2024 Abstracts

Reconciling Variation and Interconnections in Stream Network Organic Matter Degradation and Microbial Community Activity Across Scales


Robert Danczak1* (robert.danczak@pnnl.gov), Vanessa Garayburu-Caruso1, Firnaaz Ahamed2, Mikayla Borton3, Kevin Ryan4, Hyun-Seob Song2, Kelly Wrighton3, James Stegen1, Tim Scheibe1


1Pacific Northwest National Laboratory, Richland, WA; 2University of Nebraska–Lincoln, NE; 3Colorado State University, Fort Collins, CO; 4U.S. Geological Survey, New York Water Science Center, Troy, NY



Substantial amounts of dissolved organic matter (DOM) are transported throughout river ecosystems and undergo abiotic and biotic interactions with the surrounding ecosystem. Despite this importance, researchers know little regarding the spatial scaling of DOM or the microbial communities degrading it. To investigate these concepts, researchers leveraged high-resolution DOM characterization, microbial sequencing, and novel data science approaches. The team observed linear relationships between stream size and both DOM functional diversity and the number of potential biochemical transformations in the Yakima River Basin (YRB). Results from five other watersheds revealed that, while the types of relationships observed in the YRB were not universal, catchment-specific spatial variables were significantly related to transformation count indicating spatial scaling patterns for DOM. A machine learning approach was used to investigate the bioavailable component of DOM and indicated that thermodynamic favorability, the number of carbons, and carbon-to-nitrogen ratios were important molecular formula properties when predicting respiration rates. Researchers combined DOM characterization data with shotgun sequencing and identified putative connections between microbes and DOM at the continental U.S. (CONUS)-scale. The team identified 2093 unique metagenome assembled genomes belonging to 27 phyla and found that microbial metabolism became dominated by clades capable of using simple carbon compounds as watersheds increased in size. These studies revealed that DOM has spatial scaling connected to land cover and stream size while the microbial communities more closely mirrored predictions posited by the River Continuum Concept.