sulfide, and soil water salinity. The redox potential of a soil can be used as a measure of the 

 stress imposed on plants by waterlogging. Reduction potentials in waterlogged soils range from 

 +350 mV to -350 mV. Conditions that produce +350 mV to -125 mV make nitrogen and 

 phosphorus more available to plants than in drained, oxidized soils (Mitsch and Gosselink 1986). 

 However, if the redox potential of the soil becomes highly reducing, specialized anaerobic bacteria 

 will convert sulfate to hydrogen sulfide, which can be toxic at high concentrations (Patrick and 

 DeLaune 1977). Hoar (1975) showed that hydrogen sulfide production should occur at a shallower 

 depth in managed marshes than in unmanaged marshes. But Hoar did not detect a difference 

 between the concentration of dissolved hydrogen sulfide in the managed marsh and in the 

 unmanaged marsh. He did not evaluate the effect on plant growth of the slight difference in redox 

 potential in the upper layer of soil. 



Hoar (1975) noted that the free -soil-water salinities fluctuated with water salinities. During his 

 study there was an unusually large amount of rainfall, and the water in the upper end of the 

 Barataria Basin was fresher than during the previous year. The weirs buffered incoming fresher 

 waters with the slightly saltier water present from the previous year. As a result, free -soil-water 

 salinities in marsh affected by weirs averaged 6.0 ppt and in marsh unaffected by weirs averaged 

 5.6 ppt. 



Effects on Waterfowl 



Chabreck (1968) reported that migrant ducks concentrated in managed ponds on Marsh Island 

 because they were attracted by the abundance of food and water. During January, February, and 

 March, low tides ranged from 0.33 m to 0.43 m below sea level, and Chabreck and Hoffpauir 

 (1962) computed that a -0.67 m tide would drain 2.4% of the managed ponds and 84.0% of the 

 unmanaged ponds. 



Spiller and Chabreck (1975) made monthly aerial counts of waterfowl in nine managed marsh 

 ponds and nine unmanaged ponds in upper Barataria Basin (Figure 1). Seventy-four percent of 

 the birds counted were present during winter months, 75% of which were found in managed 

 ponds. The greatest difference in duck use between areas was in December and February and 

 was attributed to the lack of water in unmanaged ponds. 



Effects on Non-game Birds 



Spiller and Chabreck (1975) also compared use of managed ponds and unmanaged ponds by 

 non-game birds (mostly wading birds, gulls, and terns; Figure 2). Most of these birds feed on 

 small fish and crustaceans and are therefore dependent on water to provide suitable habitat. Most 

 of the non-game birds counted throughout the year were counted in winter, during which time 

 more were in the managed ponds than in the unmanaged ponds. This difference was attributed 

 to the lack of water in the unmanaged marsh. The authors reported that during other winter 

 months, the non-game birds stayed in the unmanaged ponds as they drained because the marine 

 organisms on which the birds fed became concentrated in pools. As the north winds continued, 

 water drained from these ponds and the birds moved to the managed ponds, which still contained 

 food and water. When the north winds abated, water returned to the unmanaged areas and the 

 birds dispersed. Because the cycles usually occur over a period of several days, no significant 

 difference in use by non-game birds was detected between the managed and unmanaged areas 

 during the other winter months, even though the birds may have used one type more than the 

 other at different times. 



145 



