176 R. T. Prentki et al. 



equation implies that the energy of adsorption decreases linearly as the 

 amount of the sediment particle covered by P increases and that a plot of 

 X against log C should be linear. Therefore, the less phosphorus there is 

 the more strongly it is bound. Comparison of the slope of the Temkin 

 isotherm for Barrow pond sediments with the slope for fertilized soils 

 revealed that the soils had a much smaller phosphate buffering intensity 

 than the sediments. In this sense, buffering intensity is a measure of the 

 tendency of a solution in contact and in equilibrium with a sediment fo 

 resist a log C change resulting from addition or withdrawal of sorbed 

 phosphorus. 



The buffering intensity, which is the slope of the Temkin isotherm, 

 can be approximated by a single number, the phosphate sorption index 

 (PSI). This is the ratio of A' to log C and is obtained by adding 1500 ng P 

 to a gram of sediment and measuring the amount taken up. The higher the 

 PSI, the more strongly the sediment binds phosphate. In the intensively 

 studied ponds the PSI was 359 to 540 while in the other ponds investigated 

 the PSI was 318 to 728. These PSFs are 50 to 250 times higher than those 

 found to control phosphorus concentrations in a stream at Hubbard 

 Brook, N.H. Thus, the sediments of the Barrow ponds are strongly 

 buffered. 



It is likely, then, that DRP concentrations in the pond are controlled 

 by the phosphate sorption by sediments, and that this, in turn, is controlled 

 by the concentration of exchangeable inorganic P in the sediment. A 

 survey of DRP and oxalate extractable P (which approximates total 

 inorganic P) showed a correlation coefficient of 0.56 over a series of ponds 

 so there is certainly some relationship. A negative relationship was found 

 between organic phosphorus and oxalate extractable phosphorus in the 

 sediment so it is possible that it is the rate of mineralization of the organic 

 P that controls the amount of inorganic P. Another process that may be 

 operating is the trapping of DRP during the spring runoff. Perhaps the 

 best demonstration of the importance of the sorption equilibrium was the 

 excellent correlation between the log of the plankton primary production 

 and the PSI of sediments from the intensively studied ponds. 



Organic Carbon 



The dissolved organic carbon (DOC) was defined as the material 

 passing through a glass fiber filter; the effective cutoff was 0.8 ^im. 

 Meltwater contains little DOC so concentrations in the pond were low, 

 4 to 5 mg DOC liter', immediately after the ice melted. As soon as the 

 sediments thawed, the DOC quantity increased; a peak of 15.6 mg DOC 

 liter"' was reached on 5 July. The concentration then became relatively 

 constant at 10-14 mg DOC liter"' until late August when rain sometimes 

 diluted the water. Concentrations became very high as the ice sheet 

 thickened in September. 



