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Richard D. Bardgett - One of the best experts on this subject based on the ideXlab platform.

  • The impact of agricultural soil erosion on Biogeochemical Cycling
    Nature Geoscience, 2010
    Co-Authors: John N. Quinton, Gerard Govers, Kristof Van Oost, Richard D. Bardgett
    Abstract:

    Soils are the main terrestrial reservoir of nutrients, such as nitrogen and phosphorus, and of organic carbon. Synthesizing earlier studies, we find that the mobilization and deposition of agricultural soils can significantly alter nutrient and carbon Cycling. Specifically, erosion can result in lateral fluxes of nitrogen and phosphorus that are similar in magnitude to those induced by fertilizer application and crop removal. Furthermore, the translocation and burial of soil reduces decomposition of soil organic carbon, and could lead to long-term carbon storage. The Cycling of carbon, nitrogen and phosphorus are strongly interrelated. For example, erosion-induced burial of soils stabilizes soil nutrient and carbon pools, thereby increasing primary productivity and carbon uptake, and potentially reducing erosion. Our analysis shows soils as dynamic systems in time and space. Soils are the main terrestrial reservoir of nutrients such as nitrogen and phosphorus, and of organic carbon. Data synthesis reveals that soil erosion can result in lateral fluxes of these nutrients at comparable magnitudes to those induced by fertilizer application and crop removal.

  • the impact of agricultural soil erosion on Biogeochemical Cycling
    Nature Geoscience, 2010
    Co-Authors: John N. Quinton, Gerard Govers, Kristof Van Oost, Richard D. Bardgett
    Abstract:

    Soils are the main terrestrial reservoir of nutrients, such as nitrogen and phosphorus, and of organic carbon. Synthesizing earlier studies, we find that the mobilization and deposition of agricultural soils can significantly alter nutrient and carbon Cycling. Specifically, erosion can result in lateral fluxes of nitrogen and phosphorus that are similar in magnitude to those induced by fertilizer application and crop removal. Furthermore, the translocation and burial of soil reduces decomposition of soil organic carbon, and could lead to long-term carbon storage. The Cycling of carbon, nitrogen and phosphorus are strongly interrelated. For example, erosion-induced burial of soils stabilizes soil nutrient and carbon pools, thereby increasing primary productivity and carbon uptake, and potentially reducing erosion. Our analysis shows soils as dynamic systems in time and space.

Lawrence W. Harding - One of the best experts on this subject based on the ideXlab platform.

  • Two decades of tropical cyclone impacts on North Carolina’s estuarine carbon, nutrient and phytoplankton dynamics: implications for Biogeochemical Cycling and water quality in a stormier world
    Biogeochemistry, 2018
    Co-Authors: Hans W. Paerl, Joseph R. Crosswell, Nathan S. Hall, Karen L. Rossignol, Christopher L. Osburn, Alexandria G. Hounshell, Randolph S. Sloup, Lawrence W. Harding
    Abstract:

    Coastal North Carolina (USA) has experienced 35 tropical cyclones over the past 2 decades; the frequency of these events is expected to continue in the foreseeable future. Individual storms had unique and, at times, significant hydrologic, nutrient-, and carbon (C)-loading impacts on Biogeochemical Cycling and phytoplankton responses in a large estuarine complex, the Pamlico Sound (PS) and Neuse River Estuary (NRE). Major storms caused up to a doubling of annual nitrogen and tripling of phosphorus loading compared to non-storm years; magnitudes of loading depended on storm tracks, forward speed, and precipitation in NRE-PS watersheds. With regard to C Cycling, NRE-PS was a sink for atmospheric CO_2 during dry, storm-free years and a significant source of CO_2 in years with at least one storm, although responses were storm-specific. Hurricane Irene (2011) mobilized large amounts of previously-accumulated terrigenous C in the watershed, mainly as dissolved organic carbon, and extreme winds rapidly released CO_2 to the atmosphere. Historic flooding after Hurricanes Joaquin (2015) and Matthew (2016) provided large inputs of C from the watershed, modifying the annual C balance of NRE-PS and leading to sustained CO_2 efflux for months. Storm type affected Biogeochemical responses as C-enriched floodwaters enhanced air–water CO_2 exchange during ‘wet’ storms, while CO_2 fluxes during ‘windy’ storms were largely supported by previously-accumulated C. Nutrient loading and flushing jointly influenced spatio-temporal patterns of phytoplankton biomass and composition. These findings suggest the importance of incorporating freshwater discharge and C dynamics in nutrient management strategies for coastal ecosystems likely to experience a stormier future.

  • two decades of tropical cyclone impacts on north carolina s estuarine carbon nutrient and phytoplankton dynamics implications for Biogeochemical Cycling and water quality in a stormier world
    Biogeochemistry, 2018
    Co-Authors: Hans W. Paerl, Joseph R. Crosswell, Nathan S. Hall, Karen L. Rossignol, Christopher L. Osburn, Alexandria G. Hounshell, Randolph S. Sloup, Bryce R Van Dam, Lawrence W. Harding
    Abstract:

    Coastal North Carolina (USA) has experienced 35 tropical cyclones over the past 2 decades; the frequency of these events is expected to continue in the foreseeable future. Individual storms had unique and, at times, significant hydrologic, nutrient-, and carbon (C)-loading impacts on Biogeochemical Cycling and phytoplankton responses in a large estuarine complex, the Pamlico Sound (PS) and Neuse River Estuary (NRE). Major storms caused up to a doubling of annual nitrogen and tripling of phosphorus loading compared to non-storm years; magnitudes of loading depended on storm tracks, forward speed, and precipitation in NRE-PS watersheds. With regard to C Cycling, NRE-PS was a sink for atmospheric CO2 during dry, storm-free years and a significant source of CO2 in years with at least one storm, although responses were storm-specific. Hurricane Irene (2011) mobilized large amounts of previously-accumulated terrigenous C in the watershed, mainly as dissolved organic carbon, and extreme winds rapidly released CO2 to the atmosphere. Historic flooding after Hurricanes Joaquin (2015) and Matthew (2016) provided large inputs of C from the watershed, modifying the annual C balance of NRE-PS and leading to sustained CO2 efflux for months. Storm type affected Biogeochemical responses as C-enriched floodwaters enhanced air–water CO2 exchange during ‘wet’ storms, while CO2 fluxes during ‘windy’ storms were largely supported by previously-accumulated C. Nutrient loading and flushing jointly influenced spatio-temporal patterns of phytoplankton biomass and composition. These findings suggest the importance of incorporating freshwater discharge and C dynamics in nutrient management strategies for coastal ecosystems likely to experience a stormier future.

Seth G John - One of the best experts on this subject based on the ideXlab platform.

  • Biogeochemical Cycling of Fe and Fe stable isotopes in the Eastern Tropical South Pacific
    Marine Chemistry, 2017
    Co-Authors: Seth G John, Joshua Helgoe, Phoebe Lam, Tim Devries, Tom Weber, Chris M. Marsay, Emily Townsend, Keith Moore, Alessandro Tagliabue, Claire Till
    Abstract:

    The basin-scale distributions of iron (Fe) and Fe isotopes provide important insights into the Biogeochemical Cycling of this growth-limiting micronutrient in the ocean. Here we present new observations of dissolved Fe concentrations and stable isotope ratios (δ56Fe) from the US GEOTRACES Eastern Pacific Zonal Transect GP16. The western portion of the transect is characterized by low dissolved Fe concentrations with a heavy δ56Fe signature of +0.4 to +0.6‰, similar to the dust-influenced North Atlantic deep waters. This is punctuated by Fe inputs from hydrothermal vents along the East Pacific Rise, with a δ56Fe of -0.3‰. One striking feature of the transect is a large plume of high dissolved Fe and low δ56Fe (0 to -0.5‰) in the east, near the Peru margin. Here, maximum dissolved Fe occurs between 1000 and 3000m and the elevated concentrations persist over 1000km from the margin. The region of markedly lower δ56Fe extends even further, to roughly 4000km offshore. The mid-slope depth at which this plume occurs (1000-3000m) is at odds with current conceptual and numerical models of Fe inputs along continental margins, which predict a shallower and more restricted dissolved Fe maximum (upper-slope; ~100-1000m). Here, we explore four possible explanations for the mid-slope Fe plume: (1) Fe fluxes are actually higher from mid-slope sediments; (2) the mid-slope plume is transported from a remote region (3) mid-slope Fe originates from resuspended sediments in a very persistent form, which remains in the dissolved phase for longer than Fe released from the upper-slope; (4) Fe is supplied from upper-slope sediments, and then transferred to greater depth by reversible scavenging onto sinking particles. Simple modeling is used to show that both input of persistent Fe from mid-slope sediments and reversible scavenging could explain the data. Flux of a more persistent chemical form of Fe from the mid-slope would be consistent with other tracers such as particle composition and228Ra, which suggest that lithogenic sediments are preferentially resuspended at this depth, but may be at odds with the low δ56Fe signature. Reversible scavenging is consistent with both Fe concentrations and δ56Fe. Whatever its provenance, the plume observed near the Peru margin impacts Fe concentrations and δ56Fe throughout the entire eastern South Pacific region, suggesting that the roles of persistent Fe input and reversible scavenging should be appraised in fully coupled iron-carbon cycle models in order to better understand the global Cycling of Fe and δ56Fe.

  • Biogeochemical Cycling of cadmium isotopes along a high resolution section through the north atlantic ocean
    Geochimica et Cosmochimica Acta, 2015
    Co-Authors: Tim M Conway, Seth G John
    Abstract:

    Abstract Cadmium (Cd) is a bioactive trace element in the oceans, with a nutrient-like distribution that closely matches dissolved phosphate. Seawater-dissolved stable Cd isotope ratios (δ114Cd) are a relatively new parameter, which show much promise for furthering our understanding of the Biogeochemical Cycling of Cd in the oceans. Here we present a high-resolution paired section of dissolved Cd concentrations and dissolved δ114Cd from 21 open-ocean stations along the US GEOTRACES GA03 transect through the North Atlantic Ocean. Dissolved Cd concentrations along the section are strongly influenced by water-mass distribution and the Cycling of Cd. The highest dissolved Cd concentrations (400–540 pmol kg−1) are associated with Antarctic-sourced water masses, whilst biological uptake in the surface ocean results in a strong vertical gradient in dissolved Cd towards the surface, reaching as low as 0.03 pmol kg−1 in western surface waters. Dissolved δ114Cd is also characterized by a vertical gradient from ∼+0.2‰ in the deep ocean to +2‰ to +5‰ in the Cd-depleted surface ocean (relative to NIST SRM 3108). This variability in δ114Cd can be ascribed to mixing of Antarctic and North Atlantic water masses, together with fractionation due to in situ biological uptake of light Cd in the very surface ocean. Subtle deviations from this overall pattern of dissolved Cd concentration and dissolved δ114Cd are observed within low-oxygen waters off North Africa, where a dissolved Cd deficit relative to phosphate is associated with higher dissolved δ114Cd values. Together with elevated particulate Cd and Ba, this suggests that Cd sulfide precipitation is occurring within the water column of the North Atlantic, constituting a potentially important sink for isotopically light Cd. Additionally, the first measurements of dissolved δ114Cd within a hydrothermal plume at the Mid-Atlantic Ridge show that Cd is scavenged from the dissolved phase, leaving the remnant dissolved Cd isotopically heavier. Constraining the significance of these marine sinks for dissolved Cd is important, not only for our understanding of the marine Biogeochemical Cycling of Cd in the modern oceans, but also for the successful application of the microfossil Cd/Ca proxy and the development of δ114Cd as a tracer for past-ocean Biogeochemical Cycling.

  • the Biogeochemical Cycling of zinc and zinc isotopes in the north atlantic ocean
    Global Biogeochemical Cycles, 2014
    Co-Authors: Tim M Conway, Seth G John
    Abstract:

    Zinc (Zn) is a marine micronutrient, with an overall oceanic distribution mirroring the major macronutrients, especially silicate. Seawater Zn isotope ratios (δ66Zn) are a relatively new oceanographic parameter which may offer insights into the Biogeochemical Cycling of Zn. To date, the handful of published studies of seawater δ66Zn show the global deep ocean to be both remarkably homogeneous (approximately +0.5‰) and isotopically heavier than the marine sources of Zn (+0.1 to +0.3‰). Here we present the first high-resolution oceanic section of δ66Zn, from the U.S. GEOTRACES GA03 North Atlantic Transect, from Lisbon to Woods Hole. Throughout the surface ocean, biological uptake and release of isotopically light Zn, together with scavenging of heavier Zn, leads to large variability in δ66Zn. In the ocean below 1000 m, δ66Zn is generally homogeneous (+0.50 ± 0.14‰; 2 SD), though deviations from +0.5‰ allow us to identify specific sources of Zn. The Mediterranean Outflow is characterized by δ66Zn of +0.1 to +0.3‰, while margin sediments are a source of isotopically light Zn (−0.5 to −0.8‰), which we attribute to release of nonregenerated biogenic Zn. Mid-Atlantic Ridge hydrothermal vents are also a source of light Zn (close to −0.5‰), though Zn is not transported far from the vents. Understanding the Biogeochemical Cycling of Zn in the modern ocean begins to address the imbalance between the light δ66Zn signature of marine sources and the globally homogeneous deep oceans (δ66Zn of +0.5‰) on long timescales, with overall patterns pointing to sediments as an important sink for isotopically light Zn throughout the oceans.

John N. Quinton - One of the best experts on this subject based on the ideXlab platform.

  • The impact of agricultural soil erosion on Biogeochemical Cycling
    Nature Geoscience, 2010
    Co-Authors: John N. Quinton, Gerard Govers, Kristof Van Oost, Richard D. Bardgett
    Abstract:

    Soils are the main terrestrial reservoir of nutrients, such as nitrogen and phosphorus, and of organic carbon. Synthesizing earlier studies, we find that the mobilization and deposition of agricultural soils can significantly alter nutrient and carbon Cycling. Specifically, erosion can result in lateral fluxes of nitrogen and phosphorus that are similar in magnitude to those induced by fertilizer application and crop removal. Furthermore, the translocation and burial of soil reduces decomposition of soil organic carbon, and could lead to long-term carbon storage. The Cycling of carbon, nitrogen and phosphorus are strongly interrelated. For example, erosion-induced burial of soils stabilizes soil nutrient and carbon pools, thereby increasing primary productivity and carbon uptake, and potentially reducing erosion. Our analysis shows soils as dynamic systems in time and space. Soils are the main terrestrial reservoir of nutrients such as nitrogen and phosphorus, and of organic carbon. Data synthesis reveals that soil erosion can result in lateral fluxes of these nutrients at comparable magnitudes to those induced by fertilizer application and crop removal.

  • the impact of agricultural soil erosion on Biogeochemical Cycling
    Nature Geoscience, 2010
    Co-Authors: John N. Quinton, Gerard Govers, Kristof Van Oost, Richard D. Bardgett
    Abstract:

    Soils are the main terrestrial reservoir of nutrients, such as nitrogen and phosphorus, and of organic carbon. Synthesizing earlier studies, we find that the mobilization and deposition of agricultural soils can significantly alter nutrient and carbon Cycling. Specifically, erosion can result in lateral fluxes of nitrogen and phosphorus that are similar in magnitude to those induced by fertilizer application and crop removal. Furthermore, the translocation and burial of soil reduces decomposition of soil organic carbon, and could lead to long-term carbon storage. The Cycling of carbon, nitrogen and phosphorus are strongly interrelated. For example, erosion-induced burial of soils stabilizes soil nutrient and carbon pools, thereby increasing primary productivity and carbon uptake, and potentially reducing erosion. Our analysis shows soils as dynamic systems in time and space.

Zichen Xue - One of the best experts on this subject based on the ideXlab platform.

  • isotopic evidence for complex Biogeochemical Cycling of cd in the eastern tropical south pacific
    Earth and Planetary Science Letters, 2019
    Co-Authors: Ruifang C Xie, Martin Frank, Mark Rehkamper, Patricia Grasse, Tina Van De Flierdt, Zichen Xue
    Abstract:

    Abstract Over the past decades, observations have confirmed decreasing oxygen levels and shoaling of oxygen minimum zones (OMZs) in the tropical oceans. Such changes impact the Biogeochemical Cycling of micronutrients such as Cd, but the potential consequences are only poorly constrained. Here, we present seawater Cd concentrations and isotope compositions for 12 depth profiles at coastal, nearshore and offshore stations from 4°S to 14°S in the eastern tropical South Pacific, where one of the world's strongest OMZs prevails. The depth profiles of Cd isotopes display high δ 114 / 110 Cd at the surface and decreasing δ 114 / 110 Cd with increasing water depth, consistent with preferential utilization of lighter Cd isotopes during biological uptake in the euphotic zone and subsequent remineralization of the sinking biomass. In the surface and subsurface ocean, seawater displays similar δ 114 / 110 Cd signatures of 0.47 ± 0.23‰ to 0.82 ± 0.05‰ across the entire eastern tropical South Pacific despite highly variable Cd concentrations between 0.01 and 0.84 nmol/kg. This observation, best explained by an open system steady-state fractionation model, contrasts with previous studies of the South Atlantic and South Pacific Oceans, where only Cd-deficient waters have a relatively constant Cd isotope signature. For the subsurface to about 500 m depth, the variability of seawater Cd isotope compositions can be modeled by mixing of remineralized Cd with subsurface water from the base of the mixed layer. In the intermediate and deep eastern tropical South Pacific (>500 m), seawater [Cd] and δ 114 / 110 Cd appear to follow the distribution and mixing of major water masses. We identified modified AAIW of the ETSP to be more enriched in [Cd] than AAIW from the source region, whilst both water masses have similar δ 114 / 110 Cd . A mass balance estimate thus constrains a δ 114 / 110 Cd of between 0.38‰ and 0.56‰ for the accumulated remineralized Cd in the ETSP. Nearly all samples show a tight coupling of Cd and PO4 concentrations, whereby surface and deeper waters define two distinct linear trends. However, seawater at a coastal station located within a pronounced plume of H2S, is depleted in [Cd] and features significantly higher δ 114 / 110 Cd . This signature is attributed to the formation of authigenic CdS with preferential incorporation of lighter Cd isotopes. The process follows a Rayleigh fractionation model with a fractionation factor of α 114 / 110 Cd seawater-CdS = 1.00029. Further deviations from the deep Cd–PO4 trend were observed for samples with O2