Các hệ sinh thái cửa sông: Những đặc trưng cơ bản, tài nguyên và định hướng cho việc phát triển bền vững

KHOA HOC CONG NGHE<br /> <br /> <br /> CAC HE SIIMH THAI CIJA SOIMG: IMHUIMG DAC TRUIMG<br /> CQ BAIM, T A I IMGUYEIM V A DflMH HUQIMG CHO VIEC<br /> P H A T TRIEIM BEIM VUIMG<br /> Vfl Trung Tangi<br /> T6MTAT<br /> Noi dung bai bao gioi thieu nhung dac trung co ban ciia mot dang thiiy vuc chuyen tiep o vung bien nhiet<br /> doi: he ciia sdng, trong dd chiia dung nhung sinh canh dac thii vdi nhimg loai sinh vat cd ngudn gdc bien,<br /> rdng nhiet va rdng mudi da tao nen nhiing dang tai nguyen to ldn cho su phat trien kinh te-xa hdi cua cac<br /> tinh duyen hai. Thd manh cua viing cita sdng gdm dat mdi bdi va cac san pham cua dat, tai nguyen da dang<br /> sinh hpc, cung nhu tidm nang phat trien giao thdng, mo mang du lich sinh thai. Hon niia the ky qua, hang<br /> van ha dat mdi ria cac chau thd dugc chinh phuc nhd quai de lan bien. Nghe khai thac bien, trudc het la<br /> khai thac va nudi trdng hai san da cd nhiing ddng gdp quan trpng cho nen kinh te qudc dan. Tuy nhien, mat<br /> trai cua nd la khai thac cdn chira dung nhieu yeu td bat hpp li va kem ben vung: quai de lan bien d at, thieu<br /> qui hoach, lam xao trdn canh quan, gay lang phi tai nguyen; khai thac hai san qua miic, nudi trdng thuy san<br /> thieu su quan li, chat lupng mdi trudng suy giam... do dd, de lai nhieu hau qua sinh thai khdng kem nang<br /> ne nhu bd lai dat hoang hda do quai de khdng thanh, thu hep rimg ngap man (RNM), gay d nhidm mdi<br /> trudng... Truo'c thuc trang dd, bai bao neu len nhtrng nguyen tic va nhiing dinh hudng co ban cho khai thac<br /> va sir dung tidm nang dat dai va da dang sinh hpc viing cira sdng mdt each hpp li cho su phat trien kinh te -<br /> xa hdi mdt each bdn vung.<br /> Tir khoa: He sinh thdi cua song, phdt trien ben vitng.<br /> <br /> <br /> Cke he ciia song (CS) 11 noi chuyen tiep giiia Cic he CS dang trong trang thai phit trien<br /> nuoc ngpt vl nuoc man, a do nuoc ngpt hoa trpn co thong qua boat dpng boi tii-blo mon hoac dat lan<br /> miic dp voi nuoc man do boat dpng ciia thuy trieu. bien hoac bien lln dat va dly bien dpng, do do chtia<br /> Vtmg CS la mpt bp phan ciia doi bien ven bo (coastal dung nhieu riii ro tiem an, doi khi rIt khoe het doi<br /> zone), nlm trong truong tuong tie giQa luc dia-dai voi doi song con nguoi.<br /> duong-khi quyen ma true tiep la tuong tic song-bien. Dieu kien song cua vung CS, nhlt la dp muoi<br /> Bo bien nuoc ta trai ra gin 13 vl dp vl bi chia cit luon bien dpng trong bien dp Ion, ttr 0,5 den 30(32)<br /> thanh timg doan boi cac he thong song, tii do hinh %o voi toe dp nhanh theo khong gian vl thoi gian,<br /> thinh nen vung CS rpng Ion, hlu nhu 6m lly toln bp phu thupc vao cic chu ki mfia cua khi hau (mua lu vl<br /> khoi nuoc ven bo. Dpc bo bien, he CS co the gom cic kief tren cac song) vl chu ki thuy trieu.<br /> dang sau: Cic CS chau tho, CS hinh ph^u, chuoi dim Phan bo trong vting CS 11 nhting loli sinh vat<br /> pha ven bien mien Trung, vung vinh nong ven bo vl rpng nhiet vl rpng muoi, hinh thanh nen cac nhom<br /> cic sinh lay ngap trieu dupc phti boi rung ngap man sinh thii dac trung: nhom sinh vat nuoc ngpt thich<br /> (RNM) 6Tay Nam bp [8]. nghi voi dp muoi thap o phin diu CS, nhom sinh vat<br /> I. niHUniG DAC TRUNG Cff BAN CUA CAC HE CUA SONG CS chinh thiic, nhom sinh vat bien rpng vl hep muoi<br /> 1. Nhiing tinh chit ehung xam nhap vio vung thIp CS vl nhom sinh vat di cu<br /> qua CS (di cu song-bien hoac bien-song) de sinh sin<br /> Cic CS CO tuoi lich su tre hon so voi nhieu he ttt<br /> (Vu Trung Tang, 1994).<br /> nhien khic. Su ra doi ciia cic he CS hien dai gin lien<br /> voi lich su hinh thinh bo bien, khoing duoi 2000- Khu he sinh vat CS co tuoi Uch su tre hon so voi<br /> 3000 nam ve truoc. Dieu nly co anh huong quyet cic khu he phan bo a eke he sinh thii khic tren can<br /> dinh den qua trinh thich nghi v l tien hoa ciia cic loai hoac bien, chu yeu co nguon goc bien. Do do, so loli<br /> song trong vung. thich nghi dupc voi dieu kien song a vung CS khong<br /> nhieu, nhung o day nho tiitra huong nguon tiiu'c an<br /> phong phu, it ke tiiu chung thuong phat tiien hung<br /> tiiinh ve so lupng, tao nen san lupng cao cho khai thac.<br /> GS. TS. Dai hpc Qudc gia Ha Ndi<br /> <br /> NONG NGHIEP VA PHAT TRIEN NONG THON - SO 10 - THANG 10/2009<br />  KHOA HOC CONG NGHE<br /> <br /> khi tiitu cudng<br /> <br /> <br /> <br /> Vung CS nhu mpt cai bIy, bIy vio day nguon<br /> muoi khoing va chat htfu co tir luc dia dupc cac dong<br /> song mang ra hoac fit bien mang vao va dupc hinh<br /> thinh fai ch6, trong do mun ba htfu co dong vai tro<br /> quan trpng nhlt cho cac loai an mun ba (detritivore),<br /> NGHi CA<br /> mpt nhom uu the, tham gia chinh vio sir chuyen hoa<br /> vat chit va nang lupng cua he cua song (hinh 1).<br /> »• Antiirctiep — ^ . Con duong van chuyen vat chat chinh<br /> ^ Phan giai va hoan lai duoi dang nguon thiic an hiru c o khac. 2. Nhiing die di^m riSng ciia cic dang cua song<br /> Cac duong bau due la nguon khoi dau cho cac xich thiic in<br /> Tren quan diem dpng lire cua moi tuong tac<br /> Hinh 1. Ludi thtic in die tnmg eho cic ht da song song-bien, ngoai nhtfng tinh chit chung nhat nhu<br /> nhi$t ddi, gom xich thtic in chin nuoi, xich mun bi hthi neu a tren, cac CS con dupc dac trtmg boi nhting net<br /> ca vi xidi thiic in thim thiu, trong d6 xich thti 2 dong rieng cua minh (bing 1).<br /> vaiti-6quan trong bie nh& trong su ehuyen tii vit chit<br /> vi ning hiong trong vung (Vti TVung Tang, 1976,1999.)<br /> Bing 1. Nhiing die tnmg ca ban v6 di^u kifen tu nhi^n ctia cic ht cita song<br /> TT CAC DANG CUA SONG NHUNG D A C T R U N G CO B A N<br /> Day la viing sut lim kien tao dupc den bii. Dpng luc dong sdng<br /> Cic ciia song chiu tho: chiem uu the vdi tong lupng nudc ngpt va phii sa Ion, nudc CS bi<br /> 1 Chau tho song Hong ngpt hda manh, dat lan bien vdi toe dp cao, tao nen chau tho, cac bai<br /> va chau thd song Cuu long trieu biin cat, cac dao cira song va tien chau tho. Phan bo trong viing<br /> chii yeu la nhUng loai sinh vat nudc lp.<br /> Day la viing sut lun kien tao khong dupc den bii. Tong lupng nudc<br /> ngpt va lupng tai phii sa cua cac song thap, dong tridu uu the dua<br /> nudc man xam nhap sau vao npi dia, tao nen luc bao mdn manh ddi<br /> 2 Cic cua song hinh phSu<br /> vdi long sdng, bd", bai...do dd,^cu'a sdng ngay mdt loe rdng ra bien,<br /> bien lan din dat hen. Phan bd trong viing chu yeu la nhirng loai sinh<br /> vat nudc lo.<br /> Pha dupc hinh thanh nhd su xuat hien bd' cat phia ngoai, dm lay mdt<br /> xoang nudc phia trong dupc gpi la pha, trong dd ddng sdng chay ra<br /> bien mpt each an toan. Ngoai cira cua cac con sdng, pha cd ciia<br /> rieng cua minh lien thdng vdi bien. Trong miia mua, nudc sdng ldn,<br /> 3 Cic p h i midn Trtmg cac pha hoat dpng nhu nhimg ho chiia, phan bo trong pha chii yeu<br /> la nhiing loai nudc ngpt, nhung trong miia khd, lupng ddng chay<br /> thap, khdi nudc ciia pha bi man hda do nudc bien xam nhap vao;<br /> quIn xa sinh vat miia nay gom chii yeu nhirng loai nuoc Ip va lp man<br /> (meso- va polyhahne).<br /> Day la vimg dIt thap phat trien o' dong bing phu can sdng Ciiu<br /> Long vdi su thdng tri cua cay RNM. Nguon nudc ngpt va lupng phii<br /> Cic sinh Iiy ngip tridu dupc phu sa nhan tir sdng Cim Long thdng qua he thdng sdng-rach chIng<br /> 4.<br /> boi RNM a Tay Nam bp chit, hda trpn vdi nud-c bien xam nhap vao nhd boat ddng cua thuy<br /> trieu Bien Ddng va vinh Thai Lan. Sinh vat song trong vimg chu yeu<br /> la nhting loai nud-c lo.<br /> Dupc hinh thanh bdi nhieu nguyen nhan do su an sau cua bien vao<br /> npi dia, su hda tan cua cac tudng da, su ndi dao vdi bd, v.v... Cac vung<br /> vinh cung cd the nhan nud'c ngpt tir mpt so sdng sudi vdi luu lupng<br /> Cac vung, vinh nong thap, khdi nud'c man chiem uu the, thdng tri, do dd "che dp CS" chi<br /> 5<br /> venbdf xuat hien tam thdi. Phan bd trong viing chti yeu la nhirng loai sinh vat<br /> ciia khdi nud'c ven bd (neritic), chung cd the hoan thanh tat ca cac<br /> giai doan phat trien ca the cua minh ngay trong vinh.<br /> <br /> NONG NGHIEP VA PHAT TRIEN NONG THON - SO 10 - THANG 10/2009<br />  KHOA HOC CONG NGHE<br /> <br /> <br /> 3. Khai thic vi su dung cic dang tii nguydn ven bien lai dupc boi voi toe dp trung binh<br /> 10,8 ha/nam.<br /> Tii nguyen vung ciia song gom dat vl cic sin<br /> pham cua dat, nuoc va cac san phim tii nuoc, nguon Nhin chung, ria CTSH co khoang 20% chieu dai bo<br /> nang lupng sach (gio, thuy trieu), tiem nang phat bien bi xoi 16 voi tdc dp khi manh. Dac biet khu vuc<br /> trien giao thong vl du lich sinh thii. Chp Con-Van Ly (Hai Hau, Nam Dinh) trong 30 nam<br /> (1936-1966) dif da mat di 650 hati-enchieu dii 30 km,<br /> a. Ddt vd su dung ddt tdc dp trung binh 11 10-15 m/nam. Nhieu di tich nhu<br /> Str boi dip 6 ria cac chau tho 11 tien de quan mieng gieng, cong ling, thIp chuong nha thd'... nlm<br /> trpng cho cong cupc quai de lan bien, mo rpng dat trong sdng nudc, cich bd tii 500 den tren 1000 m.<br /> dai. Chau tho song Hong (CTSH) co dien tich Theo mdt tdng kef khic, bd bien CTSCL cung cd<br /> khoang 15.000 km^, con chau tho song Cuu Long hien tupng tuong ttr. Phia dong, tii Ghenh Hio den<br /> (CTSCL) CO dien fich Ion gin gIp 3 lln nhu the, cue nam mui Ca Mau bd bien hi xdi Id manh, nhlt 11<br /> khoang 40.000 km^ vl hing nam vin tiep tuc tien ra d cac huyen Dim Doi, Ngpc Hien. Trong giai doan<br /> bien voi toe dp cao, co noi den 80-120 m/nam nhu 6 1968-2004, dac biet 11 khoang thdi gian 1968-1987,<br /> fly nam CTSH hay tai cua Dai (song Tien) va fay bien da gam sau vao dat lien tii 0,5 den 2 km. Do dd,<br /> nam miii Cl Mau. dien tich dat hi mat chimg 8.367 ha, trung binh<br /> Cac kef qui khao sat cua Tran Dtic Thanh va 220 ha/nam. Ngupc lai, phia tay Ca Mau, nhlt 11 fir<br /> nnk. (2000) chi ra ring, a ven bien CTSH fir nam ciia song Bay Hip den Dat Mui, bd dich chuyen ra<br /> 1930-1965, dat dupc boi them ll 445,8 ha/nam, dien bien, noi xa nhat den 4 km, noi gan nhlt 2-3 km, nhd<br /> tich bi xoi lo la 32,33 ha/nam, can bing boi-lo la dd, dien tich dIt ven bien d day da tang len khoang<br /> +416,47 ha/nam. Nhu vay, tren 145 km chieu dai bo 7.494 ha, trung binh gin 200 ha/nam. Day 11 noi<br /> bien chau tho o giai doan nly toe dp lan bien trung dupc bdi fu manh, tao nen cho RNM phat trien vl md<br /> binh 11 28,7 m/nam. Trong thoi gian 1965-1990, dien rdng, trong khi dd doan bd tft ciia song Ong Ddc den<br /> tich boi 11 469,9 ha/nam, con lo 11 47,85 ha/nam, An Minh (Kien Giang) va tft Rach Gil den Ha Tien it<br /> cin can b6i-16 11 +422,5 ha/nam voi tdc dp lan bien cd bie'n dpng (Nguyfen Manh Hung, 2009).<br /> trung binh 29,1 m/nam. Giai dpan 1990-1998, can can Dit bai bdi ven bien sau khi chinh phuc, dupc su<br /> boi tti-xoi lo +639,7 ha/nam voi toe dp trung binh la dung vdi nhieu muc dich, chu yeu 11 noi dinh cu, md<br /> 44 m/nam, cao hon so voi cic giai dpan truoc. rpng dif nong nghiep, nuoi trdng thuy san, trdng va<br /> Ngupc voi qui trinh bdi fu 11 su xoi lo cua bo fu bd rtmg phdng hp ven bien.<br /> bien. Truoc thap ki 80 cua the ky truoc, doan bo tir Ngoai nhung ling xa mdi ra ddi d phia trong de<br /> Ciia Diem Di^n den Thuy Xuan (Thai Thuy, Thii bien, theo cac thdng ke (D6 Dinh Sam va nnk, 2005),<br /> Binh) hi bio mon ca bo vl day voi toe dp tuong ting dien tich dat ngap man ven bien dupc danh gil la<br /> la 13 m/nam vl 4 cm/nam (Vtt Trung Tang va nnk., 606.792 ha, bao gdm trong dd dat dupc phu bdi RNM,<br /> 1985), nhtmg khi RNM dupc phuc hoi, toln tuyen dat NTTS vl chua su dung dupc het ke trong bing 2.<br /> <br /> <br /> Bing 2. Phin bo di6ntichDNM, RNM vi dim NTTSti-ongcic khu vuc a Vi$t Nam<br /> Dien tich dat Dien tich cd RNM Dien tich khdng cd Dien tich ao dam<br /> TT Khu vuc ngap man RNM NTTS<br /> ha % ha % ha % ha %<br /> Tdng sd 606.792 100,0 155.290 100,0 225.394 100,0 226.075 100,0<br /> 1 Ddng Bic 65.000 10,71 22.969 14,80 27.194 12,06 14.837 6,56<br /> 2 DB Bic bd 57.345 9,45 20.842 13,42 22.651 10,05 13.852 6,13<br /> 3 Bac Trung bp 30.974 5,10 2.300 1,48 22.167 9,83 2.505 1,11<br /> 4 Nam Trung bd 13.068 2,15 700 0,45 * * 12.368 5,50<br /> 5 Ddng Nam bd &TP HCM 67.100 11,06 26.092 16,80 37.540 16,65 3.468 1,50<br /> 6 DBSCL 373.305 61,52 82.387 53,05 111.873 49,63 179.045 79,20<br /> Ngudn: Dd Dinh Sdm vd ct, (2005). Ddu (*) - khong thdng ke duac vi dien tich qud nho<br /> <br /> <br /> NONG NGHIEP VA PHAT TRIEN NONG THON - SO 10 - THANG 10/2009<br />  KHOA HOC CONG NGHE<br /> <br /> <br /> Cfing vdi tii nguyen dat vl sinh vat, vung CS cdn trudng. Nhd ngudn thiic an phong phii, vitng CS 11<br /> cd ngudn cit, cac khoing chit, dac biet la sa khoing "vudn uom" au the cua cac loli ddng vat bien, noi<br /> chua: Oxittitan,zircon, monazit, imenhit.. vdi trif lupng nuong tua, lan trdn ke thu, noi kiem an va bai de cua<br /> cong nghiep. Dly cdn 11 noi phit trien cong nghiep nhieu loli, 11 ciia ngd cua cac loli di cu song-bien (cl<br /> giao thong bien (ddng va siia chtia tau, xly dung cang), chinh) hay bien-song (ca mdi, cl chay).<br /> cic CO sd che bien hai san, nhieu noi trd thinh nhifng Cac ket qua nghien ciiu ciia nhieu tac gia ve fhlnh<br /> khu an duong va du lich sinh thii hip din. phin cac nhdm loli sinh vat CS dien hinh dupc tdng<br /> b. Da dang sinh hoc hpp lai vl tiinh bIy d bing 3 {Vu Trung Tang, 1994,<br /> 2009). Ngoli sd lupng loli phong phu, trong vung CS<br /> Do lich sti hinh fhlnh, su phan hda cao ve noi<br /> cdn tdn tai cic he stiih thii va noi sdng rat dac sic:<br /> sdng, nhat 11 trong RNM, tham cd bien vl su bien<br /> RNM, tham cd bien, cic bai trieu tran, cic dao CS, bd<br /> dpng cua cic dieu kien sdng... nen mtic da dang sinh<br /> dl dly hang ddng den cic ao dim NTTS, v.v... Trong<br /> hpc (DDSH) ctia he CS khi cao, tao cho cic loai<br /> dd xuat hien rat phong phu noi sdng cho cic loli.<br /> sdng dn dinh trong dieu kien bat dn dinh ciia moi<br /> Bing 3. S6 lugng eie nhdm loii sinh vit trong eie h^ cua song nudc ta<br /> Quang CS chau Tam Pha Dam Dam Cira sdng<br /> Cac nhdm Dam Dam<br /> Ninh - Hai thd Bac Giang- Lang 0 Nha Ciru Long<br /> sinh vat Tra 6 Thi Nai<br /> Phdng bd Cau Hai Cd Loan Phu<br /> Macrophyta - 120-192 54 - 31 «30 136 104 -<br /> Phytoplanktton 185 183 357 99 85 - 185 116 278<br /> Zooplankton - 185 38 38 38 - 64 44 36<br /> Zoobenthos 135-500 177-183 75 45 19 36 192 172 a 200<br /> Cdc lodi cd 280 226 171 115 38-67 133 114 93 155<br /> Nguon: VU Trung Tang, 1994, 2009, tdng hap tie nhieu tdc gid.<br /> <br /> II. HIEN TRANG SU DUNG TAI NGUYEN VA NHUNG THACH THUC Miai thac vl NTTS 11 lpi the so sinh ndi troi nhd<br /> Ttr lau, vung CS da trd fhlnh dia bin boat ddng nhtfng dieu kien thuan lpi ciia vung. Nghien ciiU ciia<br /> manh me cua cic linh vuc kinh te. Nhin chung, viec A B. Longhurst vl D. Pauly (1987) chi ra ring,<br /> khai thac fli nguyen nhu quai de lan bien, chinh khoing 50% sd loli cl bien cd ddi sdng phu thupc vio<br /> phuc cac vfing dif mdi, khai thic RNM, dinh cl vl viing CS nhiet ddi vl khong it hon 10-15% nhu the ddi<br /> NTTS, khai khoing... thudng chay theo lpi ich rieng vdi vung can nhiet ddi. Mdi quan he nay tiiy thupc<br /> cua cic nganh. Ttr dd, din den tinh trang, lpi ich cua vio tiing loli, timg giai doan phat trien khac nhau<br /> nganh nly chdng lai lpi ich cua nglnh khic, lpi ich ciia ddi sdng. O cic CS on ddi, nhu CS thupc ddng<br /> trudc mit mau thuin vdi lpi ich lau dii. Kem theo dd bing Louisiana, cd den 35-72% cic loli vl tren 90% sd<br /> 11 sir quIn ly non kem, mang tinh don nglnh, khong lupng cl the da sti dung CS nhu "vudn uom" cua<br /> phu hpp vdi clu tnic phtic tap, nhtmg rat thdng nhat chung.<br /> cua cic he sinh thii CS, dua den viec buy hoai va su Blaber S. J. M. (1980) cdn khang dinh, dai bp<br /> dting lang phi tai nguyen. Nhieu dien tich RNM bi ddn phan ca CS nhiet ddi va can nhiet doi khong mang<br /> ha, nhieu dien tich NTTS do nang suit suy giam hi bd "ban chat ctia song" ml la nhdm dac tnmg cua ngu<br /> hoang; bai de, noi kiem an cua cac loli dpng vat bien gidi vung bien nong, ntrde due vdi dd mudi rIt bien<br /> bi khuly dao, htty hoai vl 6 nhi§m, v.v... do dd, sir phit ddng. Nhat 11 d cic bien phia Nam va Dong nam A,<br /> trien kinh te-xa hpi cua vung trd nen kem ben vifng. fay Phi vl phia bic My La tinh, noi nhan lupng nudc<br /> Tuy fli nguyen cua vung CS da dang, song khong Id tii nhtfng he thdng song ldn nhu: An HI,<br /> DDSH 11 dang then chdt, mang tinh ddn bay cho su song Gang (An Dp), Brakmaputi-a (Bangladesh),<br /> phit trien KT-XH cua cic huyen ven bien. Song nhat Mekong (Dong Duong), Congo (tay Phi), Amazon<br /> thiet viec khai thic vl su dung cic dang tai nguyen (Brasil)... Do dd, trong sd 142 loli cl nghien ciiu d<br /> chi dupc dtmg a mtic tdi tm ml khong dupc vupt qua Nam Phi (Whitfield, 1994), cd tdi 71% sd loai la nhung<br /> gidi ban chiu dung cua chung. dai dien hoac holn toln hay mdt phan ddi sdng phu<br /> thupc vio vung CS,ti-ongdd, cl CS chiem 28% vl cl<br /> <br /> NONG NGHIEP VA PHAT TRIEN NONG THON - SO 10 - THANG 10/2009<br />  KHOA HOC CONG NGHE<br /> <br /> bien rpng mudi 43%, sd cdn lai 11 nhirng loli ca bien vang lai (21%), mpt sd loai la ca nudc ngpt rdng mudi<br /> hep mudi, xuat hien vdi sd lupng if nhu nhiing khach (5%) vl nhiing loli di cu qua vung CS ''^°^~<br /> <br /> Mugil cephalus Scomberoides lysan<br /> <br /> Cu'a s6ng& ven bd'<br /> S: