Lecture 9 Flashcards
what soil texture is soil crusting commonly seen & why?
clay
especially occurs if there is poor organic matter
what does bare soil develop?
crust
what is the result of a crusted soil?
Surface layer becomes hard & impermeable to water
Seedlings may fail to emerge from crusted
soils
plant growth impeded
Poor aeration
what are the causes of soil crusting in urban soils? (5)
low organic matter
rainsplash distintegrates soil aggregations & fine soil particles fill in pore space
compaction of the surface layer
high sodium content leads to horizontal alignment & creates a “skin”
atm deposition of petroleum-based aerosols and particulates can make soil more water repellent
what are the causes of an increase in pH in urban soils? (4)
de-icing agents (calcium or sodium chloride)
runoff from concrete surfaces (calcium carbonate accumulates)
atm pollutants
Release of calcium from construction rubble (cement, bricks, plaster, etc.)
what does compaction or crusting of soils limit?
gaseous diffusion & water movement
what effect do physical barriers (sidewalks or containers) have on soils? (3)
aeration
drainage – horizontal movement is often impeded
restrict root growth
why do urban soils lack typical organic matter cycling?
Leaves, clippings & plant material are often
removed
microbial activity is low due to lack of organic matter
poor nutrient replacement
what are the 2 nutrients urban soils are often low in? are they macro or micro nutrients?
N & P
macro
what is the result of a small soil volume?
rapid nutrient depletion
what contaminants in urban soils affect their physical & biological properties?
wood, glass, concrete, bricks, plastic, gravel, etc.
how do pesticides contaminants become present in urban soils?
previous land use
brought topsoil
Often applied by homeowners without using appropriate application rates or protection
spills or improper disposal of containers
used for cosmetic reasons
how do heavy metal contaminants (cadmium, lead, mercury) become present in urban soils?
Combustion of fossil fuels, industrial activity, waste water,
how do organic waste contaminants (manures, sewage sludge, etc.) become present in urban soils?
Often transported with topsoil, or purposely applied
how do salt contaminants (mainly de-icing agents) become present in urban soils?
Common problem on boulevards and near street edges or sidewalks (runoff)
