Oral Presentation Freshwater Sciences 2023

Dissolved organic matter influence on microbial communities and productivity in the Warrego and Darling Rivers (#32)

Manisha Shakya 1 , Sarah Mika 1 , Leah Mclntosh 1 , Lindsey Frost 1 , Michael Shackleton 2 , Andre Siebers 2 , Sarah Green 2 , Ewen Silvester 3 , Ivor Growns 1 , Aleicia Holland 3
  1. School of Environment and Rural Science, Faculty of Science, Agriculture, Business and Law, University of New England, Armidale, NSW, Australia
  2. Centre for Freshwater Ecosystems, Department of Environment and Genetics, La Trobe University, Wodonga, Victoria, Australia
  3. Department of Environment and Genetics, La Trobe University, Wodonga, Victoria, Australia

Dissolved organic matter (DOM) differs spatially and temporally within freshwaters, sitting along a continuum between terrestrially-derived humic material of high molecular weight, aromaticity and C/N ratio through to aquatic microbially-derived highly proteinous material of low molecular weight, aromaticity and C/N ratio. DOM forms the basis of aquatic food webs, and its concentration, type, composition and bioavailability influence the composition of microbial communities, which in turn influences river productivity.

The Warrego and Darling River systems in North-West NSW are highly heterotrophic, with carbon consumption greatly exceeding instream production. This study aimed to investigate the influence of dissolved organic matter (concentration and composition) on microbial communities within the Warrego-Darling to identify the processes that regulate productivity within these systems.

We collected water samples in March and April 2022 and quantified and characterised DOM through optical and analytical techniques and microbial communities (fungi, bacterioplankton and phytoplankton) through metabarcoding. Chamber experiments were also conducted at three sites in April to assess pelagic and benthic productivity.

DOM was shown to differ between rivers, with the Darling containing higher amounts of allochthonous humified humic DOM, whereas the Warrego contained DOM of more microbial nature high in proteinous material and biopolymers. Both rivers differed in their microbial communities; with differences significantly related to the types and characteristics of DOM present. Pelagic and benthic productivity differed between sites, with the site containing a mixture of DOM from the Warrego and the Darling recording the highest autotrophic and heterotrophic productivity and also containing the most diverse microbial community. Our results suggest that the type of DOM present in river systems determines its microbial community and productivity. Our results also suggest waters containing a mixture of DOM  types may contain more diverse microbial communities leading to enhanced productivity outcomes.