Seasonal contrasts in carbon resources and ecological processes on a tropical floodplain

Abstract

1. Globally, tropical floodplains are highly productive ecosystems. This is largely because of predictable seasonal rains providing replenishing floodwaters that stimulate nutrient turnover which, in turn, substantially boosts both primary and secondary productivity. This is associated with concomitant shifts in the types of primary producers and associated food webs. 2. The Magela Creek floodplain on Kakadu National Park in northern Australia is one of the most studied tropical freshwater ecosystems in Australia and provides an opportunity to collate and examine information on organic carbon sources and pathways through food webs to gain a fundamental understanding of how these systems may function. 3. We reviewed biophysical information published since the early 1980s to construct an assessment of the carbon resources for the channel and floodplain. 4. We conclude that macrophytes, largely in the form of grasses and aquatic plants, produce the greatest above-ground biomass on the Magela Creek floodplain. Although macrophytes provide suitable substrata for the attachment of epiphytes, they do not appear to be an important carbon source for aquatic consumers themselves. Nevertheless, macrophytes do provide critical seasonal food and habitat structure for other producers and consumers on the floodplain, such as the abundant magpie geese. 5. We developed a generalised conceptual food web and carbon budget contrasting the 'wet' and 'dry' seasons for the Magela Creek system, as a representative of tropical seasonal floodplain systems. 6. Our conceptual model of tropical floodplains indicates that knowledge of the seasonal and spatial links and exchanges between the floodplain and the river is critical in understanding ecosystem function.