Removal of vegetation from the watershed may influence stream tempera- 
ture in several different ways. Water temperature may be increased by 
the removal of riparian vegetation from the streambank. A survey in 
Connecticut (20) revealed a stream temperature increase of 10 degrees 
along a half-mile section in which all brush had been removed. The feed- 
ing of sun-warmed ground-water into the stream from the logged area may 
increase water temperature. A general lowering of stream height as a 
result of hydrologic changes to the watershed following logging might 
increase water temperatures above normal during warm months, and lower 
it during cold months. Snow accumulation and period of snowmelt might 
be affected by clearcutting. 
Stream temperature exerts its influence on various phases of the life 
cycle of the salmon during all months of the year. Pink and chum salmon 
fry do not remain in the streams but migrate to salt water soon after 
hatching. The fry of other species may spend one or more years in the 
parent stream. 
Objectives of this phase of the study include a determination of fresh 
water temperatures under natural conditions, and the magnitude of change, 
if any, following logging. A secondary objective includes determination 
of the relationship between water temperature and such factors as air 
temperature, stream height, and precipitation. 
Maximum Fresh Water Temperature 
Donaldson and Foster (6) found that young sockeye salmon fingerlings 
were not able to tolerate water temperatures as high as 78° F. for more 
than a few days, and were able merely to maintain themselves at tempera- 
tures of 70° F. Donaldson (5) found that tolerance of king salmon eggs 
varied with stage of development. Eggs exposed to 67° F, died in every 
stage of development, while those exposed to 65° F. and 63° F. did not 
show appreciable mortalities until after the stage of development associat- 
ed with the approach of hatching. An exposure of six days to 65° killed 
nearly 50 percent of the eggs. Ninety percent mortality occurred when 
the eggs were exposed 10 days to 67° temperatures, 16 days at 65°, and 
25 days at, 6a. 
Stream temperatures in Southeast Alaska are moderate. Mean monthly 
water temperatures of the study streams are shown in table 7. The 
highest mean monthly temperature for any stream from 1950 to 1953, 
inclusive, was only 55.1° F. The maximum monthly mean for any single 
month of record was only 57.4° F. Highest mean monthly temperature 
occurred either in July or August in all streams,.=2 
Maximum instantaneous water temperatures are shown in table 8. The 
highest instantaneous temperature recorded on any stream was 66° F., 
occurring twice during the period. These maximum temperatures occurred 
15/ Sub-surface water temperature. Temperature elements were placed 
in depressions in the stream bottom in order to protect them from 
freezing, and from debris and ice-flow. This practice is expected to 
give reliable results as the temperature of running water is relatively 
uniform. 
2 ois 
