From: PO4::"WHITMOR@NERVM.NERDC.UFL.EDU" "Tom Whitmore" 23-JAN-1996 13:35:32.37 To: Multiple recipients of list DIATOM-L CC: Subj: sediment sample prep. I'm interested in opinions about preparing diatom samples from lake sediments. The protocol in our lab currently is to freeze dry samples, then grind them in a mortar and pestle prior to subsampling for diatoms. I realize that diatoms are small and cushioned by sediment during grinding, but does anyone have specific knowledge about whether this procedure is likely to increase breakage of diatom valves? This procedure is conveninent for other analytical needs, but is not the one I would prefer for diatom analyses. From: PO2::"stoermer@UMICH.EDU" "Gene Stoermer" 23-JAN-1996 14:24:40.39 To: Multiple recipients of list DIATOM-L CC: Subj: Re: sediment sample prep. On Tue, 23 Jan 1996, Tom Whitmore wrote: > I'm interested in opinions about preparing diatom samples from > lake sediments. The protocol in our lab currently is to > freeze dry samples, then grind them in a mortar and pestle > prior to subsampling for diatoms. I realize that diatoms are small > and cushioned by sediment during grinding, but does anyone have > specific knowledge about whether this procedure is likely to > increase breakage of diatom valves? This procedure is conveninent > for other analytical needs, but is not the one I would prefer for > diatom analyses. > We have looked at that specific issue, and the news is not good. Grinding (same process your lab uses) doesn't trash the diatoms as badly as one would first suspect, but the degree of breakage is highly situation dependent, apparently affected by both the sediment type (can be variable within a single core) and the species of diatoms present. If you count fragments, grinding is probably tolerable. If you don't, I would be dubious lof results. ***************************************************************** Eugene Stoermer, University of Michigan Internet e-mail address: stoermer@umich.edu Voice Phone: 313-764-5238 Fax: 313-747-2748 ***************************************************************** From: PO2::"EYH@WPO.NERC.AC.UK" "Elizabeth Haworth" 24-JAN-1996 04:22:14.68 To: Multiple recipients of list DIATOM-L CC: Subj: Grinding diatoms In response to Tom Whitmore's and Gene Stoermer's remarks on grinding diatoms. DON'T DO IT - the results favour the small round ones and ae disaster for long needle-like forms which break very readily. Maj Britt Florin once told me that she wasted 6 months work on similarly treated samples. Do try to get part of the orginal sample, moist for preference, so that you can use your own preparation techniques. Also to be avoided are samples oven dried for sediment density or water content. Having been familiar with Blelham Tarn's sediments with a 50% well preserved Asterionella assemblage, I once examined these dried samples and was astounded to find them full of small round knobs, and a few shards!!!! The Fragilaria crotonensis was unrecognizeable! This explained why I found early post-glacial Asterionella when earlier researchers failed to do so; my samples were untreated. Liz Haworth Institute of Freshwater Ecology Ambleside, UK. E.Haworth@ife.ac.uk