Ngliien ciiu - Trao (
Danh gia thiet hai gd rimg ngap man Can Giof do Ghat diet c6 cua quan ddi Mjf sur dung
trong chien tranh of Viet Nam
O PHAM VAN LOt, BUt HOAI NAM Vidn Khoa hgc Mdi trudng NGUYEN HUY DUNG, T R A N V A N CHAU
Vidn Diiu tra Qui hoach ritng
T
rong cudc chidn tranh xam luge cua qudn ddi My tai mien Nam Viet Nam tif ndm 1961 ddn nam 1971 da tien hanh mgt chidn dich ddc biet mang mat danh Ranch Hand, trong chidn djch nay quan ddi My da thuc hien hang loat cdc phi vu rai chai dgc hda hgc huy diet ritng, dat ndng nghiep. Hdu qua cua chat ddc hda hgc dd lai la rat Idu ddi, sau han 40 ndm gan 4 trieu ha rimg, hdng ngdn hecta ddt ndng nghiep bj nhiem ddc vdn chua canh tdc duoc, nhidu vung dd't van dang bj d nhi^ nang ne.Mac dd cdng tac khac phuc hdu qua phuc hdi cdc vung dai va rung bf anh hudng chdt diet co (CDC) da vd dang duac Chinh phu Viet Nam quan tdm nhung do cdn thidu cdc ca sd khoa hgc dd tinh todn va lue chgn gldi phdp khac phuc hieu qua thi viec xdc dinh thiet hai Id het sdc quan trgng. Trong chuyen dd ndy, chung tdi tien hanh dp dung phuang phdp ddnh gia thiet hai true tiep vd thiet hai gidn tidp da dexudi ddtinh todn thi diem cho ri^g ngdp man Can Gid biphun rai CDC cua My. Titdd danh gid phuang phdp dp dung vd bd sung hodn thien nham dp dung tinh todn toan bd cho cdc rimg ngdp man bj phun rai CDC cua toan mien Nam, VietNam.
Phirong phap ddnh gia thiet hai
T r o n g khudn kho d d tai c a p Nhd nude thude C h u o n g trinh KHCN-33/11-15, de tai dp d u n g p h u o n g phdp tinh todn thidt hai da d u p c nghien cCfu de xuat: Si!f d u n g p h u o n g phdp c h d n g xdp ban do S D D 1/1.000.000 trUde vd s a u thdt ky phun rai C D C t r o n g chien tranh vdi ban do
phun rai CDC d l xac djnh didn vd tfnh t o d n thiet hai tryc tiep {tru" lupng go), gidn tiep. Ket hpp dp d u n g phuong phdp danh gia thay doi trijf lUpng cacbon tai hai thdi d i l m khdc nhau glijfa 2 thdi d i l m 1965 va 1990 d l ti'nh toan thiet hai cacbon tai rCfng ngdp mdn (RNM) Can Gid CI TP. Hd Chl Minh do CDC cOa My si!r dung trong chien tranh d Viet N a m .
Dac diem Huyen C i n Gid Can Gid Id mdt huyen ven bien, vdi dien tich 70.422 ha.
Dien tieh rUng chii yeu cCia huyen la RNM vdi dien tfch la 48.891 ha, chiem 69,4% tong dien tich t u nhidn.
Qua ket qua chdng xep ban do gial doan 1965-1990 cho thay bien ddng cOa cac loai dd't, loai rUng tren dia ban huyen Can Gid,
Tai n g u y e n v g Mdi t r a o n g | Kyi-Ttiang 12/2015 2 1
Nam 1965 10 15 16 17 Tong
Bang 1-Biin dong cAc loai 6it, loai nmg giai doan 1965-1990 (Bon vi tinh: ha)
Nam 1990 10
26597.39 3354.66 1775.62 31727.67
14 3157.47 96.05 243.36 3496.88
15 6571.02 3743.52 2611.18 12925.72
16 119.47 72.13 62.82 254.42
17 5954.34 554.57 1083.06 7591.97
Tong ^ 42399.69
7748.8 72.13 5776.04 55996.68 Ngu6n: Vien BTQHR-2014.
BSng 2. Dien tich, i<h6'i luang g6 bi thiet hai do CBHH TT.
1.Dien tfch (ha)
2.Truf luong trung binh (mVha) 3.T6ng khdi ludng thiet hai (m^)
Nhdm loai cay Dirdc 21200
111,3 2359560
Nhdm cac loai cdn lai cua RNM 21200
50 1060000
Tong 42400 3.419.560 RNM giam tU 48.891 ha ndm
1965 giam xudng cdn 35.784 ha ndm 1990 (tUc Id mat 13.107 ha rCmg tuong duong giam 26,8%
dien tich), sau khi da cd 12 ndm trdng va phuc hdi tu nhien rCfng ngdp man trong todn vijng.
Dien tich bj rai CDC tren dja bdn cCia huyen Id rat Idn vdi 42.399 ha, chidm 86,7% ting dien ti'ch, trong do didn tich bj rai cd mat dp eao la 37.798 ha, chiem 77,3 % dien tfch bi rai CDC. Vdi ddc diem ciia RNM la rat mdn earn vdi cdc loai CDC, ndn ddi v6i RNM da bi rai CDC thi gan nhu toan bd cay rUng se bj chet trong lan rai dau tien. Nhiimg dien tfch rCfng da bj rai nhieu iin thi he sinh thdi rUng tai do hau nhu bi phd hCiy hodn todn.
Sd lieu thdng ke dien tfch cdc loai dat, loai rUng ndm 1990 eho thd'y, tdng dien tich RNM ciia huyen Can Gid la 35.874 ha.
trong do didn tfch bj rai CDC cd
31.728 ha va 4146 ha dien tfch rUng tren dat khdng bj rai CDC.
Bien dpng dien tich cac loai dd't, loai rCmg giai doan 1965-1990
Didn tfch rUng bien ddng do chuyln doi muc dfch SDD trong vung 6i phdt trien KT-XH, mdt sd dien tieh RNM, ritng nude lp, rCrng DUa nude, Mai dam...
chuyln sang dat ndng nghiep, dd't nudi trdng thOy san... Do vay, dien tfch RNM trong vung tuy da dupc trdng mdi vd khoanh nudi phuc hdi, nhung dien tfch RNM van ft hon dien tich ndm 1965.
Cdsddetinh thiet hai Kdt qua danh gid qua anh ve tinh va thue dja cho thay, dien tfeh RNM bj rai CDC cCia My trong ehien tranh Id bj ehet hodn todn, do vay toan bd dien tfch RNM bi rai CDC 6 Can Gid dupc tfnh Id dien tfch rang bi phd hOy hodn todn. Dya vdo ket qua nghien eUu ciia Vu
Vdn Cuong (1964) ve cdu true thanh phan lodi RNM Can Gid, cd the thay loai DUdc chiem khoang 50% trong to thdnh cac lodi cay RNM Can Gid. Ddy la CO sd de tfnh thidt hai do anh hucJng eCia CDC.
Tinh dien tich rCfng bj pha huy do CDC
De tfnh toan lupng gd da bj thiet hai do CDC thi vide tfnh toan thidt hai tryc tiep dua vao viec chdng xep ban do 2 thdi ky, da tfnh dupc lupng gd eOa moi trang thai rUng bj thidt hai. Lupng gd h\
thiet hai gidn tiep thdng qua qua trinh tfch luy tdng trudng ehi tfnh cho 1 chu ky phuc hdi rimg vdi thdi gian 20 ndm la hpp ly, phiJ hop vdi pham vj 1 xa trong dilm bj rai CDC.
Theo ket qua bang 1, didn tfch rifng bj rai CDC eCia huyen Can Gid Id 31.728 ha, bao gom dien tich bj rai ci 3 mat dd cao, trung binh, thap. Do gid trj vd khdi lupng khdc nhau, nen dya 2 2 Tai nguydn VQ Moi trudng | Ky 1 - TMnfl 12/2015
B i n g 3. Thl$t hai gia tri cac bon do mSt rimg ngap man STT
1 2 3
Thiet hai Mat rUng hoan to^n Mat lupng tang trudng ciia rUng
T6ng cong
EF 115 26.2
Dien tich (Ha)
13107 13107
Tong C02e (Tan)
1.507.305 343.666 1.850.971 vao to thdnh lodi de tfnh khdi
lupng ci^a eae lodi. Ddi vdi RNM, ehOng tdi chia lam 2 nhdm: Nhdm gd Dudc va nhdm cde lodi cdy g5 edn lal. Theo ket qua nghien cCfu cCia Phdn Vidn Dieu tra quy hoach rUng Nam bd, trCr lupng trung binh RNM la 111,3 m3/ha; trQ lupng gd ciia cdc loai khac trinh binh Id 50 m3/ha.
Dua vao anh vd tinh vd thuc dja cho thay, dien tfch RNM bi rai CDC Id bj chdt hodn todn, do vay thiet hai trUe tiep do CDC gdy ra chfnh Id todn bd dien tfch rUng bj chet hodn todn. Vi vay, lupng go bj thiet hai la tryc tidp se dddc tfnh CI bang 2 nhu sau:
Khdi lupng gd bj mat gidn tiep do mat lUpng tdng trUdng eCia rCmg: Qua kdt qua tfnh todn suat tdng trudng ldm phan viing Ddng Nam bd, vDng DBSCL cho thay, suat tdng trudng bien ddng Xit 1,3% - 1,8%. Trong tfnh todn lupng gd mat do t9 Id tdng trudng, ehOng tdi dijng suat tdng trudng binh quan ehung lam phan Id 1,4% vi trong qua trinh sinh trudng cd xuat hien lupng go mat do dao thai ty nhien, khd dd, khai thac.
Khdi iugng thiet hai gidn tidp
= 3.419.560 m3 x 1,4 (%) x 20 ndm = 957.477 m^
Nhu vdy, thidt hai ve khdi lupng gd RNM huyen Can Gid do CDC Id bang tong khdi lUpng go
mat hoan toan cdng vdi khdi lupng go mat glan tiep se tfnh dupc la khoang 4,3 trieu m^.
Dien tich rCmg va dat rimg bj tan pha do CDC can phuc hoi Ap dung phuong phap chi phf d l tfnh gid trj thidt hai ddi v6i dat khdng the trdng rUng do bj CDC. Odi vdi trudng hpp nay se thdng ke dien tfch dat khdng trdng rUng dupc eho tUng dja phuong d l tfnh thiet hai quy d l i thdnh tien thdng qua tfnh gia thanh 1 ha cdy dUng ciia trang thai rirng vide phue hdi lai he sinh thai rUng, neu nhu trong dia phuong dd cd didn tfeh dat loai nay. Gid trj didn tfch khdng phuc hdi dupc se tfnh theo gid phuc hdi rUng ty nhien hodc lay theo don gia d l trdng 1 ha rifng cdy ban dia.
Theo thdng ke dien tich RNM bj pha hCiy hodn toan dung bang didn tfch rUng bi rai CDC la khoang 42.000 ha. Ddy la co sci d l tinh thiet hai.
Tinh toan thiet hai trQ*
lupng cac bon
Trdn eo set ket qua tfnh todn trit lupng CO2 cde trang thai rUng bj phd hCiy hodn toan, ket qua tfnh trtJ" lupng thiet hai cdc bon dupe the hidn ci bang 3:
Qua ket qua bang 3 cho thay, ting thidt hai tru lupng cdc bon rCfng ngdp mdn Can Gid do CDC tinh dupc la khoang: 1,8 trieu tan C02e.
Ket luan
Phuong phap danh gia thiet hai tdi nguydn rUng cay go d l danh gid tai cde vung bj anh hucfng eCia CDC Id co cd s6 vd hoan todn cd the dp dung dupe va da danh gia thidt hai ddi vdi gd rUng ngdp man tai huyen Can Gid. Ket qua dd tfnh todn 6\igc dien tfeh rimg bi CDC pha hi!iy hodn toan Id 42.400 ha, khdi lupng go bj thiet hai Id khoang 4,3 trieu m^. TrQ lUpng cacbon bj thiet hai la khoang 1,8 trieu tan C02e trong giai doan 1965-1990.
Tai lieu tham khao 1. Phijng TCfu Bdi, Iran Qude Dung (2004), Danh gid tac hai eOa chat ddc hod hge dd'i vdi tham thuc vdt rimg vCing trgng diim - De tai ed'p Nhd nude.
2. Nguyen Xudn Cy (1986),
"Mpt sd dac trung hoa hgc cOa dat Feralit vang do va dat phii sa thung lung A Ludi, Binh Tn Thien nhtfng hdu qua cija CDHH ddi vdi dp phi cda ddt". Bao cdo HTQG lan 2 ve chat khai quang, diet CO.
Nguygn Huy Dung va cdng su (2013): "Xay dung phuang phdp, danh gia thiet hai vi tdi nguyen rCfng, ndng nghiep, da dang sinh hgc bj anh hudng cOa chat dpc hda hge st? dung do My sd dung trong chidn tranh Viet Nam".m
Tai nguyen yg Mdi tradng | Kjfl-Tiling 12/2015 2 3
