Sử dụng chỉ số chất lượng nước CCME WQI đánh giá nước thuỷ lợi

7/27/2019 S dng ch s cht lng nc CCME WQI nh gi nc thu li

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Nghin cu khnng sdng ch s cht lng nc (CCME WQI) trong nh gi nh

hng ca cc ngun thi n h thng knh mng thy li

1. GII THIU

Cc thy vc nc mt l nhng h sinh thi nhy cm do nm a hnh trng, d chu

nh hng ca cc ngun nc thi, bao gm nc thi sinh hot, nc thi cng nghip, nngnghip v nc chy trn cng vi cht thi ca cc khu vc ln cn. Rt nhiu thy vc nc ta

nm trong tnh trng be da nng n, gy ra hng lot cc vn mi trng nh tnh trng

ph dng, suy gim cht lng nc, ph vcn bng h sinh thi, gy suy gim hoc cn tr

s dng. Trong s cc thy vc t nhin v nhn to, h thng knh mng vng nng thn

ng vai tr cp nc cho sn xut nng nghip chim n 80% nhu cu vnc ca mt quc

gia nng nghip ang pht trin, ng thi chu nh hng t tp hp phc tp cc loi ngun

thi khc nhau. Do cht lng nc knh mng thy li nh hng trc tip n cht lng

nng sn, m quan vng nng thn v nh hng gin tip n sc khe ca con ngi nn vic

nh gi cht lng nc bao gm nh gi nh hng ca ngun thi trnn cp thit.

Tuy nhin, vic nh gi cht lng nc chcn c theo mt thng s hoc mt nhm

cc thng s nht nh khng phn nh ht tnh cht ca mt thy vc cng nh mc nh

hng ca cc ngun thi n cht lng nc thy vc do chu nh hng phc tp t cc

yu t bn ngoi. Bn cnh , vic s dng cc thng sn l sgy kh khn cho vic nh

gi so snh cc thy vc vi nhau cng nh so snh din bin cht lng nc trong mt khong

thi gian di. Khi cn mt cng cnh ch smi trng cho php nh gi tng hp cht

lng nc mt cch chnh xc, khch quan v c gi tr trong qun l mi trng ni chung v

qun l cht lng thy vc ni ring. Khc vi cc ch s nh gi cht lng nc khc,

CCME WQI (Ch s cht lng nc Canada) khng gii hn cc thng s thnh phn trong mt

tp hp hu hn, m linh ng trong s dng cc thng s hal, ha hc v sinh hc trong

nh gi cht lng mi trng. Do , CCME WQI c khnng s dng rng ri trong cc i

tng nc cng nh mc ch s dng khc nhau.

2. I TNG, PHNG PHP NGHIN CU

2.1. i tng nghin cu

Trong nghin cu ny chng ti la chn ra hai h thng knh mng thy li mang

nhiu tnh cht i din vc im nhn thi ca loi hnh thy vc ny:

Hai h thng mng thy li thuc trng i hc Nng nghip H Ni: Mng C1 di

50m, rng trung bnh 5m, su trung bnh 0,5m nhn nc thi t hot ng canh tc la ch

yu theo kiu chy trn. Mng C2 gm nhnh chnh di 300m vi 14 nhnh ph, su trung

bnh 0,7 m, ni su nht l 1,2m; l mng ti kt hp nui trng thy sn, nhn nc thi sinh

hot v nc thi chn nui (ln) tp trung qua cc cng thi. kim chng nh hng ca

ngun thi phc hp i din cho loi hnh mng thy li vng nng thn, ly mu i chng

mng C3l mng thy li chnh ca x Ph ng, huyn Gia Lm, H Ni.


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2.2. Phng php nghin cu

a. Quan trc din bin cht lng nc

nh gi cht lng ngun thi: i vi mng C1, ly mu trn rung la im tho

nc vo mng, i vi mng C2 ly mu ti cc ca cng thi, i vi mng C3 ly mu

gn trm bm tsng ung, ni ng thi tip nhn nc thi sinh hot v chn nui.nh gi cht lng nc: ly 3 im i din trn mi on mng, s dng phng

php ly mu nc mt theo TCVN 5996-1995. Thi gian quan trc t thng 7/2007 n thng

6/2009 vi tn sut mt tun mt ln. Cc thng s phn tch gm: DO, pH, Eh c o trc tip

ti hin trng; BOD5c xc nh bng phng php nui cy; COD c xc nh bng

phng php chun ; N-NH4+c xc nh bng phng php so mu Nessler;N-NO3

-c

xc nh bngphng php so mu; P-PO43-c xc nh bng phng php Oniani

b.nh gi hin trng cht lng nc

nh gi cht lng nc so snh vi tiu chun nc mt TCVN 5942: 1995, QCVN

08-2008, tiu chun nc thy li TCVN 6774: 2000. S dng ch s CCME WQI (Canadian

Council of Ministers of the Environment Water Quality Index) nh gi tng hp cht lng

nc trn cc h thng knh mng in hnh c la chn. Gi trCCME WQI c tnh

ton trc tip bng phn mm tnh CCME WQI phin bn 1.1, trong :

( )Trong : F1 biu th t l phn trm s thng svt chun

F2 biu th t l phn trm s thi im vt chun ca mt thng s

F3 biu th tng mc vt chun ca mt thng s, mt thi im.

Trong nghin cu ny, da vo hin trng cht lng nc, chng ti la chn ra cc

thng s DO, Eh, pH, N-NH4+, N-NO3

-, P-PO43-, BOD5v COD tham gia thnh lp ch s.

Kt qu ch s CCME WQI dao ng trong khong t0 n 100% c nh gi theophn hng

cht lng nc (bng 1).

Bng 1. nh gi cht lng nc theo thang im ca CCME WQI

Cht lngCCME

WQI (%)Cht lng nc v biu hin

(I) Rt tt (khng nhim)

95100Nc c bo v, khng c se do hay nh hng suy yu, gn visch t nhin hoc mc tinh khit

(II) Tt ( nhim nh) 8094Nc c bo v, nhng e do hoc nh hng rt t, t c s khc bitvi sch tnhin, t tiu chun

(III) Trung bnh (nhim trung bnh)

6579Nc c bo vthng xuyn, nhng vn c th bnh hng, mi cbiu hin nhim/di tiu chun.

(IV) Xu ( nhim) 4564Nc thng xuyn be do bi tc nhn nhim, biu hin nhim

trong mt s khong thi gian.(V) Rt xu ( nhimrt nng)

044Nc lun b e do hoc b nh hng, nhim hoc di mc tiuchun nhiu ln trong thi gian di.


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3. KT QU V THO LUN

3.1.Hin trng cht lng nc thng qua cc thng s thy ha

Mng C1 l mng thy li ch nhn nc ma, nc x thi tcnh ng la v nc

chy trn, v th c thcoi l mng tiu nc ca khu vc canh tc la. Mng C2 l ni

tip nhn nc thi sinh hot ca khu dn c, nc thi chn nui v nc chy trn vn cy nqu, mng c vai tr cung cp nc ti v nui trng thy sn. Do nhiu nguyn nhn khc

nhau m ngi ta gi mc nc ca chai mng ny n nh, t c slu thng gia chng vi

cc h thng thy li khc. V vy c thcoi mng C1 ch nhn nc thi t sn xut la,

mng C2 nhn nc thi sinh hot v nc thi t hot ng chn nui. kim chng nh

hng ca nc thi n cht lng nc mt cc h thng knh mng thy li, chng ti nh

gi cht lng nc h thng mng C3, nhn ngun thi phc hp gm nc thi canh tc la,

nc thi chn nui v nc thi sinh hot.

Gi tr trung bnh v khong bin ng cc thng s quan trc trong thi gian nghin cu

tthng 7 nm 2007 n thng 6 nm 2009 c trnh by trong bng 2. T kt qu quan trc c

thnh gi chung v cht lng nc ca cc i tng nghin cu:

Bng 2: Cht lng nc thng qua mt sthng sthy ha

Thng

sn v

Mng C1 Mng C2 Mng C3 QCVN 082008Khong TB Khong TB Khong TB

DO mg/l 1,207,52 3,451,34 1,207,14 3,681,46 0,935,20 3,291,43 >2

pH - 6,328,08 7,270,4 6,828,31 7,450,33 6,997,25 7,10,1 5,59

Eh mV -46379 16574 -45276 13767 -50200 82100 >200 (*1)

N-NH4+

mg/l 0,019,746 2,152,47 0,3720,802 5,394,20 0,156,12 3,422,13 < 0,5

N-NO3- mg/l 0,021,64 0,240,29 0,041,30 0,390,33 0,060,27 0,140,07 < 10

P-PO34-

mg/l 0,011,46 0,330,29 0,023,261 0,870,74 0,170,94 0,490,27 < 0,3

BOD5 mg/l 1,833,8 17,06,1 9,944,0 23,06,42 14,026,2 21,64,3 < 15

COD mg/l 16108 5120 24128 6619 3260 479 < 30

(*1) Gi tr Eh nm trong mc oxy ha

Din bin th pH v th oxy ha kh ca cc h thng mng cho thy nhiu c im

ca cc thy vc nc ng chu nh hng ca cc ngun thi ngoi: gi tr pH nm trongkhong trung tnh n hi kim; qu trnh sinh hc trong nc ch yu l qu trnh kh vi th

oxy hakh thp (


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Tuy nhin, khi so snh cht lng nc ca ba h thng knh mng, mng C1, ch

nhn nc thi t canh tc la, cht lng nc chu nh hng mnh ca dinh dng v c ha

tan c bit l NH4+ v PO4

3-c mt trong phn bn gy d tha cc thnh phn ny trong nc.

i vi mng C2 chu nh hng t nc thi chn nui v nc thi sinh hot vi lng thi

ln (trn 80 m3/ngy, chim mt phn ln trong nc u vo ca mng), mc nh hng

ca nc thi phc tp hn, c th k n: suy gim oxy ha tan, gim th oxy ha kh, lm

giu dinh dng hu c, ph dng do dinh dng v c. Cng do , mc suy gim cht

lng nc do ngun thi bn ngoi ca mng C2 l nghim trng nht. L mt mng nhn

ngun thi phc hp, mng C3 nm trung gian gia hai loi h thng thy li trn, mc d

nhn mt lng ln cht thi sinh hot v chn nui nhng do l mt h thng mng thy li

ln, cung cp nc ti cho khu vc x Ph ng, c cp nc thng xuyn do trm bm t

sng ung, nn cht lng nc c ci thin r rt.

Hnh 1: Bin ng gi tr mt s thng s quan trc theo ma

Trn ton b thi gian nghin cu: Gia ma ma v ma kh trong thi gian quan trc

c s khc bit ng k v tt c cc thng s quan trc. Gi trDO, pH, Eh cao hn v bin

ng mnh hn trong trong sut ma kh nm 2007 (I) v ma kh nm 2008 (III), trong khi

cc gi tr ny ca chai i tng nghin cu n nh v thp hn trong ma ma nm 2008

(II) v ma ma nm 2009 (IV). Trong cc thng snh gi cht lng nc th DO ph thuc

cht ch nht vo thi tit th hin r s khc bit theo ma. Nng cc cht dinh dng ha

tan dng NH4+, NO3

-, PO34-, dinh dng hu c c th hin di dng BOD5v COD bin

ng phc tp hn do chu nh hng ca nhiu yu t trong c ch x thi, nhng c

cng xu hng trn. Do nh hng ca ch kh hu vo ma ma, mc xo trn ca thy vc

ln nn gi tr DO v Eh trong cc h thng mng tng trong thi gian ny. Ngc li, do nh

hng ca ngun thi v mc hot ng ca sinh vt trong nc vo ma ma, tng ng vi

thi gian c nhit cao, s dng nc cho canh tc la ln v lng x thi nc thi sinh hot

ln, nn cht lng nc suy gim mnh i vi cc gi tr dinh dng v hu c.


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Do , c th kt lun loi hnh x thi khc nhau nh hng khc nhau n cht lng

nc ca h thng tip nhn. Khi xem xt ng thi cht lng nc mt trong mng v cht

lng nc cp vo mng, cht lng nc trong mng ph thuc lng x thi v mc

cc thng s xem xt trong nc thi. Khi nng cc cht nhim trong nc thi vo mng

tng, cht lng nc trong mng nhanh chng suy gim v ngc li, khi nng cc cht

nhim trong nc thi gim, cht lng nc mt c xu hng phc hi. nh gi mi tng

quan ny, s dng kim nh tng quan theo phn phi Student:

Gi tr kim nh: Z = 21

2

n

R

Rvi n l s mu; R l h stng quan gia cht

lng nc thi a vo mng v cht lng nc trong mng tng ng vi tng thng s.

Bng3:Kt qukim nh tng quan gia cht lng thi v cht lng nc mng

i tng DO pH Eh N-NH4+

N-NO3-

P-PO34-

BOD5 COD

MngC1

n 33 65 65 65 65 65 33 33

R 0,503 0,472 0,453 0,683 0,582 0,610 0,412 0,382

Z 3,240 4,252 4,031 7,430 5,684 6,109 2,520 2,302

MngC2

n 72 72 72 72 72 72 72 72

R 0,634 0,632 0,609 0,636 0,537 0,355 0,520 0,661

Z 6,860 6,817 6,426 6,888 5,321 3,177 5,088 7,371

Xem xt gi tr kim nh Z ti mc ngha 0,05 bin ng ca cc thng s thy ha

mng C1 v C2 u ng vi gi thuyt cht lng nc ph thuc vo cht lng ngun thi

vo thy vc. Nh vy, hu c l nguyn nhn gy suy gim nghim trng cht lng nc

mng nhn nc thi sinh hot v chn nui trong khi dinh dng ha tan nh hng mnh hn

n mng nhn nc thi canh tc.

3.2. nh gi nh hng ca ngun thi da trn ch s cht lng nc (WQI)

i vi cc h thng mng trong nghin cu ny, din bin theo thi gian quan trc v

gi trWQI c xc nh da trn tp hp cc thng s: DO, pH, Eh, BOD5, COD, N-NH4+, N-

NO3- v P-PO4

3- s dng chun c so snh l cc tiu chun cho php c ch ra trong bng 1.

WQI (%)

Mng C1

Mng C2

Mng C3

Hnh 2. Phn bgi trWQI ca c i tng nghin cu


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So snh thang tiu chun nh gi ca CCME WQI, cht lng nc ca ba i tng

nghin cu ch yu thuc v ba mc: trung bnh (III), xu (IV) v rt xu (V). Phn b gi tr

CCME WQI ca hu ht cc i tng nghin cu c dng phn b chun, gi trWQI mng

C1 tp trung trong khong 5060%; gi tr WQI mng C2 tp trung trong khong thp hn t

3040%; gi tr ca mng C3 tp trung trong khong 3545%.Nh vy, cht lng nc tt

nht mng C1, xu nht C2 v t trung bnh C3 nhng u nm mc rt xu n xu

th hin cho qu trnh nhim ttrung bnh n nng. iu ny ph hp vi nh gi cht lng

nc da trn cc thng sn l.

Tm li, kt qunh gi cht lng nc thng qua cc ch s ring l v kt qunh

phn mc cht lng nc v khi qut din bin cht lng nc da theo ch s c nhiu im

tng ng cho thy khnng s dng CCME WQI nh mt cn c c tnh khoa hc trong nh

gi cht lng nc. CCME WQI cho php chn lc mt tp hp cc thng s nht nh c th

ln n hng trm thng s, tuy nhin trong nghin cu ny chn ra 8 thng si din cho tnhtrng thy vc l knh mng nhn nc thi. c im thy vc nhn nc thi canh tc chu

nh hng mnh ca dinh dng N, P ha tan trong nc thi; lng dinh dng hu c v

nng oxy ha tan quyt nh cht lng nc h thng mng nhn nc thi sinh hot v

chn nui th hin qua cc thng s DO, BOD5 v COD. Cn c vo mc nh hng ca cc

thng s trong ngun thi n cht lng nc ba i tng nghin cu khc nhau, chng ti

xc lp ch s cht lng nc cho cc thng sdinh dng (WQI1) v ch s cht lng nc

cho cc thng s oxy v hu c (WQI2). Do tp hp cc thng su vo cho vic tnh ton ch

s WQI khc nhau nn cht lng kt qu ch s WQI ca cng mt i tng ti cng mt thi

im c mc chnh lch nht nh:

Bng 4: Kt qunh gi mc khc bit gia ba chsWQI

i tng Mng C1 Mng C2 Mng C3

Loi ch s WQI 1 WQI 2 WQI WQI 1 WQI 2 WQI WQI 1 WQI 2 WQI

Gi tr trung bnh 48,2 58,1 51,9 48,4 39,7 42,2 46,5 44,9 46,0

Phn b ccmc cht

lng theoWQI (%)

V 36,0 21,3 16,0 29,3 74,7 72,0 28,6 42,9 42,9

IV 60 45,3 77,3 70,7 22,7 28,0 71,4 57,1 57,1

III 4,0 30,7 6,7 0 2,7 0 0 0 0

II 0 2,7 0 0 0 0 0 0 0

H s tng quan R 0,92 0,39 1 0,63 0,69 1 0,66 04 1

Nu ch s rt gn (WQI 1 v WQI 2) ng tin cy nh gi cht lng nc knh

mng thy li, th phn mc cht lng nc i tng nghin cu phi gn ng nht vi ch

sWQI ban u. nh gi c mc ny, c th so snh kt qu ba ch s vi cc tiu

chun: Gi tr trung bnh, phn mc cht lng nc v mc tng quan gia ch s rt gn

v ch sban u. T kt qu so snh, d dng nhn thy i vi mng chu nh hng ca

nc thi t canh tc la, gi tr ch s rt gn WQI 1 cn c vo cc thng sdinh dng N, Pc thnh gi c cht lng nc ca thy vc c v din bin v phn mc cht lng.


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Trong khi , cc h thng knh mng nhn nc thi sinh hot (C2 v C3) gi trWQI 2 cn

c vo thng s hu c v oxy ha tan li c din bin gn st vi gi trWQI ban u.

Hnh 5: Phn bgi trWQI , WQI 1 vWQI 2 ca mng C1 v mng C2

Nh vy, trong nh gi cht lng nc thy vc ch nhn nc thi t hot ng canh

tc la c th s dng ch s cht lng nc CCME WQI da trn cc thng sdinh dng ha

tan N v P; i vi thy vc ch nhn nc thi t sinh hot v nc thi chn nui vi lu

lng ln, th ch s xy dng da trn cc thng sdinh dng hu c v oxy ha tan c th

phn nh tt trng thi ca thy vc.Ngc li, nhng thy vc nhn nc thi phc hp cn

c nh gi da trn ch scn c vo tt c cc thng si din cho tnh cht ngun thi

ny (bao gm cdinh dng hu c v v c).

4. KT LUN V XUT

Nc thi sinh hot v nc thi chn nui gy suy gim mnh cht lng nc h thngknh mng thy li chu tc ng, cht lng nc suy gim trn nhiu kha cnh: suygim oxy ha tan, gia tng cht hu c, giu dinh dng v c, thay i cc qu trnh ha

lsinh hc trong nc. i vi mng nhn nc thi t hot ng canh tc nng nghip,

cht lng nc ph thuc cht ch vo mc dinh dng v c trong ngun thi. Mng

thy li nhn nc thi sinh hot ph thuc lng hu c t dng vo. Cc h thng mng

thy li nhn ngun thi phc hp khng ch ph thuc vo ti lng thi m cn ph thuc

vo nhiu yu tkhc nh lng nc cp, mc s dng

nh gi cht lng nc cc h thng knh mng thy li da vo CCME WQI cho thyngun nc thi canh tc gy suy gim nh cht lng nc thy vc tip nhn trong khi

ngun nc thi sinh hot v nc thi chn nui cha x l gy suy gim nghim trng

cht lng nc h thng tip nhn. ng thi cho thy thy mt ch s nhim tng hp

khng nhng gip n gin ha kt qu quan trc cht lng nc m cn phn nh chnh

xc din bin ca thy vc di nh hng ca ngun thi.

i vi nhng thy vc ch tip nhn bit r vc tnh ngun thi, ta c thcn c voc tnh ny la chn mt nhm cc thng s nht nh khi m t cht lng nc bng

ch s CCME WQI nhm lm gim chi ph thc hin quan trc m vn m bo tnh khchquan ca nh gi.


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TI LIU THAM KHO

1. Chnh L, H thng chth v chsmi trng nh gi v so snh hin trngmi trng gia cc thnh phtrn lu vc sng, Science & Technology Development,

Enviroment &Resources, Tp 9, 2006

2. Hunh th Minh Hng, Nguyn Thanh Hng, Nguyn Vn Dng, Qun l thng nht vtng hp cc ngun thi gy nhim trn lu vc h thng sng ng Nai - Vin Mi

trng v Ti nguyn - HQG TP HCM, Cc Bo vmi trng, b TNMT - Tp ch

pht trin KHCN tp 9, Mi trng v Ti nguyn, 2006

3. Tn Tht Lng, Xy dng chscht lng nh gi v quan l cht lng nc hthng sng ng Nai - Trng cao ng ti nguyn v mi trng TP HCM, 2007

4. Canadian Water Quality Guidelines for the protection of Aquatic life - CCME WaterQuality Index 1.1 Technical Report, 2010

5. Canadian Water Quality Guidelines for the protection of Aquatic life - CCME WaterQuality Index 1.1 User's Manual, 2010

SUMMARY: Studying possibility to use the water quality index (CCMEWQI ) i n assessing

the impact of emission sources to the system of i rr igation canals

The status of water quality of irrigation canal systems typical of waste: farm-wastewater,

domestic wastewater and animal-wastewater is monitored with physical and chemical

parameters: DO, pH, Eh, BOD5, COD, N-NH4+

, N-NO3-

and P-PO43-

. The water quality of theirrigation system is being affected by nutrients and organic matter from different sources. Water

quality of irrigation system heavily dependent on the type of waste and waste load into the

canals. Domestic wastewater and animal husbandry are the direct cause leading to the degree of

organic contamination in serious subjects. CCME WQI index is suitable for general assessment

of water quality to reduce the implementation costs of monitoring and ensuring the objectivity of

the evaluation.

Documents

Sử dụng chỉ số chất lượng nước CCME WQI đánh giá nước thuỷ lợi