Spatial and temporal variability of macrophyte growth and productivity in the Amazon floodplain
Date
2009-09-15T14:58:18Z
Authors
Silva, Thiago Sanna Freire
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Abstract
The main objective of the present thesis was to investigate the spatial and temporal variability of macrophyte growth and productivity in the Amazon floodplain, and the possible effects of this variability on the carbon budget of the floodplain.
In Chapter 3, two methods for estimating macrophyte biomass were compared in terms of accuracy and applicability to the Amazon floodplain conditions. Phenotypic variation was large enough to preclude indirect (phenometric) modelling of biomass, while direct sub-sampling was able to account for this variation. Sub-sampling also allowed reduction on the biomass sampling effort, presenting the best trade-off between accuracy and coverage for macrophyte biomass measurements in the Amazon floodplain.
In Chapter 4, annual net primary production (NPP) of macrophytes was estimated for a large lake on the eastern Amazon floodplain, and the uncertainty associated with these measures was assessed, offering a comparison of previous estimates of macrophyte productivity in the Amazon region. Annual net primary production was estimated at 2400 – 3500 g m-2 yr-1, with above water production between 650 – 1100 g m-2 yr-1, and below water production between 1700 and 2600 g m-2 yr-1. Echinochloa polystachya (Poaceae) and Paspalum fasciculatum (Poaceae) were the most productive species, followed by Paspalum repens (Poaceae), Hymenachne amplexicaulis (Poaceae), and Oryza perennis (Poaceae). The four main sources of uncertainty in the estimates were macrophyte taxa, location, sampling design, and lack of measurements of dead material loss.
Chapter 5 presented a new object oriented method for combining radar and optical image time series to characterize seasonal evolution of macrophyte cover for an eastern Amazon floodplain lake. Macrophyte cover varied between 104 and 198 km2 (10% and 20% of total floodplain area, respectively) and exhibited significant changes both seasonally and inter-annually. Two distinct growth strategies were observed: short-lived communities that thrived during low water periods and year-long communities able to survive flooding year-round. Although the majority of the macrophyte carbon fixation derived from the latter, about 17% of macrophyte NPP was attributed to the short-lived communities, which depend directly on the flood levels for a given year. The increased frequency of droughts predicted for the Amazon system could potentially result in an increase on the macrophyte-derived carbon input to the Amazon floodplain.
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Keywords
macrophytes, Amazon, remote sensing, mapping, carbon, producitivity, radar, modeling, wetlands, biogeochemistry