Assimilatory uptake rather than nitrification and denitrification determines nitrogen removal patterns in streams of varying land use

Arango, Clay P.; Tank, Jennifer L.; Johnson, Laura T.; Hamilton, Stephen K.

doi:10.4319/lo.2008.53.6.2558

Cited by 71 publications

(51 citation statements)

References 55 publications

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“…denitrification and DNRA) such as oxygen conditions (water column DO concentrations) and organic carbon (benthic organic matter content) (Tiedje 1988), although U did increase in response to lower DO concentrations. This suggests that much of the demand for NO 3 ( in the Taupo streams during summer was probably assimilatory and is consistent with other studies showing that assimilatory processes tend to dominate instream NO 3 ( uptake (Mulholland et al 2004(Mulholland et al , 2008Arango et al 2008).…”

Section: Discussionsupporting

confidence: 78%

Land use influences stream nitrate uptake in the Lake Taupo catchment

Matheson¹,

Tank²,

Costley³

2011

New Zealand Journal of Marine and Freshwater Research

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We quantified nitrate (NO 3 ( ) uptake during summer for 11 streams draining into oligotrophic Lake Taupo. Nitrate uptake lengths (S w ) ranged from 258 to 12035 m, uptake velocities (V f ) ranged from 0.2 to 6.8 m/day and removal efficiencies (P r ) ranged from 1% to 59%. Nitrate uptake velocities and areal uptake rates were, respectively, 9-and 26-fold higher for streams in pasture and pine forest land use than in native vegetation. However, average NO 3 ( export from these streams was also 8-fold higher. Our results suggested that NO 3 ( uptake velocity (V f ) was highest in streams with higher dissolved phosphorus (P) concentrations and flow velocities, and smaller benthic substrate size, which were characteristic of catchments dominated by pasture and pine forest land use. Uptake (as removal efficiency, P r ) accounted for an average 16% of the stream NO 3 ( export to Lake Taupo. However, since most uptake is assimilatory, removal from the water column is likely to only represent temporary sequestration of NO 3( and a conversion of inorganic to organic and/or particulate N.

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Section: Discussionsupporting

confidence: 78%

Land use influences stream nitrate uptake in the Lake Taupo catchment

Matheson¹,

Tank²,

Costley³

2011

New Zealand Journal of Marine and Freshwater Research

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“…Others have found that biotic assimilation represented a substantial portion of the nitrate uptake in various aquatic systems (Webster et al 2003;Mulholland et al 2004;Arango et al 2008). Rates of biotic N uptake, standing stock, and turnover were not quantified in Second Lake.…”

Section: Discussionmentioning

confidence: 99%

Nitrogen retention in a floodplain backwater of the upper Mississippi River (USA)

James

2009

Aquat. Sci.

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Backwaters connected to large rivers retain nitrate and may play an important role in reducing downstream loading to coastal marine environments. A summer nitrogen (N) inflow-outflow budget was examined for a flow-regulated backwater of the upper Mississippi River in conjunction with laboratory estimates of sediment ammonium and nitrate fluxes, organic N mineralization, nitrification, and denitrification to provide further insight into N retention processes. External N loading was overwhelmingly dominated by nitrate and 54% of the input was retained (137 mg m -2 day -1 ). Ammonium and dissolved organic N were exported from the backwater (14 and 9 mg m -2 day -1 , respectively). Nitrate influx to sediment increased as a function of increasing initial nitrate concentration in the overlying water. Rates were greater under anoxic versus oxic conditions. Ammonium effluxes from sediment were 26.7 and 50.6 mg m -2 day -1 under oxic and anoxic conditions, respectively. Since anoxia inhibited nitrification, the difference between ammonium anoxic-oxic fluxes approximated a nitrification rate of 29.1 mg m -2 day -1 . Organic N mineralization was 64 mg m -2 day -1 . Denitrification, estimated from regression relationships between oxic nitrate influx versus initial nitrate concentration and a summer lakewide mean nitrate concentration of 1.27 mg l -1 , was 94 mg m -2 day -1 . Denitrification was equivalent to only 57% of the retained nitrate, suggesting that another portion was assimilated by biota. The high sediment organic N mineralization and ammonium efflux rate coupled with the occurrence of ammonium export from the system suggested a possible link between biotic assimilation of nitrate, mineralization, and export.

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“…The ability to measure both ecosystem metabolism and nutrient dynamics at comparable temporal scales for whole stream ecosystems has provided elegant demonstrations of the direct coupling between nitrogen cycling and metabolism (e.g., Hall and Tank 2003, Hall et al 2009). Streams have also provided more nuanced understanding of the indirect effects of metabolism on N assimilation and denitrification (Hoellein et al 2007, Arango et al 2008, Mulholland et al 2008, as well as the coupling of N and P cycles (Cross et al 2005, Schade et al 2011.…”

Section: Introductionmentioning

confidence: 99%

Diel phosphorus variation and the stoichiometry of ecosystem metabolism in a large spring‐fed river

Cohen

Kurz

Heffernan

et al. 2013

Ecological Monographs

107

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Abstract. Elemental cycles are coupled directly and indirectly to ecosystem metabolism at multiple time scales. Understanding coupling in lotic ecosystems has recently advanced through simultaneous high-frequency measurements of multiple solutes. Using hourly in situ measurements of soluble reactive phosphorus (SRP), specific conductance (SpC), and dissolved oxygen (DO), we estimated phosphorus (P) retention pathways and dynamics in a large (discharge, Q ' 7.5 m 3 /s) spring-fed river (Ichetucknee River, Florida, USA). Across eight multi-day deployments, highly regular diel SRP variation of 3-9 lg P/L (mean ;50 lg P/ L) was strongly correlated with DO variation, suggesting photosynthetic control directly via assimilation, and/or indirectly via geochemical reactions. Consistent afternoon SRP maxima and midnight minima suggest peak removal lags gross primary production (GPP) by ;8 hours. Two overlapping processes were evident, one dominant with maximum removal near midnight, the other smaller with maximum removal near midday. Hourly [Ca] measurements during three 24-hour deployments showed consistent afternoon minima, suggesting that calcite precipitates as GPP increases pH and mineral saturation state. Resulting P coprecipitation was modeled using SpC as a [Ca] proxy, yielding a diel P signal adjusted for the primary geochemical retention pathway. P assimilation, the dominant diel signal, was computed by interpolating between daily concentration maxima, both with and without geochemical adjustment, and converting concentration deficits to fluxes using discharge and benthic area. Adjusting for calcite co-precipitation yielded assimilation rates (13.7 6 5.8 mg PÁm À2 Ád À1) strongly correlated with GPP, accounting for 72% 6 9% of gross removal, and ecosystem C:P stoichiometry (466 [6 12]:1) consistent with dominant vascular autotrophs (478 [6 24]:1). Without adjusting for co-precipitation, covariance with GPP was weaker, and C:P implausibly high. Consistent downstream P accumulation, likely from P-rich porewater seepage, varied across deployments (3-22% of total flux) and co-varied with discharge and respiration. Asynchronous N and P assimilation may arise from differential timing of protein and ribosome production, with the latter requiring maximal carbohydrate stores and minimal photolytic interference. This study demonstrates direct and indirect coupling of biological, hydrological, and geochemical processes and the utility of high-resolution time series of multiple solutes for understanding these linkages.

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Assimilatory uptake rather than nitrification and denitrification determines nitrogen removal patterns in streams of varying land use

Cited by 71 publications

References 55 publications

Land use influences stream nitrate uptake in the Lake Taupo catchment

Land use influences stream nitrate uptake in the Lake Taupo catchment

Nitrogen retention in a floodplain backwater of the upper Mississippi River (USA)

Diel phosphorus variation and the stoichiometry of ecosystem metabolism in a large spring‐fed river

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