Relevance of tributary inflows for driving molecular composition of dissolved organic matter (DOM) in a regulated river system

Suman Acharya; Aleicia Holland; Gavin Rees; Andrew Brooks; Daniel Coleman; Chris Hepplewhite; Sarah Mika; Nick Bond; Ewen Silvester

doi:10.1016/j.watres.2023.119975

Relevance of tributary inflows for driving molecular composition of dissolved organic matter (DOM) in a regulated river system

Water Res. 2023 Jun 15:237:119975. doi: 10.1016/j.watres.2023.119975. Epub 2023 Apr 13.

Authors

Suman Acharya¹, Aleicia Holland², Gavin Rees³, Andrew Brooks⁴, Daniel Coleman⁴, Chris Hepplewhite⁴, Sarah Mika⁵, Nick Bond², Ewen Silvester²

Affiliations

¹ Department of Environment and Genetics, Centre for Freshwater Ecosystems, School of Agriculture, Biomedicine and Environment, La Trobe University, Albury/Wodonga Campus, 3690 Wodonga, VIC, Australia. Electronic address: 20123710@students.latrobe.edu.au.
² Department of Environment and Genetics, Centre for Freshwater Ecosystems, School of Agriculture, Biomedicine and Environment, La Trobe University, Albury/Wodonga Campus, 3690 Wodonga, VIC, Australia.
³ CSIRO Land and Water, Institute for Land, Water and Society, Charles Sturt University, 2640 Thurgoona, NSW, Australia.
⁴ Department of Planning and Environment, Surface Water Science, NSW, Australia.
⁵ School of Environmental and Rural Science, University of New England, Armidale, NSW, Australia.

PMID: 37104936
DOI: 10.1016/j.watres.2023.119975

Abstract

River regulation by dams can alter flow regimes and organic matter dynamics, but less is known about how unregulated tributaries regulate organic matter composition and processing in the regulated river below the confluence. This study reports on water chemistry, especially dissolved organic matter (DOM) concentration and composition (dissolved organic carbon (DOC), organic nitrogen (DON), organic phosphorus (DOP) and combined amino acids (DCAA)) along the regulated Tumut and unregulated Goobarragandra (tributary) rivers under different flow conditions (base flow vs storm event) in south-east Australia. The tributary was significantly different from regulated and downstream sites during base flow conditions with higher temperature, pH, buffering capacity, DOC and nutrient concentrations (DON, DOP, DCAA). DOM characterisation by spectrometry and size exclusion chromatography revealed that the tributary contained a higher proportion of terrestrially derived humic-like and fulvic-like DOM. In contrast, regulated and downstream sites contained higher proportion of microbially derived DOM such as low molecular weight neutrals and protein-like components. Storm pulses of tributary flows into the regulated system, influenced both concentration and composition of DOM at the downstream site, which more strongly resembled the tributary site than the regulated site during the storm event. Additionally, we found that the tributary supplied fresh DOM, including small organic molecules to the regulated system during storm events. The presence of these different types of labile DOM can increase primary productivity and ecological functioning within regulated river reaches downstream of tributary junctions. This has important implications for the protection of unregulated tributary inflows within regulated river basins.

Keywords: Flood; Fluorescence; Hydrology; Organic matter dynamics; River management.

MeSH terms

Dissolved Organic Matter*
Nitrogen / chemistry
Phosphorus
Rivers* / chemistry

Substances

Dissolved Organic Matter
Nitrogen
Phosphorus