Impact of climate change on wetland ecosystems: A critical review of experimental wetlands

Climate change is identified as a major threat to wetlands. Altered hydrology and rising temperature can change the biogeochemistry and function of a wetland to the degree that some important services might be turned into disservices. This means that they will, for example, no longer provide a water purification service and adversely they may start to decompose and release nutrients to the surface water. Moreover, a higher rate of decomposition than primary production (photosynthesis) may lead to a shift of their function from being a sink of carbon to a source. This review paper assesses the potential response of natural wetlands (peatlands) and constructed wetlands to climate change in terms of gas emission and nutrients release. In addition, the impact of key climatic factors such as temperature and water availability on wetlands has been reviewed. The authors identified the methodological gaps and weaknesses in the literature and then introduced a new framework for conducting a comprehensive mesocosm experiment to address the existing gaps in literature to support future climate change research on wetland ecosystems. In the future, higher temperatures resulting in drought might shift the role of both constructed wetland and peatland from a sink to a source of carbon. However, higher temperatures accompanied by more precipitation can promote photosynthesis to a degree that might exceed the respiration and maintain the carbon sink role of the wetland. There might be a critical water level at which the wetland can preserve most of its services. In order to find that level, a study of the key factors of climate change and their interactions using an appropriate experimental method is necessary. Some contradictory results of past experiments can be associated with different methodologies, designs, time periods, climates, and natural variability. Hence a long-term simulation of climate change for wetlands according to the proposed framework is recommended. This framework provides relatively more accurate and realistic simulations, valid comparative results, comprehensive understanding and supports coordination between researchers. This can help to find a sustainable management strategy for wetlands to be resilient to climate change.     

Modelling carbon isotopes of carbonates in cave drip water

C isotopes in cave drip water are affected by both the C isotope composition of soil air and host rock carbonate. Furthermore, the C isotope composition of cave drip water strongly depends on the calcite dissolution system, i.e., open, closed and intermediate conditions. Here, we present a calcite dissolution model, which calculates the ¹⁴C activity and δ¹³C value of the dissolved inorganic carbon of the drip water. The model is based on the chemical equations describing calcite dissolution (). The most important improvement, relative to previous models, is the combination of the open and closed system conditions in order to simulate the C isotope composition during intermediate states of calcite dissolution and the application to carbon isotope measurements on cave drip waters from Grotta di Ernesto, Italy. The major changes in the C isotope composition of the drip water occur in response to variations in the open-closed system ratio. Additionally, the ¹⁴C activity and the δ¹³C value of the drip water depend on changes in the partial pressure of soil CO₂. Radiocarbon and δ¹³C values of the Grotta di Ernesto drip water are well reproduced by the model.     

Benthic nitrogen cycling traversing the Peruvian oxygen minimum zone

Benthic nitrogen (N) cycling was investigated at six stations along a transect traversing the Peruvian oxygen minimum zone (OMZ) at 11°S. An extensive dataset including porewater concentration profiles and in situ benthic fluxes of nitrate (NO₃⁻), nitrite (NO₂⁻) and ammonium (NH₄⁺) was used to constrain a 1-D reaction-transport model designed to simulate and interpret the measured data at each station. Simulated rates of nitrification, denitrification, anammox and dissimilatory nitrate reduction to ammonium (DNRA) by filamentous large sulfur bacteria (e.g. Beggiatoa and Thioploca) were highly variable throughout the OMZ yet clear trends were discernible. On the shelf and upper slope (80-260 m water depth) where extensive areas of bacterial mats were present, DNRA dominated total N turnover (?2.9 mmol N m⁻² d⁻¹) and accounted for ?65% of NO₃⁻ + NO₂⁻ uptake by the sediments from the bottom water. Nonetheless, these sediments did not represent a major sink for dissolved inorganic nitrogen (DIN = NO₃⁻ + NO₂⁻ + NH₄⁺) since DNRA reduces NO₃⁻ and, potentially NO₂⁻, to NH₄⁺. Consequently, the shelf and upper slope sediments were recycling sites for DIN due to relatively low rates of denitrification and high rates of ammonium release from DNRA and ammonification of organic matter. This finding contrasts with the current opinion that sediments underlying OMZs are a strong sink for DIN. Only at greater water depths (300-1000 m) did the sediments become a net sink for DIN. Here, denitrification was the major process (?2 mmol N m⁻² d⁻¹) and removed 55-73% of NO₃⁻ and NO₂⁻ taken up by the sediments, with DNRA and anammox accounting for the remaining fraction. Anammox was of minor importance on the shelf and upper slope yet contributed up to 62% to total N₂ production at the 1000 m station. The results indicate that the partitioning of oxidized N (NO₃⁻, NO₂⁻) into DNRA or denitrification is a key factor determining the role of marine sediments as DIN sinks or recycling sites. Consequently, high measured benthic uptake rates of oxidized N within OMZs do not necessarily indicate a loss of fixed N from the marine environment.     

Water relations and hydraulic architecture of two Patagonian steppe shrubs: Effect of slope orientation and microclimate

On a local scale, topography influences microclimate, vegetation structure and the morpho-physiological attributes of plants. We studied the effects of microclimatic differences between NE- and SW-facing slopes on the water relations and hydraulic properties of two dominant shrubs of the Patagonian steppe in Argentina (Retanilla patagonica and Colliguaja integerrima). The NE-facing slope had higher irradiance and air saturation deficits and lower soil water availability and wind speed than the SW-facing slope. Predawn and midday Ψ_L and osmotic potentials were significantly lower in shrubs on the NE-facing slope. Osmotic adjustment and more elastic cell walls helped the plants to cope with a more xeric environment on NE-facing slope. Higher water deficits on NE-facing slope were partially compensated by a higher leaf and stem water storage. While stem hydraulic efficiency did not vary between slopes, leaf hydraulic conductance was between 40% and 300% higher on the NE-facing slope. Changes observed in leaf size and in SLA were consistent with responses to mechanical forces of wind (smaller and scleromorphic leaves on SW-facing slope). Morpho-physiological adjustments observed at a short spatial scale allow maintenance of midday Ψ_L above the turgor loss point and demonstrate that leaves are more responsive to microclimatic selective pressures than stems.     

Impact of climate change on wetland ecosystems: A critical review of experimental wetlands

Climate change is identified as a major threat to wetlands. Altered hydrology and rising temperature can change the biogeochemistry and function of a wetland to the degree that some important services might be turned into disservices. This means that they will, for example, no longer provide a water purification service and adversely they may start to decompose and release nutrients to the surface water. Moreover, a higher rate of decomposition than primary production (photosynthesis) may lead to a shift of their function from being a sink of carbon to a source. This review paper assesses the potential response of natural wetlands (peatlands) and constructed wetlands to climate change in terms of gas emission and nutrients release. In addition, the impact of key climatic factors such as temperature and water availability on wetlands has been reviewed. The authors identified the methodological gaps and weaknesses in the literature and then introduced a new framework for conducting a comprehensive mesocosm experiment to address the existing gaps in literature to support future climate change research on wetland ecosystems. In the future, higher temperatures resulting in drought might shift the role of both constructed wetland and peatland from a sink to a source of carbon. However, higher temperatures accompanied by more precipitation can promote photosynthesis to a degree that might exceed the respiration and maintain the carbon sink role of the wetland. There might be a critical water level at which the wetland can preserve most of its services. In order to find that level, a study of the key factors of climate change and their interactions using an appropriate experimental method is necessary. Some contradictory results of past experiments can be associated with different methodologies, designs, time periods, climates, and natural variability. Hence a long-term simulation of climate change for wetlands according to the proposed framework is recommended. This framework provides relatively more accurate and realistic simulations, valid comparative results, comprehensive understanding and supports coordination between researchers. This can help to find a sustainable management strategy for wetlands to be resilient to climate change.     

First record of Karydomys (Rodentia, Mammalia) from the German part of the North Alpine Foreland Basin

Karydomys, a rare genus of cricetid rodents from the Middle Miocene of central Europe, had previously been reported only from the Swiss part of the North Alpine Foreland basin; documented evidence from the German part was lacking. This paper describes several new specimens of Karydomys from the German localities Höll and Laimering 3. A correlation of both localities to the Bavarian local biostratigraphic scale OSM F is proposed. Taxonomically, the fossils are most probably linked to K. wigharti from Hambach 6C (north-west Germany), and thus assigned to K. cf. wigharti. In spite of the scarcity of Karydomys fossils in the Upper Freshwatermolasse, the taxon is an important biostratigraphical marker because of its short stratigraphical range.     

Wavelength dependence of angular diameters of M giants: an observational perspective

We discuss the wavelength dependence of angular diameters of M giants from an observational perspective. Observers cannot directly measure an optical-depth radius for a star, despite this being a common theoretical definition. Instead, they can use an interferometer to measure the square of the fringe visibility. We present new plots of the wavelength-dependent centre-to-limb variation (CLV) of intensity of the stellar disc as well as visibility for Mira and non-Mira M giant models. We use the terms 'CLV spectra' and 'visibility spectra' for these plots. We discuss a model-predicted extreme limb-darkening effect (also called the narrow-bright-core effect) in very strong TiO bands which can lead to a misinterpretation of the size of a star in these bands. We find no evidence as yet that this effect occurs in real stars. Our CLV spectra can explain the similarity in visibilities of R Dor (M8IIIe) that have been observed recently, despite the use of two different passbands. We compare several observations with models, and find that the models generally underestimate the observed variation in visibility with wavelength. We present CLV and visibility spectra for a model that is applicable to the M supergiant α Ori.     

The first rotation periods in Praesepe

The cluster Praesepe (age ∼650 Myr) is an ideal laboratory to study stellar evolution. Specifically, it allows us to trace the long-term decline of rotation and activity on the main sequence. Here, we present rotation periods measured for five stars in Praesepe with masses of 0.1–0.5 M_⊙– the first rotation periods for members of this cluster. Photometric periodicities were found from two extensive monitoring campaigns, and are confirmed by multiple independent test procedures. We attribute these variations to magnetic spots co-rotating with the objects, thus indicating the rotation period. The five periods, ranging from 5 to 84 h, show a clear positive correlation with object mass, a trend which has been reported previously in younger clusters. When comparing with data for F–K stars in the coeval Hyades, we find a dramatic drop in the periods at spectral type K8–M2 (corresponding to 0.4–0.6 M_⊙). A comparison with periods of very low mass (VLM) stars in younger clusters provides a constraint on the spin-down time-scale: we find that the exponential rotational braking time-scale is clearly longer than 200 Myr, most likely 400–800 Myr. These results are not affected by the small sample size in the rotation periods in Praesepe. Both findings, the steep drop in the period–mass relation and the long spin-down time-scale, indicate a substantial change in the angular momentum loss mechanism for VLM objects, possibly the breakdown of the solar-type (Skumanich) rotational braking. While the physical origin for this behaviour is unclear, we argue that parts of it might be explained by the disappearance of the radiative core and the resulting breakdown of an interface-type dynamo in the VLM regime. Rotational studies in this mass range hold great potential to probe magnetic properties and interior structure of main-sequence stars.     

Cave bear occupation in Schwabenreith Cave,Austria, during the early last glacial: constraints from 230Th/U‐dated speleothems

The cave bear was a prominent member of the Upper Pleistocene fauna in Eurasia. While breakthroughs were recently achieved with respect to its phylogeny using ancient DNA techniques, it is still challenging to date cave bear fossils beyond the radiocarbon age range. Without an accurate and precise chronological framework, however, key questions regarding the palaeoecology cannot be addressed, such as the extent to which large climate swings during the last glacial affected the habitat and possibly even conditioned the final extinction of this mammal. Key to constraining the age of cave bear fossils older than the lower limit of radiocarbon dating is to date interlayered speleothems using ²³⁰Th/U. Here we report new results from one such site in the Eastern European Alps (Schwabenreith Cave), which yielded the highest density of bones of cave bear (Ursus spelaeus eremus). Although dating of the flowstones overlying this fossiliferous succession was partly compromised by diagenetic alteration, the ²³⁰Th/U dates indicate that the bear hibernated in this cave after about 113 ka and before about 109 ka. This time interval coincides with the equivalent of Greenland Stadial 25, suggesting possible climate control on the cave bear's habitat and behaviour. © 2019 The Authors. Journal of Quaternary Science Published by John Wiley & Sons Ltd