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<br />Appendix to question No. 8-d
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<br />Periodic samplin~ of surface soil and vegetation in
<br />sub31pinc meado~. $yrucc. and 3spen co~unities ~a~
<br />carried OtiC" along five transects in the target area
<br />in an attenpt to dete~ine th~ disposition of silver
<br />~odide nucleacinR agent used in the Sa~ Juan snoy au
<br />mentation project. Samp es 0 0 13ge, ~tter. an
<br />sOLI ~ere taken at several elevations along the tran
<br />sects, when possible du~ing spring and fall. tc allo~
<br />:nonit"rill';; of silv~r content and 5ih'e. movement in
<br />the target area. To gain a_~ditlonal information all
<br />silver dyna~!cs, laboratory studies of silver Qove-
<br />ment in 5011 collli~5. analyses ot silver disposition
<br />and rnavecent in the ~lClnity at ground-based genera-
<br />tor sites, and analyses of available data on silver
<br />in uater and snow ~ere comp1eced. The available data
<br />shou no si n.lt1cant increases in silVer content uere
<br />detected on the tar~~t area, an n soce cases, s vel
<br />levels In samples ta4en at the end of the monitoring
<br />appeared to be 10~~r than in samples taken at the be: .
<br />~innin~ of the prograc. Silver tends to be retained
<br />in surface soil and lTtter. though some movement to
<br />subsurface soil was ooserved. Silve~ ~ootenC of
<br />streamflow did not .l.nJicate trenaSTr"-~~i1ver content
<br />-which could be attobuted to the see-:::-: ,g program.
<br />
<br />INTRODUCTION
<br />
<br />Theoretical considerations of the behavior of silver
<br />iodide indicate a low solubility of the co~pound and
<br />an extreme probability of rapid immobilization in the
<br />soil system. These point to unlikely ecological im-
<br />pact, but it ~~s considered necessary to undertake 3
<br />monitoring program on the target area to determine
<br />~hethe~ additions of seeding material could be de-
<br />tected. and whether seeded material could be taken up
<br />by the major plant cornrnurities on the target area.
<br />
<br />Objectives
<br />
<br />.v L To lIleasut:e the level of silver in the terrestrial
<br />l' ecosystems of the target area on a periodic basis, 1n
<br />order to determine whether increases of silver can be
<br />detected.
<br />~ 2. To evaluate silver disposition surrounding seeding
<br />generator sites. to determine possible movement of
<br />silver through physical and biological processes.
<br />~ 3. To study silver movement through soils in labora-
<br />tory systems. to better understand what influences
<br />seeding agent accumulation ,and movement.
<br />~ 4. To analyze areal and te:mporal trends in silver
<br />concentration of snow and streamflow in the target
<br />area from available non-experimen~al data.
<br />- Sec+"o""S O...:'1t'ed-
<br />. CO~"tLUSIO~S
<br />
<br />Tht't:c v~ar's '::!.onitorina of silver concentrations i!l
<br />~cliage, litter, and soil of aspen, spruce, and grass.
<br />c-o;nr:.m:1.ities in the San Juan tan:et area of toe lJpper.
<br />Colorado River Pilot Project has shown no significant
<br />chan~e5 iro these concentrations over the period of
<br />sanpling. An analysis of ~ample nu~bers required to
<br />detect annual additions of 0.002 to 0.006 ppm dry
<br />~~tgh~ of silver from cloud seeding to spruce litter,
<br />indicates that detection of the lower annual addition
<br />
<br />would require about 200 samples per year for 5 years
<br />a: the 95 percent confidence level for each compon-
<br />ent. Ii the variance of silver concentration can be
<br />reduced froo 0.08 to 0.02 ppk the pr~sent sa~pling
<br />program should be adequate to detect an annual addi-
<br />tion of 0.002 ppm after 4 years. At the Pagosa
<br />Springs generator site No. 25 silver levels in
<br />foliage, litter, soil. and grass in s~ring 1973,
<br />were generally slightly lower than inlspring 1972.
<br />bu~ still so~ewhat higher than before seeding com-
<br />menced in fall 1970. Concentrations showed a general
<br />decline fro~ ~xi~um levels at 10-20 m, to background
<br />levels at about 200 m from the site.
<br />
<br />Mean values of silver concentrations on the target
<br />area show that spruce litter (0.18 ppm, ash basis)
<br />and foliage (0.17 ppm. ash basis) have significantly
<br />higher silver concentrations than spruce soil (0.08
<br />ppm, ash basis). On a dry weight basiS, silver con-
<br />centration in soil is siKniflcantlv Kreacer than 10
<br />f~lia e in all three ve etation types. A
<br />seasona tren or s ver concentrat~ons-rn
<br />both 5011 and vegetation indicated higher concentra-
<br />tions 'ia-,o:;pring than in fa.;.:. istimates of total
<br />~-.:~l the forest ecosy'.:~;;ms indicate that the top
<br />60 cm of soil conta~n the t~lk of the silver. about
<br />700 tices that in seeded sno~ and 2000 times that
<br />presen= in the fo1ia~e. Foliar washing indicated
<br />s1gn1t1cant surrace oeposition. S~ll piloe tests
<br />of soil leaching and plant uptake processes indicated
<br />strong root adsorption of silver and inh~bit10n of
<br />plant uptake.
<br />
<br />Althou h silver concentrations in snow..were found to
<br />be too variable to show statistical y s gn t cant
<br />differences between sites in the target area and
<br />others to the west ana east ot ~t, coe ~ean s~~ver
<br />concentration in snow on the target area is about
<br />~~s high as the downwind mean, and three tices
<br />as hi;;.:.:' as the upwind mean. Total seeding intensilY
<br />-cr:e:-~"Z; AgI burned by all generators per month)
<br />~as noc a &ood predi~tor of silver conc~ntration in
<br />sno~ at ~olt Creek Pass. No siKnificant differer.ce~
<br />1n silver concentration of streamflow could be found
<br />between 5 streams including 3 on the. target area a~d
<br />2 to the \,;est \upw~nd) ot 1t. }lean annuaJ,. $~iver
<br />concentration tor the L1ve stre&m9 incr~a9cd fro~
<br />(0.1 r 0.3) x 10-10 g Iml in 1971 to (0.6 % 1.1) x
<br />10-10 g /ml in 1973. However. mean metric conversion
<br />discharge also iccreased from 2.9 oJ/see (103 cfs) in
<br />1971 to 4.5 m'/sec (160 cfs) io 1973. }~though a
<br />relationship ~bvio~sly exists between discharge and
<br />silver conce~'ration in individual streams, no
<br />g~n~ral predictive model could be d~velbp~d bet~een
<br />the tve paT3n~ters.
<br />
<br />rt.a:h~::l.J,:i.c.,: "7\~.':21 ;~.r th~ =:ovm:.~nt or ~;:l\'~: [[".J;:'
<br />.si.lv,o,t icdic!~ :hr'1ugh a soil c:olu.":1n 'Ja!'> .:ie;\.....tv-,,~.~
<br />J,n~ teste;d. :t indicates. th3~ the silver concentra-
<br />tion .in :he soil solution at any given time is best
<br />~epresented by a kinetic-type reaction, coupled with
<br />. 3n Insig~iflcant equilibrium-type reaction. A high
<br />. 3dsorp~io~ ra~~ constant controls the initial
<br />teaction, but 10 to 30 percent of input silver con-
<br />.~entration 1s likely to ~ove through the profile.
<br />
<br />:/ .~ Steinhoff. H.
<br /> .1u.i!l Mount.Jins.
<br /> Collins.
<br />- I'reser:t <lddress;
<br />
<br />\..'. and J. D. Ives (Eds.). 197~. Ecob~i::..l il.l;'.J.c,::
<br />Colorado. San Juan Ecolol!.}' PruJt::c:" final R",?()t'::.
<br />
<br />of ~r.c""'p;lck :lugme.nt3thm b ::h~ SB"
<br />C010radu Sta::~ poiv, ?ub1., ~~rt
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<br />United Nations Educ.:I.1~io:1al, S(.~(j:ltifi.:. ar:." C';l~l~r,: ""r:~..r:iz,Hion, Pi'l:~is. ;:';""':'ic:-e.
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<br />A-8d-l
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