ABSTRACT
There is a growing concern that large cities are reaching a size where the beneficence of nature is being surpassed in terms of providing fresh water, breaking down the pollution loads generated by city-based activities (or through dilution, rendering them less hazardous), providing all the raw materials that city producers and consumers use, and yielding cheap and easily exploitable energy sources. The preceding pages have noted many examples of local ecosystems’ carrying capacities being exceeded: freshwater withdrawals exceeding aquifers’ natural rate of recharge; levels of organic pollutants from industries, sewers and urban run-off exceeding the capacities of rivers and estuaries to break them down; and city-based demands for wood-fuel, timber and bricks exacerbating deforestation, soil erosion and loss of agricultural land. Urban areas often expand over prime agricultural land; so too do waste dumps to cope with the increasing volume of solid wastes generated by city-based producers and consumers. In many cities, there are problems of acid rain that damages soils, trees and crops in surrounding areas.
