ABSTRACT 



Tile drainage systems of the San Joaquin Valley were 

 monitored for nutrients (nitrogen and phosphorus). The 

 objectives were to determine: (l) the average nutrient 

 concentrations In tile drainage, (2) the magnitudes of 

 annual, areal and seasonal variability of nutrients and 

 discharges, (3) If a possible correlation exists between 

 nutrients and agricultural practices, and (^) If existing 

 soil conditions Influence nutrient concentrations and flows. 

 From this Information It will be possible to determine the 

 algal growth potential (AGP) of the waste, and the degree 

 of treatment required for removal of AGP . 



Average discharges, nutrient concentrations and total 

 dissolved solids were calculated for different years, months, 

 physiographic positions, soil series, and valleywide areas 

 of Interest. Average nutrient concentrations in the compos- 

 ited drainage from the Valley were found to be 19-3 mg/l for 

 nitrate -nitrogen, 0.09 mg/l for phosphate -phosphorus, and 

 3,625 mg/l for total dissolved solids; average discharge was 

 1.4 ac-ft/ac. Nutrient levels in the composited drainage 

 did not change appreciably from year to year. Variability 

 of nutrients was observed for different seasons; a twofold 

 decrease in nutrients was attributed to dilution by irriga- 

 tion and denltrification. Nitrogen was three times more 

 concentrated in drainage from one out of four major tiled 

 areas investigated. The high nitrogen levels were attrib- 

 uted more to Indigenous concentrations in certain alluvial 

 fan soils and their parent materials than fertilization. 

 Low nitrogen levels found in drainage from basin soils were 

 believed caused by denltrification. Phosphorus was seven 

 times higher in the drainage from the southernmost area than 

 the other areas Investigated. These extraordinarily high 

 levels (0.69 mg/l) were attributed to indigenous concentra- 

 tions in certain soils made available by anaerobic soil 

 conditions. High dischairge in the northernmost area (2.3 

 ac-ft/ac) was believed to be caused by rapid lateral 

 hydraulic conductivity and surrounding irrigation Influence. 



This report was prepared by the California Department of 

 Water Resources in conjunction with other agricultural waste- 

 water studies which were conducted by the United States 

 Bureau of Reclamation and the Water Quality Office of the 

 Environmental Protection Agency. 



Key words: agricultural waste, tile drainage, nutrients, 

 composited drainage, nutrient variability, 

 indigenous concentrations. 



Ill 



