28 



disposal of paper mill wastes into the river. No other station is so 

 influenced. 



Examination of Fig. 10 shows that organic carbon levels lower than 

 the average are generally confined to the approaches to Portland Harbor 

 and the offshore stations. Stations with organic carbon levels 

 considerably higher than average occur in a group in lower Casco Bay off 

 Portland and Falmouth and at scattered sites close to land in the upper 

 Bay. In an attempt to elucidate potential controlling factors of 

 organic carbon distribution, organic carbon levels are regressed against 

 bottom depth (complex factor), mean grain size and distance from 

 Portland, the principal population and industrial center. Significant 

 relationships exist for both bottom depth and mean grain size (Figs. 11 

 and 12). These relationships suggest that organic carbon levels 

 decrease with increasing depth and increase with decreasing mean grain 

 size. The correlation coefficients are -0.4756 and 0.7742, 

 respectively, and both are significant at the 99.9% level. We show 

 above, however, that bottom depth and mean grain size are themselves 

 related and therefore, it is not clear from this analysis whether 

 organic carbon level is influenced by one or both of these factors. By 

 employing multiple regression analysis, it is shown that organic carbon 

 level is significantly related only to mean grain size (Table 3) . 



