AbstractHigh sediment loads from agriculture and construction sites are a major source of surface water contamination in Puerto Rico. The use of anionic polyacrylamide polymers (PAM) is quickly gaining recognition as a cost-effective short-term erosion control strategy. In this study we evaluated the effectiveness of different dosages and formulations of anionic PAM in a highly weathered soil (Corozal clay—Typic Hapludult) of the tropics under steep slope (20%) conditions. A series of indoor box experiments were conducted according to guidelines of the National Research Project for Simulated Rainfall. Three formulations of PAM, namely, SOILFLOC™ 300 E, SOILFIX™ LDP, and a synthetic formulation from Aldrich Chemical Company (PAM-Ald) were evaluated at the following rates: 0 (control), 20 kg/ha, 80 kg/ha, and 120 kg/ha of active ingredient. Simulated rainfall (7 cm/h) experiments were conducted at: one, two, eight, 30 and 60 days after polymer application. Additions of PAM at rates of 80 and 120 kg/ha significantly reduced sediment concentration in runoff relative to that of the control and of the 20 kg/ha PAM rate. At their highest rates, all PAM products reduced sediment runoff by more than 75% relative to the control in all events. The effectiveness of the 20 kg/ha PAM rate was lost after two rainfall events. At the third runoff event the percentage sediment concentration reduction (relative to that of the control) was less than 50% for the 20 kg/ha PAM-Ald formulation and less than 20% in the case of SoilFloc. Time to runoff was largely influenced by soil moisture content. In the last two rainfall events (30 and 60 days after PAM application), time to runoff was also significantly influenced by PAM rate. Runoff occurred faster with the control and the low PAM rate relative to that of the high PAM rates. These results could be attributed to the effects of surface sealing and enhancement of rill formation at the surface of the control and the low (20 kg/ha) PAM treatments. Sixty days after PAM application, estimates of cumulative sediment production for the 30-minute runoff event were 2.3 Mg/ha in the control treatment vs. 0.18,0.07, and 0.08 Mg/ha for the 120 kg/ha rate of SoilFloc, SoilFix, and PAM-Ald, respectively.
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