Passage V

Rain causes sediment runoff (erosion) of rangelands, which is affected by vegetation (grasses, leaves, and branches) and animal trampling. Scientists conducted 2 experiments using identical-sized plots of soil with slight slopes. Two soils that differed primarily in their sand content were used. Soil 1 contained 60% sand and Soil 2 contained 25% sand. Sprinklers simulated rainfall. It was noted that rain first collected in soil depressions, such as hoofprints, then overflowed and eroded the soil. Sediment runoff was measured at the bases of the plots in grams per square meter (g/m²), following 1 hour of rain.

Experiment 1

Vegetation cover was simulated using window screens having various mesh sizes. The larger the number of mesh squares per inch, the greater the simulated vegetation cover. One plot was left uncovered, and screens of various mesh sizes covered the other plots. Table 1 shows the sediment runoff from each plot.

Experiment 2

Animal trampling was simulated by leading a 500-kilogram (kg) cow back and forth over 2 plots of each soil type until 30% of one and 60% of the other were covered with hoofprints. One additional plot of each soil type was left untrampled. Rainfall was simulated as in Experiment 1. The depth of water stored in hoofprints, in centimeters(cm), is shown in Table 2, and the sediment runoff produced by erosion is shown in Table 3.