Modern groundwater reaches deeper depths in heavily pumped aquifer systems.

Deep groundwater is an important source of drinking water, and can be preferable to shallower groundwaters where they are polluted by surface-borne contaminants. Surface-borne contaminants are disproportionately common in 'modern' groundwaters that are made up of precipitation that fell since the ~1950s. Some local-scale studies have suggested that groundwater pumping can draw modern groundwater downward and potentially pollute deep aquifers, but the prevalence of such pumping-induced downwelling at continental scale is not known.

Stable isotope signatures of hydration water in secondary mineralization on UO.

Hydrated secondary mineralization readily forms on the surface of UO particles exposed to humidity in an oxidizing environment. The oxygen stable isotope composition of the secondary uranium oxide may reflect that of the water vapor, as well as the hydrogen and oxygen stable isotopic composition of the mineral hydration water. The geospatial organization of δH and δO values of atmospheric humidity and precipitation is increasingly well understood, which suggests that the hydrogen and oxygen stable isotopes in secondary mineral hydration water may yield information on the environment in which the mineralization formed.

Simplified Method for the In Situ Collection and Laboratory Analysis of Cosmogenic Tracers (Sulfur-35 and Sodium-22) to Determine Residence Time Distributions and Water Ages.

The use of cosmogenically produced sulfur-35 ( = 87 days) and sodium-22 ( = 2.6 years) as intrinsic tracers can provide valuable information on catchment hydrology, flow paths, and subsurface storage. A new and straightforward method was created to determine the activities of both S and Na in various water sources by pumping large volumes (up to 1000 L) of water through cation- and anion-exchange resin columns in the field to collect sodium and sulfate ions and simple chemistry in the lab.

Water vapor exposure chamber for constant humidity and hydrogen and oxygen stable isotope composition.

Rationale: Water vapor exposure experiments have applications for studying water physisorption and chemisorption hydration and hydroxylation reactions on a wide variety of material surfaces. The stable isotopes of hydrogen and oxygen in the water molecule are useful tracers of water exchange mechanisms and/or rates in such vapor exposure experiments.

Methods: We designed and built a humidity chamber system that uses membrane-mediated liquid-vapor exchange of water followed by mixing with dry air to control the relative humidity of air and its δ H and δ O isotopic composition.

Analysis of air mass trajectories to explain observed variability of tritium in precipitation at the Southern Sierra Critical Zone Observatory, California, USA.

Understanding the behavior of tritium, a radioactive isotope of hydrogen, in the environment is important to evaluate the exposure risk of anthropogenic releases, and for its application as a tracer in hydrology and oceanography. To understand and predict the variability of tritium in precipitation, HYSPLIT air mass trajectories were analyzed for 16 aggregate precipitation samples collected over a 2 year period at irregular intervals at a research site located at 2000 m elevation in the southern Sierra Nevada (California, USA). Attributing the variation in tritium to specific source areas confirms the hypothesis that higher latitude or inland sources bring higher tritium levels in precipitation than precipitation originating in the lower latitude Pacific Ocean.

Stormwater and fire as sources of black carbon nanoparticles to Lake Tahoe.

Emitted to the atmosphere through fire and fossil fuel combustion, refractory black carbon nanoparticles (rBC) impact human health, climate, and the carbon cycle. Eventually these particles enter aquatic environments, where they may affect the fate of other pollutants. While ubiquitous, the particles are still poorly characterized in freshwater systems.