Carbon and Nutrient Budgets 469 



long-term temperature average. Furthermore, for the years 1972-1977 

 litter bag data suggest that, on the average, decomposition exceeded pro- 

 duction at the same site (Chapter 9). Because of the many possibilities for 

 error, we used various independent methods and combinations of meth- 

 ods to calculate the carbon budget of wet meadow tundra. These meth- 

 ods differ in the calculated magnitude of carbon imbalance in 1971, but 

 all agree that there was a net gain of 40 to 120 g C m~^ in that year (Table 

 12-4). Therefore, although methodology may be responsible for part of 

 the observed discrepancy between total ecosystem carbon fixation and 

 ecosystem respiration, this carbon imbalance was probably real. The car- 

 bon budget in Figure 12-1 is based on actual field measurements, where 

 possible, rather than calculated values. Although the latter show greater 

 self-consistency, they require steady state assumptions. The extent of 

 agreement between field methods indicates that the carbon balance of 

 coastal tundra and other terrestrial ecosystems may deviate substantially 

 from steady state in any given year. Similarly, Woodmansee et al. (1978) 

 suggest that steady state conditions are an unrealistic assumption in eco- 

 system nutrient budgets. 



Inorganic Nutrients 



Nutrient Input 



The presence of permafrost within tens of centimeters of the ground 

 surface limits the amount of thawed soil that is available for weathering. 

 The remainder of the frozen nutrient capital could be tapped only in the 

 event of disturbance or climatic fluctuations that result in deeper thaw. 

 Judging from clay mineralogy, the rate of chemical weathering of miner- 

 als in thawed soil is negligible, due primarily to low temperature (Hill 

 and Tedrow 1961). Hence, the coastal tundra at Barrow apparently de- 

 pends largely upon the atmosphere for nutrient input. This contrasts 

 strongly with most temperate systems where weathering represents the 

 primary source of nutrient supply (Cole et al. 1967, Ovington 1968, 

 Likens and Bormann 1972). 



The arctic climate and the general global atmospheric circulation 

 patterns severely Hmit atmospheric nutrient input. Arctic tundra regions 

 receive little precipitation. The presence of sea ice minimizes the amount 

 of sea spray that could carry nutrients inland from the Beaufort Sea. 

 Snow cover, wet surfaces and distance from agricultural and urban cen- 

 ters render dry nutrient fallout negligible. The annual atmospheric inputs 

 of nitrogen and phosphorus (Figure 12-2) are an order of magnitude less 

 than those characteristic of temperate systems (Ovington 1968). The 

 resupply of phosphorus and cations to the ecosystem must occur not 



