Humic shallow lakes 4 South America 4 floodplain 4 photosynthesis 4 phytoplankton 4 primary production 4 shallow water 4 Floodplain wetland 2 Parana River 2 Periphytic algae 2 Phytoplankton 2 Pico-, nano- and microphytoplankton 2 Primary production 2 Productivity 2 Subtropical wetland 2 algae 2 biomass 2 carbon isotope 2 dominance 2 fractionation 2 humic lake 2 humic substance 2 macrophyte 2 periphyton 2 picoplankton 2 seasonality 2 size structure 2 subtropical region 2 water column 2 wetland 2