TABLE 11 



AVERAGE DISCHARGE, NUTRIENT CONCENTRATIONS, 

 AND TOTAL DISSOLVED SOLIDS BY MAJOR TILED AREAS 



1967 AND 1968 



Major Tiled 'Discharge :Nitrate-:Phosphate-: Total 

 Ar.oQQ * / ^j. / x :Nitrogen: Phosphorus: Dissolved 

 Areas .(ac-ft/ac). (^/i) . ^^^/-^^ iSolids (mg/l) 



Byron-Westley 2.3 8.5 O.O9 2,17C 



Westley-Gustine O.69 9.0 O.O6 2,740 



Gustine-Mendota 1.12 32.8 O.O7 4,130 



Tulare Lake 0.57 9.6 O.69 3,760 



content of drainage from systems in the northern and 

 southern areas tends to dilute the high nitrogen level that 

 might otherwise occur in drainage from the entire study area, 



Phosphorus . In drainage composited by different areas, 

 phosphorus was found in much lower concentrations than was 

 nitrogen. The highest concentrations were observed in 

 drainage from the southern sirea (Tulare Lake). Phosphorous 

 concentrations there averaged 0.69 mg/l, about seven times 

 higher than any other area. 



Total Dissolved Solids . Drainage from the Gustine-Mendota 

 area was the highest in TDS concentrations. TDS concentra- 

 tions in the composited drainage from the Byron-Westley and 

 Westley-Gustine areas were about 1,000 rng/l lower than the 

 drainage from the other two areas. The difference in the 

 average TDS in drainage between the Gustine-Mendota and 

 Tulare Lake areas was small . 



Variability Due to Agricultural Practices 



Tile drainage flow as well as nutrient concentrations are 

 generally affected by certain agricultural practices. Irriga- 

 tion, cropping, and fertilization practices and their effects 

 upon tile drainage are discussed in this subsection. 



Influence of Crops on Tile Discharge 



Certain heavily irrigated crops directly influence flows in 

 tile drainage systems. When irrigated, rice, alfalfa, and 

 cotton crops produced almost immediate increases in drainage 



53 



