Basin-scale hyporheic zone respiration in the Columbia River Basin
Abstract
Stream ecosystem generates unexpectedly high amounts of CO2 into the atmosphere. While the hyporheic zone (HZ) respiration accounts for a large portion of whole stream CO2 emission, studies in quantifying HZ respiration are lacking, especially for large watershed/basin scales. In this study, we use a process-based, basin-scale model to quantify HZ respiration and the key factors controlling its spatial variability across the Columbia River Basin (CRB). Our modeling approach combines empirical substrate models and three microbially driven reactions to computing aerobic and anaerobic respiration for each reach of the National Hydrography Dataset (NHD) within the CRB. The modeled respiration patterns are characterized by high spatial variability at the sub-basin to reach scales. Among the nine sub-basins composing the CRB, the Lower Columbia and the Williamette, which receive the higher amounts of precipitation, have higher cumulative respiration amounts. At the reach scale, aerobic respiration is the dominant process, representing approximately 97 % of the total respiration across the CRB. We find important patterns with channel size; medium-size rivers (4th to 6th order streams) produce the highest aerobic and total respiration amounts. Land use also plays a critical role in the spatial patterns of respiration. Reaches in forest areas have the highest aerobic respiration while those in urban areas have the highest anaerobic respiration. A Variable Importance Analysis (VIA) suggests that hyporheic exchange flux controls most of the spatial variability in HZ respiration, dominating over other physical variables such as residence time and biogeochemical variables such as stream dissolved organic carbon (DOC), nitrate, and dissolved oxygen (DO). With the importance of hyporheic exchange flux being larger for aerobic respiration than for anaerobic respiration, this study suggests that a parsimonious river reaction network can quantify the basin-scale HZ respiration and provide insights into the key factors controlling its spatial variation over multiple scales. Future efforts will focus on improving the estimation of the HZ exchange flux and the implementation of spatially explicit parameterizations for the reactions of interest.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2021
- Bibcode:
- 2021AGUFM.H33J..04S