stations. The annual species Suaeda maritima, Lycium 

 carolinianum^ and Umonium nashii were occasionally 

 found at the stations. 



Open Water and Pore Water Chemistry 



Four replicate open water samples were collected from 

 the water adjacent to the sampling transects. Two 

 replicate sediment pore water samples were collected 

 using lysimeters placed within the transect sediments at 

 the 0, 49 and 99 m marks. Lysimeters were made of 

 PVC pipes (6 cm diameter, 60 cm length) with 

 horizontal slits cut in the lower 30 cm to allow for the 

 passive movement of water into the pipe. Prior to 

 sampling, lysimeters were pumped dry and aDowed to 

 refill. If water were unavailable, sediment samples 

 were taken and later centrifuged to extract pore water. 

 After being centrifuged, salinity of pore water samples 

 was determined using a refractometer. Oftentimes, the 

 sediment was too dry to extract any water, and 

 therefore data were not acquired on several sampling 

 dates. In the field, open water sahnity was recorded 

 witli an Orion conductivity meter and reported in ppt. 

 AU samples were collected in botdes and placed on ice 

 for later determination of ammonium (NH4*) and 

 nitrite plus nitrate (NO, + NO3) levels. 

 Concentrations of NH4*, and NO, + NO3 were 

 determined using standard colorimetric techniques 

 (Parsons ^/-a/. 1984). 



Freshwater flow through Rincon Bayou and direct 

 precipitation were also measured during the 

 demonstration period (Chapter 3). Daily data for these 

 two freshwater variables were summed according to 

 the periods tmmediately preceding each vegetation 

 sampling date to allow comparison with salinity values. 



Transect Sampling 



Seasonal vegetation distribution and abundance were 

 quantified using transect sampling (Bertness and 

 Ellison 1987). Generally, sampling occurred in the late 

 spring (~June), late summer (~September), late fall 

 (~December) and mid-winter (~January). The 

 sampling schedule was based on a previous study in the 



Nueces Delta, which suggested that the emergent 

 vegetation exhibits peaks and declines in growth at 

 different times of the year. Annual species were noted 

 to increase in cover during the late spring but were 

 non-existent throughout the summer, fall and winter. 

 Additionally, many species exhibited a reduction in 

 cover during the late fall because of the shedding of 

 their leaves. Late summer sampling was chosen 

 because the plants typically experience several months 

 of increased temperatures and decreased rain. Mid- 

 winter sampling was selected because it is the time of 

 year when plant cover is typically low, but annual 

 species seedling growth has begun. 



In June 1995, three permanent transects were 

 established, one at each station. The transects were 

 99 m long and 8 m wide (792 m^ at the Reference 

 Station and Station II (Figure 6-2), and 103 m long and 

 8 m wide (824 m^ at Station III. At all three stations, 

 the transect lines were spaced at 3 m inter\^als for the 

 first 9 m of the transect. At the Reference Station and 

 Station II, the lines were spaced at 10 m intervals 

 between 9 and 99 m. Each transect extended 

 perpendicularly from the vegetation line at the water's 

 edge. The transect lines were spaced closest together 

 near the water's edge because this was expected to be 

 the part of the transect showing the greatest variation 

 in degree of tidal inundation and soil moisture. 

 Station III differed in transect size and sampling 

 intervals because a small channel intersected the 

 transect between the 47 m and 57 m marks, resulting in 

 the occurrence of three water's edges at this station. 

 The transect design for Station III was different from 

 the Reference Station and Station II because there was 

 no area large enough to encompass at least a 99 m 

 transect direcdy along Rincon Bayou. However, the 

 difference in transect design was inconsequential 

 because the three stations were uniquely different, and 

 direct statistical comparisons between the stations was 

 not necessary. At Station III, the lines were spaced at 

 10 m intervals between 9 and 39 m, 8 m between 

 39 and 47 m, 10 m between 47 and 57 m, 3 m inten'^als 

 between 57 and 63 m and 10 m inter\'als between 

 63 and 103 m. The transects were sampled at 2 m 

 intervals along the horizontal transect lines, for a total 



6-4 



Vegetation Communities 



