Abstract
Densely populated urban areas, which have developed over the last century, depend heavily on centralized water supply, sewage treatment plants, and hydroelectric or thermal power generation with vast demand of cooling water. Considerable areas have been drained or sealed, and the short-circuited water cycle has been distorted. Large rivers have been converted to shipping canals with the permanent risk of accidental pollution. Technical means such as sewage treatment, air filters, emission control and lake and soil restoration measures have contributed to correct the environmental damage. However, a balance sheet for irreversible matter losses (mainly base cation charges) from the urbanized areas and the surrounding landscape into the sea shows ever-increasing trends. These losses are destabilizing the ecosystems.
In this paper, management of the water cycle in urban areas, together with the coupled matter cycles, is discussed. Particular reference is given to Metropolitan Berlin, with a network of shipping canals, which move biologically treated waste, containing base cations and nutrients to the surrounding rural areas. This could create manageable productive wetlands and re-establish soil fertility. At the same time, the natural cooling system close to the urban areas will be improved by providing more areas with permanent vegetation.
In addition, reduction of the present large oscillations of the groundwater table, resulting from groundwater pumping and its recharge with less polluted surface water, is contemplated. The widely used shoreline infiltration of the Havel River should then be eliminated and the severe damage of the littoral vegetation in large sections of the Havel River system be avoided.
