INTRODUCTION 



Large increases in sediment loads in stream channels can create intolerable 

 changes to material size composition of salmonid spawning areas (Platts and Megahan 

 1975) . The more commonly used methods to detect and determine the magnitude of these 

 intolerable changes are, however, often inadequate. 



The metal core tube (McNeil 1964), which is primarily used in Idaho and other 

 areas in the Pacific Northwest, does not determine the vertical and horizontal 

 stratification of the redd sediment particle size distribution. Therefore, this 

 method could be biased in determining the true effects of sediments on embryo and 

 alevin survival. Salmonid embryo and alevin survival rates have usually been estimated 

 by sampling stream channel materials with 6- to 12-inch (152 to 305 mm) tube core 

 samplers. The substrate particle size distribution of the samples collected is then 

 used to estimate potential survival rates. These estimates may not be accurate 

 because the sediment particle size is (1) limited to the size the coring tube can 

 encase, (2) the sample is completely mixed so no interpretation can be made of verti- 

 cal and horizontal differences in particle size distribution, (3) the sampling depth 

 is limited by both water depth and the length of the collector's arm, (4) the core 

 tube can push larger particle sizes out of the collecting area, (5) suspended sediments 

 in the core can be lost, and (6) the individual sample size is limited to the core 

 tube diameter. Therefore, the core samples collected may be biased to certain particle 

 sizes . 



This report describes a new freeze sampling method similar to those developed by 

 Walkotten (1976) and Lotspeich and Reid (in press). Walkotten (1976) originally 

 developed the freeze core method to lessen the biases previously discussed in samp- 

 ling channel sediments. Our recent unpublished work, as well as Ringler's (1970), 

 comparing the tube core sampler with the freeze core sampler, suggests, however, that 

 the single probe method may be biased toward larger size sediment particles. We 

 believe one of the main reasons for this bias is that the freeze probe collects 

 larger size particles on the core perimeter more readily than it collects smaller 

 size particles. The smaller size particles may fall off in a higher weight ratio 

 during core extraction. Lotspeich and Reid (in press) have attempted to solve 

 some, of these problems by using three freeze probes instead of one. Our new method 

 helps eliminate the perimeter bias by allowing a much larger sample to be taken. The 

 previous methods also have a tendency to take uneven amounts of substrate in the 

 vertical direction, thus collecting more sediment at one depth than another. The 

 new system takes a uniform sample. 



The new method, as does the methods used by Walkotten (1976) and Lotspeich 

 and Reid (in press) allows collection of the eggs and alevins in the redd at any 

 stage of development, will function at any air or water temperature or stream depth, 

 and will determine the horizontal and vertical location of the eggs and alevins. 

 The new system uses C0 2 more efficiently and alleviates problems of clogging from 

 dry ice. The method will take a sample of any size that can be lifted and transported 

 and will allow the complete redd or selected parts of the redd to be analyzed in the 

 laboratory in a near natural condition. The method has the potential for improving 

 our estimates of embryo and alevin survival rates and identifying causes of their 

 mortality. 



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