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<br />
<br />The lhree most l.:o01mon]) dl..,tccted herbicides at the two agricuhural monitoring sites in the L'COL (one sill.'
<br />each inlhc Grand and Uncompahgre Valley~) also were among the lOp 10 herbicides detected in surface-water
<br />samples at 61 agricultural "ill.''' in 35 nationally di<;tribulcd ;">.:AWQA Study Units. The percentages of samples
<br />with detections for atrazine. ;lIaclllo(. and mctolachlor are shown beluw and are oast-.J on llIore than 1.550 sam-
<br />ple., for the national sites and 39 samples at the L:COL ..ill'S. Alrazine. alachlor. and mt"lolachlor are commonly
<br />w_ed fliT weed control in corn. Alachlor and metol;H.'hlor arc also u..ed for weed control in dry ~all". Other herbi-
<br />cides Ihal wefe frequenll)' dCICi:tcd
<br />(presentlll OWT onc-third of the ...am-
<br />pIt's) in the veOL but not shown in
<br />the gmph incluue tritluralin. DCPA.
<br />~A-D, cyanazine, and deethylatrazine
<br />~ (a breakuown product of atrazine).
<br />0.045 a::
<br />Z uJ These herbicides also were commonly
<br />0.040 0 l-
<br />;::.;:; detected at other agricultural ~ites
<br />. ~
<br />0035 a: w across !he l\ation, ~lcdian l.'oncentru-
<br />, ~
<br />0,030 ~ ~ tions of the commonly delected herbi-
<br />0,025 5 ~ ddes in Ihe UCOL were less than or
<br /><.) 8 similar 10 (he median concentralion...
<br />0,020 Z a:
<br />.0- u for Ihe nalional sites. Concelllrations
<br />0,015 ~
<br />~ of atrazine and metolachlor were less
<br />0,010
<br />than the Canadian guidelincs for the
<br />protectirm of aquatic life 11.& 1lg!L for
<br />atrazine and 7.8 ~lglL for metolachlor
<br />(Environment Canada. 1999)]. Guide-
<br />lines have nOI been established for
<br />alachlor.
<br />
<br />"'v-~
<br />
<br />...
<br />~
<br />N
<br />~
<br />
<br />EXPLANATION
<br />CJ 62 Agncullufe srtes l,om NAWQA Study Unrts
<br />OJ 2 Agncult1Jre 511e& from the UCOL
<br />. Median concentrahon
<br />. Me<han iess than 0,002 j.lgtL
<br />
<br />. I
<br />I ~ I
<br />I
<br />I , ,.-
<br />, ,
<br />I ,
<br />, - I
<br /> I .
<br /> , ,
<br /> I
<br />I ,
<br />I . .' : -
<br /> ,'. .
<br />
<br />90
<br />
<br />r
<br />~
<br />
<br />eo
<br />
<br />~
<br />~
<br />w
<br />~
<br />~ ~
<br />~ z
<br />~ Q 50
<br />" ~
<br />old
<br />&!i:i 40
<br />~ 0
<br />z
<br />w
<br />"
<br />~
<br />w
<br />~
<br />
<br />70
<br />
<br />60
<br />
<br />30
<br />
<br />20
<br />
<br />"
<br />
<br />o
<br />
<br />Atrazine
<br />
<br />HERBICIDE
<br />
<br />w.llcr ,.1I11pk, fftlm thl' :-ame :'IIC'.
<br />Ph1hahly l1el..ause thl'...l' nmlpllunu,
<br />arl' rd:lli\"el~ m...\lluhlc m \\atl'r.
<br />lkl.urTl.'nl'e of organlll"hlorine pc'-
<br />Ill..'idl'''. l.\en al hI\\' CllIll..l.'ntration...,
<br />i.. Ix'cllming Inaca:o.lIlgl~ rl'k\':lnt
<br />1x'l..:J.lhc of re...'enl evidence linking
<br />the..e t'\lmpounJs 10 enuex.'rine Ji.,-
<br />n1ptiolltGlloJhrl'd and (lther"
<br />1997l.
<br />
<br />:o...Ulrknt COlIl'l'ntralinn... in
<br />...tn'mn... Olnd ri\l'r~ rl'lll'l't puint
<br />and Illlllpoinl :-Olln.l'''i, :'\:ltlOnal
<br />background ":l'IKenlfation.. have
<br />been dt"ll'nnined for 'Otlll' form.. l)1
<br />nutrienl< 1l11~llllItwgen in "rream..
<br />{I,O mg/I.!. nitr:ilL' III ,tre:1m.,
<br />(0,6 mg,'Ll. and Illt:.!1 phlhphoru.. in
<br />
<br />0050
<br />
<br />0,005
<br />
<br />o
<br />
<br />AJacttlor
<br />
<br />Metolachlor
<br />
<br />,{re:1m, (0,1 mg/Ll (U,S. Gcologi-
<br />cal Sur\cy. 1l.J99). Kelall\"l' ...mll.cn-
<br />tration:o. of nulrients III ...urfilce
<br />watl'r are IinkeJ !11thI.' amount-. and
<br />type" Ilf ...uh..tance, u...l.'d and UiS4
<br />...'har!;t'd in difkrl'nt Ianu-u..l' ,el-
<br />ling.... The...e ..utl..laIKe... can Ihen
<br />real..h thl' ...trcam through poilll
<br />..lIUrl.'e..l...u..:h:1'" wa...ll'\l;ller Ji....
<br />char,gclllr nonpoinl ...our..:e~ (...ul'h
<br />a... prcl'ipit:llion or runoff (Will agri-
<br />cultural area...!. E...tm1ated amllunb
<br />01 fertiliz.cr applied during 1997 in
<br />Ddta, ~Ie...a. and ~tontrme COlln-
<br />tie,.. \\t"rt" al:lolll 1-l,IOO.OOO pounds
<br />l,f IlItrogen and I.SOO.OOO pound..
<br />l'( pho...phoru, dcffre~ Stoner.
<br />U.S Geol\lgil."al SUf\'e~. wrinen
<br />
<br />L'OlllIllUII., ~oooJ. Fertili/er use in
<br />the...l.' c(luntie... aC("(lulHl'd for aDout
<br />77 pcrcl.'nt llf thl' tlltal e"tim:Hl'J
<br />fi.'rtililr.:r usage for the UCOL.
<br />:\ulril'nt l'lltln'ntroltioll_'" in
<br />ana... llf agrkultural !ollld m.t'
<br />l\crl' ~clIl'rall~ gn'atl'r than in
<br />an.'<J"i of olhl'r hllld l"'C!I. ~ledi:1n
<br />c,lncelllrauun' llf amtlllmia. nilrile
<br />plu' nitrate, liltal phmphl1ru..., uis.
<br />'\lln:d ph(l..plwru:o., and l'rtlwphlh-
<br />phJtC' \\ ere gre:ltt"r :1t agnculture
<br />sill'.. than :It Ihe C\lh'r:1do Plateau
<br />referl.'nce and mixed land-u~e ~itt"..
<br />Itig. l-l). The CilloT.lll,' Plalcau
<br />referenct" ,jle ha.. some limiled
<br />agrkulture upstream 11i\'C'stodJ
<br />ha) meJdl.l\\'I. ,\.1 i~ nN repre!'.elHa-
<br />
<br />~l:1JI.)r Finding... 17
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