TABLE 7 



AVERAGE DISCHARGE, NUTRIENT CONCENTRATIONS, 

 AND TOTAL DISSOLVED SOLIDS FROM SAN JOAQUIN VALLEY TILE DRAINAGE SYSTEMS 



Annual Averages ^Welghtedj 

 C)WR (Bull. 127) :UCLA:DWT^ Nutrient Investlg. : Grand 

 195^-^31"^^ -.TgU^-Agbb 15b7 I9bb 19Bg~:Averagei'^ 



Parameters 



Discharge (ac-ft/ac) NR 



Nitrogen (NO3-N, mg/l) 21.0 



Phosphorus (PO4-P, mg/l) 0.15 



Total Dissolved Solids (mg/l) 6,500 



Number of Systems Sampled 29 



0.72 1.5 1.3 I.'* l.'* I.'* 



25.1 18.6 18.6 19.9 19.'* 19.3 



0.08 NR 0.12 0.10 0.05 0.09 



NR 4,550 3,100 3.200 3.550 3.625 



4 7 40 42 20 



1/ Values are arithmetical averages. 

 7/ Weighted average based on flow. 

 NR = No record . 



Variability of Nutrient Concentrations 

 and Tile Discharge with Time 



Long-term and short-term variabilities of average nutrient 

 and TDS concentrations and discharges are discussed In this 

 subsection. 



Long-term Nitrogen Variability 



Long-term variability deals with the changes In average 

 discharge observed from the study area over several years 

 and the related changes of nutrient concentrations that take 

 place In the composited dralnsige . Variability of nitrogen 

 In Individual tile systems Is also compared. 



Composited Drainage . Although the figures In Table 7 

 represent the weighted average values for the different 

 periods of study, some variability exists between years. 

 The differences In discharges and tile drain constituents 

 between years are small, considering the number of tile 

 systems sampled and the geographical areas represented for 

 any given period. For Insteince, In 1962 the highest average 

 nitrogen concentration (25.I mg/l) occurred In the composited 

 drainage from four tile systems within the Gustlne-Mendota 

 area. In 29 systems sampled In 1959-63, most of which were 

 situated In the same area, the concentration was only 

 4.1 mg/l less. 



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