0.11 percent phosphorus pentoxide by weight. Laboratory 

 tests indicate that the shell fragments contained from 

 0.12 to 0.15 percent phosphate. Also, during the investiga- 

 tion the odor of hydrogen sulfide gas was detected in 

 several augered holes where high water table conditions 

 existed. Anaerobic conditions, indicated by the presence 

 of the hydrogen sulfide gas, in effect lower the soil pH 

 which results in acidic conditions within the soil and a 

 consequent release of phosphates (25). 



Variability Due to Physiography 



An apparent association between quantity and quality of the 

 tile drainage and the physiographic positions of the drain 

 systems led to an investigation of this aspect of tile 

 drainage. As already pointed out, fertilizer application 

 rates did not always correlate with the concentrations 

 observed or pounds of nitrogen dischsirged in tile drainage. 

 During the course of the study, it became evident that 

 certain tile drainage systems occupying alluvial fan posi- 

 tions discharged effluent containing high concentrations of 

 nitrogen, whereas systems located in the basin rim and basin 

 position generally had lower nitrogen concentrations. 



Discharge 



The highest average discharges were derived from tile 

 systems located in the older alluvial fan positions. 

 Several systems in the northern area with exceptionally high 

 flows were so located. Although these systems dischcU'ged 

 greater quantities of effluent than did tile drains located 

 in other major tiled area.s , they were typical of other 

 drains not being sampled in that area. Several individual 

 drains located on older alluvial fans of the central area 

 also had high discharges. 



Nutrients and Total Dissolved Solids 



The composited drainage from tile systems within basin and 

 basin rim positions was significantly lower in nitrogen 

 than that from alluvial fans. 



Phosphorus was six times more concentrated in the drainage 

 from tile systems occupying basin positions than other 

 positions . 



Composited drainage from tiles located in the basin rim 

 position was the highest in TDS, followed by the basin 

 position . 



61 



