An improvement on the management of biomass removal from vegetated channels and the methods used in runoff research
Soil erosion is a process that can lead to many environmental problems if not properly controlled. Agricultural practices have been implemented that inhibit the detachment of soil particles. When soil particles become detached and entrained in runoff, the soil particles can be transported to rivers, lakes and streams. Increasing levels of sediment in rivers, lakes, and streams can cause eutrophication, decreased light penetration, decreased biological diversity and altered channel dynamics. Conservation practices, such as grassed waterways and vegetated filter strips, are put in place to intercept overland flow and cause sediment deposition to decrease the amount of sediment delivered to bodies of water. A goal of the United States is to replace 30% of fossil fuels with biofuels by 2030. To accomplish this goal, biomass may have to be removed from conservation practices, including grassed waterways and vegetated filter strips. The goal of this dissertation was to determine the impact of biomass removal from vegetated channels during low intensity storms and to improve the methodology used to study sediment dynamics during run off experiments.
The first study in this dissertation evaluated the effects of grass species and biomass removal in vegetated channels during low intensity-short duration storms. In June 2006, 24 channels were created that measured 2 m x 10 m. The treatments of grass species (big bluestem, corn, smooth bromegrass, and switchgrass) and biomass removal (removed, not removed) were applied to the channels in a split plot arrangement. Three times in 2007 and 3 more times in 2008, a 787 L load of water with suspended sediment was drained on the head and sides of each experimental unit and the entire load of water that ran off was collected, weighed, and sampled for sediment concentration. Biomass removal increased runoff and sediment by an average of 15% over the two years of the study. The channels planted to perennial C4 grasses were most effective at reducing runoff and sediment export, while the corn was consistently the least effective at reducing runoff and sediment export.
The second objective of this study was to apply sediment fingerprinting techniques to small-plot runoff experiments to determine the relative contribution of the plot and applied sediment to sediment exported from small plots. Sediment-free water was applied to the head and sides of constructed vegetated channels in March and September of 2008. A 10 L sample of the runoff was collected, the water was evaporated from it, and the remaining sediment was ground and analyzed for total C. Water mixed with soil material obtained from a different part of the landscape and with a higher soil C content than that of the plot soil was applied to the head and sides of the vegetated channels, the mixture was sampled as it was applied, and the resulting runoff from the plot was sampled. These runoff samples were processed and analyzed for total C similarly to those collected when sediment-free water was introduced to the upper end of the plot. Based on differences in total C of the plot soil and the introduced soil material, a linear relationship was developed allowing the sediment exiting the plot to be partitioned between that soil material introduced with the inflow and that soil coming from the plot bed. The sediment C content was entered into the linear equation to determine the percent plot-derived sediment in the runoff. When soil material mixed with water was introduced to the plots, on average 20.5 % of the sediment in runoff was derived from within the plot. The sediment trapping efficiency of the vegetated channels was very high (over 90%) and, accounting for percent plot-derived sediment, had little effect on sediment trapping efficiency.