366 



J. E. Hobbieet al. 



cm depth, this oscillation appeared to be 12 hours out of phase with the 

 surface temperatures (Figure 8-7, Figure 3-5). The diffusion rate within 

 the sediment was tested by injecting ^''C02 and proved to be 0. 1 67 cm hr ' 

 at 7°C. This rate will vary, of course, as a gradient of the CO2 

 concentrations and of the temperature change but it is rapid enough to 

 account for the discrepancies. 



From day to day, the respiration rates within a pond fluctuated 

 greatly (Figure 8-8). The highest rates were measured in June 1973 

 immediately after the ice melted. This peak corresponds to early-season 

 peaks in bacterial numbers in the sediment (Figure 8-1) and peaks in 

 activity in the water (Table 8-4); it is likely caused by wintertime release of 

 organic nutrients from microbes and other organic matter. This high rate 

 of respiration undoubtedly occurred each year but was missed in 1971 and 

 1972. Similar early season respiration maxima have been found in the soils 

 at Barrow (Brown et al., in press). 



The total amount of CO 2 released from the sediments varied from 

 year to year but did correlate with the total amount of solar radiation and 

 with benthic algal production (Figure 8-8, Table 8-10). When the amount 

 released is corrected for the additional input from the rooted plant zone, 

 where rates are 2.5 times higher, the whole-pond average is 24.9, 22.9, and 

 15.1 g C m~^ yr~' for 1971, 1972, and 1973, respectively. These values 

 are 47 to 78% of the macrophyte decomposition rate of 32 g C m " ^ yr ~ ' 

 (Table 8-9) but the variability of the respiration data do not allow too fine 

 a comparison to be made. Core respiration rate is also much lower than 

 the total pond respiration estimate of 50 g C m~' made in 1971 (Coyne 



TABLE 8-10 Annual Measurements of Solar Radiation, Temperature, Algal 

 Production and CO 2 Flux for 1971 to 1973 



1971 



1972 



1973 



Solar radiation 



— 2 —1 



(cal cm summer ) 

 (June-August) 



50,048 39,573 32,225 



Water temperature 

 o 

 ( C average daily) 



5.7 



8.5 



5.8 



Benthic algal production 



— 2 — 1 



(g C m summer ) 



10.1 



8.9 



4.1 



Annual CO2 flux 

 pond center 



—2 —1 



(g C m summer ) 



13.7 



11.7 



8.3 



Annual CO2 flux 



pond center and macrophyte zone 



—2 —1 



(g C m summer ) 



24.9 



22.9 



15.1 



