acteristics of estuaries. Evaluation of changes 

 detrimental to estuarine biota is aided by infor- 

 mation on the hydrological conditions existing 

 before the alterations. 



The hydrology and biology of the Galveston 

 Bay system are being studied or have been 

 studied by various State, Federal, and private 

 agencies. Studies contributing significant infor- 

 mation on the hydrology of this system include 

 those by Reid (1955, 1956, and 1957); Cham- 

 bers and Sparks (1959); Arnold, Wheeler, and 

 Baxter (1960); Zein-Eldin (1961); Chin (1961); 

 Odum et al. (1963); Pullen (1969); Baldauf 

 (1970); and Copeland and Fruh (1970). 

 Gloyna and Molina (1964), using data from 

 State, Federal, and private agencies, compiled a 

 report for the Texas Water Pollution Control 

 Board on the water c(uality of the bay system. 

 The observations analyzed and reported in the 

 present paper and all hydrological data col- 

 lected by personnel of the Estuarine Program, 

 National Marine Fisheries Service, Galveston, 

 Texas, from 1958 through 1967 were pub- 

 lished by Pullen and Trent (1969). 



The objectives of our study were to: (1) 

 summarize bottom temperature, salinity, dis- 

 solved organic nitrogen, total phosphorus, and 

 dissolved oxygen data in relation to three 

 habitats and five bay areas, and (2) determine 

 the temporal and spatial distributions and 

 ranges of these parameters and some of the 

 relations and mechanisms affecting their distri- 

 butions. 



STUDY AREA AND METHODS 



The Galveston Bay system, located on the 

 upper Texas coast, has a water area of about 

 1,360 km^ (Figure 1). Water is exchanged with 

 the Gulf of Mexico through three tidal passes. 

 About 85% of this exchange is through Bolivar 

 Roads Tidal Pass, about 14% through San Luis 

 Pass, and about 1% through Rollover Pass (U.S. 

 Corps of Engineers, personal communication). 

 Two major navigation channels— the Houston 

 Ship Channel, connecting Houston to the Gulf 

 of Mexico, and the Gulf Intracoastal Waterway, 

 running southwesterly through the marsh areas 

 of the lower bays— pass through the system. 

 The tidal range is 0.5 m in the lower portion of 

 the system and 0.3 m in the upper (U.S. 



WEST BM 

 "^AN LUIS PASS 



BOLIVAR ROADS 

 TIDAL PASS 



Figure 1. The Galveston Bay system and associated 

 watersheds. 



Department of Commerce, Coast and Geodetic 

 Survey, 1969). Winds, as reported by U.S. 

 Weather Bureau data for Galveston, Texas, are 

 predominantly southeasterly in the sumrner 

 and northerly in the winter. Thirty-seven years 

 (1931-67) of data collected by the U.S. 

 Weather Bureau in Galveston show the mean 

 annual rainfall to be 113 cm and the mean air 

 temperature 20.8° C. 



Most freshwater inflow to the bay system is 

 from the Trinity and San Jacinto watersheds 

 (Figure 1). Stream discharge data for the Trin- 

 ity and San Jacinto watersheds were obtained 

 from the U.S. Geological Survey. Annual 

 stream flows averaged about 7 billion m^ for 

 the Trinity and about 2 billion m^ for the San 

 Jacinto watersheds. The drainage area of the 

 Trinity watershed is 46,540 km^ and that of 

 the San Jacinto watershed is 10,298 km^. 

 Average annual precipitatipn over the water- 

 sheds generally varies from 89 cm at Dallas to 

 114 cm at Houston (U.S. Bureau of Reclama- 

 tion, 1964). 



The bay system was divided into the fol- 

 lowing geographic areas for this study: Lower 

 Galveston, mid-Galveston, Upper Galveston, 

 East, and Trinity Bays (Figures 1 and 2). West 

 Bay was not included in this study. 



The bay areas were further divided into 

 peripheral, open-water, and channel habitats 

 (Figure 2). Station numbers and locations 

 indicated in Figure 2 are those reported by 

 Pullen and Trent (1969). The peripheral habi- 

 tat was in water depths less than 1.2 m; the 

 open-water habitat was in depths of 1.2 to 3.0 

 m; and the channel habitat was in depths 



