes in Jiaojiang Estuary since 1980s.

3.3.Nutritional statusand its impact factors in Jiaojiang Estuary

3.3.1.Eutrophication assessment

The sea surface eutrophication index in the Jiaojiang Estuary since the 1980s is given in Table 4.The eutrophication indexwas less than 0.5 during the 1980sand 1990s，indicating satisfactory nutritional status in these periods.Itwas greater than 3 after the year 2000，signifying that the eutrophication index had reached a high level.

The horizontal distribution of the eutrophication index in the Jiaojiang Estuary is shown in Fig.6，which displays a decreasing trend seaward from the estuary.The highest eutrophication index occurred at station S0 in the period of 2003-2005 and in 2011.In 2007 and 2008，the eutrophication index was highestat station S1，and almost all of the indexes weregreater than 3，w ith theexception of thevaluesatstations S3 and S4，indicating that the eutrophication range expanded seaward during this period.The regionw ith an eutrophication index greater than 5 moved seaward constantly，but the trend was less distinct than that of salinity.The pollution status of the open sea im proved as the region of high nutrition receded back toward the estuary.As shown in Fig.7，the vertex positions of the contour for the eutrophication value of 5 were at（28°40′12′N，121°33′66′E），（28°40′12′N，121°35′36′E），（28°38′24′N，121°35′44′E），（28°39′36′N，121°37′00′E），and（28°41′24′N，121°34′12′E）in 2003，2005，2007，2008，and 2011，respectively.The vertex position of the contourmoved 3.47 km from 2005 to 2007 and 3.71 km from 2007 to 2008. The high-nutrition region retreated toward the estuary from 2008 to 2011.

Fig.6.Horizontal distributions of eutrophication index in Jiaojiang Estuary in different years.

Fig.7.Change of contour for eutrophication index of 5 in Jiaojiang Estuary.

3.3.2.Organic pollution assessment

The variation of the sea surface organic pollution index in the Jiaojiang Estuary since the 1980s is shown in Table 4.The water quality is considered to be in a good conditionwhen the index is less than 1，as in the 1980s.However，it rose to avalue greater than 1 and less than 2 in the 1990s，indicating a safe condition in the Jiaojiang Estuary.The index was greater than 4 and fluctuated constantly after 2000，demonstrating serious water pollution.

Thehorizontaldistribution of the organic pollution index in the Jiaojiang Estuary is given in Fig.8，show ing a decreasing trend seaward from the estuary.As shown in Fig.9，the vertex positions of the contour for the organic pollution index of 5 were at（28°40′12′N，121°32′24′E），（28°40′48′N，121°33′00′E），（28°38′24′N，121°33′36′E），and（28°39′36′N，121°34′12′E）in 2003，2005，2007，and 2008，respectively. The vertex position of the contour moved 1.53 km seaward from 2003 to 2005 and 6.25 km toward the reclamation areas in 2007 and then 2.58 km back toward the estuary in 2008.

As shown in Fig.10，the am ounts of industrial wastewater and domestic sewage increased continuously in the Jiaojiang Estuary from 2005 to 2010.The amount of domestic sewage increased from 9.28×107t to 1.381×108tw ith an annual growth rateof 9.7%.Mostof the industrialwastewater reached the emission standard after treatment，while the domestic sewage was discharged w ithout treatment，and thus it is considered a driving factor of eutrophication，w ith a correlation coefficient of 0.73.The oil content，shown in Table 2，displays an increasing trend in the estuary and is also another cause of water environmental pollution.

This study dem onstrates that the estuary exhibited a satisfactory nutritional status during the 1980s and 1990s，and the eutrophication index and organic pollution index were both higher than 3 after 2000.The calculated eutrophication and organic pollution indexeshave been very high in recent years，as corroborated by the results of Sun et al.（2012）.The eutrophication dynamics were closely related to reclamation activities.Therewere periodsw ithout reclamation during the 1980s and 1990s，an accelerated developmental period from 2001 to 2003，and a large-scale reclamation period from 2007 to 2009.The correlation coefficient between eutrophicationand reclamation was 0.76.The area for aquaculture reached 769 hm2in 2009，and the planned area for offshore development reached 3 000 hm2.The amounts of nitrogen，phosphorus，and oil em issions as a result of reclamation projects and aquaculture activitiesare important factors that determine thewater quality of the Jiaojiang Estuary.

Fig.8.Horizontal distributions of organic pollution index in Jiaojiang Estuary in different years.

Fig.9.Changeof contour fororganic pollution index of5 in Jiaojiang Estuary.

Fig.10.Amounts of industrial wastewater and domestic sewage in Jiaojiang Estuary.

3.4.Aquatic ecosystem health assessment

Based on the results of aquatic ecosystem health assessm ent of the last 30 years in the Jiaojiang Estuary，as shown in Fig.11，the dynam ics of the aquatic environm ent can be divided into four stages.In stage 1 from the 1980s to the 1990s，the standard score for ecosystem health was high，and the health status of the aquatic ecosystem was classified as level 1，indicating that the aquatic ecosystem was disturbed minimally by outside factors in this period.In stage 2 from 2000 to 2003，the health status of the aquatic ecosystem deteriorated from level 1 to level 4，indicating a heavy disturbance.In stage 3 from 2004 to 2005，therewas a period of improvement of the aquatic ecosystem，w ith the standard score reaching 0.75 in 2005，and the health status reachinglevel 1.In stage 4 from 2006 to 2011，there was a period of deterioration of the aquatic ecosystem，and the health status decreased to level 4.The water quality in this stage was deplorable，indicating that the aquatic ecosystem had been heavily disturbed.

The water quality in the Jiaojiang Estuary declined generally from the 1980s to 2011.The health status was modulated by all the factorsmentioned above.The correlation between the suspended matter concentration and the health status of the aquatic ecosystem was not significant in this study.However，the suspendedmatter concentration is an important indicator of aquatic ecosystem health.An increase in suspended matter concentration and turbidity restricts the growth of aquatic plants and the biological processes of the native nekton（Stevenson et al.，1993）.In addition，the investigation showed a significant linear correlation between the number and density of species and salinity in the estuary.The changes in the biological community w ill lead to themodification of the aquatic ecosystem in the estuary and affect the aquatic ecosystem health（Ye，2005）.The standard score of salinity was 0.14 in 2007 and 2008，and correspondingly，the comprehensive standard score of the health status of the aquatic ecosystem in the Jiaojiang Estuary was only 0.33，dem onstrating a significant positive correlation between the two values，w ith a correlation coefficient of 0.93.The extent of eutrophication range and imbalance of the nitrogen-to-phosphorus ratio may cause changes in the composition of dominant algae species.In this study，there was a negative correlation between the health status of the aquatic ecosystem and the nutritional status in the Jiaojiang Estuary，w ith a correlation coefficient of-0.71.

Fig.11.Aquatic ecosystem health assessment for Jiaojiang Estuary.

4.Conclusions

The dynamics of suspended matter，salinity，and nutrients were investigated in the Jiaojiang Estuary based on historical data from the last 30 years，and a comprehensive health assessment of the aquatic ecosystem for this area was performed.The natural and human factors were explored.The main conclusions are as follows:

（1）The suspended matter concentration fluctuated in the estuary，and the range of high concentration expanded continually.Suspended sedim ent is a critical factor affecting the suspended matter concentration in the estuary.The generation ofwater-insoluble debris caused by the solid waste em ission inevitably leads to an increase in suspended matter concentration，and reclamation is another human factor affecting the suspendedmatter concentration.

（2）The salinity showed an overall decreasing trend，and the region w ith low salinity continually moved seaward. Precipitation and surface water resources can be incentives for salinity change in the Jiaojiang Estuary.The salinity showed asignificantnegative correlationw ith the reclamation rate.

（3）The estuary exhibited a satisfactory nutritional status during the 1980s and 1990s，and the status has become severe in recent years.Anthropogenic discharge of industrial wastewater and domestic sewage is a driving factor affecting the nutrient concentration.Nitrogen，phosphorus，and oil emissions as a result of reclamation projects and aquaculture activity are important factors determining the water quality in the Jiaojiang Estuary.

（4）There was a significant positive correlation between the health of the aquatic environment and salinity，w ith a correlation coefficient of 0.93.The correlation coefficient between the health status and nutritional status was-0.71，while the correlation betw een the health status of the aquatic ecosystem and the suspended m atter concentration was not as significant as that of the other two factors.

（5）The dynamics of the aquatic environment in the Jiaojiang Estuary were characterized by four stages:sustainable health from the 1980s to the 1990s，continued deterioration from 2000 to 2003，improvement from 2004 to 2005，and secondary deterioration from 2006 to 2011.It is apparent that the Jiaojiang Estuary is faced w ith imminent environmental pressure.

（6）Foundational understanding of the environmental situation in the Jiaojiang Estuary is imperative for improvementof management and sustainable utilization of water resources. Themost important thing for improvementofwater quality is pollution investigation and control.Furthermore，the effectsof ocean engineering，such as land reclamation，and industrial development on the marine environment should be given ample attention，and measures should be taken for effective regulation.

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This work was supported by the Soft Science Research Project of the Zhejiang Association for Science and Technology（GrantNo.KX12E-17）and the Research Projectof the Zhejiang Environmental Protection Bureau（Grant No.2012A 033）.

*Corresponding author.

E-mail address:hznu_bzhou@126.com（Bin Zhou）.

Peer review under responsibility of HohaiUniversity.

http://dx.doi.org/10.1016/j.wse.2015.01.007

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