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International Journal of
Environmental Research
and Public Health
Article
Contrasting Eutrophication Risks and
Countermeasures in Different Water Bodies:
Assessments to Support Targeted
Watershed Management
Tong Li, Chunli Chu *, Yinan Zhang, Meiting Ju and Yuqiu Wang
College of Environmental Science and Engineering, Nankai University, Tianjin 300350, China;
love777_happy@126.com (T.L.); zhangyn2011@whu.edu.cn (Y.Z.); jumeit@nankai.edu.cn (M.J.);
yqwang@nankai.edu.cn (Y.W.)
*Correspondence: chucl@nankai.edu.cn; Tel.: +86-138-2138-5387; Fax: +86-222-350-6446
Academic Editor: Yunlin Zhang
Received: 19 May 2017; Accepted: 25 June 2017; Published: 29 June 2017
Abstract:
Eutrophication is a major problem in China. To combat this issue, the country needs
to establish water quality targets, monitoring systems, and intelligent watershed management.
This study explores a new watershed management method. Water quality is first assessed using
a single factor index method. Then, changes in total nitrogen/total phosphorus (TN/TP) are
analyzed to determine the limiting factor. Next, the study compares the eutrophication status
of two water function districts, using a comprehensive nutritional state index method and geographic
information system (GIS) visualization. Finally, nutrient sources are qualitatively analyzed. Two
functional water areas in Tianjin, China were selected and analyzed: Qilihai National Wetland
Nature Reserve and Yuqiao Reservoir. The reservoir is a drinking water source. Results indicate that
total nitrogen (TN) and total phosphorus (TP) pollution are the main factors driving eutrophication
in the Qilihai Wetland and Yuqiao Reservoir. Phosphorus was the limiting factor in the Yuqiao
Reservoir; nitrogen was the limiting factor in the Qilihai Wetland. Pollution in Qilihai Wetland is
more serious than in Yuqiao Reservoir. The study found that external sources are the main source of
pollution. These two functional water areas are vital for Tianjin; as such, the study proposes targeted
management measures.
Keywords:
eutrophication; single factor evaluation; comprehensive eutrophication state index;
watershed management
1. Introduction
Eutrophication is a significant worldwide environmental problem. Eutrophication is a form
of water pollution, caused by excessive loading of dissolved and particulate organic matter and
inorganic nutrients (C, N, and P). Eutrophication risk refers to the possibilities and consequences of
eutrophication [
1
]. Visible effects of eutrophication include the development of planktonic scum and
rooted plant biomass, increased algal growth, the death of fish, increased sedimentation, decreased
dissolved oxygen concentration, and reductions in water transparency [2].
As the population has increased in coastal watersheds, there has been an increase in the transport
of nutrients to lakes, ponds, and estuaries [
3
,
4
]. The resulting eutrophication has had many adverse
effects within the estuaries [
5
–
7
]. For example, increased nitrogen loading can lead to phytoplankton
blooms [
5
,
7
]. These blooms, in turn, lead to the loss of important estuarine habitats, such as sea grass
meadows. Sea grass meadow loss is associated with the loss of important commercial shell fish and
finfish species, such as cod [
8
], bay scallops [
9
], and blue crabs [
10
]. Eutrophic estuaries can also
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Int. J. Environ. Res. Public Health 2017,14, 695 2 of 18
suffer from anoxia [
11
], harmful algal blooms, and brown tides [
12
]. Regime shifts from macrophyte
dominance to phytoplankton dominance have also been widely reported, in locations such as Lake
Christina, Lake Karibaand and Lake Krankesjon [
13
–
15
]. These changes are driven by various factors,
such as climate, nutrients, lake depth, and lake size [16].
China is a rapidly developing country, and eutrophication has become the most widespread water
quality problem [
17
]. The eutrophication of most lakes and reservoirs in China seriously threatens the
regional ecological environment and water security, and has restricted the sustainable development of
society and the economy. In past decades, excessive nutrient loading has led to algal blooms in Lake
Chao [
18
,
19
], Lake Dianchi [
20
], and Lake Tai [
21
,
22
]. The rapidly accelerating pace of eutrophication
in lakes across the country has forced the government to set ambitious lake restoration goals [23].
In general, phosphorus (P) supply is thought to regulate algal production in freshwater
lakes [
24
–
27
]. In contrast, nitrogen (N) supply is the predominant constraint in many estuaries
and shallow marine environments [
28
,
29
]. Integrating numerical modeling of P and N based on
monitoring, assessing, and predicting the state and changes in watershed nutrients is needed to control
eutrophication and management [30].
In China, management tools and policies are proposed and implemented at the provincial
level [
31
]. Therefore, management strategies are best considered within a single region. Compliance
with water quality indicators has historically been used as the standard threshold for triggering
management measures. This approach does not consider the differences in system responses in
different regions. Further, few eutrophication control strategies reflect the differences in lake basin
characteristics [
32
]. Many past studies have considered the quality of a specific water body; however,
few studies have considered different functional water areas in a region. Further, using traditional
water quality criteria alone is insufficient to measure eutrophication levels. Traditional water quality
standards are generally based on toxicological tests. Toxic or harmful substance concentrations or
thresholds have served as an assessment baseline; however, there is a negative feedback mechanism
between these concentrations and the health of aquatic organisms [
33
]. The lake nutrient standard
is a nutrient variable threshold that corresponds with lake ecosystems; this value reflects the most
natural conditions (the state before the large-scale interference of human activity) [
34
], at which N, P,
and other nutrients have fewer toxic effects on aquatic organisms.
This background highlights the importance of developing targeted management measures to
reduce eutrophication and potentially harmful phytoplankton activity. Different water bodies have
different water quality targets, hydrological characteristics, and different surroundings. Different
water quality targets should be set based on different water uses, allowing the adoption of targeted
management measures.
This study investigated two different water bodies within one region, to assess their different
water targets. These water bodies are located in Tianjin Province in north China, and have different
water functions and quality targets. This study selected and analyzed their eutrophication indicators,
to identify water quality responses to load reduction and other appropriate management measures.
The first water body is the Yuqiao Reservoir, a lake that provides drinking water. It has second class
water quality requirements under the GB3838 Chinese water quality standard. The second water body
is a core area of the Qilihai Reserve, which is one of the National Nature Reserves. It has first class
water quality requirements under the GB3838 Chinese water quality standard.
The goal of this study was to develop an effective watershed management method. First, water
quality was assessed using the single factor index method, and then reassessed by analyzing changes of
TN/TP to determine the limiting factor. The eutrophication statuses of the two water bodies were then
compared based on the comprehensive nutritional state index method and geographic information
system (GIS) visualization. Finally, nutrient sources were qualitatively analyzed and management
measures were proposed. This included exploring different eutrophication treatment and management
measures based on specific loads. There were three key study components: (A) an entrophic index
system was established; (B) a time series analysis was conducted to reflect eutrophication trends;
Int. J. Environ. Res. Public Health 2017,14, 695 3 of 18
and (C) recommendations were made based on contrasts between the eutrophication analysis and
nutrient source analysis.
2. Materials and Methods
2.1. Study Area
Two water bodies with different functions were selected as the study areas. Figure 1shows their
locations. One is the Yuqiao Reservoir, which provides drinking water and it is located in the north of
Tianjin. The other is the Qilihai Wetland, which preserves natural ecological diversity as a national
nature protection area. It is located in the middle of Tianjin. The two reservoirs provide different water
functions and have separate water quality requirements.
Int.J.Environ.Res.PublicHealth2017,14,695 3of17
2.MaterialsandMethods
2.1.StudyArea
Twowaterbodieswithdifferentfunctionswereselectedasthestudyareas.Figure1shows
theirlocations.OneistheYuqiaoReservoir,whichprovidesdrinkingwateranditislocatedinthe
northofTianjin.TheotheristheQilihaiWetland,whichpreservesnaturalecologicaldiversityasa
nationalnatureprotectionarea.ItislocatedinthemiddleofTianjin.Thetworeservoirsprovide
differentwaterfunctionsandhaveseparatewaterqualityrequirements.
Figure1.LocationofthetwostudiedwaterbodieslocatedinTianjinProvinceinChina.
TheYuqiaoReservoir,locatedinJiCountyinChina’sTianjinProvince(40°02’N,117°25’E),
wasformedin1965tomeetwaterneeds,mainlyhydropowerandirrigation.Ithasbeentheonly
watersupplyinTianjinCity(populationofmorethan10million)since1983.Theriver’stotalareais
1627km2.Theaveragewaterdepthis4.3m;thetotalcapacityis1.559billionm3;andthecontrolled
drainageareaisapproximately2060km2.TheShaheRiver,theLinRiverandtheLiRiverarethe
maintributaries.Thesouthbankofthereservoirissteepandthenorthshoreisarelativelyflatplain.
Thereservoir‐controlledwatershedisatemperatecontinentalmonsoonsub‐humidclimate.The
annualaveragetemperatureis10.4to11.5°C;andtheannualaverageprecipitationis748.5mm,
mainlyconcentratedfromJunetoSeptember[35].
Watersafetyposesaseriousthreatinthisarea.Accordingtothe“RegulationsontheProtection
ofDrinkingWaterSources”ofChina,drinkingwatersourceprotectionareasshouldbeclassified
basedondifferentwaterqualitystandardsandprotectionrequirements.Asadrinkingwatersource
protectionarea,YuqiaoReservoirisgenerallydividedintoprimaryprotectedareasandsecondary
protectedareas;ifnecessary,quasi‐protectedareascanbeadded.Theregulationsnotethat
protectedareasatalllevelsshouldhavecleargeographicalboundaries,andalllevelsofprotected
areasandquasi‐protectedareasshouldprovideclearwaterqualitystandardsanddeadlinesfor
achievingthem.Cross‐regionalrivers,lakes,reservoirs,watertransportchannelsintheregion’s
upperreachesshouldnotaffectthedownstreamwaterqualitystandardsoftheYuqiaoReservoir.
WaterintheYuqiaoReservoirisconsideredaprimaryprotectedarea.Theregulationsstatethat
Figure 1. Location of the two studied water bodies located in Tianjin Province in China.
The Yuqiao Reservoir, located in Ji County in China’s Tianjin Province (40
◦
02’ N, 117
◦
25’ E),
was formed in 1965 to meet water needs, mainly hydropower and irrigation. It has been the only
water supply in Tianjin City (population of more than 10 million) since 1983. The river’s total area is
1627 km
2
. The average water depth is 4.3 m; the total capacity is 1.559 billion m
3
; and the controlled
drainage area is approximately 2060 km
2
. The Shahe River, the Lin River and the Li River are the
main tributaries. The south bank of the reservoir is steep and the north shore is a relatively flat
plain. The reservoir-controlled watershed is a temperate continental monsoon sub-humid climate.
The annual average temperature is 10.4 to 11.5
◦
C; and the annual average precipitation is 748.5 mm,
mainly concentrated from June to September [35].
Water safety poses a serious threat in this area. According to the “Regulations on the Protection of
Drinking Water Sources” of China, drinking water source protection areas should be classified based on
different water quality standards and protection requirements. As a drinking water source protection
area, Yuqiao Reservoir is generally divided into primary protected areas and secondary protected
areas; if necessary, quasi-protected areas can be added. The regulations note that protected areas at all
levels should have clear geographical boundaries, and all levels of protected areas and quasi-protected
areas should provide clear water quality standards and deadlines for achieving them. Cross-regional
Int. J. Environ. Res. Public Health 2017,14, 695 4 of 18
rivers, lakes, reservoirs, water transport channels in the region’s upper reaches should not affect
the downstream water quality standards of the Yuqiao Reservoir. Water in the Yuqiao Reservoir is
considered a primary protected area. The regulations state that quality standards for primary protected
areas should not be lower than those of the “GB3838-88 Surface Water Environmental Quality Standard”
Class II standard.
In the protected area of the Yuqiao Reservoir, all activities that may damage or destroy the
ecological balance of the environment and forests, water, vegetation and water sources are prohibited.
This includes dumping industrial waste, garbage, feces, and other city wastes into the waters; the
use of highly toxic and high pesticide residues; the abuse of fertilizers; planting and raising livestock,
poultry, and aquaculture activities; and all tourism activities and other activities that may cause water
pollution. In addition, no construction may discharge pollutants into the water body; reconstruction
projects must reduce pollutant discharges; and original sewage outfalls must cut sewage discharge to
ensure that the water quality in the protected area meets prescribed water quality standards.
Wetlands are known as the “kidney of the earth.” Each wetland is a natural community, formed
by the interaction of land and water systems [
36
], and having multiple ecological functions. The Qilihai
Wetland (39
◦
17’ N, 117
◦
34’ E) is located in Ninghe County in eastern Tianjin, on the west bank of the
Bohai Bay. In 1992, the Qilihai Wetland was approved by the government as a national marine nature
reserve. The government is responsible for protecting and managing the natural environment and
ecosystems of the Shell embankment, which is an oyster reef containing rare ancient coastal relics
and wetlands in China [
37
]. The Qilihai Wetland covers 45.15 km
2
and has many ecological functions.
It provides water for surrounding rivers, controls flooding, and prevents soil from desertification.
The Qilihai Wetland is a national marine area with precious ancient coastal ruins; the wetland’s natural
environment and its ecosystem are clear targets for protection and management.
As wetlands have become over-developed by human activities, the biological diversity has
decreased, and ecosystem services and other functions have been degenerated [
38
]. The water
environment has been polluted with heavy eutrophication and significant nitrogen, and the water
resources have decreased. Based on these factors, the Qilihai Wetland national nature reserve should be
managed by the appropriate administrative department within the provincial people’s government or
under the State Council [
39
]. All units and individuals should be obligated to protect nature resources
in Qilihai Wetland, and the government should have the right to report and prosecute any unit or
individual that has destroyed or occupied the reserve. No production facilities should be built in the
core area and buffer zone of the Qilihai Wetland.
As in the reservoir area, in the Qilihai Wetland, it is prohibited to build production facilities that
may pollute the environment and destroy resources or landscapes; for other construction projects, the
pollutant emissions should not exceed national and local pollutant emission standards. For facilities
already built in the study area, any pollutant discharges that exceed state and local government
standards should be treated within a prescribed time limit. If damage has been caused, remedial
action must be taken. These rules should keep water quality in Qilihai Wetland at or above the first
grade of Environmental Quality Standard for Surface Water. The following activities are prohibited in
the wetland: logging, grazing, hunting, and fishing, reclamation, burning, quarrying and dredging.
In addition, it is prohibited to visit and conduct tourism projects in the Qilihai Wetland. Construction
in the peripheral protection zone must not damage the environmental quality of the Qilihai Wetland.
If damage has been caused, it must be corrected within a set time limit.
2.2. Water Quality of the Two Reservoirs
Many scholars have developed different water quality evaluation methods [
40
]. Single factor
assessment methods are widely used for rivers [
41
], reservoirs, and lakes. For example, Yang et al. [
42
]
assessed groundwater quality using a single factor and concluded that the groundwater quality in the
southern region Ordos basin was generally poor when considered in terms of national groundwater
quality standards. A comprehensive index approach, such as the Water Quality Monitor (WQM), was
Int. J. Environ. Res. Public Health 2017,14, 695 5 of 18
developed by the National Sanitation Foundation (NSF) [
43
]; other modified, but sound, water quality
indicators have been developed based on this approach [
44
]. Most studies use physical, chemical, and
biological characteristics to evaluate existing water quality and pollution statuses [
45
]. For example,
physical characteristics include dissolved oxygen (DO), hydrogen ion concentration (PH), transparency
(SD) and temperature [
46
]. Chemical characteristics include total nitrogen (TP), total phosphorus
(TN), chemical oxygen demand (COD), biochemical oxygen demand (BOD), petroleum, and heavy
metals [
47
]. Biological characteristics include chlorophyll a, benthos biomass, and diversity of rare
species [
48
]. TN and TP are often used to indicate the degree of nutrient contamination in a water
body; transparency reflects the clarity of the water body; the permanganate index (COD
Mn
) reflects
organic and inorganic oxidizable substance pollution in the water; and chlorophyll a (Chl-a) reflects
the amount of phytoplankton in the water. We have used these as indicators to assess the water quality
of the two reservoirs.
Based on the hydraulic characteristics of the surface water, three monitoring points (Figure 2a)
were established in the Yuqiao Reservoir. We collected data from the three monitoring points in
the Sanchakou, the reservoir center, and the dam. The average measures across the three locations
provided the data for analysis. In addition, we set up three monitoring points around Bird Island
(Figure 2b) in Qilihai Wetland Nature Reserve and used the annual average of the three monitoring
points to reflect water quality.
Int.J.Environ.Res.PublicHealth2017,14,695 5of17
usephysical,chemical,andbiologicalcharacteristicstoevaluateexistingwaterqualityandpollution
statuses[45].Forexample,physicalcharacteristicsincludedissolvedoxygen(DO),hydrogenion
concentration(PH),transparency(SD)andtemperature[46].Chemicalcharacteristicsincludetotal
nitrogen(TP),totalphosphorus(TN),chemicaloxygendemand(COD), biochemical oxygen demand
(BOD),petroleum,andheavymetals[47].Biologicalcharacteristicsincludechlorophylla,benthos
biomass,anddiversityofrarespecies[48].TNandTPareoftenusedtoindicatethedegreeof
nutrientcontaminationinawaterbody;transparencyreflectstheclarityofthewaterbody;the
permanganateindex(CODMn)reflectsorganicandinorganicoxidizablesubstancepollutioninthe
water;andchlorophylla(Chl‐a)reflectstheamountofphytoplanktoninthewater.Wehaveused
theseasindicatorstoassessthewaterqualityofthetworeservoirs.
Basedonthehydrauliccharacteristicsofthesurfacewater,threemonitoringpoints(Figure2a)
wereestablishedintheYuqiaoReservoir.Wecollecteddatafromthethreemonitoringpointsinthe
Sanchakou,thereservoircenter,andthedam.Theaveragemeasuresacrossthethreelocations
providedthedataforanalysis.Inaddition,wesetupthreemonitoringpointsaroundBirdIsland
(Figure2b)inQilihaiWetlandNatureReserveandusedtheannualaverageofthethreemonitoring
pointstoreflectwaterquality.
(a) (b)
Figure2.(a)SamplingpointsforYuqiaoReservoir;(b)SamplingpointsforQilihaiWetlandNature
Reserve.
Thesinglefactorindexmethodisarelativelysimpleandusefulmethodtoassesswaterquality
[49]andisusedtoevaluatethewaterqualityinthisstudy.
Thesinglefactorindexevaluationmethodispresentedas:
, ,
,
Inthisexpression,Si,jisthestandardindexofthewaterqualityparameteriatpointj.Ci,jisthe
concentrationofwaterqualityparameteriatjpoint(mg/L);Cs,iiswaterqualitystandardi,(mg/L),
whosevalueisregulatedbythestandardof“surfacewaterenvironmentalquality”(GB3838‐2002)in
Table1.
Table1.Cs,jofthetworeservoirs(mg/L).
IndicatorsCODMnTNTPChl‐aSD
GradeI20.20.02‐‐
GradeII40.50.025‐ ‐
GradeIII610.05‐ ‐
2.3.EutrophicationSituation
Differentscholarshaveproposedmanyeutrophicationevaluationmodels[50–53].Yangetal.
usedaseriesofartisticneuralnetworkstodevelopaneutrophicationassessmentmodelfor
aquaculturewaterareas[54].Wuetal.establishedahybridmodelcombiningwaterquality
Figure 2.
(
a
) Sampling points for Yuqiao Reservoir; (
b
) Sampling points for Qilihai Wetland
Nature Reserve.
The single factor index method is a relatively simple and useful method to assess water quality [
49
]
and is used to evaluate the water quality in this study.
The single factor index evaluation method is presented as:
Si,j=Ci,j
Cs,i
In this expression, S
i,j
is the standard index of the water quality parameter iat point j.C
i,j
is the
concentration of water quality parameter iat jpoint (mg/L); C
s,i
is water quality standard i, (mg/L),
whose value is regulated by the standard of “surface water environmental quality” (GB3838-2002) in
Table 1.
Table 1. Cs,j of the two reservoirs (mg/L).
Indicators CODMn TN TP Chl-a SD
Grade I 2 0.2 0.02 - -
Grade II 4 0.5 0.025 - -
Grade III 6 1 0.05 - -
Int. J. Environ. Res. Public Health 2017,14, 695 6 of 18
2.3. Eutrophication Situation
Different scholars have proposed many eutrophication evaluation models [
50
–
53
]. Yang et al. used
a series of artistic neural networks to develop an eutrophication assessment model for aquaculture
water areas [
54
]. Wu et al. established a hybrid model combining water quality indicators and
ecological response indicators to assess eutrophication, and then applied it to assess the status
of eutrophication from 2007 to 2008 in the southwest Bohai Sea [
55
]. Huo et al. established a
region-specific lake eutrophication assessment standard using a frequency distribution method based
on Chl-a concentration [
56
]. Liu et al. used a water quality modeling-based scenario analysis approach
to quantitatively evaluate how eutrophication in Lake Dianchi responded to an under-construction
water diversion project [
57
]. These evaluation methods have advantages and disadvantages; many are
subjective, and calculations are complex, error-prone, and inconvenient.
Based on the China Environmental Monitoring Center’s “Lake Reservoir eutrophication
evaluation methods and classification of technical requirements,” many scholars use an integrated
nutritional status index method to assess eutrophication in lakes. The comprehensive nutritional status
index method has matured and the evaluation range is more comprehensive than other nutritional
index methods. The evaluation factors comprehensively consider indexes such as TN, TP, SD, Chl-a
and COD
MN
. Further, the method has mitigated the single evaluation factor ’s lack of evaluation.
We used the eutrophication index to assess the eutrophication of the two reservoirs. The equation is:
TLI (∑) =
m
∑
j=1
Wj×TLI(j)
In this expression, TLI (
Σ
) is the comprehensive nutritional status index; W
j
is a normalized
weighted value of index j; and TLI (j) is the eutrophication evaluation universal index of index j.
Studies by Jin summarize the correlation coefficient between the Chl-a and other parameters in
China’s lakes and reservoirs; these provide an important basis for calculating weights [
58
]. With Chl-a
as the reference parameter, the normalized correlation weight of the index j parameter is calculated
as follows:
Wj=r2ij
∑m
j=1r2ij
In this expression, r
ij
is the correlation coefficient between the index j parameter and the reference
parameter Chl-a; m is the number of evaluation parameters. Table 2shows the correlation between the
Chl-a and other parameters in Chinese lakes (reservoirs).
Table 2. The correlation between lake parameters (reservoir), Chl-a, and rij, r2ij and weights (Wj).
Parameter Chla TP TN SD CODMn
rij 1 0.84 0.82 −0.83 0.83
r2ij 1 0.7056 0.6724 0.6889 0.6889
Wj0.26626 0.18787 0.17903 0.18342 0.18342
After calculating the eutrophication index, we classified reservoir eutrophication into five different
grades according to the grading standards. Table 3lists these grades. In the same nutritional state,
the higher the index value, the more severe the nutritional level.
Table 3. Grading standards of eutrophication.
Grades Values
Oligotrophic TLI (∑) < 30
Mesotrophic 30 ≤TLI (∑)≤50
light eutrophic 50 < TLI (∑)≤60
middle eutrophic 60 < TLI (∑)≤70
hyper eutrophic TLI (op) > 70
Int. J. Environ. Res. Public Health 2017,14, 695 7 of 18
3. Results and Discussion
3.1. Physical and Chemical Characteristics of Water Quality
Tables 4and 5show the physicochemical characteristics of the water samples; Figure 3a,b show
the Single Factor Pollution Index. According to the surface water environmental quality standard
classification and water environment basic project standard limit (National Standard of the People’s
Republic of China, Environmental Quality Standards for Surface Water, GB3838-2002), the Yuqiao
Reservoir’s surface water quality is consistent with second class water environmental quality standards.
For the Qilihai Wetland, the surface water quality is consistent with first class water environmental
quality standards.
Table 4. Monitoring results of the water environment single indices in Yuqiao Reservoir.
Test Items 2010 2011 2012 2013 Standard Interval
CODMn 3.933333 3.733333 4.603333 3.2 II ≤4
III ≤6
TN 1.013667 0.816667 4.266667 2.333333 II ≤0.5
III ≤1
TP 0.023333 0.033333 0.056667 0.05 II ≤0.025
III ≤0.05
Chl-a 13.53333 10.41 16.4 10.66667 -
SD 0.5 0.8 0.83 0.9 -
Table 5.
Monitoring results of the water environment single indices in Qilihai Wetland Nature Reserve.
Test Items 2010 2011 2012 2013 Standard Interval
CODMn 22.30 17.53 28.33 14.99 I≤2
V≤15
TN 1.69 2.45 2.43 3.08 I≤0.2
1.5 < V ≤2.0
TP 0.192 0.168 0.268 0.167 I≤0.02
0.2 < IV ≤0.3
Chl-a 87.209 33.45 92.85 54.70 —
SD 0.38 0.18 1.23 0.27 —
The average concentration of COD
Mn
in the Yuqiao Reservoir ranged from 3.2 to 4.6 mg/L; the
single factor pollution index of COD
Mn
ranged from 0.800 to 1.151 with an average value of 0.967.
In 2012, the average concentration of COD
Mn
exceeded the limit for water quality criteria Grade II,
but in 2013 there was a significant decline. The COD
Mn
pollution index at the sampling stations met
the expected class of water quality standards except in 2012. The TN concentration was higher than
the limit for water quality criteria Grade II during the monitoring period. The single factor pollution
index of TN ranged from 1.633 to 8.533, with an average value of 4.215. The single factor pollution
index exceeded Grade II of the water quality standards for four years. This indicates the significance
of nitrogen pollution.
In recent years, the TP concentration continued to rise. The single factor pollution index of TP
ranged from 0.933 to 2.267 with an average value of 1.633. From 2011 to 2013, the single factor pollution
index exceeded the Grade II of water quality standards. Further, the transparency value was lower
than the lake eutrophication standard of 2.4 m, indicating that the reservoir was eutrophic. Table 4and
Figure 3b show the COD
Mn,
TN and TP concentration trends in the Qilihai Wetland Nature Reserve;
the concentrations fluctuate, but all of them exceed the surface water environmental quality standards
of the first Grade and some exceed Grade IV. In 2011 to 2013, the nitrogen concentration significantly
exceeded Grade V of the surface water environmental quality standard.
Int. J. Environ. Res. Public Health 2017,14, 695 8 of 18
Int.J.Environ.Res.PublicHealth2017,14,695 7of17
3.ResultsandDiscussion
3.1.PhysicalandChemicalCharacteristicsofWaterQuality
Tables4and5showthephysicochemicalcharacteristicsofthewatersamples;Figure3a,bshow
theSingleFactorPollutionIndex.Accordingtothesurfacewaterenvironmentalqualitystandard
classificationandwaterenvironmentbasicprojectstandardlimit(NationalStandardofthePeople’s
RepublicofChina,EnvironmentalQualityStandardsforSurfaceWater,GB3838‐2002),theYuqiao
Reservoir’ssurfacewaterqualityisconsistentwithsecondclasswaterenvironmentalquality
standards.FortheQilihaiWetland,thesurfacewaterqualityisconsistentwithfirstclasswater
environmentalqualitystandards.
(a)
(b)
Figure3.(a)TrendinthesinglefactorpollutionindexforYuqiaoReservoir;(b)Trendinthesingle
factorpollutionindexforQilihaiWetlandNatureReserve.
Table4.MonitoringresultsofthewaterenvironmentsingleindicesinYuqiaoReservoir.
TestItems20102011 2012 2013 StandardInterval
CODMn3.9333333.7333334.6033333.2II≤4
III≤6
TN1.0136670.8166674.2666672.333333II≤0.5
III≤1
TP0.0233330.0333330.0566670.05II≤0.025
2010 2011 2012 2013
1
2
3
4
5
6
7
8
9
Single factor pollution index
Time/year
CODMn
Total nitrogen
Total phosphorus
2010 2011 2012 2013
7
8
9
10
11
12
13
14
15
16
Single factor pollution index
Time/year
CODMn
Total nitrogen
Total phosphorus
Figure 3.
(
a
) Trend in the single factor pollution index for Yuqiao Reservoir; (
b
) Trend in the single
factor pollution index for Qilihai Wetland Nature Reserve.
The single factor pollution index of COD
Mn
ranged from 7.495 to 14.165 with an average value
of 10.390. The single factor pollution index of TN ranged from 8.45 to 15.40 with an average value
of 12.06. The single factor pollution index of TP ranged from 8.35 to 13.40, with an average value
of 9.91. And the transparency was also lower than the lake eutrophication standard which is 2.4 m.
Of these values, the nitrogen concentration is particularly significant, indicating the serious pollution
impacting the water quality of Qilihai Wetland. TN and TP were the main factors in these two water
areas that exceed the standard.
As mentioned above, the single factor indexes of COD
Mn
and TP in Qilihai Wetland were almost
10 times the indexes of Yuqiao Reservoir. There are many reasons for high COD
Mn
concentrations in
Qilihai Wetland, including industrial and agricultural activities, other discharges, domestic sewage,
and rubbish. In addition, the chlorophyll concentration in Qilihai Wetland is much higher than the
concentration in Yuqiao Reservoir. This may be because the industrial wastewater and domestic
sewage surrounding Qilihai Wetland and the farmland shore generated more surface runoff with more
nutrients. This supports algae growth and reproduction. The results of the single factor pollution
index method follow in Figure 3.
3.2. Ratio Changes of TN/TP
The TN/TP ratio continuously fluctuated in the two water bodies. The total nitrogen levels were
related to ammonia nitrogen and nitrite levels in water. Ammonia nitrogen in the water was also
Int. J. Environ. Res. Public Health 2017,14, 695 9 of 18
not stable. After biological assimilation, the remaining dissolved oxygen was present in sufficient
conditions. Many nitrifying bacteria oxidized to nitrite nitrogen. In the flood season, a variety of
nitrifying bacteria and dissolved oxygen were reduced, leading to ammonia nitrogen and nitrite
nitrogen conversion. The transformation process resulted in excessively large ammonia and nitrite
nitrogen concentrations over the course of a few months. Therefore, the total nitrogen increased;
on the contrary, it decreased. However, during the drought period, due to the role of denitrification,
anaerobic, or hypoxia, nitrate nitrogen (NO
3−
) served as an acceptor. This reduced other gaseous
oxides of nitrogen or nitrogen. This leads to the reduction of nitrate nitrogen and total nitrogen in
water, gradually reducing the water storage capacity. The reservoir’s water storage capacity affects
TP changes, because when the water storage capacity is gradually reduced, it promotes sediment
redox, mineral dissolution and adsorption, and bacteria and microbe metabolism. This includes
hydrodynamics or bioturbation [
59
]. This resulted in phosphorus being released from the sediments;
the phosphorous then becomes an endogenous source contributing to the water phosphorus load.
Many factors modify the demand and supply of N and P for phytoplankton in the upper
lake waters. However, the TN/TP ratio helps predict which of the two most commonly limiting
macronutrients will become the most growth limiting under well-illuminated, stratified conditions [
60
].
In addition, the TN/TP ratio is an important factor affecting algal growth; it reflects the production
cycle and phytoplankton production in the water body [
61
]. Researchers generally believe that when
the TN/TP ratio is 10:1–25:1, there is a linear correlation between algae growth and nitrogen and
phosphorus concentration. This benefits algae growth, which is prone to eutrophication [62].
During the monitoring period, the TN/TP ratios in the Yuqiao Reservoir progressed from 43, 25,
75, and 47 from 2010 to 2013. The TN/TP ratios in the Qilihai Wetland progressed from 9, 15, 9, and
18 from 2010 to 2013. The TN/TP ratios in Qilihai Wetland ranged 10:1 and 25:1 from 2010 to 2013,
favoring algae growth. The TN/TP ratio in the Yuqiao Reservoir did not support algae growth during
the monitoring period. Algae growth and reproduction processes require a variety of nutritional
elements. If a certain nutrient is relatively low, growth and reproduction processes will be limited.
This element is called the “main limiting nutrient” [
60
]. Laguna et al. [
63
] noted that when TN/TP
exceeds 16, the phosphorus is in a restricted state; when TN/TP is less than 16, the nitrogen is in a
restricted state. Thus, phosphorus was the limiting factor in the Yuqiao Reservoir; nitrogen was the
limiting factor in the Qilihai Wetland.
3.3. Eutrophication Evaluation
Table 6shows the TLI of Yuqiao Reservoir from 2010 to 2013. TN, Chl-a, and SD level (the three
nutritional status indexes) were high. The degree of eutrophication in the Yuqiao Reservoir was highest
in 2012, with levels decreasing in decreasing degrees in 2013, 2010, and 2011. Water quality was in a
mesotrophic state (30
≤
TLI (
∑
)
≤
50) except during 2012 and 2013. The water quality in 2012 and 2013
was in light eutrophic state (50 < TLI (
∑
)
≤
60). This shows that from 2010 to 2013, Yuqiao Reservoir
water quality ranged between a mesotrophic and light eutrophic state. Eutrophication in 2012 was the
most serious. This may have been because of the self-purification capacity [
64
] of the Yuqiao Reservoir,
leading to an overall declining trend for the reservoir. Overall, the Yuqiao Reservoir water quality in
2010 to 2013 was still relatively good.
Table 7shows the TLI of the Qilihai Wetland Nature Reserve from 2010 to 2013. The nutritional
status index of TN showed a significant upward trend; strict measures are recommended to regain
and maintain control. The nutritional status index of TP, COD
Mn
, Chl-a, and SD fluctuated frequently
across the four years, indicating an unstable water environment. The degree of eutrophication of
Qilihai Wetland was highest in 2013, and declined across 2011, 2012, and 2010. The wetland was
in a hyper eutrophic state (TLI (
∑
) > 70) for a long time, and the eutrophication trend continues to
rise. The nutritional indexes all significantly exceeded the standard. This shows that from 2010 to
2013, the water quality of Qilihai Wetland Reserve was significantly polluted, and already in a hyper
eutrophic state.
Int. J. Environ. Res. Public Health 2017,14, 695 10 of 18
According to Environmental Quality Standards for Surface Water (GB3838-2002), Qilihai Wetland
Nature Reserve falls within the scope of the first class. Yuqiao Reservoir falls within the second or
third class. With respect to monitoring results, the degree of eutrophication of Qilihai Wetland Nature
Reserve was far above the Yuqiao Reservoir (Figure 4).
1
(a)
(b)
Figure 4. Cont.
Int. J. Environ. Res. Public Health 2017,14, 695 11 of 18
2
(c)
Figure 4.
(
a
) Eutrophication trends in Yuqiao Reservoir in 2010 and 2011; (
b
) Eutrophication trends in
Yuqiao Reservoir in 2012 and 2013; (
c
) Eutrophication trends in Qilihai Wetland Nature Reserve from
2010 to 2013.
Table 6. Nutrient state index of Yuqiao Reservoir from 2010 to 2013.
Year TN TP CODMn Chl-a SD TLI (∑
∑
∑)
2010 54.75995 33.33215 37.53206 53.29199 64.62706 48.99333
2011 51.09924 39.12455 36.14339 50.44245 55.50898 46.74031
2012 79.10711 47.74196 41.71763 55.37848 54.79479 55.57921
2013 68.88323 45.70931 32.04144 50.70696 53.22399 50.06019
Table 7. Nutrient state index of Qilihai Wetland Nature Reserve from 2010 to 2013.
Year TN TP CODMn Chl-a SD TLI (∑
∑
∑)
2010 63.4189 67.55978 83.70305 73.52582 69.95113 70.80658
2011 69.70973 65.39123 77.29874 63.11916 84.44709 71.23871
2012 69.57088 72.97568 90.07175 74.2065 47.16393 71.09521
2013 73.58631 65.29427 77.23796 68.46024 76.58107 71.8827
3.4. Analysis of Nutrient Sources
The information above indicates that nutrients are the main cause of eutrophication. However,
the nutrient inputs differ between different water areas. As such, we analyzed nutrient sources from
both internal and external sources.
Int. J. Environ. Res. Public Health 2017,14, 695 12 of 18
3.4.1. Internal Sources
Sediment is an internal source of eutrophication, both in the Qilihai Wetland and in the Yuqiao
Reservoir. Sediments contain abundant nutrients and accumulate year to year. Accumulation is
particularly high in the summer, when there is more light, the water temperature is high, and nutrients
are easily released [65]. Therefore, the nutrients in the sediments are a driver for eutrophication.
Cheng [
66
] determined the total amount of contaminated sediment in Yuqiao Reservoir, which
contributes less to the water pollution than other sources. Past studies have shown that the total
nitrogen in the Qilihai wetland sediments was relatively enriched [
67
]. However, the nitrogen
analysis presented above is the limiting factor in the Qilihai Wetland, which is a relatively low
nutrient level relative to algae growth. Therefore, the sediment pollution contributes less to the
nutrient source. Nitrogen accumulation in the Qilihai Wetland is also due to human activities [
68
].
The sediment contributes little to the nutrient sources of the two water areas; the main source comes
from external sources.
3.4.2. External Sources
Point source controls around the Qilihai Wetland and the Yuqiao Reservoir have achieved certain
results, gradually reducing industrial point source pollution around the Qilihai Wetland and Yuqiao
Reservoir [
35
]. Non-point source pollution in the region comes from different sources, the pollution
load is large, and the pollution rate is very high.
In the Yuqiao Reservoir, where water inflow is generally stable, all nutrient types increased. There
are 129 villages close to the reservoir’s water environment [
69
]. As the number of urban residents
has increased, the amount of phosphorus containing detergents and domestic sewage discharge has
also increased, but the sewage treatment rate remained at almost zero. As the economy developed,
there was an increase in the cultivated land upstream of the Yuqiao Reservoir, with extended planting
times [
70
]. This increased the use of different chemical fertilizers and pesticide varieties; as the dosage
increased, farmland fertilizer was lost through surface runoff into the Yuqiao Reservoir. More recently,
the rapid development of aquaculture has led to the discharge of fish bait, small amounts of fertilizer,
and other fish products into the reservoir. This has accelerated the eutrophication rate. In addition,
there has been a decrease in the area of the Yuqiao Reservoir covered by aquatic plants [
69
], narrowing
the aquatic plant growth range. One plant species dominates the area, providing a basis for the further
algae growth.
The Qilihai Wetland Nature Reserve is one of the most eco-diverse ecological landscapes in Tianjin.
As such, it attracts tourists from all over the world, and tourism has been rapidly developing [
71
].
However, excessive tourism and tourists transfer the metabolites of tourist activities into the Qilhai
Wetland system, destroying the water environment. Tourism development has also expanded the
number and variety of dining establishments around the wetland. The wastes produced by dining
establishments further pollute the Qilihai Wetland’s water quality. Because of rapid aquaculture
development, there is also fishpond pollution in the Qilihai Wetland Nature Reserve [
72
]. The fish
bait and other fertilizer used to feed fish hinder water resources flow. This reduces the water’s
self-purification capacity, giving rise to water contamination. Similarly, the poor management of
aquatic organism distribution has also increased eutrophication of the Qilihai Wetland.
3.5. Management and Measures
Because it is the only water source in Tianjin, the water quality in the Yuqiao Reservoir is closely
linked to the life and health of its residents. This has attracted the attention of both government agencies
and residents, who work together to protect the Yuqiao Reservoir water quality. Several industries
around the reservoir that significantly polluted the water have been dismantled [
66
]. In addition,
residents work to consciously enhance reservoir awareness.
Int. J. Environ. Res. Public Health 2017,14, 695 13 of 18
There are many laws and regulations governing nature reserves, however, there are not enough
management institutions in the Qilihai Wetland to fully implement relevant conservation policies.
Due to a decentralized protection approach, the lack of sufficient infrastructure, and a lack of strong
financial support, the water pollution has become more serious. In addition, outreach about protected
areas has been insufficient; residents lack a sense of protection consciousness [
73
,
74
]. These factors
have resulted in greater pollution in the Qilihai Wetland than in the Yuqiao Reservoir. To prevent the
deterioration of eutrophication in Yuqiao Reservoir and in the Qilihai Wetland natural reserve, stricter
treatment methods and management measures are needed.
Appropriate control and management measures are needed; however, it is unwise to control
either nitrogen or phosphorus pollution alone. Based on the situation around the two water areas,
management policies are needed to improve water quality.
Appropriate measures are needed to introduce controls for different pollution sources. For
industrial pollution, the government should allocate special funds to address the pollution, close
polluting enterprises, and use advanced technology to reduce pollution emissions and production.
With respect to urban waste, the government should unify garbage collection and establish sites for
sanitary landfills. To address source pollution, the government can remediate water quality through
ecological restoration, dredging, and other technical means [
75
]. We recommend rehabilitating water
quality based on wetland type and water characteristics [
76
]. This may include establishing relevant
laws and regulations to regulate aquaculture and fisheries, strengthening poultry manure management,
applying the rational use of fertilizers and pesticides, strengthening the ability of vegetation to absorb
excess nutrients, paying attention to the rational distribution of aquatic organisms, and controlling
soil erosion.
In addition to these steps, the government should strengthen governance and management,
and at the same time, strengthen awareness. This includes encouraging local people to learn more
about environmental protection. Further, increasing the application of remote sensing, GIS and other
technical means will assist in eutrophication management, improve the targeted effects of management,
and promote effective management. In addition, due to the location and other characteristics of the
Yuqiao Reservoir, it is important to pay attention to and control nitrogen and phosphorus pollution
in the upstream river and around the river. It is also important to prohibit the development of
unsustainable tourism and to plan wetland structures rationally in the Qilihai Wetland.
Wetland water quality parameters are often related to hydrological processes and the growth
season of wetland vegetation [
74
]. Effective management requires carrying out dynamic monitoring
of the Qilihai Wetland water quality, establishing automatic prediction and alarm systems, and
strengthening research. Managing water functions is an important way to manage water resources.
A hierarchical management system combines river basin management and regional management to
form a water resources management system. Therefore, for the Qilihai Wetland Nature Reserve, which
has higher water quality requirements, management should be strengthened. At the same time, the
government cannot ignore the Yuqiao Reservoir management. To improve water quality in the long
term and bring water quality in line with water quality standards, governments and stakeholders
must restore and protect environmental quality through management tools, scientific research, and
technology projects. The government should also establish a protection target responsibility system
and quantitative assessment management approach. For different functional water areas in a region,
the government should be hierarchically managed and water areas should be managed to achieve
higher water quality standards.
This study does have a few limitations. First, the water quality assessment indicators could be
increased, allowing a more comprehensive analysis of results. In addition, while this article proposes
unilateral solutions, a more detailed quantitative or qualitative analysis would better determine
pollution mechanisms and more specific solutions. As the self-purification capacity of the Yuqiao
Reservoir and Qilihai Wetland Nature Reserve decline, further study of the ecological evaluation index
could accurately describe the problems. This highlights additional areas for future study.
Int. J. Environ. Res. Public Health 2017,14, 695 14 of 18
4. Conclusions
This study analyzed two typical water bodies in Tianjin, China, with different water quality
targets. Water quality was first assessed using the single factor index method; changes in TN/TP were
then analyzed to determine the limiting factor. Next, the eutrophication status of the two water areas
were compared, using a comprehensive nutritional state index method and geographic information
system (GIS) visualization. Finally, nutrient sources were qualitatively analyzed and management
measures were proposed.
In the Yuqiao Reservoir, the COD
Mn
concentration met the water quality standard every year
except 2012. The TN concentration fluctuated frequently; it consistently exceeded the standard.
The overall TP concentration exceeded the standard from 2011 to 2013. The Chl-a concentration
was consistent with the regular pattern .In contrast, the COD
Mn
, TN, and TP concentrations in the
Qilihai Wetland Nature Reserve fluctuated, but they all exceeded the surface water environmental
quality standards of the first level, as well as standards at Grade III or Grade IV. The change of Chl-a
concentration was particularly problematic. The water quality in the Qilihai Wetland was particularly
serious. The single factor index indicates that TN and TP were the main factors in the two areas that
led to the standard being exceeded.
The TN/TP ratio in the water bodies in the two study areas fluctuated continuously. During
the monitoring period, the TN/TP ratios in the Yuqiao Reservoir from 2010 to 2013 were 43, 25, 75,
and 47 respectively. The TN/TP ratios in the Qilihai Wetland from 2010 to 2013 were 9, 15, 9, and
18 respectively. Thus, phosphorus was the limiting factor in the Yuqiao Reservoir; nitrogen was the
limiting factor in the Qilihai Wetland.
From 2010 to 2011, the eutrophication level of the Yuqiao Reservoir was consistently in the
mesotrophic state. In 2012 and 2013, it was in a light eutrophic state. Because the surface water
environmental quality standard was classified as the first class, the Qilihai Wetland Nature Reserve
was consistently in a hyper eutrophic state from 2010 to 2013. Although there were some eutrophication
problems in the Yuqiao Reservoir, the pollution in the Qilihai Wetland was more serious.
The analysis shows that external pollution is the main source of pollution in the Yuqiao Reservoir
and the Qilihai Wetland. The main nutrient sources for the Yuqiao Reservoir come from the upper
reaches of the rivers that feed it; the nutrient load is excessive due to aquaculture development and the
poorly managed distribution of aquatic organisms. In the Qilihai Wetland, nutrients are mainly caused
by excessive tourism, aquaculture, and agriculture development.
Targeted management measures are needed to prevent the water quality of the Yuqiao Reservoir
and the Qilihai Wetland from continuing to deteriorate. These measures should be driven based
on different pollution sources; they require, however, an improvement in the area’s hierarchical
management system.
Water quality needs to meet the requisite standards and prevent harm to the human body. This
involves protecting water quality, and maintaining the economic and ecological benefits of wetlands
and reservoirs. To maintain both ecological and socio-economic significance, it is important to learn and
master the status quo and improve management efficiencies before implementing local government
policies. This is the primary message from this study.
Acknowledgments:
Research was supported by National Key Technology R&D Program (Grant
No.2015BAJ01B00) and Key Project of Tianjin Municipal Education Commission (Study on the strategy and
countermeasures of promoting the transformation and upgrading of industry to green low-carbon and service in
Tianjin, 2014ZD). The authors would also like to thank the editors and anonymous reviewers for their insightful
comments and suggestions.
Author Contributions:
Chunli Chu conceived and designed the framework; Tong Li and Yuqiu Wang analyzed
the data; Tong Li and Yinan Zhang wrote the paper; Chunli Chu and Meiting Ju contributed to improving
the article.
Conflicts of Interest: The authors declare no conflict of interest.
Int. J. Environ. Res. Public Health 2017,14, 695 15 of 18
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