The CRCS Build-a-Museum Team Newsletter

Newsletter Number 04 - September 15, 2004 :

Research at LSU which produces natural history collections worthy of preservation in a museum:

This newsletter segment is the first of a series on research which yields natural history collections. Such research is an integral part of education at LSU. Some of it focuses on Louisiana itself and provides new insight into our state's story. Other projects range around the globe.

The following article focuses on types of fossils which may be new to our readers, but which provide paleoenvironmental information which larger fossils often cannot.  ( click on the images to enlarge )

Modern Forest Phytolith Reference Collection and Distributional Analog, Catahoula Lake, Louisiana

Background: Catahoula Lake is the largest and most unusual freshwater lake in Louisiana. It is one of only 10 sites in the United States designated as a Wetland of International Importance by the Ramsar Convention. Hundreds of thousands of migratory water fowl and shorebirds pass through or over-winter at the lake annually. Numerous archeologic sites, some dating back to Paleo-Indian time, occur around the lake and indicate that Native Americans utilized the rich food resources of the lake for thousands of years.

What makes the lake unusual is that it undergoes a wet and dry cycle annually that leaves most of the lake bed exposed during the late summer and fall. In ancient times, wild animals, including the now extinct eastern elk, grazed on the lush vegetation that grew on the lake bed as the water level fell. Settlers turned their hogs and cattle loose on the exposed lake bed during the summer to take advantage of the same bounty, and feral pigs are still to be seen rooting around during low water.

The age and origin of the lake are unknown because the sediments that underlie the lake have never been studied. These deposits are a natural archive containing a detailed record of floods and climatic changes that have affected the area during the existence of the lake.

Dr. John H. Wrenn (Center for Excellence in Palynology, Department of Geology and Geophysics, LSU,Baton Rouge) and his students, Lawrence Febo, Rebecca Tedford, and Robin Camors are conducting the first geologic and paleontologic study of Catahoula Lake. They took two sediment cores about 22 and 27 meters long during October, 2003 for micropaleontologic, sediment, and absolute age dating analyses.

Preliminary examination revealed the presence of abundant microfossils in the sediments, including pollen, diatoms, sponge spicules, chrysophyte cysts, and phytoliths. These environmentally sensitive fossils provide the key to unraveling the history of climate changes that have affected the lake through time. Phytoliths, in particular, will provide a record of the plants that grew around the lake in the past.

What are phytoliths? Plants draw water and dissolved silica up from the ground and pump it through their vascular system. The silica may become concentrated enough within or between plant cells that it precipitates, forming siliceous phytoliths. The shape of the phytoliths often reflects the internal structure of the plant cells in which they formed. When the plant dies, their phytoliths are released and become part of the soil where the plant grew. Since they are composed of silica, essentially glass, they are resistant to weathering and can persist for thousands, even millions, of years in sediments or rocks. Some species of plants produce diagnostic phytoliths, whereas other phytoliths may be characteristic of a larger group of plants, such as a genus or a family.

The recovery of distinctive phytoliths from a sediment sample indicates that the plant that produced the phytoliths formerly grew at the site where the sample was collected. If the climatic and environmental preferences of the phytolith parent plants are known, that data can be used to reconstruct the environmental and climatic conditions that prevailed at the time that the phytoliths were formed and deposited.

However, before phytoliths can be used in a new area, it is necessary to determine what plants produce phytoliths and if any them are diagnostic for various plants. This must be done because there are many plants whose phytolith production has yet to be determined. In addition, it is important to determine the distribution of phytoliths is in modern soil under the living plant communities. Once this is established in an area of study, the modern phytolith assemblages can be used to interpret the ancient phytoliths contained in buried sediments, such as those sampled by Catahoula Lake Cores No. 1 and 2.

To address the first need, a Comparative Phytolith Reference Collection is being built of the 33 most abundant plants living in the shoreline and mixed hardwood forests that occur within the U. S. Catahoula Lake National Wildlife Refuge (CLNWF). Samples of these plant taxa, consisting of leaves, flowers, or stems, have been obtained for phytolith extraction from the Louisiana State University Herbarium, Baton Rouge, or the University of Florida Natural History Museum Herbarium in Gainesville. Field collecting at the CLNWF has provided supplemental material. These samples have been processed by both dry ash and chemical oxidation methods to extract their phytoliths. A "Phytolith Atlas" of the modern plant samples is being built. This will be a fundamental tool for study of the soil samples and, eventually, the lake cores.

The second prerequisite for studying a new area requires building a Modern Distributional Analog of the phytolith assemblages preserved in the forest soils. This needs to be done for the floral communities in each new study area because few such analog models currently exist. Standard pinch (small surface) samples were collected from the upper one centimeter of forest soil at multiple points within a 10 m2 area and mixed to form a composite sample for each square. Twenty such squares were sampled, yielding 20 composite samples. These were processed by acid digestion to destroy unwanted organic matter in the sample and to extract siliceous microfossils, including phytoliths. Five hundred phytoliths will be identified, classified, and counted for each Modern Analog soil samples to provide a statistically robust characterization of the phytolith assemblage on the forest floor.

Scientific Benefits: students are closely involved in all aspects of this project including sample collection and processing, data collection on the microscope, and building the "Phytolith Atlas". The experience gained during this project will help prepare them for a career in science.

Much of the pioneering work in phytolith distribution was conducted in grass lands of the Great Plains. Few phytolith Modern Distributional Analogs exist for eastern North America or the southeastern United States: even fewer exist for forest lands. This study will enhance our understanding of forest plant phytolith communities, particularly in the central Gulf Coast. Results will be applicable to the studying the paleoenvironmental and paleoclimatic record of Catahoula Lake cores and will help provide paleoenvironmental and paleoclimatic control needed for understanding the archeological sites around Catahoula Lake and in the central Louisiana (J. Saunders, Louisiana State Archeologist,Monroe,LA; pers. com.).