3.6pM respectively. The corresponding N:P ratios were 2.5:1 and 1.4:1 

 indicating that nitrogen would be the potentially limiting nutrient, as the 

 ratio of N:P taken up by phytoplankton is much higher than this. The nitrate 

 concentrations in the fresh and saline source waters are 6.9 and 3.5 y M, 

 respectively. Since the estuary's nitrate concentration ranges between 3.6 

 and 6.7 pM it is probable that nutrient loading from sewage in the river has 

 elevated nutrient concentrations throughout the estuary by about 1 to 2 pM. 



Flushing of this estuary by tidal exchange and runoff is very rapid (figure 5- 

 32). The salinity distribution supports this conclusion. The two sampling 

 sites, which are less than 2 miles (3.2 km) apart, span a wide salinity range 

 (2.3 to 31.6 ppt) . Apparently, ocean water does not penetrate far into the 

 estuary and the large tidal exchange relative to subtidal volume ensures that 

 the nutrients in the estuary will be flushed rapidly to the coastal waters. 

 No other nutrient data are available for this estuary. 



Kennebec estuary . The entrance to the Kennebec is about 35 feet (11 m) 

 deep and thus may have a low supply of nitrate from sea water. The Kennebec 

 also receives a supply of salt water from the Sheepscot via the Sasanoa River 

 (a net exchange of fresh water in the opposite direction takes place; see 

 "Hydrography" above). As a result, the actual nitrate concentration in the 

 saline source is expected to be somewhere between 1.7 pM, (on the basis of the 

 sill depth) and 9.2 pM if all the saline water were to enter from the 

 Sheepscot estuary via the Sasanoa River. 



Measurements made in September, 1978, indicate that at Bath and Phippsburg 

 salinities were 5.26 and 23.38 ppt and nitrate concentrations were 18.7 and 

 8.7 yM, respectively. The N:P ratios were 17:1 and 7.3:1, respectively, which 

 suggests that nitrogen is the potentially limiting nutrient over most of the 

 estuary. The coastal source water would have an expected nitrate 

 concentration of 4.0 yM and the fresh water would have an expected 

 concentration of 21.5 pM (Garside, unpublished ) . The high value of nitrogen 

 in fresh water may be attributable to the local sewage outfall rather than to 

 all the fresh water entering the estuary. The complexity of the sources of 

 seawater and freshwater exchange between the Sheepscot estuary and the 

 Kennebec estuary makes a simple application of a mixing model less than 

 satisfactory. 



Because the Kennebec has both a large fresh water flow and a large tidal 

 exchange relative to its low tidal volume nutrients from the ocean water would 

 not be expected to penetrate far into the estuary and rapid flushing would 

 tend to minimize the residence time of nutrients from the fresh water in the 

 estuary. On this basis the Kennebec is not expected to be a highly 

 productive estuary; however, the complex circulation and nutrient source 

 distribution may increase the productivity of this estuary. Three sources of 

 nutrient data on the Kennebec system are available. The USGS's gaging and 

 water quality station at Bingham reports nitrate plus nitrite nitrogen, as 

 well as Kjeldahl nitrogen. Mean nitrate plus nitrite was 8 UM with a seasonal 

 high in winter and low in summer ranging from 13.6 to 5 PM, respectively. 

 Total Kjeldahl nitrogen was about twice that of the mean inorganic nitrogen 

 with no seasonal trend. This input would be an insignificant source of 

 support for primary production in the estuary. 



5-62 



