The Big Island weir was constructed on National Audubon Property in cooperation and 

 accordance with State Wildlife Refuge practices at the time. The weir was constructed to prevent 

 conditions of saltwater intrusion and marsh overdrainage by local and regional construction of deep 

 water channels (most notably, channelization of Southwest Pass and of Freshwater Bayou, dredging 

 of Four Mile Cut, and the earlier construction of the Mcllhenny and Brunner Canals on the 

 sanctuary). Semi-impoundments were constructed also to enhance habitat for fish and animal life 

 by encouraging aquatic vegetation growth (Larrick and Chabreck 1976). Fisheries work by Herke 

 (1979) and Herke et al. (1987) have shown that semi-impoundment by fixed-crest weirs decreases 

 fishery usage and yield. 



Toms Bayou (TB) remains a pristine marsh watershed. No major deepwater channels are near, 

 the system is free-flowing, and only minor non-diversionary ditching has occurred in the upper 

 portion of the watershed. 



Two sampling stations were installed in both TB and BI bayou watersheds (Meeder 1986). One 

 station was placed in the downstream (D) and one in the upstream (U) portions of each watershed. 

 Marsh differences between upstream and downstream sites were elevation (Table 1), plant species 

 composition, and distance from bayou mouths. 



Instruments placed at each station included a Stevens F-Type water-level recorder, with QMT 

 clocks set for 16 days, placed on a 4-inch-diameter perforated pipe hand-driven into the marsh; a 



Table 1. Summary of marsh site characteristics. 



a TBU = Toms Bayou upstream marshes 

 TBD = Toms Bayou downstream marshes 



b BIU = Big Island upstream marshes 

 BID = Big Island downstream marshes 



c aboveground biomass (g dw/m 2 ) 



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