Chemistry 147 



FIGURE 4-26. Concentrations (yig P g~^) of organic phosphorus 

 in the sediments of the IBP watershed ponds. 



oxalate Pi (^g P g"') = (-0.41) OP {ng P g^)+564, (r- -0.50*), 

 suggesting a low rate of m situ mineralization. If Pond B is assumed to be 

 3,000 years old (Chapter 3), then the annual net mineralization rate 

 necessary to produce the organic and inorganic phosphorus concentrations 

 would be less than 0.1 Mg P (g sediment) " ' . This mineralization hypothesis 

 would require low-centered polygons, such as those that existed before the 

 ponds, to retain most of their phosphorus in organic form. The single 

 analysis of a low-centered polygon soil indicates that 82% of the soil 

 phosphorus is in organic form; this is consistent with this hypothesis. 

 Additionally, the five "new" pond sediments from within the former lake 

 bed have five of the seven highest OP to total P ratios (0.61 to 0.79) in the 

 18 samples of the watershed sediments. 



An alternative hypothesis arises from the Pond B phosphorus budget 

 (see Table 4-20). The average net gain of inorganic phosphorus of 0.5 mg P 

 m~' yr~^ and the net loss of organic phosphorus of 1.2 mg P m ' yr~' 

 suggest a slow leaching of organic phosphorus and an even slower capture 

 and binding of transient phosphate anions. The gain of 0.4 unit of 

 inorganic phosphorus per unit loss of organic phosphorus is identical to 

 the regression slope of —0.4 for oxalate Pi against OP for ponds in the 

 watershed. This hypothesis implies that these tundra ponds are not in 

 steady state, but are extremely slowly, over thousands of years, increasing 

 their inorganic phosphorus concentrations. This does not necessarily mean 



