c 

 o 



ro 



3 



(/) 

 O 



Q. 

 O 



C 

 Q) 

 O) 

 O 



1995 



Figure 4-10: Nitrogen to phosphorous (N:P) ratios at all water column stations (except Station 62) for each 

 sampling date. 



remains the typical pigment measured by fluorometric 

 techniques but is often accompanied by a 

 phaeopigment estimate after the addition of acid. 



Chlorophyll 



Chlorophyll concentrations (which are an estimate of 

 plant biomass in the water) were quite large during the 

 demonstration period, with a large number of values 

 > 100 |j,g/l (Figure 4-11). The smallest concentrations 

 were mosdy measured in the Nueces River (Station 68), 

 but aU other sites had some values > 1 50 (ig/1, which 

 could be described as bloom conditions. These 

 biomass accumulations of plankton partially drive the 

 large rates of primary production in the Nueces Delta. 



Water Column Production 



Water column primary production is a combination of 

 phjrtoplankton biomass and the growth rate of 

 individual cells. Therefore, combinations of high 

 biomass or high growth rates can produce large rates 

 of primary production. The rate of primary 

 production is a function of nutrient availability and 

 incident radiation to the phytoplankton cells. 



The '''C experiment conducted as part of this 

 demonstration project indicated that the average rate 

 of primary production is about 3 gC/m'/day 

 (Figure 4-12), but higher values were typically as large 

 as 10 gC/m"/day. One extremely high rate 

 (38 gC/m"/day) was obtained at Station 63 before the 

 opening of the Nueces Overflow Channel as a result of 

 a bloom of filamentous blue-green algae. Frequendy 

 the Nueces River station (68) had the lowest rates, but 

 all Rincon Bayou stations showed large responses 

 during inflow events, particularly during the summers 

 of 1997 (Events 16 and 17) and 1999 (Events 29 and 

 33). The observed rates of primary production in the 

 upper Nueces Delta were larger than values for Nueces 

 Bay (StockweU 1989), and the highest rates were equal 

 to the largest observed in up-welling areas in the ocean. 



Assimilation Index 



The assimilation index is the rate of primary 

 production normali2ed to the chlorophyll biomass. 

 This index is useful to determine if the specific growth 

 rates of phytoplankton cells are large enough to create 

 bloom conditions. Typical assimilation index values of 

 50 to 100 mgC/m^/day/fjgChl are observed for many 

 phytoplankton spring blooms. 



4-12 



Water Column Productivity 



