INTRODUCTION 



Intermediate and brackish tidal marshes are some of the most productive and, unfortunately, 

 some of the fastest disappearing coastal ecosystems in the Gulf Coastal Region (Craig et al. 1979). 

 The major reason for large losses of intermediate and brackish marsh is saltwater intrusion. Several 

 natural and human-induced factors influence the rate of saltwater intrusion and resultant marsh loss 

 (Salinas et al. 1986). They are: 1) regional subsidence, 2) eustatic sea-level rise, 3) freshwater and 

 sediment diversion away from coastal marshes, 4) deep-water channel and levee construction for 

 navigation and hydrocarbon production, and 5) improper or insufficient marsh management. In 

 general, the effects of these vary from locality to locality depending upon distance from the Gulf 

 of Mexico or a tidal water source, amount of freshwater head in drainage basin, amount of 

 available sediment, degree of minerals production, and presence of structures affecting natural 

 hydrologic patterns. 



The National Audubon Society's long-term interest in marsh ecology and management is based 

 on recognition of the national importance of the Nation's wetlands, recognition of the special 

 importance of southwest Louisiana's marshes to numerous waterfowl and non-game wildlife species, 

 both resident and migratory, and land stewardship. The Society's interest and research in coastal 

 wetlands began with the work of Robert Allen and Alexander Sprunt in the 1930's and 1940's. The 

 Audubon Society's research program was the first founded by any private conservation group and 

 has expanded continuously since its origin. 



The National Audubon Society's Paul J. Rainey Wildlife Sanctuary was established in 1926 by 

 bequest from the estate of Paul J. Rainey. The sanctuary consists of 26,000 acres of intermediate 

 and brackish water marshes in Vermilion Parish. The Society is obliged by deed to provide habitat 

 for wintering snow geese. Marsh management is, therefore, centered around the production of 

 Scirpus olneyi, the snow goose's preferred forage. Management practices include prescribed 

 burning, water management, and muskrat population control. 



With the recent quantification of marsh loss in Louisiana by numerous studies, identification of 

 many processes causing marsh loss, and serious questions arising on the effects of marsh 

 management practices, the Society's interest in quantifying its own management practices intensified. 

 In 1984, a long-term study was begun which will span 6 years. The purpose of the study is to 

 identify and quantify marsh processes, quantify marsh management practices, and provide a data 

 base sufficient to evaluate ongoing processes and future changes in the system. 



This report compares the hydrology, salinity, and vegetation characteristics over a 2-year period 

 (May 1985 to May 1987) between two adjacent marsh watersheds-the free-flowing Toms Bayou 

 and the semi-impounded Big Island Bayou. 



METHODS 



Location and Site Description 



Both Toms and Big Island Bayous flow northward, each draining several thousand acres of marsh. 

 A steel piling fixed -crest weir was placed near the mouth of Big Island (BI) Bayou in 1967. The 

 Big Island watershed is further modified by the loss of portions of the westernmost watershed by 

 the construction of the Mcllhenny Canal and adjacent levee in the early 1900's and the construction 

 of ditch systems connected to the Mcllhenny Canal by way of additional small scale fixed-crest 

 weirs. These later structures have been added in the past 25 years. 



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