12 



J. E. Hobbie 



amounts of DRP in the water. In a series of intensively-studied ponds 

 (Figure 1-8), the concentration of DRP in the water column could even be 

 predicted from a single measurement of the sediment phosphorus that 

 could be extracted with oxalate. In the same ponds, the oxalate- 

 extractable phosphorus appeared to be directly related to the 

 photosynthesis rate of planktonic algae (Figure 1-9). Thus, we conclude 



Air 



FIGURE 1-10. Nitrogen standing crop and fluxes in the water and sedi- 

 ments of a tundra pond on 12 July 1971. Units are mg N nr- for the con- 

 centrations and mg N nr' day' for the fluxes. The amounts and flux 

 rates were measured whenever possible; some are calculated from the 

 data in Figure 1-5. 



