| Autor: |
Tureţcaia AB; Department of Earth and Planetary Sciences, The University of Texas at Austin, Austin, Texas 78712, United States., Garayburu-Caruso VA; Pacific Northwest National Laboratory, Richland, Washington 99352, United States., Kaufman MH; Pacific Northwest National Laboratory, Richland, Washington 99352, United States.; Department of Earth, Environment, and Physics, Worcester State University, Worcester, Massachusetts 01602, United States., Danczak RE; Pacific Northwest National Laboratory, Richland, Washington 99352, United States., Stegen JC; Pacific Northwest National Laboratory, Richland, Washington 99352, United States.; School of the Environment, Washington State University, Pullman, Washington 99164, United States., Chu RK; Environmental Molecular Sciences Laboratory, Richland, Washington 99352, United States., Toyoda JG; Environmental Molecular Sciences Laboratory, Richland, Washington 99352, United States., Cardenas MB; Department of Earth and Planetary Sciences, The University of Texas at Austin, Austin, Texas 78712, United States., Graham EB; Pacific Northwest National Laboratory, Richland, Washington 99352, United States.; School of Biological Sciences, Washington State University, Pullman, Washington 99164, United States. |
| Abstrakt: |
Hyporheic zones (HZs)─zones of groundwater-surface water mixing─are hotspots for dissolved organic matter (DOM) and nutrient cycling that can disproportionately impact aquatic ecosystem functions. However, the mechanisms affecting DOM metabolism through space and time in HZs remain poorly understood. To resolve this gap, we investigate a recently proposed theory describing trade-offs between carbon (C) and nitrogen (N) limitations as a key regulator of HZ metabolism. We propose that throughout the extent of the HZ, a single process like aerobic respiration (AR) can be limited by both DOM thermodynamics and N content due to highly variable C/N ratios over short distances (centimeter scale). To investigate this theory, we used a large flume, continuous optode measurements of dissolved oxygen (DO), and spatially and temporally resolved molecular analysis of DOM. Carbon and N limitations were inferred from changes in the elemental stoichiometric ratio. We show sequential, depth-stratified relationships of DO with DOM thermodynamics and organic N that change across centimeter scales. In the shallow HZ with low C/N, DO was associated with the thermodynamics of DOM, while deeper in the HZ with higher C/N, DO was associated with inferred biochemical reactions involving organic N. Collectively, our results suggest that there are multiple competing processes that limit AR in the HZ. Resolving this spatiotemporal variation could improve predictions from mechanistic models, either via more highly resolved grid cells or by representing AR colimitation by DOM thermodynamics and organic N. |
