Poor pollen preservation? A problem of the past! Pick another proxy! Help Me, Opal Phytoliths. You’re My Only Hope Lusteck, Robert, Thompson, Robert, and Myrbo, Amy LacCore/Limnological Research Center, University of Minnesota, 500 Pillsbury Dr SE, Minneapolis, MN 55455

Isolating Phytoliths from Lake Sediments Abstract Phytoliths are present in many lacustrine environments, but often in fairly low Sediments recovered from lake cores often present an excellent matrix for the quantities. This procedure is intended to concentrate the phytoliths while removing as recovery of plant remains. This has enabled researchers to reconstruct past floral regimes, typically through the identification of pollen and/or macroscopic much extraneous material as possible. The procedure is fairly quick and inexpensive. plant remains. However, the vagaries of preservation do not always allow for the survival of these remains. Opal phytoliths present another viable option for 1.First, samples are placed in 50 ml centrifuge tubes with distilled water. Potassium hydroxide (KOH) environmental reconstruction. Phytoliths are microscopic silicates formed in the is added and the samples are placed in a hot water bath for 30 mins. KOH helps to remove humic tissues of many plants. Phytoliths are extremely durable (outside pH extremes) and can often be identified with useful taxonomic specificity. While phytoliths acids and to break up organic materials, especially lignin, and acts as a mild deflocculant. Samples commonly are employed in archaeology, their use in lacustrine contexts could are rinsed twice with distilled water. be greatly expanded. 2.Hydrochloric acid (HCl) is added and samples are again placed in a hot water bath for 30 mins. Phytolith research has been hampered by the issues of multiplicity and redundancy—plants often make multiple types of phytoliths and related plants This helps to remove any carbonates that may be in the sample. make similar phytoliths. That being said, many plants do make phytoliths that 3.Following a rinse with distilled water, nitric acid (HNO3) is added and the samples returned to the are family, genus or species specific. Furthermore, many plant species make 60 micron screen assemblages of phytoliths that are recognizable when taken as a whole. Secure hot water bath for 1 hour. The nitric acid bath removes most of the remaining organic material. identification requires a strong comparative collection. By extracting phytoliths Samples are rinsed 2-3 times with distilled water. from modern plant specimens, we have started to construct a (publically 4.Concentrated hydrogen peroxide (30% H2O2) is added and samples again are placed in a hot available) phytolith database that will enable us to make identifications and construct analog floral communities. Additionally, phytoliths can be difficult to water bath for 30 mins. separate from the more abundant diatoms commonly found in lacustrine 5.Following a distilled water rinse, bleach (5.25% NaClO) is added and samples are placed in a hot sediment. Here we present a method to extract phytoliths from lake sediments Perch Lake, MN and comparative samples in order to construct a robust description of past floral water bath for an additional 20 minutes. Samples are rinsed with distilled water. The organic communities. Using a combination of chemical baths and microsieves, we have material should now be completely removed from the samples. been able to concentrate phytoliths into usable frequencies from small amounts 6.Most of what remains should be silicates, including phytoliths, diatoms, sand, silts and clays. To of sediment (5 cc or less). Samples are spiked with a non-siliceous microsphere to facilitate statistical calculations, such as influx rates and ubiquity. This is part remove the latter, microsieves are used. The samples are rinsed first through 60 micron screens. of a larger project to examine the history of wild rice (Zizania palustris) in This will remove the sand and many whole diatoms. Minnesota lakes. Phytoliths have provided evidence for Zizania in contexts where macrofossils have been absent and pollen has been equivocal. 7.Samples are then rinsed in a 7 micron screen. The material that is rinsed through the screen is discarded, while what remains in the screen is retained. Samples are returned to 50 ml centrifuge What’s aa phytolith?phytolith? tubes and rinsed with alcohol to replace the water. The whole of this procedure can be done in 1-2 7 micron screen days and results in a pretty clean sample. Unfortunately, diatoms (mostly broken frustules) will Opal phytoliths are created inby many plants plants as they as deposit they deposit silica silicain and in and often dominate the sample, but can be readily distinguished from most phytoliths. around cells during thetheir plant’s lifetimes. life. BecauseBecause ofof thethe durabledurable naturenature ofof silica, phytoliths accurately record/reflect the cell structure of the What can you use phytoliths for? plants in which they formed. Although they have been known about for some time, phytoliths have had limited use in the geosciences, particularly in lacustrine contexts. Here we examine the use of -Phytoliths are extremely durable. In many areas of the world and in many phytoliths in documenting the presence of wild rice and present an depositional environments, pollen and/or macro-fossil preservation is poor or effective method for extracting phytoliths from lake sediments. non-existent. Phytoliths can be used in these places as a proxy indicator of Perch Lake Phytolith Percentages vegetation.

-There are many plants that make phytoliths that, like pollen, can be identified to family, genus, or species level.

-Phytoliths can be used as a check on other proxy data. For example, here

Zizania we have used phytoliths to examine the history of wild rice (Zizania palustris) in palustris northern Minnesota. Grass pollen (presumably wild rice) recovered from Perch Lake peaks early in the core and sharply declines at deeper levels. Macro- fossils are almost entirely absent below 20 cm. Phytolith analysis, however, shows that grasses have been a major component of the lake’s past, and that Zizania specific phytoliths can be detected in significant amounts throughout Making aa comparativecomparative collection collection the past several hundred years. In order to make a comparative collection, phytoliths must be extracted This information would not have been known had we not from modern plants. There are many different ways to do thisthis. (refs). Here weHere Perch Lake Pollen Percentages wehave have chosen chosen a quick a quick and and easy easy method. method. Plant Plant samples samples are areplaced placed in 50 in ml50 coupled phytolith and pollen research. mlcentrifuge centrifuge tubes tubes to whichto which nitric metric acid acidis added. is added. These These samples samples are thenare then References placed in a hot water bath for 1 to 2 hours. Distilled water is added and Lentfer, C.J., Boyd, W.E. 1998 A comparison of three methods for the extraction of phytoliths from sediments. Journal of Archaeological Science 25: 1159-1183. samples are centrifuged at 3000 rpm for 5 mins. The supernatant is Lentfer, C.J., Boyd, W.E. 2000 Simultaneous extraction of phytoliths, pollen and discarded and samples are rinsed with distilled water 2-3 more times. spores from sediments. Journal of Archaeological Science 27: 363-372. Finally, the water is replaced with alcohol through a series orof 22--33 alcoholalcohol Madella, M., Powers-Jones, A.H., Jones, M.K. 1998 A simple method of extraction of opal phytoliths from sediments using a non-toxic heavy liquid. Journal of rinses. We use alcohol because it evaporates quickly when placed on a Archaeological Science 25: 801-803. heated microscope slide and thus does not interfere with the slide Powers, A.H., Gilbertson, D.D. 1987 A simple preparation technique for the study of opal phytoliths from archaeological and quaternary sediments. Journal of mounting medium (optical(Norland cement). 61 optical cement). Archaeological Science 14: 529-535. Zhao, Z., Pearsall, D.M. 1998 Experiments for improving phytolith extraction from soils. Journal of Archaeological Science 25: 587-598. Zizania aquatica