Trace Chemical Analyses of Water and Soil during the WWMPP: Results and Implied Environmental Impact

One concern often voiced with respect to operational and research cloud seeding programs relates to the fact that the seeding agent silver iodide (AgI) contains a potentially toxic metal (silver) and that the use of such a seeding agent might constitute an environmental hazard, despite the fact that the AgI molecule is chemically neutral and thus not bioavailable to living tissues. These concerns especially are voiced regarding aquatic and wetland ecosystems. As such, trace chemical analysis of water bodies and, to a lesser extent, sediments and soils that are potentially impacted by cloud seeding activities, has been performed increasingly over the past decade.

During the last five years of the Wyoming Weather Modification Pilot Project (WWMPP), the Desert Research Institute (DRI) has been conducting water sampling and associated trace chemical analysis of lakes and streams in the Medicine Bow, Sierra Madre and Wind River ranges after the conclusion of seeding activities and the onset of the spring/summer snow melt season. Such sampling has been done in part to address the concerns discussed in the preceding paragraph. Also, for the case of the Wind River Range, the relatively extensive water sampling and analysis done for water bodies in that range serves as a potential validation of positive seeding effects in addition to analysis of snow samples discussed in a companion paper (provided that serious confounding of results does not occur from other sources of Ag, such as mine drainage, in the water bodies). For the past two years, DRI has also conducted trace chemical analyses of near-surface (5 cm depth) soils adjacent to the water bodies sampled, under the assumption that melting snows may leave behind a signature of enhanced (above natural background) Ag concentrations that should be highly correlated with the Ag concentration in the adjacent water body, provided that: a) not too much time has passed between melt-off from the soil and the sampling date, and b) no heavy liquid precipitation events have washed away any residual Ag in the upper soil.

In this presentation we will provide a brief review of what has been found in previous studies of Ag concentrations in water bodies and soils potentially affected by cloud seeding, and put our results within the context of these previous studies. We will also comment on the utility of such analyses as a prime indicator of positive seeding effects within the Wind River range, and thus the utility of future operational seeding programs in the Wind River range should such programs be conducted