December GEOLOGY and GSA TODAY media ...(roles in concentrating Earths rich resou...)

Geologic origins of salinization in a semi-arid river: The role of sedimentary basin brines
James Hogan et al., University of Arizona, SAHRA / Dept. of Hydrology and Water Resources, Tucson, Arizona 85721, USA. Pages 1063-1066.

Rivers in semi-arid and arid regions exhibit increasing amounts of salt (salinity) downstream. Often this trend is attributed to the concentrating effect of evaporation and plant transpiration related to irrigated agriculture. In contrast, the results of Hogan et al.s investigation of the Rio Grande River in Colorado and New Mexico suggest that geological sources of salt added by groundwater discharge have a greater impact than agricultural effects. Through detailed sampling of the surface water, Hogan et al. identified a series of salinity increases. These increases were typically located at the downstream end of sedimentary basins, where the regional groundwater flow system typically discharges to the river. Using geochemical methods, they show that these increases result from localized discharge of high-salinity groundwater, which is fingerprinted as a sedimentary brine source with an estimated age of millions of years. Hogan et al.s calculations indicate that while these groundwater fluxes are very small relative to the overall flow in the Rio Grande, they are the dominant solute input and, when combined with downstream evaporation and transpiration, result in salinization. The recognition of a substantial geologic salinity source for the Rio Grande implies that alternative salinity management solutions, such as interception of saline groundwater, might be more effective in reducing salinity than changes in agricultural practices.

Nonlinear slope-dependent sediment transport in cinder cone evolution
Jon Pelletier and Michael L. Cline, University of Arizona, Department of Geosc
'/>"/>