Stages in a Paleoecological Study

Although each paleoecological study is unique, depending on the research problems, geographical area of study, site type, expertise of the paleoecologists, age of the sediments, etc., there are several stages that are common to many, if not all, Quaternary paleoecological studies.

1. Definition of research problem. Careful definition of the research problem and hypotheses to be tested is important at the outset, as paleoecology is a very labor-intensive and time-consuming activity. A poorly designed project results in a considerable waste of time and effort.

2. Selection of site to be sampled. Careful site selection is essential if the research questions are to be answered. Site selection requires not only knowledge of the study area and its geology, topography, and hydrology but also knowledge of the ecology and land use of the possible sites to be selected (Figure 2). Exploratory studies are invaluable.

3. Selection of coring site. Once a site has been selected, the next stage is to select where to take a core of the sediments for paleoecological study. In general, the aim is to maximize between-site variability and hence to minimize within-site variability. Experience has shown that the deepest point in a basin is often the place where within-site variations are minimal and is thus the preferred place for sediment coring. Again exploratory studies are invaluable.

4. Collection of sediment cores. There are several different types of coring devices. The choice depends on many factors, including water depth, nature of the sediments to be sampled, amount of sediment needed for study (pollen analysis only needs 1 cm3 of sediment, whereas paleoentomology requires large volumes), temporal resolution required, and remoteness of the study site. Details of suitable coring devices can be found in the works given

Figure 2 Lille Kjelavatn, a small lake at 1000 m in southern Norway. This is an ideal site for a paleoecological study as the lake is small and relatively deep ensuring that the pollen record is from the catchment (watershed) and the sediments are undisturbed; the surrounding slopes are gentle and there is no sedge-swamp around the lake ensuring that terrestrial plant macrofossils are washed into the lake; and the bedrock is acid, thereby minimizing errors in radiocarbon dating.

Figure 2 Lille Kjelavatn, a small lake at 1000 m in southern Norway. This is an ideal site for a paleoecological study as the lake is small and relatively deep ensuring that the pollen record is from the catchment (watershed) and the sediments are undisturbed; the surrounding slopes are gentle and there is no sedge-swamp around the lake ensuring that terrestrial plant macrofossils are washed into the lake; and the bedrock is acid, thereby minimizing errors in radiocarbon dating.

in Table 2. The most common type is illustrated in Figure 3, along with a sediment core.

5. Sampling and describing sediments. This involves describing the sediments in terms of physical properties (e.g., color, stratification, and water content), humification (degree of decay), and composition (clay, silt, sand, organic detritus, mud, etc.). The subsampling resolution depends on the research questions and the rate of sediment accumulation. In some arctic lakes where the last 10 000 years may be represented by only 1 m of sediment, sampling at 10 years intervals requires a sampling resolution of every 1 mm. Such sampling must be done in the laboratory using specially constructed equipment. Time spent on careful sampling is time well spent, because contaminated samples are worthless.

Last WM and Smol JP (eds.) (2001) Tracking Environmental Change Using Lake Sediments, Vol. 1: Basin Analysis, Coring, and Chronological Techniques. Dordrecht: Kluwer.

Last WM and Smol JP (eds.) (2001) Tracking Environmental Change Using Lake

Sediments, Vol. 2: Physical and Geochemical Methods. Dordrecht: Kluwer. Smol JP, Birks HJB, and Last WM (eds.) (2001) Tracking Environmental Change Using Lake Sediments, Vol. 3: Terrestrial, Algal, and Siliceous Indicators. Dordrecht: Kluwer.

Smol JP, Birks HJB, and Last WM (eds.) (2001) Tracking Environmental Change

Using Lake Sediments, Vol. 4: Zoological Indicators. Dordrecht: Kluwer. Jones TP and Rowe NP (eds.) (1999) Fossil Plants and Spores. London: The

Geological Society. Birks HJB and Gordon AD (1985) Numerical Methods in Quaternary Pollen

Analysis. London: Wiley. Birks HJB (1998) Numerical tools in palaeolimnology - progress, potentialities, and problems. Journal of Paleolimnology 20: 301-332.

6. Dating. An absolute chronology is essential in almost all Quaternary studies. For the last 150 years, radio-metric-dating techniques involving 210Pb, 137Cs, and 241Am are invaluable. For the last 15 000 years, radiocarbon dating is the major chronological tool.

7. Collecting paleoecological data. A very wide range of data types can be collected, including physical, chemical, and biological data (see Table 1).

8. Presentation of paleoecological data. The resulting data may be complex and it is a challenge to present the results ofseveral paleoecological analyses in a clear and effective way. Much thought is required and many critical questions need to be considered - should all variables be presented when there may be 200 diatom taxa present, should the data be presented as relative percentages or 'absolute' accumulation rates, should the data be plotted on a sediment age scale or on an estimated age scale? Numerical techniques can be valuable in summarizing the patterns of variation within and between different data sets from the same sediment sequence.

9. Interpretation. There are two major approaches to the interpretation ofpaleoecological data: (1) paleoecological reconstructions, a primarily descriptive approach where the emphasis is on reconstructing past biota, populations, communities, landscapes, and ecosystems; (2) ecological paleoecology, a hypothesis-testing approach where the emphasis is on interpreting the observed changes in terms ofunderlying causes.

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