were only found at the Reference site (Stations 63 and 

 64) and only during 1999. The relatively low nitrate 

 concentrations obsen^ed throughout the data record 

 would provide a low level maintenance for 

 phjlioplankton growth but would certainly not provide 

 nutrients needed to fiiel bloom conditions. 



Ammoniutn (NH4) 



Ammonium is the form of nitrogen most commonly 

 released by rec)'cling of organic matter or excretion by 

 higher organisms. Accordingly, ammonium is often 

 called "regenerated" nitrogen. Shallow environments 

 such as the Nueces Delta and Nueces Bay tend to 

 increase the relative amounts of regenerated nitrogen 

 compared to nitrate (which is often called "new" 

 nitrogen because it has been newly added to the 

 ecosystem by advection or inflow). 



The concentrations of ammonium observed during the 

 demonstration period were usually larger than nitrate 

 concentrations (Figure 4-5). The Nueces River station 

 (Station 68) often had the smallest ammonium levels, 

 while the upper Rincon Bayou stations (65 and 66) 

 were sometimes largest. The central Rincon Bayou 

 stations (60 and 61) occasionally contained the largest 



ammonium concentrations. There was no obvious 

 direct relationship between salinity and ammonium at 

 any of the station sites. 



Nitrite (NOj) 



Nitrite is the form of nitrogen that is intermediate 

 between nitrate and ammonium for its valence state 

 and is not typically observed in large concentrations in 

 most estuarine or marine environments. 



During the demonstration period, the small concen- 

 trations of nitrite resulted from either nitrification or 

 denitrification processes (Figure 4-6). Estuarjr 

 ecosystems tend to have both nitrification and 

 denitrificaion processes occurring at the same time by 

 specific microbes for each. Large concentrations of 

 nitrite {e.g., >1 jimole/1) indicate that special conditions 

 existed for a short time. 



Dissolved Inorganic Nitrogen (DIN) 



DIN is the sum of the nitrate, nitrite and ammonium 

 forms of nitrogen. This amount represents the total 

 inorganic nitrogen nutrients available for uptake by 

 plants. Because all three forms of nitrogen are readily 



1995 



1996 



1997 



1998 



1999 



Figure 4-4: Nitrate concentrations at all water column stations (except Station 62) for each sampling date. 



4-8 ♦♦♦ Water Column Product! viiy 



