STUDIES OF COLIFORM BACTERIA IN THE SEA 



71 



ing the flood tide all of the contours are shifted upstream, and the gradients 

 of salinity distribution with depth are more gradual. 



An important contribution of water circulation to the disposal of 

 pollution is the rate of dilution of the contaminated water. This occurs, 



High Scf>ool Spire 



NAUTICAL MILES 



Fig. 7. The ratio between the observed and the expected bacterial counts at various 

 locations in Mount Hope Bay at different stages of the tide. The expected numbers 

 are computed by correcting the numbers introduced in the Taunton River (N.E. 

 corner of chart) by the degree of dilution with sea water. 



not only by horizontal mixing, but also by the vertical mixing of the sur- 

 face water with the more saline deeper water. The rate of this mixing 

 is increased as the density gradient between the surface and deeper waters 

 decreases. As shown by the salinity contours in Figure 6 vertical mixing 



