Forest Fires and Erosion: Sediment Analysis of Little Lake, Oregon

Rebecca A. Puta

Background

Records of how the climate and vegetation may have changed in an area over time are

found and can be analyzed from a multitude of sources, such as lake and ocean sediments, wind-

blown deposits, ice cores, tree rings, and coral, in addition to historical documents (US Global

Change Research Program, 2003). Paleolimnology (Cohen, 2003) is the study of ancient lake

sediments and the significant paleoenvironmental records preserved in them. These deposits are

records of past vegetation, climate and forest fire frequency changes that span several thousands

of years. Examining these sediments and the organic remains in them gives us a better

understanding of how these systems respond to changes similar in scale to those predicted to

occur in the near future (i.e. global warming). Although lake studies are common, the linkage

between these systems and landscape evolution are not. This study will analyze sediments from

Little Lake to compare with charcoal analysis conducted by Dr. Colin Long of UW-Oshkosh to

test if there are correlations between them.

Little Lake is a small lake located in western Oregon, nestled in the Coastal Range forests

between the Pacific Ocean coast and the Cascade Mountains at 44°10’03” N, 123°35’01”W.

Cool wet winters and warm dry summers characterize the climate of the Oregon Coast Range

(Hemstrom and Logan, 1986). The lightning storms that occur during the dry summer period are

most likely the main source of the forest fires that are quite common in this area, but the logging

industry has also provided the area with an effective ignition source over the last 200 years

(Agee, 1993). As seen in Figure 1 below, the Little Lake area is now predominantly covered by

a second-growth Douglas fir forest. Several other species of hardwood trees occupy the area, but

rushes, sedges, and grasses comprise the land within 60 meters of Little Lake (Worona and

Whitlock, 1995).

Several studies have been done on the pollen analysis, charcoal and organic matter of the

Little Lake site, which has led to the determination that the climate of this area was colder and

drier approximately 42,000 years ago, and that the land supported an array of vegetation much

different from that of the present day. The previous charcoal analyses of the Little Lake

sediments also correlate to changes in forest fire frequency and intensity over time (Long and

Whitlock, 2002). Little research and analysis have been done on the particle-size analysis of

Little Lake sediment, which could provide valuable insight into what sediments have been

covering the immediate landscape and has been deposited into the lake, whether from erosion or

from a fire event, and possibly the intensity of the fire event. This study has the potential to

unlock a copious amount of information about the environmental changes of the past and present

at Little Lake.

The Project

Dr. Colin Long of UW-Oshkosh has been studying Little Lake for over 10 years and is

considered one of the foremost experts of the site. Dr. Long has already collected 152 samples

from Little Lake and is conducting charcoal analysis on them. He sent the samples to UW-

Platteville for organic matter content analysis and particle-size analysis. This project will use the

commonly accepted methods of loss on ignition, charcoal separation, and particle size analysis

on the sediment samples from Little Lake. While each method/test is important to the project,

the most significant is the particle size analysis because it has the potential to unlock the most

about this area and how its environment has changed over time. Researchers studying this area

have concentrated primarily on organic and charcoal matter in the Little Lake sediments, leaving

the door wide open for a vast amount of information that could be derived from particle-size

analysis of the sediment. The data derived from the laboratory tests of this project will be used

to relate any changes in sediment size to possible changes in the frequency or intensity of past

forest fires in the area, whether those fires also affected the changes in the type of sediment that

accumulated at the Little Lake site, and how being up or down wind of the fires may have

affected sediments in the lake. All of this information may then be used and tied together to

determine what the past climate of the area may have looked like and how drastically or minutely

it has changed compared to the climate of the present day.

The Solution

The loss on ignition (LOI) procedure has shown strong correlations with determining the

organic and carbonate content in lake sediments according to Heiri, Lotter, and Lemcke (2001).

The weight percent of organic matter and carbonate content in the 152 sediment samples will be

determined by loss on ignition (LOI) following Heiri, Lotter, and Lemcke (2001). LOI uses

Figure 1: Photograph of Little Lake, Oregon provided by Dr. Colin Long.

sequential heating in a Leco TGA 701 Thermogravimetric Analyzer muffle furnace. The

samples are heated to 550°C and 950°C, which are temperatures that organic matter and

carbonate are combusted. The samples are weighed before and after they are heated. The latter

weight is subtracted from the former, which is then divided by the initial weight and multiplied

by 100 to determine the weight percent of organic matter and carbonate content.

Prior to particle-size analysis, the samples must first undergo a charcoal separation

because it could affect the analyses. Ferrous sulfate will be used to cause any charcoal to float

from the sediments. The density of the ferrous sulfate falls between charcoal and sand/silt grains

so the charcoal tends to float on top of the liquid. Samples will be pretreated for charcoal

removal at the Williams Laboratory in the UW-Madison Geography Department. These

pretreatments will take about one week and require travel from Platteville to Madison during the

summer. This quick and simple method has been shown to produce good, useful results.

Lastly, particle-size analysis will be performed following Sperazza (2004), to determine

the size of the sediments in each of the samples and how the size changes among the samples.

Laboratory equipment available for this is a Malvern Mastersizer 2000E laser diffraction

particle-size analyzer. This is a fairly inexpensive and easy to perform procedure that returns

very precise and easy to analyze results on the particle size of the samples run. In the laboratory,

the samples will be dispersed by chemical treatment (NaHMP) and ultrasound, and analyzed on

the Malvern Mastersizer 2000E following Sperazza et al. (2004). Each sample takes

approximately ten minutes to analyze. The data for the samples are then represented on a graph

that shows the particle size of the sediment (in micrometers, µm) and change in volume. The

peak of the curve indicates what the sediment is primarily comprised of, and as the curves from

other samples are also placed on the graph, it is easy to see the minute or significant changes in

the particle size from sample to sample. Figure 2 is an example of the data from the particle-size

analysis of three soil samples taken from the Platteville Gun Range, which indicates that while

all three samples are significantly comprised of clay sediment, there are small changes in the

amount of clay found in each sample. The Malvern Mastersizer is not only a simple and efficient

method of particle-size analysis, but also displays the resulting data in a very understandable and

easy to decipher format.

Dissemination Plan

There are a multitude of ways to disseminate the results of this project, primarily at

scientific poster sessions and professional meetings in the fields of geology and geography. If

the lab work can be completed before October 2008, the first presentation could be at the

National Geological Society of America (GSA) meeting. This meeting will be held in Houston,

Particle Size Distribution

0.1 1 10 100 1000

Particle Size (µm)

0

1

2

3

4

5

6

7

Volu

me (

%)

Figure 2: An example of what the

data from a particle-size analysis

will look like. This was a sample

of sediment taken from the

Platteville Gun Range.

Texas, and will allow some of the most recognizable, experienced, and influential professionals

in the fields of geography, geology, and sedimentology to see and hear about the results of the

project firsthand. If the work cannot be completed in this amount of time, though, there is a

regional meeting for the North-Central Section of the GSA that will be held in Ypsilanti,

Michigan in April 2009, and allows for the same type of presentation to professionals in the

same fields of study, but concentrated in this particular section of the United States. The results

of this project will also be presented at the UW-Platteville Research/Poster Day, the ‘Posters in

the Rotunda’ for scientific posters and research held annually in Madison, WI, the UW System

Undergraduate Research Symposium, as well as at any other scientific research/poster sessions

available in the area that this project qualifies for. There is also the possibility of assisting in the

publishing of a professional research paper that ties together the results of this project with the

information that Dr. Colin Long has on the area, and the conclusions that can be made related to

paleoenvironments and paleolimnology.

Benefits

This project not only benefits scientists studying how paleoenvironments changed or

were affected in this area, but it also has many personal benefits for me. By majoring in

Geography, with a particular interest in Physical Geography, this project will illuminate the

possibilities of what types of research are currently being done and what jobs will need to be

filled. It will also give me the skills and knowledge of how to conduct my own research project,

as well as how to use common, modern techniques that influence the way research is done. My

career plans are to work outdoors conducting research on soil, rocks, plate tectonics, and

possibly even volcanoes. Having the laboratory, analytical, and dissemination knowledge and

experience will only further increase my abilities and likeliness of finding a position in field

research. This project could very well be the hand that turns the knob on the opening door of my

future in physical geography.

Bibliography

Agee J.K. 1993. “Fire ecology of Pacific Northwest forests.” Island

Press: Washington, D.C.

Cohen, A.S. 2003. Paleolimnology. Oxford University Press. 3-5.

Heiri, O., Lotter, A., and Lemcke, G. 2001. “Loss on ignition as a method for estimating

organic and carbonate content in sediments: reproducibility and comparability of results.”

Journal of Paleolimnology 25: 101-110.

Hemstrom, M.A., and Logan, S.E. 1986. “Plant association and management

guide Siuslaw National Forest.” USDA For. Serv.

Rep. No. R6-Ecol 220.1986a.

Konert, M., Vandenberghe J., 1997. “Comparison of laser grain size analysis

with pipette and sieve analysis: a solution for the underestimation of the clay

fraction.” Sedimentology 44, 523-535.

Last, M. and Smol, J. 2001. Tracking Environmental Change Using Lake Sediments, Volume 1:

Basin Analysis, Coring, and Chronological Techniques. Kluwer Academic Publishers. 1.

Long, C. and Whitlock, C. 2002. “Fire and Vegetation History from the Coastal Rain Forest of

the Western Oregon Coast Range.” Quaternary Research, 58: 215-225.

Sperazza M., Moore, J.E., Hendrix, M.S., 2004. “High-resolution particle size

analysis of naturally occurring very fine-grained sediment through laser diffractometry.”

Journal of Sedimentary Research 74, 736-743.

US Climate Change Science Program: Paleoenvironment and Paleoclimate.

http://www.usgcrp.gov/usgcrp/ProgramElements/paleo.htm October 12, 2003

Whitlock, C. and Larsen, C. 2001. Tracking Environmental Change Using Lake Sediments,

Volume 3: Terrestrial, Algal, and Siliceous Indicators. Kluwer Academic Publishers. 75-76.

Worona, M.A. and Whitlock, C. 1995. “Late-Quaternary vegetation and climate history near

Little Lake, central Coast Range, Oregon.” Geological Society of America Bulletin 107, 867-

876.