Degree Type


Date of Award


Degree Name

Doctor of Philosophy


Theses & dissertations (Interdisciplinary)


Water Resources

First Advisor

Steven K. Mickelson


The dissertation Chapter 3 grazing/vegetative filter strip (VFS) buffer research project quantifies the effects of grazing management practices and VFS buffers on losses of runoff (RO) with total solids (TS), nitrate-nitrogen (NO3-N), ortho-phosphorus (PO4-P), and total-phosphorus (TP) during natural rainfall events. Three grazing management practices (5.1-cm [2-in] continuous grazing [con], 5.1-cm [2-in] rotational grazing [rot], and no grazing [ng] control) and three VFS buffers comprised nine treatment combinations. The plot areas were on uneven terrain with up to 15 percent slopes and consisted of approximately 100 percent smooth brome (Bromus inermis Leyss.). Average paddock and VFS buffer plant tiller densities were approximately 62M and 93M tillers/ha, respectively. Results from 2001 and 2002 show no significant differences (p < 0.10) in average losses of RO, TS, NO3-N, PO 4-P, and TP among the nine treatment combinations. The 2003 results also show no significant differences (p < 0.10) in losses of RO, TS, PO 4-P, and TP. However, the 2003 results indicate significantly higher (p < 0.01) losses of NO3-N from "10:1ng" treatments compared to all other treatment combinations and reflect a possible tendency towards elevated losses in some "ng" treatments from "con" treatments in 2001 and 2002. Runoff analysis results indicate grazing management practices did not significantly affect runoff losses (p < 0.10). These results and other research findings suggest the relatively higher 2003 event precipitation, antecedent moisture, concentrated surface flow conditions, dense cool-season smooth brome, and forage nutrient cycling processes may have contributed to the potential shift of elevated losses to the non-grazed "ng" treatments. Results also suggest warm-season grasses like switchgrass (Panicum virgatum L.) could be incorporated into certain paddock areas in a rotational grazing management program to improve grazing efficiency and reduce RO and contaminant losses. The dissertation Chapter 4 windrow composting/VFS buffer study quantifies the effects of windrow composting practices and VFS buffers on losses of runoff (RO), runoff percent of rainfall (RO%), total solids (TS), nitrate-nitrogen (NO3-N), ortho-phosphorus (PO 4-P), and total-phosphorus (TP) during natural rainfall events. The 1:1 and 1:0.5 area ratios represented a 6 m x 23 m (20 ft x 75 ft) fly ash composting pad area compared to VFS buffer areas of equal and one-half size, respectively. All treatments had three replications for a total of nine runoff plots distributed in a randomized complete block design. Results from the study indicate significantly higher levels (p < 0.05) of RO, RO%, TS, NO 3-N, PO4-P, and TP from the 1:0 control plots compared to the 1:1 and 1:0.5 plots. Results also show the 1:1 and 1:0.5 VFS buffer treatments were not significantly different (p < 0.05). Average runoff loss reductions from the 1:1 and 1:0.5 plots were 98 and 93 percent, respectively, compared to the 1:0 control plots. These results reflect the effectiveness of VFS buffers for reducing runoff and contaminant losses from a windrow composting site. We hypothesize the significantly lower PO4-P losses in runoff may be attributed to potential chemical and physical effects of the fly ash composting pad material. The dissertation Chapter 5 hydrologic modeling study calibrated and validated a hydrologic model for predicting runoff volume losses from a windrow composting site with VFS buffers. The site also included a composting pad surface constructed of fly ash obtained from a local coal-fired power generating station. Observed runoff and physical attribute data from six rainfall events during 2002-2004 at a central Iowa windrow composting research site were used in the model evaluation. These data included average runoff volumes from three compost windrow:VFS buffer area ratio treatments (1:1, 1:0.5, and 1:0 [no buffer] control), each replicated to comprise a total of nine plots. Calibration simulations indicated good agreement of simulated runoff data to observed data for all 1:1, 1:0.5, and 1:0 (no-buffer control) VFS buffer treatments. The 1:0 (control) treatment plots also indicated good data agreement for all calibration and validation simulations. However, validation simulations resulted in overpredictions for the 1:1 and 1:0.5 VFS buffer runoff volumes that were most significant in the 2004 late rainfall events period. Results from this initial study with limited data indicated that alternatives to soils data-derived VFS buffer surface infiltration and runoff functions should be considered to potentially improve model prediction accuracy. These results and other research findings suggest that possibly the fly ash composting pad material and age of the research site may have contributed to the overpredicted 1:1 and 1:0.5 VFS buffer runoff validation simulation results. (Abstract shortened by UMI.)



Digital Repository @ Iowa State University,

Copyright Owner

David Franklin Webber



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OCLC Number




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190 pages