al., 1970). Mean monthly temperatures reach peaks in July and August; January 

 is usually the coldest month of year. Mean annual temperatures for this re- 

 gion approach 2l0C, or 70^ (Gagliano et al., 1970). Southeastern Louisiana 

 experiences infrequent "northers" (cold air masses) during the winter; the low 

 temperatures are usually well-buffered by the time a front reaches the delta. 



Two of the most destructive hurricanes in history have come ashore near 

 the Delta Refuge: Betsy in 1965 and Camille in 1969. Resulting economic 

 (structural) damage was extreme, but the disruption of refuge ecosystems was 

 moderate and transient. Flood water completely covered the marshes, thus 

 reducing the destruction of the substrate by wave action; the storm's concomi- 

 tant precipitation nullified the adverse effects of salinity. Large vegeta- 

 tional losses occurred as a result of the sweeping action of wind and water, 

 but recovery was essentially complete after one year (Chabreck and Palmisano, 

 1973). 



Vegetation . The fringe of the delta system is subject to the influence 

 of marine waters. Consequently, there is a zone of salt marsh, dominated by 

 smooth co.rdgrass, grading into a narrow zone of brackish marsh. Plants 

 typical of this latter strip are roseau cane, saltgrass, leafy threesquare 

 ( Scirpus robustus ), and marshhay cordgrass. 



The vegetation of the bulk of the Delta Refuge is typical of fresh 

 marshes. This is because the largest proportion of surface area consists of 

 open ponds, which are flushed by a large volume of fresh water from the Mis- 

 sissippi River; the average discharge is approximately 12,742 m3/sec, or 

 450,000 ft3/sec (Gagliano et al., 1971). 



The natural levees support stands of black willow ( Salix nigra ), ground- 

 sel, coffeebean ( Sesbania exaltata ), and other woody plants. Dogtooth grass 

 ( Panicum repens ) frequently dominates the slopes of the levees. 



Examination of refuge files indicates that species composition of the 

 open ponds exhibits extreme variability through time. This is a consequence 

 of the dynamic forces - primarily hurricanes and river discharge patterns - 

 that interact and control the physical and chemical characteristics of the 

 water column and substrate. Dominant species are ephemeral, and drastic 

 changes in composition may occur within a one-yr period (Valentine, 1970; 

 Chabreck and Palmisano, 1973). Since 1970, the dominant submerged species 

 have included southern naiad ( Najas quadalupensis ), pondweeds ( Potamogeton 

 spp.), widgeongrass ( Ruppia maritima ), and coontail. Floating plants such as 

 water hyacinth, duckweed ( Lemna minor ), and alligatorweed are abundant, except 

 after hurricanes (Chabreck and Palmisano, 1973). Roseau cane, Eurasian 

 watermilfoil ( Myriophyllum spicatum ), water hyssop, bull tongue, and delta 

 duckpotato ( Sagittaria platyphylla ) dominate the emergent zones. 



71 



