HS2.1.5 | Advances in forest hydrology

HS2.1.5

EDI

Forests primarily regulate water, energy, and carbon cycles. Maintaining forest functional integrity is fundamental to the sustainability of ecosystems, societies, and human development as described in the UN Sustainable Development Goals.
Global change and anthropogenic intervention are putting enormous pressure on forests, affecting the ecosystem services they provide through water quantity and quality, and biogeochemical cycles. The conventional wisdom that forest hydrology emphasizes the role of forests and forest management practices on runoff generation and water quality has expanded in light of rapid global change. Some of the largest pristine forest areas are in the tropics and have undergone drastic changes in land use in recent decades. Although novel modeling and observational techniques have been applied as alternatives to develop cutting-edge research, these tropical systems remain notably underrepresented in hydrological studies compared to temperate regions, especially concerning long-term experimental setups and monitoring networks.
Improving our understanding of how hydrological processes in the forest are determined by time-invariant factors and time-varying controls, as well as how forest catchments respond to dynamic environmental conditions and disturbances, will depend critically on understanding forest-water interactions. Building this knowledge requires interdisciplinary approaches in combination with new monitoring methods and modeling efforts.
This session brings together studies that will improve our understanding and stimulate debate on the impact of global change on hydrological processes in forest systems at different scales.
We invite field experimentalists and modelers working in forests from boreal to tropical regions to submit contributions that:
1) Improve our understanding of forest (eco)hydrological processes using an experimental or modeling approach or a combination of both;
2) Assess the hydrology-related impacts of land use/cover change and environmental disturbances on forested systems;
3) Feature innovative methods and observational techniques, such as optical sensors, tracer-based experiments, monitoring networks, citizen science, and drones, that reveal new insights or data sources in forest hydrology;
4) Include interdisciplinary research that supports consideration of overlooked soil-plant-atmosphere components in hydrological studies.

Convener: Alicia CorreaECSECS | Co-conveners: Daniele Penna, Luisa Hopp, Rodolfo NóbregaECSECS
Orals
| Mon, 24 Apr, 14:00–15:45 (CEST)
 
Room 2.17
Posters on site
| Attendance Mon, 24 Apr, 10:45–12:30 (CEST)
 
Hall A
Posters virtual
| Attendance Mon, 24 Apr, 10:45–12:30 (CEST)
 
vHall HS
Orals |
Mon, 14:00
Mon, 10:45
Mon, 10:45

Orals: Mon, 24 Apr | Room 2.17

The oral presentations are given in a hybrid format supported by a Zoom meeting featuring on-site and virtual presentations. The button to access the Zoom meeting appears just before the time block starts.
14:00–14:05
14:05–14:25
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EGU23-10827
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ECS
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solicited
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On-site presentation
Matthias Beyer, Kathrin Kuehnhammer, Joost van Haren, Angelika Kuebert, Christian Birkel, Ricardo Sanchez-Murillo, and John Marshall

As a consequence of global change, forests worldwide are undergoing a restructuring process. The expectations for forests of the future are ambitious: Providing resilient forest ecosystems that capture large amounts of carbon but also provide stable groundwater recharge rates. To balance the interests of both forestry and water management authorities, scientists and practitioners need to be able to investigate and predict which forest types and combinations of tree species are most likely to fulfill these needs.

Methods based on the analysis water stable isotopes have been used extensively for studying water uptake depths of vegetation, groundwater recharge, transit times, and water sources in general. Despite being arguably the superior tool when not only amounts but also knowledge of the sources of an (eco-)hydrological flux are needed, the highly dynamic nature of water transport processes within the soil-plant-atmosphere continuum (SPAC) could hardly be captured in the past. With the advent of  laser spectroscopy in the last decade, we are now able to measure water stable isotopes continuously and in all compartments of the SPAC.

In this keynote, we present and review the most recent advances (2016-now) of combined soil and plant in-situ water isotope measurements carried out in different ecosystems worldwide. We then critically discuss the gain in process-understanding of in-situ monitoring approaches and demonstrate how in-situ methods could be integrated with traditional and novel methods to advance forest hydrology.

In-situ and semi-in-situ (i.e., sampling of water vapor) water stable isotope methods have been greatly improved within the last five years. Initial disadvantages (e.g., comparability to traditional methods, complicated & laborious setup & maintenance, expensive) have been carefully addressed, and improvements have been implemented. Recent research has proven that i.) highly dynamic and heterogenous processes (e.g., stem flow, groundwater recharge through preferential pathways, change of uptake depths in response to rainfall/drought, disentangling water use of different tree species in mixed forests) can be captured exceptionally well using in-situ isotope methods; ii.) water-vapor equilibration methods represent the isotope composition of mobile water better compared to destructive methods, and iii.) using continuous water isotope data reduces parameter uncertainties in SPAC modeling.

In summary, we state that the benefits of using in-situ or semi in-situ techniques outweigh the disadvantages by far and strongly encourage the water stable isotope community to integrate them regularly into studies of dynamic soil-plant-atmosphere feedbacks.

How to cite: Beyer, M., Kuehnhammer, K., van Haren, J., Kuebert, A., Birkel, C., Sanchez-Murillo, R., and Marshall, J.: Dynamic processes require appropriate methods to capture them: Why in-situ water stable isotope monitoring needs to become a standard method in forest hydrological research, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10827, https://doi.org/10.5194/egusphere-egu23-10827, 2023.

14:25–14:35
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EGU23-9930
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On-site presentation
Kegan Farrick and Nicola Mathura

Throughout the Caribbean, hillside quarrying has become a common practice. While these activities remove large sections of the critical soil zone, very little work has been done on how hillside quarrying impacts rainfall runoff response and catchment water storage. We hypothesised that the removal of the critical soil zone during hillside quarrying will increase the timing and magnitude of streamflow response to storm events due to its close proximity to the river, while also reducing the overall storage of the watershed. The aim of this study is to understand the landuse impacts on rainfall runoff response and catchment storage. A paired catchment study between the 3.6 km2 Acono (forested) and the adjacent 3.6 km2 Don Juan (quarried) watersheds in Trinidad and Tobago was conducted using a hydrometric and geochemical approach. Direct measurements of rainfall and streamflow and bi-weekly water sample collections for geochemistry and stable isotopes of 18O and 2H from rainfall, baseflow, soils, springs and groundwater were done. Fraction of young water (Fyw) an inverse transit time proxy was computed along with the mean transit time distributions (MTTDs) by sine wave fitting were used as important descriptors of runoff generation and the catchment storage. The quarried watershed had higher streamflow levels during the wet season than the forested watershed. However, during the dry season there is a reversal.. The quarried watershed responded faster to rainfall events with a lag time between 1–3 hours with a higher peak rate of streamflow versus a lag time of 2-4 hours in the forested watershed with a lower peak rate of flow. In the upper quarried watershed 18.4 % of the stream water were younger than 0.46 years and 20.3% were younger than 0.55 years in the lower portion of the catchment. In the upper forested catchment 5.2 % of the stream water was younger than 2.71 years whereas 4.7% of the stream water was younger than 3.04 years in the lower catchment. The data suggest that the quarry leads to the faster delivery of water during storm events while also reducing the overall storage in the catchment. With an anticipated increase in hillside quarrying, this study provides important information for land use and water resource managers.

How to cite: Farrick, K. and Mathura, N.: Hillside Quarry Impacts on Streamflow and Stormflow response in a Tropical Watershed:  A Geochemical and Hydrometric Investigation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9930, https://doi.org/10.5194/egusphere-egu23-9930, 2023.

14:35–14:45
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EGU23-14167
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ECS
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On-site presentation
Lan Wang-Erlandsson, Ruud van der Ent, Arie Staal, Patrick Keys, Delphine Clara Zemp, Ingo Fetzer, Makoto Taniguchi, and Line Gordon

Rainfall is a key determinant of tropical rainforest resilience in South America and Africa, of which a substantial amount originates from terrestrial and forest evaporation through moisture recycling. Both continents face deforestation that reduces evaporation and thus dampens the water cycle, and climate change that increases the risk of water-stress induced forest loss. Hence, it is important to understand the influence of forest moisture supply for forest rainfall during dry periods. Here, we analyze mean-years and dry-years dry-season anomalies of moisture recycling in the South American (Amazon) and African rainforests (Congo) over the years 1980-2013. Annual average reliance of forest rainfall on their own moisture supply (ρfor) is 26 % in the Amazon and 28% in the Congo forest.  In dry seasons, this ratio increases by 7% (or ~2 percentage points) in the Amazon and up to 30 % (or ~8 percentage points) in Congo. Dry years further amplify dry season ρfor in both regions by 4-5 %. In both Amazon and Congo, dry season amplification of ρfor are strongest in regions with a high mean annual ρfor. In the Amazon, forest rainfall self-reliance has declined over time, and in both Amazon and Congo, the fraction of forest evaporation that recycles as forest rainfall has declined over time. At country scale, dry season ρfor can differ drastically from mean annual ρfor (e.g., in Bolivia and Gabon, mean annual ρfor is ~30% while dry season ρfor is ~50 %). Dry period amplification of ρfor illuminates additional risks of deforestation as well as opportunities from forest conservation and restoration, and is essential to consider for understanding upwind forest change impacts on downwind rainfall at both regional and national scales.

How to cite: Wang-Erlandsson, L., van der Ent, R., Staal, A., Keys, P., Zemp, D. C., Fetzer, I., Taniguchi, M., and Gordon, L.: Dry seasons and dry years amplify the Amazon and Congo forests’ rainfall self-reliance, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14167, https://doi.org/10.5194/egusphere-egu23-14167, 2023.

14:45–14:55
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EGU23-496
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ECS
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On-site presentation
Pauline Saurat, Pilar Llorens, Loujain Alharfouch, and Jérôme Latron

Forest cover influence the isotopic composition of precipitation before it eventually reaches the ground, especially through rainfall interception processes. Many plot scale recent studies focusing on throughfall and stemflow fluxes have demonstrated the role of forest canopy cover in (mostly) enriching their isotopic signature. However, the common approach in small catchments (even forested ones) remains to sample rainfall only at one single location (generally in an open area), assuming that the spatial variability of the isotopic composition of precipitation is small. Only a handful of studies have focused on the spatial variability of the isotopic composition of precipitation, and very few have included the role of forest cover. Nonetheless, a correct characterization of the isotopic composition of the incoming precipitation is essential in isotope-based catchment hydrology, for example to proceed hydrograph separation, as well as for process understanding or models development.

The aim of this study is to investigate the spatio-temporal variability of the isotopic composition of precipitation in a small Mediterranean catchment (0.6 km²) where forest cover roughly 2/3 of the catchment. Precipitation was sampled at the event scale in 31 locations across the catchment with bulk collectors consisting of plastic funnels (130mm diameter) connected to a 0.5-L plastic bin positioned 100cm above ground before each rain event and collected the day after. The sampling locations were distributed ±80m along 5 elevation lines every 50m (from 1150 to 1350m), 15 in open areas and 16 under forest (i.e., collecting throughfall). The percentage of canopy cover above each sampling location was determined using hemispherical photographs. For all events, rainfall was also measured every 5min at 3 locations with tipping bucket rain gauges and meteorological variables at 2 locations (at the ground level and above the forest canopy). Sampled events were analysed both altogether and separating open areas and under forest locations to determine the factors affecting the spatio-temporal variability of the isotopic composition of precipitation at the catchment scale and their relative influence.

Results show that mean δ18O of the events for the whole catchment varied from -11.96 to -3.6‰ along the year, with a mean coefficient of variation of 39%. Locations under forest were always more enriched than in open areas at the same elevation (+0.67‰ on average). Data analysis using the time stability approach (Vachaud et al., 1985) showed that forest locations had lower persistence of δ18O spatial patterns than open areas, indicating that spatial variability of isotopic composition was less predictable in forest locations compared to open areas. The elevation effect on δ18O, often observed in open area locations, was much less apparent in forest locations, confirming that forest introduced additional complexity on the spatial variability of the isotopic signal. Our findings highlight the actual need of taking into account the effect of both elevation and forest cover to assess a catchment scale representative isotopic composition of precipitation.

How to cite: Saurat, P., Llorens, P., Alharfouch, L., and Latron, J.: Influence of forest cover on the spatio-temporal heterogeneity of the isotopic composition of precipitation at the small catchment scale, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-496, https://doi.org/10.5194/egusphere-egu23-496, 2023.

14:55–15:05
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EGU23-6746
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On-site presentation
Friedrich J. Bohn, Sabine Attinger, Charlotte Kihm, and Anke Hildebradt

Ecosystem functions of temperate forests are expected to be severely impacted by future climate change - particularly hydro-meteorological extremes (heavy precipitation events, droughts, and heat waves) that will increase in frequency, duration, magnitude, and extent. Previous studies have shown that both structural and tree species diversity may act as buffers against the impacts of climate extremes.

To better understand the influence of structural and tree species diversity, we use two models to analyze the influence of species and structural diversity on hydrologic dynamics during recent drought events. The well-equipped test sites are located in central Germany and represent typical forests in this area. One model is the individual forest gap model FORMIND. Using a newly developed technique, it allows us to analyze local heterogeneous patterns on a 2 meter scale of carbon and water cycling, flow, and water stress, and their relationship to structural and species diversity. The second model is mHM, a mesoscale hydrological model. We parameterize mHM for two catchments in central Germany (Nägelstedt and Upper Saale). We further analyze the relevance of local heterogeneity in structural and species diversity and the resulting local heterogeneity in water fluxes on the fluxes at the mesoscale.

This two-model and interdisciplinary workflow allows us to consider various soil-plant-atmosphere interactions in drought disturbed ecohydrological systems

How to cite: Bohn, F. J., Attinger, S., Kihm, C., and Hildebradt, A.: Modeling interactions of water fluxes with species and structural diversity in temperate forests, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6746, https://doi.org/10.5194/egusphere-egu23-6746, 2023.

15:05–15:15
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EGU23-2852
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On-site presentation
Taehee Hwang, Lawrence Band, Christopher Oishi, and Hojeong Kang

Ongoing warming due to climate change has generally led to lengthened growing seasons and subsequent changes in evapotranspiration (ET) and streamflow seasonality. This has been well studied in seasonally dry, snowmelt dominated watersheds, but not in humid, temperate forested watersheds without significant seasonal snowmelt. In this study, we investigate how seasonal streamflow patterns have responded to variability in vegetation phenology in the southern Appalachians over the last four decades. We characterize seasonal shifts in low-frequency streamflow peaks using 50th percentiles of cumulative daily precipitation, streamflow, and soil moisture measurements, and investigate interactions with remotely sensed, long-term greenup anomalies in the deciduous-dominated forested watersheds. After removing a dominant precipitation control, one-day earlier greenup is associated with about one-day early spring flow peak at the low-elevation deciduous catchment. This indicates that the strong dependency of seasonal flow regimes on precipitation is mediated by warming-induced extended growing season, especially by early greenup. In contrast, we find less significant correlations of the greenup anomalies on flow percentiles of an adjacent evergreen and a high-elevation deciduous catchment. At a plot scale, similar correlations of cumulative soil moisture days were found only at an upslope topographic position, where precipitation also showed tighter coupling with soil moisture patterns than downslope. This indicates that early greenup in deciduous forests leading to early ET increase, in turn results in early soil moisture dry-down patterned by hillslope positions, and earlier seasonal streamflow peaks and subsequent declines. Our study suggests that spring flow peaks are likely to shift earlier by warming-induced early greenup even in snow-free regions, which has great implications for future freshwater availability in the southeastern US.

How to cite: Hwang, T., Band, L., Oishi, C., and Kang, H.: Early greenup impact on seasonal streamflow and soil moisture dynamics in humid, temperate forests, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2852, https://doi.org/10.5194/egusphere-egu23-2852, 2023.

15:15–15:25
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EGU23-15252
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ECS
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On-site presentation
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Caitlin Lewis, Martin Lukac, Elena Vanguelova, and Matthew Ascott

Forest ecosystems are typically associated with good water quality; an ecosystem service often claimed as a benefit of afforestation schemes. However, legacy effects of historical land use, plus decades of elevated nitrogen deposition inputs from traffic pollution, and agricultural and industrial activities in combination with higher nitrogen scavenging by forests, have led to elevated nitrate leaching from forested lands across Europe. Elevated nitrate leaching threatens the quality of surface and groundwater. It is also related to soil acidification and depletion of base cations, compromising the nutritional status of the soil and, subsequently, current and future trees generations. Several variables that affect the response of nitrate leaching to elevated deposition inputs have previously been identified in long-term forest monitoring datasets. Here we collated a European-scale dataset from published literature of throughfall nitrate concentrations and nitrate leaching, and variables affecting this relationship, e.g. soil type, surrounding land use and climate, broadening the evidence beyond these long-term monitoring datasets.

We identified a variation in response to elevated deposition between coniferous and broadleaved forests. This could be partly attributed to the former land uses typically associated with the different tree species. Broadleaf forests planted on former arable land exhibited a different response to elevated deposition than afforested heathlands/grasslands and conifers planted on arable land. An age effect was also observed, with nitrate leaching from forest soils increasing with tree age until 80 years old for conifers and 50 years old for broadleaves, then declining as trees aged further. This research provides evidence to assess the timescale over which afforestation schemes can deliver expected benefits to water quality. It also highlights that considering former land use is important to identify locations in forested landscapes where groundwater nitrate concentrations may be elevated.  

How to cite: Lewis, C., Lukac, M., Vanguelova, E., and Ascott, M.: Former land use and tree age affects nitrate leaching from European forest soils, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15252, https://doi.org/10.5194/egusphere-egu23-15252, 2023.

15:25–15:35
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EGU23-17269
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ECS
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On-site presentation
Daphné Freudiger, Bernd Ahrends, Henning Meedenburg, Birte Scheler, and Ulrike Talkner

Temperate forests provide ecosystem services such as protecting water environment, timber and fuel production, carbon sequestration, and reduction of nutrient loss. During the last decades, large forest areas were decimated world-wide by bark beetle attacks. Under climate change, drought and higher temperatures increase the risk of infestation. Future forest ecosystem services are therefore at risk of deterioration and it is essential to understand how bark beetle attacks and following management practices influence nutrient cycling, nitrate (NO3) and dissolved organic carbon (DOC) fluxes in seepage water. After dieback, accelerated mobilization of nutrients can be expected due to an increase in mineralization rates and the lack of plant nutrient uptake, whereas the lack of litter input may reduce nutrient leaching. The significantly reduced interception and evapotranspiration might furthermore increase soil water contents and seepage fluxes. Regeneration strategies (e.g. site clearance vs. keeping the dead trees, natural vs. artificial regeneration, regeneration with nurse crops) are decisive for the extent and persistence of the impact of calamities on water quality and quantity. We use a meta-data-analysis to gather knowledge out of approx. 60 studies around the world, to assess the expected behaviours of DOC and NO3 concentrations in seepage water and streams after bark beetle outbreaks in temperate forests and to identify gap of knowledge. Most studies focussed on nitrate leaching and only few on DOC. Overall, DOC concentrations increase in seepage water and streams directly after dieback, reaching a peak 2 to 3 years after disturbance. In the opposite, the first evidences of increased NO3 concentrations are visible approximately one year after disturbance and peak is reached within 3 to 10 years (on average after 5 years), when DOC decreases. NO3 maxima never exceeded drinking water limit. In all studies, DOC and NO3 concentrations recovered to pre-event or, in some cases, were even below the pre-dieback conditions only few years after the peak. Forest ecosystems seem therefore to be resilient to disturbances showing overall rapid recovery of ecosystem functions. However, the timing and duration of the concentration peaks largely differed among the studies, which might be explained by the extent and velocity of tree dieback in the studied areas, the harvest management practices and the type of vegetation re-growth after disturbance, but also by the local climatic conditions and the catchment size. Only few studies specifically analysed these effects on nutrient fluxes and their results differ considerably. More research is needed for assessing the influence of different regeneration strategies after calamities on water quality risks in forested catchments. A bark beetle attack currently decimating the Norway Spruce forest in the well-monitored Lange Bramke catchment (Harz, Germany), offers a unique opportunity to answer this question. With long-term datasets of NO3 and DOC concentrations in stream and the recent installation of a network of lysimeters at three soil depths in a) a healthy forest area, and infested areas b) with dead trees standing, and c) with site clearance, we will be able to better understand the effect of regeneration strategies on nutrient fluxes.    

How to cite: Freudiger, D., Ahrends, B., Meedenburg, H., Scheler, B., and Talkner, U.: How do bark beetle outbreaks impact water quality in temperate forested catchments?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17269, https://doi.org/10.5194/egusphere-egu23-17269, 2023.

15:35–15:45
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EGU23-13089
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ECS
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Highlight
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Virtual presentation
Ye Su, Meijun Li, Wei Shao, and Jerker Jarsjö

Tree mortality triggered by bark beetle infestation can significantly affect terrestrial carbon and water balances. However, how to improve the parameterization of the stomatal conductance to express the dynamics of ecosystem disturbance remains unclear. A subalpine forest located in the Rocky Mountains experienced a severe bark beetle outbreak in 2008, which provided a unique opportunity to investigate carbon and water flux changes covering the periods of pre-infestation (2005-2007), infestation (2008-2009), and post-infestation (2010-2014). Affected by bark beetle infestation, the stomatal conductance during the summer season (July and August) significantly reduced from 0.0018 m/s in the pre-infestation period to 0.0011 m/s in the infestation period. The decrease in stomatal conductance was not solely caused by the decrease of LAI, but also related to variation in parameter g1 in three commonly-used models of Ball-Barry, Leuning, and Medlyn. The parameter g1 was related to water use efficiency (WUE), and WUE values increased in the infestation period and decreased in the post-infestation period providing evidence that the physiological behavior was significantly changed due to bark beetle infestation. As for the simulation of transpiration, the fitted parameter significantly improved the accuracy in comparison with recommended parameterization. With the inclusion of temporally varied stomatal conductance, estimated transpiration during the infestation period and post-infestation period was improved by 4.3%~13.6% in comparison with the unvaried parameterization fitted in the pre-infestation period. Accounting for the temporally varied stomatal conductance parameters in response to disturbed environments may improve the description of stomatal conductance leading to better model performance in estimated water and carbon balances.

How to cite: Su, Y., Li, M., Shao, W., and Jarsjö, J.: Large-scale shifts in transpiration dynamics following bark beetle infestation: Stomatal conductance responses, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13089, https://doi.org/10.5194/egusphere-egu23-13089, 2023.

Posters on site: Mon, 24 Apr, 10:45–12:30 | Hall A

The posters scheduled for on-site presentation are only visible in the poster hall in Vienna. If authors uploaded their presentation files, these files are linked from the abstracts below, but only on the day of the poster session.
A.37
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EGU23-3830
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ECS
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On-site presentation
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Andrea Rabbai, Doris E. Wendt, Giulio Curioni, Susan E. Quick, A. Robert MacKenzie, David M. Hannah, Nicholas Kettridge, Sami Ullah, Kris M. Hart, and Stefan Krause

Afforestation, as one of the major drivers of land cover change, has the potential to provide a wide range of ecosystem services (ES). Aside from carbon sequestration, it can improve hydrological regulation by increasing soil water storage capacity and reducing surface water runoff.  However, afforested areas are rarely studied at the appropriate time scale to determine when changes in soil hydrological processes occur as the forest grows. This study investigates the seasonal soil moisture and temperature dynamics, as well as the event-based responses to precipitation events and dry periods between a mature and juvenile forest ecosystem over a 5-year time period. Generally, soil moisture was higher in the juvenile forest than in the mature forest, indicating less physiological water demand. However, following the 2018 drought, soil moisture dynamics in the growing juvenile plantation began to match those of the mature forest, owing to canopy development and possibly also to internal resilience mechanisms of the young forest to external perturbations. On the other hand, soil temperature dynamics in the juvenile plantation followed air temperature patterns closely, indicating lower thermal regulation capacity compared to the mature forest. While our findings reveal that an aggrading juvenile plantation achieves mature forest soil moisture dynamics at an early stage, well before maturity, this was not the case for soil temperature. Our results shed light on long-term trends of seasonal and event-based responses of soil moisture and temperatures in different-aged forest systems, which can be used to inform future assessments of hydrological and ecosystem responses to disturbances and forest management.

How to cite: Rabbai, A., Wendt, D. E., Curioni, G., Quick, S. E., MacKenzie, A. R., Hannah, D. M., Kettridge, N., Ullah, S., Hart, K. M., and Krause, S.: Soil moisture and temperature dynamics in juvenile and mature forest as a result of tree growth, hydrometeorological forcings, and drought., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3830, https://doi.org/10.5194/egusphere-egu23-3830, 2023.

A.38
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EGU23-12770
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On-site presentation
Václav Šípek, Nikol Zelíková, Lukáš Vlček, Jitka Toušková, and Miroslav Tesař

An understanding of the spatial and temporal variation of soil moisture is essential for studying other hydrological, biological, or chemical soil processes, such as water movement, microbial activity, and biogeochemical cycling. The study focuses on the description of soil water dynamics at several sites with different types of forests and their health status. Specifically, the results are based on the thorough description of the soil water regime under spruce forest in two mountainous plots. At one plot the measurements are supplemented with site influenced by bark beetle attack and at another site the comparison with beech forest. The analysis was based on soil water regime measurements from several vegetation seasons (comprising wet and dry years). We investigated both column average soil water content and also its vertical distribution. The water balance of the soil column was studied by the bucket-type soil water balance model.

It was shown that the forest type is an important factor controlling the rate of evapotranspiration which in turn influences the soil water regime, especially in dry periods. In wet periods, the differences among particular sites were negligible. In dry periods, the soil was slightly wetter in the site affected by the bark beetle outbreak in the surface soil layer and drier in the deeper soil layer. Similarly, the beech and spruce forest differences were most pronounced in dry periods. In this case, the beech forest was more efficient in terms of evapotranspiration water consumption which resulted in drier soil compared to spruce covered plot. In the spruce site, the soil was regularly drier only at the beginning of the season which was given by different interception rates during winter. The differences between spruce and beech forest were based namely on the water consumption efficiency and differences in interception rates, vertical distribution of the roots, and soil hydraulic properties.

This research was supported by the Technological Agency of the Czech Republic (SS05010124), SoilWater project (EIG CONCERT-Japan), and the institutional support of the Czech Academy of Sciences, Czech Republic (RVO: 67985874).

How to cite: Šípek, V., Zelíková, N., Vlček, L., Toušková, J., and Tesař, M.: Soil moisture regime under different forest types, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12770, https://doi.org/10.5194/egusphere-egu23-12770, 2023.

A.39
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EGU23-1457
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On-site presentation
Sibylle K. Hassler, Jefferson S. Hall, Michiel van Breugel, and Helmut Elsenbeer

Landscapes in the humid tropics are undergoing change in land cover. Besides ongoing deforestation of old-growth forest there is also natural regrowth and active reforestation. These changes in land cover affect soil hydrological properties, eg. saturated hydraulic conductivity (Ks), and thus influence hydrological flow paths. While it has been well documented that removing forest in favour of pasture establishment frequently leads to soil compaction and hence increased occurrence of overland flow and erosion, the effect of reforestation on soil hydraulic properties is less studied, especially not in terms of longer time series of forest regrowth.

We monitored the development of Ks in three reforested catchments in the Panama Canal Watershed, two reforestation trials with native species and teak and a secondary succession, over the course of 10 years. We measured Ks on undisturbed soil cores from the depths of 0-6 and 6-12 cm, applying the constant-head method. We compare the results to a previous study based on a space-for-time substitution in the same area.

Our results show a marked increase in Ks variability in both depths after the first five years of measurement. This points to a non-uniform influence of vegetation development across the catchments. Median Ks values in the topsoil increased at all three reforestation sites over the course of the monitoring period and reached values that considerably exceeded those previously measured in 100 year-old forests in the region, which appears at odds with an assumed continuous increase of Ks with increasing forest age. Further comparisons with soil and vegetation characteristics will be used to explain this apparent contrast.

How to cite: Hassler, S. K., Hall, J. S., van Breugel, M., and Elsenbeer, H.: Changes in saturated hydraulic conductivity during forest regrowth over 10 years in the humid tropics, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1457, https://doi.org/10.5194/egusphere-egu23-1457, 2023.

A.40
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EGU23-14582
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On-site presentation
Andis Kalvans and Iluta Dauškane

Air temperature and hence potential evapotranspiration trends are clearly positive worldwide, while precipitation trends are unclear largely due to large inherent variability. Apparently, because of climate change increasing evapotranspiration is likely to lead to depletion of soil water reserves in many ecosystems, but ecosystem feedbacks can have a nonlinear impact of the water regime. For example, in a hemi boreal forest at a hydric setting, higher evapotranspiration due to higher temperatures can lead to improved soil aeration, facilitating the rejuvenation of woody vegetation and further increase of transpiration. Process-based soil water models can be used to investigate such phenomena. However, the models need to be validated. Long time series of the forest soil water regime are sparce. Instead, the tree-ring width data (chronology) can be used as a proxy for growing conditions in the past, as the soil water regime has the firs order controlling factor. We are constructing a Hydrus-1D soil-water model for three hydric forest sample plots in Latvia using the e-obs data set for model forcing. The model results then are compared to the local tree-ring chronology, particularly examining pointer years as extreme cases for evaluating hydrological situation. The model will provide opportunity for scenario investigation of the interactions between climate and soil water regime in hemiboreal forest ecosystem. This work was supported by ERDF postdoctoral research project “Groundwater and soil water regime under climate change” (No. 1.1.1.2/VIAA/3/19/524).

How to cite: Kalvans, A. and Dauškane, I.: Comparing tree ring chronology and soil water model for a hydric hemiboreal forest, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14582, https://doi.org/10.5194/egusphere-egu23-14582, 2023.

A.41
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EGU23-13837
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ECS
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On-site presentation
Marius G. Floriancic, Scott T. Allen, Raphael Meier, Lucas Truniger, James W. Kirchner, and Peter Molnar

Forests modulate precipitation and evapotranspiration fluxes. One important – yet often overlooked - component in the forest water cycle is the forest-floor litter layer. Leaves and deadwood retain significant amounts of annual precipitation and enhance subcanopy humidity. At the “Waldlabor Zurich” ecohydrology field site we conducted numerous experiments to quantify the water fluxes from and to the forest-floor litter layer. We estimated the total retention capacities of needle, broadleaf and deadwood litter, assessed the litter water content before and after precipitation events, and measured soil moisture in litter-covered and litter-free plots. We used micro lysimeters to estimate evaporation from the litter layer and measured subcanopy humidity and temperature at different heights above the forest floor to assess the effect of evaporation on subcanopy microclimate.

Storage capacities of needle litter and broadleaf litter averaged 3.1 and 1.9 mm, respectively, with evaporation timescales exceeding 2 days, whereas deadwood stored ~0.7 mm of precipitation, and retained water for >7 days. Deadwood water retention increased with more advanced decomposition. Together the forest floor litter layer reduced soil water recharge, reduced soil evaporation rates, and insulated against ground heat fluxes thus impacting snowmelt patterns. Timeseries of deadwood water content revealed a diel cycle of stored water, water content increased during nighttime due to condensation of dew and fog and decreased during the day when vapor pressure deficit and evaporation were high. The water evaporating from the forest‐floor litter layer increased humidity, decreased temperature, and reduced vapor pressure deficit in the subcanopy atmosphere. Although, the absolute amounts of water storage in the forest-floor litter layer are relatively small, these storages were frequently filled and emptied with every precipitation event, thus effecting the overall soil water recharge. Overall, 18% of annual precipitation, or 1/3 of annual evapotranspiration, were retained in the forest-floor litter layer suggesting that overlooking litter interception may lead to substantial overestimates of recharge and transpiration in many forest ecosystems.

How to cite: Floriancic, M. G., Allen, S. T., Meier, R., Truniger, L., Kirchner, J. W., and Molnar, P.: Forest-floor litter and deadwood cycle significant amounts precipitation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13837, https://doi.org/10.5194/egusphere-egu23-13837, 2023.

A.42
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EGU23-4325
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ECS
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Highlight
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On-site presentation
Yupan Zhang, Yuichi Onda, Yiliu Tan, Hangkai You, Thuy Linh Pham, Asahi Hashimoto, Chenwei Chiu, Takashi Gomi, and Shiori Takamura

The multidimensional arrangement of upper canopy features is a physical driver of energy and water balance under various canopies, and standard modeling approaches integrate leaf area index (LAI) and canopy closure (CC) to describe canopies. However, it is unclear how the canopy affects the component and interception of rainfall within the forest system. We generated multi-layered forest point clouds from trunk to canopy using fusion of drone and terrestrial LiDAR data then classified wood and foliage elements using a clustering algorithm to build a high precision physical model for describing throughfall, stemflow and interception. The experiment was conducted in the thinning plantation forest located in Tochigi prefecture, Japan. Rainfall observation for the three components is important for model development. Throughfall was computed from 20 rain gauges distributed on a grid under the forest canopy, 3 stemflow collectors was set up around the tree trunks connected to a bucket with water level sensor. We developed a capacity model to describe canopy saturation with foliage points, a voxel-based method was used to create 3D representations of forest canopies, and an analysis of these point-derived canopy structures and volume were performed to assess the canopy's capacity to contain rainfall. For stemflow modeling, we use a runoff model to simulate the additional rainfall accumulates to the tree trunk through branches when the tree canopy is saturated. Preliminary simulation results show that: (1) fusion and registration of drone and terrestrial LiDAR data can greatly improve the point cloud accuracy and enrich the information contents such as coordinate geo-reference and filling of missing structures; (2) a strong correlation between the rainfall observed canopy interception results and the estimated canopy volume, and the volume-based interception prediction model has a high accuracy, with an R2 from 0.84 to 0.91 compared to past observations. (3) stemflow is related to the projected volume of the canopy and the proportion of wooden structure point clouds, and as the runoff path increases, there is a greater probability that oversaturated precipitation will concentrate on the trunk rather than drip off. High accuracy physical model of tree canopy can well describe the interactions between the rainfall to canopy and illustrate the mechanism.

 

How to cite: Zhang, Y., Onda, Y., Tan, Y., You, H., Pham, T. L., Hashimoto, A., Chiu, C., Gomi, T., and Takamura, S.: Estimation of rainfall interception from merged drone and terrestrial LiDAR data by modeling 3D canopy structure in plantation forest, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4325, https://doi.org/10.5194/egusphere-egu23-4325, 2023.

A.43
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EGU23-17565
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ECS
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On-site presentation
Riccardo Valentini, Jim Yates, Andrea Petroselli, Alexis Yaroslavtsev, Flavia Tauro, Francesco Renzi, and Shahla Asgharinia
The science of forest digitalization via technological innovation offers an opportunity to develop new methods for mass monitoring forest resources. A key constraint has been cost restraints preventing the mobilization and collection of big data to efficiently capture, store, and analyze retrieved data. The Internet of Things (IoT) and advances in microprocessing are steadily changing this. The TreeTalker® is a multisensory IoT-driven platform designed to detect and collect information on individual trees, where its nested sensor approach captures several key ecophysiological parameters autonomously and in quasi-real time at a relatively low cost.
Here we combine a new additional probe for the detection of soil parameters, mainly soil temperature and soil moisture. The aim of this study was to design a compatible soil probe with TreeTalker® platform with reasonable accuracy maintaining the principle of lower cost for mass monitoring. For this purpose, two surficial sensing frequency domain-based soil probes with 50 and 3000 kHz bands were designed and integrated into the TreeTalker® platform for real-time and continuous soil data collection. In order to demonstrate the capability of the new additional part, a three-phase experimental process was performed including (1) sensor sensitivity analysis, (2) sensor calibration using eight different soil types, (3) a survey on signal correlation with soil water content and soil matric potential and (4) long-term field data monitoring.
A negative linear correlation was demonstrated under temperature sensitivity analysis for both types of probes, and for calibration, nonlinear regression analysis was applied to collected samples, explaining the relationship between the sample volumetric water content (collected by digital scale) and the sensor frequency output. Based on a preliminary trial, we investigate that frequency signal has a stronger correlation with soil matric potential (R2= 80%) rather than soil water content (R2= 62%) due to the sensitivity of the probe under free and bound water. This opens a new window for water potential measurement which is a key parameter for the understanding of Plant-Soil interactions. Furthermore, in a field scenario, three TreeTalkers were mounted near the commercial precise soil sensors, so-called TDR systems (time domain reflectometry) to analyze the accuracy of the low-cost soil probe in comparison to TDR system for both wet and dry seasons in silty-loamy soil type. The results revealed a better correlation for collected data in the wet season than in the dry period. We also present an innovative electrical impedance analysis for detecting soil water potential and soil water content.  system for both wet and dry seasons in silty-loamy soil type. The results revealed a better correlation for collected data in the wet season than in the dry period.

How to cite: Valentini, R., Yates, J., Petroselli, A., Yaroslavtsev, A., Tauro, F., Renzi, F., and Asgharinia, S.: A Tendency Toward Further Advancement In Forest Digitalization Via Combined Sap Flow, Spectrometer, Soil, And Microclimate Data, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17565, https://doi.org/10.5194/egusphere-egu23-17565, 2023.

A.44
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EGU23-8182
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On-site presentation
Thomas Pluntke, Christian Bernhofer, Thomas Grünwald, Maik Renner, and Heiko Prasse

Climate changes are expected to trigger changes in all water budget components at any scale. For Central Europe, higher evapotranspiration (ET) rates are already observed, other factors like land use or land cover characteristics change in parallel, but experimental evidence of the interdcations is limited, as it requires challenging long-term measurements. We take advantage of the well-documented hydro-meteorological dataset from the forested research catchment Wernersbach in Saxony, Germany, covering 52 years between 1968 and 2019 (Pluntke & Bernhofer et al., 2023).

We analyzed hydro-climatological time-series for linear trends and for breakpoints. Significant positive trends were found for global radiation, mean air temperature and grass-reference evaporation, as well as for the difference between catchment precipitation and runoff (P-R; hydrological estimate of ET). Precipitation increased and runoff decreased over the 52 years, but not significantly.

Air temperature and global radiation show significant breakpoints around 1988 and 1996, respectively, with below average conditions before and above average conditions after the breakpoints. Temperature change is associated with global warming, and possibly with the independent regional effect of air pollution. Since the 1960s, large sulphur dioxide emissions from fossil fuel burning led to a high aerosol density in the troposphere reducing solar radiation over most of Europe and North America. While this effect was reduced by filtering the emissions elsewhere in the early 1980s, it continued in neighboring parts of today’s Germany, Poland, and Czech Republic until the early 1990s. Breakpoint of grass reference evaporation coincides with air temperature (1988), and the breakpoint of P-R is a few years later.

We attributed changes in ET to changes in land use and climate by applying an adapted Budyko framework and enabled insights into their interactions. The sulphur dioxide emissions triggered widespread forest dieback in regions over 600 m in Saxony. Consequences were decreasing ET in the 1970s/1980s. The Wernersbach catchment (390 m) shows a similar tendency (not significant). Since the 1990s, both climate (increasing atmospheric demand) and land use (healthier forest stands and improved management practices) led to an increase of ET. In 2010s, climate induced damages of forest stands (due to droughts, storms, snow load, and bark beetle infestations) led to a drastic decrease of ET in Wernersbach despite favorable climatic conditions for ET. Since the intensity and frequency of such extreme events are likely part of climate change, they may cause greater regional changes in the water balance than direct effects of climate change, and may cause lasting damage to Ecosystem Services of forests, like flood mitigation, or carbon sequestration.

Our results show the need for climate adaptation measures in forests, such as the establishment of a more site-specific mixed forest, and a sustainable  forest management.

 

References

Pluntke T. & Bernhofer C., Grünwald T., Renner M., Prasse H.: Long-term climatological and ecohydrological analysis of a paired catchment – flux tower observatory near Dresden (Germany). Is there evidence of climate change in local evapotranspiration? J Hydrol 617 (2023), https://doi.org/10.1016/j.jhydrol.2022.128873

How to cite: Pluntke, T., Bernhofer, C., Grünwald, T., Renner, M., and Prasse, H.: Climate and land use induced changes in evapotranspiration - experimental evidence from a forested catchment in Germany, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8182, https://doi.org/10.5194/egusphere-egu23-8182, 2023.

A.45
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EGU23-2853
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ECS
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On-site presentation
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Qiqi Wang, Yuquan Qu, Kerri-Leigh Robinson, Heye Bogena, Alexander Graf, Harry Vereecken, Albert Tietema, and Roland Bol

Deforestation has a wide range of effects on hydrological and geochemical processes. Dissolved organic carbon (DOC) dynamics, a sensitive environmental change indicator, is expected to be affected by deforestation, with changes in atmospheric sulfur (S) deposition compounding this. However, how precisely anthropogenic disturbance (deforestation) under a declining atmospheric S input scenario affects the underlying spatiotemporal dynamics and relationships of river DOC and sulfate with hydro-climatological variables e.g., stream water temperature, runoff, pH, total dissolved iron (Fetot), and calcium (Ca2+) remains unclear. We, therefore, examined this issue within the TERENO Wüstebach catchment (Eifel, Germany), where partial deforestation had taken place in 2013. Wavelet transform coherence (WTC) analysis was applied based on a 10-year time series (2010–2020) from three sampling stations, whose (sub) catchment areas have different proportions of deforested area (W10: 31%, W14: 25%, W17: 3%). We found that water temperature and DOC, sulfate, and Fetot concentrations showed distinct seasonal patterns, with DOC averaging concentrations ranging from 2.23 (W17) to 4.56 (W10) mg L-1 and sulfate concentration ranging from 8.04 (W10) to 10.58 (W17) mg L-1. After clear-cut, DOC significantly increased by 59, 58% in the mainstream (W10, W14), but only 26% in the reference stream. WTC results indicated that DOC was negatively correlated with runoff and sulfate, but positively correlated with temperature, Ca2+, and Fetot. The negative correlation between DOC with runoff and sulfate was apparent over the whole examined 10-year period in W17 but did end in W10 and W14 after the deforestation. Sulfate was highly correlated with stream water temperature, runoff, and Fetot in W10 and W14 and with a longer lag time than W17. Additionally, pH was stronger correlated (higher R2) with sulfate and DOC in W17 than in W10 and W14. In conclusion, WTC analysis indicates that within this low mountainous forest catchment deforestation levels over 25% (W10 and W14) affected the coupling of S and C cycling substantially more strongly than “natural” environmental changes as observed in W17.

How to cite: Wang, Q., Qu, Y., Robinson, K.-L., Bogena, H., Graf, A., Vereecken, H., Tietema, A., and Bol, R.: Deforestation alters dissolved organic carbon and sulfate dynamics in a mountainous head water catchment—A wavelet analysis, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2853, https://doi.org/10.5194/egusphere-egu23-2853, 2023.

A.46
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EGU23-12766
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ECS
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On-site presentation
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Sean Adam, Maximilian Lau, and Conrad Jackisch

Climate change in combination with forest management practices is leading to increased DOC release from a forested reservoir catchment in the western Ore Mountains in Germany. The most significant sources of DOC loadings are likely several disturbed patches of former peatland in the catchment. We suspect that the soil water availability and subsequent variable hydrological connectivity of water pools in the shallow subsurface could be major factors for DOC mobilisation impeding the drinking water production in the region.

We present data from almost one year of intensive monitoring in two small catchments (1 ha) located on i) a shallow histosol with a highly compacted mineral subsoil and ii) a regolithic cambisol. Catchment drainage was constantly observed for water levels and in situ spectroscopy to infer discharge rates and DOC concentrations. Soil moisture and temperature, surface temperature and irradiation were continuously measured along the slope gradient. During monthly campaigns in the vegetation period, pore water samples were taken from high and low points of 15 m grid cells spanning the catchments.

In our poster, we would like to discuss our findings that pore water availability is non-uniformly distributed suggesting discrete subsurface flow paths in the catchments. In low moisture conditions, subsurface water pools can be isolated from the pore water network. We argue that disconnected pools accumulate DOC during low moisture conditions, which is then released when the pools are reconnected during strong precipitation events.

How to cite: Adam, S., Lau, M., and Jackisch, C.: DOC mobilisation from forest soils governed by intermittent hydrological connectivity of subsurface water pools, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12766, https://doi.org/10.5194/egusphere-egu23-12766, 2023.

Posters virtual: Mon, 24 Apr, 10:45–12:30 | vHall HS

The posters scheduled for virtual presentation are visible in Gather.Town. Attendees are asked to meet the authors during the scheduled attendance time for live video chats. If authors uploaded their presentation files, these files are also linked from the abstracts below, but only on the day of the poster session. The button to access Gather.Town appears just before the time block starts.
vHS.13
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EGU23-2052
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Virtual presentation
Chung-Te Chang, Jun-Yi Lee, Jyh-Min Chiang, Hsueh-Ching Wang, and Jr-Chuan Huang

Vegetation growth is sensitive to climatic variations which has a critical implication for hydrological regimes. However, the intertwined associations of climate-phenology-hydrology have rarely been explored in tropical/subtropical regions particularly. In this study, we synthesize hydroclimate records in forested watershed, central Taiwan for last five decades (1975-2020), and the results indicate that the incidences of meteorological and hydrological droughts are becoming prominent after 2001. We further examine the influences of temperature and precipitation on vegetation growth of watershed scale using EVI (enhanced vegetation index) derived from MODIS (Moderate Resolution Imaging Spectroradiometer) at monthly scale, and explore the effects of seasonal precipitation on the variations of landscape phenology and following watershed streamflow between 2001 and 2020. The EVI and temperature shows a linear relationship (R2 = 0.50, p < 0.001) without time-lag effect, whereas EVI and precipitation exhibits a log-linear relationship with two months lag (R2 = 0.40, p < 0.001), showing the accumulative rainfall during relatively dry period (winter-spring) is crucial for vegetation growth. Structural equation modeling reveals that earlier start of growing season (SOS) caused by relatively high spring rainfall (February-March) leads to longer growing season (LOS) and higher P-Q deficit (precipitation minus runoff) during the growing season. Nevertheless, the large amount of precipitation during growing season has no effect on the end of growing season (EOS), LOS and P-Q deficit. Realizing the vegetation growth responding to climatic variations is necessary for current and future hydrologic regime, especially under changing climate.

How to cite: Chang, C.-T., Lee, J.-Y., Chiang, J.-M., Wang, H.-C., and Huang, J.-C.: The climate-vegetation interactions and subsequent hydrological effect of a subtropical forested watershed, central Taiwan, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2052, https://doi.org/10.5194/egusphere-egu23-2052, 2023.