Earth Science: Human Environmental Impact – Cities
Until well into the 18th century, most people were living in agricultural areas. This changed with industrialization, when more and more people migrated into the cities—rather unnatural ecosystems.
Urban environments were built by hu- mans according to their ideas and requirements. They are influenced by abiotic factors such as climate, water, light, and heat, and have little in common with natural ecosystems. Most urban areas are covered by buildings, roads, and footpaths. The pavement seals soil in and thus prevents precipitation from permeating the ground; this consequently disturbs the natural material exchange between the air and soil.
Unpaved areas are much dryer compared to the surrounding areas outside of the city. This is in large part due to the effects of targeted drainage. The ground also suffers from other factors such as road salt and industrial waste. The urban climate is also different from the climate of surrounding areas. The many buildings store significant quantities of heat during the day and release it during the night.
Fossil fuel is constantly burnt by heaters, power plants, and industrial facilities. High building densities in cities also prevent the exchange of air masses, due to the lack of wind and evaporative cooling, which are themselves the results of a lack of vegetation. In addition, frequent smog days are the result of particles and fumes from exhaust pipes in the air, preventing the release of heat energy into the atmosphere.
This is why the annual average temperature is at least one degree higher in cities than in surrounding areas. There are also fewer days of freezing and the humidity can be up to ten percent lower. Moreover, biodiversity is significantly lower in urban areas compared to natural ecosystems, as living conditions are comparatively unfavorable for most plants and animals.
Nevertheless, urban residential areas offer many opportunities for small habitats. These are mainly areas such as gaps in the pavement of sidewalks or mulched areas around urban trees with limited opportunities to grow due to landscaping maintenance. Even large cities are frequently visited by several invading species.
For example, common pigeons (Columba livia) or the common kestrel (Falco tinnunculus), which would originally nest on rocky walls, find suitable nesting areas in tall city buildings. They now live year-round in many of our cities.
LICHEN AS A BIOLOGICAL INDICATOR
In some cities, lichen is used as a biological indicator to test air quality. Lichen is very sensitive to pollutants as well as changes in climate. If fruticose lichen still grows in an urban area, it is said to have clean air.
If lichen mainly consists of foliose lichen, then the air is considered slightly polluted (50-70\u.g of sulfur dioxide/m^3). The air is considered to be polluted (70-100 u.g of sulfur dioxide/m^3) if crustose lichen are dominant or heavily polluted (more than 100 [u.g sulfur dioxide/m^3) if only few crustose lichen are growing in an area.
ISSUES TO SOLVE
SUBURBAN RECREATIONAL AREAS Nowadays even the areas surrounding many cities are changing and losing their natural characteristics as they are intensively used and modified for recreational purposes.
These ecosystems require many protective measures to ensure that they do not disappear.