Soil Deterioration in Cities; the Dark Side of Asphalt

The networks that tie our world together are indeed vast constructions, none more so than the roadways that tie our cities, towns and villages together. Roadways the world over are predominantly made of asphalt, an impervious, petroleum-based substance that includes aggregate such as sand or gravel. This same product is used in the installation of the expansive parking lots that characterize suburban development.

What makes asphalt all the more problematic is the fact that water cannot pass through it. As a result, asphalt – in addition to paving the world over – not only dries out the ground below it, but gradually warms the environment in which it is used.

Beyond ecological and aesthetic complexities, asphalt’s chemical makeup also represents a very real threat in both the short and long term. For one thing, asphalt has very high thermal mass properties through which it can retain heat generated from the sun. Said heat is slowly released from pavement over time, creating the heat island effect, which is responsible for increasing temperatures in some cities by as much as ten per cent relative to surrounding rural areas.

Because asphalt is manufactured out of oil, moreover, it releases substantial volatile organic compounds (VOCs) during its production, including carcinogens benzene and toluene. Due to the intricate molecular structure of such compounds, poisonous effects are very real long after the release of VOCs from their points of origin. In other words, paved roads contribute to the disintegration of safe, healthy environments in which acts as simple as breathing connote veritable dangers.

As mentioned, asphalt wreaks havoc on the way water interacts with its natural world. Normally, rainfall is absorbed into the ground as it comes down from the sky, where is it either consumed by plants or integrated into groundwater. As the latter accumulates, it transforms into rivers, streams and lakes. Asphalt disrupts this process completely, as runoff finds itself diverted into sewers where contact with VOCs is inevitable. Forever tainted, sewage water ends up contaminating natural water sources, compromising the water cycle indefinitely.

Nonetheless, the vast asphalt cover represents an unprecedented opportunity to green cities, simply by replacing pavement with trees, brush, and gardens. In fact, the pervasiveness of car parks in proximity to dense population centres translates into the realistic goal of creating urban agricultural hubs in cities around the world.

Furthermore, removing asphalt allows soil to absorb much needed rain and air, in turn enabling plants to reach rich minerals deep beneath the ground, while stabilizing the water cycle. By extension, if local agricultural practices are to take shape, it is first and foremost vital to end the construction of roads, a process to be followed by the elimination of paved land in urban areas.

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