3-56 



causing extensive freezing in the harbor during January and February. 

 As a result of heavy rains, 1972 runoff was greater than other years, 

 resulting in reduced salinity values. Spring and fall stratification 

 due to spring snowmelt and fall runoff respectively were regular occur- 

 rences. Dissolved oxygen levels peaked in the colder months and during 

 major phytoplankton blooms; minimiom concentrations were observed in 

 midsxmiiner. Dissolved oxygen increased more slowly in 1974, 1975, and 

 1975 from summer minima to winter maxima than in other years. Trans- 

 parency and pH did not vary substantially from year to year. 



Winter temperature minima occurred in January or February and 

 summer maxima occurred in July or August in all years. Temperature was 

 most variable in the inner harbor, relatively remote from the moderating 

 influence of Long Island Sound. 



In all years, stratification patterns were primarily dependent 

 on precipitation and runoff within the tributary basins . Temperature is 

 less important than salinity in controlling density, and hence strati- 

 fication; thus the river mouths and inner harbor were stratified most 

 often and most dramatically. Relatively stable thermal stratification, 

 typical of less well-mixed, deeper coastal areas, was not characteristic 

 of New Haven Harbor in any years studied. This is indicative of a high 

 degree of turbulent mixing due to wind and tidal effects in this shallow 

 harbor . 



Dissolved oxygen concentrations showed typical seasonality, 

 with reduced levels in summer months. This summer reduction is caused 

 by a decrease in oxygen soliibility (which is inversely related to both 

 temperature and salinity) and by increased BOD from heightened bacterial 

 decomposition of organic wastes , which is also directly related to 

 increased temperatures. In the inner harbor, there were many DO read- 

 ings below 4.0 ppm in July, August and September in all years. Higher 

 and less variable concentrations were typical of the outer harbor. 

 Unusually high values in near-surface layers may be attributable to 

 production of oxygen through active photosynthesis by phytoplankton, or 

 to exceptionally strong turbulent mixing. 



