Tiiu ban: Khoa hgc cong nghe Bien ISBN: 978-604-913-015-1
Sir SUY THOAI HE SINH THAI CO BIEN VEN BO VIET NAM THE REGRESSION OF SEAGRASS BEDS AT THE
COASTAL WATERS OF VIET NAM
Nguyen Thi Thu, Nguyen Van Tien, Chu The Cudng, Cao Van Luo-ng va nnk Vien Tai Nguyen va Mdi trudng Bien, Sd 246 phd Da Ning, Hai Phdng
Email: [email protected] Tdm tat:
Su suy thodi nghiem trong hi sinh thdi thdm cd biin dugc nhdn thdy ro ret qua su suy gidm diin tich phdn bd vd do phii cdc thdm cd so vai 10 -15 ndm trirac ddy. Mirc do suy thodi diin tich vd do phii thdm cd biin khdc nhau a mdi khu vuc.
Chimg phu thudc vdo mirc do tdc ddng tir mdi truang tu nhiin, cdc hogt ddng kinh ti xd hdi vd y thirc bao vi chimg tgi mdi dia phuang. Nhin chung diin tich vd do phii cdc thdm cd ven ba da bi suy gidm trung binh khodng 50%. Mdt sd nai da bi mdt hodn todn nhu mdt sd viing bdi triiu Qudng Ninh, Hdi Phdng, Kiin Giang.
Vimg triiu Cira Dgi (Qudng Nam) diin tich thdm cd biin ndm 2009 da suy gidm han 70% so vai trirac ddy 15 ndm. Mat khdc sir suy thodi cimg thi hiin thdng qua cdc sd lieu vi ngudn lgi sinh vdt ddc trirng tren cdc thdm cd biin. Dd Id sir suy gidm tdi hdng chuc, hdng trdm ldn ngudn lgi cd ngua tgi thdm cd Phu Qude, ngudn gidng cd Dia, cd Hdng tgi thdm cd ddm phd Tam Giang - Cdu Hai.
Abstract:
The regression on the distribution areas and cover percentage of seagrass beds is very strong in comparing to 10 -15 years ago. The regress levels that depend on the impacts from the natural progress and the economical activities and the conservation awareness lo them is different at every coastal areas. In general speaking, the distribution areas and cover percentage of seagrass beds is decreased above 50%. In some distributed areas as Quangninh, Haiphong coastal tidal flats seagrass seem be loosen nearly complete. The distribution areas of seagrass beds that measured in 2009 at Cua Dai river mouth (Quangnam Province) is decreased about 70%o when comparing to its 1995. On the others hand, the regress of seagrass beds was also reflected in the decreasing about ten times since of some typical living resources such as: seahorse in Phuquoc, Siganus, Lutjianus, Lethrinus fishs in Tam Giang - Cau Hai and Cua Dai
Md dau
Cd bien (seagrass) la nhdm thue vat bac cao ed hoa sdng ngap chim dudi bien. Cac tham cd bien khdng nhiing la mot dang ngudn lgi bien ma cdn la mot he sinh thai (HST).
Tham cd bien la nai sdng quan trong de duy tri sir sdng d bien, dac biet la viing bien ven bd nhiet ddi. Gia trj ciia cd bien toan thi gidi udc tinh khoang 3, 8 nghin ti (trillion) USD (Costansa, 1997). 6 viing Biin Ddng gia tri 1 ha cd biin khoang 212.000 USD (UNEP, 2004).
Nude ta cd bd bien dai hon 3000 km vdi cac viing nude trieu cira sdng, viing nude ven bd trong cac thuy vuc dac biet nhu he dim pha Mien Trung la nai tap trung phan b l ciia rit nhilu loai cd biin. Chung tao thanh nhirng bai cd bien rdng ldn tir Quang Ninh tdi Kien Giang. Nhung nghien cim diu tien vl he sinh thai cd bien trong khudn khd cac de tai cip bd,
cap nha nude dugc tiln hanh do Vien Tai nguyen va Mdi trudng bien, Vien Hai duong hoc Nha trang tir nam 1986 din nay cho thay he sinh thai cd bien dat den gia trj cao nhat ciia nd nhd cac chiic nang sinh thai. Cd the thay sir phan bd va phat trien ciia cae bai cd bien gan lien vdi sir phan bd va phat trien ciia hau het cac loai ngudn lgi hai dac san cd gia trj kinh te cao trong cac viing nude ven bd va bien dao. Dd la cac loai thiiy hai san qui hiem nhu tdm he, ca ngua, ca dia, ca mii tao nen ngudn thu nhap va sinh cu tdt cho cdng ddng ven bien Viet Nam
Tuy nhien trong nhirng nam gan day ap lire tir nhiing thay ddi ve mdi trudng, khi hau va cac sir phat trien cac boat ddng kinh te bien nen he sinh thai (HST) tham cd bien kha manh me. Chiing dang bj suy thoai nghiem trong. Vi the de tai KC 09.26/06.10 do Vien Tai Nguyen va Mdi trudng bien de xuat da dugc phe duyet va thue hien tir 2009-2010. Trong dd mirc do suy thoai HST tham cd bien ven bd va nguyen nhan gay ra nd da dugc danh gia nham cd dugc cac giai phap, ke hoach quan li, bao ve, phuc hdi cac tham cd va bao tdn ngudn lgi sinh vat ven bd.
1. Bien dong thanh phan loai cd bien
Tdng sd loai cd bien Viet Nam 14 loai, trong dd thanh phan loai cd bien viing nude phia bac gdm 9 loai khdng da dang nhu d cac viing nude phia nam (14 loai) va tdng sd loai.
Sir da dang ban d cac viing nude phia nam chu yeu tao nen do cac loai chi phan bd d cac viing ven cac dao xa bd. Sir da dang loai cao theo xu hudng tang dan tir vimg can nhiet ddi phia bac tdi viing nhiet ddi phia nam [7]
Ket qua khao sat kiem tra nam 2009-2010 tai cac tham cd bien viing trieu Cira Dai (Quang Nam) va dam pha Tam Giang - Cau Hai (Thira Thien Hue) cho thay chua cd sir suy giam hay mat di ciia loai cd bien nao. Dac biet luu y khi van thay sir phan bd kha rdng rai ciia loai cd xoan Halophila becarii d cac viing trieu Cira Dai, viing trieu Tam Giang - Cau Hai, trong khi nd dang bj suy giam rat nhanh d cac nude Ddng Nam A
2. Suy giam dien tich phan bd va do phii cac tham cd bien
Chi do thuy trieu bien ddi theo cac vT do sudt doc viing trieu ven bd tao nen nhieu sinh canh, khu vuc phan bd cd bien cd do ngap nude va dja hinh tram tich khac nhau. Cac vuc nude cd do mudi bien ddi tir nude Ig, Ig man d ven bd tdi nude man ven cac dao, cac bai trieu biin cat, cat bun ven sdng, trong cac dam pha, hoac cat bim mjn ven cac dao ciing vdi khdi nude cd do trong cao va kha cao tir Quang Ninh tdi Nghe An, Quang Binh, Hue. Quang Nam, Binh Thuan, Khanh Hoa va Kien Giang deu phii hgp vdi sir phan bd va phat trien ciia cac loai khac nhau tao nen tham cd bien [6]. Tir nhiing nghien ciin dau tien ve cd bien d Viet Nam dugc tiln hanh tir nam 1995 den nghien ciiu trong 2006, dien tich cac tham cd bien dugc xac djnh tdi ban 17000 ha [8]
cac khao sat kilm tra nam 2009-2010 trong khudn khd dl tai KC 09.26/06.10 chii ylu tap trung vao cac bai cd cd dien tich ldn, do phii va da dang bai cd cao va ddng thdi ciing la noi chju nhieu tac ddng tir cac yeu td bien ddi tir mdi trudng tu nhien ciing nhu cac boat ddng phat trien kinh te xa hdi ven bd nhu viing trieu Quang Ninh, Quang Binh, Quang Nam va dam pha Tam Giang - Cau Hai (Thira Thien Hue).
Ket hgp cae nghien cim trudc day vdi ket qua tinh toan sa bd tir khao sat kiem tra 2009 -2010 dugc sir bien ddng dien tich va do phii tai mot sd tham cd ven bd trinh bay trong bang 1. Cac khao sat tir trudc nam 2000 cho thiy cac bai cd phan b l d khip viing trilu cira sdng Tien Yen - Ha Cdi. Cac tham cd dien tdi hon 300 ha vdi do phu trung binh tdi 30-70%
ciia loai cd he Zoster a japonica.Vixng nude ven bd Hai Phdng gIm bai trilu cira Lach Huyen da timg cd bai cd rdng 100 ha. Tham cd trong he dim pha Thira Thien Hul bao phii tren dien
Tiiu ban: Khoa hgc cong nghe Bien ISBN: 978-604-913-015-1
tich hang nghin ha.v.v... Sau khoang 10 nam, cac khao sat kilm tra tai mdt sd khu vuc thay hiu hit cac bai cd bien viing ven bd (^uang Ninh bj viii lap bdi trim tich, cac tham cd viing trieu cira sdng Hai Phdng da bj san lap thanh cac khu vuc ciu cang, khu dd thi, khu cdng nghiep, bin pha, da gin nhu khdng cdn thay cac bai cd. Khu vuc viing trilu Cira Gianh, Cua Nhat Le (Quang Binh) dien tich cac bai cd giam hon 50% do hiu hit dien tich viing trieu hai ben cira sdng Nhat Le da bj quay thanh dam nudi. Hon 100 ha cd bien khu vuc Cau Thanh Ba da bj bao ke da quay thanh au thuyen va cd bien dang bj tan pha vi neo tau va d nhiem dau.
Tai dim pha Tam Giang - Ciu Hai dien tich cd bien theo Nguyen Van Tien tang tir 1000 ha nam 2000 tdi 1800 ha nam 2006 do phat hien them mot sd bai cd mdi. Den nay sau khi so bd tinh dien tich cac khu san lip cho xay dung cac cau cang, khu dd thj va cac dam nudi tren cac cdn, dien tich cd biin udc cdn khoang 1000 ha. Khao sat nam 2009-2010 tinh toan dugc cac bai cd cd dien tich phan bd ldn, nhd khac nhau nhu Cdn Te, Con DTnh, Cdn Dai, Con Ndi, Cin Hgp Chau, Ba Cdn v.v. diu bj suy giam ve dien tich phan bd va do phii do cac dam nudi mdi dip theo dang ke da (Cdn DTnh), bj xdi Id (Cdn Sao), cac bai san lap lam cang ca d Phu Thuan, Phii Hai va cac ldp dang sao day dac tao ldp biin phu tren be mat cd. Do phii trong nhiing khu vuc nay cdn rat kem cd khi chi tdi 10-15%). Mat khac ket qua thu dugc trong dgt kiem tra kha nang phuc hdi tu nhien tham cd tai dam pha sau du an giam thieu cac nd sao da cho thay do phii cd bien tai cac khu vuc tren da dugc cai thien nhieu sau 2 nam.
Bdng I. Diin tich phdn bd vd do phii cdc thdm cd biin ven ba phia Bdc Viet Nam
stt
1
2
4
Dia diem
Quan g Ninh
Hai Phdn
g
Nam Djnh Nghe
Dam Budn Vung Ha Cdi Vung Dam Ha
Dam Nha Mac
Dam Dinh Vu
Bai Gia Luan Dam Trang
cat
Cira Each Huyen
Cdn Ngan Cira Hoi
Ket qua ed trudc (trudc nam 2002)
Dien tich (ha) 100 150 80 500
120 2 60 100
30
Do phu
(%)
30-80
20-50
15-65
Kiem tra 2009-2010 Dien
tich (ha) 0 0 0 100
0 0
20
Do phii
(%)
0 0 0 10-20
0 0 0 0 0 5-10
Nguyen nhan
Bj tram tich tir lii quet viii lap
Bj tram tich tir lii quet viii lap
Bj tram tich tir lii quet viii lap
Da nhd cho nudi tdm
Da san lap xay dung Da san lap xay dung Da san lap xay dung Da san lap xay dimg Da san lap xay dung Mdi tim thiy 2010
8
9
10
|An Quan
g Binh Thira Thien Hul
Quan g Nam
Sdng Gianh Nhat Le Dam Lap An
Tam Giang- Cau Hai Cira Dai
1
500 200 120
1000 250
50-100 50-80 30-60
30-70 50-70
200 40 40
700 130
20 15 10-30
20-50 30-50
Da san lap xay dimg Da lam dam nudi tdm
Bj dao len khi khai thac vat lieu xay dung
Da san lap xay dimg va lam dam nudi Da san lap xay dung va bj tram tich, rong tap che phii
Ngugc lai, mdt sd viing nhu Cdn Man, Cdn Son, Cdn Dai vdi dien tich bai cd da phat trien them tdi gan 100 ha vdi do phii tdi 70-80%, chieu dai cd tdi hon 20 cm.
Ket qua tren day phii hgp vdi danh gia sir suy giam dien tich cac tham cd ciia Nguyen van Tien, 2009 khi cho rang tir 1997 den 2004 (sau 7 nam), dien tich cac tham cd bien tai Vung Ha Cdi (Quang Ninh) da giam khoang 85% va tai bai trieu cira sdng Tien Yen mat 100%. cac bai cd trong cac dam pha phia Bac Trung Bd dien tich giam khoang 50% trong khi dien tich tham cd trong cac dam pha phan Nam Trung Bd giam it ban chi tdi 20-30%. Mat khac thay dien tich cd bien d bai trieu Vung Bau, Phii Qude mat di 100%.
3. Suy giam thanh phan loai va sd luoTig dong vat song trong tham cd bien
Thdng ke cho thay cac tham cd bien la nai cu tru, mdi trudng sinh san thuan lgi va la noi tao ra ngudn thirc an thu hut sir tap trung ciia cac loai sinh vat sdng ciing vdi cd bien. Ket qua nghien ciiu tai tat ca cac viing cd bien tap trung d Viet Nam cho thay, mat do ddng vat day d trong cac tham cd bien cao hon d ben ngoai tham cd bien: tir 1,5 den 5,2 lan. Da phat hien 323 loai ddng vat day, 219 loai rong bien, 214 loai ca bien, 178 loai va cac don vi taxon ngudn gidng (tdm, cua, ca), 60 loai Than mem Chan bung, 10 loai hai sam, 5 loai ca ngua, 8 loai tdm he, 4 loai cau gai v.v sdng trong tham cd bien. Do dd, nhung tham cd bien cd vai trd rit quan trong trong viec tao ra cac bai khai thac hai san cd gia trj kinh te cao (Nguyen Van Tiln, 2009). Kit qua nghien cim ngudn gidng tdm ca tai viing trieu Cira Dai va dam pha Tam Giang - Ciu Hai cho thiy mat do gidng tdm, ca da giam 2-3 lan so vdi ket qua cd dugc nam 1999 - 2000. Mat khac ti le cac loai ca kinh te chi thj cho ngudn lgi ca tren tham cd bien nhu ca Hdng, ca He va ca Dia cdn rat thap, trung binh chua tdi 1%.
Ngoai cac loai sdng kem neu tren tham cd bien cdn la nai sdng va la ngudn thirc an chinh ciia hai loai ddng vat dugc liet ke trong danh sach ciia lUCN va CITES, do la Dugong va riia bien. Nhiing nam gan day cd bang chimg ve sir suy giam nhanh chdng ciia Dugong tren toan the gidi, dac biet la d Ddng Nam A, trong dd cd cac khu vuc cd cac tham cd da tirng rat ldn d Viet Nam nhu Ha Cdi (Quang Ninh). Cdn Dao, Phu Qude, Binh Thuan
4. Nguyen nhan gay suy thoai HST cd bien
4.1. Suy thodi do bien ddi khi hdu vd mdi tru&ng tir nhien
- Lu lilt vd hgn hdn: Bien ddi khi hau gay ra ban ban, lam thay ddi tuong tac sdng biin ddng nghTa lam tang qua trinli ket keo ngay trong cac viing nude cira sdng ma trudc day cd do trong cao, cd bien tdt tuoi nhu Cira Dai, da gdp phan lam giam tic do sinh trudng va phat
Tiiu ban: Khoa hgc cong nghe Bien ISBN: 978-604-913-015-1
triln cua cd. Ben canh do la sir phat trien cua cac loai rong tdc vdn ua do man va ham lugng dinh dudng cao da bam lay va bao phu thanh ldp tren bl mat tham cd Cira Dai. Viing trieu cira sdng Tien Yen noi chju tac ddng true tiep ciia cac tran lii quet, tham cd biin rdng hon 300 ha da bj viii lip hoan toan dudi ldp tram tich thd day hang chuc cm. Hon niia viec ngot hda dot ngot trong miia mua do mua ldn ciing gdp phan lam suy giam va mit di cac bai cd cira sdng ven bd.
- Bdo: Viing vjnh Bic Bd, Bac Viet Nam, hang nam cd khoang 3-5 tran bao vdi tdc do gid cao nhit la 50m/s. Bao, nude trieu dang, gid ldn lam tang cac boat ddng sdng tren nen day. cac bai cd biin quanh dao Cd Td (Quang Ninh), Cdn Dao (Ba Rja - Viing Tau) va Nam Yit (quin dao Trudng Sa) bj anh hudng nghiem trong ciia sdng khi bao. Loai cd chinh bj anh hudng d day la Thalassia hemprichii. Nam 1997, tran bao Linda da lam mat di bai cd dot tre Thalassodendron ciliatiim da tin tai tir nam 1996 trd ve trudc, nhung sau tran bao, loai nay khdng cdn nira (sdng gid danh bat gdc va cat phii). Do tac ddng cua con bao Linda va con ngudi, khoang 20-30% dien tich cd da bj mat d Cdn Dao. Trudc khi con bao den, mat do cd Halophila ovalis la 2250 chii /m^, sau dd giam di cdn 1551 chdi /m^ (Nguyen Xuan Hda va Trin Cdng Binh, 2002).
4.2. Suy thodi do phdt trien cdc hoat dgng kinh te Men
- Phuang phdp ddnh bdt hiiy diet: Ckc bai cd bien la mdi trudng sdng cho nhieu loai ddng vat bien, trong dd cd nhieu loai hai san cd gia trj kinh te cao vi vay ma cac boat ddng khai thac hai san tren cac bai cd dien ra lien tuc. Danh ca bang ludi gia cao (cao bay) da lam tan tac bai cd d vung Bau, dao Phii Qude.Viec thu lugm, dam dap va dao bdi ddng vat sdng trong bai cd bien d viing trieu Sdng Han va Cira Viet da anh hudng ldn den cac bai cd bien (trdc gdc, diit gay, cudn trdi). Vao thdi ky con nude rdng trong thang d dam Thiiy Trieu (Cam Ranh), hang tram ngudi dung thudng, cudc ban cao de cao xdi dam dap len nen day cac bai cd bien de bat gia bien {Lingula sp) va ngao, sd. Hoat ddng nay huy hoai khdng it bai cd (Nguyen Hun Dai va cdng sir, 2002).
- Ddo ddp ao nudi trdng thiiy sdn: Trong khoang 5-7 trudc day, cac dam nudi tdm ca phat trien nhanh d viing ven bien, nhieu dam nudi thiiy san dugc quai dap ngay tren bai cd bien. Tham chi cac dang dd, nd sao ciing khoanh vay ngay tren cac bai cd bien phuc vu nudi trdng thiiy san. Dien tich cac bai cd bien tai vjnh Cam Ranh (Khanh Hoa) bj suy giam nhieu.
Dien tich phan bd ciia loai cd bien Enhalus acoroides a dam Thiiy Trieu nam 1998 bj mat 20- 30%. O nhiing vimg bj suy thoai khdng the tim dugc nhiing cay cd mang hoa, qua va hat.
Dieu nay cho thay kha nang phuc hdi tu nhien ciia cd bien rat thap va cd bien se bj mat neu he sinh thai tiep tuc bj tac ddng (Nguyen Hiin Dai va cdng sir, 2002).
- Cdng trinh xdy dung ven ba biin: Viec dd thj hda vimg ven bien, ven dao va xay dimg khu vuc phat trien kinh te nang ddng, nhieu thanh phan (cang bien, khu djch vu, du Ijch...) da anh hudng nhieu tdi cac tham cd biin viing ven bd. Chi trong nam 2009, viec xay khu au thuyen ben Cau Thanh Ba, Quang Binh da xda sl 100 ha cd biin.
- O nhiim khdi nuac: Do rat nhieu hoat ddng kinh te dan sinh tai viing nude cira sdng ven bd ciing nhu tac dong tir phia thugng nguIn theo sdng ra vimg trieu cira sdng. KhIi nude bj phi dinh dudng se lam tang ham lugng vat la limg va ket keo, tao ra sir phat triln manh ciia thue vat phii du va rong bien se can trd sir phat triln ciia tham cd bien. Mat khac hiu hit cac bai cd bien nam gan nhiing noi neo dau cua tau thuyen. Dau thai tir tau va thuyen danh ca gay hai cho cd bien. Dau lam hdng cd, dac biet la la chii va la non va ciing lam d nhiem nen day.
5. Ket luan
Cd sir suy giam nghiem trong vl dien tich phan bd va do phu cac tham cd bien ven bd Viet Nam. Cho tdi 2006 udc tdng dien tich khoang ban 17.000 ha. Hien nay HST cd bien darig bj suy thoai nghiem trong vdi dien tich mit di trung binh tren 50%. Mdi trudng sdng khac nghiet da lam suy thoai ca chit lugng quin xa cd khi sinh khIi, chieu dai cd giam d hau het cac khu vuc khao sat.
Cd nhieu nguyen nhan dan tdi sir suy thoai cac tham cd bien ven bd. Cd the thay tdc do suy thoai cac tham cd phu thudc sir phan bl ciia chiing d timg loai thuy vuc bj chju cac tac ddng bat lgi tir mdi trudng tu nhien va phat trien kinh tl xa hdi khac nhau. Nguyen nhan chu quan chinh dan den suy thoai HST cd bien la do nhan thiic yeu ve vai trd va tam quan trong ciia cd bien nen da it chii y den chiing trong qui hoach tdng the ven bien. Cac tham cd phan bd d viing trieu cira sdng ven bd chju tac ddng tir cac bien ddi mdi trudng tu nhien va xa hdi manh ban cac tham cd bien trong cac dam pha va ciing la nhirng khu vuc cd tham cd bj suy thoai nghiem trong nhat. Hang nghin ha bai cd bien thudc viing trieu cira sdng ven bd Quang Ninh da gan nhu bj mat hoan toan chii yeu do tac ddng tir cac tham hoa tu nhien (mua, lii).
Trong khi cac tham cd phan bd trong cac dam pha Mien Trung bj suy giam it hon va chu yeu do cac tac ddng tir cac boat ddng phat trien kinh te nhu dap dam, khai thac thuy san, quay nd sao gay ra.
TAI LIEU THAM KHAO
1. Costanza R., R., d'Arge, R., de Groot, S. Farber, M. Grasso, B. Harmon, K. Limburg, S. Naeem, R.V. O'Neill, J. Paruelo, R.G. Raskin, P. Sutton and M. van der Velt, 1997.
The value of the world's ecosystem services and natural capital. Natural 387, 253-60 2. UNEP, 2004. Seagrass in the South China Sea. UNEP/GEF/SCS Technical
Publication No3.
3. Nguyen Hiiu Dai, Pham Hiin Tri, Nguyen Thj LTnh va Nguyen Xuan Vy, 2002. Sir suy giam cac bai cd bien d Khanh Hda va kha nang phuc hdi ciia chiing. Bao cao Hdi nghj Biin Ddng. Nha Trang 6 -19/9/2002.
4. Nguyen Xuan Hoa va Trin Cdng Binh, 2002. Giam sat tham cd bien va quan the Dugong d Cdn Dao giai doan 1998-2002. Bao cao Hdi thao WWF Bao tdn Dugong va Mdi trudng Cd Biin, Ha Ndi 20-21/1/2003.
5. Nguyen Van Tiln, Dang Nggc Thanh va Nguyen Him Dai, 2002. Cd bien Viet Nam:
thanh phin loai, phan bo, sinh thai - sinh hoe. Nha xuat ban Khoa hoe ky thuat. 165 trang.
6. Nguyen Van Tiln (chii bien), Le Thanh Binh, Nguyen Hiru Dai et al, 2004. Tien tdi quan ly he sinh thai cd bien Viet Nam. Nha xuat ban Khoa hoc va ky thuat, Ha Ndi.
132 trang
7. Nguyen Van Tien, 2009. Mot sd van de ve quan li he sinh thai cd bien d Viet Nam.
Tuyen tap Hdi nghj khoa hoc toan qude ve sinh hgc bien va phat trien ben viing. Trang 151-157.
