HS10.1

Nonvascular plants like mosses are often overseen; however, they are important players in the soil-atmosphere interface in regard to water exchange. Mosses are especially known for their influence on surface runoff, infiltration, soil water content as well as soil evaporation. Moreover, they can enhance soil moisture by water uptake from dew, vapor or fog. Due to their ability to colonize a variety of different environments, such as temperate, boreal, alpine, arctic and dryland ecosystems, mosses are found all over the world. According to their wide distribution, the impact of mosses on soil hydrology is thus assumed to be of great relevance globally. In particular, the specific influence of different moss species and according soil substrates on water movement has been largely disregarded in this context.

In this study, we examined infiltration, percolation and evaporation patterns in moss-covered soil substrates typical for Central European forests during and after rainfall simulations. Soil substrates were sampled at four sites in the Schönbuch Nature Park in South Germany with different kinds of bedrock with varying soil texture and pH. Additionally, one acrocarpous and four pleurocarpous moss species common in central European forests were examined, either collected in Schönbuch Nature Park or cultivated in the lab. Substrates were filled into metal infiltration boxes (30 x 40 cm) to a height of 6.5 cm and mosses were placed on top of the substrates half a year prior to the experiment for acclimatization and rootage. The experimental setup consisted of duplicates of 6 differently combined soil substrate-moss cover samples. Using biocrust wetness probes (BWP), water content values were calculated from measurements of electrical conductivity during one hour of artificial irrigation and subsequent dehydration for 71 hours. BWPs were located in three positions per sample: a) in 3 cm soil depth, b) at the soil surface, and c) in the moss layer. Electrical conductivity and temperature at each BWP position, as well as air temperature and air humidity, were measured in 10 s intervals during the experiment.

Expecting a relation between infiltration, percolation, evaporation and maximum water content of moss species and soil substrates, we furthermore measured their maximum water storage capacities. As we assumed a high relevance of moss surface area on water storage capacities as well as evaporation rates, we also determined surface and leaf area indices of the studied moss species.

First results show relations between air humidity and moss as well as soil moisture. In addition, we observed different water content trends during percolation, infiltration and evaporation between the studied samples. Maximum water storage capacities differed significantly between the moss species with the loosest and the moss species with the densest structure. Preliminary results indicate that moss surface areas and maximum water storage capacities are not correlated. Since the data analysis is currently still in progress, further results will be presented at vEGU21.

How to cite: Thielen, S. M., Gall, C., Nebel, M., Scholten, T., and Seitz, S.: Soil-Moss-Relations: The path of water from dripping to infiltration, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8390, https://doi.org/10.5194/egusphere-egu21-8390, 2021.

How to cite: Demir, G., Metzger, J. C., Filipzik, J., Fischer, C., Michalzik, B., Friesen, J., and Hildebrandt, A.: Net precipitation assessment in a grassland and soil moisture response at plot scale in a temperate climate, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10038, https://doi.org/10.5194/egusphere-egu21-10038, 2021.

The interception process is an important redistributor of water fluxes, which can considerably affect terrestrial evaporation. Not only the canopy intercepts water, but also from the forest floor significant amounts of water vapor return to the atmosphere. Remaining forests are important areas to evaluate the possible effects of climate change on the water partitioning process. Despite the hydrologic and ecosystem services offered by Cerrado forests, the interception process, as well as climate change threats on the evaporative flux of such forests, are still unknown. This study attempts to anticipate the possible impacts on the forest floor interception process in Cerrado stricto sensu considering future scenarios of climate change. To accomplish this, we used data of field monitoring from June 2017 to February 2020 in an undisturbed Cerrado s.s. forest in São Paulo State, Brazil. We calibrated and validated an improved version of the Rutter interception model (Rutter et al., 1971), which includes interception from the forest floor. Projected climate change scenarios were obtained from the National Institute for Space Research (INPE, Brazil) from 2006 to 2099 with 5km spatial resolution generated by Eta-HadGEM2-ES regional climate model under representative concentration pathway (RCP) 4.5. The results indicate increased rainfall and decreased potential evaporation in the decade 2041-2060. By the Rutter model, the total interception increased for this period (2041-2060) associated with decreased forest floor evaporation. During the first (2006-2020) and the last (2081-2099) decades, the predictions suggest an increase of 2.4% on the average annual percentage of forest floor evaporation, also an increase of minimum annual interception percentages (from 17.1% to 18.7%). Thus, our results demonstrate the relevance of forest floor to the interception process and suggest that it can be even more relevant in the future due to the climate changes.

How to cite: Rosalem, L., Gerrits-Coenders, M., A. A. Anache, J., S. Sone, J., Schwamback, D., Campos, A., and Wendland, E.: Climate change effects on forest floor interception in woody Cerrado ecosystem, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11514, https://doi.org/10.5194/egusphere-egu21-11514, 2021.

Modeling stomatal response to soil drying is of crucial importance for estimating transpiration fluxes. There is a critical need for a better quantification of the impact of soil water limitation on vegetation in order to predict more accurately the impact of climate change on natural ecosystems and adapt agricultural practices.

Recently, we proposed a simple conceptual model, which predicts how soil and plant hydraulics affect transpiration.  This model reconciles soil- and root-based perspectives on drought stress and defines a 3D surface, which represents the maximum possible transpiration rate that can be sustained by a soil-plant system. The shape of this surface shows two distinct zones: a linear zone where the increase of transpiration is proportional to the difference of potential between soil and root and a non linear part in which an increase of E generates a huge decrease of leaf water potential. We show that this nonlinearity is mainly controlled by below ground hydraulic conductance. We hypothesize that plants should avoid this non linear zone by (1) adapting their short term stomatal regulation and (2) ensuring long term coordination between canopy and root hydraulics with growth. It implies that difference in soil hydraulics will lead to contrasted plant hydraulic and structural vegetation properties. Evidences exist at plant scales that this coordination exists. We further discuss how this might affect (agro-)ecosystem-water relations.    

How to cite: Javaux, M. and Carminati, A.: Impact of soil hydraulic properties on water-soil-plant relations, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15969, https://doi.org/10.5194/egusphere-egu21-15969, 2021.

The high tropical Andes ecosystem, known as páramo, provides important hydrological services to densely populated areas in the Andean region. In order to manage these services sustainably, it is crucial to understand the biotic and abiotic processes that control both water quality and fluxes. Recent research in the páramo highlights a knowledge gap regarding the role played by soil-vegetation interactions in controlling soil-water processes and resulting water and solute fluxes.

Here, we determine the hydrological and geochemical fluxes in four soil profiles in the páramo of the Antisana´s water conservation area in northern Ecuador. Water fluxes were measured biweekly with field fluxmeters in the hydrological year Apr/2019- Mar/2020 under two contrasting vegetation types: tussock-like grass (TU) and cushion-forming plants (CU). Soil solution was collected in parallel with wick samplers and suction caps for assessing the concentrations of dissolved cations, anions and organic carbon (DOC). In addition, soil moisture was measured continuously in the upper meter of the soil profile, i.e. first three horizons (A, 2A and 2BC), using water content reflectometers. The vertical water flux in the upper meter of each soil profile was simulated using the 1D HYDRUS model. We carried out a Sobol analysis to identify sensitive soil hydraulic parameters. We then derived water fluxes by inverse modeling, based on the measured soil moisture. We validated the calculated water fluxes using the fluxmeter data. Solute fluxes were estimated by combining the water fluxes and the soil solution compositions.

Our preliminary results suggest that water fluxes and DOC concentration vary under different vegetation types. The fluxmeter data from the 2A horizon indicates that the cumulative water flux under TU (2.8 - 5.7 l) was larger than under CU (0.8 – 1.1 l) during the dry season (Aug-Sep and Dec-Jan). However, the opposite trend was observed in the wet season for maximum water fluxes. Moreover, the DOC concentration in the uppermost horizon was higher under CU (47.3 ±2.2 mg l^-1) than under TU (3.1 ±0.2 mg l^-1) vegetation during the monitoring period. We associate the water and solute responses under different vegetation types to the contrasting soil hydro-physical and chemical properties (e.g., saturated hydraulic conductivity and organic carbon content) in the uppermost soil horizon. Our study illustrates the existence of a spatial association between vegetation types, water fluxes and solute concentrations in Antisana´s water conservation area. By modelling the hydrological balance of the upper meter of the soil mantle, the water and solute fluxes will be estimated for soils with different vegetation cover.

How to cite: Páez-Bimos, S., Vanacker, V., Villacis, M., Calispa, M., Morales, O., Molina, A., Delmelle, P., Lahuatte, B., De Bievre, B., and Muñoz, T.: Linking soil water and solutes fluxes to soil properties and vegetation types: insights from a case-study in the high tropical Andes of Ecuador, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7934, https://doi.org/10.5194/egusphere-egu21-7934, 2021.

Computational Fluid Dynamics (CFD) has been established as a relevant technique to investigate the qualitative and quantitative characteristics of complex environmental flows, such as transient storage zones. In numerical studies involving mass transport of solutes and sediment (e.g., mean retention time and mass exchange rate), one fundamental variable is the turbulent Schmidt number (Sct) which defines the ratio of momentum diffusivity to mass diffusivity in turbulent flows, and thus affects the concentration of solute within the solution impacting on the estimation of mass related variables. This is particularly important for transient storage zones, such as lateral cavities and groyne fields, as they are known for their role in nutrient retention and release, and sediment entrapment. This numerical study aims to examine the influence of the turbulent Schmidt number in the mean retention time and mass exchange rate between a channel and a vegetated/non-vegetated lateral cavity.

The cavity was L = 0.25m long (x-axis), W = 0.15m wide (y-axis) and had a depth of H = 0.10m (z-axis). The aspect ratio between the width and the length resulted in 0.6 which corresponded to a single circulation system (Sukhodolov et al., 2002). The flow had a bulk velocity of U = 0.101 m/s that corresponds to a Reynolds number of 9000. The vegetation drag was represented by an anisotropic porous media calculated with the Darcy-Forchheimer model (Yamasaki et al., 2019), the vegetation density was constant at a = 0.1332%. Large Eddy Simulation (LES) was applied to define the flow field in that domain, using the Wall Adapting Local Eddy-viscosity (WALE) to account subgrid effects. A passive scalar was injected inside the lateral cavity to investigate its transport and diffusion in a range of Sct from 0.1 to 2.0. The numerical results of the flow field were validated using literature experimental data considering 3 different meshes to achieve mesh independence (Xiang et al., 2019).

The effect of Sct variation was, then, analysed in both vegetated and non-vegetated scenarios, for a total of 40 different simulations. The volumetric average scalar concentration in the cavity was fitted into a first-order decay model (C = C₀.e^-t/T_D), where C₀ = 1 is the initial concentration, t  (s) is time and T_D  is the mean residence time. The mass exchange rate was defined as k = W/(T_D.U) . Preliminary results showed in the vegetated scenarios a limited effect of Sct on the mass exchange rate, which varied from 1% if the Sct value was doubled.

References

Sukhodolov, A., Uijttewaal, W. S. J. and Engelhardt, C.: On the correspondence between morphological and hydrodynamical patterns of groyne fields, Earth Surf. Process. Landforms, 27(3), 289–305, doi:10.1002/esp.319, 2002.

Xiang, K., Yang, Z., Huai, W. and Ding, R.: Large eddy simulation of turbulent flow structure in a rectangular embayment zone with different population densities of vegetation, Environ. Sci. Pollut. Res., 26(14), 14583–14597, doi:10.1007/s11356-019-04709-x, 2019.

Yamasaki, T. N., de Lima, P. H. S., Silva, D. F., Preza, C. G. de A., Janzen, J. G. and Nepf, H. M.: From patch to channel scale: The evolution of emergent vegetation in a channel, Adv. Water Resour., doi:10.1016/j.advwatres.2019.05.009, 2019.

How to cite: Oliveira, L., Queiroz, F., Yamasaki, T., Janzen, J., and Gualtieri, C.: Effects of the Turbulent Schmidt Number on the Mass Exchange of a Vegetated Lateral Cavity, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5708, https://doi.org/10.5194/egusphere-egu21-5708, 2021.

Predicting plant responses to drought is a long-standing research goal. Since stomata regulate gas-exchange between plants and the atmosphere, understanding their response to drought is fundamental. Current predictions of stomatal behavior during drought mainly rely on empirical models. These models may suit well to a specific set of plant traits and environmental growth conditions, but their predictive value is doubtful when atmospheric and soil conditions change. Stomatal optimization offers an alternative framework to predict stomatal regulation in response to drought for varying environmental conditions and plant traits. Models which apply this optimization principle posit that stomata maximize the carbon gain in relation to a penalty caused by water loss, such as xylem cavitation. Optimization models have the advantage of requiring a limited number of parameters and have been successfully used to predict stomatal response to drought for varying environmental conditions and species. However, a mechanism that enables stomata to optimally close in response to water limitations, and more precisely to a drop in the ability of the soil-plant continuum to sustain the transpiration demand, is not known. Here, we propose a model of stomatal regulation that is linked to abscisic acid (ABA) dynamics (production, degradation and transport) and that allows plants to avoid excessive drops in leaf water potential during soil drying and increasing vapor pressure deficit (VPD). The model assumes that: 1) stomatal conductance (g_s) decreases when ABA concentration close to the guard cells (C_ABA) increases; 2) C_ABA increases with decreasing leaf water potential (due to higher production); and 3) C_ABA decreases with increasing photosynthesis (e.g. due to faster degradation or transport to the phloem). Our model includes simulations of leaf water potential based on transpiration rate, soil water potential and variable hydraulic conductances of key elements (rhizosphere, root and xylem), and a function linking stomatal conductance to assimilation. It was tested for different soil properties and VPD. The model predicts that stomata close when the relation between assimilation and leaf water potential becomes nonlinear. In wet soil conditions and low VPD, when there is no water limitation, this nonlinearity is controlled by the relation between stomatal conductance and assimilation. In dry soil conditions, when the soil hydraulic conductivity limits the water supply, nonlinearity is controlled by the excessive drop of leaf water potential for increasing transpiration rates. The model predicts different relations between stomatal conductance and leaf water potential for varying soil properties and VPD. For instance, the closure of stomata is more abrupt in sandy soil, reflecting the steep decrease in hydraulic conductivity of sandy soils. In summary, our model results in an optimal behavior, in which stomatal closure avoids excessive (nonlinear) decrease in leaf water potential, similar to other stomatal optimization models. As based on ABA concentration which increases with decreasing leaf water potential but declines with assimilation, this model is a preliminary attempt to link optimization models to a physiological mechanism.

How to cite: Wankmüller, F., Zarebanadkouki, M., and Carminati, A.: A model of stomatal closure driven by nonlinearities in soil-plant hydraulics, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12524, https://doi.org/10.5194/egusphere-egu21-12524, 2021.

Root water uptake (RWU) in grasslands is determined by species composition, climate and soil hydraulic properties. Generally, plant communities are adapted to their environment, showing different rooting patterns along climate gradients. Due to climate change, ecosystems are exposed to shifts in precipitation patterns and rising temperatures, causing the need to adapt rooting strategies. RWU is mainly driven by plant transpiration and soil hydraulic status in the rooting zone. Soil hydraulic properties depend strongly on soil texture, which has been observed to influence rooting depth, increasing the root length from fine to coarse soils. Secondly, precipitation patterns affect the typical soil moisture status, and subsequently the rooting depth. Global models suggest that in dry environments RWU should move deeper, to enhance the plant available soil water. However, few studies have at the same time considered the effect of climate and soil properties on RWU depth, although soil properties vary substantially and probably more than precipitation patterns due to climate change.

Biogeochemical models suffer from uncertainty in subsurface hydrological processes, RWU being an important part of it. Thus, ecohydrological models are needed for an integration in larger context biogeochemical models. The trend of ecological models is towards high parameterized models, implying high uncertainty and challenging calibration for those parameters. Especially in the subsurface, parameters are often unknown and are usually impossible to derive from direct measurements. In this project, a simple, parsimonious bucket model was implemented, solving the water balance equation for a multi-layer soil profile. The objective of this work is to predict maximum required RWU depth required to satisfy potential evapotranspiration across established experimental grassland sites with different climate and soil water retention properties. For this we use soil moisture measurements, textures and hydraulic properties determined in three grassland sites of the Nutrient-Network (NutNet) across a climate gradient. We test the sensitivity of the model towards climate and soil hydraulic parameters. First model results show a high sensitivity of RWU depth besides to dynamics to climate, also to soil water retention determined by texture and organic matter content in the soils.

How to cite: Adamczewski, R., Westermann, S., and Hildebrandt, A.: Modeling root water uptake depth driven by climate and soil texture using a simple bucket model approach, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16434, https://doi.org/10.5194/egusphere-egu21-16434, 2021.

Vegetation establishment, growth, and succession in riparian ecosystems are linked to river and groundwater dynamics. This is especially true in Alpine gravel-bed rivers with wide floodplains and a strong river-aquifer exchange. Here we provide data evidence of riparian plant response to short-term groundwater table fluctuations in a braided gravel-bed river (Maggia). We used indirect physiological variables for photosynthesis and transpiration – stomatal conductance g_s and daily variation in stem diameter ΔD_d – which we measured at six mature riparian trees of the Salicaceae family, one Populus nigra and one Alnus incana specimen at two sites during two growing seasons. The site where g_s measurements were conducted showed a greater depth to groundwater with higher variability compared to the site were dendrometers were placed.

We analysed the data by means of two different random forest regression algorithms for the two study sites. One with the transpiration-induced daily tree diameter drop during the growing season 2017 as the dependent variable, and one with the raw g_s measurement sequence, obtained on 10 days throughout the growing season 2019, as the dependent variable. In both algorithms the independent variables consisted of meteorological measures (locally measured and at valley scale) and of groundwater and river stages near the individual plants. We also separated the g_s measurements into low and high groundwater stage conditions observed during the g_s field campaign and applied traditional regression analysis of g_s on vapor pressure deficit VPD and global radiation r_g for the 2 groundwater stage conditions separately.

The data analyses demonstrate that:

(a) short-term variation of the groundwater table affects riparian vegetation: at the site with deeper groundwater, the water table depth was the best predictor of g_s variability, while at the site with shallower groundwater, temperature and vapor pressure deficit were the best predictors of ΔD_d  variability;

(b) instantaneous stomatal conductance is related to vapor pressure deficit (VPD), but conditioned by groundwater levels, with higher stomatal conductance for the same radiative input and VPD when the water table was higher.

(c) local micro-climate measured at tree locations had a stronger predictive power for g_s than valley scale climate, suggesting local climate may be an important control on vegetated stands on gravel bars.

Even though the considered plants are located in close proximity to the river and could be considered to be unaffected by water stress, our analysis provides evidence of riparian trees undertaking physiological adjustments to transpiration in response to groundwater stage, depending on their riparian floodplain settings. In the heavily regulated Maggia river this has implications on the minimum flow release by dams, as prolonged periods of low water stage in the river will lead to a decrease in groundwater stage, and subsequently in reduced growth of phreatophytic riparian plants on the floodplain. We argue such plant-scale measurements should be helpful for the optimisation of flow release levels in regulated riparian systems.

How to cite: Martinetti, S., Fatichi, S., Floriancic, M., Burlando, P., and Molnar, P.: Near stream groundwater table fluctuations impact transpiration rates of riparian plants: a field study with stomatal conductance and dendrometry measurements, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9899, https://doi.org/10.5194/egusphere-egu21-9899, 2021.

The Italian initiative WATZON (WATer mixing in the critical ZONe) is a network of instrumented sites, bringing together six pre-existing long-term research observatories monitoring different compartments of the Critical Zone - the Earth's permeable near-surface layer from the tops of the trees to the bottom of the groundwater.  These observatories cover different climatic and physiographic characteristics over the country, providing information over a climate and eco-hydrologic transect connecting the Mediterranean to the Alps. With specific initial scientific questions, monitoring strategies, databases, and modeling activities, the WATZON observatories and sites is well representative of the heterogeneity of the critical zone and of the scientific communities studying it. Despite this diversity, all WATZON sites share a common eco-hydrologic monitoring and modelling program with three main objectives:

1) assessing the description of water mixing process across the critical zone by using integrated high-resolution isotopic, geophysical and hydrometeorological measurements from point to catchment scale, under different physiographic conditions and climate forcing;

2) testing water exchange mechanisms between subsurface reservoirs and vegetation, and assessing ecohydrological dynamics in different environments by coupling the high-resolution data set from different critical zone study sites of the initiative with advanced ecohydrological models at multiple spatial scales;

3) developing a process-based conceptual framework of ecohydrological processes in the critical zone to translate scientific knowledge into evidence to support policy and management decisions concerning water and land use in forested and agricultural ecosystems.

This work provides an overview of the WATZON network, its objectives, scientific questions, and data management, with a specific focus on existing initiatives for linking data and models based on WATZON data.

How to cite: Borga, M., Penna, D., Paolo, N., Francesco, C., Ferraris, S., Rigon, R., Allocca, C., Amin, A., Bertoldi, G., Brighenti, S., Canone, D., Cassiani, G., Censini, M., D'Amato, C., Fabiani, G., Gentile, A., Marchina, C., Romano, N., Luisa, S., and Giulia, Z.: WATZON: the Italian network of ecohydrology and critical zone observatories, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16287, https://doi.org/10.5194/egusphere-egu21-16287, 2021.

Water limitation provides the potential to hinder the productivity of agricultural systems especially in arid and semi-arid regions. In agroforestry systems interactions between trees and crops range from mutually beneficial to critically competing, shaping the demand for resources, such as water. In this study, we investigated the hydrological effects of an Italian Alder (Alnus cordata) windbreak on an irrigated blackberry plantation near Stellenbosch, South Africa. We determine the key components of the water budget in the system and compare them at two positions: alongside the windbreak, and amongst the crop away from the windbreak’s influence.

We measured soil water content depth profiles in the summer months, from October 2019 to March 2020, in both locations with four consecutive time domain reflectometry (TDR) tube sensors, each integrating over 20 cm depth. Potential evapotranspiration (ET) was estimated from site based meteorological observations. We surveyed and classified the local soil, and defined soil chemical and physical properties (e.g. texture, matrix potential). The windbreak structure was measured on a single tree basis (e.g. tree height, volume and biomass) using manual and terrestrial laser scanning methodologies.

The data indicate that high potential ET, caused by high summer temperatures and strong winds, dominates the water budget at the study site, exceeding the water input of the drip irrigation. We found differences in the water dynamics between the two sites, e.g. greater soil water content at greater distances from the windbreak. Possible reasons are: (1) the water demand of trees increases underground competition for water, and/or; (2) microclimatic conditions closer to the windbreak increase ET. Modelling of the windbreak influence on the ET and further analysis of water fluxes will be conducted as next steps to combine the results from the sensors and the joint field campaign.

How to cite: Hoffmeister, S., Bohn Reckziegel, R., Kestel, F., Maier, R., Sheppard, J. P., and Hassler, S. K.: Hydrological effects of combining Italian alder and blackberry in an agroforestry system in South Africa, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2879, https://doi.org/10.5194/egusphere-egu21-2879, 2021.

Mixed species forest stands have been advocated over monoculture stands for afforestation around the globe as they can be more resilient to pests and diseases. However, in arid and semi-arid regions, whether such forests are suitable for future climate conditions remains to be addressed. The overall objective of this study is to analyze ecohydrological processes of indigenous, drought-tolerant tree species in a Mediterranean mixed plantation forest. The specific objectives are i) to quantify transpiration of pine (Pinus brutia) and cypress (Cupressus sempervirens) trees and ii) to analyze the effects of environmental variables (meteorology and soil moisture) on transpiration. The study site is located in Athalassa Forest Park, in Cyprus. The site has a surface area of 10 ha with an average slope of 4%. Average annual rainfall is 315 mm with a mean daily minimum temperature of 5° C during winter and a mean daily maximum temperature of 37° C during summer. The site was converted in 2011 from rainfed agriculture to a mixed forest by planting seedlings of different tree and shrub species. The study site is located on two sedimentary formations: Athalassa (calcarenites interlayered with sandy marls) and Nicosia (siltstones and layers of calcarenites). Soil depths up to 1 m can be found on top of the impervious and semi-pervious strata. 

The research field was stratified in two spatial geological units (strata). In each stratum, two P. brutia and two C. sempervirens trees were randomly selected (total eight trees) for sap flow monitoring with sensors (heat ratio method) attached to the tree trunks. In addition to the random trees, two representative (one per species) neighboring trees were selected where sap-flow sensors were installed and mid-day leaf water potential (pressure chamber) and stomatal conductance (porometer) were measured. Forty-five soil moisture sensors were installed between the representative trees at depths of 10 cm, 30 cm and 50 cm.

Data from November 2020 to January 2021 indicated that mean sap flow rate per tree (cm³ h^-1) is higher for C. sempervirens (min: 161, max: 503) than P. brutia (min: 68, max: 266). Total rainfall during these months was 88 mm, most of which fell in three main rainfall events (between 20 and 30 mm per event). Mean soil moisture before rain (15-day average) was 5% for all soil depths. After the rain, soil moisture was 12% for 10 and 30 cm depths and 8% for 50 cm. The increase in soil moisture resulted in 1.6 times higher transpiration for C. sempervirens and 1.4 times higher transpiration for P. brutia. The leaf water potential of C. sempervirens increased from -2.6 MPa before the rain to -0.8 MPa after the rain, whereas it remained near -0.5 MPa for P. brutia. This research of the different plant water-use strategies can contribute to an improved selection of species for afforestation in arid and semi-arid regions.

This research has received support from the Water JPI (Joint Call 2018) FLUXMED Project, funded through the Cyprus Research and Innovation Foundation.

How to cite: Djuma, H., Bruggeman, A., Eliades, M., Venetsanou, P., Zoumides, C., and Siakou, M.: Transpiration rates of pine (Pinus brutia) and cypress (Cupressus sempervirens) trees in a Mediterranean mixed plantation forest, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9525, https://doi.org/10.5194/egusphere-egu21-9525, 2021.

Vegetation strongly affects the water cycle, and the interactions between vegetation and soil moisture are fundamental for ecological processes in semiarid regions. Therefore, characterizing the variation in soil moisture is important to understand the ecological sustainability of cropping systems towards food security. The present study aims at exploring factors and mechanisms influencing soil moisture variability in the Faidherbia albida (FA) parkland at Sob basin located in the center of Senegal [1]. Volumetric soil moisture content at multiple depths was monitored at 15 locations distributed along a transect (upper slope, mid-slope and lower slope) and different FA tree position (under, at the limit and outside canopy) from August to October 2020. A portable TRIME Time Domain Reflectometry (TDR) Tube Probe (IMKO, Germany) was used to determine soil volumetric moisture content while being placed at specific depth intervals inside a PVC access tube set up at each location. Soil moisture was monitored at 10 cm interval from 20 to 420 cm during the rainy season from July to October 2020. Results of soil moisture profiles along the transects exhibit two main zones based on the standard deviation (SD) and the inflection of the coefficient of variation (CV): shallow soil moisture (SSM) and deep soil moisture (DSM). For SSM observed at 20-60 cm of the soil layer, both mean soil moisture and SD increase with depth, the lowest mean value (8%) being observed at the top surface. This soil layer is influenced by rainfall infiltration and daily evaporation. For DSM observed at 70-420 cm, the moisture pattern can be further divided into 4 soil sublayers taking the mean soil moisture vertical distribution as reference: (i) a rainfall infiltration layer (70-160 cm) which appears mainly influenced by cumulative rainfall infiltration in addition to transpiration of grassland and crops (shallow root system); (ii) a rainfall-transpiration layer (170-250 cm) which is still an infiltration layer but more influenced by crops transpiration; (iii) a transpiration layer (260-350 cm) which can be recharged by rainfall infiltration during heavy rainfall and supply deep root system; and (iv) deep transpiration layer (360-400 cm) which has DSM that can be influenced by extremely deep root vegetation such as FA. The factors influencing the soil water content varied with the topography. The soil water content SWC (mean and median value of 27.2 and 29.6% respectively) in the lower slope was significantly higher than that at middle (mean and median value of 14.4 and 13.2 % respectively) and upper slope (mean and median value of 16.8 and 18.4 % respectively). At last, soil water content was positively correlated with the distance from the FA, regardless the slope. The higher water content for both SSM and DSM was observed outside the FA canopy. This result refutes the initial hypothesis of higher SWC under trees and support a more detailed analysis of the infiltration capacity in relationship with the FA position.

How to cite: Diongue, D., Orange, D., Faye, W., Roupsard, O., Do, F., Jourdan, C., Stumpp, C., Fall, A. N., and Faye, S.: Influence of trees and topography on soil water content in semi-arid region, the case of an agro-silvo-pastoral ecosystem dominated by Faidherbia albida (Senegal), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9060, https://doi.org/10.5194/egusphere-egu21-9060, 2021.

Two important threats to the sustainable functioning of seminatural grasslands in temperate zones are (1) nutrient loading due to agricultural fertilization and pollution, and (2) the increase of extreme drought events due to climate change. These threats may cause substantial shifts in species diversity and abundance and considerably affect the carbon and water balance of ecosystems. The synergistic effects between those two threats, however, can be complex and are poorly understood. Here, we experimentally investigated the effects of nitrogen addition and extreme drought (separately and in combination) on a seminatural temperate grassland, located in Freiburg (South Germany). To study the grassland response, we combined eddy-covariance techniques with open gas exchange systems. Open gas exchange chambers were connected to an infrared gas analyzer and water isotope spectrometer, which allowed the partitioning of net ecosystem exchange and evapotranspiration. In addition, leaf level physiological responses, e.g. leaf gas-exchange and water potentials, as well as vegetation parameters, e.g. species richness, species abundance, leaf area index, were assessed.

Our results suggest that grassland communities, strongly weakened in their stress response by nitrogen loading, can substantially lose their carbon sink function during drought. Over the growing season (April-September), the carbon sequestration of the studied grassland was reduced by more than 60% as a consequence of nitrogen addition. Nitrogen addition in combination with precipitation reduction decreased carbon sequestration by 73%. We observed more efficient N utilization in grasses compared to forbs. However, these clearly specific responses of the different functional groups to N loading, both functional groups were able to maintain homeostasis of leaf carbon and water fluxes. Thus, strong declines in the (community) carbon sequestration and water use efficiency were not related to leaf physiological responses in assimilation and transpiration. Instead, nitrogen addition caused a significant loss in forb species (−25%) and precipitation reduction promoted a strong dominance of grass species at season start. Consequently, the resulting grass-dominated and species-poor community suffered from a strong above-ground dieback during the dry summer months, likely caused by lower water use efficiency and weaker drought adaptations of the species community. 

Eutrophication can severely threaten the resilient functioning of grasslands, in particular when drought periods will increase as predicted by future climate scenarios. Our findings emphasize the importance of preserving high diversity of grasslands to strengthen their resistance against extreme events such as droughts.

How to cite: Dubbert, M., Kübert, A., Piayda, A., Werner, C., and Rothfuss, Y.: Impact of combined nitrogen loading and long-term drought on a semi-natural temperate grassland - achieving a process based understanding across scales, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8048, https://doi.org/10.5194/egusphere-egu21-8048, 2021.

Combating eutrophication requires holistic mitigation measures aimed at reducing agricultural losses of nitrogen (N) and phosphorus (P) from field sources to aquatic systems. This need will become critical in the future as increased flashiness, expected from changing climate and growing food demand, will further accelerate N and P pollution. Agricultural headwater streams are the main entry point of diffuse nutrient and particulate losses to stream networks. These streams are often channelized with a trapezoidal design, which effectively convey excess water from fields but also nutrients and soil particles to recipient water bodies. In addition, trapezoidal ditches with steep stream banks are sensitive to erosion and require routinely dredging to maintain their drainage function.

This project will advance the knowledge of processes governing nutrient and sediment retention in agricultural streams in Sweden by focusing on two-stage ditches (SDs) which are new type of mitigation measure. In SDs, the stream channel is surrounded by incised floodplains that increase the hydrological connectivity between stream and riparian zone during high flows. When floodplains are inundated, water residence time increases which allow deposition of suspended particles and biogeochemical processing of nutrients and organic matter. With slower water velocities in SDs at high flows, bank erosion may also be minimized. Existing studies in the US and Finland have found that SDs can mitigate N, P and sediment losses, compared with traditional trapezoidal ditches. This project is the first of its kind to evaluate the efficiency and stability of 10 different SDs in Swedish conditions over 3 years, situated in catchments with diverse agricultural land use and soil characteristics.

In this presentation, we show the details of experimental setup and preliminary results. A sampling has been setup in SD reaches to monitor seasonal sedimentation rate and aggradation since construction. This is coupled with both low- and high-frequency water quality monitoring and measurements of nitrogenous gas emissions from denitrification in sediments. We discuss the success factors in terms of placement and design of SDs to enhance ecosystem functions (self-purification, erosion and flood prevention). These factors determine SDs’ effectiveness in retention of water, N, P and sediments and their suitability as mitigation measure.

How to cite: Hallberg, L. and Bieroza, M.: Improving understanding of hydrological and biogeochemical processes controlling the effectiveness of two-stage ditches in reducing eutrophication, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13103, https://doi.org/10.5194/egusphere-egu21-13103, 2021.

Turloughs, the focus of this study, are ephemeral lakes and they are mostly groundwater dependent. They are present mostly in Ireland and have been compared hydrologically to polje for the period inundation and lacustrine deposits. They are flooded for some periods across the year (typically in the winter) but usually dry up in summer months. Turloughs are protected under the Water Framework Directive (WFD, Directive 2000/60/EC) and the EU Habitats Directive (92/43/EEC). Ecosystem services can be defined as the conditions and processes through which natural ecosystems sustain and fulfil human life. These can be classified as provisioning, regulating, and cultural and examples of them are water and raw materials production, flood risk attenuation, carbon sequestration. The determination of the ecosystem services can help analyse different scenarios linked to pressures like road drainage schemes, water supply and wastewater disposal.

Seven turloughs (Blackrock, Lough Coy, Lough Aleenaun, Lough Gealain, Caranavoodaun, Skealoghan, Coolcam) have been selected from a previous study and samples of waters were collected monthly to determine carbon and nutrients. Carbon and nutrients were also determined on soil samples taken from the turlough catchment. The overwhelming majority of wetlands act as long-term sinks for CO₂. To determine whether this is the case for some of the turloughs in the study, greenhouse gases from soils and water were monitored and balances were worked out. Ecosystem services were quantified through various models which had to be adapted to the special conditions present in the turloughs.

The seven turloughs have different hydrological characteristics. Hydrology is the main driver of vegetation distribution therefore ommunities are distributed in zones arranged along the flooding gradient. Aquatic invertebrates also show a succession of communities through the hydroperiod.

The seven turloughs studied provide a variety of hydrological characteristics, habitat, soil and vegetation and offer different ecosystem services. Each ecosystem service was quantified using appropriate models. Almost all the turloughs are at risk from anthropic activities and potentially from climate change. Important ecosystem services for these turloughs are flood mitigation, nutrient retention, carbon sequestration, habitat preservation and recreational activities.

How to cite: Delle Grazie, F. M. and Gill, L.: Ecosystem services provided by groundwater dependent wetlands in Irish karst, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4082, https://doi.org/10.5194/egusphere-egu21-4082, 2021.

Mediterranean temporary ponds are very shallow ponds, isolated from permanent water bodies, which undergo a periodic cycle of flooding and drought, and have a characteristic flora and fauna adapted to this alternation. This habitat is mainly distributed in dry and sub-arid areas. Mediterranean temporary ponds are identified as one of the worldwide biodiversity hotspots and constitutes therefore a priority habitats according to the Natura 2000 network of the European Union (3170*, Council Directive 92/43/CEE). The development of flora and fauna in this type of ecosystem is defined by the natural length of the hydro-period. However, little is known about the hydrological functioning of these very specific hydrosystems. DespiteHS10 this protective conservation status, this habitat has suffered continuous degradation and loss disappearing at a fast rate due anthropogenic impacts and climate pressures. In most cases, temporary wetland disappearance is unintentional and related to a lack of understanding of its hydrological functioning within the watershed.

The aim of this work is, hence, to use the tools of the isotope hydrology to increase our basic understanding of the hydrological functioning of the Mediterranean temporary ponds. Our study focuses on the Musella temporary pond located in Southern Corsica (France) which undergoes important man-induced and climatic pressures. During one full hydrological cycle, surface and groundwater levels, major ions, stable isotopes of the water molecules as well as field parameters (temperature, pH, electrical conductivity, dissolved oxygen) have been measured every month.

Results bring information on the water quality, chemical stability and temporal evolution in terms of surface water level as well as potential connection with the underlying carbonated aquifer. The stable isotopes inform about the origin of water, its mixing processes with groundwater, and its evaporative status through time.

Flooding and drying processes of the Musella temporary pond are now better constrained and documented projections can now be set up towards the resilience of the hydrosystem considering the future consequences of climate change in the Mediterranean region.

How to cite: Mattei, A., Sorba, L., Garel, E., Santoni, S., Orsini, S., and Huneau, F.: Mediterranean Temporary Ponds: using isotope hydrology tools to describe and understand their behaviour, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2795, https://doi.org/10.5194/egusphere-egu21-2795, 2021.

In carbonate rock regions, the bedrock compositions strongly influence regolith properties that, in turn, might play the primary role in plant growth and hydrological processes. Since bedrock experiences uneven weathering processes due to different regolith materials in a karst area, how hydrological functions of bedrock layer and overlying vegetation rely on the bedrock weathering degree is seldom investigated. The objectives of this study are to quantify the impacts of climate change and reforestation on runoff in a watershed with two main bedrocks (dissolvable carbonate rock in karst area and detrital rock in non-karst area) in southwest China. The analyses are firstly executed by decomposion of the hydro-meteorological series into two series (T1, 1992-2003 and T2, 2004-2015), which have different hydro-meteorological responses due to reforestation. This study investigates the impacts of climate change and reforestation on runoff using two approaches: the sensitivity-based approach (Budyko hypothesis) is applied to estimate the overall watershed change in runoff attributed to human activities and climate change, and a distributed hydrological model based on simple soil water balance routing is used to estimate change in runoff and hydrographs in the two main bedrock areas. The results show that the hydrological modelling overestimates climate induced decrease of streamflow (88.6%), compared to estimated result by the Budyko formula (76.6%). The decrease of mean precipitation from T1 to T2 in the non-carbonate area is very close to the carbonate area, the proportion of the climate change induced decrease of streamflow in the non-carbonate area (86.3%) is less than the carbonate area (90.5%), indicating that the drier climate tendency takes a greater effect on decrease of streamflow in the carbonate area than the non-carbonate area. By contrast, there is a greater alteration of land cover/use in the non-carbonate area than the carbonate area. These findings will help develop a better understanding of the impact of climate change and reforestation on runoff in southwest China.

How to cite: Cai, L., Chen, X., and Zhang, Z.: Streamflow change induced by climate change and vegetation recover in a karst region of southwest China, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3629, https://doi.org/10.5194/egusphere-egu21-3629, 2021.

Water courses that recurrently cease to flow represent a large part of drainage networks, and are expected to expand with global warming and increased exploitation of water resources. Common classifications of the regime of these temporary streams are based on the statistics of zero flow events. This is partly practical because these statistics can be obtained from flow records or model simulations and the results can be used for some environmental regulations or management purposes.

Nevertheless, it is well known that the main hydrological control on riverine aquatic life is the presence-absence of water rather than its flow regime. Disconnected pools that frequently remain in temporary streams after flow cessation provide valuable refuges for aquatic life, which can last up to all year round. An operational characterisation of the hydrological regime of temporary streams useful for ecological purposes must therefore take into account at least the three main aquatic phases that they undergo: flow, disconnected pools and dry stream bed. However, gauging stations and the derived hydrological models may only marginally inform about the possible occurrence of disconnected pools after the cessation of flow.

In order to facilitate the implementation of the European Water Framework Directive to the temporary streams, an operational approach has been developed to describe and classify the regime of temporary streams and to assess their degree of hydrologic alteration, relevant to aquatic life. This approach is encapsulated in the freely available TREHS software. The first step of this approach is the gathering of information on the frequency of the three aquatic phases using diverse sources of information, such as flow records and simulations, in situ observations, interpretation of aerial or terrestrial series of photographs, and interviews with local inhabitants or technicians familiar with the riverine systems. Up to six metrics describing these frequencies and their temporal patterns of occurrence are used to determine the natural and observed stream regime, and to assess the degree of hydrological alteration.

The combination of the complementary frequencies of the three main aquatic phases allows the description of the regime of every stream as a point in a ternary plot, where the three vertices of the triangle represent the perennial streams, the perennial pools and the terrestrial systems, respectively. This ternary plot assists the classification of the regime of any stream that takes into account the statistics of the main proxies of the occurrence of aquatic habitats. The TREHS software also provides a classification of the regimes in the ternary plot that groups the regimes of assumed ecological significance and uses terms that are conflict-free from the current classifications. Furthermore, TREHS users can easily define new regime classes in this plot according to the ecohydrological characteristics of their streams.

How to cite: Gallart, F., Cid, N., Llorens, P., Latron, J., Bonada, N., Soria, M., and Prat, N.: An operational method for the ecohydrological classification of temporary rivers and streams, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4360, https://doi.org/10.5194/egusphere-egu21-4360, 2021.

Salinizing surface water is a large problem worldwide. In many areas agriculture is dependent on surface water irrigation, but there is an increasing fresh water scarcity. Due to natural and anthropogenic processes the salt concentration of surface water has risen and this problem is predicted to increase in the future. Prioritizing on when fresh water is needed and when brackish or salt water could be possible is therefor necessary. However, this holds not only for agricultural systems, but also for natural areas which are currently overlooked. In deltaic areas – such as The Netherlands – sea water is flowing further inland via rivers during summer. In addition to this, in the hinterland, artificial drainage of low-lying polders leads to a salt groundwater surplus that is discharged into rivers and surface water reservoirs. These processes lead to salinization and could potentially affect plant biodiversity and ecosystem functioning in surface water fed ecosystems, wetlands, and riparian zones. One of such a surface water fed ecosystems is an abandoned turf extraction site ‘De Botshol’ in The Netherlands. Floating root mats have developed from peat baulks into the open water of old turf ponds. These mats can harbor a great deal of protected terrestrial, typically glycophyte (i.e. optimally encountering < 300 mg Cl.l-1), plant species related to a floating fen habitat. Currently the surface water quality of Botshol is brackish and this provided us with an opportunity to follow the local salt route through space and time. Surface water salt concentrations fluctuated slightly between winter-spring: 1400 mg Cl.l-1 and summer-autumn: 1900 mg Cl.l-1 and we linked this to root zone processes and the plant community. We used a pore water extraction setup using micro- and macrorhizons placed at 30 – 60 – 200 cm from the edge of a floating root mat. Along this transect we measured at 10 – 25 – 50 – 70 cm depth. Via this setup we were able to find that the root zone salt concentrations fluctuated with surface water concentration, however there was a substantially lower salt concentration in the soil layer. Root zone concentrations still reached above 500 mg Cl.l-1 and this might explain differences in community composition in comparison with a fresh floating fen ecosystem (e.g. ‘Nieuwkoopse Plassen’, The Netherlands). We present this work to empirically link hydrology and ecology in relation to surface water salinization, but also to practically inform water boards and nature managers to understand possibilities and limitations of surface water salinization in relation to fen restoration and protection.

How to cite: Huizinga, M., Aerts, R., van Logtestijn, R. S. P., van der Zee, S. E. A. T. M., and Witte, J.-P. M.: The salt route through time and space: Following horizontal and lateral intrusion of brackish surface water into a natural floating root mat and its plant community., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13391, https://doi.org/10.5194/egusphere-egu21-13391, 2021.

The interplay between riparian vegetation and water flow in vegetated water bodies has a key role in the dynamic evolution of aquatic and terrestrial ecosystems in wetlands and lowlands. The present study analyzes the effects of the spatial distribution of reed (Phragmites australis (Cav.) Trin. ex Steud.) beds, an invasive riparian species extremely widespread in wetland and lowlands worldwide, on the main hydraulic and hydrodynamic properties of an abandoned vegetated reclamation channel located in Northern Tuscany, Italy. A field campaign was carried out to obtain Leaf Area Index (LAI) and Normalized Difference Vegetation Index (NDVI) of reed beds through both ground-based and Unmanned Aerial Vehicle (UAV) methodologies, and to correlate them to the channel’s flow dynamic and water quality main features. Then, Hydrodynamic simulations of the vegetated reclamation channel were performed and validated based on the experimental measurements of the hydraulic and vegetational parameters acquired in the field to build up a robust model to be employed also in future Ecohydraulic researches. The evidences of this study constitute useful insights in the quantitative analysis of the correlation between the spatial distribution of riparian vegetation stands in natural and manmade vegetated water bodies and their hydrodynamic and water quality main features.

How to cite: Lama, G. F. C.: The effect of reed beds distributions on the Ecohydraulic dynamics of wetlands and lowlands: experimental analyses and simulations, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-558, https://doi.org/10.5194/egusphere-egu21-558, 2021.

Ephemeral pools are geographically isolated wetlands commonly found in temperate forests of northeastern North America. These wetlands are usually hydrologically isolated from the surface water network but in some conditions can be connected to local groundwater flow. They fill at maximal capacity following spring snowmelt and dry out during summer. They contribute to forest biodiversity by providing breeding habitats for amphibians during their spring and early summer period of hydrological activity. However, ephemeral pools are poorly understood and rarely studied because of their small dimensions and temporary hydrology. This work presents the final results of a five-year study aimed to acquire new knowledge on ephemeral pool hydrology to go beyond the anecdotical pool and to understand the conditions and processes that driving their hydrology. A large number of pools (39) located in the Canadian Shield forest were instrumented to monitor hourly water level variations in the pool and in the neighboring and underlying fractured bedrock aquifer. They were also described in extensive details for their geomorphological features and water levels over a period from one to five years (April 2016 to July 2020). The first rather surprising result from this work is that, although the pools are all located in bedrock depressions, they cover a wide range of morphologies. Their maximum sizes vary from 29 to 1866 m² and their maximal volumes vary from 4 to 654 m³. Their maximum water depths are also highly contrasted, ranging from 0.14 m to 2.03 m. The pool depressions are overlain by mineral sediments (silt to fine sand with occurrences of coarse sand and gravel) of contrasted thicknesses (0 m to 1.70 m). An organic matter layer of highly varying thickness (0.12 m to 1.24 m) was observed at all sites above the mineral sediments. Despite these varied morphological conditions, all the pools have similar hydrological patterns throughout the year and these patterns are highly resilient to meteorological conditions. They dry out between the end of May and the end of July, rapid temporary refilling during important summer rainfall events, and partially refilling in autumn following more frequent rainfall events and lower evapotranspiration. The results show that surface water levels are maintained when the underlying sediments are saturated. Otherwise, the ephemeral pools lose water by infiltration to the underlying aquifer. Water level variations within the pools are positively and significantly correlated with net precipitation (P – PET). Hydroperiods vary between 28 days (2020) and 86 days (2017), reflecting the year-to-year meteorological variability. The mean hydroperiod is significantly correlated to spring rainfall (April to June), but also to the volume of water stored in the pool, and to the pool surface area. This study provides a unique and original dataset that contribute to better understand the hydrodynamics and resilience to anthropogenic (forestry) and natural (climate change) impacts of a wetland type that is rarely studied but provide crucial habitats for forest biodiversity.

How to cite: Roux, M., Larocque, M., Nolet, P., and Gagné, S.: Influence of morphometric parameters and meteorological conditions on ephemeral pool hydrology in the Canadian Shield forest, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12564, https://doi.org/10.5194/egusphere-egu21-12564, 2021.