Research Description

For the research conducted in this portion of the study, we hypothesize that (1) PAM can be used to decrease saturated hydraulic conductivity (Ksat) of soil material, and (2) the presence of suspended sediment can increase the efficiency of PAM use. The main objectives in this portion of the study are to:
1. evaluate to what extent PAM effects hydraulic conductivity and infiltration rates of three soils of different textures; and,
2. better understand the physical mechanisms leading to the decrease in infiltration.

For this second objective, this study considers three possible physical mechanisms that reduce seepage. Specifically we consider that: (1) PAM-treated water is more viscous than untreated water, such that infiltration rates are reduced; (2) PAM physically plugs large soil pores, especially in coarser grained canal sediments; and (3) PAM itself becomes a low-conductivity layer when treating finer-grained soils.

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Research Description

Batch sorption experiments were conducted to determine the sorption coefficient of AMD in different soil types and to develop equilibrium sorption isotherms. These experiments were designed to yield data necessary to perform predictive modeling on the fate and transport of AMD in soil. With an increased understanding of AMD fate and transport through soil and groundwater systems, a more thorough evaluation of the use of PAM for treating unlined water delivery canal systems can be made.

Research Description

This research addresses the role natural microorganisms in determining the longevity of PAM and fate of residual AMD in the canal environment. Previous work has shown that environmental microorganisms can utilize both PAM and AMD as nitrogen and carbon sources. To date we have perfected media and methods enabling the isolation, quantification, and routine cultivation of PAM/AMD-utilizing microorganisms in pure culture from environmental samples, and we can measure AMD degradation in liquid culture. These expanded microbiological capabilities are being used in concert with DNA-based approaches to identify representative AMD degrading microorganisms from our growing culture collection to explore the diversity of microorganisms which consume AMD in the environment.

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Research Description

In this study, we exposed aqueous solutions of commercial linear anionic PAM to summer sunlight conditions and included humic acid and iron (ferrous sulfate) in some of the samples to model natural waters. The goal was to assess the stability of PAM under environmental conditions typical of the summertime irrigation season and to particularly look for evidence of AMD enrichment.

Research Description

Commercial crystalline linear anionic polyacrylamide (PAM) is capable of absorbing many times its mass of water up to complete dissolution by incorporating the water into the polymer structure through dipole interactions and hydrogen bonding. When added to an excess of water, anecdotal evidence indicates that the polymer requires an hour or less to completely hydrate. Because of the uncertainty associated with anecdotal evidence, it is important that hydration times are actually measured and that a relationship with temperature can be established. PAM hydration time was measured in deionized (DI) water and in 0.005M calcium sulfate solutions at a number of different water temperatures in the approximate range 5-30 degress C. We assumed that hydration time was related to solution viscosity, which would increase and then reach an approximate constant value. Measurements of the release of residual acrylamide (AMD) monomer are also investigated and related to PAM hydration.

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Research Description

Results of earlier field applications have implied that PAM depositing onto canal bottom can be resuspended. The resuspension could become an important source of PAM in the canal water, after the original PAM flocs have settled from the initial PAM application. Using the approach of flume experiments coupled with saturated soil columns, we will determine the critical shear stress of flow above which the PAM treated soil layer will break, and PAM in this layer could be entrained into the flow. For soil columns with the same PAM treatment (same critical shear stress), a shear stress-erosion rate curve will be obtained and critical shear stress will be analyzed from this curve. Different concentrations of PAM solution will be applied to obtain soil columns with different critical shear stress. Finally, an equation for the erosion rate versus effective shear stress will be derived from the experimental data, so that it may be incorporated into the predictive tools.

Research Description

Response of Daphnia (magna and pulex) to PAM and AMD treatments will be investigated in the laboratory experiments as a part of ‘impact on receiving waters’.

A large number of Daphnia neonates born within 24 hours will be grown in the laboratory at various concentrations of PAM and AMD to study their life histories such as growth, mortality, reproduction etc. Any abnormalities in their behavior, reproduction, mortality etc. will be recorded. Effects of PAM and AMD will be examined by comparing differences between control and treated animals. It will allow us to better understand the downstream transport of PAM as well as its impact on zooplankton (if there is any). This experiment will be synchronized with BMI community response sampling.