Floodplain forests

Field Studies. We have attempted to compare the relative availability of actinides to small mammals living in contaminated environments near ORNL. Shrews, rats and mice have been collected from a 30 year old contaminated floodplain forest ecosystem ( ). Cotton rats (Sigmodon hispidus) have been collected from the banks of a former liquid radioactive waste pond which contains Pu, Am and Cu in sediments and shoreline vegetation. Analyses were performed by isotope dilution mass spectrometry (U, Th and Pu) or by alpha spectrometry (Pu, Am and Cm). 

Figure 4. Comparative accumulation of actinides by small mammals from contaminated soil or sediment relative to the accumulation of plutonium-239. Accumulation factor (AF) = concentration of nuclide in the internal small mammal body -- concentration of nuclide in dry soil. Twelve shrews and seven rats and mice from a floodplain forest were composited to yield four and three separate analyses, respectively. Twelve cotton rats inhabiting the banks of a liquid waste pond (3513) also were analyzed.

In this chapter we discuss the distribution and the development of plant communities in floodplain areas, mainly of the big whitewater rivers, focusing on factors such as diversity, species composition, biomass and primary production. Based upon these factors, we also discuss the annual dynamics of bioelements stocks and their turnover through herbaceous and floodplain forest communities. Finally, we examine the implications of such nutrient dynamics and turnover for the aquatic biota. We do not address carbon and nutrient budgets, as these are thoroughly discussed in chapter 14. 

Table 13.5 Comparative structural data of some Amazonian floodplain forests investigations of studies on floristics in Amazonian inundation forests.

The floristic composition of floodplain forests is described by several forest inventories covering the complete Amazon basin. Detailed information is available from central Amazon forests in the vicinity of Manaus with inventories of about 17 ha of varzea forest from the Ilha de Marchantaria, Costa do Marrecao, and Costa do Barroso (Worbes 1983, 1986, Revilla 1991, Worbes et al. 1992, Klinge et al. 1995) and from igapo forests (Keel and Prance 1979, Revilla 1981, Worbes... 

Diversity patterns are an important feature in the analysis of tropical forest communities. However, a comparison of existing studies is difficult because size and shape of plots, diameter limit of the included individuals, and criteria of site selection may differ considerably (Table 13.5). A simple but helpful measure is the calculation of species per 100 stems (Klinge et al. 1995) (Table 13.5). Another severe problem is that all individuals can not be identified to species level. In all reports a varying percentage of unidentified taxa is present. This reason impedes a calculation of indices of similarity or diversity. The generally observed trends in changing species diversity of Amazonian floodplain forests are as discussed below. 

On nonflooded sites in Amazonia, species richness increases from east to west, from 87 species ha i near Belem (Black et al. 1950) to over 179 species ha near Manaus (Prance et al. 1976) and more than 200 species in Ecuador (Balslev et al. 1987). Gentry (1982, 1990) explained species richness generally increases as annual precipitation increases. However in the same direction diversity increases in the floodplain forests from 53 species per ha in Para (Pires and Koury 1959) to over 135 species in Mamiraua (Ayres 1993) to 149 species at the Rio Napo (Balslev et al. 1987). The human influence on species composition in floodplain forests is a poorly investigated factor however, forests of the eastern Amazon have been exposed to deforestation and severe exploitation for longer times than western forests. In the varzea of the Solimoes river, selective logging nearly caused the extinction of... 

Balslev, H., J. Lutteyn, B. 011gaard, and L. B. Holm-Nielsen. 1987. Composition and stmcture of adjacent unflooded and floodplain forest in Amazonian Ecuador. Opera Botanica 92 37-57. 

Furch, K. 1997. Chemistry of Vaizea and Igapo soils and nutrient inventory of their floodplain forests. In The Amazonian Floodplains Ecology of a Pulsing System, ed. W. J. Junk (Ecological Studies. Springer-Verlag, Berlin), pp. 47-68. 

Kubitzki, K., and A. Ziburski. 1994. Seed dispersal in floodplain forest of Amazon. Biotropica. 26(1) 30-43. 

Putz (1997) estimated production as uptake of i C by periphyton that grew on artificial cellulose-acetate substrata suspended in several habitats near Manaus. Her results could not be used to compute an areal value for periphyton associated with floating macrophytes due to the complex surface of the natural substrata. To extrapolate her results to areal rates in floodplain forests requires an estimate of leaf area in the euphoric zone per unit area of water. Alves (1991) reported between about 0.5 and 1.5 m2 of leaves in the euphoric zone of flooded forest per m2 of water for simplicity we used 1.0. Based on net productivities measured by Putz (1997) at a site dominated... 

For the entire floodplain herbaceous macrophytes accounted for the largest share of total primary production, 65%, followed by floodplain forests, periphyton and phytoplankton which accounted for 28%, 5% and... 

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