Variation of organic matter quantity and quality in streams at Critical Zone Observatory watersheds

Miller, Matthew P.; Boyer, E. W.; McKnight, Diane M.; Brown, Michael G.; Gabor, R. S.; Hunsaker, Carolyn T.; Iavorivska, Lidiia; Inamdar, Shreeram; Johnson, Dale W.; Kaplan, Louis; Lin, Henry; McDowell, William H.; Perdrial, Julia

doi:10.1002/2016wr018970

Cited by 23 publications

(13 citation statements)

References 85 publications

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“…We estimated (Text S8; Binkley et al, ) that stream water DON losses were the same as NO 3 − ‐N losses, that is, 0.08 kg N ha −1 yr −1 , and NH 4 + ‐N losses were 0.02 kg N ha −1 yr −1 . Thus, the export of TDN in stream water was estimated as 0.18 kg N ha −1 yr −1 , which was similar to the 2009 average reported in Miller et al (). The gaseous loss of N 2 O‐N from the watershed was measured as 0.73 kg N ha −1 yr −1 , while loss as NH 3 ‐N was not detectable (measured by PAS, data not shown).…”

Section: Resultssupporting

confidence: 85%

Nitrogen Budget and Topographic Controls on Nitrous Oxide in a Shale‐Based Watershed

Weitzman

Kaye

2018

JGR Biogeosciences

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The high spatial and temporal variabilities of nitrous oxide (N2O) emissions from the soil surface have made it difficult to predict flux patterns at the ecosystem scale, leading to imbalances in nitrogen (N) budgets at all scales. Our research sought to quantify topographic controls on the sources or sinks of N2O in the soil profile to improve our ability to predict soil‐atmosphere N2O fluxes and their contribution to watershed N budgets. We monitored surface‐to‐atmosphere N2O fluxes for 2 years in the Susquehanna Shale Hills Critical Zone Observatory in central Pennsylvania. Topographically convergent flow path locations had significantly higher surface N2O flux rates than nonconvergent flow path locations in the summer, but not other seasons. Overall, N2O fluxes were a large percentage (~19%) of total ecosystem N losses, and nearly twice as large as stream N export. Surface N2O fluxes were better correlated with concentrations of O2, N2O, and NO3− in shallow soil layers (<30 cm) than deeper soils. Following decades of anthropogenic atmospheric deposition and additional N from shale weathering, watershed N inputs (~8 kgN ha−1 yr−1) are greater than outputs (~3.7 kgN ha−1 yr−1). Our research revealed patterns of N cycling that are distinct from many other watersheds that have been extensively studied to understand N saturation; despite showing no other symptoms of N saturation, the watershed had high upland N2O losses, especially in convergent flow paths during summer. High upland N gas losses may be a mechanism that maintains N limitation to biota in the Shale Hills catchment.

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Section: Resultssupporting

confidence: 85%

Nitrogen Budget and Topographic Controls on Nitrous Oxide in a Shale‐Based Watershed

Weitzman

Kaye

2018

JGR Biogeosciences

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“…Many other multiyear measurements common to all CZOs enable hypothesis testing. For example, characterization of dissolved organic matter (DOM) measured with similar methodology across five CZOs revealed a strong role for CZ structure in setting the origin, composition, and fate of DOM in streams (Miller et al, 2016). In another example, a coordinated effort emerged to measure and understand the relationships among solute concentrations and water discharge in streams (e.g., Kirchner, 2003;Godsey et al, 2009).…”

Section: The Nine Emergent Roles Of Czosmentioning

confidence: 99%

Designing a network of critical zone observatories to explore the living skin of the terrestrial Earth

et al. 2017

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Abstract. The critical zone (CZ), the dynamic living skin of the Earth, extends from the top of the vegetative canopy through the soil and down to fresh bedrock and the bottom of the groundwater. All humans live in and depend on the CZ. This zone has three co-evolving surfaces: the top of the vegetative canopy, the ground surface, and a deep subsurface below which Earth's materials are unweathered. The network of nine CZ observatories supported by the US National Science Foundation has made advances in three broad areas of CZ research relating to the co-evolving surfaces. First, monitoring has revealed how natural and anthropogenic inputs at the vegetation canopy and ground surface cause subsurface responses in water, regolith structure, minerals, and biotic activity to considerable depths. This response, in turn, impacts aboveground biota and climate. Second, drilling and geophysical imaging now reveal how the deep subsurface of the CZ varies across landscapes, which in turn influences aboveground ecosystems. Third, several new mechanistic models now provide quantitative predictions of the spatial structure of the subsurface of the CZ.Many countries fund critical zone observatories (CZOs) to measure the fluxes of solutes, water, energy, gases, and sediments in the CZ and some relate these observations to the histories of those fluxes recorded in landforms, biota, soils, sediments, and rocks. Each US observatory has succeeded in (i) synthesizing research across disciplines into convergent approaches; (ii) providing long-term measurements to compare across sites; (iii) testing and developing models; (iv) collecting and measuring baseline data for comparison to catastrophic events; (v) stimulating new process-based hypotheses; (vi) catalyzing development of new techniques and instrumentation; (vii) informing the public about the CZ; (viii) mentoring students and teaching about emerging multidisciplinary CZ science; and (ix) discovering new insights about the CZ. Many of these activities can only be accomplished with observatories. Here we review the CZO enterprise in the United States and identify how such observatoriesPublished by Copernicus Publications on behalf of the European Geosciences Union. 842 S. L. Brantley et al.: Designing a network of critical zone observatories could operate in the future as a network designed to generate critical scientific insights. Specifically, we recognize the need for the network to study network-level questions, expand the environments under investigation, accommodate both hypothesis testing and monitoring, and involve more stakeholders. We propose a driving question for future CZ science and a "hubs-and-campaigns" model to address that question and target the CZ as one unit. Only with such integrative efforts will we learn to steward the life-sustaining critical zone now and into the future.

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“…In this context, sediment-water interactions within floodplains can attenuate or accentuate nutrient and pollutant loads in groundwater (Naiman and Décamps, 1997;Tockner and Stanford, 2002;Pinay et al, 1991;Tabacchi et al, 1998). This behavior is particularly important within the Upper Colorado River Basin (UCRB), where groundwater discharge contributes the majority of total net surface outflow (Miller et al, 2016). In combination with subsurface or hyporheic exchange, groundwater discharge regulates surface water quality (Findlay, 1995).…”

Section: Introductionmentioning

confidence: 99%

Understanding controls on redox processes in floodplain sediments of the Upper Colorado River Basin

Noël

Boye

Kukkadapu

et al. 2017

Science of The Total Environment

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Floodplains, heavily used for water supplies, housing, agriculture, mining, and industry, are important repositories of organic carbon, nutrients, and metal contaminants. The accumulation and release of these species is often mediated by redox processes. Understanding the physicochemical, hydrological, and biogeochemical controls on the distribution and variability of sediment redox conditions is therefore critical to developing conceptual and numerical models of contaminant transport within floodplains. The Upper Colorado River Basin (UCRB) is impacted by former uranium and vanadium ore processing, resulting in contamination by V, Cr, Mn, As, Se, Mo and U. Previous authors have suggested that sediment redox activity occurring within organic carbon-enriched bodies located below the groundwater level may be regionally important to the maintenance and release of contaminant inventories, particularly uranium. To help assess this hypothesis, vertical distributions of Fe and S redox states and sulfide mineralogy were assessed in sediment cores from three floodplain sites spanning a 250km transect of the central UCRB. The results of this study support the hypothesis that organic-enriched reduced sediments are important zones of biogeochemical activity within UCRB floodplains. We found that the presence of organic carbon, together with pore saturation, are the key requirements for maintaining reducing conditions, which were dominated by sulfate-reduction products. Sediment texture was found to be of secondary importance and to moderate the response of the system to external forcing, such as oxidant diffusion. Consequently, fine-grain sediments are relatively resistant to oxidation in comparison to coarser-grained sediments. Exposure to oxidants consumes precipitated sulfides, with a disproportionate loss of mackinawite (FeS) as compared to the more stable pyrite. The accompanying loss of redox buffering capacity creates the potential for release of sequestered radionuclides and metals. Because of their redox reactivity and stores of metals, C, and N, organic-enriched sediments are likely to be important to nutrient and contaminant mobility within UCRB floodplain aquifers.

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Variation of organic matter quantity and quality in streams at Critical Zone Observatory watersheds

Cited by 23 publications

References 85 publications

Nitrogen Budget and Topographic Controls on Nitrous Oxide in a Shale‐Based Watershed

Nitrogen Budget and Topographic Controls on Nitrous Oxide in a Shale‐Based Watershed

Designing a network of critical zone observatories to explore the living skin of the terrestrial Earth

Understanding controls on redox processes in floodplain sediments of the Upper Colorado River Basin

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