Author
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Lentz, Rodrick |
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Submitted to: Geoderma
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 11/24/2014 Publication Date: 3/1/2015 Publication URL: http://handle.nal.usda.gov/10113/60503 Citation: Lentz, R.D. 2015. Polyacrylamide and biopolymer effects on flocculation, aggregate stability, and water seepage in a silt loam. Geoderma. 241-242:289-294. Interpretive Summary: Researcher’s seek a more renewable and natural alternative for water soluble anionic polyacrylamide (PAM), a highly-effective, petroleum-derived polymer used in agriculture to control erosion and reduce water seepage from unlined irrigation structures. Particular concerns arise when PAM is used in irrigation canals, because it contains a minute quantity of acrylamide monomer, a suspected human carcinogen. This study evaluated two anionic polymers: a bacteria-produced polysaccharide (biopolymer) and a PAM with comparable molecular weight and charge density characteristics to compare their ability to flocculate soil colloids, stabilize soil aggregates, and influence effective hydraulic conductivity (seepage loss). Results suggest that the biopolymer would be less effective than PAM for reducing water erosion owing to its lesser flocculation and aggregate-stabilizing potential. However, the biopolymer could be a more desirable alternative to PAM for controlling seepage from unlined irrigation canals and reservoirs because it (i) can be used effectively at lower concentrations, (ii) is considered more environmentally friendly, and (iii) is produced from a renewable resource. Use of the biopolymer in unlined irrigation canals could significantly reduce seepage losses, which typically exceed 100 million acre-feet of water worldwide. Technical Abstract: Researcher’s seek a more renewable and natural alternative for water soluble anionic polyacrylamide (PAM), a highly-effective, petroleum-derived polymer used in agriculture to control erosion and reduce water seepage from unlined irrigation structures. This study evaluated two anionic polymers: a bacteria-produced polysaccharide (biopolymer) with 10-20 Mg/mol molecular weight (MW) and 30% charge density, and a PAM (12-15 Mg/mol MW, 30% charge density) to compare their ability to flocculate soil colloids, stabilize soil aggregates, and influence effective hydraulic conductivity (seepage loss). The biopolymer most effectively flocculated the colloids at a concentration of 1 mg/L, but was still 30% less effective than PAM at 1 mg/L and 50% less effective than 10 mg/L PAM treatments. The aggregate stability test included the polymers listed above as well as lower-MW representatives of each type (MW = 0.2 to 0.5 Mg/mol). Overall, both polymers increased the stability of 1- to 2-mm-diam., silt loam aggregates, though PAM was 1.35x more effective than the biopolymer, 88.7% vs. 65.5%. These results suggested that the biopolymer’s bulkier molecular conformation limited the extension and flexibility of the molecule in solution, compared to PAM. After 140 hr, the biopolymer reduced seepage loss rates 21%, while PAM increased loss rates 1.6-fold, compared to controls. These data suggest that the biopolymer would be less effective than PAM for reducing water erosion owing to its lesser flocculation and aggregate-stabilizing potential. However, the biopolymer could be a more desirable alternative to PAM for controlling seepage from unlined irrigation canals and reservoirs; it (i) can be used effectively at lower concentrations, (ii) is considered more environmentally friendly, and (iii) is produced from a renewable resource. |
