HE CA

HQI NGHI KHOA HQC TOAN Q U Q C V £ SINH THAI VA TAI NGUY£N SINH VAT LAN THLf BA

THANH PHAN KHU HE CA VUNG T m / O N G LUtJ VA TRUNG LUXJ

SONG DONG NAI DUOI TAC DONG CUA CAC CONG TRINH THUY DIEN NGUYEN KIEM SON Vien Sinh thdi vd Tdi nguyen sinh vgt Song Ddng Nai cd tiem nang rit Idn vl thiiy dien vdi 8 bac thang tren luu vyc thupc cac tinh Lam Dong, Dak Ndng v i Dik Lii. Miia mua keo dai tir thing 5 din thing 10, luu lugng nude chilm tdi 80-90%, trong miia khd, luu lugng ddng chay rit nhd. Trong khudn khd nghien cim hien trang dieu kien ty nhien va dinh gii tic dgng mdi tmdng trudc khi xay dyng cic dap thuy dien Ddng Nai 3, 4, 5 va dy bio bien ddi sau khi xiy dyng xong cac cdng trinh thuy dien tren den ngudn Igi thuy sinh vat vi c i trong sdng Ddng Nai ciing nhu gdp phin bao ve sy nguyen ven Vudn Qudc gia (VQG) Cit Tien.

I. PHUONG PHAP NGHIEN CUtJ

Chiing tdi da tiln hinh 5 chuyen khio sit: dgt thing 9/2001, dgt thing 7/2004, dgt thing 7/2005, dgt thing 7 - thing 8/2007 va dgt thing 8/2008 d cic suoi, hi, dim vi cac chg tir thanh pho Da Lat den cic huyen, cac xa dgc hai ben bd sdng Ddng Nai noi cd cac cong trinh thuy dien Dong Nai 3, 4, 5 vi cic thuy vyc nim trong pham vi VQG Cat Tien. Trong cic dgt khio sat, dieu tra vi phdng van dan tu tren thugng luu sdng Ddng Nai den VQG Cat Tien, da thu thap va sir dung cic tu lieu ve thinh phan loai c i da cdng bd hoac chua cdng bd tir 1997 den nay ciia cic CO quan vi tic gia nhu Vien Sinh hgc nhiet ddi (1999), H.D.Dat, T.N.Tri (2001), H.D.Dat (2001), H.D.Dat, N.M.D. Linh (2001), Vien Mdi trudng va Phit triln bin vumg (2004), P.H.Khanh (2005). Chup anh cic mau ci, cac loai thiiy sinh vat chinh vi canh quan luu vyc nghien ciru. Diing GPS xic djnh vi tri thu miu tai cic diem nghien curu. Ngoai ra, cdn phdng van ngudi dan dinh ci d nhtrng dia diem tren de hieu them ve thanh phan loai ca qua cic anh mau da cd sin, cung nhu tim hieu inh hudng ciia qui trinh xay dung dap thuy dien Dong Nai 3, Dong Nai 4, Dong Nai 5 len ddi sdng dan cu viing ha du sdng.

II. KET QUA NGHIEN CUU

1. Thanh phan ca tir thugng nguon den VQG Cat Tien

Sau khi tiln hinh thu thip, khio sat, nghien cim 17 viing tir thugng ngudn xudng din VQG Cat Tien thiy rang sudi, ao viing Di Lat vi hd Tuyen Lim cd 55 loai ci thupc 16 hg, 6 bg.

Trong dd, 32 loii dang dugc dimg lim thyc pham. Rien^ trong ho Tuyen Lam cd 37 loii, sudi Datania cd 19 loii vi sudi Nam Qua cd 6 loii. Nhilu sudi can, nhd, khdng cd ci hay chi cd loai ca Khong tudc va ci An mudi. Khu he c i sudi, ci sdng Dong Nai va ca nuoi d cic hd ao thugc luu vyc cic dap thuy dien Dong Nai 3, 4, 5 vi VQG Cit Tien con phong phu, nhung cic loii ci thupc bg ci Trich hau nhu khdng thiy xuit hien, sau khi dip thuy dien Tri An di vao hoat ddng.

Qua phong vin dan dinh c i dia phuang dya tren inh miu cic loai ci vi tharn khao cic ket qua khao sat trudc diy cua cic nhi nghien ciiai, cung nhu kit qua khao sit tryc tiep cho thay khu he ca d day cd 207 loii thugc 34 hg, 12 bd (bang 1). Trong dd chi cd 9 loai cd frong Sach Dd Viet Nam, 2 loii cd trong CITES vi 1 loii die him.

Cad trong VQG Cit Tien vi phu can rit da dangvi cung song trong nh^lu sinh canh, dieu ki?n song khic nhau: c i ua nude chiy manh, c i cd thi sdng d ci nude chiy lan nude tTnh, ci ua tinh hay nude chiy nhe. Theo dinh dudng, cd thi chia ra cic nhdm ci dir, ca iri miin ba him co va tao, ci in tap. Nhilu loii ci thich nghi vdi dilu kien thilu dxy trong dim liy vdi nhieu ciy thuy sinh ram rap. Mgt so loai ci cd the nudi frong bl ci cinh, rit dep nhu ci Man {Scleropages formosus ) , ci Ning hai hay ci Cdm (Chitala omata), ck May {Gyrinocheilus aymonien,

Gyrinocheiluspennocki), ck Sic budm {{Trichogaster trichoptems).

HQI NGH! KHOA HOC TOAN Q U O C V £ SINH THAI V A TAI N G U Y £ N SINH VAT l^N THLf BA Bdng 1

B$, b9 1

Thanh phan loai

2 3 , 4 5

ca d ddng sdng Dong Nai va vung phu can

So loai

6 1 7 8 9 10 11 I. BO ca Chinh Anguillifonnes 1. Ho ca Chinh

Anguillidae

11. Bp ca Mem Osteoglossiformes 2. Ho caMcm

Osteoglossidae 3. H o c a That lat

Notopteridae

1

12 13 14 15 16

1? 1?

1 1

III. Eg ca Nhai Beloniformes 4. Ho ca Soc

Adrianichthyidae 5. Hp caNhai

Belonidae 6. Ho ca L'un kim Hemiramphidae

1

1 1

1 1

IV. Bo ca Trich Clupeiformes 7. Ho c4 Trich

Clupeidae 8. Hoca Trong

Engraulidae

3? 4?

1?

1 2

I 17

1

1 3

1 2 3

2?

1?

V. Bo ca Characiformes 9. Ho ca

Characidae

1 1 1 1 1

VI. Bo ca Chep Cvpriniformes 10. Hoca Chep

Cyprinidae 11. Ho ca Bam da BaUtoridae 12. Ho ca Chach

Cobitidae 13. Ho ca May Gyrinocheilidae

14

1 16

2 11 2

3

1 32

1 1 1

17

1 2

1 8

1

9 11

2 37

2 2

8 24 37 1 2

21

2 50

1 3 1

85 5 9 2 VII. Bo ca S6c Cyprinodontiformes

14. Hoca Bit muoi Poeciliidae

4 4 2 1

VIII. Bp ca Nheo Siluriformes 15. Hp Akysidae

16. Ho ca LJng Bagridae 17. Hp caTre

Clariidae 18. Hp caTra

Pangassidae 19. HpcaTra nho Schilbeidae

20. Ho ca Nheo 4 2

1 1

1 2

1 4

3 2

1

2 2 3

2 1 1

2 1

1 1

3 2

1 2

1

1 5 2 1 1 4

3 2 1

1 8 2 1

6 13

2

2 1 10

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Silundae 21. Hoca Chien

Sisoridae

1 3 2 1 3 3 5

IX. Bp ca Vupc Perciformes SHjdSciincc

ngCt

QatMc 23. Ho ca Ro Anabantidae 24. HQ ca Chuoi,

caLoc Channidae 25. Hp ca Ro phi

Cichlidae 26. Hp ca B6ng den Eleotridae 27. Hp ca Bong irjng Gobiidae 28.HociMui Helostomatidae

29. Hp ca Ro bienNandidae ]O.HpcaTaitu?ig Osphronemidae,

Belontidae 1 4

3 1

1 5

2

3 1

2 1 3

1 4

3 2 1

2 1 2

1 1 1

2

1 2

3 2

1

3 1

1

I 3

2

2 1 3

3

1

1 2

1 1

1

1

2 1 3

1 1 1

1 4

1

1 6

1

1 4

1 1 1 1 7

X. Bp ca Mang lien Synbranchiformes 31,HpcaChach

song Mastacembelidae

32. Hp Lucm Synbranchidae

1 1

1

2

1 1 1 1

XI. Bp ca Ngva xucmg Syn B.HjcaNaa'iiiig

SynRnathidae

1 1

1 1 1

2

1 1 4

1 5

1

[»nathiformes j

1

XII. Bp ca Npc Tetrapdontiformes | 34. Hp ca Noc

Telraodontidae

Tong 32 37 19 6 53 42 10 18 29 29 56 27

1

34 69 40 100

1

171 Ghi chu: 1-32 loai ca nude ngot bdn d cha Da Lat; 2-Hd Tuyen Lam (37 loai); 3-Su6i Datania (19 loai); 4- Suoi Nam Qua (6 loai), 5-53 loai thugc khu vuc thuy dien Dong Nai 3; 6-42 loai (7/2004 co 28 loai va 1/2008 co 29 loai) d vimg thi tran Gia NghTa; 7-10 loai d suoi thuoc Da Lat; 8-18 loai a vimg Di Linh; 9-29 loai (16 loai vao thing 7 nim 2004 va 24 loai vao thing 1/2008) d viing Bao Lam; 10-29 loai d viing Gia NghTa thugc Dong Nai 4; 11-56 loai viing suoi Dik Plao thuoc Dong Nai 3;12-27 loai d Dak Rlap; 13-34 loai d chan dap Dong Nai 5;14- 69 loai ca d Nam Cat Tien (VQG Cat Tien), nam 2003;15-40 loai ca d Bau Sau, nam 2000-2005; 16-100 loai ca d Cat Lgc, nam 1997-1998; 17-171 loai ca d toan bo cac thuy virc thugc VQG Cat Tien.

2. Hifn trang nudi trong thuy san va khai thac thuy san d luu vyc cac ho thuy difn Dong Nai 3,4,5 va Vudn Quoc gia Cat Tien

Danh bit ca d suoi Dik Plao vi sdng Ddng Nai thudc luu vuc ho thuy dign Dong Nai 3 , 4. 5 chii ylu bing ludi, chai, ciu va dinh sa tir cudi miia mua den hit miia khd, thudng khai thic chinh vu tir thing 11 nam frudc din thing 3 nim sau. Bdn - nim hd chuyen danh bit ci tren Uiiic song nay, vao thdi dilm 1999 vl frudc, hai ngudi tren mgt thuyin (ghe) khai thic mgt dem

<lat tir 20kg den 100kg, frung binh 30-40kg ci. Cic loii khai thic chinh la cic loai ci thugc bg caChep va bd ca Nheo nhu ci Me, ci Me vinh, ci Ngua, ca Liii, ci Chien. LTdc tinh cd khoang

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30-50 tin ca dugc khai thic hing nim (H.D.Dat va T.N.Tri, 2001). Phia ha luu sdng Ddng Nai, cd hang tram ngudi danh bit ca tu nhien, mac dii khdng xac dinh dugc cu the, nhung udc tinh hang nam khai thac hang trim tin ci, cung cip cho dan dja phuang va cac thanh phd Idn quanh viing nhu thanh phd Hd Chi Minh va Bien Hda, Da Lat. Do ngudi dan khdng y thuc dugc viec bao ve ngudn lai thuy san trong do ci la chii yeu, da diing chat nd, kich dien de danh bit huy diet, gay tdn that vl ngudn Igi, vi thi sin lugng ca ngay cang giam sut. Tren cic chg Gia Nghia (Dik Ndng), Di Linh (Lam Ddng) cic chau ban c i dam, c i sudi, ca sdng Ddng Nai chi cd tir 0,5kg din 2kg vao nhieu thdi dilm thing 7/2004, dgt thing 7/2005, dot thing 7 - thing 8/2007 vi dgt thing 8/2008. Cic loai ci chinh Ii ci Qua, ca Ldc, ca Rd, c i Diec, c i Tre tring, ci Tre vang, ci Me vinh, ci That lit, ci Sic budm, c i Ldng tong vach, ca Tring, ca Dam, ci Bdng tring nhd, ci Sdc, Luan, ca Chach bim.

n i u nhu tit ca cic loai c i tren sdng Ddng Nai vi cic thuy vuc thudc VQG Cat Tien va vimg phu can diu diing lam thyc pham. Trong sd niy, cd tdi 45 loii cd gia tri kinh te ddi vdi dja phuang. Bii lai sin lugng thuy sin bj giim ngoai ty nhien thi dien tich mat nude nhu ao, dam, ho nudi trdng thuy sin vdi 16 loii ca nudi kinh te thudc luu vyc hd thuy dien Ddng Nai 3 - Ddng Nai 4, D dng Nai 5 ting len, hien co khoing 4.000ha. Sin lugng thuy sin danh bit nim nhilu nhit dat khoang 187 tin, trong khi dd sin lugng nudi trdng thuy san dat 1.731 tin. Khiic sdng Ddng Nai gin thj tran Ddng Nai cdn cd hing chuc ngudi nudi c i Idng tren sdng ket hgp vdi danh bat ca ty nhien. Cic loii ci nudi chu yeu la ca Trim cd, ca Bdng tugng, ci Dieu hdng.

3. Danh gia anh hudng ciia cac cdng trinh thuy difn len nguon Igi ca va nguon nude Do viing cd dja hinh thuan lgi de xay dyng cac hd chira, lai cd ngudn nude mua khi Idn (I.600mm/nam-5.190 mm/nam), nen khu vyc thudc luu vyc sdng La Ngi - Ddng Nai tir tren thugng ngudn da xay dyng dap thuy dien Da Nhim, thuy dien Dai Ninh, thuy dien Da Mi - Ham Thuan, xudng den hd thuy dien Tri An. Hien nay, dang cd dy kien xay dyng them 8 hd thuy dien tren 8 bac thang dia hinh cd ten ggi nhu Ddng Nai 2, 3, 4, 5, 6, 7. Chinh vi thi viec xky dyng va van hanh hd thuy dien Ddng Nai 3, Ddng Nai 4, Ddng Nai 5 phu thudc nhilu vao chi do thuy vin vkykn hanh ciia cic bic thang thuy dien tren thugng ngudn. Mat khic, cung can luu y den nhu cau bao ve ngudn nude nggt cho dai bd phan dan cu thanh thi ddng due d dudi ha luu nhu Tp. Hd Chi Minh vi Bien Hoa, ma theo nhu Le Trinh (1998) dy kien phai bio ve ngudn nude loai A tren sdng Ddng Nai tir cau Long Binh len thugng ngudn: sdng Cii qua KCN Bien Hoa I, Tp. Bien Hoi, hd Tri An vi cic chi luu d Lam Ddng, Dak Lik. Mgt vin dl nira cin luu tam den la bio ve che dg thuy van va tpin vgn cua VQG Cat Tien ben dudi hd thuy dien Dong Nai 5, hien dang nghien cuu khio sit de xay dyng.

Hd thuy dien Ddng Nai 3 (5.600ha), dung tich toan bd chi cd 124.lOW va dung tich him ich Ii 37.10 V , luu lugng chay qua 223,7 mVs (N.N.Duy, N.X. Hda, 2003).) vi cac hd Ddng Nai 4 (400 ha) va Dong Nai 5 (828 ha), nlu hoat dgng deu dan, se lam cho khi hau vung nay them dju mat vio miia khd. Mat khac, viec cd cic hd thuy dien Da Nhim, Dai Ninh, Thic Ma, Trj An vi hd Dau Tieng, se anh hudng den dudng ding man 4%o d phia ha luu vao mua khd. Cin luu tam duy tri ddng chiy mdi trudng khoang 10% luu lugng ddng chiy miia khd tir sau dip Ddng Nai 3 de tranh bi khd can mgt khue sdng sau dap. Hd thuy dien Ddng Nai 3, Ddng Nai 4, Ddng Nai 5 hinh thanh se lam cho he sinh thai thuy vyc viing niy thay ddi cin bin. Trong vai nim diu do lugng mim ba him ca ting manh nen sinh vat ndi se phat triln manh, keo theo do la cic loai ca ndi va ci an mim ba him ca se phit trien nhanh. Cac loii sinh vat diy se kem phat triln do nude sau va lugng bdi ling xudng diy lam hdng n i n d i y cu, tao Idp phu mdi. Cac loai ci di cu, ua de d viing cd nude chay, nen d i sdi se phii chuyen len thugng nguon cic chi luu hoic se giim sd lugng. Nhung do dip dap thuy di?n, nhilu khue sdng bj chin lai theo cic bac thang thuy dien, nen cac loai c i di cu ndi sdng se khd vugt qua dap chin vi se bi mit din.

^ Dap thuy dien Ddng Nai 5 nim cich dap thuy dien Ddng Nai 4 (dang thi cdng) khoang 50km ve phia ha luu. Mac dii ca hai dap thuy dien Ddng jslai 3 va Dong Nai 4 dang xiy dyng, nhung

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theo dan dia phuang (xa Dak Nia) cho biet, chua thay cd anh hudng gi din sin xuit va nude tirdi, nude sinh hoat ciia dan vi dan d day xay nhieu dap cd nhd dl liy nude tudi cho cay ca phe va cay hat tieu, cdn nude sir dung cho sinh hoat thi diing nude gilng khoan. Do cd dudng vio song, nen lugng c i dinh bit dugc cung kha cao, khdng thua kem so vdi thugng ngudn dap thuy dien Ddng Nai 3 va thuy dien Ddng Nai 4 trudc day. Hd thuy dien Dong Nai 5 cd dien tich khoang 828ha mat nude, do do ddc hai ben bd sdng Idn, nen chilu rdng long hi chi khoing 500m, chieu dai hd ke tir chin dap_Ien thugng ngudn khoang 17-18 km. Ngudn nude cung cip chinh cho thuy dien Ddng Nai 5 van lanudc tir thuy dien Ddng Nai 3 vi Dong Nai 4 dilu tiet hoat ddng phit dien chay xudng. Vi the, luu lugng 213,1 mVs tir Ddng Nai 3 vi luu lugng bd sung tir pham vi luu vyc 5,17 m /s tir Dong Nai 4, chinh Ii luu lugng ddng chay ddi vdi ho thuy dien Dong__Nai 5 (218, 27 m^/s ). Do Dong Nai 5 nim q u i ^ i n VQG Cit Tien, nen ci tu VQG Cat Tien van thudng xuyen di len thugng ngudn luu vyc kiem in d viing cd nhilu di gap ghlnh vai rong reu bim diy vi nhu ci Mdm triu {B. behri). Chinh vi the, khi xay dyng dip thuy dien Dong Nai 5 nen nghT den thiet ke dudng ci vugt dap len tren long hd de bio v? ngudn Igi thuy sinh vat ndi chung vi ci ndi rieng. Tuy nhien, viec thiet ke dudng cho ci di cu vugt dap thuy dien chua bao gid dugc xiy dyng d Viet Nam.

Nhu vay, sau khi hoin thanh xay dyng hd thuy difn Ddng Nai 3, 4, 5 se tao ra he sinh thii ho chira nhin tao vdi ba yeu td chinh: (1) Hinh thii ciia ho dang sdng vdi hai bd doc cd do die Idn

15-25° d gan chin dip. Luu lugngnudc chiy se hoan toan phu thudc vio che do boat ddng ciia cac td miy thuy dien theo thiet ke 213,1 m Is; (2) Chat lugng nude d mirc tmng binh hay phi dudng, cd the bi anh hudng bdj cac chit thai tir cic khu din cu do thi vi chit bio ve thuc vat troi xudng hd tir vigc phun thudc chdng sau benh cho khu trdng rau, hoa, cay ci phe vi cay hd tieu. Sy bdi ling ting len d thuy dien Ddng Nai 5 cdn do chat thii tir khu khai thic bd xit nhom c viing Nhin Co; (3) Hoat ddng khai thic ca, nudi c i ldng be vi giao thdng van tii dudng thiiy phat trien cic khu cdng nghi?p mdi, khu do thi mdi, hoat dgng che bien ci phe khi thu hoach qua chin, lim ting khi ning nhiem ban ngudn nudc.De sau niy de khai thic ci trong hd Dong Nai 3, 4, 5 can dgn sach ciy cdi trong viing Idng hd. Mat khac ciing giim thieu cic cay rimg thoi rira giy d nhiem ngudn nude trong thdi gian dau ngin sdng. Xay dyng thuy dien Ddng Nai 5, each ranh gidi VQG Cat Tien khoing 1,5km, chac chin inh hudng manh den ngudn nude d cac Biu (vi dy Bau Siu) trong VQG Cit Tien vi ngudn Igi ci se giim theo.

in. KET LUAN

Khu he ca trong ddng sdng Ddng Nai tir thugng nguon den VQG Cit Tien vdi h? thdng sdng suoi va cic biu nude da dang, phong phu, mgt viing dit ngap nude theo miia rgng Idn nen rit nhilu cinh quan dep dugc phan chia theo timg sinh cinh khic nhau vdi cic die trung phanbd loai khic nhau. Khu h? ci d day cd tdi 207 loai thugc 34 hg, 12 bg, trong dded 9 loai ci nim trong Sich Dd Vi?t Nam, rat die trung cho viing dit ngap nude d Ddng Nam A vi the gidi. Tuy nhien, da bj mat di cic loii ca di cu thugc bd ci Trich vi ci Chinh. Bii lai, cd tdi 16 loii ci dang nuoi trong cic ao, hd, ldng be.

Can bio ve nguyen ven VQG Cit Tien khi thiet kl xiy dyng cic cdng trinh thuy dien vi khai thac khoing sin phia thugng luu.

Can duy tri ddng chiy mdi tmdng sau cic dap thuy dien khoang 10% luu luang nude lien tuc hang ngiy trong miia khd dl trinh lam ddng sdng khd can sau dip thuy dien Dong Nai 3.

TAI LifU THAM KHAO

1. Nguyen Nggc Duy, Nguyen Xuan Hoa, 2003: Cdng trinh thuy dien Dong Nai 3 tren song Ddng Nai. Bio cio nghien cim kha thi (hieu chinh-Ian 2). Tip I. Thuyet minh. 78 trang.

2. Nguyen Nggc Duy, Nguyen Xuan Hoa, 2003: Cdng trinh thuy dien Dong_Nai 4 tren song Ddng Nai. Bio cao nghien curu khi thi (hi?u chinh Ian 2. Tip 1. Thuyet minh. 69 trang.

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3. Hoang Due Dat, Thai Nggc Tri, 2001: Khao sat ngu loai va tmh hmh nghe ca d sdng Ddng Nai tren doan thudc vimg qui hoach xay dyng thuy dien Ddng Nai 3 va Ddng Nai 4.

Tuyen tap cdng frinh nghien cuu khoa hgc cdng nghe (1999-2000). Nxb. Khoa hgc va Kp thuat. Hi Ngi, fr.: 377-380.

4. Hoang Dire Dat, 2001. Ve thanh phin cac loii c i d Bau Siu Vudn Quoc gia Cat Tien.

TuyIn tip cdng frinh nghien curu khoa hgc cdng nghe (1999-2000). Nxb. Khoa hgc va Ky thuat. Hi Ngi, fr.: 375-376.

5. Hoang Dixc Dat, Nguyen Manh Duy Linh, 2001: Khao sit sa bd cac loii ca cic thuy vyc thudc khu bio tdn thien nhien Cit Lgc, huyen Cit Tien, tmh Lam Ddng. Tuyen tap cdng frinh nghien cim khoa hgc cdng nghe (1999-2000). Nxb. Khoa hgc vi Ky thuat. H i Ndi, fr.: 384- 389.

6. Hoang Due Dat, Thai Nggc Tri, 2001. Danh luc ve cac loai ca nude nggt thudc cac viing nghien cuu. Tuyen tip cdng trinh nghien curu khoa hgc cdng nghg (1999-2000).

Nxb. Khoa hgc vi Ky thuat, Ha Ngi, fr.: 396-405.

7. Pham Hihi Khanh, 2005: Nghien cuu quin ly, bao tdn va sir dung bin vimg he sinh thai dit ngap nude Vudn Qudc gia Cit Tien. Luan vin Thac sy khoa hgc Lam nghigp. Ha Tay, 144 trang.

8. Huynh Nhung, 1998: Dinh gii hien trang su dyng dat phuc vu cho viec xiy dyng cdng trinh thuy dien Ddng Nai 6. Tuyen tap cic cdng trinh nghien cuu dia ly. Nxb. Khoa hgc v i Ky thuat. H i Ngi, tr.: 410 - 419.

9. Le Trinh, 1998: O nhiem ngudn nude vi de xuat phan vung chat lugng nude cic sdng chinh luu vyc Ddng Nai- Sai Gdn. Tuyen tap cic bio cao khoa hgc tai hdi nghj mdi trudng toan qudc nam 1998. >Jxb. Khoa hgc v i Ky thuat. H i Ndi, tr.: 447-460.

F I S H S P E C I E S C O M P O S I T I O N IN U P S T R E A M AND M I D - S T R E A M S E C T I O N S O F D O N G N A I R I V E R U N D E R I N F L U E N C E

O F H Y D R O P O W E R D A M S

NGUYEN KIEM SON SUMMARY

Dong Nai River has hydropower potential with 8 hydropower stations on the fributaries and mainstream. Based on projects such as the Environment Impact Assessment (EIA) of hydropower stations Dong Nai 3, 4, 5 that aim to conserve the Cat Tien National Park, 207 species of fish belonging to 34 families, 12 orders are recorded. Among them, 9 species are listed in the Red Book of Vietnam. Some species from order Clupeiformes and Anguilliformes can not migrate up pass the hydropower dam. These species may disappear from these areas. 16 fish species are growing in aquacultural ponds and floating cages. Regulation of the flowing current by activities of the hydropower stations Dong Nai 3, 4, 5 may impact the environment and change water levels of Bau Sau and other water pools in the Cat Tien National Park and may cause drying of some down-river's parts of hydropower dam Dong Nai 3. There is a need to keep environmental flows about 10% of total flowing discharge every day in the dry season.