. The ecology of delta marshes of coastal Louisiana : a community profile. Marsh ecology -- Louisiana; Wetlands -- Louisiana. Mississippi Amife Tickfaw Pearl. eo i \^[j^EP[MILIOli_.* , "^ ^T^Lwi, n I PONTCHARTRAIN. jATCHAFALAyA\ 1 G U i /^ MISSISSIPPI ,'^^v|R DELTA O F M £ X / C Figure 10. Freshwater inflows to the Mississippi Delta. (Oata from IJSGS 1978). Discharges are in cuinecs. All discharges are for water year 1978 except Mississippi River, which is a long-term mean representing the combined average annual discharge above the confluence of the lower Mississippi (10400 cumecs) and t
. The ecology of delta marshes of coastal Louisiana : a community profile. Marsh ecology -- Louisiana; Wetlands -- Louisiana. Mississippi Amife Tickfaw Pearl. eo i \^[j^EP[MILIOli_.* , "^ ^T^Lwi, n I PONTCHARTRAIN. jATCHAFALAyA\ 1 G U i /^ MISSISSIPPI ,'^^v|R DELTA O F M £ X / C Figure 10. Freshwater inflows to the Mississippi Delta. (Oata from IJSGS 1978). Discharges are in cuinecs. All discharges are for water year 1978 except Mississippi River, which is a long-term mean representing the combined average annual discharge above the confluence of the lower Mississippi (10400 cumecs) and the Atchafalaya (5000 cumecs) Rivers. centimeter per year (Figure 11a). This is double the rate anywhere else along the eastern United States coast (Table 3). Superimposed on this long-term trend is a seasonal variation in mean water level that itself has an excursion of 20 - 25 cm. This bimodal variation (Figure lib) occurs consistently throughout the different salinity zones of the delta, with peaks in the spring and late sunmer. In the Barataria basin the spring maximum increases in an inland direction, that is from salt toward fresh marshes, possibly because of the considerable volume of surplus precipitation during this time of the year (Baumann 1980). The seasonal changes in water level are attributed to several interacting factors. Water level varies inversely with barometric pressure which averages 1,021 millibars (mb) during December and January and 1,015 mb during early summer and fall. Several investigations have shown that water level decreases nearly 1 cm for each mb increase in barometric pressure ( Lisitzin and Pattullo 1951). Thus the expected mean seasonal range in water level as a response to barometric pressure is approximately 6 cm or 25 percent of the total observed range. In addition, the seasonal warming (expansion) and cooling (contraction) of nearshore waters contribute to a seasonal high in the late summer and a low in January and February. These a
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