Impacts of urbanization on the groundwater resources in Shahrood,Northeastern Iran:Comparison with other Iranian and Asian cities
Gholam A.Kazemi
数不胜数的拼音
Faculty of Earth Sciences,Shahrood University of Technology,Shahrood,P.O.Box 316-36155,Iran
财务管理的内容
a r t i c l e i n f o Article history:
Received 24December 2008
Received in revid form 6March 2010Accepted 15April 2010
Available online 28April 2010Keywords:Cesspit
Groundwater temperature Nitrate
Shahrood-Iran Asia
Urbanization
a b s t r a c t
Urbanization may lead to the contamination of groundwater and/or it may alter the hydrogeological regime.Shahrood is a medium size city in northeastern Iran,underlain by an alluvial aquifer.Analysis of 45samples collected from the Shahrood Plain’s aquifer in 2003and 2005revealed that:(1)Shahrood’s wastewater disposal wells and deep cesspits have led to the nitrate pollution of groundwater (up to 140mg/L NO 3–NO 3);(2)urban recharge has lowered the groundwater temperature and pH and (3)urbanization has possibly resulted in the incomplete interaction between various flow compartments of the aquifer.In four other Iranian cities,Gorgan,Kerman,Zahedan and Mashad,urbanization has led to water quality deterioration,alarming ri of groundwater levels endan
gering foundations of the build-ings as well as collap of ‘qanat’s galleries.The maximum concentration of nitrate (MCN)in groundwater in all the cities has been compared with the ratio of population/rainfall in each city.A similar exerci has been carried out for Asian megacities.The show that MCN in an urban aquifer is directly controlled by population and average annual rainfall.This has rious implications for the management of urban groundwater resources and suggests that the current world population growth rate and the likely reduc-tion in the atmospheric precipitation induced by global warming will further deteriorate the quality of such resources.
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1.Introduction
The impacts of urbanization and urban centres on the hydro-geological regime and the quality of groundwater resources have been the subject of substantial investigations over the past 25years (McFarlane,1984;Morris et al.,1994;Klimas,1995;Cro-nin et al.,2003;Taniguchi et al.,2007).As a conquence,this area of rearch is now very well documented and a number of books have been specifically allocated to this topic (Wilkinson,1994;Chilton et al.,1997;Lerner,2003;Howard,2006).However,the subject continues to attract the attention of scientist
s (e.g.Ro,2007;Cutter,2007;Kagawa.,2009).This level of interest stems mainly from the rapidity of urban development during last half a-century.In 1950,29%of the world population lived in urban areas;this incread to 49%in 2007and is expected to reach 60%by 2030as estimated by Population Reference Bureau (PRB,2007).Furthermore,the rate of urban population growth in differ-ent parts of the world varies widely.In Africa and Asia,it has dou-bled during 1950–2007,while it has for the same period en a ri of 23%and 41%in North America and Europe,respectively.The dis-crepancy in growth rate caus different impacts on groundwater resources emphasizing the need for local studies.
Urbanization often results in the deterioration of groundwater quality (Tellam,1995),but it may also freshen groundwater by reducing its total dissolved solids (TDS)content.For instance,McFarlane (1984)showed that in Perth,Western Australia,urban-ization improved the quality of underlying unconfined groundwa-ter resources.There,fresh,high quality roof runoffs are directed into Perth’s aquifer through a large number of shallow houhold wells leading to positive impact on groundwater quality and quan-tity.Urbanization generally leads to the elevated levels of nitrate,boron,chloride,sulphate,pathogens,and more site-specific addi-tives if proper wastewater and wage discharge facilities are not installed.Taniguchi et al.(2007)has recently demonstrated that urb
an development increas groundwater temperature,which in turn produces changes in chemistry and groundwater flow dynamics.
Urbanization also results in the depletion of groundwater re-sources through urban abstraction,or it may increa the volume of water stored in the aquifer via leakage from pipelines,wer systems or urban infiltration basins (Lerner,1990).In the early stages of the establishment of an urban centre,production bore-holes target the local underlying aquifer becau of the easy acces-sibility and lower supply costs.In contrast,a large volume of external water is usually conveyed into the cities –sometimes over significant distances –to fulfil the expanding water needs as cities
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grow up.The transferred water,the quality of which is often differ-ent from that of the local aquifer,forms a new source of recharge that was not previously part of the hydrogeologic system.
The current study shows for thefirst time that urbanization may reduce the temperature of groundwater,alter the groundwa-terflow systems and increa the acidity of the groundwater.It comp
ares the impacts of urbanization in Iranian cities of Shahrood, Gorgan,Kerman,Zahedan and Mashad and highlights the signifi-cant role of wastewater disposal wells and deep cesspits in trans-ferring pollutants to the aquifers,as well as the paramount influence of rainfall and population.In some of the cities,ur-ban-induced ri in the groundwater levels during the last20years has reached an alarming depth of one meter below ground surface. This has created great concerns especially with regard to the stabil-ity of foundation of structures as well as the strength of surface soils.The ri in water level has also resulted in the blockage and collap of the traditional groundwater abstraction system known as‘Qanat or Ghanat’.At the end of this paper,analys are pre-nted which show that the concentration of nitrate in an urban aquifer is controlled by the number of population and the average local rainfall.This hypothesis has been successfully tested for the studied Iranian cities and for thefive megacities of Asia;Seoul, Manila,Jakarta,Bangkok and Taipei.
2.Urban population in Iran and the characteristics of Shahrood
Urban population in Iran has tripled from15.7millions in1976 to47.9millions in2006(Fanni,2006and2006Census data avail-able at:www.sci.ir:80/portal/faces/public/census85/census85. natayej–accesd October2007).This means that some32million more people live in urban centres today as compared to30years ago.Inde
ed,both urban and overall population growth rate in Iran is higher than the world average(Fig.1).This places an enormous stress on the urban groundwater resources,quantity wi and quality wi.A number of recent studies have dealt with the im-pacts of different cities in Iran on the quality of their underlying aquifers(Khazaei,2001;Lashkaripour and Ghafoori,2002;Shahpa-sandzadeh et al.,2005;Joekar-Niasar and Ataie-Ashtiani,2009). The topic has also attracted considerable attention from rearch-ers in a number of Iranian universities.As is the ca with Shahrood,most Iranian cities overlie alluvial fans which are usually good sources of groundwater yet,at the same time,vulner-able to pollution.
Shahrood with an area of17km2is a medium size city in north-eastern Iran,located400km to the east of the capital,Tehran and 80km to the south of the Caspian Sea(Fig.2).Between1996–2006, Shahrood’s population grew by28%,from105,000to135,000.At prent,the city has no werage network;however,the construc-tion work commenced in2004with the initial projection offive years to complete,but this has not happened as yet.In the interim, all buildings in Shahrood are rved by on site cesspits which are up to25m in depth and one meter in diameter.
Residential buildings may have one,two or three cesspits depending on the size,type and some cultural ethics.Deeper cess-pits are preferred becau they do not require frequent cleaning and rem
oval of the sludge.It should be added that roof and yard runoffs are often discharged into the houhold cesspits.Nation-wide,cesspits are the main form of disposals of houhold wastes for74%of the residential complexes;werage network is pro-vided for24%of the hous and only0.5%have ptic tanks in-stalled(2006Census data).The remaining1.5%,mostly villagers, u some other primitive forms of disposal.Among the cities cho-n for this study,only Mashad and Zahedan,have up to20%of their residential buildings connected to werage network;the rest are rved solely by onsite cesspits.
3.Hydrogeological ttings and land u in Shahrood Plain
The Shahrood plain aquifer is an unconfined alluvial aquifer (Fig.3)that extends from the limestone/dolomitic mountains in the north of the city to the marly–gypsiferous outcrops in the south.Due to the lack of significant topographic relief,eastern and western boundaries of the aquifer are not well defined.The average depth to water table is approximately100m;it is higher in the northern parts and lower in the southern ctions where theflow system reaches lowland areas.The overall groundwater flow direction is from north to south,though there is also a less sig-nificant westwardflow line in the southern end.Generally, groundwater salinity increas from north to south.Elongated Al-borz Mountain chain to the north of Shahrood,act as a barrier to the rains originat
ing from the Caspian Sea.Hence,the average an-nual rainfall in Shahrood,despite vicinity to the Caspian Sea,is only154mm.A more comprehensive treatment of the hydrogeol-ogy and groundwater resources of Shahrood can be found in Kaz-emi et al.(2001)and Kazemi(2004).
About400production boreholes and six qanats[Qanat,or Gha-nat,a traditional system of groundwater extraction,is a near hor-izontal gallery which yields water by gravity]tap Shahrood aquifer to yield122Mm3of water annually primarily for agricultural u (Bakhshi,1998).The city municipality,which supplies water for the city green areas,also runs a small number of wells.None of the production boreholes or qanats is ud as potable water supply sources.Production bores are generally deep and in cas reach up to300m.Deep wells have varying yields of up to4500m3/day.
Shahrood city,a few villages,various types of farms and vine-yards overlie Shahrood aquifer.Shahrood is famous throughout Iran for its grapes.However,cereals(wheat,barley and oats),sugar beet and other vegetables,as well as apricot and cherry orchards are also common,extending right through the city neighbour-hoods.Shahrood farmers traditionally apply large quantities of fer-tilirs to boost the production rate and to compensate for the deficiency of organically poor soils of the region(Berenji,1998). Conquently,there is the potential risk of groundwater contami-nation from agricultural activities.
花花宇宙陈慧琳4.Materials and methods
Some10%of the Shahrood aquifer production 38 boreholes,were sampled duringfive days in July2003(Fig.3).A number of boreholes were re-sampled for checking the accuracy of analysis.Sampling locations were lected both inside and out-side the city boundary.All samples were collected in the morning and analyzed immediately the same day in the afternoon for
行之将至
pH, G.A.Kazemi/Physics and Chemistry of the Earth36(2011)150–159151
中堂镇NOÀ
3,POÀ3
4
胰酶肠溶胶囊,SOÀ2
4
,ClÀ,B+3,and electrical conductivity(EC).Field
measured parameters included EC and temperature.The reason for measuring limited number of ions(not all major ions)is the fact that previous urbanization studies have generally demonstrated changes in the ions only(Morris et al.,1994;Foster et al., 1998).Also,the intention was to reduce the cost and to avoid a large temporal difference between samples.Sample number13, was collected from upgradient of Shahrood in an unimpacted(pris-tine)location to be ud as a reference for comparison purpos (e Fig.3).There is no human activity clo to this well and the extracted water is conveyed to some distances.
A Hach EC meter model Co150,a Metrohm744pH meter,and a normal alcohol thermometer were ud to measure EC,pH and temperature,respectively.Water samples were analyzed using a variety
of methods such asflame photometry,titration and,in par-ticular,a Palintest TM Standard Photometer7000.The results of the laboratory analysis andfield data are prented in Table1.In Octo-ber2005,eight wells were re-sampled(Samples No.9,13,14,26, 28,29,34and38)in order to asss the temporal variations of the groundwater chemistry(Table2).At this occasion most of the wells were off-production.
For Mashad,the data by Lashkaripour and Ghafoori(2002)and that of Jafari Gharieali(2008),For Zahedan the result of the work by Khazaei(2001),for Kerman that of Haj Malek(2008)and for Gorgan,the publication by Shahpasanzadeh et al.(2005)have been ud.Two of the(Jafari Ghariehali,2008;Haj Malek,2008)are MSc thes undertaken at the Faculty of Earth Sciences,Shahrood University of Technology.The paper by Hosono et al.(2009),per-sonal communication with Y.Umezawa(Nagasaki University, 2008)and a number of websites specifically(/statistics/largest-cities-population-125.html)have been ud to obtain the data for megacities of Asia.5.Discussion
5.1.Nitrate,phosphate and chloride concentration
Analysis of2003samples show that the concentration of nitrate (as NOÀ
3
)in17samples is25mg/L or higher and reaches up to 140mg/L in one well(Table1).In pristine groundwater(Sample 13),nitrate concentration is7.6mg/L.Hounslow(1995)ts the threshold of contamination for nitrate at10mg/L,and World Health Organization’s(WHO)permissible limit for nitrate in drink-ing water has been t at45mg/L.In this rearch,Hounslow’s cri-terion,reinforced by the nitrate concentration of reference sample, has been adopted to classify samples.WHO’s standard is mostly for health purpos and does not easily lead to the detection of anthro-pologic contamination.Bad on thefigures and information, samples clearly fall under two categories:
(1)Unpolluted samples who nitrate concentration is less than
10mg/L.
(2)Polluted samples who nitrate concentration is above
25mg/L.
小记者There is only one outlying sample(Sample21)with11mg/L of nitrate which does notfit into this classification;however,it can be safely regarded as a pollution free sample.Of the17polluted samples,
14lie within the city boundary(Table1and Fig.3),clearly reflecting the impact of urbanization on the quality of groundwater.
The average concentration of phosphate in polluted and unpol-luted samples is not significantly different.It is0.38mg/L for pol-luted and0.32mg/L for pristine ones.In addition,the mg/L ratios of(NO3/PO4Â10)for polluted and unpolluted samples are
1850 Fig.2.Location of the study area(Shahrood)in northeastern Iran.The other studied cities are also shown.
and390,respectively;significantly different.The show that urbanization has markedly incread the nitrate content but agri-cultural practices,though intensive,have not raid the concentra-tion of phosphate(It is a valid assumption to consider fertilizers as a stronger source for phosphate as compared to urbanization). Nevertheless,it is likely that this difference is due to the fact that agricultural practices are diffu sources of nutrients which are ap-plied at the soil surface.Also,POÀ3
4
is strongly adsorbed in most diments(Goldberg and Sposito,1984;Sah and Mikkelson, 1986)and it will thus take long time to movefirst into the unsat-urated zone and then saturated zone.In contrast,disposal wells and cesspits are den-concentrated sources of nitrate,which are dug deep into the unsaturated zone.To highlight this,it should be pointed out that effluent from a cesspit contains a total nitrogen content of25–60mg/L(Canter,1997).This makes them a specifi-cally threatening source especially if their year-round wetness is taken into account.
Urbanization has also resulted in an increa in the mg/L ratio of Cl/SO4.The average value of this ratio is1.03for polluted samples and0.86for unpolluted samples.Wastewater is the most likely source of extra ClÀin groundwater beneath the city.It should be pointed out that Cl and SO4concentrations(not the ratio)are high in samples5,6,7,8,14,15,16and23,located outside of the city boundary,which reflect the impact of gypsum and marl on the chemical composition of groundwater as is discusd in para-graphs ahead.A difficult to justifyfinding is that the average con-centration of B+3in the polluted samples is0.55mg/L which is lower than0.72mg/L for the unpolluted samples.It should be nev-ertheless added that bothfigures reprent tho of contaminated waters as natural rain and ground waters contain only between 0.02and0.1mg/L boron(Custodio and Llama,1983).
Ten samples have similar or slightly less nitrate than the refer-ence sample.The are divided into two groups.Group A which in-clude samples4,5,6,7,8and23and Group B which include samples2,9,14and30.Group A have high EC values due to the influence of marl and gypsiferous formations in the south of the Shahrood plain.Denitrification could be the cau of low nitrate in the samples.It occurs as a result of pyrite oxidation through following reaction(Kölle,1988)and gives ri to sulphate concentration:
14NOÀ
3
þ5FeS2þ4Hþ!7N2þ10SO2À
4
þ5Fe2þþ2H2O搬迁补助费
It is clearly en that the concentration of sulphate in the samples (and also Sample14from Group B)is high and leads to high SO4/EC and SO4/NO3ratios.Average SO4/EC ratio for the samples is0.24 while it is0.135for the remaining samples.Similarly,SO4/NO3ratio of the samples is190,much higher than10for the rest.It is also likely that salinity-triggered denitrification similar to what happens in coastal aquifers(Santoro et al.,2006)is responsible for the
low region and the location of the sampled boreholes.Note that shallow-rooted crops and orchards,apart from
nitrates.Sample30from Group B has a low nitrate due to its very low EC value(477l S cmÀ1),the lowest in all samples which reflects its pristine condition.It is,however,difficult to justify the low ni-trate concentration of the remaining samples2,9and14of Group B.One possibility is the anoxic condition where there are insuffi-cient oxygen to produce nitrate from ammonia or other nitrogen compounds.
5.2.Temperature and pH
Thefield temperature of water samples ranges from14.2°C to 19°C.Interestingly,Fig.4a shows that the temperature is less than 15.3°C for samples who nitrate concentration is above40mg/L; sample25is the only exception.The samples are from boreholes located within the city.This means that boreholes within the city boundary pump colder waters.Note that samples17,18and19, outside and samples25and26inside city boundaries are located very clo to the borderline.This transitional(edge)positions pro-hibits a perfect exponential relationship between groundwater’s nitrate and temperature.The average temperature of groundwater in the Shahrood aquifer is17°C(Ka
zemi,2003),about three de-grees warmer than that of the cold,high-nitrate waters.This clearly shows that urban recharge(cesspits,lawn watering,road runoff,leaking water pipes,etc.)has lowered the temperature of
Table1
Field data and chemical analysis of water samples in July2003.
Sample EC(F)T(°C)pH EC(L)NOÀ3POÀ3
4
SOÀ24ClÀB+3Cl/SO4NO3/PO4Â10 11078187.61106280.15160150 2.10.9450.3 289018.27.5789960.251401650.6 1.1824 3710177.617499.20.368064 1.50.8025.6 43900177.24397060.2410008800.650.8825 54740197.324710 6.80.299809300.80.9523.4 68200197.2380207.20.2819002550 1.15 1.3425.7 77600197.317480 5.60.72195020001 1.037.8 8552017.57.155520 6.40.3318008800.750.4919.4 973217.57.68753 6.80.19901300.4 1.4435.8 10880187.6189210.4 1.22701800.450.678.7 1189718.37.599028.80.231601000.450.6338.3 12P127714.57.37130086.80.341351150.450.85255 1355314.57.645517.60.1266580.50.8863.3 141
667177.541653 5.60.23302250.650.6828 152070177.48209080.34103800.750.9326.7 161440197.8214507.60.072642300.350.87108.6 17963187.859689.20.121361200.450.8876.7 18P113717.57.681153340.251541800.45 1.17136 19P979177.5298631.60.171281300.45 1.02185.9 20P997177.67101424.80.211521200.50.79118 21941187.797911.20.221481100.60.7450.9 221320187.5813318.80.382602050.50.7923.2 232030167.412070 6.40.274103000.550.7323.7 24P93016.57.5494225.20.251261000.550.79100.8 25P98517.87.521031720.351381100.50.80205.7 26P95117.87.595138.40.331081350.4 1.25116.4 27P134414.87.151408540.392281200.50.53138.5 28P1032157.2710331400.31112110 1.150.98451.6 29P153214.27.3115371200.291421550.55 1.09413.8 30477198.0148360.2668340.650.5023.1 3139418.78.034027.60.2752390.450.7528.1 32P1109167.6111838.40.351361400.45 1.03109.7 33P1439167.19144331.60.431382500.65 1.8173.5 34P146314.57.0614661040.541521600.65 1.05192.6 35P148814.97.071488700.361081500.45 1.39194.4 36P147014.57.131467830.571721950.55 1.13145.6 37a P153214.27.2715331360.731441800.55 1.25186.3 38P134414.87.2613491040.411321600.5 1.21253.7 39P105215.27.481083500.371401050.550.75135.1 40b P105215.27.48108545.60.49136980.550.7293.1 Units:mg/L,EC:l S cmÀ1,P:polluted sample.
a Duplicate of sample29.
b Duplicate of sample39,F:field,L:lab.
Table2
Field data and chemical analysis of water samples in October2005.
Sample EC(F)T(°C)pH EC(L)NOÀ
3POÀ34SOÀ24
ClÀB+3Cl/SO4NO3/PO4 974717.97.67757 6.80.451001450.65 1.4515.1 13553–7.815667.60.2660760.65 1.2729.2 14170518.17.41170711.20.173202750.750.8666 26P106717.87.541054500.131241700.7 1.37385 28P109215.87.251089540.111121200.6 1.07491 29P151715.27.1815181040.251651900.9 1.15416 34P151514.97.0615061040.111501800.85 1.2945 38P138115.97.2813771000.11322000.55 1.521000 Units:mg/L,EC:l S cmÀ1,F:field,L:lab.,P:polluted sample.
154G.A.Kazemi/Physics and Chemistry of the Earth36(2011)150–159
groundwater as it incread the nitrate concentration.This rais the question of why the contaminated groundwater is colder than the ambient groundwater?
(A)Lower temperature of the contaminated groundwater is most probably due to the lower temperature of city municipal water.Shahrood municipal water is supplied by Bastam and Mojen aquifers,located in the higher altitude(150m and400m higher) some10and30km,respectively,to the north of Shahrood.The average temperature of the aquifers is14.5°C and11.6°C, respectively(Kazemi,2003);2.5–5.4°cooler than
fer.The low temperature of background sample–
indeed due to its location being in higher altitude.
colder water of the water sources correlates well
–contaminated urban impacted groundwater in
aquifer.It should be added that passage of urban
unsaturated zone during the earlier times absorbs the
heat of such environment.This leaves latter recharge
the heat of the unsaturated zone.
(B)Chemical reactions in the aquifer triggered by
ban recharge,who quality is different,with the
water may also reduce the groundwater temperature.
pointed out that denitrification is a process that temperatures.Therefore,cold urban recharge reduces
tion rate in the aquifer,and as a conquence
concentration.
(C)Severe drought during1994–2006has led to
the production rate of most of the boreholes which
aquifer.In contrast,the discharge rate of the bores
either incread or remained constant.To further
argument,the drop in groundwater level in Shahrood
pared with that of Plain of Mayamey which is
40km apart.For Shahrood,water level drop for a14
from1994to2008is9.56m while for Mayamey it (Karami et al.,2009).This diffeence is attributed to the i
mpact of urban recharge and suggests that the quantity of such recharge is appreciable,sufficient to reduce the groundwater temperature.
Similar to temperature,the pH values of the polluted samples are generally lower than that of the unpolluted samples(Fig.4b). This can be attributed to the nitrification of ammonium in high ni-trate groundwaters which is accompanied by relea of hydrogen ion:
NHþ
4
þ2O2!NOÀ
3
þ2HþþH2O
It could also be due to anaerobic fermentation of dissolved organic matter of wastewater,which produces volatile fatty acids(VFAs) such as acetic acids and in some cas lactic acids and CO2.
5.3.Flow system
Urbanization has not only affected the quality and recharge of groundwater,it appears to have also influenced theflow system of the Shahrood aquifer.The city has acted as a hydraulic barrier preventing interaction between variousflow compartments of the aquifer;there is little mixing between groundwater originating from different recharge points.This is inferred from the large dif-ferences between EC values of groundwaters in nearby boreholes. For instance,samples14,15,and16(in the east)have much higher ECs than nearby samples of25and26.Considering that the groundwaterflow has a westward component too,it is expected that the aforesaid two groups have comparable ECs.Of cour, the role of marl and calcareous formations to the north of samples 14,15and16in raising EC should not be ignored.Similarly,sam-ples10and11(in the south)with ECs of less than900l S cmÀ1are completely different from their adjacent samples38, 36,and33who ECs are over1400l S cmÀ1.In addition,in the north of the city,the EC of groundwater is very low and does not appear to mix with waters underlying Shahrood.This phenome-non,incomplete mixing,takes place either due to the incread hydraulic head or the development of a groundwater mound as shown in Fig.5.It also could be due to the disturbance and com-paction of the geological materials underlying the city.The hypothes need to be further tested by more rearch.The thick alluvium nature of the plain composing various proportions of dif-ferent grain sizes provides the necessary ingredient for compaction
Development of groundwater mound under an urban centre and its
systems.
G.A.Kazemi/Physics and Chemistry of the Earth36(2011)150–159155
