The potential for water contamination is great in areas where land use is both urban and agricultural. Such land uses can load the surface water and groundwater with nutrients and toxic trace metals. Water pollution can be further increased when natural watersheds have been altered by human activities. The surface and groundwaters of the Middle Rio Grande, NM, USA are part of one such ecosystem.
Because redox processes are important controls on nutrient cycling and contaminant transport, it is vital to understand the redox zonation of an aquifer. This research has been conducted to address such biogeochemical zonation in the shallow alluvial aquifer of the Middle Rio Grande bosque - a threatened riparian forest. To characterize the groundwater chemistry of this aquifer, groundwater, Rio Grande water, and aquifer sediment samples were collected at two sites flood capable Belen and non-flooding Albuquerque South Valley.
Comparisons of groundwater and river water samples show that the groundwater is better connected to its surface water source at 13 m depth. Wells at 3 and 5 m have reduced dissolved oxygen conditions, allowing for denitrification, metal reduction, and sulfate reduction to occur. The use of dialysis multi-level samplers has documented the occurrence of these processes in the upper 2.5 m of the aquifer. Additionally, concentrations of redox sensitive anions (nitrate and sulfate) and the conservative tracer chloride are increased due to hydrochemical processes. Groundwater uptake by bosque vegetation at the zone of greatest root density concentrates these solutes in the groundwater.
Floodwater is depleted in oxygen and nitrogen compounds, but enriched in all other chemical parameters. The mobilities of the redox-sensitive trace metals Mn and Fe are enhanced by the dissolution of solid phase metal-oxides during flooding. This dissolution also releases phosphate.
Earth and Planetary Sciences
Level of Degree
Department of Earth and Planetary Sciences
First Committee Member (Chair)
Second Committee Member
Third Committee Member
Clifford N. Dahm
Block, Susan E.. "Biogeochemistry Of The Middle Rio Grande Bosque: Links Among Surface Water, Groundwater, And Sediments." (2002). https://digitalrepository.unm.edu/eps_etds/315