36(2). 131-138 Tap chi CAC KHOA HOC V£ TRAI P A T
DAC DIEM T R A M TICH GIONG CAT HUYEN CAU NGANG VA TRA CIJ TINH TRA VINH
VA K H A N A N G CHITA N u ' d c NGOT
NGUYEN VAN LAP, TA THI KIM OANH Email- [email protected]
Vi^n Dfa ly Tdi nguyen Tp. HCM, Vien Hdn Idm Khoa hoc vd Cong nghe Viet Nam Ngay nhan bdi: 17 - 12 - 2013
L M f r d a u
Khu vuc huyen Cdu Ngang vd Trd Cu co vi tri dja \</ ve phia nam tinh Tra Vinh vd ndm giSa hai sflng C6 ChiSn va song Hdu. Phia dong va nam gidp huy?n Duyen Hai, phia tay giap song Hau, phia bdc gidp huy?n Chau Thanh vd Tieu Can {hinh 1). Tong dien tich dat tu nhien khu vuc la 68,302,97 ha, ddn s6 khoang 310.000 nguai, trong d6 nguiri ddn tOc Kho Me khodng 35- 40% vd canh tdc none nghiep Id chu yeu nen d6i song ngu6i ddn c6n nhieu kh6 khdn. Qud trinh thanh tao va phdt trien chdu tho song Ciru Long trong thai Holocen mugn dd hinh thdnh khu vyic Cdu Ngang va Tra Cii c6 dja hinh trung, phdng xen ldn dia hinh cao ciia h§ thong giong cdt, chay lien tuc theo hinh vong cung vd song song vai duang bcr bien hien tai.
Giong cdt dugc thanh t^o 6 b o bien, vi v | y hinh thdi vd tuoi ciia trdm tich giong cat thuong chi thi cho vj tri, hinh dang va thoi gian thdnh tao duong bg biln c6. Gi6ng cdt thuong dugc cdu tao bai cdt mjn, cao dp trung binh khoang 3-5m tren muc nu6c bien [2, 3] vai nIn ddt nen de nen dugc ngucri ddn djnh cu sinh s6ng, xay dung ldng, xom, duang giao thdng,... va canh tac hoa mdu.
Tr4m tich gidng cat la vet tich ciia duang btr bien c6 [1, 2] rdt co y nghTa trong viec khoi phuc c6 dja 1;^ vd tifin h6a ciia chdu tho, ngodi ra, do dac diim thdnh t^o, trdm tich giong cat co tiem nang chiia nguon tdi nguyen nuac nggt rat quy a khu vyc ven bien. Nudc trong giong cat chu yeu la nu<5rc mua thdm vao vd dugc khai thdc bdng gieng khoi ho$c gieng khoan o dg sdu khoang 4-6 m Nguon nudc trong giong cdt tuy co trir lugng ban chi vd ch^t lugng nuoc chua ddm bao la nuoc
sach, nhung dap iing dugc mgt phan nhu cdu nuoc sinh boat va san xuat cua nguoi ddn dia phuang.
Nuoc trong giong cat c6 chi tieu ly hoa thay doi, hien tugng phen hoa hay man hoa thuong xdy ra vao miia nang khi khai thdc can kiet. Vi nhu cdu khai thae sir dung ngay cang gia tang nen viec thieu nuac ngpt va nhiem man ngay cang trdm trpng trong nhiing ndm gdn day, Huong den myc tieu phdt trien kinh te vd cdi thien doi song ciia ngutri dan, viec cung cdp nuoc sach sinh hoEit n6ng thon la nhu cdu cdp thiet, Vi vdy, viec nghien ciru d | c diem trdm tich he thong giong cdt, cdu tnic tram tich giong cdt vd cdc trdm tich lien quan cho phep xac dinh dac diem phdn bo vd khd n3ng chita nuac cita giong cat. Bdi bdo trinh bdy cdc ket qua nghien ciiu ve dac diem trdm tich he thong giong cat khu vuc Cdu Ngang vd Tra Cii lien quan d^n khd nang chiia nuac nggt trong giong cdt.
2. Tai Ii£u vd phirong phap nghien cihi Nghien cim dac diem tram tich giong cat huyen Cau Ngang vd Tra Cii tinh Tra Vinh dugc thue hien tren ca so ke thira so do tram tich viing chdu tho song Cliu Long [2], ban do hien trang sii dung ddt tinh Trd Vinh ndm 2010 ty le 1:50.000 [5], dnh ve tinh Landsat-7, ETM+ nam 2011. Ngoai ra, con tham khao cac thong tin, tu lieu lien quan den nuac sinh boat vd sdn xudt vimg nong thon tinh Tra Vinh.
Trong nghien ciiu ndy, cong tdc khao sdt thyc dia thu thap tdi lieu vd phan tich trong phong thi nghiem dugc thue hien nhu sau-
Khoan Idy mau tram tich 12 loi khoan (dg sdu 4 -lOm/loi khoan) vd 2 ho ddo (do sau l,8-2,0m) de
thue nghiem tham tai hien tnrang. Do muc n u a c ciia 85 gieng khoi vdo miia mua va nang, tong so 5 dgt dugc thue hien tir thang 4/2012 den thang 10/2013. Mdu nuoc trong giong cat dugc lay tir gieng khoi, gieng khoan va do gid tri pH vd dp man, ngoai ra hdm lugng sat tong, ammonium vd nitrate ciing dugc xac dinh bang phuong phdp phdn tich nhanh - Fieldkit. Tren co so ket qua phan tich tai hien truang, cdc mdu nuoc nay dugc chgn va phan tich trong phong thi nghiem theo muc tieu nghien ciiu. Cdc vi tri khoan, dao va lay mdu nuac dugc xac dinh bang GPS va chuyen sang he tpa dp V N 2 0 0 0 .
Do dia hinh tuyen mat cat giong cat bang may do toan dac dien tii NTS-320 SERIES o 4 vi tri dac trung, trong do sir dung 2 moc dja chinh co cao dp dia hinh va 2 cao do gia dinh ve tren ban do dia hinh ty le 1:25.000. Tai lieu nay dugc su dung d&
xdc dinh su thay doi muc nuac trong giong cdt theo miia mua vd nang.
Phan tich mdu trong phong thi nghiem gdm'67 mau thdnh phdn cdp hat, 24 mau cau tnic tram tich, 15 mdu tdo silic. Xdc dinh dac tinh c a ly ciia ddt tir 2 loi khoan gom do 16 rong, dp dm, khd ndng thdm.
Ngodi ra 5 mdu tuoi giong cdt bang phuong phap phdn tich nhiet huynh quang thach anh (OSL) dugc sii dung tii de tdi hgp tdc nghien cum voi Cue Dja chdt Nhat Ban (AIST).
Phan tich mau nuac trong phong thi nghi€m dugc thue hi6n tai Trung tam phan tich cong nghe cao Hoan Vu {VILAS 357). Cac chi tieu hoa hge nuoc vd phuong phdp phdn tich tuang iing bao gom ammonium (phuang phap Ref. SMEWW 4500-NHj-F,2012); bicarbonat (phugng phdp SMEWW 2320, 2012); sulfate, chloride, nifrate (phuong phap SMEWW 4500, E-2012); natri, kali, calci, magie (phuang phap SMEWW 3125,2012- ICP-MS); sdt tdng (phuong phap SMEWW3500- Fe.B,2012) va tong khoang vo eg (phuang phdp Ref. AOAC 920.193,2012).
SflOOTRAMTiCH III vt:^ C M NC \NG \ V TR \ C I
^^',
Hinh 1. So do trdm iich khuc vuc nghien ci>u
3. K i t q u i v i t h i o la$D
SJ. B^ £im phdn ho vd syrphdl triin hf thSng g^g cit khu v{fr nghiin ciru
Khu vvc huy^n Cau Ngang vd Trd Cii mang tinh chit chung ciia viing dong bdng ven bien d6ng bdng sdng Cmi Long, c6 dja hinh bdng phdng, do cao khodng 0,4-2m bj chia cdt boi cdc gidng cat Unh cdnh cung c6 dO cao 2-5m. Cdc vimg triing, phdng xen lln cdc giSng cat, dia hinh dgc theo hai b6 s6ag thudng cao, phan phia tay khu vuc Id vimg d^t th^p cua dam m$n, bj cdc gidng cdt chia cdt thdnh nhieu vimg triing c\ic bd, iihi€u noi chi a dg cao 0,5-0,8m nen hdng ndm thuong bi ngap 0,4- 0,8m trong thdi gian 3-5 thdng. Dja hinh cao nhdt tren 4m gom dinh cdc gidng cdt phdn bd d Nhi Trudng, Long San (Cdu Ngang); Nggc Bian (Tra Cu). Dja hinh thip nhdt dudi 0,4m tap trung tai cac viing triing d T^p Son, Ngai Xuyen (Tra Cii); M^
Hod, My Long, Hi^p M J (Cdu Ngang). Nhirng viing dat thap dp cao trung binh chi khoang 0,5 m bao g6m trung giila giong, dam mdn (hinh 1). Nhin chung dja hinh khd thdp vd tuong ddi bdng phdng vdi cao trinh binh quan phd bien Id 0,4m &kn +2m.
Cdc gi6ng cdt chay dai theo hudng ddng bdc - tdy nam cd kich thudc khde nhau ve chieu rpng, chieu ddi vd dd cao vdi chi^u rdng 100-380m, chiSu dai 400-2.000m, dg cao 2-5m so vdi myc nudc bien.
V^ cdu tnic hinh thdi, cdc gidng cdt thudng dgc trung bdi giSng ch£ nhdnh gdm mgt giong chinh cd chieu rgng va chieu ddi khd ldn va che ra nhihig nhdnh giong phy cd kich thudc nhd hon.
Cdc lo^t giong che nhdnh phan bd d Nhj Trudng, Thu^n Hda, Long Son, Nggc Bien, Ddn Xudn.
Giong cdt cd chieu ddy khodng 1,8-5,5m, ddy nhdt is dinh giong, giam ddn ve phia chdn gidng vd chan giong cdt thudng hi phu Idp bdi ldp set - bdt ciia trim tich ddm Idy giiia gidng ho5c tram tich ddm mjn. Tram tich giong cdt cd thanh phan chii yeu la cdt mjn mdu xdm, xdm phdt nau vdng chiia oxit- sflt d phin tren vd cdt min mau xdm d phdn dudi.
H? th6ng gi6ng cdt khu vyc Cdu Ngang, Tra Cii thdnh t^o vd phdt trien trong su tien hda chung cua dong bing hji chdu thd sdng Ciru Long vao thdi Holocene mugn. Cdc lo?t giong cat chi thi vj tri, hinh d^ng vd thdi gian thdnh t^o ciia dudng bd bien c6 trong khu vyc. Day la sy bdi tich lien tuc ciia chdu thd ti^p noi tir v^t tich dudng bd bien cd cd tudi 4.500 ndm d Cai L^y [1]. K^t qua phan tich tuii OSL ciia gi^ng cdt khu vyc Cdu Ngang va Trd Cli cho thiy lo^t giong Kim Hda. Hiep Hda, Nhj
Trudng, Tan Hiep, Ngai Xuyen c6 tudi 1620 ± 90 nam trudc hien tai (Ntht); loat gidng Thuan Hda, Long Son, Long Hiep cd tudi 1590 ± 90 Ntht; loat giong Thanh Son, Tram Giang co tudi 1100 ± 60 Ntht; loat gidng Tra Cii, Dai An cd tudi 970 ± 50 Ntht vd loat gidng My Hda, Hiep My phia ddng nam khu vuc cd tudi 770 ± 40 Ntht {hinh 1). Vk phia nam gidp ranh gidi huyen Duyen Hai loat gidng NgQ L^c cd tudi 520 ± 30 Ntht dugc t i ^ ndi bdi cdc loat gidng tre han cho den bd bien hien tai ciia Trd Vmh [4]. Ddi sanh vdi tai lieu tiin hda tram tich khu vuc ven bien tinh Trd Vinh thugc huyen Duyen Hdi, cd the lien he loat gidng cat hay bd bien cd tudi 1100 vd 770 Ntht d khu vuc huyen
Cdu Ngang va Tra Cii vdi trdm tich set-cat va cat bai trieu d do sdu -6m va -2,5m tuang iing trong 16 khoan TVl khu vuc Ngii Lac huyen Duy6n Hdi [4]. Day id chiing cti ro rdng eiia sy bdi tich lien tuc ra phia bien cua chdu thd sdng Cuu Long tai Tra Vinh trong Holocene mugn.
3.2. Dac diem trdm tich gidng cdt vd cdc dan v/
trdm lich liin quan
Dac diem tram tich gidng cdt vd cdc trdm tich lien quan qua cac ldi khoan dugc mo td trong hinh 2. Ket qua nghien ciiu dugc tdng hpp tren 2 mat cdt dia chat tram tich AB va CD (hinh 3). Dia tang tram tich khu vuc gidng cat dugc chia thdnh 3 phan tir dudi len tren nhu sau:
(i) Tram tich tien chau thd (delta front) cd thanh phan cat min, cat bdt mau xam phdt xanh. Tram tich ndy thudng phan bd d dp sdu khoang -6 den -7m (dudi muc nudc bien hien tai), dugc phii ben tren bdi trdm tich bdi trieu, Ket qud phan tich thanh phan cdp hat cho thdy khodng 63-72% cat, 19-33%
set-bdt va 5-10% manh thue vdt. Tren ca sd tudi tuyet ddi C''' dugc xac dinh trong Id khoan TVl d ranh gidi phia nam khu vuc nghien ciru, cd the xdc dinh tudi trdm tich tien chdu thd Id khodng 1826 Ntht d dp sdu -12m, vd ben dudi Id trdm tich set- bdt sudn chdu thd (pro-delta) ddy khodng 10m cd tudi khoang 1962 vd 2719 Ntht d do sau • 16m vd - 20m tuong iing [4].
(ii) Tram tich bai trieu gdm cat, bdt- cat, set - bgt vd set thudng cd mau nau xam, nau phdt xanh, chieu ddy trung binh khoang 3-6m vd cd cdc thau kinh set - bgt, set - bgt - cat hoac cdt. Cau tnic tram tich dac t^^mg la phdn ldp ggn sdng vd trieu. Trdm tich cdt vd bdt-cat bai trieu thudng cat chiem uu the vdi thdnh phdn cdp hat khodng 55-82% cat. 28-
133
40% set-bdt va 8-15% manh tbuc vat. Thanh phdn cua mgt sd gidng loai diatom mdi trudng nudc cdp hat trong trdm tich set-bdt bai trieu gdm man - Ig nhu Coscinodiscus spp., Thalassiosira khodng 70-88% set-bdt, 14-20% cat va 8-14% eccentrica, Nitzschia sigma, Cyclotella styrolus, manh thue vat. Tram tich bai trieu cd sir hien dien C. caspia vd Nitzschia spp.
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Hinh 3 M^t cSt dia chat trim tich AB vS CD (iii) Tuy theo vj tri va diSu kien thdnh tao, tram tich bdi t h i y tri6u dugc phu Ifin tren bdi cac tram tich d l ty nhien, gidng cat, trung giiia gidng vd ddm mdn. Trong khu vyc nghien ciiu, de ty nhien phdn bo h^n che d ven sdng Cd Chien thupc xa My Long Bdc. Trdm tich gidng cdt phdn bd tren di?n tich rpng ldn; phdn phia ddng thupc huyen Cdu N|ang vd phdn phia bdc huyen Trd Cii, he thdng gidng cdt dugc bao quanh bdi tram tich trung giiia gidng, Khu vyc phia tay nam he thdng gidng cat xen kS vdi trdm tich dam mdn (hinh 1).
Trdm tich triing giiia gidng thudng phdn bd gitta 2 hp thdng gidng cat, cd thanh phan set. set- bpt xdm phdt nau. deo mdm vdi chiSu day khoang l,2-2,5m. Trdm tich triing giiia gidng thudng phu tren trdm tich bdi tridu cd thdnh phdn set, set - bdt ho^c set - bpt - cat xdm xanh.
Trdm tich gidng cat d$c trung a ldi khoan ndng L02 vd L35 {hinh 2) vai thdnh phdn chii ydu Id cdt mjn cd mdu xdm vdng, vdng nhat bj oxit hda nhe d phan trfin. K^t qud phan tich thanh phan cdp hat cho thiy khodng 78-94% cat mjn, 4-12% cat vira, 3-12% bgt-sit, vd mgt it kat von sat. Chiku day khodng l,8-5.5m, gidng cdt b^ day nhat d dinh giong, hai ben chan gidng chi^u ddy gidm dan vd noi ddy cdt thudng bj phii lap bdi ldp set - bgt ciia trim tfch trung gifta giong ho$c trdm tich ddm man.
Tram tich dam man gom set - bdt xdm nau den xdm sdng vdi cac ldp mdng hoac thdu kinh cat- bpt Cdu true trdm tich thudng dong nhdt vdi nhieu hang sinh vdt va hiiu co mdu ndu den ndu den.
Tram tich ndy thudng cd chieu day khodng 1,3- 2,7m. Ket qud phdn tich thanh phdn cdp hat cho thdy set - bgt uu thi, khodng 62-83%, 5-18 % cat vd 14-22% tan tich thyc vdt.
3.3. Khd ndng chua nudc trong giong cdt Dac diim phan bd tang chira nudc trong gidng cat d huyen Cau Ngang vd Tra Cii dugc xac djnh tren co sd cau tnic trdm tich gidng cdt va cac trdm tich lien quan. Ve mat dia mao, gidng cdt cd dja hinh cao khoang 2,5-4m, keo ddi hen tuc hoac ndi tiep nhau tao thanh hinh cdnh cung cd hudng ddng bac - tay nam, Gidng cat Id noi cd dja hinh cao so vdi cac trung thap xung quanh nen dugc ngudi dan dia phuang tap trung sinh sdng, xdy dyng den, chiia, ducmg giao thdng va trdng hoa mdu Gidng cat dugc tim thdy phd bien vdi dia hinh cao vd keo dai (khoang 4-15km) d khu vuc trung tdm hai huyen keo dai tir thi tran Cau Ngang, xa Nhj Trudng (huyen Cdu Ngang) den xa Ngpc Bien va xd Dai An huyen Trd Cii. Gidng cat cd dja hinh thdp hon va phdn bd rdi rac d khu vuc tay bdc va ddng nam khu vyc nghien ciiu. Tdng di?n tich
135
gidng cat d hai huyen Cdu Ngang vd Tra Cii la khoang 6.785 ha. Tren co sd cdt dia tdng cdc loi khoan va mat cdt dia chat tram tich, cdu tnic gidng cat cd dang thdu kinh la tdng chiia nudc ngpt, ngudn nudc bd cdp chii yeu tir nuac mua. Thau kinh cdt dugc tim thay d phdn tren ciing ciia mat cdt va Id ra tren mat ddt, chieu day khodng 2,5- 5,5m trong dd ddy nhat d dinh va mdng dan ve hai ben chan gidng. Hai ben chan gidng cat dugc gidi h^n bdi cac trdm tich set, set- bdt trung giiia gidng hoac ddm lay man la Idp each nudc vd ben dudi gidng cat Id tram tich cat vd/ hoac set- bpt- cat bai trieu {hinh 3).
Tmh chdt co ly cua trim tich gidng cdt dugc xac dinh tren eg sd thyc nghiem tai hien trudng vd phdn tich trong phong thi nghiem. Trdm tich gidng cdt dac trung bdi trang thai ddt chat theo chi^u sdu va cd kha nang tham nudc vdi luu lugng thdm tir l,20-2,92m^/m% va dp Id rong khoang 33-49%.
Dieu ndy cho thdy gidng cat cd the trir dupc mpt lugng nudc ldn khoang 33-49% th€ tich ciia gidng cat. Do do, nudc mua dugc bd cap tu nhien vao mua mua ddng thdi cd thd iing dung bd sung nhdn tao nudc ngpt vao gidng cat vdo mua ndng.
Do ngudn bd cap nudc nggt tu nhien cho gidng cat Id nudc mua nen trii lugng nudc chira thay ddi theo mua. Khdo sdt thay ddi muc nudc trong gidng cdt dugc thue hien 5 dot vdo miia nang va miia mua tir thdng 4/2012 din thang 10/2013 tai cdc gieng khoi sii dung cho sinh hoat va dn udng cita ngudi dan huyen Cau Ngang va Tra Cii. Tdng sd khoang 85 gieng khoi dupc khdo sat vd 4 mat cdt dac trung dugc xdy dyng dd danh gid thay ddi muc nudc vao miia mua vd miia nang Ket qua nghien ciru trong hai ndm cho thdy myc nudc cd gia tri thdp nhat khodng -0,6m din +0,7m vao thdng 4/2012 va cao nhat khoang +2,8m din + 3,4m vdo thang 10/2012 (hinh 4b, e vd d). Thay ddi muc nudc trong ndm ciing da dugc tdng hpp tir sd lieu do nam 2012. Vao miia ndng, thang 4/2012 muc nudc d vi tri khd thdp khoang +0,2m din -Hi,6m (hinh 4a). Ddu miia mua khi nhan lugng nudc mua bo cap myc nudc dugc ndng len dat gid trj +0.5m den +2.0m vao thdng 7/2012; va dat muc nudc cao nhdt khodng +2,lm din +3.4m vao thang 10/2012 (hinh 4b). Ket qua ndy cho thdy giOa miia mua va ndng myc nudc thay ddi khoang l,8-2,6m (hinh 4a, b) trong dd thay ddi dang ki xdy ra noi dia hinh cao hay dinh gidng. Kit qua nghien ciiu cho thdy myc nudc d khu vyc dinh gidng ludn cao hon hai ben chan gidng va cd d p g vdng phia dinh ddng dang vdi dia hinh ciia gidng cdt; diiu nay cung da 136
dugc xdc dinh khi khdo sat muc nuoc trong gi6ng cdt huyen Ba Tri tinh Bin Tre (Nguyen Van L|p, 2011: Ddnh gia va khai thdc tong the tdi nguySn nudc nggt phuc vu san xudt va phat trien kinh te khu vyc ven bien huyen Ba Tri tinh BSn Tre, de tdi cdp Vien KH&CNVN). Muc nudrc co dang vdng ddng ke vdo mua nang va ddu mua mua (thdng 3,4 vd 7) va tro nen thodi hem vao cudi miia mua (thdng 10) khi cd lugng nudc mua dii ldn dugc bd cap vao gidng cat. Ket qua cho thdy kich thudc thdu kinh nudc nggt tang len vao miia mua va gidm di vdo miia nang; lugng nudc trong gidng cat s8 thay ddi phu thudc vao miia trong nam vd miic d$
khai thdc cua ngudi ddn dia phuong.
3.4. Chdt luong nu&c trong giong cdt
Chat lugng nudc trong gidng cat dupc xac dinh tren ca sd phan tich hda hge cua 16 mau nudc gieng khoi vd gieng khoan, ddng thdi xac djnh dugc 2 loai hinh nudc nhu sau:
(i) Nude trong gidng cat thupc loai hinh bicarbonat- chlorua- natri vd cd dp man khodng 0- 0,1 g/L dugc sii dung cho sinh boat vd an udng.
Hdm lugng (mg/L) cac anion va cation cd gia tri tuang ung nhu sau: bicarbonat (HCO3"): 122-306;
chloride (Cl'): 99,8-209; natri (Na*): 58,9-118;
sulfate (S04^"): 7,4-111; kali (K^): 20- 50,7; calci (Ca^*): 20,6-59,2; magne (Mg^*): 21,2-35,8; Sdt tdng (Fe): KPH-0,78; Tdng khoang vd ca (TKVC):
393-693. Ket qud nay cho thay hdm lugng cac ion va anion thudng thdp din trung binh va dao ddng khdng nhieu.
_ (11) Tdng nudc Ig ndm ben dudi thdu kinh nudc gidng cat d do sau khoang 12-18m cd dd mdn khodng 1,2-4 g/L thudng dugc sii dung cho cho tudi ray hoac chan nudi gia siic. Kit qua phan tich cho thdy nudc ndy thudc loai hinh chlorua- bicarbonat- natri- magne, ham lugng (mg/L) cac ion vd anion cd gia tri kha cao, trong do Cl". 209- 765; Na*: 118-333; TKVC: 694- 1688, HCO3 ':
275-306; SO/": 53,5; K^: 29,9; Ca'"": 91,0; Fe:
KPH-0,45; Mg'*: 105. Kit qua cho thdy hdm lugng cdc ion vd anion cd gid tri khd cao so vdi nudc trong gidng cat, dac biet cdc ion chloride, natri vd tdng khoang vd ca co gia tri rdt cao,
Nudc trong gidng cat noi cdc giing khoi d dia
hinh cao vd trung binh thudng khdng bi nhilm mdn
va sat, noi dupc giu ve sinh tdt khdng bi nhilm
huu CO. Kit qua phdn_ tich cho thdy hdm lugng
(mg/L) SO4'" thuong thdp khodng 7,4-53,5; dg iTi$n
0-0,lg/L; Fe: KPH- 0,25; NH4*: KPH-0,5; N03:
0,36-6,0; TKVC: 200-393. Tuy nhien, cdc giing khoi nm c6 dja hinh t h ^ hay chda gidng cdt thudng b) nhiem ni$n vao miia ndng vdi dp mdn khoang l,7-2,5g/L cd noi din 3,5g/L. Ham lugng (mg/L) cac anion vd ion thudng cao, trong do S04^"
: 274- 395; CT: 209-360; Na*: 118-200; dac biet NH4* vd N 0 3 ' cd gid trj ika lugt la 3,48-9,3 vd 20,1-73,4, vd Fe kha cao khodng 0,78-1,86. Diiu ndy cho thdy ngoai vi^c bi nhilm man, nudc cdn bi nhilm pben va nhilm hOu co.
Kit qua nghien cihi trfin cho thdy tdng chiia nudc trong gidng cdt cd dang thdu kinh nhan lugng nudc mua bd cdp true tiep vao miia mua. Vi v|y nudc ngpt trong thdu kinh gidng cdt cd ngudn gdc tft nudc mua va ndm tren tdng nudc Ig trong trdm tich cdt, cdt - bpt bdi trifeu bSn dudi. Vdo mua mua.
qud trinh bd cap tu nhien xdy ra, khi nudc mua dugc bd cap vao gidng cat thi thau ldnh nudc nggt gia tang va nam ben tren tdng nudc Ig- man ben dudi. Vdo miia nang, khi lugng nudc nggt trong thau kinh gidng cat hi suy giam, tang nudc Ig- man ben dudi se xam nhap len tren lam nhiem man tdng nudc trong gidng cdt. Vi vay, viec bd sung nhan tao ngudn nudc nggt tir he thdng kenh muang vdo gidng cat can dugc thyc hien nham ban che va ngan chan su xdm nhiem nudc Ig-mdn tir ben dudi vao gidng cdt. Tren ca sd kit qud nghien cmi nay, bd sung nhan tao nudc nggt vao gidng cdt cd th6 thyc hien dugc, vi vay can tim ngudn nudc kenh muang an toan khdng bi nhilm hda chat va ndng dugc de bd cap nhdn tao lam gia tang trii lugng nudc trong gidng cdt vao mua ndng.
• - - " ^ V
ThangO4/2012 Thanc04r>013 ^ x. • •' . u - - i - u - TT.- A->iini 1 *= v^'-vij Vl tn gieng khoi va ky hieu
• Thang 07/2012 Thang 10/2013 1 ' ^ ^ ' ^ Thang 10/2012 ^
. / \ ^ Dia hmh giong cat
Hinh 4. Thay doi mg-c nud'c giong cat a. tuy^n T 1 , b, tuyen T2, c, tuy^n T3, d. tuyen T4
4. K^t lu$n
D{lc diim tram tich vd sy phdt tnen cua h?
thdng gidng cdt huypn Cau Ngang vd Tra Cii da dugc xdc dinh. Hf thong gidng cat hinh cdnh cung
phan bd phd bien d khu vyc nghien cuu theo
hudng tay bac - ddng nam, dia hinh cao, thanh
phdn chii yeu la cat mm hat vdi dien tich khoang
6.785 ha. Cdc loat gidng cdt chi thi vj tri. hinh dang
vd thcfi gian thdnh tao dudng bd bien cd cd tudi tir
1371620 din 770 Ntht tren co sd ket qud phdn tich tudi OSL.
Tdng chiia nudc trong gidng cat cd dang thau kinh, dugc bd cdp ty nhien tii ngudn nudc mua nen lugng nudc thay ddi theo miia trong ndm. Thay ddi muc nudc khoang l,8-2,6m gifla miia mua va mua ndng. Nudc trong gidng cat la nudc nggt thugc loai hinh bicarbonat- chlorua- natri dugc ngudi dan dia phuang sir dung an udng va sinh boat. Vao mua ndng, khi khai thdc mdt lugng Idn nudc trong gidng cdt thi nudc Ig ben dudi se xam nhdp vd nhilm man nudc trong gidng cat.
Gidng cat d khu vyc ven bien Id tdi nguyen dac biet can dugc quan ly vd bdo ve, dac biet trong bdi cdnh bien ddi khi hau, ngudn nudc sinh hoat viing ven bien ngay cdng khd khdn. Khi gidng cat bi khai thdc vd pha hiiy, the tich gidng cat bi gidm thi khd nang chiia nudc ciia gidng cat se bi suy gidm lam gia tang nguy co nhiem man nudc trong gidng cdt.
Ddy Id mpt phdn ket qua nghien ciiu de tai VAST05.05/12-13, chiing tdi xin chdn thanh cam on Vien HLKHCN Viet Nam da cap kinh phi vd tao dieu ki?n thudn lgi thyc hien nhiem vu nay; ddy cung la mpt phan ket qua de tai ma sd 105.01- 2012.24 Quy NAFOSTED; cam on Cue Dia chdt Nhdt Bdn (AIST) giup xac dinh tudi nhiet huynh
quang thatch anh (optically-stimulated luminescence) OSL ciia ttim tich gidng cdt.
TAIUBUDAN
[1] Fontaine, H.. 1970: Trace d' un ancien rivage marin a Cai lay (du Vietnam). Archives Geologique, Saigon Vietnam 13, 147-154.
[2] Nguyen Van Lap. Ta Thi Kim Oanh, Tateishi, M., 2000: Late Holocene depositional environments and coastal evolution of the Mekong River Delta, Southern Vietnam. Journal of Asian Earth Science 18, 427-439.
[3] Tg^ Thi Kim Oanh, Nguyin Vdn Lap, 2006:
Tudng trdm tich Holocen tuang img vdi dao dong myc nudc bien vimg VTnh Long - Trd Vinh, Ddng Bang Song Cuu Long, Tap chi Cac Khoa hpc ve Trai Ddt, T.28, 3, 329-335'.
[4] Tq Thi Kim Oanh, Nguyin Vdn Lap, Huynh Thi Thanh Tdm, Nguyin Thi Mong Lan, Phgm Cong Luyen, 2012: Trdm tich gidng cdt huyfin Duyen Hai tinh Tra Vinh va tien hda Holocen chau thd sdng Cuu Long, Tap chi Cdc Khoa hge vi Trai Ddt, T.34, 3DB, 335-340.
[5] Sd Tai nguyen vd Mdi trudng tinh Trd Vinh, 2010: Ban do hien tr^ng su dyng ddt tinh Tra Vinh nam 2010 tyle 1/25.000.
Sedimentary characteristics of sand dunes in Cau Ngang and Tra Cu Districts, Tra Vinh province and their freshwater - bearing capacity
Sedimentary characteristics of sand dunes and related deposits in Cau Ngang and Tra Cu Districts, Tra Vinh province are clarified to confinn fres h water-be a nng capacity In the study area, 05 OSL ages of sand dunes are dated from 1620 ± 90 years before present (BP), 1590 ± 90; 1100 ± 60, 970 ± 50 and 770 ± 40 showing the sand dune system of this area had been evolved in progradation of Mekong river delta in late Holocene.
Distribution features of aquifer in sand dune in Cau Ngang and Tra Cu are identified on the base of sedimentary structures of sand dunes and surrounding deposits. Aquifer in sand dune with lenticular fonns is recharged naturally by rainy water so the water volumn is changed upon the season The change of water level is appoximately of 1 8 -2.6 during dry and wet seasons Freshwater-beanng in sand dune is Bicarbonate-clorur-natnum. In the wet season, rainy water is natural recharge source; in the dry season, fresh water from canal or small nver would be good artificial recharge source to increase groundwater reserves
