Most importantly, the establishment of Salicomia higelovii 

 corresponded to a decrease in bare area at all three 

 vegetation sampling stations, with the decreases in bare 

 area being proportional to the increase in S. higelovii 

 cover. Decreases in bare area coxild have direct affects 

 on the functionality of the marsh. Other studies have 

 noted that halophyte species, which can occupy bare 

 areas following disturbance events through sexual 

 (seed) reproduction, can act to reduce soil salinity 

 concentrations by shading the soil surface and by 

 actively up-taking salts. The reduction in soil salinity 

 can eventually allow the establishment of dominant and 

 persistent perennial species. These plants can then 

 provide stable habitat and food for many small 

 organisms and for a variety of permanent and 

 migratory birds, as well as provide large amounts of 

 plant biomass to the detrital food-web, which boosts 

 productivity of higher trophic levels. Without the 

 expansion of vegetation into bare space, the 

 functionality of that marsh area would be 

 compromised. 



The response of Salicomia higelovii also differed after 

 freshwater inflow events when compared to those that 

 were mainly precipitation-mediated. In the late fall 

 1998, a major flow event flooded the Rincon Overflow 

 Channel and significandy increased the number of 

 plants that emerged the following spring compared to 

 the number seen after a precipitation only event. In 

 June 1999, total Salicomia higelovii cover at Station II was 

 52%, which was 26% greater than that seen at the 

 Reference Station. In June 1998, prior to the October 

 1998 composite hydrographic event {i.e.. Events 21 

 through 27), percent cover at the two stations was 

 approximately equal (11% and 13%). The similar 

 amount of cover during the spring 1998 could be 

 explained by heavy rains (> 23 cm, or 9 inches) which 

 occurred during fall of 1997, presumably affecting both 

 stations the same amount, although Station II was also 

 affected by fresh water diverted through the Rincon 

 Overflow Channel. 



Peaks in the percent cover of the perennial succulent 

 ^atis maritima occurred after gradual precipitation 

 inputs, but decreased after major hydrographic events 

 which flooded the station. The decline was most likely 

 due to the species' inability to tolerate waterlogged and 



anaerobic soils for extended periods. Increases in cover 

 were noted several months following a major event if 

 the soils had time to dry {i.e., no other flooding events 

 occurred). 



In summary, freshwater inputs via precipitation or 

 project diversions reduced salinity concentrations in the 

 upper Nueces Delta, and vegetation cover increased as 

 a result. Although large flooding events initially served 

 as a disturbance resulting in decreased adult plant 

 cover, it appears that the likelihood of long-term 

 successful establishment might be enhanced by the 

 increased opportunity of freshwater inflow. 



INTEGRATION OF PROJECT 

 EFFECTS 



The overall effects of the demonstration project on the 

 ecology of Rincon Bayou and the upper Nueces Delta 

 were positive to the environment (Table 7-1), and were 

 attributable to the re-introduction of fresh water. Prior 

 to the demonstration project, Rincon Bayou was not 

 direcdy connected with the river {i.e., it was a dead-end 

 channel). Average salinity concentrations were 

 consistentiy higher in the upper delta than in Nueces 

 Bay. These conditions were alleviated in the upper and 

 central segments of Rincon Bayou by increased 

 freshwater flow through the Nueces Overflow 

 Channel. 



The increased opportunity for freshwater inflow also 

 changed nutrient cycling and primary productivity in 

 the upper delta. Generally, nitrogen occurs in the water 

 column in three main forms: ammonia, nitrate and 

 nitrite. Without inflow, the dominant form of nitrogen 

 in the upper delta was ammonia, which was likely 

 derived from the recycling of (decaying) organic matter. 

 Also, water levels were generally low, as shallow as only 

 a few centimeters, and the substrate was covered by 

 mats of filamentous blue-green algae {i.e., 

 cyanobacteria). Although productivity (per unit 

 volume) from these mats was high, the total volume of 

 production was low because the total amount of water 

 was small. Furthermore, cyanobactena are not food 



Chapter Seven ^ 1-1 



