4 research outputs found
Rethinking Aerobic Respiration in the Hyporheic Zone under Variation in Carbon and Nitrogen Stoichiometry
Hyporheic zones (HZs)zones of groundwater–surface
water mixingare 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
Rethinking Aerobic Respiration in the Hyporheic Zone under Variation in Carbon and Nitrogen Stoichiometry
Hyporheic zones (HZs)zones of groundwater–surface
water mixingare 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
Rethinking Aerobic Respiration in the Hyporheic Zone under Variation in Carbon and Nitrogen Stoichiometry
Hyporheic zones (HZs)zones of groundwater–surface
water mixingare 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
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Water Table Dynamics and Biogeochemical Cycling in a Shallow, Variably-Saturated Floodplain
Three-dimensional variably saturated
flow and multicomponent biogeochemical
reactive transport modeling, based on published and newly generated
data, is used to better understand the interplay of hydrology, geochemistry,
and biology controlling the cycling of carbon, nitrogen, oxygen, iron,
sulfur, and uranium in a shallow floodplain. In this system, aerobic
respiration generally maintains anoxic groundwater below an oxic vadose
zone until seasonal snowmelt-driven water table peaking transports
dissolved oxygen (DO) and nitrate from the vadose zone into the alluvial
aquifer. The response to this perturbation is localized due to distinct
physico-biogeochemical environments and relatively long time scales
for transport through the floodplain aquifer and vadose zone. Naturally
reduced zones (NRZs) containing sediments higher in organic matter,
iron sulfides, and non-crystalline UÂ(IV) rapidly consume DO and nitrate
to maintain anoxic conditions, yielding FeÂ(II) from FeS oxidative
dissolution, nitrite from denitrification, and UÂ(VI) from nitrite-promoted
UÂ(IV) oxidation. Redox cycling is a key factor for sustaining the
observed aquifer behaviors despite continuous oxygen influx and the
annual hydrologically induced oxidation event. Depth-dependent activity
of fermenters, aerobes, nitrate reducers, sulfate reducers, and chemolithoautotrophs
(e.g., oxidizing FeÂ(II), S compounds, and ammonium) is linked to the
presence of DO, which has higher concentrations near the water table