A major spring flood in 2022 in the Goulburn River, Victoria, resulted in a peak flow of 81,700 ML/Day at the McCoy's Bridge gauge on the 19th October. The flow exceeded the overbank flow level (28,000 ML/Day) at this site two days earlier and remained above this overbank level until the 29th November. There was large scale, extended inundation of the floodplain; some of this water slowly drained back into the river channel.
Stream metabolism has been measured at this site since 2014 as part of the Commonwealth Environmental Water Office's Long Term Intervention Monitoring and then, since 2019, the Monitoring, Evaluation and Research Program. Stream metabolism provides daily estimates of rates of gross primary production (GPP) and ecosystem respiration in the river. GPP can be equated to production of food ('organic carbon') for the aquatic foodweb.
This talk will probe the idea that the extended flood duration and return flows would provide a large boost to in-river nutrient supplies, thereby enhancing GPP. To investigate this hypothesis, summertime GPP immediately post-flood will be contrasted with pre-flood rates. A longer term response will be assessed by looking at summertime 2023-24 GPP rates.