Comparison Between Years 



Relation to Nitrogen 



Mean concentrations of phosphorus between 

 years were similar in 1964, 1965, and during 

 the first half of 1966 (Figure 13). Beginning in 

 June 1966, phosphorus concentrations 

 increased markedly from a level of about 5 ng 

 at/liter in the habitats sampled and reached an 

 all years' maximum of about 20 ng at/liter 

 during the fall. Values remained above average 

 (about 5pg at/liter) the remainder of the year. 



rO 20 10 20 10 20 

 jiN fEB MaH 



10 20 10 20 10 20 10 20 lO 20 

 APR Mar JUN JUL auG 



10 20 ;0 20 10 20 

 SEP OCT NOV 



10 20 

 DEC 



Figure 13. Mean values of total phosphorus by date, 

 habitat, and year in the Galveston Bay system, 

 1964-66. 



Relation to River Discharge 



River discharge from the Trinity or San 

 Jacinto watersheds was not closely correlated 

 with phosphorus levels in any of the habitats or 

 bay areas (Table 10), although phosphorus 

 concentrations in the system reached the 

 greatest levels following the period of greatest 

 stream flow in 1966 (Figures 6 and 11). 



Table 10.— Correlation coefficients (r) between average 

 weekly stream flow and concentrations of total phos- 

 phorus, 1964-66. 



el Peripheral 



IS -0.2fce 



0-20 -0 10 



2B 0.01 



Phosphorus and nitrogen values were pos- 

 itively correlated each year (r = 0.43, d.f. = 328 

 in 1964; r = 0.39, d.f. = 757 in 1965; and r = 

 0.36, d.f.= 382 in 1966). 



DISSOLVED OXYGEN 



Dissolved oxygen levels in the system varied 

 from a minimum of 0.2 ml /liter in East Bay to 

 a maximum of 13.6 ml/liter in Upper 

 Galveston Bay. Annual low and high values, 

 respectively, were 2.4 and 13.6 ml /liter in 

 1964, 0.9 and 13.4 ml/liter in 1965, and 0.2 

 and 10.8 ml/liter in 1966. 



Comparison Between Habitats 



Within each bay area and year, dissolved 

 oxygen concentrations were usually lowest in 

 the channel and highest in the peripheral and 

 open-water habitats (Table 11, Figure 14). The 

 greatest variations in oxygen concentrations 

 between habitats occurred in Upper Galveston, 

 mid-Galveston, and East Bays. 



Table 11.— Comparisons of annual mean concentrations 

 of dissolved oxygen (ml/liter) between habitats 

 within bay area in the Galveston Bay system, 

 1964-66. 



Habitats compared and mean Degrees 



oxygen 



> S.gniricance level = ^%. *♦ Significance level = i% 



10 



