252 P. L. Gersper et al. 



adjacent control plots, suggesting lack of movement of phosphorus 

 (Barel and Barsdate 1978). 



Other Effects 



Considerable quantities of both nitrogen and phosphorus can be 

 transferred directly to available pools in the soil during a lemming high. 

 During these population peaks lemmings consume up to 40 g m'^ yr' of 

 graminoid plant material, nearly 50% of the annual aboveground pro- 

 duction, and most of the minerals in this are excreted. However, this ef- 

 fect on available pools of nitrogen and phosphorus may be relatively in- 

 significant during population lows, when consumption may fall below 1 

 g m"^ yr"' (Chapter 10). Nitrogen is mainly excreted in the urine and is 

 immediately available to plants and microorganisms. Phosphorus is dis- 

 tributed between urine and feces (Barkley 1976). Leaching experiments 

 using an analogue of the surface runoff showed over 90<^o removal of 

 phosphorus from feces in 24 hours (Chapin et al. 1978). During a high 

 year, lemming feces would release about 90 mg P m"^ 



The freeze-thaw effect, described by Saebcf (1968) for Sphagnum 

 peat, is another way nutrients may be transferred from unavailable to 

 available pools. After freezing and thawing, peat samples showed con- 

 centrations of dissolved and dilute acid-soluble phosphorus several times 

 higher than did the control samples. The solution concentration returned 

 to control values after remaining thawed for 48 hours, but values for 

 acid-soluble phosphorus remained somewhat above controls for the 

 same time period (Saebd 1968). Patterns of dissolved and resin- 

 exchangeable inorganic phosphorus in the soils of the coastal tundra at 

 Barrow indicate that the same effect is occurring (Barel and Barsdate 

 1978). A similar effect was observed in solution concentrations of am- 

 monium and nitrate (Barel and Barsdate, unpubl.) and in soluble carbo- 

 hydrates in soils of other areas (Gupta 1967). These similarities, and the 

 lack of any effect on calcium levels, indicate that the freeze-thaw mech- 

 anism may involve a physical disruption of the organic matrix. The me- 

 chanics of the effect, and its magnitude, are still unclear. 



The mineral fraction of the soil contains a significant fraction of the 

 total phosphorus pool in non-exchangeable form (Chapin et al. 1978). 

 Chemical transformation of the mineral matrix in which the phosphorus 

 is bound would allow the transfer of some phosphorus to the exchange- 

 able pool. Although weathering rates are low in arctic conditions (Doug- 

 las and Tedrow 1960), this source of inorganic phosphorus may not be 

 negligible under the low-phosphorus regime of the wet meadow soils. 



