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<br />tV t.1..1..'.1.71 n'~ r-r LCO:.Q{;-l CAt EfFECTS ~IF S ~ L;T~ 10:;" n:: SEE.DI :;G AGE~;7);
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<br />::'G,.21d .:.. Klein"::' .:;nc ~_jd..,rc' .. :;,';:c;
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<br />
<br />Accumulatio~ of silver iodide tr~
<br />~eather modification ~ill result in ~G
<br />overt toxicity eff~cts. but may r~~~ilt
<br />in a slight delay in biologic31
<br />pro.c€sscs.
<br />
<br />Y.!.!l Steinhoff, H.'.J., and J.D. ryes (Ids). 1976. Ecolo~icBl impacts of sno\,'pBck.
<br />Mountains. Colorado. ~Qn Juan E:colC'~y Project. Final Report. Colorado State
<br />~I Present address: Dept. of ~icrobiolo~y. Colorado State Univ., ~t. Collins, Co.
<br />
<br />ABSTRACl
<br />
<br />The possible effects of silver iod:de seeding abent
<br />accumulation in surface soils of the San Juan area
<br />~ere investigated by use of labor~tory studies in-
<br />volving Arthrobacter - silver interactions, treatment
<br />of soils ....ith varied fOnT.s .anci l~'\'els of silver, by
<br />examination of silver gradients surrounding seeding
<br />generator sites, and by use of treatment p:o~s in
<br />spruce, aspen, and subalpine meadow comrr,un1tles
<br />located in the San Juan sno~ augncntation area. Lab-
<br />oratorY studies have sho..." that on a short-ter::: basis,
<br />silver' iodide or seeding generator burn mixtures at
<br />hi~her than field concentration sho.... only slight
<br />effects on microbial gro....th or enz}~e function, ....hile
<br />free silver ions, even at part-per-billion levels,
<br />can caus~ marked changes in microbial activities.
<br />These effects ....ere lessened in the presence of sailor
<br />complexing ions. However, under field conditions on
<br />a 3 year basis, silver iodide appears to have a great-
<br />er potential for altering soil decomposer functions
<br />than silver from silver ion. The presence of silver
<br />from silver iodide - sodium iodide complexes, again at
<br />higher than background levels, in the San Juan target
<br />area led to a gradual increase in soil organic matter
<br />content in spruce and aSpen surface soils. ~o such
<br />incr~ase was observed in the subalpine meado~ plot.
<br />Silver from silver nitrate tended to concentrate more
<br />in upper plant portions than silver from silver iodide,
<br />although silver from silver iodide ~as more closely
<br />associated ~ith ehe plane roots. These effects ~ere
<br />only observed using silver levels lQ-lOOX expected
<br />field accumulation levels. Based on the available
<br />literature and experiments carried out to date, the
<br />accumulation of silver iodide seeding agent does not
<br />~ppear to present an ecological threat, although con-
<br />tinual monitoring of test systems should be carried
<br />out to extend the time period over ~hich this conclu-
<br />sion can be tested.
<br />
<br />OBJECTIVES AND HYPOTHESES
<br />
<br />1.
<br />
<br />To monitor soil microbial activities in the San
<br />Juan area. to determine if possible silver accre-
<br />tion is influencing s011 micropial processes,
<br />"I..... ..."....3..,"'''' ~{""~~",..:.,:. 1':-':<" ::;,,:;.u:;:.: .,.:~:::: ....._-~
<br />silver additons have been made in aspen, sprUCe,
<br />and grass communities.
<br />To measure mlcrob1al responses to silver gradients
<br />present in the vicinity of the Pagosa Sprlngs gen-
<br />erator site No. 2~, and the Emerald Hountain slte.
<br />To determine the existence ot poss1ble sub-lethal
<br />effects ot varted slJ.ver J.eve.lS oliO :!UI\l'~ un
<br />microbial roc~sses, lncludlng ettects on mlcrobl-
<br />al viability and capa i ltleS to trans orm su -
<br />strates requir~ng enzymatic aaaptatlon ana energy-
<br />p'rocuction processes.
<br />To determine if soil microbes are capable of
<br />transforming silver present as silver iodlde to
<br />additional silver forms, and to determine physio-
<br />logical mechanisms ~hich may result in silver
<br />trans format 1 ons.
<br />To determine if assay procedures for varjed silver
<br />formS in soil can be developed.
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<br />3,
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<br />4,
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<br />5,
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<br />6,
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<br />These objectives have been SUlr.r::arized in a series of
<br />hypotheses:
<br />
<br />"-.'Hypothesis 1.
<br />
<br />12.5
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<br />Hypothesis II. Laboratorv studies can give an indica-
<br />tion of the degree of possible di~in-
<br />u~tion of microbial ~ctivity ~hich
<br />might re$ult fro~ silver accu~ulation.
<br />:Hypotr.~sis III. Seil bacteria can cause a chnng~ in
<br />silver iodice to fcr.:-.s more e:;sily
<br />taken up hy plants. This modific2tion
<br />of silver forrr. may ~tlke it necessary
<br />to carry out experir..ents under field-
<br />related conditions as much as possible.
<br />
<br />-Ar1""y,,~S S-i!!ct;o"s O":'~.tre4-,'
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<br />I
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<br />SUx:-'.;..RY
<br />
<br />Based on ~ork carried out on the possible ecolc~ic~~
<br />effects of silver iodide seeding agent accumulation in
<br />soils of the San Juan area, the fo110....i08 conclusions
<br />can be dra'\ol'O:
<br />
<br />1. The accumulation of silver iodide nucleatin~ agent~
<br />presents 9o~overt-danger to h~ans. plants or ~ni-
<br />mals. bas~d on available literature anc ~ork car-
<br />ried cut under this study for a 3 .ear oeriod.
<br />2. Silver ion c~n caUSe decreased ~ro~th and enz~~e
<br />induction in a soil Arthrobacter SPecies at l-~Q
<br />ppb free silver ion. The effect observed is depen-
<br />dent on other anions and cations present. Soil
<br />decreases the activity of free silver ions.
<br />3. SilVer from silver iodide or burn mixtures does
<br />not sho~ such effects on mlcroOlaJ. gro~tn or en-
<br />zymatic activity. Generally 10-100 ppm ot Agl
<br />torm sllver 1S required to observe effects on
<br />grovtn. vlab111ty, and enz}~e 1nduction.
<br />4. Free silver lon fro~ silver iodide dissociation at
<br />5~6 ppb can cause' observable effects on l'ioicro_
<br />organisms. To achieve this silver level
<br />100-200 ppm of silver as silver iodide are re-
<br />quired.
<br />5. Microorganisms can cause reduction of free silver
<br />ion or silver iodide to metallic silver. Amine-
<br />type materials may be responsible for this reduc-
<br />tion.
<br />6. Silver iodide added at 1000 ppm shovs no immediate
<br />effects on soil respiration processes.
<br />7. Attempts to establish respiration indices for test
<br />soils across the impact area were not successful
<br />due to short-term variability of soil. moisture and
<br />
<br />..L'..r'........Lo.JI<::.
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<br />8,
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<br />Silver accumulation in the vicinity of t....o seeding
<br />generator sites did not caUSe decreases ln mlcro-
<br />bial respiration. Silver tended to accumulate and
<br />remain in the surface SOlI zone ln Splte or ex-
<br />tended vater percolatlon through the zone.
<br />A subalpine meadow test plot installed for 3 years
<br />using silver lodlde and slIVer nltrate at i. 10,
<br />100 ppm surface soil levels did not sho~ changes
<br />in decomposer functions vhich could be related to.
<br />this treatment.
<br />Silver from silver iodide moved to upper plant por-
<br />tions to a lesser extent than silver from silver
<br />nitrate.
<br />Silver from silver iodide uas more closely associ-
<br />ated ~ith plant roots than silver from silver ion.
<br />After 3 years, silver from these t~o differing
<br />original forms have not equilibrated to forms
<br />which ~il1 give similar activities.
<br />In spruce and aspen plots, imposition ~ith silver
<br />iodide tends to be related to increased organic
<br />matter retention in the test systems. No such
<br />relationships were Observed with equivalent treat-
<br />ments using silver from silver nitrate (silver
<br />ion).
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<br />9,
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<br />10,
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<br />111.
<br />'12.
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<br />113,
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<br />augmentation
<br />Univ. Pub!..
<br />80523.
<br />
<br />in tne San Juan
<br />For t Coll ins.
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