Bay. Salinities in tiie peripheral and open-water 

 habitats of East Bay were similar to those in 

 mid-Galveston and Upper Galveston Bays, 

 whereas salinities in the Intracoastal Waterway 

 (channel habitat) were lower than those in the 

 Houston Ship Channel. This anomalous situa- 

 tion in East Bay is probably related to drainage 

 of a large marsh adjacent to the Intracoastal 

 Waterway and to reduced saltwater intrusion in 

 the waterway as compared with the Ship Chan- 

 nel. 



Comparison Between Years 



For between-year comparisons, salinity data 

 for all bay areas were combined by habitat and 

 by year and plotted by date for the bay system 

 (Figure 5). The data indicated a general 

 decrease in salinity in ail habitats from 1963 to 

 1966. The smallest difference in salinity be- 



10 2C 10 20 10 20 10 ro 10 20 10 20 lO 20 10 20 10 20 10 20 10 20 10 20 

 JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC 



Figure 5. Mean values of bottom salinity by date, 

 iiabitat and year in the Galveston Bay system. 

 1963-66. 



tween years (about 4%o) was in March and 

 April, and the greatest difference between 

 years (about 20%o) was in May and June. 

 Differences of 10%3 or greater between years 

 were observed from May to September in the 

 peripheral and open-water habitats. The chan- 

 nel habitat, which generally had the least sa- 

 linity variation between years, had differences 

 of 10%o or greater from May through June. 



Seasonal trends varied between years in all 

 habitats, although minimum salinities always 

 occurred during the winter and spring and 

 maximum salinities always occurred during the 

 late summer and fall. 



Relation to River Discharge 



The relation between river flow and max- 

 imum, minimum, and mean salinity in the bay 

 system is shown in Figure 6. The Trinity and 

 San Jacinto watersheds discharged between 2.5 



Figure 6. Maximum, minimum, and mean salinity 

 compared with stream flow in the Galveston Bay 

 system, Texas, 1963-66. 



billion m^ of water in 1963 and 10.1 billion 

 m^ in 1966. Of the yearly totals, the Trinity 

 watershed contributed 75% or more of the 

 total discharge each year. Salinities were 

 inversely correlated with stream discharge (r = 

 -0.60, d.f. = 96 for the Trinity and r = -0.37, 

 d.f. = 96 for the San Jacinto watersheds) with 

 the upper bay areas responding quickly to 

 changes in stream flow (Figures 4 and 6). 



The maximum water discharge during the 4 

 years occurred in 1966, initiating a marked 

 reduction in salinities in the peripheral and 

 open-water habitat of all bay areas (Figures 4 

 and 5). Salinities in the channel habitat are 

 primarily controlled by tidal waters from the 

 Gulf and, thus, were less affected by freshwater 

 inflow than those in the other habitats. 



Salinity Isopleths 



Annual isohalines for the bay system, and an 

 isohaline constructed from the 4 years of data, 

 are shown in Figure 7. Average salinities of 

 10%jor greater were recorded near the Trinity 

 River in 1963-64, whereas the 10% isohaline 

 shifted westward toward Upper Galveston Bay 

 in 1965 with increased freshwater inflow. In 

 1966, saUnities averaged below 10%oin Trinity 

 Bay. Lower Galveston Bay, which is adjacent 

 to the Gulf, averaged 25%o or greater in 

 1963-64, but not in 1965-66. In general, the 

 system changed from a high-salinity regime 

 brought on by a drought period in 1963-64 to 

 a low-salinity regime in 1965-66 as a result of 

 high rainfall and river discharge. 



The areal distribution of average salinities 

 for the 4-year period showed that salinities in- 

 creased from east to west and north to south in 

 the system. The configuration of the isohalines 



