Since the 1850s, cultivation and clear Modern agriculture has increased the rate of soil erosion in the upper Mississippi River basin. Around the world, agriculture strips soil up to 100 times faster than natural processes. They also take away arable land, clog waterways and threaten long-term environmental sustainability. But scientists have so far struggled to separate out the effects of land-use changes over the past 20,000 years and the transition from the last Ice Age.
To determine whether current agricultural practices are sustainable, researchers in Minnesota recently measured the rate at which soil eroded during the Ice Age transition and compared it to modern-day agricultural erosion. They focused on Trout Creek, a tributary of the Mississippi River. This tributary has two stepped formations, or terrace, A river bank representing the past floodplain before the river eroded to its present height.
The oldest upper terrace is approximately 14 meters (50 ft) above the lower terrace, which is approximately 8 meters (26 ft) above the modern floodplain. Scientists studying the nearby area suggest that the terraces contain deposits from the last ice age 20,000 years ago. the last glacial maximum, Until today.
On the upper terrace, the researchers collected a cylindrical sample of sediment about 4 centimeters (1.5 inches) wide and 6 meters (20 feet) deep by pushing an empty cylinder into the ground, like a straw inserted into a layer cake. sediment core. They collected slices of this core from 2 meters (6 feet) and 6 meters (20 feet) to determine the age of the terraces.
Some particles in the sediment capture electrons while buried and release them when exposed to light. So the researchers stimulated these electrons by shining light into a slice of the sediment and measured the intensity of the light emitted. light stimulated luminescence. Brighter emissions indicate that the deposits are older and have been buried for a longer period of time. Using this method, they determined that the deeper sediment slices were 22,000 years old and the shallower sediment slices were 20,000 years old, dating the terraces to the Last Glacial Maximum.
The team then drilled a hole in the upper terrace with an auger and collected the deposit in a 25-centimeter (10-inch) wide plastic tube. They took four samples from a depth of 0 to 2 meters (0 to 6 feet) and one sample from a depth of 6 meters (20 feet). They believe that the minerals in the sediments quartz It produces a radioactive form of the element beryllium, known as beryllium. 10becomes very low when exposed to the sun 10“Be” means the deposit was quickly buried and had little exposure to sunlight. The team measured the following concentrations: 10We went into each sediment sample and used an online calculator to estimate how quickly it would erode. The researchers calculated that 0.073 millimeters (0.003 inches) of surface sediment was removed per year during the Last Glacial Maximum.
The researchers collected a similar sample from the lower terrace and used photostimulated luminescence to confirm that it was between 22,000 and 14,000 years old. This terrace was a floodplain during the transition period from the Last Glacial Maximum. ice agewhere temperatures have risen and permafrost has retreated. They measured the concentration of 10Samples taken from this terrace showed that 0.049 millimeters (0.002 inches) of surface sediment had been removed per year.
Finally, the researchers measured 10Step inside modern floodplain sediment samples deposited between 14,00 years ago and today. They found that the sediment was eroding by 0.053 millimeters (0.002 inches) per year during that period. Its speed was slower than that of an ice age, but similar to that of a deglaciation.
The researchers compared their findings to the average soil loss due to modern agriculture reported by four previous scientists who studied the region. They found that modern agriculture removes an average of 0.60 millimeters (0.02 inches) of soil per year. This is 8 to 12 times higher than all the natural erosion rates they calculated.
They concluded that the recent surge in soil loss from agriculture has significantly exceeded that caused by the largest natural climate change in recent Earth history. Human erosion has shown a “hockey stick” upward trend similar to that seen in global temperatures, suggesting that similar trends may exist throughout the Earth system. The research team concluded that modern agricultural practices are currently not sustainable. Measures such as reintroducing native plants can help curb this trend, but further research is needed to determine how best to limit long-term erosion.
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Source: sciworthy.com
