The varying role of water column nutrient uptake along river continua in contrasting landscapes

Reisinger, Alexander J.; Tank, Jennifer L.; Hall, Robert O.; Baker, Michelle A.

doi:10.1007/s10533-015-0118-z

Cited by 42 publications

(33 citation statements)

References 60 publications

(60 reference statements)

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“…1), and we parameterized the transformation efficiency of dissolved NO3 to gaseous N 2 O in terms of two Damköhler numbers (Materials and Methods and SI Text). In headwater streams that are typically small and shallow, microbially mediated denitrification occurs mainly within the benthic-hyporheic zone (35). Headwater stream hydrodynamics at and within the streambed (hyporheic flows) is the main factor controlling the flux of dissolved nutrients to the microbial assemblages that control biogeochemical transformations (Fig.…”

Section: Resultsmentioning

confidence: 99%

Role of surface and subsurface processes in scaling N ₂ O emissions along riverine networks

Marzadri

Dee

Tonina

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

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118

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Riverine environments, such as streams and rivers, have been reported as sources of the potent greenhouse gas nitrous oxide (N 2 O) to the atmosphere mainly via microbially mediated denitrification. Our limited understanding of the relative roles of the nearsurface streambed sediment (hyporheic zone), benthic, and water column zones in controlling N 2 O production precludes predictions of N 2 O emissions along riverine networks. Here, we analyze N 2 O emissions from streams and rivers worldwide of different sizes, morphology, land cover, biomes, and climatic conditions. We show that the primary source of N 2 O emissions varies with stream and river size and shifts from the hyporheic-benthic zone in headwater streams to the benthic-water column zone in rivers. This analysis reveals that N 2 O production is bounded between two N 2 O emission potentials: the upper N 2 O emission potential results from production within the benthic-hyporheic zone, and the lower N 2 O emission potential reflects the production within the benthic-water column zone. By understanding the scaling nature of N 2 O production along riverine networks, our framework facilitates predictions of riverine N 2 O emissions globally using widely accessible chemical and hydromorphological datasets and thus, quantifies the effect of human activity and natural processes on N 2 O production.riverine networks | greenhouse gas | N 2 O | emission scaling law | N 2 O emission potentials R iverine environments, such as streams and rivers, have been identified as hotspots of microbially mediated denitrification, where nitrate (NO3) is converted to both nitrogen gas (N2), which constitutes the majority of Earth's atmosphere, and nitrous oxide (N 2 O), the potent greenhouse gas responsible for stratospheric ozone destruction (1). Denitrification has been observed to occur within both bulk-oxic (2) and anoxic environments (3-5) of both benthic (i.e., sediment-water interface) and hyporheic (i.e., near-subsurface) zones of streams and rivers. Whereas the benthic zone is the ecological region of the streambed, where both aquatic fauna and flora can be found (4, 6), the latter is the band of streambed material mainly saturated of stream water (7). The benthic zone is at the interface between water and sediment and the upper boundary of the fluvial hyporheic zone. Current understanding suggests that riverine N 2 O production occurs predominantly in these two environments, reflecting two distinct biogeochemical transformation zones (6), irrespective of system size from headwater streams to rivers. The produced N 2 O is then exchanged with the atmosphere through diffusive evasion, with dynamics that depend on N 2 O concentrations of the water in relation to atmospheric equilibrium (6, 8), stream hydrodynamics, temperature, and the air-water gas exchange rate (9). Although it is understood that microbially mediated denitrification is responsible for a large proportion of N 2 O production in riverine networks (6, 10, 11), quantifying these emissions is challenging becau...

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Section: Resultsmentioning

confidence: 99%

Role of surface and subsurface processes in scaling N ₂ O emissions along riverine networks

Marzadri

Dee

Tonina

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

Self Cite

118

147

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“…) and/or in the water column (Reisinger et al. ). These two uncertainties are deserving of further study.…”

Section: Discussionmentioning

confidence: 99%

“…4), although U assim-WAT was generally higher than U assim-PUC . Given that we already accounted for NH 4 + -N uptake due to dissimilatory processes (e.g., nitrification), this mismatch was likely due to inaccuracies in the upscaling of assimilatory uptake, as well as the omission of the probable role of microbial uptake in the hyporheic zone (Hall et al 2009a) and/or in the water column (Reisinger et al 2015). These two uncertainties are deserving of further study.…”

Section: Patterns Of Compartmental Nh 4 + -N Uptakementioning

confidence: 99%

Partitioning assimilatory nitrogen uptake in streams: an analysis of stable isotope tracer additions across continents

Tank

Martı́

Riis

et al. 2017

Ecological Monographs

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Abstract. Headwater streams remove, transform, and store inorganic nitrogen (N) delivered from surrounding watersheds, but excessive N inputs from human activity can saturate removal capacity. Most research has focused on quantifying N removal from the water column over short periods and in individual reaches, and these ecosystem-scale measurements suggest that assimilatory N uptake accounts for most N removal. However, cross-system comparisons addressing the relative role of particular biota responsible for incorporating inorganic N into biomass are lacking. Here we assess the importance of different primary uptake compartments on reach-scale ammonium (NH 4 + -N) uptake and storage across a wide range of streams varying in abundance of biota and local environmental factors. We analyzed data from 17 15 N-NH 4 + tracer addition experiments globally, and found that assimilatory N uptake by autotrophic compartments (i.e., epilithic biofilm, filamentous algae, bryophytes/macrophytes) was higher but more variable than for heterotrophic microorganisms colonizing detrital organic matter (i.e., leaves, small wood, and fine particles). Autotrophic compartments played a disproportionate role in N uptake relative to their biomass, although uptake rates were similar when we rescaled heterotrophic assimilatory N uptake associated only with live microbial biomass. Assimilatory NH 4 + -N uptake, either estimated as removal from the water column or from the sum uptake of all individual compartments, was four times higher in open-than in closed-canopy streams. Using Bayesian Model Averaging, we found that canopy cover and gross primary production (GPP) controlled autotrophic assimilatory N uptake while ecosystem respiration (ER) was more important for the heterotrophic contribution. The ratio of autotrophic to heterotrophic N storage was positively correlated with metabolism (GPP: ER), which was also higher in open-than in closed-canopy streams. Our analysis shows riparian canopy cover influences the relative abundance of different biotic uptake compartments and thus GPP:ER. As such, the simple categorical variable of canopy cover explained differences in assimilatory N uptake among streams at the reach scale, as well as the relative roles of autotrophs and heterotrophs in N storage. Finally, this synthesis links cumulative N uptake by stream biota to reach-scale N demand and provides a mechanistic and predictive framework for estimating and modeling N cycling in other streams.

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“…Reduced contact between sediment and the water column is often assumed to reduce N retention in rivers [e.g . , Alexander et al ., ] despite nutrient uptake also occurring in the water column of streams and rivers [ Reisinger et al ., ], and assimilation or dissimilatory reduction of N by water column biota in larger rivers may offset any decrease in N removal by the sediment. If water column processes offset reductions in benthic N removal, riverine N removal may be higher than previously considered in watershed models [ Alexander et al ., ; Wollheim et al ., ].…”

Section: Introductionmentioning

confidence: 99%

Sediment, water column, and open‐channel denitrification in rivers measured using membrane‐inlet mass spectrometry

et al. 2016

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Riverine biogeochemical processes are understudied relative to headwaters, and reach-scale processes in rivers reflect both the water column and sediment. Denitrification in streams is difficult to measure, and is often assumed to occur only in sediment, but the water column is potentially important in rivers. Dissolved nitrogen (N) gas flux (as dinitrogen (N 2 )) and open-channel N 2 exchange methods avoid many of the artificial conditions and expenses of common denitrification methods like acetylene block and 15 N-tracer techniques. We used membrane-inlet mass spectrometry and microcosm incubations to quantify net N 2 and oxygen flux from the sediment and water column of five Midwestern rivers spanning a land use gradient. Sediment and water column denitrification ranged from below detection to 1.8 mg N m À2 h À1 and from below detection to 4.9 mg N m À2 h À1 , respectively. Water column activity was variable across rivers, accounting for 0-85% of combined microcosm denitrification and 39-85% of combined microcosm respiration. Finally, we estimated reach-scale denitrification at one Midwestern river using a diel, open-channel N 2 exchange approach based on reach-scale metabolism methods, providing an integrative estimate of riverine denitrification. Reach-scale denitrification was 8.8 mg N m À2 h À1 (95% credible interval: 7.8-9.7 mg N m À2 h À1 ), higher than combined sediment and water column microcosm estimates from the same river (4.3 mg N m À2 h À1 ) and other estimates of reach-scale denitrification from streams. Our denitrification estimates, which span habitats and spatial scales, suggest that rivers can remove N via denitrification at equivalent or higher rates than headwater streams.

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The varying role of water column nutrient uptake along river continua in contrasting landscapes

Cited by 42 publications

References 60 publications

Role of surface and subsurface processes in scaling N ₂ O emissions along riverine networks

Role of surface and subsurface processes in scaling N ₂ O emissions along riverine networks

Partitioning assimilatory nitrogen uptake in streams: an analysis of stable isotope tracer additions across continents

Sediment, water column, and open‐channel denitrification in rivers measured using membrane‐inlet mass spectrometry

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The varying role of water column nutrient uptake along river continua in contrasting landscapes

Cited by 42 publications

References 60 publications

Role of surface and subsurface processes in scaling N 2 O emissions along riverine networks

Role of surface and subsurface processes in scaling N 2 O emissions along riverine networks

Partitioning assimilatory nitrogen uptake in streams: an analysis of stable isotope tracer additions across continents

Sediment, water column, and open‐channel denitrification in rivers measured using membrane‐inlet mass spectrometry

Contact Info

Product

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Role of surface and subsurface processes in scaling N ₂ O emissions along riverine networks

Role of surface and subsurface processes in scaling N ₂ O emissions along riverine networks