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Measurements of deuterium in the local interstellar medium have revealedlarge variations in D/H along different lines of sight. Moreover, recent {\itFar Ultraviolet Spectroscopic Explorer} (FUSE) measurements find D/H to beanticorrelated with several indicators of dust formation and survival,suggesting that interstellar deuterium suffers significant depletion onto dustgrains. This in turn implies that the total deuterium abundance in the localGalactic disk could be as high as $\sim 84 %$ of the primordial D abundance. Itwas proposed that the infall/accretion of pristine gas is needed to explainsuch a high deuterium abundance. However, we point out that the infall neededto maintain a high present-day D/H is, within the preferred models, in tensionwith observations that gas represents only some $\sim 20%$ of Galactic baryons,with the balance in stars. We study this tension in the context of a wide classof Galactic evolution models for baryonic processing through stars, which showthat deuterium destruction is strongly and cleanly correlated with the drop inthe gas fraction. We find that FUSE deuterium observations and Galactic gasfraction estimates can be reconciled in some models; these demand a significantinfall rate of pristine material that almost completely balances the rate ofstar formation. These successful models also require that the average fractionof gas that is returned by dying stars is less than 40% of the initial stellarmass. Cosmological implications of dust depletion of D in high-redshift systemsare discussed.

FUSE Deuterium Observations: A Strong Case For Galactic Infall