Seasonal variations of phosphorus in the composited tile 

 drainage were comparable to that of nitrogen; that is, 

 summertime decreases were attributed to dilution in the soil 

 caused by irrigation. The highest average concentrations 

 were observed in January (about 0.2 mg/l); the lowest 

 occurred in July (about 0.09 mg/l). 



In conclusion, the present composite drainage from the major 

 tiled areas investigated is not indicative of phosphorous 

 concentrations in future valleywide drainage. Phosphorous 

 concentrations could increase as a result of drainage from 

 other lakebed areas having soils similar to that in the 

 Tulare Lake area. Based on predicted drain flows for the 

 year 2020, average concentrations in the drainage would be 

 0.23 mg/l. 



Total Dissolved Solids 



Total dissolved solids (TDS) averaged 3,625 mg/l in the 

 combined valley drainage for 1962 to I969 . Long-term changes 

 between years were very small; TDS averaged 3,100 mg/l for 

 1967, 3,200 mg/l for 1968 and 3,550 for 1969. Higher 

 average concentrations were observed for drainage composited 

 during the earlier studies when only a few tile systems from 

 the Gustine-Mendota area were investigated. 



TDS concentrations, however, did vary in drainage from 

 individual tile systems. The levels ranged from 1,320 mg/l 

 to 1^,600 mg/l for Intensively monitored tile systems. A 

 few isolated tile drains were found to be much higher in TDS; 

 for example, one experimental tile system exceeded 100,000 

 mg/l at the lowest flows. 



Seasonal and areal variability of TDS was great for drainage 

 composited from the major tiled areas. TDS averaged about 

 3,500 mg/l in the winter and decreased to about 2,500 mg/l 

 during the summer. 



Drainage from the central area (4,130 mg/l) and southern 

 area (3,760 mg/l) was much higher in TDS than the drainage 

 from tile systems located in the two northern areas. 

 Drainage from the Byron to Westley area averaged 2,170 mg/l -■ 

 the Westley to Gustine area averaged 2,7^0 mg/l. 



TDS concentrations have been predicted to decrease signifi- 

 cantly in future drainage from the San Joaquin Valley. 

 Although long-time changes were not observed in the data 

 available during this investigation, it is believed that a 

 decrease in TDS would be inevitable if the existing monitor- 

 ing program was continued for a longer period. 



