Flow, water quality and algae in the Katherine River, tropical Australia

The Katherine River lies in the Australian wet/dry tropics where flows are highly seasonal and dominated by surface runoff in the wet season (Dec-Mar) and groundwater during the dry season (June-Oct). Wet season flows are deep and turbid, with high velocities, and are not favourable to primary production. During the transition between the wet and dry seasons, the reduction in flow and increased groundwater coincides with increased water clarity. This transition can be traced by the ionic chemistry of the river in the Katherine River downstream of Katherine township. Increased water clarity and reduced flows combine to favour primary production, which is initially dominated by phytoplankton but succeeded by benthic algae when the depth and water clarity permit photosynthesis at the riverbed. Over the dry season flow, water quality remains largely unchanged until the first runoff events of the wet season.