Floodplain lakes productivity

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... 

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... 

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. 

In Amazon floodplain lakes, daily water column respiration usualiy exceeds planktonic gross photosynthesis, and dissolved oxygen is usually undersaturated (Melack and Fisher 1983). Wissmar et al. (1981) and Richey et al. (1988) found Amazon flood-plain lakes to be consistently undersaturated in O2 and supersaturated in CO2. The deficit of oxygen in these systems is a consequence of high respiration to production ratios. 

Quay et al. (1995) reported lower respiration to production ratios (1 to 1.7) in seven Amazon floodplain lakes. These ratios were derived from stable isotope ratios of dissolved oxygen in surface waters where light availability and photosynthesis are often high. The higher ratios calculated by B. R. Forsberg were based on depth-integrated rates and thus more accurately reflect the total pelagic carbon balance. 

Doyle, R. D. 1991. Primary production and nitrogen cycling within the periphyton community associated with emergent aquatic macrophytes in an Amazon floodplain lake. Ph.D. Thesis, University of Maryland, p. 269. 

Schmidt, G. W. 1973. "Primary production of phytoplankton in the three types of Amazonian waters. 3. Primary productivity of phytoplankton in a tropical floodplain lake of Central Amazonia Lago Castanho, Amazonas, Brazil." Amazoniana 4 379-404. 

The total organic carbon balance for lakes on the central Amazon floodplain can be examined by comparing total inputs due to primary production and external loading with total losses (Table 14.4). The combined input of organic carbon due to primary production, river import and local runoff was estimated at 117.3 Tg C yr. Combined losses due to biogenic gas emission and... 

As is evident throughout our review, a much wider diversity of lakes and floodplain environments must receive the attention of limnologists. Additional measurements of periphyton productivity, of burial of C, N, and P in sediments, of nitrogen fixation and denitrification, and of carbon dioxide emissions, especially, are needed. A further challenge is to investigate biogeochemical processes in the ATTZ, and to link these processes with the whole floodplain ecosystem. 

Closed systems, such as the wetlands that receive most of their water from precipitation (e.g., bogs, pocosins, and some seasonal or ephemeral wetlands), are oligotrophic and typically have low primary productivity. Increased inputs from surface and ground water can increase primary productivity in fens and marshes. (Table 5.5) Wetlands that receive pulses of nutrients, such as river floodplains, littoral zones in lakes, and tidal marshes, are typically very productive (Sharitz and Pennings, 2006). 

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