Dissolved organic carbon delivery from managed flow releases in a montane snowmelt river

Abstract

Managed flow releases are increasingly being utilised in the rehabilitation of regulated rivers to improve physical habitat condition and restore spatial connectivity. However, the potential for managed flow releases to influence basal resource availability to the downstream food web has received less attention. This study investigated dissolved organic carbon (DOC) delivery from managed flow releases from Jindabyne Dam and a regulated tributary to the Snowy River; a mixed rainfall-snowmelt river in south-east Australia. DOC concentration and load were monitored downstream of Jindabyne Dam during two high-flow dam releases and 2 month-long tributary releases provided by temporarily suspending tributary weir diversions. DOC chemical composition in the downstream Snowy River was characterised using fluorescence spectrophotometry. A negligible change or decrease in DOC concentration occurred at all monitored sites during both dam releases. In contrast, pulsed increases in DOC concentration concomitant with natural high-flow events were observed in the Snowy River during the tributary releases. The estimated DOC load delivered by the larger dam release increased 1.5-fold between sites 2 and 22 km downstream of the Jindabyne Dam. Reservoir release waters contained both humic-like and protein-like DOC fluorophores, whereas tributary releases contained only humic-like DOC fluorophores. Collectively, these results suggest that changes in DOC quantity and composition during managed dam releases reflect localised wetting and DOC mobilisation from the riparian zone whilst tributary releases deliver storm-associated pulses of terrestrial DOC flushed from the catchment. The unique DOC regimes associated with dam and tributary-sourced water releases may influence ecosystem functioning in the downstream river.