entering the estuary during the summer months. The winter nutrient 

 concentration has little influence on the estuary or its phytoplankton 

 productivity, as phytoplankton productivity is low in winter. In the 

 Sheepscot estuary, for example, winter production is only 10% of that in the 

 summer and nutrients are not likely to be limiting at that time in Maine 

 estuaries (Garside et al. 1978). 



The distribution of nitrate versus salinity in the Sheepscot Estuary in 

 September 1976 is shown in figure 5-31. Extrapolation of a line through these 

 data points to the maximum salinity expected close to the mouth of the estuary 

 (32.8 ppt) indicates a source water containing just over 9 PM nitrate. This 

 water was tentatively identified by Garside and coworkers (1978) as Maine 

 Intermediate Water, and described by Hopkins and Garfield (1979) as having a 

 salinity of 32.5 ± 0.5 ppt and a temperature of 4.5 ±1.5 C. It is a rich 

 source of oceanic nutrients that is available to the Sheepscot Estuary because 

 of its relatively deep entrance. In coastal Maine a concentration of 9 uM 

 nitrate is considered a relatively high concentration. 



Since the relationship between nutrient concentration and salinity can be 

 expected to be linear in the early fall only a pair of nutrient/salinity 

 values would be needed to describe the distribution and determine the nutrient 

 concentration in ocean water entering any Maine estuary. Data gathered in 

 September, 1978, in a number of Maine estuaries (Presumpscot , Kennebec, 

 Sheepscot, Damariscotta , Penobscot, Machias, Cobscook Bay, and the St. Croix) 



a. 



(0 



12 



10 



28 



1 



29 



30 31 



Salinity °/oo 



32 



_l 

 33 



Figure 5-31. 



Nitrate concentration (uM) and salinity (ppt) in the Sheepscot 

 estuary in September 1976 (Garside et al. 1978). 



5-56 



