THE EFFECTS OF FRESHWATER INFLOW ON SALINITY AND ZOOPLANKTON POPULATIONS 

 AT FOUR STATIONS IN THE NUECES-CORPUS CHRISTI AND COPANO-ARANSAS 

 BAY SYSTEMS, TEXAS FROM OCTOBER 1972 - MAY 1975 



Richard D. Kalke 



University of Texas Marine Science Institute 

 Port Aransas Marine Laboratory 

 Port Aransas, Texas 



ABSTRACT 



Between October 1972 and May 

 1975, two periods of major freshwater 

 inflow (June-November 1973 and August 

 and September 1974) affected zoo- 

 plankton populations in the Nueces- 

 Corpus Christi and Copano-Aransas Bay 

 Systems. Inflows resulted in re- 

 placement of estuarine species with 

 freshwater species and the lowering 

 of salinities to near parts per 

 thousand (ppt) . Populations of the 

 calanoid copepod, Acartia tonsa, were 

 lowest during maximum inflow but 

 sharply increased following salinity 

 increases as small as 1 to 3 ppt. 



INTRODUCTION 



During the period October 1972 

 through May 1975 the Texas Water De- 

 velopment Board and the City of Cor- 

 pus Christi funded a project to moni- 

 tor the effect of freshwater inflow 

 on the phytoplankton, zooplankton, 

 and benthic communities in the 

 Nueces-Corpus Christi and Copano- 

 Aransas Bay Systems. Increased muni- 

 cipal, agricultural, and industrial 

 usage of fresh water prompted the 



need for research in determining re- 

 quirements of freshwater inflow into 

 Texas estuaries. 



The study area was located with- 

 in the south central climatological 

 division (Texas Water Development 

 Board 1968) between 27°40' and 28°10' 

 north latitudes and 96°50' and 97°30' 

 west longitudes. The average annual 

 precipitation in this climatological 

 division was 84.4 cm. 



Aransas Bay, composed of Copano , 

 Aransas, Redfish, St. Charles and 

 Carlos bays, has about 5.7x10 ha and 

 has an average of 81.3 cm annual 

 rainfall (Texas Water Development 

 Board 1968). Aransas Bay, histori- 

 cally, has received about 7.3x10 m 

 of fresh water annually. Physical 

 characteristics of the Aransas Bay 

 system, i.e. water circulation, 

 drainage, and oyster reef distribu- 

 tion, are given by Parker (1959) 

 and Gunter (1945). According to 

 Gunter minimal amounts of water, if 

 any, from the Nueces-Corpus Christi 

 Bay intrude into the Aransas Bay 

 system. Collier and Hedgpeth (1950) 

 give a detailed analysis of the hy- 

 drography of the study area. 



The Corpus Christi Bay system is 

 composed of Nueces, Oso, and Corpus 



i >-4 



