Quantitative and qualitative characterization of DOM excreted by <i>Ephemera</i> mayflies in stream ecosystems

  Aquatic insects play an important role in the biogeochemical cycling of freshwater ecosystems, particularly through their release of dissolved organic carbon (DOC) and related compounds. Among them, Ephemera mayflies are one of the key collector-gatherers that process fine particulate organic matter (FPOM). Recent studies have shown that Ephemera larvae convert ingested FPOM into dissolved organic matter (DOM), thereby contributing directly to stream DOC pools. We characterized the DOM excreted by Ephemera larvae using DOC analysis and excitation–emission matrix (EEM) fluorescence spectroscopy. Rearing experiments were conducted on E. orientalis and E. japonica in ultrapure and natural stream water under controlled laboratory conditions. Water samples collected over 10 days were analyzed for DOC and fluorescent DOM. Both species showed increases in DOC concentration and in the intensities of protein-like fluorescence peaks (Ex/Em ≈ 275/330 nm) and humic-like peaks (Ex/Em ≈ 350/425–440 nm; 275/450 nm), confirming that Ephemera larvae excrete DOM containing both labile and humified components. Moreover, E. japonica, which inhabits steep upstream reaches, excreted higher DOC concentrations and stronger fluorescent DOM signals than E. orientalis, a downstream species. These results indicate species-specific differences in DOM production and suggest that E. japonica may contribute disproportionately to DOM cycling in headwater ecosystems.

Presentation Preference: Poster

Primary Presenter: YUKO SUGIYAMA, Okayama University of Science (yuko-sugiyama@ous.ac.jp)

Authors:

Yuko Sugiyama, Okayama University of Science  (yuko-sugiyama@ous.ac.jp)

Yota Kitaue, Okayama University of Science  (yotakitaue@icloud.com)

Ryota Nojima, Okayama University of Science  (r25nml7ia@ous.jp)

Tatsuaki Saito, Okayama University of Science  (tat-saito@ous.ac.jp)