More Like this

1. Quantifying energy use efficiency via entropy production: a case study from longleaf pine ecosystems

   https://doi.org/10.5194/bg-16-1845-2019  

   Wiesner, Susanne ; Staudhammer, Christina L. ; Stoy, Paul C. ; Boring, Lindsay R. ; Starr, Gregory ( January 2019 , Biogeosciences)

   Abstract. Ecosystems are open systems that exchange matter and energy with theirenvironment. They differ in their efficiency in doing so as a result of theirlocation on Earth, structure and disturbance, including anthropogenic legacy.Entropy has been proposed to be an effective metric to describe thesedifferences as it relates energy use efficiencies of ecosystems to theirthermodynamic environment (i.e., temperature) but has rarely been studied tounderstand how ecosystems with different disturbance legacies respond whenconfronted with environmental variability. We studied three sites in alongleaf pine ecosystem with varying levels of anthropogenic legacy and plantfunctional diversity, all of which were exposed to extreme drought. Wequantified radiative (eff_rad), metabolic and overall entropychanges – as well as changes in exported to imported entropy(eff_flux) in response to drought disturbance and environmentalvariability using 24 total years of eddy covariance data (8 years per site).We show that structural and functional characteristics contribute todifferences in energy use efficiencies at the three study sites. Our resultsdemonstrate that ecosystem function during drought is modulated by decreasedabsorbed solar energy and variation in the partitioning of energy and entropyexports owing to differences in site enhanced vegetation index and/or soilwater content. Low eff_rad and metabolic entropy as well as slowadjustment of eff_flux at the anthropogenically altered siteprolonged its recovery from drought by approximately 1 year. In contrast,stands with greater plant functional diversity (i.e., the ones that includedboth C₃ and C₄ species) adjusted their entropy exports when facedwith drought, which accelerated their recovery. Our study provides a pathforward for using entropy to determine ecosystem function across differentglobal ecosystems.

    

   more » « less
2. Using Metabolic Energy Density Metrics to Understand Differences in Ecosystem Function During Drought

   https://doi.org/10.1029/2019JG005335  

   Wiesner, Susanne ; Stoy, Paul C. ; Staudhammer, Christina L. ; Starr, Gregory ( February 2020 , Journal of Geophysical Research: Biogeosciences)

   Terrestrial ecosystems obtain energy in the form of carbon‐containing molecules. Quantifying energy acquisition and dissipation throughout an ecosystem may be useful for describing their resistance and resilience to disturbances. Three longleaf pine savannas with different vegetation composition—a result of variation in soil moisture and land use legacy—were used as a case study to test energy‐based metrics of ecosystem metabolic function. Available energy from gross ecosystem exchange of CO₂and its dissipation into metabolic energy density (E_M) and energy storage were used to identify differences in drought recovery over an 8‐year period. Sites with higher plant functional diversity in the understory stored more energy and lowered their E_Mby ~20% when adapting to drought. In contrast, the site with greater abundance of woody understory and overstory species relied on stored energy twice as often as the more diverse sites. The absence of native understory species, due to anthropogenic legacy, prolonged ecosystem‐scale drought recovery by 1 year. This study provides the tools to understand differences in site metabolic energy dynamics and has the potential to identify site characteristics that indicate greater vulnerability to disturbances. Metabolic energy density can be applied to any global ecosystem and provides a first step to describe coupled carbon and energy allocation in ecosystems, which may be used to further refine ecological theory and its management implications.

    

   more » « less
3. Modeling the physiology of the aquatic temnospondyl <i>Archegosaurusdecheni</i> from the early Permian of Germany

   https://doi.org/10.5194/fr-20-105-2017  

   Witzmann, Florian ; Brainerd, Elizabeth ( January 2017 , Fossil Record)

   Abstract. Physiological aspects like heat balance, gas exchange, osmoregulation, and digestion of the early Permian aquatic temnospondyl Archegosaurus decheni, which lived in a tropical freshwater lake, are assessed based on osteological correlates of physiologically relevant soft-tissue organs and by physiological estimations analogous to air-breathing fishes. Body mass (M) of an adult Archegosaurus with an overall body length of more than 1m is estimated as 7kg using graphic double integration. Standard metabolic rate (SMR) at 20°C (12kJh⁻¹) and active metabolic rate (AMR) at 25°C (47kJh⁻¹) were estimated according to the interspecific allometry of metabolic rate (measured as oxygen consumption) of all fish (V_O2 = 4. 8M^0. 88) and form the basis for most of the subsequent estimations. Archegosaurus is interpreted as a facultative air breather that got O₂ from the internal gills at rest in well-aerated water but relied on its lungs for O₂ uptake in times of activity and hypoxia. The bulk of CO₂ was always eliminated via the gills. Our estimations suggest that if Archegosaurus did not have gills and released 100% CO₂ from its lungs, it would have to breathe much more frequently to release enough CO₂ relative to the lung ventilation required for just O₂ uptake. Estimations of absorption and assimilation in the digestive tract of Archegosaurus suggest that an adult had to eat about six middle-sized specimens of the acanthodian fish Acanthodes (ca. 8cm body length) per day to meet its energy demands. Archegosaurus is regarded as an ammonotelic animal that excreted ammonia (NH₃) directly to the water through the gills and the skin, and these diffusional routes dominated nitrogen excretion by the kidneys as urine. Osmotic influx of water through the gills had to be compensated for by production of dilute, hypoosmotic urine by the kidneys. Whereas Archegosaurus has long been regarded as a salamander-like animal, there is evidence that its physiology was more fish- than tetrapod-like in many respects.

    

   more » « less
4. Detecting the permafrost carbon feedback: talik formation and increased cold-season respiration as precursors to sink-to-source transitions

   https://doi.org/10.5194/tc-12-123-2018  

   Parazoo, Nicholas C. ; Koven, Charles D. ; Lawrence, David M. ; Romanovsky, Vladimir ; Miller, Charles E. ( January 2018 , The Cryosphere)

   Abstract. Thaw and release of permafrost carbon (C) due to climate change is likely tooffset increased vegetation C uptake in northern high-latitude (NHL)terrestrial ecosystems. Models project that this permafrost C feedback mayact as a slow leak, in which case detection and attribution of the feedbackmay be difficult. The formation of talik, a subsurface layer of perenniallythawed soil, can accelerate permafrost degradation and soil respiration,ultimately shifting the C balance of permafrost-affected ecosystems fromlong-term C sinks to long-term C sources. It is imperative to understand andcharacterize mechanistic links between talik, permafrost thaw, andrespiration of deep soil C to detect and quantify the permafrost C feedback.Here, we use the Community Land Model (CLM) version 4.5, a permafrost andbiogeochemistry model, in comparison to long-term deep borehole data alongNorth American and Siberian transects, to investigate thaw-driven C sourcesin NHL (&gt;55^∘N) from 2000 to 2300. Widespread talik at depth isprojected across most of the NHL permafrost region(14million km²) by 2300, 6.2million km² of which isprojected to become a long-term C source, emitting 10Pg C by 2100,50Pg C by 2200, and 120Pg C by 2300, with few signs ofslowing. Roughly half of the projected C source region is in predominantlywarm sub-Arctic permafrost following talik onset. This region emits only20Pg C by 2300, but the CLM4.5 estimate may be biased low by notaccounting for deep C in yedoma. Accelerated decomposition of deep soilC following talik onset shifts the ecosystem C balance away from surfacedominant processes (photosynthesis and litter respiration), butsink-to-source transition dates are delayed by 20–200 years by highecosystem productivity, such that talik peaks early (∼2050s, although boreholedata suggest sooner) and C source transition peaks late(∼2150–2200). The remaining C source region in cold northern Arcticpermafrost, which shifts to a net source early (late 21st century), emits5 times more C (95Pg C) by 2300, and prior to talik formation dueto the high decomposition rates of shallow, young C in organic-rich soilscoupled with low productivity. Our results provide important clues signalingimminent talik onset and C source transition, including (1) late cold-season(January–February) soil warming at depth (∼2m),(2) increasing cold-season emissions (November–April), and (3) enhancedrespiration of deep, old C in warm permafrost and young, shallow C in organic-rich cold permafrost soils. Our results suggest a mosaic of processes thatgovern carbon source-to-sink transitions at high latitudes and emphasize theurgency of monitoring soil thermal profiles, organic C age and content, cold-season CO₂ emissions, andatmospheric ¹⁴CO₂ as key indicatorsof the permafrost C feedback.

    

   more » « less
5. Dried, closed-path eddy covariance method for measuring carbon dioxide flux over sea ice

   https://doi.org/10.5194/amt-11-6075-2018  

   Butterworth, Brian J. ; Else, Brent G. ( January 2018 , Atmospheric Measurement Techniques)

   Abstract. The Arctic marine environment plays an important role inthe global carbon cycle. However, there remain large uncertainties in howsea ice affects air–sea fluxes of carbon dioxide (CO₂), partially dueto disagreement between the two main methods (enclosure and eddy covariance)for measuring CO₂ flux ($F_{\mathrm{CO}{}_{\mathrm{2}}}$). The enclosure method has appearedto produce more credible $F_{\mathrm{CO}{}_{\mathrm{2}}}$ than eddy covariance (EC), but is notsuited for collecting long-term, ecosystem-scale flux datasets in suchremote regions. Here we describe the design and performance of an EC systemto measure $F_{\mathrm{CO}{}_{\mathrm{2}}}$ over landfast sea ice that addresses the shortcomingsof previous EC systems. The system was installed on a 10m tower onQikirtaarjuk Island – a small rock outcrop in Dease Strait located roughly35km west of Cambridge Bay, Nunavut, in the Canadian Arctic Archipelago. Thesystem incorporates recent developments in the field of air–sea gasexchange by measuring atmospheric CO₂ using a closed-path infrared gasanalyzer (IRGA) with a dried sample airstream, thus avoiding the known watervapor issues associated with using open-path IRGAs in low-flux environments.A description of the methods and the results from 4 months of continuousflux measurements from May through August 2017 are presented, highlightingthe winter to summer transition from ice cover to open water. We show thatthe dried, closed-path EC system greatly reduces the magnitude of measured$F_{\mathrm{CO}{}_{\mathrm{2}}}$ compared to simultaneous open-path EC measurements, and for thefirst time reconciles EC and enclosure flux measurements over sea ice. Thisnovel EC installation is capable of operating year-round on solar and windpower, and therefore promises to deliver new insights into the magnitude ofCO₂ fluxes and their driving processes through the annual sea icecycle.

    

   more » « less