Many rivers in Australia have had their natural hydrology massively altered to meet the needs of irrigated agriculture and reliable water supplies during warmer months. Many studies have examined the effects of these 'reversed' annual hydrology patterns on several key aspects of riverine ecosystems, including those within the Murray-Darling Basin. However, one important aspect where there is still a paucity of information and insight is the effect on the energy base of the aquatic foodweb i.e. the amount of organic carbon being produced through gross primary production (GPP) and consumed through ecosystem respiration (ER).
Whole stream metabolism measurements can provide daily estimates of these key parameters and such measurements have been conducted continuously in the Goulburn River catchment downstream from the Goulburn Weir (Lake Nagambie) since 2012 as part of the Commonwealth-funded LTIM and then MER programs. This talk will use the most recent 3-year period of this data (May 2023-May 2026) from two sites in the Goulburn and two further sites in the Broken catchment, all of which have major flow alteration though regulation. Seasonal patterns in GPP and ER will be compared to those in the nearby Ovens catchment where sites vary from unregulated (Myrtleford) to some regulation further downstream (a major tributary is regulated). In addition to the GPP and ER comparison, I will also discuss and compare the load of organic carbon (which may be considered "fish food") created each day and how regulation may significantly alter the amount of organic carbon produced each season (with potential effects on fish populations).