The urban soil generally lacks the organic matter cycling and its nutrient
contribution that typifies the soil of the natural ecosystem. Nutrient-containing
(especially nitrogen, sulfur and phosphorus) leaves, litter, and animal remains
are removed as wastes, or are produced in small quantities due to stressful
conditions. Also, some urban soils do not rest on parent material or bedrock
and do not receive the benefit of nutrients released from inorganic mineral
weathering. The weathering of building rubble may be beneficial to nutrient
cycling, but ion imbalance must be considered as a potential problem.
Restricted vertical and lateral water movement inhibits the movement of solutes
from an enriched to an impoverished area.
Organic matter is a major source of energy for most soil-inhabiting
organisms. If lacking, the soil organism population is limited and the activity is
reduced below natural soil levels. In fact, some components of the organism
population may be absent. Because of limited moisture and aeration, it is
reasonable to expect the nitrifying and nitrogen-fixing bacteria to be limited in
urban soils. Without the organic horizons present, as in forest or agricultural
soils, many soil invertebrates are lacking, especially earthworms, further
contributing to the reduced degree of aggregation and the rate of nutrient
cycling. The anaerobic conditions created by high moisture levels and reduced
aeration favors fermentation bacteria which produce methane, ethane,
hydrogen sulfide, nitrous oxide, fatty acids, alcohols and esters - all detrimental
or toxic to most plants favored in urban design.
The urban soil generally lacks the organic matter cycling and its nutrient
contribution that typifies the soil of the natural ecosystem. Nutrient-containing
(especially nitrogen, sulfur and phosphorus) leaves, litter, and animal remains
are removed as wastes, or are produced in small quantities due to stressful
conditions. Also, some urban soils do not rest on parent material or bedrock
and do not receive the benefit of nutrients released from inorganic mineral
weathering. The weathering of building rubble may be beneficial to nutrient
cycling, but ion imbalance must be considered as a potential problem.
Restricted vertical and lateral water movement inhibits the movement of solutes
from an enriched to an impoverished area.
Organic matter is a major source of energy for most soil-inhabiting
organisms. If lacking, the soil organism population is limited and the activity is
reduced below natural soil levels. In fact, some components of the organism
population may be absent. Because of limited moisture and aeration, it is
reasonable to expect the nitrifying and nitrogen-fixing bacteria to be limited in
urban soils. Without the organic horizons present, as in forest or agricultural
soils, many soil invertebrates are lacking, especially earthworms, further
contributing to the reduced degree of aggregation and the rate of nutrient
cycling. The anaerobic conditions created by high moisture levels and reduced
aeration favors fermentation bacteria which produce methane, ethane,
hydrogen sulfide, nitrous oxide, fatty acids, alcohols and esters - all detrimental
or toxic to most plants favored in urban design.
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