Because these organisms are highly seasonal, monthly 

 sampling of epifauna would likely be required. 



Vegetation 



Certain vegetation species have also proved to be 

 useful indicators of the timing and quantity of 

 freshwater inundation needed to promote sexual 

 reproduction and plant expansion in hypersaline 

 marshes. Annual species like Salicomia bigelovii, for 

 which successful establishment can only occur if soil 

 salinity concentrations are reduced to a level that 

 alleviates the osmoticaUy induced seed dormancy, could 

 provide relevant information regarding the timing and 

 quantity of fresh water needed to promote sexual (seed) 

 colonization in hypersaline salt marshes. Because this 

 species occurs only after significant freshwater 

 inundation events during the fall and early winter, 

 spring-time biomass samples may be useful in 

 indicating relative plant productivity between the 

 stations. 



During the demonstration project, seasonal changes in 

 emergent vegetation cover and biomass were measured 

 and correlated to overall delta productivity in response 

 to freshwater inflow. However, several changes in the 

 sampling procedure could significandy contribute to 

 future monitoring. These changes include the addition 

 of shorter and more closely spaced transects, more 

 detailed sampling of pore water salinity concentrations 

 and focus on the colonization of opportunistic species 

 following major precipitation and inflow events. 

 Primarily, additional vegetation transects should be 

 established in several places located direcdy on Rincon 

 Bayou. While sampling in the tidal flats near the 

 Rincon Overflow Channel {i.e.. Station II) indicated 

 changes after major flow events, vegetational changes 

 direcdy along the upper portions of Rincon Bayou 

 likely occurred after freshwater flow through the 

 Nueces Overflow Channel during relatively smaller 

 positive-flow events. A useful approach would be to 

 sample four transects all on Rincon Bayou, with the 

 first transect being located close to the Nueces 

 Overflow Channel and the fourth transect being near 

 Nueces Bay. Shorter transects with closer sampling 

 lines may provide a more detailed picture of vegetation 

 changes {e.g., 50-m long transects with sampling lines 



spaced 2-m apart). Most importandy, every effort 

 should be taken to ensure that salinity measurements 

 are acquired on each sampling date. Ideally, pore water 

 salinity measurements would be taken at 10-m intervals 

 (if a shorter transect were used) rather than 

 50-m intervals, as accurate and complete salinity 

 measurements are key to understanding the effects of 

 firesh water and consequent changes in ■vegetation. 



Modeling 



The demonstration monitoring program documented 

 changes in biological productivity and species 

 composition in relation to the alteration of the 

 fireshwater inflow regime. There is an opportunity to 

 integrate the various data components of this study to 

 determine; 1) how the marsh would have responded 

 during the demonstration period without project 

 diversions, and 2) how the marsh ecology would 

 respond to different fireshwater inflow conditions 

 Considerably more data would need to be collected to 

 provide these answers through field studies. 



A numerical model could be developed to calculate 

 productivity changes in response to prescribed inflow 

 events. One such modeling concept {e.g., the 

 conceptual model presented in Chapter 7) has already 

 been outlined. Once developed, this model could be 

 used to stmidate productivity in Nueces Delta with and 

 without the demonstration project by using the existing 

 monitoring data to calibrate the model. The change in 

 productivity with and without freshwater inflow would 

 allow calculation of the percent change due to the 

 observed restored flow volume. This change would be 

 a direct estimate of the benefits of the demonstration 

 project. Furthermore, the modeling of other fresh 

 water input scenarios could be used to estimate the 

 benefits of particular permanent diversion project 

 designs. 



A numerical model would also improve the 

 understanding of how the marsh functions under 

 various conditions. Model sensitivity studies could 

 determine transition points within the ecosystem, as 

 well as how to maximize benefits with adjustments in 

 the timing and amount of freshwater inflow. 



Chapter Eight ♦ 8-3 



