Submitter Withdrawn International Conference on River Connectivity (Fish Passage 2018)

Longitudinal shift in Dissolved Organic Matter (DOM) source, concentration and characteristics detected when comparing an altered flow and free-flowing river gradient. (52993)

Luke McPhan 1 2 , Kim Jenkins 1 2 , Lee Baumgartner 2 , Paul Humphries 2 , Andy Baker 1
  1. University of New South Wales, Randwick, NSW, Australia
  2. Charles Sturt University, Thurgoona, NSW, Australia

Conceptual models of carbon flow in rivers provide useful frameworks for discussing resource use and carbon flow within river systems, however, they remain largely untested with respect to alterations caused by regulation structures.  Whilst these models give some idea of contributions to river carbon by allochthonous and autochthonous resources, there is a lack of knowledge surrounding the transformation and distribution of the most bioavailable carbon pool in river systems, the dissolved organic matter (DOM). We analysed the DOM pool along two rivers, one flow altered and the other free-flowing aiming to determine the following; 1) if there was a significant difference in DOM character and concentration between systems from headwaters to lowlands, 2) to identify longitudinal patterns in DOM character and concentration between rivers as predicted by the serial discontinuity concept (SDC), and 3) to quantify if discharge influenced DOM character and concentration. Using benchtop spectroflurometry to obtain absorbance and fluorescence estimates, we calculated an array of absorbance (S275-295, SR), fluorescence (Peak Ratios C:M; C:T; M:T) and concentration parameters to be analysed in a linear mixed model framework.

The characteristics of DOM across similar locations between rivers differed significantly from headwaters to lowland floodplain areas. DOM above and below the dam on the regulated river differed significantly and align with findings presented in the SDC. Research continues into the interpretation of absorbance parameters of DOM though our findings support the fact that discharge shapes DOM character. We found a positive relationship between discharge and molecular weight of DOM (S275-295) suggesting that micro-organisms dependant on DOM derived from autochthonous primary production (Peak T) and fresh allochthonous material (Peak C) will benefit from periods of flood and high discharge whilst those dependent on DOM from degraded allochthonous carbon will dominate during periods post flooding through to those of drought.