RESULTS 



Salinity 



The water column overlying sediments in the study 

 area changed on var)'ing temporal scales because of 

 natural conditions (e.g., wet and dry periods) as well as 

 hydrographic events through the Nueces Overflow 

 Channel (Figure 5-2). Salinity ranges during the 

 demonstration period were extreme in Rincon Bayou, 

 varying from freshwater conditions (< 0.5 ppt) to 

 hyper-saline conditions (> 36 ppt). The highest 

 recorded salinity was 160 ppt (Station C) during July 

 1 996. Salinity trends appeared similar at different 

 stations but were not always the same (Figure 5-3). 

 For example, during summer 1995, Stations A and B 

 had the lowest salinity values while Station E had the 

 highest. During summer 1996, Stations C and D had 

 the highest concentrations but, during summer 1998, 

 Stations A and B had the highest. Floods during the 

 summers 1997 (Events 16 and 17) and 1999 (Events 33 

 and 34) maintained salinity values much lower than 

 during the other summers. 



In the analysis of the hydrographic effects of the 

 demonstration project (Chapter 3), a total of 37 events 

 were identified during the study period (Table 3-3). 

 Measurements of freshwater flow into and out of 

 Rincon Bayou, as well as direct precipitation, were 

 compared with benthic salinity data. Because salinity at 

 benthic stations was measured quarterly, daily rain and 

 inflow data were summed by sampling date (Table 5-1). 

 Although data from the Rincon gauge was not available 

 prior to May 1, 1996, flow into Rincon Bayou prior to 

 the opening of the Nueces Overflow Channel was zero 

 (Chapter 3). During the period after the overflow 

 channel was exca%'ated but before the Rincon gauge 

 was in place, there were some small exchange events 

 (e.g.. Event 6, which resulted from locally hea\7 

 rainfall), but these were not considered to result m 

 substantial inflow into Rincon Bayou (Chapter 3). 

 Over the entire period, rainfall events occurred 

 frequendy, but there were only four sampling dates 

 prior to which significandy large inflows of fresh water 

 were recorded (Table 5-1), includingjuly 1997 (Events 

 16), October of 1997 (Events 17 and 18), October 

 1998 (Events 21 dirough 25), and October 1999 



Figure 5-2: View of benthic Station C in upper Rincon 

 Bayou under dry (above) and wet (below) conditions. 



The dry conditions were during the summer of 1996. and 

 the flooding conditions during the summer of 1997 

 (Event 16). 



Photo courtesy of the University of Texas Marine Science 

 Institute. 



(Events 35). Only four of the 37 events identified 

 during the demonstration period (Events 16, 18, 25 

 and 36) were sufficiendy large to result in delta inflow 

 without the demonstration project and, of these, only 

 one did so appreciably (Ev^ent 25) (Chapter 3). 



Rainfall and freshwater inflow data were used to 

 determine the cumulative effects of dilution on the 

 average sahmty at each site (Figure 5-4). Hj^ersaUne 

 conditions likely resulted from near zero flows and 

 high evaporation rates, which typically occurred in 

 summer. The differences between the two treatment 

 sites indicate that "reverse estuar)'" conditions had 

 existed in Rincon Bayou before freshwater diversions 



5-6 



Benthic Communities 



