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The frequency and severity of droughts in the Alps are expected to increase due to rising air temperatures and changes in precipitation regimes. Although biomass production in humid mountain areas tends to be energy limited rather than water limited, an increase in droughts may have negative impacts on the water availability and thus agricultural yields. This study aimed to analyse the impacts of dry spells on soil moisture and yield anomalies at a montane permanent grassland site in Austria. Dry spells in the time period from 2018 to 2020 were identified using the Standardized Precipitation Index, Palmer Drought Severity Index and the Soil Moisture Anomaly Index. Data from a lysimeter climate experiment were used to evaluate drought impacts on soil water storage and grassland yield under ambient and manipulated conditions. The results indicated the occurrence of three extreme droughts between 2018 and 2020. Although the studied grassland is generally considered a nonwater‐limited ecosystem, the most extreme drought in summer 2019 caused severe and extreme yield anomalies under ambient and heated conditions. Only mild yield anomalies were observed on plots with elevated atmospheric carbon dioxide concentration. This drought‐mitigating effect was attributed to the water savings enabled by partial stomatal closure under elevated CO2. The shorter dry spells in spring and late summer 2018 led to more diverse effects; mildly to moderately negative yield anomalies were found on the heated plots, whereas the anomalies tended to be less negative or even positive on plots under ambient temperature. In contrast, some time periods without water stress showed positive effects of heating on yield. These findings suggest that drought impacts on a humid montane grassland depend on both water availability and air temperature. Higher air temperature can have positive effects on yield if the ecosystem is energy limited. However, global warming suggests a tendency from energy to water limitation, in which the increased evaporative demand of the atmosphere aggravates soil moisture droughts and thus has potentially negative effects on yield. [ABSTRACT FROM AUTHOR]

The estimation of groundwater recharge is of paramount importance to assess the sustainability of groundwater use in aquifers around the world. Estimation of the recharge flux, however, remains notoriously difficult. In this study the application of nonlinear transfer function noise (TFN) models using impulse response functions is explored to simulate groundwater levels and estimate groundwater recharge. A nonlinear root zone model that simulates recharge is developed and implemented in a TFN model and is compared to a more commonly used linear recharge model. An additional novel aspect of this study is the use of an autoregressive–moving-average noise model so that the remaining noise fulfills the statistical conditions to reliably estimate parameter uncertainties and compute the confidence intervals of the recharge estimates. The models are calibrated on groundwater-level data observed at the Wagna hydrological research station in the southeastern part of Austria. The nonlinear model improves the simulation of groundwater levels compared to the linear model. The annual recharge rates estimated with the nonlinear model are comparable to the average seepage rates observed with two lysimeters. The recharges estimates from the nonlinear model are also in reasonably good agreement with the lysimeter data at the smaller timescale of recharge per 10 d. This is an improvement over previous studies that used comparable methods but only reported annual recharge rates. The presented framework requires limited input data (precipitation, potential evaporation, and groundwater levels) and can easily be extended to support applications in different hydrogeological settings than those presented here. [ABSTRACT FROM AUTHOR]

A thorough data analysis combined with groundwater modelling was conducted in an Austrian binary karst aquifer to better understand changes in the hydrological behaviour observed at a karst spring. During a period of 4 years after a major flood event the spring hydrograph appears to be more damped with lower peak flow and higher baseflow than in the years before. The analysis of the hydrograph recession suggests that the observed hydrological change is caused by changes within the karst system rather than by varying hydro-meteorological conditions. The functioning of the aquifer and potential causes of the observed changes are further examined using the groundwater flow model MODFLOW. The simulation results suggest that a modification of hydraulic conductivity and storage within the conduit network, e.g. due to the plugging of the drainage conduits with sediments, may be the cause of the different behaviour. MODFLOW was able to reproduce the observed dynamics of spring flow, although it does not account for turbulent flow within karst conduits. Using a simplified model scenario it is demonstrated that the damping of the hydrograph is much stronger if turbulent conduit flow is taken into account. Thus, a turbulent flow model is needed to assess potential changes in the storage properties quantitatively. [ABSTRACT FROM AUTHOR]

In the years following a flood event in August 2005, the Hammerbach karst spring in Austria displayed hydraulic and physicochemical responses to recharge events that appear to be markedly different from those observed before. As likely cause of these changes the reduction of the conduit diameters resulting from redistribution of sediments during the flood event has been proposed (Birk et al., EGU2014-7550). According to Kovács et al. (J. Hydrol., 2005) the baseflow recession of mature karst aquifers generally is matrix restrained, i.e. controlled by the drainage from the low-permeability matrix but not by the conduit properties. It thus appears that the changed behavior of the Hammerbach karst spring corresponds to a shift from a matrix-restrained to a conduit-influenced flow regime. This contribution is aimed at understanding how such a shift of the flow regime may affect the recession behavior. On the one hand, conceptual recession models and the corresponding mathematical models are theoretically explored; on the other hand, the recession of the Hammerbach spring observed in the years after the flood event is analysed and compared to that before the flood event 2005. It is shown that – given some reasonable assumptions – a shift from an exponential recession under matrix-restrained conditions to a linear recession in a conduit-influenced flow regime may theoretically be expected and that the field data indeed appears to show a tendency towards such changes in the recession behaviour. [ABSTRACT FROM AUTHOR]

Pesticide leaching into groundwater may be affected by changing climate directly and indirectly. Increased temperatures, changes in precipitation intensity, amounts and seasonality are thought to be the main direct climate drivers for changing pesticide fate and transport behaviour. Although it is well understood, in which range possible factors will influence pesticide fate and transport behaviour under changing climate conditions, only few studies have investigated these impacts quantitatively (Steffens et al., Sci Total Environ 2015). Increased temperatures for example enhance degradation, increase volatilisation, weaker sorption (for most compounds) of pesticide and fasten diffusion. More intense precipitation events for example may lead to more by-pass flow, which might increase pesticide leaching. In contrast, a drier soil for example has lower hydraulic conductivities, leading to slower substance transport, but degradation rates are lower too.This study aims to assess pesticide leaching into groundwater under changing climate conditions for a region in south-eastern Austria. For this purpose, a one-dimensional pesticide fate and transport model is used. The simulations focus on different representative pesticides, with varying properties, different common soil types and different climate scenarios, rather than indirect effects, such as changing cropping patterns, crop growth or pesticide applications. This work thus contributes to a better understanding of the impacts of climate change on pesticide leaching. [ABSTRACT FROM AUTHOR]

Biodiversity, the source of origin, and ecological roles of fungi in groundwater are to this day a largely neglected field in fungal and freshwater ecology. We used DNA-based Illumina high-throughput sequence analysis of both fungal gene markers 5.8S and internal transcribed spacers region 2 (ITS2), improving taxonomic classification. This study focused on the groundwater and river mycobiome along an altitudinal and longitudinal transect of a pre-alpine valley in Austria in two seasons. Using Bayesian network modeling approaches, we identified patterns in fungal community assemblages that were mostly shaped by differences in landscape (climatic, topological, and geological) and environmental conditions. While river fungi were comparatively more diverse, unique fungal assemblages could be recovered from groundwater, including typical aquatic lineages such as Rozellomycota and Olpidiomycota. The most specious assemblages in groundwater were not linked to the input of organic material from the surface, and as such, seem to be sustained by characteristic groundwater conditions. Based on what is known from closely related fungi, our results suggest that the present fungal communities potentially contribute to mineral weathering, carbon cycling, and denitrification in groundwater. Furthermore, we were able to observe the effects of varying land cover due to agricultural practices on fungal biodiversity in groundwater ecosystems. This study contributes to improving our understanding of fungi in the subsurface aquatic biogeosphere., (© The Author(s) 2024. Published by Oxford University Press on behalf of FEMS.)