32 



Periodically, the westerly flew of air is intempted 

 by outbreaks of clear, cold continental air from 

 Ccinada. During the summer months, the westerly wincJs 

 weciken, eind oontinentid climatic oonditicaTS prevail. 

 Rain fall, cloud cover, and relative humidity are at 

 their minimum in summer. The Soil Conservation Service 

 (1981) estimates that, in latah County, the average 

 annual precipitation is 63.5 an (25 in.), the average 

 annuEd air temperature is about 6.7* C (44* F) , and the 

 average frost- free season is about 110 days. 



The climate in western Weishington is undoubtedly varwer 

 and moister than in Idaho or hkantana. 



c. Local midDclinHte: No detailed quantitative 



informatiwi available. The aquatic h2±)itats ooci^jied 

 by H. aquatilis eure probably less subject to diurnal 

 tenperature fluctuations than the atmosphere. In 

 Montana, the species often occurs along the mcirgins of 

 small ponds surrounded by heavy forest cover, and thus 

 would be shaded for much of the day. In Idaho, the 

 small pond containing Hcyo>ellia aquatilis is partially 

 shaded throughout the sunmer by tall shrubs that 

 ijimediately border it. Cold air pooling can be intense 

 during the fall, winter and spring, but is moderate 

 during most of the grcwing season due to the relatively 

 low elevation. 



2. Air and water quality requireniGnts: In Montana, water 

 sanples from nine ponds supporting H. aquatilis . eax3 three 

 pcxids not supporting the species, were analyzed to determine 

 pH and conductivity. In addition, five sanples (three from 

 iJ. aquatilis ponds, two from others) were emalyzed to 

 determine alkalinity. Ihe results of these analyses are 

 presented in Table 2. 



None of the factors analyzed appear to distinguish amc»Tg 

 ponds containing or not containing H. aquatilis . The pH 

 values for ponds with or without the species are all in the 

 neutral range (6.75-7.92). It is possible that other 

 factors which were not analyzed eure more inportant in 

 determining the suitability of a particular site for 

 si:53porting iJ. aquatilis (i.e., dissolved oxygen, 

 temperature) . 



Air quality requirements are unknown. 



3. Fhysiographic provinces: Kncwn from the Northern Rocky 

 Mountain, Columbia Plateaus, and Pacific Border provinces 

 mafped by Fenneman (1931) ; the Rocky Mountains, Columbia- 

 Snake River Plateau, and Pacific Border provinces mapped by 

 Hunt (1974) ; and the Ooluittoia Basin Province mapped by 

 Franklin and Dymess (1973). 



