Floodplain lakes

In chapter 14, John Melack and Bruce Forsberg provide a quantitative assessment of the role of floodplain lakes in regional cycles of C, N, and P. Floodplain lakes were found to be important centers of organic carbon production and delivery to the river system. The combined primary production of macrophytes, forests, periphyton, and plankton associated with floodplain lakes is estimated at 117 Tg C yri, of which only 24% is remineralized in the lakes. As a result, an estimated 90 Tg C yr are delivered to the river system by continual and seasonal exchanges. This input alone amounts to... 

During the aquatic phase plants are detached from the sediments and drift with the current. They contribute to the carbon pool of the main channel of the Amazon River and also accelerate the colonization of newly created open areas formed by the deposition of sediments. Quick colonization creates a range of different stages of allogenic succession in the floodplains. The velocity of the successional process will depend upon the stability of the habitat. Isolated floodplain lakes, where deposition rates of sediments are small, show a slow but gradual colonization process while, processes on sand bars and mud flats in the river channel are more dynamic and often reversible (Junk and Piedade 1997). 

This is consistent with the high concentrations of nutrients found in floodplain lakes where decomposition processes related mainly to herbaceous vegetation may produce concentrations of nutrients more than 20 times greater than those in the Amazon River itself (Furch 1984, Furch and Junk... 

Alves, L. F. 1993. The fate of streamwater nitrate entering littoral areas of an Amazonian floodplain lake the role of plankton, periphyton, inundated soils, and sediments. Ph.D. Thesis, University of Maryland-CEES, College Park. p. 370. 

Furch, K. 2000. Evaluation of ground water input as major source of solutes in an Amazon floodplain lake during the low water period. Verhandlung International Vereinigen Limnologie. 7(1) 412-415... 

Furch, K., and W. J. Junk. 1985. Dissolved carbon in a floodplain lake of the Amazon and in the river channel. In Transport of Carbon and Minerals in Major World Rivers, eds. E. T. Degens, S. Kempe, and R. Herrera (Geology-Palaentology Institute, University of Hamburg, Hamburg, pp. 285-298. 

Weber, G. E. 1997a. Causes of hydrochemical seasonality of major cations in Lago Camaleao, a Central Amazonian floodplain lake. Veihandlungen International Vereinigen Limnologie. 26(2) 408-411. 

Biogeochemistry of Amazon Floodplain Lakes and Associated Wetlands... 

Seven types of aquatic interfaces, with differing horizontal and vertical gradients in hydrochemical and physical characteristics, can occur in floodplain lakes river-lake interface, direct rain and through-fall—lake interface, upland stream—lake interface, lake-lake connections, epilimnion-hypolimnion interface, lake—sediment porewater interface, and lakeshore—ground-water interface. 

The strong seasonal variations in depth and extent of inundation and complex hydrologic linkages and interfaces characteristic of floodplain lakes have important influences on biogeochemical processes and fluxes. Much of our discussion in subsequent sections will elaborate upon these effects. Recent efforts to model and calculate seasonal and annual rates of biogeochemical processes in Amazon flood-... 

Following Sippei et al. (1992), we apply a simple morphological classification to Amazon floodplain lakes ria or blocked-... 

Two major types of hydrologic and morphometric information are lacking for almost all Amazon floodplain lakes stage data and bathymetric maps. Therefore, it is not possible to determine directly the seasonal and interannual changes in open water area, total flooded area, or volume of water resid-... 

For any period of time, the water balance of a floodplain lake can be expressed by the equation ... 

The first and only detailed analysis of the terms in equation 1 for an Amazon floodplain lake was performed at Lake Calado (Lesack and Melack 1991, 1995 Lesack 1993a, 1995). Lake Calado has a BA LA ratio ranging from about 7 at high water to about 28 at low water. River water invaded the lake at the start of rising level in the mainstem, but by midrising water, lake water steadily flowed from the lake into the river, while river levels continued to rise. By the end of the water year, Lake Calado had experienced a 10 m range in water level, and local runoff had contributed 57% of the total water input, river inflow 21%, rainfall directly onto the lake... 

Inflow of the turbid, nutrient-rich water of the Amazon River onto the floodplain helps sustain the floodplain s high fertility (Fisher and Parsley 1979, Setaro and Melack 1984, Engle and Melack 1993). The inflows follow complex flow paths that account, in part, for differences in productivity among floodplain lakes. For example, Melack et al. (1992) analyzed a rare cloud-free Landsat Multispectral Scanner (MSS) image of the initial stages of riverine inundation by the Amazon River which illustrated the complexity of the flow... 

Table 14.2 Average values of phytoplankton production parameters for 36 Amazon floodplain lakes.

Total daily phytoplankton production can vary considerably in Amazon floodplain lakes due to large seasonal changes in surface area linked to water-level variations. 

While many species of macrophytes in Amazon floodplain lakes are C-3 species, a... 

The complex structure and seasonal dynamics of herbaceous macrophyte communities make it difficult to estimate their total annual contribution to floodplain lake production. Annual production estimates must incorporate the cumulative, sequential production of terrestrial, semiaquatic and aquatic plant communities and the spatial and temporal variation in their distributions. To date all measurements of macrophyte production have been made in a limited area on the central Amazon floodplain near Manaus. Only a few of these estimates have included contributions of more than one species. Junk and Piedade (1993) estimated the cumulative biomass increase of three successive macrophyte communities (terrestrial, semiaquatic, and aquatic) growing under... 

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