COS 247-4 - Time to Anoxia: Oxygen Consumption in Soils Varies Across a Coastal Gradient

Thursday, August 10, 2023

8:30 AM – 8:45 AM PDT

Location: D133-134

Presenting Author(s)

KP

Kaizad F. Patel

Pacific Northwest National Laboratory, United States

Coauthor(s)

KR

Kenton A. Rod

Pacific Northwest National Laboratory, United States
JZ

Jianqiu Zheng

Pacific Northwest National Laboratory
Richland, WA, United States
PR

Peter Regier

Pacific Northwest National Laboratory, United States
FM

Fausto Machado-Silva

University of Toledo, United States
CN

Cooper G. G. Norris

Pacific Northwest National Laboratory, United States
MK

Matthew Kaufman

Pacific Northwest National Laboratory, United States
JM

J Patrick Megonigal

Smithsonian Environmental Research Center, United States
MW

Michael N. Weintraub

University of Toledo, United States
VB

Vanessa Bailey

Pacific Northwest National Laboratory, United States

Abstract: The coastal terrestrial-aquatic interface (TAI) is a highly dynamic system characterized by strong physical, chemical, and biological gradients. In particular, shifting redox conditions, due to variations of dissolved oxygen concentrations, is a strong driver of carbon availability and transformations at the TAI. However, one of the important unknowns across the TAI is how saturation drives aerobic to anoxic shifts in soils with different characteristics and inundation regimes. We hypothesized that biological and chemical differences in the soils would result in variable oxygen consumption rates across the TAI gradient. To test this hypothesis , we integrated field measurements, laboratory incubations, and model simulations for a mechanistic understanding of oxygen consumption dynamics in coastal soils.

To measure oxygen consumption rates in TAI soils, we conducted a laboratory incubation using surface and subsurface soils from a coastal TAI gradient (upland forest to transitional forest to wetland) in the Western Lake Erie region. The cores were inundated with water and incubated for two weeks. Dissolved oxygen concentration was measured continuously over the 2-week incubation period using an oxygen-sensitive optode spray.

As expected, wetland soils turned anoxic the fastest, in under 10 hours, whereas upland soils turned anoxic in 18 hours. Subsurface soils did not turn anoxic even after two weeks of saturation in the lab, and the oxygen consumption patterns suggest carbon and/or nutrient limitation in the subsurface soils. These results are consistent with in-situ redox/oxygen measurements in the field, where wetland soils exhibited highest rates of oxygen consumption along the coastal transect. These trends also closely followed AquaMEND simulations capturing 0D dynamics in these systems. Sensitivity analysis indicated that microbial activity was a strong driver of oxygen consumption in these soils, with the availability of dissolved carbon fueling microbial metabolism as the key limiting factor of oxygen consumption.

This research is part of the COMPASS-FME (Coastal Observations, Mechanisms, and Predictions Across Systems and Scales – Field, Measurements, and Experiments) project and demonstrates a strong connection between lab, field and modeling. These measurements of oxygen consumption rates provide key context for our understanding of coupled hydrological and biogeochemical processes and contribute to an enhanced understanding of redox controls on carbon and nutrient cycling across the coastal TAI.