• Issue
    Volume 123, Issue 9
    2643-3097
    September 2018

Issue Information

Free Access

Issue Information

  • Pages: 2643-2644
  • First Published: 18 October 2018

Research Articles

Open Access

Variation in Hydrogen Isotope Composition Among Salt Marsh Plant Organic Compounds Highlights Biochemical Mechanisms Controlling Biosynthetic Fractionation

  • Pages: 2645-2660
  • First Published: 01 August 2018
Key Points

  • Variation in isoprenoid and acetogenic lipid hydrogen isotope values exceeds leaf water hydrogen isotope variability
  • Dominant osmoregulatory strategies show a strong correlation with the hydrogen isotope compositions of leaf wax biomarkers
  • Leaf wax biomarkers are valuable tools for investigating metabolic adaptations to environmental stress in modern and ancient environments

Free Access

Nitrogen Fixation Occurring in Sediments: Contribution to the Nitrogen Budget of Lake Taihu, China

  • Pages: 2661-2674
  • First Published: 30 July 2018
Key Points

  • Annual sediment nitrogen fixation in Lake Taihu is estimated as 195 t N
  • Sediment nitrogen fixation contributes a minor part to the nitrogen budget of Lake Taihu
  • Sediment nitrogen fixation rates may be closely linked to sediment characteristics

Open Access

Plant Traits are Key Determinants in Buffering the Meteorological Sensitivity of Net Carbon Exchanges of Arctic Tundra

  • Pages: 2675-2694
  • First Published: 30 July 2018
Key Points

  • We calibrated and validated an ecosystem model using field data to predict carbon dynamics over 8 years in West Greenland tundra
  • Similar meteorological sensitivity of GPP and Reco leads to buffered NEE
  • Plant traits control the compensatory effect observed (and estimated) between gross primary production and ecosystem respiration

Free Access

Methane Efflux Measured by Eddy Covariance in Alaskan Upland Tundra Undergoing Permafrost Degradation

  • Pages: 2695-2710
  • First Published: 17 July 2018
Key Points

  • Arctic permafrost tundra ecosystem is an annual net source of CH4
  • Nongrowing season emissions make up 45% of annual CH4 loss
  • Thaw depth is a significant driver of growing season CH4 emissions

Free Access

Using Noble Gases to Compare Parameterizations of Air-Water Gas Exchange and to Constrain Oxygen Losses by Ebullition in a Shallow Aquatic Environment

  • Pages: 2711-2726
  • First Published: 30 July 2018
Key Points

  • Concentrations of high solubility noble gases in a salt marsh pond are predicted well by wind speed-based gas exchange parameterizations
  • However, ebullition must occur to explain concentrations of less soluble noble gases, and we infer ebullition rates from neon observations
  • Including ebullition fluxes increased daily net oxygen production by 1–21%, making it an important oxygen flux in this setting

Free Access

The Role of Ligninolytic Enzymes Laccase and a Versatile Peroxidase of the White-Rot Fungus Lentinus tigrinus in Biotransformation of Soil Humic Matter: Comparative In Vivo Study

  • Pages: 2727-2742
  • First Published: 06 August 2018
Key Points

  • Soil humic acid is decomposed in the presence of laccase as efficiently as in the presence of VP in the culture liquid of Lentinus tigrinus
  • Cell-associated secondary synthesis reactions occur during humic acid decay in the presence of laccase
  • Alkali-extractable humus components are macromolecular but not stable to oxidative enzymes once desorbed from the mineral phase

Free Access

Diel Stream Temperature Effects on Nitrogen Cycling in Hyporheic Zones

  • Pages: 2743-2760
  • First Published: 22 August 2018
Key Points

  • A multiphysics flow and transport model is used to examine the diel dynamics of temperature-dependent C and N cycling in hyporheic zones
  • Biogeochemical hotspots persisted despite dynamic and complex hyporheic zone thermal patterns
  • Bulk daily nitrate removal efficiency can be estimated assuming steady temperatures despite large instantaneous variations under dynamic temperature conditions

Free Access

Mass and Fine-Scale Morphological Changes Induced by Changing Seawater pH in the Coccolith Gephyrocapsa oceanica

  • Pages: 2761-2774
  • First Published: 23 August 2018
Key Points

  • High-resolution microscopic analyses of coccolith biominerals cultured under pH ranging from 7.4 to 9.0
  • Detection of ultrastructural changes within the biominerals to provide a mechanistic understanding of the effect of pH on biomineralization
  • Decrease in calcite mass at lowest pH corresponds to a strong reduction of the breadth of the central tube of the coccoliths

Free Access

Drivers of Dissolved Organic Matter in the Vent and Major Conduits of the World's Largest Freshwater Spring

  • Pages: 2775-2790
  • First Published: 07 August 2018
Key Points

  • Conduits feeding into the spring vent can be separated via optical parameters and linked back to source regions
  • Optical measurements that can be made in situ can be utilized to trace the source of chromophoric dissolved organic matter to the vent
  • Chromophoric dissolved organic matter at the vent is derived from conduits draining from the southwest (forested areas)

Free Access

Tracing the Impact of Coastal Water Geochemistry on the Re-Os Systematics of Macroalgae: Insights From the Basaltic Terrain of Iceland

  • Pages: 2791-2806
  • First Published: 16 August 2018
Key Points

  • This article contains Re-Os abundance and isotope data for macroalgae from Icelandic coastal waters
  • Isotope data reflect changes in basaltic weathering and estuarine or coastal mixing
  • This article provides a novel approach to trace a range of Earth system and anthropogenic processes

Free Access

Detection of Positive Gross Primary Production Extremes in Terrestrial Ecosystems of China During 1982–2015 and Analysis of Climate Contribution

  • Pages: 2807-2823
  • First Published: 16 August 2018
Key Points

  • Three years of positive gross primary production extreme events occurred in 1990, 1998, and 2013 in China during 1982–2015
  • Favorable climate extremes contributed to the positive gross primary production extreme events
  • The subtropical-tropical monsoonal region of China contributed the largest in gross primary production extremes during 1982–2015

Free Access

Predicting Nitrate Retention at the Groundwater-Surface Water Interface in Sandplain Streams

  • Pages: 2824-2838
  • First Published: 25 August 2018
Key Points

  • Partial least squares regression models successfully predicted nitrate retention and N2 production in shallow groundwater at the local scale
  • Dissolved oxygen availability and groundwater discharge were the most consistent predictors of nitrate retention
  • Nitrate retention efficiency exhibited threshold dynamics, which suggests that nitrate flux can overwhelm nitrate retention capacity

Open Access

Connection Between Root Zone Soil Moisture and Surface Energy Flux Partitioning Using Modeling, Observations, and Data Assimilation for a Temperate Grassland Site in Germany

  • Pages: 2839-2862
  • First Published: 23 August 2018
Key Points

  • Connection between root zone soil moisture and surface energy flux partitioning
  • Evaluation of two different-generation land surface models over the Falkenberg grassland site
  • Model biases in third-generation land surface models identified via data assimilation with joint state parameter update

Free Access

Climate Change to Offset Improvements in Watershed Acid-Base Status Provided by Clean Air Act and Amendments: A Model Application in Shenandoah National Park, Virginia

  • Pages: 2863-2877
  • First Published: 25 August 2018
Key Points

  • We model the potential impacts of climate change on a stream's acid-base conditions
  • Increased temperature and precipitation will likely result in decreased stream alkalinity
  • The impacts of climate change may counteract some gains provided by reduced acid deposition

Free Access

Last Millennium Adélie Penguin Mortality and Colony Abandonment Events on Long Peninsula, East Antarctica

  • Pages: 2878-2889
  • First Published: 28 August 2018
Key Points

  • Multiple lines of evidence reveal multidecadal-scale penguin mortality events on Long Peninsula, East Antarctica
  • Well-preserved penguin carcasses from the land surface and sediments have ages up to ~750 years BP
  • The mortality events were caused by heavy precipitation and related to atmospheric circulation defined by a ZW3 pattern

Free Access

B Vitamins and Their Congeners as Potential Drivers of Microbial Community Composition in an Oligotrophic Marine Ecosystem

  • Pages: 2890-2907
  • First Published: 06 August 2018
Key Points

  • Multiple biochemical forms of B vitamins are present both dissolved in seawater and in particles as measured across a Mediterranean-Atlantic transect
  • B vitamins cooccur in biogeographic patches driven by mesoscale oceanographic features that control both the microbial community and the distribution of total dissolved B vitamins
  • Model fits of microbial assemblages were significantly improved when dissolved B vitamin concentrations were included as independent variables, especially in oligotrophic regions of the oceanographic transect

Free Access

Spatiotemporal Variation of the Quality, Origin, and Age of Particulate Organic Matter Transported by the Yangtze River (Changjiang)

  • Pages: 2908-2921
  • First Published: 22 August 2018
Key Points

  • Age dynamics of particulate organic matter in Changjiang (Yangtze River) were investigated by Δ14C values
  • The contributions of biomass and pre-aged soil organic matter were dominant, regardless of the hydrological conditions
  • Dam effect and retention of fresh organic matter in the lower reaches has modified the organic matter age and composition

Free Access

Dissolved Carbon Dynamics in Meltwaters From the Russell Glacier, Greenland Ice Sheet

  • Pages: 2922-2940
  • First Published: 19 July 2018
Key Points

  • Greenland Ice Sheet supraglacial streams contribute ~50% of the dissolved inorganic carbon in subglacial discharge
  • Hydrologic transport of dissolved organic carbon from the ice sheet surface may drive subglacial microbial respiration and production of CO2
  • Evasion of CO2 from subglacial discharge to the atmosphere could act as a positive feedback between ice sheet melting and climate warming

Free Access

Predictable Oxygen Isotope Exchange Between Plant Lipids and Environmental Water: Implications for Ecosystem Water Balance Reconstruction

  • Pages: 2941-2954
  • First Published: 26 July 2018
Key Points

  • Long-chain plant-derived lipids display no oxygen exchange with water while heterogeneous lipid extracts have predictable exchange
  • The presence of iron oxyhydroxide minerals slows oxygen exchange rates, suggesting physical protection of organic material
  • Improved reconstruction of hydrologic shifts at local to landscape scales is possible using this proxy

Free Access

Stoichiometric N:P Ratios, Temperature, and Iron Impact Carbon and Nitrogen Uptake by Ross Sea Microbial Communities

  • Pages: 2955-2975
  • First Published: 16 August 2018
Key Points

  • Responses of Ross Sea microorganisms to changing dissolved N:P ratios, temperature, and Fe vary seasonally and among taxa
  • Increasing the N:P ratio of the seawater increased nitrate uptake rates, but only over short time scales and during the late-season bloom
  • Temperature elevation and Fe addition are more significant drivers of change than N:P supply ratios when Phaeocystis is dominant

Free Access

Evaluating GPP and Respiration Estimates Over Northern Midlatitude Ecosystems Using Solar-Induced Fluorescence and Atmospheric CO2 Measurements

  • Pages: 2976-2997
  • First Published: 23 August 2018
Key Points

  • Top-down constraints on ecosystem respiration are obtained by combining atmospheric CO2 and solar-induced fluorescence observations
  • Inferred ecosystem respiration suggests a systematically broader summer maximum than bottom-up estimates over the northern midlatitudes
  • Inferred ecosystem respiration shows high sensitivity to the magnitude of gross primary productivity

Free Access

An Assessment of Dissolved Organic Carbon Biodegradability and Priming in Blackwater Systems

  • Pages: 2998-3015
  • First Published: 29 August 2018
Key Points

  • The priming effect is unlikely to increase microbial remineralization of dissolved organic carbon in blackwater systems
  • Minimal dissolved organic carbon degradation and compositional changes occurred in blackwaters while leachate dissolved organic matter was highly bioavailable
  • Dissolved organic carbon biodegradability is controlled by chemical composition, particularly the contribution of aliphatic compounds

Free Access

Phosphorus Fractionation Responds to Dynamic Redox Conditions in a Humid Tropical Forest Soil

  • Pages: 3016-3027
  • First Published: 22 August 2018
Key Points

  • Shortly after redox switches, some soil P fractions showed tight coupling with iron speciation
  • Amorphous Fe and P fractions became less sensitive to redox fluctuation over time
  • Static anoxic conditions increased P extractability and enhanced iron reduction

Free Access

Modeling the Effect of Moss Cover on Soil Temperature and Carbon Fluxes at a Tundra Site in Northeastern Siberia

  • Pages: 3028-3044
  • First Published: 01 September 2018
Key Points

  • Assessing the influences of moss cover on soil temperature, active layer thickness, and carbon flux feedback at a tundra site
  • Moss-induced lower soil temperature limits carbon flux trough lower soil water availability due to the presence of ice

Free Access

Deep Unsaturated Zone Contributions to Carbon Cycling in Semiarid Environments

  • Pages: 3045-3054
  • First Published: 04 September 2018
Key Points

  • Thirty percent of CO2 annual efflux to atmosphere (60% in winter) originates from below 1 m, contrary to near 0% predicted by the ESM land models
  • We discovered an unexpectedly high dissolved organic carbon flux from rhizosphere into underlying unsaturated zone at a semiarid site
  • The mechanisms responsible for C availability, and conditions that sustain respiration at depth are expected existing in other semiarid regions

Free Access

Hydrological Controls on the Seasonal Variability of Dissolved and Particulate Black Carbon in the Altamaha River, GA

  • Pages: 3055-3071
  • First Published: 28 August 2018
Key Points

  • Hydrological controls on BC mobilization may be more complex than previously suggested
  • Seasonal dynamics suggests that PBC and DBC may be coupled during baseflow conditions but not during high flow
  • PBC export was also linked to seasonal hydrology, but sources appeared to be highly variable throughout the sampling period

Free Access

Multiyear Trends in Solute Concentrations and Fluxes From a Suburban Watershed: Evaluating Effects of 100-Year Flood Events

  • Pages: 3072-3087
  • First Published: 28 August 2018
Key Points

  • Small decreases in concentrations and fluxes of salts and major ions were observed over 12 years despite an increase in the human footprint
  • Small (<1% of mean annual) decreases in DOC concentrations were observed over a 15-year period, but DOC did not respond to discharge
  • Occurrence of two 100-year flood events had little, if any, effect on multiyear trends in concentrations, fluxes, or C-Q relationships

Free Access

Hydrologic and Edaphic Controls on Soil Carbon Emission in Dongting Lake Floodplain, China

  • Pages: 3088-3097
  • First Published: 29 August 2018
Key Points

  • Soil C emission in Dongting Lake floodplain was 264.3–307.8 g C.m-2.year-1
  • Flooding significantly inhibited soil CO2 emission but stimulated CH4 emission
  • The decline of flooding days in Dongting Lake wetlands can potentially increase soil C loss