fluorescence readings were taken on samples. The 

 amended samples were placed in diffuse lighted 

 incubators at 25 °C and additional fluorescence 

 measurements were taken daily for 3 to 4 days. The 

 mean of the four in vivo fluorescence samples was used 

 to represent the effect of the amendment additions. 

 No readings were discarded. VClien the incubations 

 were terminated, the samples were analyzed for 

 extracted {in vitro) chlorophyll content. 



Phytoplankton Pigments 



Changes in phytoplankton biomass were determined 

 using Chlorophyll A as the index of biomass. The 

 chlorophyll and pigment samples were analyzed 

 with a model 10-005RU Turner Designs fluorometer 

 which was specifically designed for pigment analyses 

 using the methodology of Hohn-Hansen et al. (1965). 

 Calibration of the in vitro chlorophyll analysis was 

 accomplished with pure chlorophyll obtained 

 commercially and standardized with a 

 spectrophotometer. Phaeopigment concentrations 

 were also determined in the same samples after 

 addition of a small amount of hydrochloric acid. 



Primary Production 



Rates of phytoplankton primary production were 

 monitored using replicate '^C incubations and natural 

 sunlight using the method of O'Reilly and Thomas 

 (1983). This method has been used for all 

 measurements in South Texas bays over the previous 

 8 years. The procedure consists of collection of 

 duplicate water samples that were inoculated with 

 '■"C isotope and incubated in a water bath for 2-3 hours 

 in fuU sunlight. Dark botde uptake was measured for 

 corrections and '''C inoculation volumes were checked 

 with replicate initial blanks. Primary production 

 '■"C measurements were analyzed with a Beckman 

 model LS5801 liquid scintillation counter that 

 employed self-calibration with known sources and 

 calculates counting efficiency. Initial carbonate 

 alkalimty was analyzed by standardized methodology of 

 25 ml of 0.01 M hydrochloric acid additions to 100 ml 

 of sample. The extremely high alkalinity of Rincon 

 Bayou often required additional aUquots of acid 

 addition until a proper pH of <3.9 was obtamed. 



Sedimented Plankton (Microphytobenthos) 



Chlorophyll — The chlorophyll content of sediment 

 was determined at each site by sub-sampling a 5-cm 

 core collected by hand. A 1-cc syringe was also used to 

 collect the sample from the upper 0.5 cm of the 

 sediment surface. Extraction and analysis of the 

 chlorophyll/phaeopigment content were conducted 

 accordifig to the same procedures as the water samples. 



Primary' Productivity — The primary production of 

 microphytobenthos was determined on 1-cc mud 

 samples from the top of 5-cm cores collected by hand. 

 The sediment was suspended in 25 ml of filtered water 

 collected at the site. Replicate '''C incubations were 

 incubated in natural sunlight for 3 to 4 hours. 



RESULTS 

 Hydrography 



Temperature 



Temperature is generally not a strong controUing factor 

 on water column primary production, but seasonal 

 temperature changes may have a secondary effect on 

 production processes. Temperature data were most 

 useful in characterizing rapid changes in environmental 

 conditions, such as sudden changes of weather during 

 winter cooling events [e.g., fironts). Long extended 

 periods of high temperature were used to identif)' 

 periods of drought and other times of stress on the 

 plant and animal populations in the upper delta. 



Salinity 



Salinity is a conservative variable because its 

 concentration is altered only by physical processes. As 

 precipitation or evaporation occurs, salinity can be 

 used to produce an accurate estimate of the quantity of 

 water added or subtracted from an estuary. In 

 addition, salinity values also give a good indication as 

 to the spatial extent of freshwater inflow events. 



In general, the upper Nueces Delta experienced a wide 

 variance of salinity concentrations during the 



4-4 V Water Column Productivity 



