Under these adverse hydrologic conditions, plant diversity and wildlife and fishery habitat quality 

 were reduced. To enhance the wildlife habitat of these marshes, Taylor and his staff constructed 

 ni.ie marsh semi-impoundments. Each semi-impoundment was managed through the use of one 

 or more flap-gated, variable-crested water control structures. Semi-impoundment 2, however, was 

 managed through the use of a variable-crested weir until 1986, when a reversible flap gate was 

 installed. Table 1 lists information concerning each semi-impoundment and its associated water 

 control structures. Two large diesel-powered low-lift pumps provided forced drainage capability to 

 the three large northern semi-impoundments (units 3, 4, and 9) via interconnecting tranasses. 

 Variable-crested water control structures located on the interconnecting tranasses allowed these 

 units to be managed independently or together. 



At LPWMA, the fresher marsh types were located in the northern and eastern areas (units 3, 

 4, and 9), whereas the more brackish marsh types were located in the southern and western areas 

 (units 1, 2, 5, 6, 7, and 8). Despite being classified as fresh, intermediate, and brackish (Chabreck 

 and Linscombe 1978), marshes throughout LPWMA were dominated by wiregrass (Spartina patens). 



METHODS 



Water Level Drawdowns 



The purpose of drawdowns at LPWMA was to enhance the production of high quality waterfowl 

 food plants in order to attract ducks. These drawdowns simulated low water conditions that 

 occurred more frequently prior to hydrologic modifications (canal construction) in the region. 



Gadwall (Anas strepera) was by far the most abundant and frequently harvested duck at 

 LPWMA. Because the preferred foods of gadwall are aquatic plants such as sago pondweed 

 (Potamogeton pectinatus), southern naiad (Najas guadalupensis) and widgeon grass (Ruppia 

 maritima), drawdowns and marsh management practices were geared primarily toward the 

 production and maintenance of these aquatic plants. A secondary objective of drawdowns at 

 LPWMA was the germination and production of annual grasses whose seeds are preferred food 

 of mallards (Anas platyrhynchos), teal (Anas spp.), and many other dabbling ducks. The ability of 

 drawdowns to stimulate germination of annual grasses and submerged aquatic vegetation has been 

 well documented (Lynch et al. 1947; Chabreck 1960; Kadlec 1962; Harris and Marshall 1963; Linde 

 1969; Fredrickson and Taylor 1982; Prevost 1987). The most commonly produced annuals included 

 flatsedges (Cyperus sp.), Walter's millet (Echinochloa walteri), and bearded sprangletop (Leptochloa 

 fascicularis). Drawdowns were normally attempted once every third to fourth year within any given 

 semi-impoundment. Drawdowns were begun in March and terminated in June or July. Although 

 three semi-impoundments had forced drainage capability, drawdowns in these areas were 

 accomplished primarily through gravity drainage. Forced drainage was occasionally used to 

 complete a drawdown when completion by gravity drainage was inadequate, or to remove 

 accumulated rainfall when it threatened an otherwise successful drawdown. 



The occurrence of several wind-induced low tides associated with frontal passages in March and 

 April greatly facilitated dewatering efforts. In order to maximize drainage during these 

 exceptionally low tides, all stop-logs were removed. Rainfall during this period often prevented 

 total dewatering. During June and July drawdowns became dependent on continued low 

 precipitation and increasing rates of evapotransportation or forced drainage. 



Four factors were necessary to achieve a successful gravity drainage drawdown: 1) setting water 

 control structures deep enough to allow drainage of ponds; 2) designing and installing water control 



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