Large Seasonal Changes Research Articles

Elevated lead mobility in sediments of a eutrophic drinking water reservoir during spring and summer seasons: Insights from isotopic signatures

Lead (Pb) pollution in sediments remains a major concern for ecosystem quality due to the robust interaction at the sediment/water interface, particularly in shallow lakes. However, understanding the mechanism behind seasonal fluctuations in Pb mobility in these sediments is lacking. Here, the seasonal variability of Pb concentration and isotopic ratio were investigated in the uppermost sediments of a shallow eutrophic drinking lake located in southeast China. Results reveal a sharp increase in labile Pb concentration during autumn-winter period, reaching ∼ 3-fold higher levels than during the spring-summer seasons. Despite these fluctuations, there was a notable overlap in the Pb isotopic signatures within the labile fraction across four seasons, suggesting that anthropogenic sources are not responsible for the elevated labile Pb concentration in autumn-winter seasons. Instead, the abnormally elevated labile Pb concentration during autumn-winter was probably related to reduction dissolution of Fe/Mn oxides, while declined labile Pb concentration during spring-summer may be attributed to adsorption/precipitation of Fe/Mn oxides. These large seasonal changes imply the importance of considering seasonal effects when conducting sediment sampling. We further propose a solution that using Pb isotopic signatures within the labile fraction instead of the bulk sediment can better reflect the information of anthropogenic Pb sources.

Long-Term and Seasonal Changes in Emission Sources of Atmospheric Particulate-Bound Pyrene and 1-Nitropyrene in Four Selected Cities in the Western Pacific

Abstract: Estimating the source contribution to polycyclic aromatic hydrocarbons (PAHs) and nitropolycyclic aromatic hydrocarbons (NPAHs) in the atmosphere is necessary for developing effective disease control and pollution control measures. The NPAH-PAH combination method (NP method) was used to elucidate the contributions of vehicles and coal/biomass combustion to seasonal and long-term urban atmospheric particulate matter (PM)-bound Pyr and 1-NP concentrations in Kanazawa, Kitakyushu, Shenyang and Shanghai in the Western Pacific region from 1997 to 2021. Among the four cities, Kanazawa demonstrated the lowest Pyr concentration. The contribution of vehicles to Pyr before and after 2010 was 35% and 5%, respectively. The 1-NP concentration was reduced by a factor of more than 1/10. These changes can be attributed to the emission control from vehicles. Kitakyushu revealed the second-lowest Pyr and the lowest 1-NP concentrations. Coal combustion was found to be the main contributor to Pyr, while its contribution to 1-NP increased from 9% to 19%. The large contribution of coal combustion is attributed to iron manufacturers. Shenyang demonstrated the highest atmospheric Pyr concentration with its largest seasonal change. Vehicles are the largest contributors to 1-NP. However, coal combustion, including winter coal heating, contributed 97% or more to Pyr and more than 14% to 1-NP. Shanghai revealed the second-highest Pyr and 1-NP concentrations, but the former was substantially lower than that in Shenyang. Coal combustion was the major contributor, but the contribution of vehicles to Pyr was larger before 2010, which was similar to Kanazawa.

Validated simulation of thermal performance of phase change material infused recycled brick aggregate in 3D printed concrete

Passive design solutions are important in reducing the amount of heating and cooling energy required to maintain thermal comfort inside a building, without adding to the problem of climate change. Phase change materials (PCMs) are a thermal energy storage passive design solution, with the ability to change phase and store heat at chosen temperatures. PCMs can be added to concrete to create PCM-concrete, a composite material with sensible and latent heat storage ability. The purpose of this research is to create an accurate 2D model which can be used to determine the heat transfer through 3D printed concrete (3DPC) building façades containing PCM. Two building façade wall sections are simulated in ABAQUS and validated by thermal tests – a reference 3DPC façade section, in which 64% of the natural aggregate is replaced with recycled brick aggregate (RBA-3DPC), and a PCM-3DPC façade section, containing the same replacement level of RBA but with PCM vacuum impregnated into the RBA. With the validated model, computational simulations of the thermal performance of the PCM-3DPC façade section with varying PCM melting temperatures and different façade surface colours are tested. Subsequently, a PCM-3DPC façade section with 100% replacement of natural aggregate with RBA, infused with PCM of two melting temperatures (such as 18 °C for activation in winter and 28 °C for activation in summer) is proposed for climates with large seasonal temperature changes. In addition, contrary to most studies, an iterative approach was used for modelling cavity convection and internal ambient temperature, and this approach is found to be necessary, so as not to over constrain the model with set façade and internal temperatures.

Climate-warming-driven changes in the cryosphere and their impact on groundwater–surface-water interactions in the Heihe River basin

Abstract. The Heihe River basin in northwest China depends heavily on both anthropogenic and natural storage (e.g., surface reservoirs, rivers and groundwater) to support economic and environmental functions. The Qilian Mountain cryosphere in the upper basin is integral to recharging these storage supplies. It is well established that climate warming is driving major shifts in high-elevation water storage through loss of glaciers and permafrost. However, the impacts on groundwater–surface-water interactions and water supply in corresponding lower reaches are less clear. We built an integrated hydrologic model of the middle basin, where most water usage occurs, in order to explore the hydrologic response to the changing cryosphere. We simulate the watershed response to loss of glaciers (glacier scenario), advanced permafrost degradation (permafrost scenario), both of these changes simultaneously (combined scenario) and projected temperature increases in the middle basin (warming scenario) by altering streamflow inputs to the model to represent cryosphere-melting processes, as well as by increasing the temperature of the climate forcing data. Net losses to groundwater storage in the glacier scenario and net gains in the permafrost and combined scenarios show the potential of groundwater exchanges to mediate streamflow shifts. The result of the combined scenario also shows that permafrost degradation has more of an impact on the system than glacial loss. Seasonal differences in groundwater–surface-water partitioning are also evident. The glacier scenario has the highest fraction of groundwater in terms of streamflow in early spring. The permafrost and combined scenarios meanwhile have the highest fraction of streamflow infiltration in late spring and summer. The warming scenario raises the temperature of the combined scenario by 2 ∘C. This results in net groundwater storage loss, a reversal from the combined scenario. Large seasonal changes in evapotranspiration and stream network connectivity relative to the combined scenario show the potential for warming to overpower changes resulting from streamflow. Our results demonstrate the importance of understanding the entire system of groundwater–surface-water exchanges to assess water resources under changing climatic conditions. Ultimately, this analysis can be used to examine the cascading impact of climate change in the cryosphere on the resilience of water resources in arid basins downstream of mountain ranges globally.

High-frequency, year-round time series of the carbonate chemistry in a high-Arctic fjord (Svalbard)

Abstract. The Arctic Ocean is subject to high rates of ocean warming and acidification, with critical implications for marine organisms as well as ecosystems and the services they provide. Carbonate system data in the Arctic realm are spotty in space and time, and, until recently, there was no time-series station measuring the carbonate chemistry at high frequency in this region, particularly in coastal waters. We report here on the first high-frequency (1 h), multi-year (5 years) dataset of salinity, temperature, CO2 partial pressure (pCO2) and pH at a coastal site (bottom depth of 12 m) in a high-Arctic fjord (Kongsfjorden, Svalbard). Discrete measurements of dissolved inorganic carbon and total alkalinity were also performed. We show that (1) the choice of formulations for calculating the dissociation constants of the carbonic acid remains unsettled for polar waters, (2) the water column is generally somewhat stratified despite the shallow depth, (3) the saturation state of calcium carbonate is subject to large seasonal changes but never reaches undersaturation (Ωa ranges between 1.4 and 3.0) and (4) pCO2 is lower than atmospheric CO2 at all seasons, making this site a sink for atmospheric CO2 (−9 to −16.8 molCO2m-2yr-1, depending on the parameterisation of the gas transfer velocity). Data are available on PANGAEA: https://doi.org/10.1594/PANGAEA.960131 (Gattuso et al., 2023a).

Atmospheric circulation compounds anthropogenic warming and impacts of climate extremes in Europe

Diagnosing dynamical changes in the climate system, such as those in atmospheric circulation patterns, remains challenging. Here, we study 1950 to 2021 trends in the frequency of occurrence of atmospheric circulation patterns over the North Atlantic. Roughly 7% of atmospheric circulation patterns display significant occurrence trends, yet they have major impacts on surface climate. Increasingly frequent patterns drive heatwaves across Europe and enhanced wintertime storminess in the northern part of the continent. Over 91% of recent heatwave-related deaths and 33% of high-impact windstorms in Europe were concurrent with increasingly frequent atmospheric circulation patterns. While the trends identified are statistically significant, they are not necessarily anthropogenic. Atmospheric patterns which are becoming rarer correspond instead to wet, cool summer conditions over northern Europe and wet winter conditions over continental Europe. The combined effect of these circulation changes is that of a strong, dynamically driven year-round warming over most of the continent and large regional and seasonal changes in precipitation and surface wind.

Evaluating Greenland surface-mass-balance and firn-densification data using ICESat-2 altimetry

Abstract. Surface-mass-balance (SMB) and firn-densification (FD) models are widely used in altimetry studies as a tool to separate atmospheric-driven from ice-dynamics-driven ice-sheet mass changes and to partition observed volume changes into ice-mass changes and firn-air-content changes. Until now, SMB models have been principally validated based on comparison with ice core and weather station data or comparison with widely separated flight radar-survey flight lines. Firn-densification models have been primarily validated based on their ability to match net densification over decades, as recorded in firn cores, and the short-term time-dependent component of densification has rarely been evaluated at all. The advent of systematic ice-sheet-wide repeated ice-surface-height measurements from ICESat-2 (the Ice Cloud, and land Elevation Satellite, 2) allows us to measure the net surface-height change of the Greenland ice sheet at quarterly resolution and compare the measured surface-height differences directly with those predicted by three FD–SMB models: MARv3.5.11 (Modèle Atmosphérique Régional version 3.5.11) and GSFCv1.1 and GSFCv1.2 (the Goddard Space Flight Center FD–SMB models version 1.1 and 1.2). By segregating the data by season and elevation, and based on the timing and magnitude of modelled processes in areas where we expect minimal ice-dynamics-driven height changes, we investigate the models' accuracy in predicting atmospherically driven height changes. We find that while all three models do well in predicting the large seasonal changes in the low-elevation parts of the ice sheet where melt rates are highest, two of the models (MARv3.5.11 and GSFCv1.1) systematically overpredict, by around a factor of 2, the magnitude of height changes in the high-elevation parts of the ice sheet, particularly those associated with melt events. This overprediction seems to be associated with the melt sensitivity of the models in the high-elevation part of the ice sheet. The third model, GSFCv1.2, which has an updated high-elevation melt parameterization, avoids this overprediction.

Permafrost degradation and nitrogen cycling in Arctic rivers: insights from stable nitrogen isotope studies

Abstract. Across the Arctic, vast areas of permafrost are being degraded by climate change, which has the potential to release substantial quantities of nutrients, including nitrogen into large Arctic rivers. These rivers heavily influence the biogeochemistry of the Arctic Ocean, so it is important to understand the potential changes to rivers from permafrost degradation. This study utilized dissolved nitrogen species (nitrate and dissolved organic nitrogen (DON)) along with nitrogen isotope values (δ15N-NO3- and δ15N-DON) of samples collected from permafrost sites in the Kolyma River and the six largest Arctic rivers. Large inputs of DON and nitrate with a unique isotopically heavy δ15N signature were documented in the Kolyma, suggesting the occurrence of denitrification and highly invigorated nitrogen cycling in the Yedoma permafrost thaw zones along the Kolyma. We show evidence for permafrost-derived DON being recycled to nitrate as it passes through the river, transferring the high 15N signature to nitrate. However, the potential to observe these thaw signals at the mouths of rivers depends on the spatial scale of thaw sites, permafrost degradation, and recycling mechanisms. In contrast with the Kolyma, with near 100 % continuous permafrost extent, the Ob River, draining large areas of discontinuous and sporadic permafrost, shows large seasonal changes in both nitrate and DON isotopic signatures. During winter months, water percolating through peat soils records isotopically heavy denitrification signals in contrast with the lighter summer values when surface flow dominates. This early year denitrification signal was present to a degree in the Kolyma, but the ability to relate seasonal nitrogen signals across Arctic Rivers to permafrost degradation could not be shown with this study. Other large rivers in the Arctic show different seasonal nitrogen trends. Based on nitrogen isotope values, the vast majority of nitrogen fluxes in the Arctic rivers is from fresh DON sourced from surface runoff through organic-rich topsoil and not from permafrost degradation. However, with future permafrost thaw, other Arctic rivers may begin to show nitrogen trends similar to the Ob. Our study demonstrates that nitrogen inputs from permafrost thaw can be identified through nitrogen isotopes, but only on small spatial scales. Overall, nitrogen isotopes show potential for revealing integrated catchment wide nitrogen cycling processes.

A bacterium from a mountain lake harvests light using both proton-pumping xanthorhodopsins and bacteriochlorophyll-based photosystems

Photoheterotrophic bacteria harvest light energy using either proton-pumping rhodopsins or bacteriochlorophyll (BChl)-based photosystems. The bacterium Sphingomonas glacialis AAP5 isolated from the alpine lake Gossenköllesee contains genes for both systems. Here, we show that BChl is expressed between 4°C and 22°C in the dark, whereas xanthorhodopsin is expressed only at temperatures below 16°C and in the presence of light. Thus, cells grown at low temperatures under a natural light-dark cycle contain both BChl-based photosystems and xanthorhodopsins with a nostoxanthin antenna. Flash photolysis measurements proved that both systems are photochemically active. The captured light energy is used for ATP synthesis and stimulates growth. Thus, S. glacialis AAP5 represents a chlorophototrophic and a retinalophototrophic organism. Our analyses suggest that simple xanthorhodopsin may be preferred by the cells under higher light and low temperatures, whereas larger BChl-based photosystems may perform better at lower light intensities. This indicates that the use of two systems for light harvesting may represent an evolutionary adaptation to the specific environmental conditions found in alpine lakes and other analogous ecosystems, allowing bacteria to alternate their light-harvesting machinery in response to large seasonal changes of irradiance and temperature.

Seasonal adjustment of leaf embolism resistance and its importance for hydraulic safety in deciduous trees.

Embolism resistance is often viewed as seasonally stable. Here we examined the seasonality in the leaf xylem vulnerability curve (VC) and turgor loss point (ΨTLP ) of nine deciduous species that originated from Mediterranean, temperate, tropical, or sub-tropical habitats and were growing on the Volcani campus, Israel. All four Mediterranean/temperate species exhibited a shift of their VC to lower xylem pressures (Ψx ) along the dry season, in addition to two of the five tropical/sub-tropical species. In three of the species that exhibited VC seasonality, it was critical for avoiding embolism in the leaf. In total, seven out of the nine species avoided embolism. The seasonal VC adjustment was over two times higher as compared with the seasonal adjustment of ΨTLP , resulting in improved hydraulic safety as the season progressed. The results suggest that seasonality in the leaf xylem vulnerability is common in species that originate from Mediterranean or temperate habitats that have large seasonal environmental changes. This seasonality is advantageous because it enables a gradual seasonal reduction in the Ψx without increasing the danger of embolism. The results also highlight that measuring the minimal Ψx and the VC at different times can lead to erroneous estimations of the hydraulic safety margins. Changing the current hydraulic dogma into a seasonal dynamic in the vulnerability of the xylem itself should enable physiologists to understand plants' responses to their environment better.

Six years of wild bee monitoring shows changes in biodiversity within and across years and declines in abundance.

Wild bees form diverse communities that pollinate plants in both native and agricultural ecosystems making them both ecologically and economically important. The growing evidence of bee declines has sparked increased interest in monitoring bee community and population dynamics using standardized methods. Here, we studied the dynamics of bee biodiversity within and across years by monitoring wild bees adjacent to four apple orchard locations in Southern Pennsylvania, USA. We collected bees using passive Blue Vane traps continuously from April to October for 6 years (2014–2019) amassing over 26,000 bees representing 144 species. We quantified total abundance, richness, diversity, composition, and phylogenetic structure. There were large seasonal changes in all measures of biodiversity with month explaining an average of 72% of the variation in our models. Changes over time were less dramatic with years explaining an average of 44% of the variation in biodiversity metrics. We found declines in all measures of biodiversity especially in the last 3 years, though additional years of sampling are needed to say if changes over time are part of a larger trend. Analyses of population dynamics over time for the 40 most abundant species indicate that about one third of species showed at least some evidence for declines in abundance. Bee family explained variation in species‐level seasonal patterns but we found no consistent family‐level patterns in declines, though bumble bees and sweat bees were groups that declined the most. Overall, our results show that season‐wide standardized sampling across multiple years can reveal nuanced patterns in bee biodiversity, phenological patterns of bees, and population trends over time of many co‐occurring species. These datasets could be used to quantify the relative effects that different aspects of environmental change have on bee communities and to help identify species of conservation concern.

Thylakoid fatty acid composition and response to short-term cold and heat stress in high-latitude Symbiodiniaceae

AbstractCoral reefs are restricted to warm waters, but are increasingly threatened by coral bleaching induced by sustained high sea surface temperatures. Coral endosymbiont thermal resilience has been proposed to depend, at least in part, on the lipid composition of their thylakoid membranes, which influences photosynthetic performance under sub- and super-optimal thermal conditions in photosynthetic organisms. Dinoflagellate symbionts of high-latitude coral reefs experience large seasonal changes in temperature, requiring a wide range of thermal tolerance, and so the thermal responses of their membrane lipids are of particular interest. Using gas chromatography–mass spectrometry, we investigated the composition and response to high- and low-temperature stress of thylakoid fatty acids of dinoflagellate symbionts isolated from corals of Lord Howe Island, the world’s southernmost coral reef. We detected genotype-specific differences in the quality of thylakoid fatty acids of two Cladocopium ITS2 consortia/genotypes, C100/118 and C111*, common local symbionts of the corals Pocillopora damicornis and Porites heronensis. The capability to adjust thylakoid fatty acid composition in response to temperature differed between distinct Cladocopium genotypes, and between the same Cladocopium consortium (C100/118) in the same coral species from different locations. Fatty acid adjustments were highly similar in response to short-term cold and heat stresses, with substantial increases in long-chain polyunsaturated fatty acids and a corresponding increase in the ratio of unsaturated to saturated fatty acids, but these changes did not correlate with the quantum yield of photosystem II. The response of thylakoid fatty acid composition to changes in temperature was a function of symbiont genotype, coral host species and, potentially, environmental history. Our data suggest the existence of common responses to high- and low-temperature stresses and that thylakoid fatty acid saturation is an unreliable predictor of photosystem efficiency under thermal stress in dinoflagellate symbionts.

The impact of a seasonal change in loading rate on the nitrous oxide emissions at the WWTP of a tourist region

Nitrous oxide (N2O) is a powerful greenhouse gas (GHG) whose production and emission must be minimised from wastewater treatment plants (WWTPs) to avoid undesirable impacts to climate change and the ozone layer. WWTPs operated in tourist regions undergo large seasonal changes to the influent loading rates of organic matter, nitrogen and phosphorus, which operators must respond to by changing their operational conditions. This study examines the impact of a change in low to high season on the N2O emissions of an activated sludge WWTP in a well-known tourist region in the Algarve, Portugal. While literature studies have suggested that increases in the nitrogen and organic loading rates can promote increased N2O emissions, we have found higher N2O emissions in the low season (7.4% kgN2O-N·kgNH4-N−1), where these loading rates were lower. It was found that the impact of accompanying operational changes to the WWTP outweighed any change caused by the increased loading rate, where the aeration rate showed a significant correlation with N2O emission dynamics. The location of the N2O fluxes observed as well as the dissolved vs gaseous N2O levels suggested that the hydroxylamine oxidation pathway was likely to be of higher relevance towards N2O production as compared to nitrifier denitrification. This study contributes towards the understanding of operational factors impacting N2O emissions at full-scale WWTPs and potential mitigation strategies.

Relationship between plasma cortisol level and bodyweight and antler size in farmed fallow deer

The aim of this study was to demonstrate the relationship between the plasma cortisol level and bodyweight and antler size in farmed male fallow deer (Dama dama) of various ages. The study involved 33 animals divided into three age groups: one year old, three years old, and older. Their bodyweight was measured and blood samples were taken twice a year during antler growth (May) and before the rut (September). Whole antlers were collected in September to measure their length and weight. The plasma cortisol concentration was determined with an immunoenzymatic method. The correlations between cortisol level and bodyweight were significant and positive in both May and September (P ≤0.05). There was a negative correlation between weight gain and change in cortisol levels (P ≤0.05). Thus, fallow deer with large seasonal changes in cortisol gained less weight from May to September. The results of the present study indicated that calmer animals with lower cortisol fluctuations should be selected for breeding, which would contribute to greater stability of weight gain.

Reed Warbler Hosts Do Not Fine-Tune Mobbing Defenses During the Breeding Season, Even When Cuckoos Are Rare

Hosts of brood parasitic cuckoos often employ mobbing attacks to defend their nests and, when mobbing is costly, hosts are predicted to adjust their mobbing to match parasitism risk. While evidence exists for fine-tuned plasticity, it remains unclear why mobbing does not track larger seasonal changes in parasitism risk. Here we test a possible explanation from parental investment theory: parents should defend their current brood more intensively as the opportunity to replace it declines (re-nesting potential), and therefore “counteract” any apparent seasonal decline to match parasitism risk. We take advantage of mobbing experiments conducted at two sites where reed warblers (Acrocephalus scirpaceus) experience (in Italy), or do not experience (in Finland), brood parasitism. We predicted that mobbing of cuckoos should be higher overall in Italy, but remain constant over the season as in other parasitised sites, whereas in Finland where cuckoos do not pose a local threat, we predicted that mobbing should be low at the beginning of the season but increase as re-nesting potential declined. However, while cuckoos were more likely to be mobbed in Italy, we found little evidence that mobbing changed over the season at either the parasitized or non-parasitized sites. This suggests that re-nesting potential has either little influence on mobbing behavior, or that its effects are obscured by other seasonal differences in ecology or experience of hosts.

MODIS PRI performance to track Light Use Efficiency of a Mediterranean coniferous forest: Determinants, restrictions and the role of LUE range

The relationship between the Photochemical Reflectance Index (PRI) and Light Use Efficiency (LUE) is well established at leaf and small canopy scales, but upscaling to ecosystem level is still a challenge. Only few studies have applied satellite-derived PRI to estimate LUE, mostly using MODIS, and although the results are promising, many external factors have been identified affecting PRI performance. The present study investigates determinants and restrictions of MODIS-derived PRI potential to follow the LUE variability of a Mediterranean coniferous forest.Daily and half-hour LUE values were calculated from eddy covariance measurements, dividing GPP by either Photosynthetically Active Radiation (PAR) or the absorbed fraction of PAR (APAR). Also, various PRI datasets were created based on different sensor (Terra, Aqua, Both), reference band (1, 12, 13) and observation/illumination angles. Overall, PRI correlated better with LUE calculated using PAR instead of APAR and Aqua PRI yielded better results than Terra. Restricting acquisitions according to observation/illumination angles improves the PRI:LUE relationship (maximum R2 = 0.512), with backscatter observations yielding the best correlations. Our findings suggest that MODIS-derived PRI is more sensitive to relatively large seasonal LUE changes, but is unable to closely follow severe drought events. Among the tested reference bands, the best results were derived using band 12 (546 - 556 nm), although the optimum reference band seems to depend on viewing conditions. The PRI:LUE relationship was further improved when half-hour LUE of the satellite overpass was used instead of daily LUE. However, it was found that the PRI:LUE relationships for the different datasets were strongly affected by the range of LUE values corresponding to each PRI group, with lower LUE variability resulting to weaker PRI:LUE correlations. LUE range effect should be accounted for in future studies, when different PRI datasets are compared and might explain the contradicting findings in the existing literature.

Soil structure and soil moisture dynamics inferred from time-lapse electrical resistivity tomography

The semi-arid sagebrush steppe in the western United States faces pressures from the agriculture industry, recreation use, invasive grasses, and a changing climate. A key to facilitating the healthy management of this ecosystem is understanding the distribution and behavior of soil moisture in the vadose zone in both natural and agricultural settings. Within unsaturated environments, soil moisture is spatially and temporally heterogeneous, and changes in porosity and permeability within arid soils complicate characterization of soil hydrologic properties. Importantly, accumulations of ‘caliche’ or pedogenic calcium carbonate in arid soils can greatly limit permeability; however, observing the role that caliche plays in the hydrologic process is difficult because the installation of in situ instruments disturbs the soils and only provides information at a single point. To investigate vadose zone processes on a broad temporal and spatial scale, we installed a 7x8m2 electrical resistivity tomography (ERT) array at the Reynolds Creek Critical Zone Observatory in southwestern Idaho. Existing soil moisture observations show that infiltration is limited to depths less than 60 cm at this site, as compared to at least 90 cm at other sites in the watershed. To capture the seasonal wetting and drying of the soils, as well as the soils’ response to rainfall events, we monitored the site bi-weekly during the spring, summer, and fall of 2015 and 2016. A time-lapse ERT array was placed adjacent to coaxial impedance dielectric reflectometry (CIDR) probes so that the time-lapse ERT data could be referenced to precise measurements of volumetric water content. In addition to the measurements provided by the ERT array and CIDR probes, soil texture analysis and soil profile descriptions from a near-by soil pit show typical arid soil morphology, with accumulations of clays and calcium carbonate in the B horizon. The resulting ERT inversions show the following soil structure: (1) a high-resistivity top layer corresponding with minor amounts of pedogenic calcium carbonate; (2) a low-resistivity intermediate layer at depths corresponding with substantial accumulations (stage IV) of carbonate; and (3) a high-resistivity deep saprolite. The resistivity of the top layer varies seasonally with changes in precipitation, while the intermediate carbonate soil layer does not. This agrees well with the changes in soil moisture with depth measured by the CIDR probes and suggests that the top of the carbonate soil layer limits infiltration. However vertical structure and cracks within the carbonate soil layer create vertical preferential flow paths; resistivity within these flow paths responds to large precipitation events and seasonal changes in soil moisture. This implies that the preferential flow paths are a conduit for soil moisture flow that is not captured by the CIDR probes. From the combined interpretation of the ERT and CIDR we conclude that soil structure and the presence of calcic soil horizons inhibits soil moisture infiltration during both the summer dry months and the winter wet flux period; however, preferential flow paths provide an important vertical connection between the deep and shallow portions of the critical zone.

Reef-building Pacific oysters record seasonal variations in water mass-properties of tidal basins from the Central Wadden Sea (North Sea)

High-resolution proxy records are needed to evaluate models simulating past, present and future climatic conditions. Before such records can be reliably employed, calibration studies have to be conducted to assess the confidence intervals of the proxies. Here, we use shells of the fast growing Pacific oyster Magallana gigas from the Central Wadden Sea, North Sea, a temperate barrier island-backbarrier tidal flat-salt marsh system with large seasonal changes of water mass-properties, for the calibration of geochemical proxies. M. gigas represents a non-native invasive species that rapidly develops oyster reefs. Calcite shells of two specimens from the intertidal and subtidal zones were sampled in high resolution yielding sub-monthly data sets. The time period represented in the shell, based on δ18O age modeling, was estimated at 8–10 years and the growth of the shells was restricted from (late) spring to (early) autumn of each year. Mg/Ca, Mn/Ca and Sr/Ca ratios of the intertidal and subtidal specimens show similar seasonal patterns. Mg/Ca and Sr/Ca ratios are investigated as high-resolution sea surface temperature (SST) proxies. Important ontogenetic effects (i.e., increasing time-averaging with increasing age) as well as inter-specimen variability are discussed as limiting factors for the proxy development. Intertidal Mg/Ca ratios show only a significant correlation to the high-resolution SST record of the Central Wadden Sea when the early ontogenetic stage is considered. Sr/Ca ratios were comparable in terms of absolute values and amplitudes to those of M. gigas in the Northern Wadden Sea, but amplitudes were decreasing with increasing age. These findings seriously hamper the application of Mg/Ca and Sr/Ca for reliable palaeotemperature reconstructions regardless of ontogenetic stage. The Mn/Ca ratios were investigated as proxy for Mn cycling in tidal basins, where it is interrelated with seasonal changes in primary production. In addition to the generally observed seasonal variability of the Mn/Ca oyster records, the subtidal Mn/Ca is significantly elevated compared to intertidal Mn/Ca. The subtidal Mn/Ca offset likely reflects differences in Mn cycling in tidal settings and could, therefore, serve in the palaeorecord as indicator to differentiate inter- and subtidal habitats in the same embedding sedimentary facies. This habitat effect has to be considered as an important factor besides environmental change when interpreting the high-resolution proxy record of fossil oysters.

Circulation patterns of biogenic ions in Young Glacial areas.

The paper focuses on the effect of ponds (geographically isolated wetlands) on water quality within internally drained areas in a river catchment. The important part of the study was the point of formation of a periodic hydrographic network of internally drained areas linked with a main river as well as the identification of the circulation pattern of ions in such a system. The aim of the study was to examine the extent to which ponds pollute the main river upon physical connection with it. Research has shown that ponds participate actively in material circulation-including that of water and biogenic ions. The hydrographic network in Young Glacial areas is subject to very large seasonal changes. In the study area, the total length of the stream network in the dry season equaled 12 km, while in the wet season almost 75 km. At the same time, almost 50% of the internally drained areas in the catchment became connected with the surface runoff network. Such large seasonal changes in the hydrographic network yield large changes in stream water chemistry. In the study area, only 6 ponds were linked to the stream network during the dry season, while in the wet season, this number increased to 125. The parts of catchments featuring the largest changes in the hydrographic network as well as the largest number of ponds temporarily linked with surface runoff networks were characterized by a high content of total nitrogen and phosphorus-up to 244.2 kg N km2 per month and 26.2 kg P km2 per month.

Greater exposure of nearshore habitats in the Bering Sea makes fish early life stages vulnerable to climate change

Marine fish species with complex life cycles undergo ontogenetic changes in their physiological and habitat requirements. Therefore, predicting how warming ocean conditions are likely to impact fish populations requires size-(age-) and habitat-specific analyses. We determined the habitat exposure and scope of adaptability of 4 shelf-oriented flatfish species in the Bering Sea to projected climate-driven warming. We quantified present day and end-of-century habitat exposure based on hindcasts and forecasts of regional ocean circulation models and quantified fish adaptability based on changes in depth distribution and from published thermal tolerances of northern rock sole Lepidopsetta polyxystra, yellowfin sole Limanda aspera, Alaska plaice Pleuronectes quadrituberculatus, and flathead sole Hippoglossoides elassodon. These 4 species complete their life cycle within the Bering Sea shelf but have different depth preferences and thermal tolerances throughout ontogeny. We found that species or size ranges that occupy the inner shelf, such as northern rock sole, yellowfin sole, and Alaska plaice, are exposed to higher seasonal variability compared to outer shelf species. While these inner shelf species are likely adapted to large seasonal changes in temperature, the future range of seasonal variability was projected to exceed their thermal tolerances. Therefore, we expect species that reside inshore during part of their life cycle and have high temperature sensitivity and limited mobility to be particularly vulnerable to climate change.