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<br />
<br />Pc d0d:. c. sar;,::> i :'(l~ 0 f su r face :;;ot I and veg~ta t ioa ia
<br />.<;uo;Jl?::.nE. m~.:tdo~:, spruce, and 3spen cOl:lr.:uniti~s \.Ias
<br />carried out along five transects in the target ar'ea
<br />in an atten?t to deccr~ine th~ dispositio~ of silv~r
<br />~od:ce nucl~a~lnp. ~?ent used in the Sa~ J~an sno~ au
<br />r.tentation pr'ojcCL San? es 0 0 lage, Hter. an
<br />soil ~ere r~~en at several elevations along the tran-
<br />~ects, ~hen ?ossible during spring and fall, tc allo~
<br />;;'10::i:.,)r1:1'>; DE :::;ilvt..'.r COn~ent and silver :nover:lent in
<br />the target a:ea. To gain a~~ditional infot::lation on
<br />silver dynar:l1cs. laburatory studies of silver ~ove-
<br />~ent 1n soil col~~,~ ~nalyses ot silver d1SpOSitlOn
<br />and mover:leat 1n the ,,7Lcinity ot ground based genera-
<br />tor sites. and analyses of available data on silver
<br />in water and SnO\.l \.Iere completed. Ihe available data
<br />sh01.l no slgnlt1ca:lt Increases 1.0 silver content IJere
<br />detected on the t~:~~t area, and in soce cases, Sllvet
<br />levels in sa~ples C~~cn at the end of the monitoring
<br />appeared to be lo~~~ than in samples taken at the be-
<br />~innin~ of the pro~r3~. Silver tends to be reta1ned- .
<br />in surface SUll a::d'rftcer. though SOr.:;e cOllement to
<br />subsurface soil W.'l.S '':;:lserved. Sil\'~~ :.ontent of
<br />strea::lflo.... did not l:"\..;lcate trendS-I:-' :~.ilver content
<br />-1.Ihich could be 3ttr~~~~~d to the se~. Z prograo,
<br />
<br />t:HROOr.;CT!ON
<br />
<br />Theoretical consid=r3tions of the behavior of silver
<br />iodide indicate a 10.... solubility of the cocpound and
<br />an extreme probability of rapid im::lobUizatioa in the
<br />soil system. These point to unlikely ecological L~-
<br />pact, but it \Jas considered necessary to undertake a
<br />monitorin~ progra:n on the target area to det.ermine
<br />1.Ihethe~ addi~ions of seeding ~aterial could be de-
<br />tected, and ~hether seeded mater~al could be taken up
<br />~y the major plant co~u~ities on the carget area,
<br />
<br />Objectives
<br />
<br />'..y L To measure the level of silver in the terrestrial
<br />l' ecosystems of the target area on a periodic basis. in
<br />order to determine whether increases of silver can be
<br />de tee ;:.ed.
<br />~ 2. To evaluate silver disposition surrounding seeding
<br />generator sites, to determine possibl~ movement or
<br />silver through physic3l and biological process~s.
<br />~ J. To study silver movement through soils in labora-
<br />tory systems, to better understand what influences
<br />seeding agent acc~ulation.and movement.
<br />t!.. To analyz.! areal and tee:poral trends in silver
<br />concentration at Sno~ and streamflow in the target
<br />area from available non-experimental data.
<br />- Sec+.o"S O....:Tre.A-
<br />'Ca~tLusIO~S
<br />
<br />T!lrce v~ar';; ':oni::or:in~ of silver conc~ntrations i:1.
<br />:clia~e, lit:er. and soil of aspen, spruce, and ~r~3s
<br />("o....~,,,~:~ies in the: San Juan tar;;:et area at cne t.pp~::-.
<br />Colorado River Pilot Project ha3 shovn no si~niticant
<br />cnan~es i~ these concentrations over the period or
<br />s3o?!ing. An analysis of sample nu~ber9 requir~d to
<br />detec:: annual additions of 0.002 to 0.006 pp::n dt7
<br />~~igh~ of silver from cloud seeding to s~ruce littce,
<br />indicaces that detection of the lower annual addition
<br />
<br />L'.'.J~.L' .'.S .:.. S::::T .;:-:
<br />
<br />.... _j I
<br />..,.-.,,'
<br />
<br />.:-~.:: r~:-.. ;,;:~: .." .... .'
<br />
<br />;,:'.;1:".
<br />
<br />~ould require a~out 200 samples per year for 5 year3
<br />a~ the 95 percent confidence level for each com?on-
<br />ent. If the variance of silver concentratIon can be
<br />reduced froc 0.08 to 0.02 pp~ the pr~sent sao?ling
<br />program s~ould be adequate to detect an annual addi-
<br />tion of 0.002 ppo after 4 years. At the pagasa
<br />Springs ger.e~ator site No. 25 silver l~vels in
<br />foliage, litter, soil, and grass in spring 197J,
<br />were generally slightly lo~er than intspria& 1972,
<br />but still sooewhat higher than before seeding coro-
<br />~enced in fall 1970. Concentrations showed a gen~ral
<br />decline fro= ~xi~um levels at 10-20 m; to background
<br />levels at abou~ 200 0 fro~ the site.
<br />
<br />Mean values of silver concentracions on the target
<br />area shov t~at spruce litter (0.18 ppo, ash basis)
<br />and foliage (0.17 ppm, ash basis) have' significantly
<br />higher silver concentrations than spruce soil (0.08
<br />ppo, ash oasis). On a dry IJeight basis, silver con-
<br />centration in soil is si~nificantly ~reater than 1n
<br />folia e in all three ve etatiOn types. A
<br />season a tren or 51 lIer concentratlons-rn
<br />both soil and vegetation indlcated higher concentra-
<br />tions ~~~- 'lpring tban in fi');'- istbates of total
<br />~- -.-, the forest ecos;:"" :;~ indicate that the top
<br />60 cm uE soil contajn the 0~tk of the silver, about
<br />700 tines that in seeded 50;1.1 and 2000 times that
<br />present in the folia~e. Foliar vashing ind1cated
<br />slgn1~1cant sur:ace aeposition. S~ll pilot tests
<br />of soil leaching a~d plant uptake processes indicat2c
<br />strong rooe adsorption of silver and inhibition of
<br />plant u?cake.
<br />
<br />AlthQugh s~ver concentrations io snow.1.Iere found to
<br />be tOO variable to shov statistically Si&nl!lCan~
<br />differences betveen sites in the target area and
<br />ochers to t~e vest and east or it, toe oean SlLV~~
<br />concentr~:ion in s~ov on the tar~et a=23 1S aoout
<br />twice l~ hi~h as <he doyovind mean, and three ti~es
<br />as hi .,~' as the up....L::d ~ean. Ioca! seeding inten.::1it.j
<br />~:'i Agl burned by all generators per oonth)
<br />~as no: a good predictor of silver conc~ntratio~ i~
<br />sno~ at ~olf Creek Pass. No si~nlficant differe~c~~
<br />in silver concea:ration of strea:llflo'-' could be ro'.!nd.
<br />bet~een 5 stre~ i::clucing J O~ the t~rset ar~a and
<br />2 to thl;: :..;e5: lU;N1nd) OC it. ~:~':1O ann\.!al s:.l'.re=
<br />conc~ntratio~ tor tne (lV~ streao~ increased fro~
<br />(0.1 = C.)} x 10-10 & /~l in 1971 to (0.6 r 1.1) x
<br />10-:0 g Iml ~n 197).. P.owever. ~ean ~~t~i~ conv~~siQn
<br />Jischar3e alSQ i:creased from 2.9 O)/5~C (103 cfs) in
<br />1971 to ~.5 oJ/see (160 ers) in 1973. ~~though a
<br />~~la~i~n~hip ~~~io~sly exists bet~een d!scha=ge and
<br />silver con=e~:raticn tn individual s:reams, no
<br />~~n~r~l ?re~~ctive ~oc~l could be d~velu?~~ b~:~e2r.
<br />ch~ t~o pa.~~~:er.::1.
<br />
<br />:;,:a:::'~::-..J::..~.-.~ -:!.::.~l. ,_. ::h~ =.0'1.~~.:~: .:r .;:l.'.'~.: :r'J:":
<br />~~iv",c i..;dic.!.e :~r'1u;h 3. >.:Iil colu=Jn ....J.~ .;;c\......:,:,:.:.'.;
<br />,}r1C t~.::1ted. ~.t indica::es :h3;: the silver concentra-
<br />~ioc 'in ::he soil solution at any given ti:ne is best
<br />:epce.::1ented by a ~inetic-type reaction, :oupled ~ith
<br />an insig~ifi:.~nt ~quilibriUQ-type reactioa. A high
<br />3dso~?~ion ra:e con3tant controls the initial
<br />reaction, but 10 to 30 percent of input siLver con-
<br />ce~tration Is likely co cove through the profile.
<br />
<br />ur ~r:o'~';>.!c.;. .lut;:;,!~:l.t:Jt~0r: Ln
<br />C~lor<ld.) SC<1=~ ~r,i.... ?ub~,.
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<br />,t Pr~gect ~JJre~s:
<br />-
<br />
<br />..... and J. D. ryes (Eds.). 197<;. E:c.Jb.~i-.::,,1 ..........__"
<br />Cotoradc. Soan JU.:in C:col<J5i' ?r.Jjec=. Fi.nal ~i:?lJr~.
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