WRRC 104(b)-Funded Research Projects Report Results

The University of Arizona Water Resources Research Center administers Section 104(b) of the Water Resources Research Act, funded by the U.S. Geological Survey. Funds support small research projects that focus on state and regional water issues, reflecting the WRRC mission of promoting understanding of critical state and regional water management and policy issues. Only faculty at Arizona state universities are eligible for 104(b) funding. Following are brief descriptions of recently completed 104(b) projects funded in 2007.

Riparian Vegetation Response to Cessation of Groundwater Pumping, Lower San Pedro River, Arizona, Principal Investigators: Gabrielle Katz, Juliet C. Stromberg, Arizona State University
This research examines the results of a river and riparian restoration project implemented by The Nature Conservancy of Arizona on the lower San Pedro River. The Conservancy removed ecosystem stressors (groundwater pumping, livestock grazing) but did not conduct any direct riparian manipulations (e.g., planting or channel modification).

A non-perennial reach of the Lower San Pedro River, vegetated by Tamarix and other drought-tolerant riparian shrubs. Photograph by Gabrielle Katz.

The restoration project was conducted at two farms on the lower San Pedro River, where irrigation pumping was stopped to allow groundwater levels to recover, and riparian zones were fenced to exclude livestock. Our goals were to describe target conditions for restoration (defined as conditions typical of perennial-flow sites), and to assess changes at the restoration sites in comparison to these targets. To this end, we tracked groundwater levels, occurrence of surface flow, and characteristics of the streamside herbaceous vegetation (plants growing alongside the low-flow stream channel) for five years. We have six study sites at the restoration farms, and six comparative reference sites located elsewhere along the river.

Modification of Conventional Wastewater Treatment Processes for Estrogen Removal, Principal Investigators: David M. Quanrud, Robert G. Arnold, Martin Karpiscak, University of Arizona
This project compared the efficiency of two full-scale municipal wastewater treatment plants, a membrane bioreactor and an activated sludge plant, to remove estrogenic activity from wastewater. Removal of estrogenic activity was more efficient in the membrane bioreactor than at the activated sludge plant. Estrogenic activity remaining in plant effluent from the membrane bioreactor and activated sludge plants represented 2 percent and 30 percent of the influent levels, respectively. Removal efficiency of total estrogenic activity paralleled expectations based on general plant performance indices. That is, plants that best removed biochemical oxygen demand and suspended solids also removed more estrogenic activity. At both plants, concentrations of estrogenic activity in sludge were less important than in effluent, although estrogenic activity in sludge did increase after anaerobic digestion.

Compound Specific Isotope Analysis of Natural Attenuation Activity in Chlorinated-Solvent Contaminated Aquifers, Principal Investigator: Mark Brusseau
In Arizona, chlorinated solvents, including tetrachloroethene, trichloroethene, dichloroethene, and vinyl chloride, are the primary contaminant at 43 of 48 state and federal Superfund sites. Recently, monitored natural attenuation, a process that uses intrinsic transformation and retention processes while carefully monitoring contaminant conditions to control and shrink groundwater plumes has come into favor as a low-cost approach for site remediation. One key step in the implementation of this promising technology is the demonstration that natural attenuation processes are occurring at a hazardous waste site. This project used compound specific isotope analysis, a relatively low-cost and rapid analytical method, to demonstrate that biodegradation of chlorinated solvents is occurring at the Park-Euclid State Superfund site.

Sources of Nitrate in Groundwaters of the Tucson Basin, Principal Investigator: Thomas Meixner
Since understanding the mechanism of contamination is the first step to understanding how to solve any contamination problem, significant efforts have been expended in the past to understand the sources and mechanisms of nitrate contamination in groundwater. This project will utilize two differing flow path transects within the Tucson basin to investigate the sources of nitrate to groundwater in the Tucson basin. The research has three objectives 1) Use geochemical and isotopic techniques to quantify groundwater sources; 2) Quantify nitrate isotopes to connect groundwater nitrate to various nitrate sources and sinks; and 3) Develop conceptual model of nitrate sources and processes along the two flowpaths using results of first two objectives and existing nitrate and groundwater geochemical data. To achieve these objectives we will collect water along two flowpaths using Tucson Water wells. Samples from each transect will be analyzed for major geochemical composition and sulfur, water and nitrate isotopes. These suites of geochemical and isotopic analyses should allow us to partition the reasons for nitrate variability in Tucson groundwater between water sources, biogeochemical sinks and mixing.

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