caged evaporation pan; four rain gauges, and a max-min recording thermometer. Vegetation plots 

 (20 x 100 m) were established for burned, unburned, and grazed treatments, and for marsh soil and 

 water sampling. The hydroperiod was calculated for the field station areas by establishing the 

 elevation at 1-m intervals for a distance of 50 m in four directions from the well. Average 

 elevation was used to determine the length of time (days) the marsh was inundated (Duever 1977). 



Salinity 



Salinity was measured by using Yellow Springs Instrument-SCT meter and an AO temperature- 

 compensated refractometer. Paired data are defined as salinity data that were taken at all stations 

 at nearly the same time or at least within the same marsh conditions (usually within a day). 



Surveying 



All stations were surveyed and referenced to U.S. Geological Survey marker AUD 2 with an 

 assumed elevation of 1.524 m above MSL. The closest known elevation marker is on Chenier au 

 Tigre and its stability is questioned. Surveying was done with a TOPCON self-leveling transect, 

 a 100-m tape, and telescoping rod marked to the nearest 0.5 cm. 



Vegetation 



Vegetation characteristics were measured by clip-plotting five 0.1-m 2 plots chosen randomly along 

 the 100-m transect. Vegetation height was measured, plants clipped at soil surface, sorted to 

 species, live and dead material sorted, stems counted, dried at 100 °C for 24 h, and weighed to 

 the nearest 0.1 g by using an O'Haus triple beam scale. Sampling was conducted at 3-month 

 intervals from April 1985 through July 1986 and in July 1987 at all stations. Four-inch-diameter 

 soil cores were taken from the lower right hand corner of each clip plot on each sampling date. 



Cores were subdivided at depths of 0-10 cm and 10-30 cm, sorted for root material, dried, and 

 weighed as belowground material. Sampling was done on all vegetation plots but only those data 

 from plots burned in the late fall or early winter were used in this report. 



Tide and Climate Monitoring 



A water-level recorder was set up at Fearman Bayou to measure tidal water fluctuations, and 

 salinity was measured at this station. Establishing water levels and salinity of incoming and 

 returning tidal water is important in interpreting marsh water-level records. Other data necessary 

 for understanding marsh hydrology are rainfall and potential evaporation, which were collected at 

 the field stations as well as the main weather station (U.S. Weather Bureau 1970). 



RESULTS 



Elevation 



Marsh surveying recorded marsh elevations every 50 m across the open marsh and at intervals 

 of 1 or 5 m along transects across field stations. The marsh surface had a slight downward slope 

 towards the north and west. Toms Bayou marshes averaged approximately 20 cm higher than Big 

 Island marshes to the west at similar latitudes (TBU= 1.371, BIU=1.178; TBD=1.436, 

 BID = 1.116 m above MSL). Both downstream stations are located in marshes developed behind 

 natural bayou levees with elevations above MSL of 1.600 m at TBD and 1.251 m at BID. Note 

 that the top of the levees are at an elevation slightly higher than the upstream marsh surfaces (0.16 



134 



