The implications of brief floodplain inundation for local and landscape-scale ecosystem function in an intermittent Australian river

Abstract

Context Floodplain inundation creates a diversity of aquatic habitats that diverge in their physical, chemical and biological characteristics through space and time, influencing site-scale ecological processes, with implications for local and landscape-scale ecosystem functioning. Aims In this study, we characterise conditions of pools on the floodplain and pools in the main channel of the Fitzroy River, north-western Australia. Methods We used linear models to investigate the spatial and temporal dynamics of top–down and bottom–up forces acting on phytoplankton and zooplankton. Key results Floodplain pools showed considerable heterogeneity compared with the main channel and were shallow and turbid with high nutrient loads, whereas main-channel pools were deep, clear and nutrient-limited. Phytoplankton and zooplankton biomass (mass per unit volume) were considerably greater and more variable in floodplain pools than in the main channel, where both were largely absent. On the floodplain, bottom–up processes drove water-column productivity (e.g. nutrients to phytoplankton to zooplankton) to a degree not observed in the main channel, providing a valuable resource pathway supporting consumer populations locally and catchment wide. We detected no top–down effects in floodplain pools and no top–down or bottom–up effects in the main channel. Conclusion Maintaining flows that inundate the floodplain and promote habitat heterogeneity in the Fitzroy River is crucial for preserving local and landscape-scale ecosystem functioning. Implications Water managers should take into account the important contribution of floodplain pools to the wider riverine ecosystem and ensure these habitats are not unduely affected by water resource development.