It is concluded that the rate of penetration of heat into the marsh peat is 

 of the order of magnitude to be expected if the interstitial water is stagnant. 



The distribution of chloride in the interstitial water at the same site is 

 given in Figure 15. The distribution suggests a steady state due to a balance 

 between a downward movement of salt water by some form of eddy diffusion 

 and an upward movement of ground water. If such movements occur they 

 must be reconciled in magnitude with the conclusions from the temperature 

 observations , 



The minimal vertical movement which might be considered is that re- 

 quired to balance the molecular diffusivity of salt. This would result in a 

 steady state distribution of chloride described by the equation: 



V5 





w^here a is the velocity of advection upward 



^ is the molecular diffusivity of salt 



3/5 is the ratio of chloride at the depth, x, to that at the surface. 



This equation yields curves which are concave downward but the fit is not good. 

 An approximate fit as shown in Figure 15 is obtained taking -^ z 0.25 cm. /sec. 

 If A is given the value of 10"-*, the diffusivity of NaCl,then a becomes 

 2.5 X 10" cm, /sec. which is only 1 percent of the velocity of the thermal 

 wave. 



If molecular diffusivity is the mechanism responsible for salt transport, 

 the associated advection will have an insignificant effect on the thermal diffus- 

 ivity. 



Arons and Stommel (1951) have developed an equation to describe the 

 steady-state distribution of salt in an ideal estuary. Fresh water is assumed 

 to enter a channel of uniform cross section at one end with a constant velocity, 

 Q,, while salt water enters the other end from a source of constant salinity, 

 S , and is mixed with the outflowing fresh water by an eddy diffusivity,^ , 

 ascribed to tidal motion, which diminishes in value with distance from the sea. 

 The steady-state concentration of salt along the channel is given by 



Vso = s (1) 



in which F is a dimensionless parameter defined by 



A. - ^Ik 



o- - F (2) 



where L is the total length of the channel, X is the distance from the source 

 of fresh water, and ■\ ^ X . 



"^ - T 



Equation (1) describes the chloride distribution in the marsh peat closely 



79 



