the response, when irrigation ended, nutrient concentrations 

 nearly always tended to return to the levels observed prior 

 to the beginning of the irrigation season. 



Nutrient, TDS, and flow variabilities were investigated hourly 

 and daily for several tile systems. As part of the ainalysis, 

 monthly variability of flows and nutrients was determined 

 for every system studied. 



Hourly , Nitrogen concentrations were first observed to vary 

 in drainage from individual systems where frequent samples 

 were collected for treatment studies (Interagency Agricul- 

 tural Wastewater Treatment Center at Firebaugh, California). 

 Investigations were later conducted at four sites to deter- 

 mine the actual nitrogen variation that occurs in drainage 

 from one hour to the next gmd to aid in determining a proper 

 sampling frequency. 



Sampling was scheduled to coincide with periods of irriga- 

 tion to make the most of possible nitrogen variations and to 

 determine the possible effects of dilution. Samples were 

 collected and analyzed by routine methods set up for the 

 monitoring program. Results of the hourly investigations 

 appear in Table 9; variable phosphorous concentrations, 

 electrical conductivity values, and flows are compared. 



TABLE 9 



HOURT.Y VAhlATION 0¥ FLOWf , IfOTRIEOTS AND ELECTRICAL 

 CONDUCTIVITY IN DRAINAGE FROM FOUR TILE DRAINAGE SYSTEMS 



System 



Flows 



TsseL 



Std. 

 Max. :Mln. ;Me8n:Dev. 



NOij-N. mj/T 



Nutrients 



Std. 

 Max.:Mln.: Mean: Dev. 



POU-P. mgJT 



rstj: 



Max. :Min. :Me8n: Dev. 



Electrical Conduqtlvlty 

 (E.C. X lO-t^l 



■. 7 ^^t37 



Max. : Mln. : Mean :Dey. 



UID 2133 382 382 382 o 12 1* 8.0 1.63 0.T5 0.13 O.56 0.16 3,000 2,900 2,950 29 



BFS 7U02 59'» 561 57110.2 k9 2k 1*0,2 6.21* 0.26 O.06 0.I6 .051 U,600 U.SOO l»,l»00 69 



FBH 3236 19'» 13lt 156 19.3 185 92 166.0 19.8 0.1*5 0.15 0.21* .073 12,000 9,1*00 11.230 716 



ecu 3550 273 103 221.22.2 1*9 18 30.0 6.1*7 I.60 0.75 I.I6 0. 10 3,000 2,200 2,6U2 239 



A mean nitrogen value was determined for weekly samples 

 collected one month before and one month after the 2^-hour 

 studies. The mean weekly values compared well with mean 

 hourly values of the same systems in three cases (Table 10) . 



Daily . At the beginning of the intensive monitoring investi- 

 gations, samples were collected at close intervals (three to 

 four days), and daily in some instances, until an appropriate 



48 



