Critical Water Pollution is Inevitable as Population Density Increases
The Moskva River is subjected to heavy pollution along its entire length, but mostly in the Moscow city zone – the zone of the biggest megacity. The first regular studies of the river date from 1898. For over a century of observations, we have accumulated a vast experience in assessing the impact of various urban factors on the river condition.
The key reason determining water purity is city population whose growth led to the increase of population density. The amount of water which is transported by a river per unit time is referred to as river water discharge. If we divide river water discharge by the population number, we obtain specific discharge of the river (SDR), i.e. the amount of water with which river can supply one resident. On account of our experience we can predict the change of the river condition using the data on population dynamics and offer various solutions to the problem of clean water.
Figure 1. Decrease in the specific discharge of the Moskva River (blue) and population growth (red) of Moscow city. The dashed line represents the construction of the additional river canal which improved water quality for almost 50 years.
In the 19th century when Moscow population was about several hundred thousands, and SDR value amounted to more than 4,000 liters of water per person per day, the quality of river water was ensured only by self-purification processes. Pollutants produced by people were partially diluted, precipitated, and disposed of naturally. As the population increased, SDR value of the Moskva River was inevitably decreasing (Fig.1), i.e. water became more and more polluted.
Later, at the beginning of the 20th century, Moscow as well as other megacities experienced a rapid growth of population reaching 200 thousand people per year. This was a catastrophe in terms of water quality, not to mention self-purification processes: the earlier constructed treatment facilities did not cope with the increased load so that untreated effluents were 20 to 40% of the total river flow.
When treatment facilities have insufficient capacity, the solution to the water quality problem may involve additional dilution of polluting effluents. In 1937, an additional canal was built to double the amount of water in the channel of the Moskva River by means of the basin of the Volga River. This decision for a certain period improved water quality and helped to increase the SDR value, although the population kept growing.
To solve the problem of the Moskva River pollution supplementary measures included sewerage system development, treatment facility improvements, and also the development of regular water monitoring system.
Our experience in analyzing the ecological situation in water-resource system of the megacity is based on a century-old experience of search and decision making for providing access to clean water. This experience enables us to use an integrated approach which includes pollutant analysis, assessment of population dynamics and population density, analysis of the evolution of treatment and hydraulic facilities. Investment in the development of such a densely populated region should always be justified by such an integrated analysis of the situation.
Full Text:
Shchegol’kova, N. M. (2007). Urban effect on the formation of the Moskva River environmental state (historical aspect). Water Resources, 34(2), 217-228.