344 THE STUDY OF PLANT COMMUNITIES • Chapter XII 



south grid pattern of blocks, which disregarded topography and 

 provided a powerful system of artificial drainage. Also great drain- 

 age projects were instituted in the earlier days of agriculture, and 

 these, too, served to speed the removal of water. 



The trend in concern over surface water proceeded from drain- 

 age projects to those dealing with flood control. Such concern is 

 still with us, and necessarily so, because of the destructiveness of 

 floods to both property and land, but, a new trend is now apparent 

 in the attempts to conserve, retain, and store water so that it may 

 be available when needed, so that water tables may be held at 

 higher levels, and so that flood waters may be controlled. Dams 

 and reservoirs are being constructed and watersheds are being 

 protected. 



A recent factor in the lowering of water tables is the great in- 

 crease of use of water in industry and the rapid increase of air- 

 conditioning. Much of the water used for the latter is wasted 

 because it is not used for any other purpose. The lowering of the 

 water table by using water for this purpose has caused much con- 

 cern in large cities. Various legislation is aimed at controlling the 

 use of this natural resource. Most large users drill their own wells, 

 but this practice is being limited. In some cities, it is required that 

 the water must be forced back into the earth at the levels from 

 which it is drawn. 



Our water supply is a natural resource just as are the others we 

 have discussed. When its availability is reduced, it affects agricul- 

 ture, industry, fish and game, recreation, and perhaps home use. 

 The trend is already in the direction of its conservation. Probably 

 it will go further. Ecological problems of many kinds will arise in 

 connection with control of water in streams and reservoirs, and 

 the effects upon water table levels. It is a part of all the applied 

 ecology we have discussed. 



Another facet of the problem of water supply is its pollution by 

 industrial waste and sewage. Here again, there are innumerable 

 problems of an ecological nature. Their solution often requires the 

 co-operation of engineers, chemists, bacteriologists, and limnol- 

 ogists. As always, when such specialists are drawn together, their 

 success is greatest when they see their own fields in relation to the 

 whole. This is the ecological approach. 



