Trees affect the direction and distribution of crucial components of the hydrological cycle, which were mostly described by measurements on the quantity of precipitation, stemflow and throughfall (TF) collected underneath the canopy. However, due to poor accessibility of tree canopies, our knowledge on hydrological processes within canopies is limited. 

We propose that canopy structure shapes the spatial distribution of incoming rainfall (RF) within the canopy as well as the intra-canopy TF composition. The Leipzig Canopy Crane facility allows to (i) determine water fluxes from above the canopies (RF) and with TF at top, mid and bottom position within the canopy of three tree species – Quercus robur, Fraxinus excelsior, and Tilia cordata, and (ii) to determine the transport of dissolved and particulate organic carbon and nitrogen with TF. In total, 81 TF collectors were set up every month for a two-weeks-period from March to October 2021.

We found amplified water fluxes in TF collectors at top and mid canopy positions compared to incoming RF fluxes, while TF volumes at the bottom decreased. Dimensions of change appear related to RF amount and tree species. Moreover, stability plot analysis indicated that spatial “hot spots” of water fluxes within canopies were temporally persistent.

Our results raise the question whether the concept of a “double-funneling of trees” introduced by Johnson and Lehmann (2006) needs to be extended to a “triple-funneling” approach involving the intra-canopy preferential flow of water and elements occurring in upper to mid canopy positions. Canopy spots with higher water and matter accumulation will alter the chemical, biological, and hydrological heterogeneity in canopy habitat structures below, with strong implications for canopy-associated microbial communities and epiphytes and ecosystem functions.

How to cite: Michalzik, B., Tischer, A., Zerhusen, P., Richter, R., Engelmann, R. A., Küsel, K., Wirth, C., and Herrmann, M.: Triple-funneling of trees? Intra-canopy preferential flow of water and elements induced by tree canopies, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6330, https://doi.org/10.5194/egusphere-egu23-6330, 2023.

It is well known that stemflow contains soluble carbohydrates. While neutral sugars play an important role in tree metabolism, data on the concentrations of neutral sugars in stemflow are scant. Neutral sugar inputs via stemflow could influence soil solution chemistry and microbial activity in near-trunk soils. Accordingly, to fill the existing knowledge gap, this study quantifies stemflow neutral sugar concentrations with respect to tree species and phenophase. The concentrations of L-rhamnose, D-glucose, D-mannose, D-galactose, L-arabinose, and D-xylose in stemflow were determined using orbitrap liquid chromatography-mass spectrometry as a function of both tree species (Betula lenta L. [sweet birch], Fagus grandifolia Ehrh. [American beech], Liriodendron tulipifera L. [yellow poplar], and Pinus rigida Mill. [pitch pine]) and phenophase (emergence, leafed, senescence, leafless for deciduous species and emergence, leafed-spring/summer, senescence, leafed-winter for pine). Overall, the median concentrations for all sugars were higher for yellow poplar and pitch pine, and by phenophase, the leafless (or leafed-winter) phenophase had the highest (galactose, arabinose/xylose) or second highest (rhamnose, glucose, mannose) median concentrations for all sugars. We recommend the quantification of neutral sugar concentrations and fluxes in studies seeking a more comprehensive understanding of the physiological ecology of wooded ecosystems.

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Funding note: This research was supported by funds from the US National Science Foundation (Award No. GCR-CMMI-1934887).

How to cite: Levia, D. F., Chang, J. L., and Epps, III, T. H.: The concentration of neutral sugars in stemflow with respect to tree species and canopy phenophase, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3577, https://doi.org/10.5194/egusphere-egu23-3577, 2023.

Soil erosion induced by rainwater in forest ecosystems is mainly determined by throughfall kinetic energy (TKE) and ground vegetation cover. TKE is determined by raindrop size and velocity as well as precipitation amounts. Lateral canopy water flow paths can create localized concentrations of throughfall as impact points with considerable high TKE. At structurally mediated woody surface drip points notably bigger canopy drips can thus be formed under forest canopy. It is also assumed that TKE per 1mm rainfall amount (i.e., unit TKE) at impact locations is considerably higher than that at general locations due to increased rain drop sizes, resulting in a higher risk of soil erosion. However, the TKE and subsequent splash erosion potential at these impact locations have rarely been described in the previous literature and have not been quantified yet. The objectives of this study are (1) to evaluate the intensity of TKE and unit TKE at an impact location and (2) to compare those with general locations and freefall kinetic energy. We measured TKE using splash cups at seven points under a beech tree in a cool temperate forest, Japan, during five rainfall events in each leafed and leafless season. Five splash cups were further installed at an open area outside the forest as a reference. A rainfall collector was installed next to each splash cup, and throughfall at each point was quantified. TKE at the impact location (9142 ± 5522 J m^-2) was 15.2 times higher than that at general locations under beech (601 ± 495 J m^-2) and 49.7 times higher than at the open area (184 ± 195 J m^-2). The ratio of TKE at the impact location to those at general locations was higher in the leafless season. Unit kinetic energy at the impact location (39.2 ± 23.7 J m^-2 mm^-1) was higher than those at general locations (22.0 ± 12.7 J m^-2 mm^-1) and at the open area (4.5 ± 3.5 J m^-2 mm^-1). The branch height at the impact location was lower than most areas at general locations, suggesting that higher unit TKE was induced by a bigger drop size. Our results imply that big-sized canopy drips in addition to intense throughfall amount generated at specific structurally-mediated points of the branch surface contribute far above the average to the erosion potential under the forest.

How to cite: Katayama, A., Nanko, K., Jeong, S., Kume, T., Shinohara, Y., and Seitz, S.: Concentrative drop impacts by a bunch of canopy drips: hotspots of soil erosion in forest, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1767, https://doi.org/10.5194/egusphere-egu23-1767, 2023.

The capture of colloidal fine suspended particles by vegetation plays an important role in water quality of the shallow aquatic system under rainfall. Quantifying impact of rainfall intensity and vegetation condition on this process remains poorly characterized. In this study, the colloidal particle capture rates under three rainfall intensities, four vegetation densities and with submerged or emergent vegetation were investigated in different travel distance in a laboratory flume. Considering vegetation as porous media, non-Darcy’s law with rainfall as a source term, was coupled with colloid first-order deposition model, to simulate the particle concentration changes with time, determining the particle deposition rate coefficient (k_d), representing capture rate. We found that the k_d increased linearly with rainfall intensity; but increased and then decreased with vegetation density, suggesting the existence of optimum vegetation density. The k_d of submerged vegetation is slightly higher than emergent vegetation. The single collector efficiency (η) showed the same trend as k_d, suggesting colloid filtration theory well explained the impact of rainfall intensity and vegetation condition. Flow hydrodynamic enhanced the k_d trend, e.g., the theoretical strongest flow eddy structure represented in the optimum vegetation density. This study is helpful for the design of wetland under rainfall, to remove colloidal suspended particles and the hazardous material, for the protection of the downstream water quality.

How to cite: Yu, C.: Capture of colloidal fine suspended particle by aquatic vegetation under rainfall, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5699, https://doi.org/10.5194/egusphere-egu23-5699, 2023.

Throughfall constitutes the majority of water  entering most forest ecosystems' root zones. Previous studies showed that throughfall patterns are temporally stable and influence soil moisture response to rainfall. However, their impact on soil water distribution ceases rapidly. The spatial variation in root water uptake was proposed as a reason for this decoupling throughfall and soil water patterns, but,  to the best of our knowdeldge experimental evidence is lacking. Therefore, we investigated root water uptake patterns with comprehensive field observations in an unmanaged forest site in the 2019 (April-August) growing season. The research site (1 ha) is a part of Hainich CZE in Thuringia, Germany. In the site, the tree community consists of 574 individuals of various ages (diameter at breast height ≥ 5cm). The European beech dominated site also hosts other temperate species such as Sycamore maple, European ash, and Norway maple. The field observation setup was composed of closely paired (within 1 m) throughfall and soil water content measurements at 34 locations. While soil water content was recorded every six minutes, throughfall was measured weekly. Moreover, we measured open rainfall in an adjacent open grassland (distance 250 m)  at the same time as  throughfall .

We derived root water uptake at each location from diurnal variations within the soil moisture time series. While daily average transpiration ranged between 0.9 mm d and 3 mm potential evapotranspiration changed between 1.8 mm and 3.1 mm. Further, we applied a linear mixed-effect model to identify controlling factors for horizontal patterns of root water uptake throughout the growing season. We found that temporally stable throughfall patterns do not influence root water uptake patterns. Instead, soil water distribution and vegetation features significantly influence local water uptake. We show that greater local soil water storage promoted root water uptake, slightly modulated by field capacity. Further, seasonally declined soil water storage, on average, likely shifted water extraction depth to deeper layers. A higher number of species is also related to higher root water uptake, which possibly signifies water competition among trees. Our findings suggest that elevated throughfall is neither taken up by roots nor retained in the soil matrix, probably due to local processes such as fast flow. Ultimately, the soil water availability and adaptation of co-existing trees to changes in accessible water storage regulate root water uptake patterns.

How to cite: Demir, G., Guswa, A. J., Filipzik, J., Metzger, J. C., and Hildebrandt, A.: Drivers of root water uptake patterns in a beech-dominated mixed forest, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9508, https://doi.org/10.5194/egusphere-egu23-9508, 2023.

Temperate hardwood floodplain forests (HFF) are highly heterogeneous and productive ecosystems threatened by anthropogenic influence and effects of global warming. Quercus robur (oaks) and Ulmus laevis (elms) are acknowledged in literature as the two highest the highest and second highest aboveground carbon biomass stores along the lower middle Elbe floodplain. Both species are adapted to the hydrological fluctuations of floodplain soils. However, in Central Europe, these hydrological fluctuations  are threatened by the IPCC (2022) expected increase of streamflow drought, soil moisture drought and lower groundwater levels, hindering key ecosystem services provided by HFF. Thus, we wanted to assess the water use patterns of both species under water limiting conditions and high vapor pressure deficit (VPD).

The study was conducted during the vegetation period of 2020 in the active floodplain of the Elbe. To understand the influence of soil texture in the soil water dynamics, two sites were selected, a sandy site located in the  high sand embankments and a loamy site, representing the low positioned sites of the floodplains. Sap flow was measured in 5 trees per species per site, using heat-ratio method devices. Additionally, 3 soil profiles per site were instrumented with volumetric water content and water tension sensors in defined depths up to 1.60 meters below ground. One week in June was selected to represent high soil water availability and one in August with less soil water availability, both periods shared similar VPD.

Both species show different reactions to soil type and water availability. Elms kept higher mean daytime sap velocity than oaks even under low water availability (~50% higher). Nonetheless, a steep decrease was recorded for the elms during August in sandy soils, what could be evidence of loss of conductivity due to cavitation. In both, the loamy and the sandy site, oaks had significantly lower mean daytime sap flow velocity than elms (E.g. in loamy soils: 13cm/h and 6cm/h, for elms and oaks respectively).  Intraspecific variability was observed for the oaks when the influence of the soil texture was considered. The oak reduced sap velocity in sandy soils significantly by approximately 50% compared to loamy soils. This indicates higher sensitivity of this species to soil texture and associated soil water potential. Furthermore, to understand the impact of soil texture on tree water use, the Jarvis model was applied. In the sandy site, under drought, the model was not able to explain the reduction in sap velocity considering potential evapotranspiration, thus under this condition soil water potential plays a stronger role in sap velocity regulation.

These results provide insights to the function that different adaptations by species and the influence of site-specific abiotic conditions could have over increased drought periods, providing information that may increment the success of restoration efforts of this ecosystem.

How to cite: Vásconez Navas, L. K., Busch, H., Thomsen, S., Becker, J., Kleinschmidt, V., Gröngröft, A., and Eschenbach, A.: Quercus robur and Ulmus laevis water use patterns differ significantly under drought conditions and high vapor pressure deficit in the active floodplain of the lower middle Elbe., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9771, https://doi.org/10.5194/egusphere-egu23-9771, 2023.

Salt marshes gain vertical elevation to persist under sea level rise by building soil through primary production and trapping inorganic sediments.  Current models assume inorganic sediments contribute positively to marsh elevation, and that plants facilitate deposition and accretion through sediment trapping, suggesting rates of sediment trapping may be positively related to primary productivity.  Here we examine a phenomenon observed in a high salinity salt marsh estuary whereby inorganic sediments contribute to coating the Spartina alterniflora canopy and we investigate whether these coatings can inhibit photosynthesis.  Using eddy covariance observations of carbon dioxide flux, chamber measurements of leaf level photosynthesis, and measurements of leaf and canopy phenology we determined that 1) during rainless periods leaf and canopy greenness decline due to coating development, which is rinsed by rain proportionally to rain amount, 2) canopy light use efficiency declines as coatings develop for up to six days, 3) leaf level quantum use efficiency increases when coatings are removed, 4) canopy light use efficiency is weakly inversely correlated with creek salinity, 5) rinsing leaves amplifies the enhancement of canopy photosynthesis by diffuse light.  This study identifies a new mechanism in which inorganic sediments can inhibit S. alterniflora photosynthesis. Further work is needed to quantify the magnitude of the effect in terms of biomass production to determine whether this is a concern for marsh accretion.  If climate change and sea level rise enhance epiphytic coating development or residence time through, for example, creek bank erosion, sediment mobilization, or by extending rain-free periods, then this process may need to be incorporated in marsh elevation models.

How to cite: O'Halloran, T. L., Furbeck, M. E., Smith, E. M., Mozdzer, T. J., and Barrett, K.: Sediment coatings reduce leaf and canopy scale photosynthesis in a salt marsh: a novel soil-plant-atmosphere linkage, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10350, https://doi.org/10.5194/egusphere-egu23-10350, 2023.

Floating Photovoltaics (FPV) technology benefits from a remarkable support worldwide for two main reasons: it produces energy for a reasonable carbon budget and it has a lower land-use footprint compared to similar renewable installations. With increasing concerns about freshwater availability, a third asset is likely to boost the momentum of FPV: the potential water savings of reservoirs. As shown in Figure 1, the FPV array is made up of buoys and photovoltaic modules that are prone to reduce the energy input and the action of vapour removal on the surface of the water basin. However, giving a precise assessment of how much water would be saved is complicated, as it relies on the technology of floaters (water surface openings) and the modified physics of the water-atmosphere interface. In this case, looking at the whole system as a canopy that acts on the water-atmosphere interface seems relevant to study the evaporative levels.

This contribution proposes a new modelling approach based on Computational Fluid Dynamics (CFD) calculations to assess the amount of water vanishing into the atmosphere when a reservoir is covered by a half-open structure. A first computational domain is built in which the PV module is explicitly represented as if it were standing in the PV array, considering modules as grid-aligned obstacles (Figure 2). The airflow located below the modules is assimilated to the canopy airflow, and modifying the module geometry has an impact on the advection-diffusion processes of the vapour at the bottom of the canopy. Evaporative rates are computed and a numerical function is created to link the rates to the velocity and direction of the wind. In order to obtain the rate at the reservoir level, a second simulation is setup using a microscale domain that encompasses a reservoir partially covered by an FPV array and the surrounding lands. The numerical function is plugged into the model so that the actions of the FPV array on the atmosphere and canopy flows are conserved during the upscaling process. The methodology is supported by a case study that includes a nominal FPV module geometry. A specific reservoir is analysed, the real elements of geographic information are digitised for this purpose, and a micrometeorological station is installed in the real reservoir. Preliminary measurements show good agreement with the humidity level predicted in the atmosphere, so spatially extrapolated results are proposed to estimate reservoir-level evaporation, and a modified advection-diffusion law related to wind velocity is proposed.

By linking local-scale interactions driven by structure effects (geometries of the floating setup) and the microclimate at the reservoir level, the contribution opens the door to floating structure optimisation with respect to water savings. Moreover, it allows one to predict how the reservoir system will be altered by the half-covered situation using lake modelling (e.g., Global Lake Modelling). This aspect is critical to better predict the evolution of physical parameters below the interface that may have a strong retroaction on the interface and the atmosphere.

How to cite: Amiot, B., Ferrand, M., Le berre, R., Vidal Hurtado, J., and Giroux--Julien, S.: Sheltering Effect from Floating Photovoltaics over the Waterbody-atmosphere Interface, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9231, https://doi.org/10.5194/egusphere-egu23-9231, 2023.

Accurate estimation of carbon assimilation and allocation plays a significant role in the plant growth and terrestrial ecosystems. The STEMMUS-SCOPE model integrates photosynthesis, fluorescence emission, and transfer of energy, mass, and momentum in the soil–plant–atmosphere continuum system, and has good performances in estimating water, energy, and carbon fluxes. However, the plant growth states (i.e., leaf area index (LAI) and plant height (PH)) are needed as inputs for running the STEMMUS-SCOPE model, and are obtained either from interpolating observations or taking as constants over the time. As a result, the physical interactions are not adequately captured between radiative transfer, plant growth and soil water movements. The objective of this study is to consider the plant growth in STEMMUS-SCOPE model via coupling a crop growth module (i.e., WOFOST module). The coupled STEMMUS-SCOPE-WOFOST model was evaluated with plant functioning measurements. The results indicate that the simulation of LAI and PH is significantly improved and consistent with the dynamic of the water stress and gross primary production (GPP). Besides, the additional generated state variables (i.e., the biomass of root, leaf, stem as well as yield) can also agree well with the observations. Finally, the interactions between the land surface fluxes, soil moisture dynamic and plant growth are all well simulated. The STEMMUS-SCOPE-WOFOST model provides a mechanistic window to link the satellite observation of solar-induced fluorescence to above- and below-ground biomass, land surface fluxes, and root zone soil moisture, in a physically consistent manner.

How to cite: Yu, D., Zeng, Y., Wang, Y., and Su, B.: Integrated modeling of radiation transfer, plant growth, and the movement of soil moisture in the soil–plant–atmosphere continuum (STEMMUS–SCOPE-WOFOST v1.0.0), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2531, https://doi.org/10.5194/egusphere-egu23-2531, 2023.

Complex ecosystems, such as mixed forests or savannahs, are poorly represented in Land Surface Models (LSM). Those models mainly use simple and efficient representations such as the “big leaf” model for the energy budget in order to minimize time calculation. However, this approach prevents them from modelling more complex processes such as intra-canopy climate or competition for water between different vegetation strata which are highly important processes in order to understand the behavior and the responses of complex and mixed ecosystems in a changing climate. Although some ecosystem-specific models start to represent the 3D structure of complex ecosystems, including competition for light, water and nutrient between species and vertical / horizontal organization, these approaches are still too complex to be fully included in global LSM. However, first steps can be made towards this direction by representing the exchanges and interactions of biophysical fluxes such as water, carbon and energy. This study proposes some first steps towards this direction. We refined the computation of the energy and water transfers in the soil –plant – atmosphere continuum, working both on the horizontal and vertical heterogeneity. On the water transfers side, we implemented the soil-plant-atmosphere continuum model developed by Tuzet et al. (2017) which introduces a proper representation of the water flow inside the vegetation and a stronger coupling between plant water status and stomatal conductance. On the energy budget point of view, we implemented the multi-layer energy budget developed by Ryder et al. (2016) which represents the exchanges and turbulent transport of light and energy within a canopy. Finally, those two works being adapted for site-level modelling, we introduced a sub-grid heterogeneity representation of the energy and water budget in order to implement those developments for global applications. The study focuses on the two first developments which are firstly tested over several forest sites where intra-canopy gradients of humidity and temperature have been measured. A model inter-comparison between two LSM who have developed a vertical multi-layer energy budget, ORCHIDEE and CLM5 (Lawrence et al. (2019)), and the forest model MuSICA (Ogée et al. (2003)) allowed to highlight some of the model strengths and weaknesses. Finally, the expected improvements for complex ecosystems modelling and future developments in ORCHIDEE based on those representations will be presented.

How to cite: Alléon, J., Bonan, G., Ghattas, J., Lansoe, A.-S., Luyssaert, S., Ogée, J., Ottlé, C., Peylin, P., Polcher, J., Tuzet, A., and Vuichard, N.: Towards a representation of complex ecosystems in the ORCHIDEE Land Surface Model, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11322, https://doi.org/10.5194/egusphere-egu23-11322, 2023.