Natural Dusts Flashcards
What is loess?
Fine sedimentary soil blown by wind, susceptible to erosion
What is the loess plateau?
Located in Northern/mid-China with an area of 640,000km^2
- Was highly fertile area and heavily used for easy farming in ancient times
- Centuries of overuse and overgrazing = one of the highest erosion rates in the world and widespread poverty
What causes desertification?
- Overgrazing by sheep, goats, and other livestock
- Cutting down trees or other vegetation
What are some methods of ecological rehabilitation at the loess plateau?
- Terrace side of ravines
- Fish scales terraces for single trees
- Introduce trees (fruit trees)
- Dune/soil stabilization with grasses, bushes
- Feed livestock in pens rather than herding
- Warping dams to create rich fertile fields in valleys (dams to capture sediment so it accumulates and can’t leave the area)
Why is it important that local people be involved in rehabilitating the land?
- Sense of shared responsibility, stewardship
- Paid for rehabilitation work
- Personal achievement and pride
- Sustainability/maintenance
China has about 22% of the world’s population, but only about
7% of it is arable land
Restoration of the loess plateau
- Occurred over an area of ~35,000km^2 (~5% total area of plateau)
- Results have reduced the massive silt loads to the Yellow River by ~1%
Where does the loess come from?
Alluvial fans in mountainous regions nearby
Dust sources (deserts) are transported and deposited by
monsoon and surface winds
Why is so much dust formed here?
- Highest known uplift rates in the world in the Himalayas
- Rapid river incision and therefore sediment production
- Unstable slopes
- Glaciation
- Erosion from freeze-thaw fracturing
- High Asia is the world’s most efficient producer of silty sediment (2-63um)
What minerals is loess composed of?
- Quartz grains (60%)
- Feldspar
- Mica
- Carbonate
How thick are loess deposits?
Up to 500m
What are some physical characteristics of loess?
- Low density
- Soft
- High porosity
- Easily erodible
- Collapse when wet
Dust particles in the body
- Smaller than 1um = absorbed into bloodstream
- Smaller than 10um = trapped in the lungs
- Size of dust on the loess plateau is mainly 5-15um
- Particles less than 100um can be inhaled into nose/mouth, but get trapped in upper airways
- Only the smallest particles (<10um) can reach the alveoli, where they contribute to the risk of disease
Most countries have an Occupational Exposure Limit Values (OELV) of
0.1mg/m^3, over an 8hr avg for respiratory crystalline silica (<10um)
