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pool caused by the other phosphate cycling pathways denoted in Figure 4- 

 19 (plankton uptake, organic phosphorus hydrolysis, vascular plant 

 secretion, litter leaching, etc.). In spite of the scatter caused by these 

 pathways a significant correlation still exists betwen oxalate Pi and log 

 DRP. This illustrates the effectiveness of the buffering and control of 

 pondwater DRP concentrations by pond sediments. 



Sediment Inorganic Phosphorus in IBP Ponds 



Secondary control of phosphate concentrations is also exerted by 

 whatever factors influence concentrations of inorganic phosphorus in the 

 sediments across the watershed. Oxalate Pi concentrations are lowest 

 within the most recently formed ponds and then increase both up- and 

 downslope (Figure 4-25). Overall, the contours are similar to those for 

 DRP. Sediment organic phosphorus (OP) concentrations are highest in a 

 broad band across the watershed center that contains all but two of the low- 

 centered polygon ponds and none of the trough ponds sampled (Figure 4- 

 26). As a result, there is a negative correlation between oxalate Pi and OP: 



FIGURE 4-25. Concentrations (^g P g'^) of oxalate Pi in the top 3 

 cm of sediments of ponds in the IBP watershed. The phosphorus 

 added in fertilization experiments in Ponds D and X has been sub- 

 tracted under the assumption that all the added P remained in in- 

 organic form in the top 3 cm. 



