Nitrogen Sinks or Sources? Denitrification and Nitrogen Removal Potential in Riparian Legacy Sediment Terraces Affected by Milldams

Inamdar, Shreeram; Peipoch, Marc; Peck, Erin K.; Gold, Arthur J.; Addy, Kelly

doi:10.1029/2022jg007004

Cited by 6 publications

(33 citation statements)

References 63 publications

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“…Upslope wells (W2 and W3) at both locations were shallower (1–1.5 m) and were augered to refusal. Soil/sediment samples collected during augering and analyzed using standard hydrometer analysis (Ashworth et al., 2001) indicated that at Chiques Creek, the average % sand, silt, and clay contents were 16%, 48%, and 35% ( n = 24), respectively, while at Christina River the corresponding values were 11%, 58%, 33% ( n = 12), respectively (Peck et al., 2022). The average soil bulk density across the sites was 1.12 ± 0.14 g cm −3 .…”

Section: Methodsmentioning

confidence: 99%

“…In US Piedmont watersheds, legacy sediment terraces are typically composed of fine‐grained (silts and clay) sediments with buried organic horizons (Lutgen et al., 2020; Mattern et al., 2020; Merritts et al., 2011; Walter & Merritts, 2008; Wegmann et al., 2012). Where milldams exist, stream and groundwater levels upstream of the dams are high and close to the soil surface resulting in persistent wet and reducing conditions in riparian soils (Merritts et al., 2011; Peck et al., 2022; Sherman et al., 2022). In contrast, where milldams have been breached or removed, streams are incised through legacy sediments, resulting in drained and oxic riparian terraces/soils that may be “perched” and hydrologically disconnected from the stream waters (Inamdar et al., 2021; Merritts et al., 2011).…”

Section: Introductionmentioning

confidence: 99%

“…In contrast, where milldams have been breached or removed, streams are incised through legacy sediments, resulting in drained and oxic riparian terraces/soils that may be “perched” and hydrologically disconnected from the stream waters (Inamdar et al., 2021; Merritts et al., 2011). While considerable attention has been paid to how milldams have affected stream geomorphology and fluvial erosion and transport (Cashman et al., 2018; Donovan et al., 2015; Miller et al., 2019), little research has focused on how milldams and associated hydrologic and biogeochemical conditions have altered riparian zone N processes and functions (Inamdar et al., 2021; Lewis et al., 2021; Peck et al., 2022).…”

Section: Introductionmentioning

confidence: 99%

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Saturated, Suffocated, and Salty: Human Legacies Produce Hot Spots of Nitrogen in Riparian Zones

et al. 2022

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The compounding effects of anthropogenic legacies for environmental pollution are significant, but not well understood. Here, we show that centennial‐scale legacies of milldams and decadal‐scale legacies of road salt salinization interact in unexpected ways to produce hot spots of nitrogen (N) in riparian zones. Riparian groundwater and stream water concentrations upstream of two mid‐Atlantic (Pennsylvania and Delaware) milldams, 2.4 and 4 m tall, were sampled over a 2 year period. Clay and silt‐rich legacy sediments with low hydraulic conductivity, stagnant and poorly mixed hydrologic conditions, and persistent hypoxia in riparian sediments upstream of milldams produced a unique biogeochemical gradient with nitrate removal via denitrification at the upland riparian edge and ammonium‐N accumulation in near‐stream sediments and groundwaters. Riparian groundwater ammonium‐N concentrations upstream of the milldams ranged from 0.006 to 30.6 mgN L−1 while soil‐bound values were 0.11–456 mg kg−1. We attribute the elevated ammonium concentrations to ammonification with suppression of nitrification and/or dissimilatory nitrate reduction to ammonium (DNRA). Sodium inputs to riparian groundwater (25–1,504 mg L−1) from road salts may further enhance DNRA and ammonium production and displace sorbed soil ammonium‐N into groundwaters. This study suggests that legacies of milldams and road salts may undercut the N buffering capacity of riparian zones and need to be considered in riparian buffer assessments, watershed management plans, and dam removal decisions. Given the widespread existence of dams and other barriers and the ubiquitous use of road salt, the potential for this synergistic N pollution is significant.

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Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Saturated, Suffocated, and Salty: Human Legacies Produce Hot Spots of Nitrogen in Riparian Zones

et al. 2022

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“…Unamended and amended DEA rates were compared pre-and post-incubation by paired t tests (α = 0.5). Ranges of %C, %N, C:N, nitrate-N, DEA, nitrification, mineralization, and nosZ for pre-incubation buried historic soils were compared to previously published values for ancient subsurface C-rich horizons (Hill & Cardaci 2004;Gurwick et al 2008b;Bernal et al 2016) and legacy sediments (Lutgen et al 2020;Lewis et al 2021;Kan et al 2023;Peck et al 2022). Correlation coefficient matrixes (α = 0.05) were calculated for historic wetland soils pre-and post-incubation to assess relationships between soil characteristics.…”

Section: Discussionmentioning

confidence: 99%

Back from the past? Assessment of nitrogen removal ability of buried historic wetland soils before and after a 1‐year incubation on a restored floodplain

Peck,

Inamdar,

Kan

et al. 2023

Restoration Ecology

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Stream, floodplain, and wetland restorations enhance water quality and ecological function; however, soil health is prioritized infrequently in restoration planning and monitoring. Buried, historic, hydric soils—common across U.S. mid‐Atlantic valley bottoms beneath legacy sediments—are not included in most floodplain restoration designs, though they may retain favorable biogeochemical characteristics and host legacy microbial communities that could support ecosystem recovery if exhumed and preserved. To assess the efficacy of including historic hydric soils in floodplain restoration for nitrogen (N) removal, we characterized pre‐Euro‐American settlement wetland soils buried below legacy sediments and now exposed along incised streambanks across the mid‐Atlantic. We compared carbon (C) and N contents; C:N ratios; nitrate‐N and ammonium‐N concentrations; denitrification rates; functional genes for denitrification (nosZ) and nitrification (amoA for ammonia oxidizing archaea [AoA] + ammonia oxidizing bacteria [AoB]); and phospholipid fatty acid biomasses of historic wetland soils with contemporary wetland soils before and after an 1‐year incubation in a recently restored floodplain. Compared to modern wetland soils, historic hydric soils buried by legacy sediment are less nutrient‐rich, have fewer functional genes for and lower rates of denitrification, and possess significantly less microbial biomass. Following the 1‐year incubation, many of these concentrations, rates, and gene counts increased in historic soils, though not substantially. Ultimately, our results suggest that while inclusion of historic, hydric soils and their legacy microbiomes is valuable for N‐removal in floodplain restoration, the recovery of historic, hydric soils is predictably slow, and attainment of restoration goals, such as increased denitrification, may require multiple years.

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“…Mean annual air temperature is 15.5 and 12.2°C for Roller and Cooch sites, respectively, while mean annual precipitation is 104 and 114 cm (NOAA, 2021). The sediments upstream of the dam at both riparian sites were predominantly silt and clay (56%–100%; Peck et al., 2022) with thickness of the riparian sediments varying between 1 and 4 m depending on the height of the dam. Organic matter in the upstream riparian sediments varied between 0.7% and 9.8% (Peck et al., 2023).…”

Section: Methodsmentioning

confidence: 99%

Riparian Groundwater Nitrogen (N) Isotopes Reveal Human Imprints of Dams and Road Salt Salinization

Inamdar,

Peipoch,

Sena

et al. 2024

Geophysical Research Letters

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Groundwater nitrate‐N isotopes (δ15N‐) have been used to infer the effects of natural and anthropogenic change on N cycle processes in the environment. Here we report unexpected changes in groundwater δ15N‐ for riparian zones affected by relict milldams and road salt salinization. Contrary to natural, undammed conditions, groundwater δ15N‐ values declined from the upland edge through the riparian zone and were lowest near the stream. Groundwater δ15N‐ values increased for low electron donor (dissolved organic carbon) to acceptor ratios but decreased beyond a change point in ratios. Groundwater δ15N‐ values were particularly low for the riparian milldam site subjected to road‐salt salinization. We attributed these N isotopic trends to suppression of denitrification, occurrence of dissimilatory nitrate reduction to ammonium (DNRA), and/or effects of road salt salinization. Groundwater δ15N‐ can provide valuable insights into process mechanisms and can serve as “imprints” of anthropogenic activities and legacies.

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Nitrogen Sinks or Sources? Denitrification and Nitrogen Removal Potential in Riparian Legacy Sediment Terraces Affected by Milldams

Cited by 6 publications

References 63 publications

Saturated, Suffocated, and Salty: Human Legacies Produce Hot Spots of Nitrogen in Riparian Zones

Saturated, Suffocated, and Salty: Human Legacies Produce Hot Spots of Nitrogen in Riparian Zones

Back from the past? Assessment of nitrogen removal ability of buried historic wetland soils before and after a 1‐year incubation on a restored floodplain

Riparian Groundwater Nitrogen (N) Isotopes Reveal Human Imprints of Dams and Road Salt Salinization

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