lb 



Figure 72. A weir in the deltaic plain marshes. The strong flow of water across the 

 weir is an indication of the effectiveness of the barrier. These structures are 

 favorite sport fishing spots (Photograph by Robert Chabreck). 



show that the production of the desired 

 emergent annuals and aquatic plants was 

 variable. Even with pumps it was not 

 possible to control water level in very 

 rainy years like 1973, and the level of 

 control decreased as the sophistication of 

 the control devices decreased. In general, 

 the better the water level management, the 

 greater the diversity and desirability of 

 the vegetation (Figure 74). 



Water level management in the 

 Rockefeller Wildlife Refuge is credited 

 with increasing waterfowl use from a peak 

 population of about 75,000 ducks in 1951 - 

 1952 to over 400,000 dabbling ducks, 

 40,000 coots and 10,000 diving ducks in 

 1958 - 1959 when the control structures 

 were put into use (Chabreck 1951). The 

 freshwater impoundments attract the most 

 ducks; use of brackish water impoundments 

 (usually areas in which water exchange 



with the surrounding marsh is not 

 completely cut off) is comparable to 

 unmanaged marshes (Chabreck et al. 1975; 

 Davidson and Chabreck 1983). 



The value of freshwater impoundments 

 for species other than ducks is not as 

 clear; fur animals, geese, and marine 

 organisms are not benefitted (Chabreck 

 1975). However, crawfish can be 



successfully raised in impoundments 

 managed for ducks (Perry et al. 1970). 

 Brackish marsh impoundments seen to yield 

 excellent crops of marine shellfish and 

 fish if the control gates are managed to 

 allow the juvenile organisms access during 

 their immigration periods (Davidson and 

 Chabreck 1983). Figure 75 summarizes the 

 effectiveness of impoundments. 



Marshes, inside impoundments and out, 

 are often burned as a management practice. 



95 



