384 WELCH AND WARD 



Physicochemical Measurements 



Measurements of temperature, pH, water transparency, solar 

 radiation, and alkalinity were made at each station on each sampling 

 date. Nitrate nitrogen, orthophosphate, and dissolved oxygen mea- 

 surements were made monthly. Water temperature at the incubation 

 depth (0.5 m) was measured with a mercury centigrade thermometer; 

 hydrogen ion concentration was measured with a pH meter in the 

 laboratory; water transparency was measured with a Secchi disk; and 

 instantaneous solar radiation in foot-candles was measured with a 

 portable light meter. The instantaneous light readings were converted 

 to total langleys for the sampling date by correlating the data with 

 data from the Texas A & M University Meteorological Center. 

 Phenolphthalein and methyl orange alkalinity were measured by 

 titration with 0.02N sulfuric acid (American Public Health Associa- 

 tion, 1971). Duplicate dissolved oxygen samples were fixed by the 

 azide modification of the Winkler method (American Public Health 

 Association, 1971). Nitrate nitrogen was measured by the ultraviolet 

 spectrophotometric method, and orthophosphate was measured by 

 the stannous chloride method using a benzene— isobutanol extraction 

 (American Public Health Association, 1971). 



Biological Measurements 



Carbon-14 techniques were used to estimate primary produc- 

 tivity, following the procedures of Goldman et al. (1974) and the 

 liquid scintillation techniques of Schindler, Moore, and Vollenweider 

 (1974). An ampul of 1 ml of NaHCOj with an activity of 5 fiCi was 

 added to each 125-ml bottle, and the bottles were incubated for 2 hr 

 between 10:00 a.m. and 2:00 p.m. Twelve hters of the large initial 

 sample were poured through a plankton net of No. 20 nylon-mesh 

 bolting cloth with 68 threads to the centimeter. The concentrate was 

 centrifuged at 1500 x ^ in the laboratory, resuspended in a known 

 volume, and counted according to the methods of Edmondson 

 (1974). 



Ten nutrient-enrichment experiments were conducted to deter- 

 mine the effect of two levels of nitrogen (NaNOg ) and phosphorus 

 (K2HPO4) at the two temperature levels by use of a factorial design 

 (Ramm and Karn, 1976; Jordan and Bender, 1973). Levels of 

 nitrogen were and 0.025 mg/liter and of phosphorus, and 0.005 

 mg/liter. 



Eight temperature -effects experiments were conducted by re- 

 versing four bottles from each station and incubating the hot-water 

 sample at Station 2 and the cool-water sample at Station 1. 



