Jan 26, 2012
Soil conservation 'flicks the dust switch'
In the 1930s the North American "Dust Bowl" saw drought and poor land management result in extensive soil erosion and economic hardship. Since then farmers have introduced measures to cut soil loss and dust formation but it's been hard to track their success. Now researchers in Canada have found that blowing dust has occurred markedly less often since 1990, indicating that such attempts are working.
"While climate does play a central role in entraining soil particles, it is mostly the actions of humans in the Canadian Prairies that expose or protect the soil," Chris Hugenholtz of the University of Lethbridge and University of Calgary told environmentalresearchweb. "Our findings demonstrate an example where human influence on the landscape can 'flick' the dust switch."
Individual farmers, as well as government agencies, have responded to soil erosion by developing programmes to promote soil conservation, says Hugenholtz. Such measures include reducing summerfallow (the practice of leaving fields unused in the growing season) and employing direct seeding to cut down on tillage and the associated disturbance of soil.
Hugenholtz, Thomas Fox and colleagues examined data for the start of the growing season, when most dust occurs, from seven sites in and near the Palliser Triangle. This is the most arid region of the Canadian Prairies. They found that blowing dust frequency declined between 1961 and 2006, as did climatic wind erosion potential – a ratio of wind power to aridity. The frequency of blowing dust exhibited a significant drop-off from 1990 onwards.
"Initially, we were concerned this step change was not real, but some artefact of changes in data collection around 1990," said Hugenholtz. "After an extensive search of metadata and many correspondences with scientists at Environment Canada, the federal agency that supplied the data used in our study, we confirmed that it was a real signal of a change in dust frequency."
The link between climate and dust also became stronger after 1990. The researchers reckon that before this date the role of climate was compounded by poor conservation management, leading to higher dust frequency and lower correlation. But after 1990 the role of climate became more prevalent because the effects of soil conservation initiatives began manifesting across the region. "It is as though land use began cancelling out after 1990, yielding a better correlation with climate," said Hugenholtz.
"Although we were unable to establish a cause–effect relation between dust and land use, we examined agricultural census data and found a steady increase in soil conservation practices since the 1960s, particularly the extent of direct seeding and summerfallow," said Hugenholtz. "We also found an expansion of soil conservation programmes in the decade preceding the change point. Overall, our findings suggest that soil conservation has had an impact in reducing airborne dust on the Canadian Prairies."
Hugenholtz believes Canadian farmers are now better equipped to handle conditions with moderate climatic wind-erosion forcing than in the past. "Extreme events will always lead to some level of erosion but under moderate conditions the likelihood of dust emission is now much lower," he said.
Projections indicate that the southern Canadian Prairies are likely to dry as climate changes. In the American southwest, scientists have suggested that climate change will bring more dust, which could have major implications for human health and ecosystems. "At this point it is too early to extend this hypothesis to the Canadian Prairies," said Hugenholtz. "With that said, one of our goals is to establish better empirical relations between climate, land use and dust before applying this knowledge to forecast future conditions. If we can get a sense of future scenarios, we may be able to offset negative impacts by being better prepared."
The scientists reported their work in Environmental Research Letters (ERL).
About the author
Liz Kalaugher is editor of environmentalresearchweb.