Displays

This study focused on Alouette River, located in south coastal British Columbia. During summer, water is released from shallow reservoir at a near-constant rate from an outlet about 6-10 m below the water  surface. Outlet temperatures in summer 2013 were initially cool hypolimnetic water, followed by alternating cool and warm water associated with an internal seiche, and finally dominated by warm epilimnetic water during the period of highest water temperature. An energy-balance model was used to evaluate potential strategies to ameliorate thermal habitat conditions for Pacific salmon downstream of the dam. Restoration of deforested banks that represented 4% of the reach length reduced daily maximum temperatures by only about 0.5 °C , while releasing more flow exacerbated temperatures during the warmest week of the year. The only effective strategy for thermal amelioration would be to release water from deeper in the reservoir.

How to cite: Moore, D. and West, D.: River temperature dynamics downstream of a shallow reservoir: process-based modelling to evaluate thermal mitigation strategies, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5984, https://doi.org/10.5194/egusphere-egu2020-5984, 2020.

Thresholds from flow–benthic fauna relationships in the light of data-scarce hydrosystems constitute an advance in implementing sustainable principles for water infrastructure management. To quantify thresholds the limits to the amount of water that can be withdrawn from Andean river networks before their natural functioning, biodiversity and ecosystem services become degraded, we conducted a whole-ecosystem experimental flow alteration. We reduced flow in the reach of a stream above a water intake from the supply system for the city of Quito, Ecuador. During the low-flow season, we diverted water using a system of weirs to accommodate streamflow in complementary percent (i.e., 90% flow deviation and 10% flow left in the stream). We performed seven reductions and kept them for seven days, during that time we sampled benthic algae chlorophyll-a concentration, flow, temperature, conductivity, light, and measured stream morphology. Our preliminary results indicate a high variability of ecological and physical responses to hydrological alterations in high-altitude tropical streams. A reduction to minimum flow similar to conditions observed for low-flows caused significant changes in stream morphology, and reductions above this threshold evidenced changes in the relative presence of major benthic algae groups.

How to cite: Rosero-Lopez, D.: Towards experimentally-based environmental flows for infrastructure management in high-altitude tropical streams, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1327, https://doi.org/10.5194/egusphere-egu2020-1327, 2020.

Stream temperature is inherently shaped by human activity, often reflecting reduced riparian cover, runoff from impervious surfaces, limited connectivity between groundwater and surface waters, and a host of other sources of water delivery, including stormwater, wastewater, and dam releases.  This is especially true in urbanized areas, where heat exchanges may be additionally altered by urban hydrology, delivering warm pulses of water during heavy storms that locally elevate water temperatures.  While this effect has been documented in several cities, no comprehensive summary of these impacts exists at regional and larger scales.  Our work documents the impact of urbanization on stream temperatures during wet and dry periods in small streams for several cities across the eastern United States.  Our work seeks to benchmark how stream temperature surges during storms and average stream temperatures in more urbanized watersheds differ from nearby forested, less-impacted sites.  We show that the occurrence and magnitude of temperature surges as well as the statistical characteristics of dry-day stream temperature varies with climate and level of imperviousness.  Interestingly, comparisons within and across cities demonstrate the complex responses of stream temperature to urbanization, suggesting that the human imprint on stream temperature signals is highly variable and reflects site specific characteristics rather than regional influences.

How to cite: Kelleher, C. and Hurst, E.: Differences between urban and natural stream temperatures across the eastern United States, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11122, https://doi.org/10.5194/egusphere-egu2020-11122, 2020.

Wetlands are increasingly considered as nature based solution as they provide valuable services and functions to the society and environment, such as water quality improvement and biodiversity support. However, while land use and climate change have been affecting the functions and service of these ecosystems, it has become important to study the large-scale behaviour of wetlands in the landscape. Consequently, previous studies have suggested to study wetlands within wetlandscapes, defined as catchments containing networks of several wetlands, in order to understand large-scale functions of wetlands and their response to land-use and climate changes. This emphasizes the ecohydrological interactions of wetlands rather than having focus of individual wetlands. However, as the concept of wetlandscape is new, its governing properties have not yet been systematically quantified.

In this paper, we quantify ecohydrological properties of individual wetlands in multiple wetlandscapes, typical for northern Europe, that may impact biodiversity and modulate nutrient flows (e.g. wetland area, wetland catchment area and wetland type) as well as characteristics of the whole wetlandscape in terms of their large-scale processes and functions. We also investigate possible systematic differences between wetlandscapes of different size. Results show that large wetlandscapes generally contained features to support different ecosystem services compare to smaller wetlandscapes. More specifically, results indicated that small wetlandscapes have a poor ability to route water through their wetlands (i.e. catch flow from the entire wetlandscape) which was in contrast to large wetlandscapes. This implies that large wetlandscapes have a higher potential for large-scale retention of nutrients and contaminants. Present result support the importance of wetlandscape studies and the priority of a wetlandscape focus in future management programs for instance targeting regions with large-scale pollution issues.

How to cite: Åhlén, I., Hambäck, P., Thorslund, J., Frampton, A., Destouni, G., and Jarsjö, J.: Wetlandscape size thresholds for multiple ecosystem service delivery, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1622, https://doi.org/10.5194/egusphere-egu2020-1622, 2020.

Ecohydrology usually refers to the effects of hydrological processes on the occurrence, distribution and patterns of plants. Here, we emphasize a new kind of ecohydrology in which the effects of hydrological processes on the occurrence of – endangered or not - wildlife become addressed via the threat of its habitat or, oppositely, where the occurrence of wildlife leads to a threat of endangered fauna. We present three examples to illustrate this.

First, the habitat of the tiger in the Terai Arc Landscape (TAL) at the foot of the Himalayas seems to increasingly become threatened by changes in the hydrological conditions. Grasslands in floodplains are an important part of the tiger habitat as these are the grounds where the tiger preferably hunts for deer as his prey. Disturbances of the water systems such as gravel and sand extraction from the river beds, intake of water for irrigation and hydropower production are increasingly happening and climate change may further alter the Himalayan water systems. This seems to disturb the grasslands in their hydrological and hydromorphological dynamics, which may negatively impact the density of deer, which may put additional pressure on the tiger populations in the nature reserves of the TAL.

Second, ungulates are important mammals in the grasslands and savannah of southern Africa. The water availability for these animals may alter upon climate change, including higher frequencies of droughts. Research suggests that the community composition of ungulates may alter by this. Here, the larger water-dependent grazers may be replaced by smaller, less water-dependent species.

Third, the beaver is well-known as hydrological ecosystem engineer. The beaver, therefore, has obtained some attention within the context of ecohydrology. The impact of the beaver as ecosystem engineer is, however, peculiar for nature reserves at the Belgian-Dutch border. Surface water with poor quality due to lack of appropriate sewage water treatment is running along nature reserves. The reintroduction of the beaver causes a rise in the surface and groundwater levels due to its dam-building activities. This induces an introduction of polluted surface water into the Dutch wetlands which contain a less eutrofied ecosystem than the Belgian ones that were fed by the polluted surface water. Nature restoration may thus go on the expense of nature degradation.

These examples show that the ecohydrology of wildlife is as fascinating and diverse as classical ecohydrology is.

How to cite: Griffioen, J., Wassen, M., and Cromsigt, J.: A plea for a novel kind of ecohydrology: the interaction between hydrological processes and - endangered or not - wildlife, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11590, https://doi.org/10.5194/egusphere-egu2020-11590, 2020.

Ephemeral (vernal) pools are small hydrologically isolated wetlands found in a large variety of environments across the world. They provide breeding habitats for amphibians during their spring and early summer period of hydrological activity. Because of their small size and intermittent nature, many questions remain unanswered about their hydrology and concerning best strategies to improve their resilience to human activities and climate change. In the peri-urban area around Montreal City (Monteregie region, Quebec, Canada), ephemeral pools are habitats to the endangered Western Chorus Frog. In an attempt to protect the remaining population and to improve the reproductive success of these frogs, a study was funded by the Quebec Ministry of forest, fauna and parks to understand the processes driving pool hydrology and especially pool hydroperiod (length of hydrologically active period after snowmelt). Fourty-eight pools located in forested, agricultural and low-density housing developments were monitored for water levels since 2015. Seven of these pools were fully characterized for bathymetry and geology (field measurements), groundwater levels (hourly monitoring) and drainage area (LiDAR data). The pools are located on relatively flat land, in shallow irregular basins within generally low permeability Quaternary sediments. The pools hold relatively small volumes of water, with maximum annual water depths between 0.2 and 1.1 m (observed in April or May). Their areas vary between 100 and 5000 m². The hydrologically active periods after snowmelt (starting after the last frost when mean temperature > 5°C over five days and ending when the pool is dry) vary between 15 and 150 days. At some sites, the hydroperiods were shorter than the required length for reproductive success of the Western Chorus Frog, which could explain the population decline. These short hydroperiods appear to be linked to the presence of human impacts in the pool vicinity. Water level reactions after precipitation are indications that pool hydrology is influenced by a relatively small contributing area rather than by their apparent drainage area (ratio Δh/rain < 4). Head gradients between water levels in the nearby sediments and pool water levels underline the role of the shallow groundwater in maintaining humid conditions in the pools and in reactivating the pools during the summer.  Simple water budget models  confirm this groundwater input and show that surface and hypodermic runoff is the main water source to the pools. The models show that, pool hydroperiods will start earlier under a changing climate, because of warmer winters, but will not necessarily be longer due to higher temperatures and increased evapotranspiration. The models will be used to estimate the effects of human interventions (e.g. drainage, residential) on pool hydroperiods, thus contributing to plan pool protection strategies that could help protect the Western Chorus Frog.

How to cite: Larocque, M., Roux, M., Gagné, S., and Olivier, C.: Better understanding the hydrology of peri-urban ephemeral pools serving as habitats for the Western Chorus Frog, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11659, https://doi.org/10.5194/egusphere-egu2020-11659, 2020.

The continued global acceleration of urbanisation increasingly requires sustainable, adaptive management strategies for land and water use in cities. Although the effects of buildings and sealed surfaces on urban runoff generation (via storm drains) and local climate (through the urban heat island effect) are well known, much less is known about how these artificial influences integrate with water partitioning in more natural urban green spaces. In particular, little is quantitatively known about how different types of urban green spaces (lawns, parks, woodland etc.) regulate the partitioning of evaporation, transpiration and groundwater recharge. To address this crucial issue, we integrated field observations with advanced, isotope-based ecohydrological modelling at the plot scale in the urban area of Berlin, Germany. Measurements of soil moisture, sap flow, and stable isotopes in precipitation, soil water and groundwater have been made over the course of one growing season. Additionally, an eddy flux tower at the site Rothenburgstraße in Berlin-Steglitz continuously collects hydroclimate data by measuring temperature, precipitation, radiation, humidity and wind speed at high temporal resolution. These data (30-min averages) have been used as input to, and for calibration of, the process-based ecohydrological model EcH₂O-iso. The model also tracks stable isotope ratios and water ages in various stores (e.g. soils and groundwater) and fluxes (evaporation, transpiration and recharge). EcH₂O-iso has successfully been used to describe the effects of vegetation cover on water partitioning in a number of studies but this is the first implementation in an urban setting. It shows that ecohydrological water use by vegetation type increases in the order forests > shrubs > grass, mainly through higher interception and transpiration. Accordingly, trees can reduce groundwater recharge by >50%, but provide cooling latent heat transfers to the atmosphere.  Similarly, ages of stored water and fluxes are generally greater under trees than grass. The results, which form the basis for future upscaling, show that urban green spaces play an important role in urban hydrology and in Berlin there is a trade-off between moderating the urban heat island effect and maintaining groundwater recharge. Consequently, it is clear that vegetation management needs to be considered in sustainable water and land use planning in urban areas to build resilience in cities to climatic and other environmental change.

How to cite: Gillefalk, M., Tetzlaff, D., Hinkelmann, R., Kuhlemann, L.-M., Smith, A., Meier, F., and Soulsby, C.: Quantifying the effects of urban vegetation on water partitioning in complex cityscapes: the potential of isotope-based ecohydrological models, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-413, https://doi.org/10.5194/egusphere-egu2020-413, 2020.

Vegetation properties such as rooting depths and vegetation cover play a key role in coupling ecological and hydrological processes. These properties are however highly variable in space and/or time and their parametrization generally poses challenges for terrestrial biosphere models (Whitley et al., 2016). Models often use static values for dynamic vegetation properties or prescribe values based on observations, such as remotely sensed leaf area index. Here, vegetation optimality provides a way forward in order to predict such vegetation properties and their response to environmental change (Schymanski et al., 2015).

In this study, we explore the utility of a combined water-vegetation model, the Vegetation Optimality Model (VOM, Schymanski et al., 2009), to predict vegetation properties such as rooting depths, foliage cover, photosynthetic capacity and water use strategies. The VOM schematizes perennial trees and seasonal grasses each as a single big leaf with an associated root system and optimizes leaf and root system properties in order to maximize the Net Carbon Profit, i.e. the difference between the total carbon taken up by photosynthesis and all the carbon costs related to the construction and maintenance of the plant organs involved. The VOM was applied along the North-Australian Tropical Transect, which consists of six savanna sites equipped with flux towers along a strong rainfall gradient between 500 and 1700 mm per year. The multi-annual half-hourly measurements of evaporation and CO₂-assimilation at the different sites were used here to evaluate the model.

The VOM produced similar or better results than more traditional models even though it requires much less information about site-specific vegetation properties. However, we found a persistent bias in the predicted vegetation cover. More detailed numerical experiments revealed a likely misrepresentation of the foliage costs in the model, which are based on a linear relation between leaf area and fractional vegetation cover. This finding, and the already favourable comparison with traditional models, implies that optimization of vegetation properties for Net Carbon Profit is a very promising approach for predicting the soil-vegetation-atmosphere exchange of water and carbon in complex ecosystems such as savannas.

References
Schymanski, S.J., Roderick, M.L., Sivapalan, M., 2015. Using an optimality model to understand medium and long-term responses of vegetation water use to elevated atmospheric CO2 concentrations. AoB PLANTS 7, plv060. https://doi.org/10.1093/aobpla/plv060

Schymanski, S.J., Sivapalan, M., Roderick, M.L., Hutley, L.B., Beringer, J., 2009. An optimality‐based model of the dynamic feedbacks between natural vegetation and the water balance. Water Resources Research 45. https://doi.org/10.1029/2008WR006841

Whitley, R., Beringer, J., Hutley, L.B., Abramowitz, G., De Kauwe, M.G., Duursma, R., Evans, B., Haverd, V., Li, L., Ryu, Y., Smith, B., Wang, Y.-P., Williams, M., Yu, Q., 2016. A model inter-comparison study to examine limiting factors in modelling Australian tropical savannas. Biogeosciences 13, 3245–3265. https://doi.org/10.5194/bg-13-3245-2016

How to cite: Nijzink, R., Beringer, J., Hutley, L., and Schymanski, S.: The influence of carbon costs and benefits on predicted vegetation behaviour along a precipitation gradient using the Vegetation Optimality Model, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10740, https://doi.org/10.5194/egusphere-egu2020-10740, 2020.

In spite of their potential as low input crops in arid and semi-arid regions, limitations in CAM (Crassulacean Acid Metabolism) modeling have made it difficult to compare the productivity and water use of CAM crops with their C3 and C4 counterparts on a consistent basis. Using the Photo3 model, which adds a malic acid storage and circadian rhythm to the widely accepted Farquhar et al. model for C3 photosynthesis, we analyze the coupling of CAM carbon assimilation and transpiration with the soil-plant-atmosphere continuum at an hourly timescale to explore the potential of prickly pear and agave in several semiarid locations. Model results are compared with experimental data and contrasted with results generated using the widely used and empirically based Environmental Productivity Index introduced by Park Nobel in 1980. Using model results for CAM as well as C3 and C4 species, we explore how agricultural productivity in these locations may be optimized by diversifying planting strategies among the three photosynthetic pathways. This work aims to assist in better understanding the potential of CAM for food and biofuel production in arid and semiarid regions of the world accounting also for environmental co-benefits related to enhanced carbon sequestration and reduced water demand in semi-arid, marginal lands.

How to cite: Porporato, A. and Hartzell, S.: Ecohydrology of CAM plants: environmental co-benefits for agroecosystems, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11906, https://doi.org/10.5194/egusphere-egu2020-11906, 2020.

Improving the efficiency and sustainability in water resources management in agricultural and agroforestry systems is becoming increasingly important in the light of the increasing pressure on agro-food production due to the growing world population growth and the changing climatic conditions. In this context, achieving an accurate quantification of the proportions of different water sources (including irrigation) taken up by plants has important ecological and economic implications for water saving and utilization. Stable isotopes of hydrogen and oxygen in the water molecule are powerful and, nowadays, affordable tracers that can greatly help to identify and quantify the seasonal water uptake patterns by plants. This tool is largely adopted in natural systems (e.g., in ecohydrological applications in forested environments) but has not been fully exploited in agricultural and agroforestry ecosystems. Here, we outline the advantages and limitations of this technique and report some examples on how it can support more traditional approaches to understand root water uptake dynamics in agricultural and agroforestry systems. Finally, we present a vision for future challenges and new research lines using isotope tracers to investigate crop water use.

How to cite: Scandellari, F., Geris, J., Hopp, L., and Penna, D.: Where do crops take their water from? Using isotopic tracers in agricultural and agroforestry systems, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18529, https://doi.org/10.5194/egusphere-egu2020-18529, 2020.

Maintenance practices restoring the hydraulic capacity of agricultural ditches (mowing, burning, chemical weeding or dredging) modify the plant communities in the short and medium term. However, the medium term modification of plant community composition, parameters and properties, and in turn the associated functions provided by ditches (water transport, propagules and sediment retention, biodiversity conservation) have not attracted much attention so far. Therefore, the main question raised in this study was the following : Do ditch maintenance practices affect plant community composition, parameters, and properties associated with water and particle transport processes (sediments, seeds), as well as biodiversity, in the medium term (two years)?

We designed an experiment to compare the effects of different maintenance practices in a Mediterranean agricultural ditch. We measured the plant richness, morphological parameters and properties of the plant community affecting ecosystem functions twice : before applying the maintenance practices and after two years of contrasting maintenance practices. We assessed the differences between practices using linear models and generalized linear models, followed by pairwise comparisons between means using the Tukey test.

Maintenance practices differently affected plant community composition, parameters and properties, such as richness, proportions of harmful plants, distribution of heights, densities, proportions of growth forms and total biomass. None of the maintenance strategies simultaneously improved the functions considered. After two years, mowing provided the highest alpha-diversity and had a low proportion of harmful plants. Burning was the practice that produced the highest total biomass and blockage factor, and therefore negatively influenced the water transport. However, this practice positively impacted seed retention and sedimentation. Our results suggest that associations of maintenance practices would preserve the trade-offs among the different functions in the medium term.

How to cite: Rudi, G., Bailly, J.-S., Caraglio, Y., Dollinger, J., and Vinatier, F.: Influence of maintenance practices on plant community properties interacting with ecosystem functions in an agricultural ditch, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9922, https://doi.org/10.5194/egusphere-egu2020-9922, 2020.

Assessing the future of water resources in terrestrial biomes is contingent on observations from climate-manipulation experiments. Global change in the Anthropocene could produce various permutations of warming, atmospheric carbon levels, and moisture availability; however the impact on ecosystem hydrology is largely studied individually (e.g., elevated CO₂ or temperature) rather than interactively. We sought to specify how various combinations of  drought, elevated CO₂ (+150 ppm, +300 ppm) and warming (+1.5°C and + 3°C) may alter the partitioning of soil moisture in the root zone of mountain grassland. Using spectral techniques, we transformed these high resolution data (i.e., 4 soil depths and every 15 min) into the frequency domain to study the interactive effects of climate change on sub-hourly to seasonal soil moisture signals. Diurnal moisture signals in heated plots (+3°C in air temperature) were up to 3x stronger (in amplitude) during summer drawdown compared to plots receiving heat and elevated CO₂ (+300 ppm). This preliminary analysis suggests that elevated atmospheric carbon may buffer heat-driven soil moisture losses in grassland root zones by reducing transpiration fluxes during seasonal dry periods.

How to cite: Reinthaler, D., Radolinski, J., Pötsch, E., and Bahn, M.: Global change in the root zone: lessons from soil moisture dynamics in a multifactor climate manipulation experiment , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18589, https://doi.org/10.5194/egusphere-egu2020-18589, 2020.

Arid lands represent one third of terrestrial surfaces with ecosystems uniquely adapted to water limitations. Arid regions are characterized by low rainfall and sparse vegetation with potential evapotranspiration (ET₀) exceeding annual rainfall (P) and surface evaporation dominating water losses. The objective was to quantify the fraction of rainwater sheltered from surface evaporation to estimate arid region vegetation carrying capacity. The surface evaporation capacitor (SEC) model was used to quantify surface evaporation from the climatic record of rainfall and potential evaporation. The SEC uses soil-specific active evaporation depth where only rainfall events that exceed its critical capacitance result in leakage into deeper layers. This “leakage” becomes protected from surface evaporation and may support vegetation or inter-annual storage. Focusing on arid regions (aridity index P/ET₀< 0.2) we illustrate the strong correlation between evaporation-protected rainwater and net primary productivity (NPP) using typical values of water use efficiency. SEC-estimated NPP values were in good agreement with observations and predictions by a state-of-the art ecohydrological model (T&C). Evaporation-protected soil water storage is generated during a few large rainfall events that exceed surface capacitance. This leakage increases with increasing rainfall variability, potentially enhancing vegetation carrying capacity by diverting larger fractions of rainfall from surface evaporation to vegetation-supporting “leakage”. The potential increase in carrying capacity and resulting vegetation cover are greatly influenced by (i) the change in rainfall variability, (ii) soil type, and (iii) surface features that concentrate or divert runoff. We discuss implications of this mechanism for global greening of arid lands and woody plant encroachment.

How to cite: Or, D., Lehmann, P., Bickel, S., and Fatichi, S.: Vegetation carrying capacity of arid regions: on the fraction of rainfall sheltered from surface evaporation, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6066, https://doi.org/10.5194/egusphere-egu2020-6066, 2020.

Mediterranean mountainous areas of shallow soil often display a mosaic of tree clumps surrounded by grass. During dry seasons, evapotranspiration (ET) cannot be met by soil moisture. However, the combined role and dynamics of water extracted from the underlying rock, and the competition between adjacent patches of trees and grass, has not been investigated. We quantified the role rock water plays in the seasonal dynamics of evapotranspiration, and its components, over a patchy landscape in the context of current and past seasonal climate changes, and land-cover change strategies. Soil water budget, using precipitation (P), ET, and soil moisture changes (ΔS; ~17 cm soil layer), suggests deep water uptake by roots of trees (f_d; 0.8 – 0.9 mm/d), penetrating into the fractured basalt below clumps and the surrounding pasture, subsidized grass transpiration in spring through hydraulic redistribution. However, in summer trees used all the deep water absorbed (0.79 mm/d; f_d > tree transpiration). A 15-year dataset shows that, with increasing seasonal drought-severity (potential ET/P) to >1.34, the vertical water flux through the bottom of the thin soil layer transitions from drainage to uptake in support of ET. A hypothetical grass-covered landscape, with no access to deep water, would require 0.68 – 0.85 mm/d more than is available from P and ΔS, forcing shortened growing season and/or lower leaf area. In summer, ET in such a landscape would be half that of the existing mosaic, with consequences to energy balance. The vegetation mosaic may represent trending equilibrium, as long-term decreasing winter precipitation and increasing spring potential evaporation suggest drying climate. Intervention policies to increase water yield by reducing tree cover will curtail grass access to rock moisture, while attempting to increase tree-related products by increasing forest cover will limit water availability per tree leaf area. Both changes may further reduce ecosystem stability.

How to cite: Montaldo, N., Corona, R., Sirigu, S., Piroddi, L., Curreli, M., and Oren, R.: Rock water as a key resource for ecosystems with thin soils: Digging deep trees subsidize patches of surficial grasses, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13480, https://doi.org/10.5194/egusphere-egu2020-13480, 2020.

Many approaches for modelling river water temperature are available, but not one exist that can be applied without restrictions. The applied method depends on data availability, dominant processes, scales and transferability. Process-based models are currently the best way to evaluate detailed management scenarios on reach scale and to understand underlying processes.  Due to limitations of data availability, however, more simplified approaches are frequently applied, where different meteorological or hydrological time series are statistically related to water temperature (or in the simplest case only using air temperature). Here, machine learning methods could help bridging a gap by allowing for more complex relationships without setting prior assumptions. They are thus integrating reasonable processes and dynamics within the catchment by learning from given data. However, up-to-date machine learning approaches have rarely been used in this field until now.

This contribution analyses a set of machine learning approaches for large-scale river temperature modelling. Deep learning methods, random forests and boosting methods are compared with the performance of commonly used simple and multiple regression models. These approaches are tested on 10 catchments with different characteristics, human impacts (e.g. hydropower, river regulation) and time series lengths (10 to 39 years). They are situated in the Austrian Alps or flatlands with areas ranging from 200 to 96.000 km². Observed data including daily means of river water temperature, air temperature, discharge, precipitation and global radiation are grouped to simple and advanced sets of input variables to analyse possible data dependencies. 

In summary, we compare up-to-date machine learning approaches for their applicability in river water temperature prediction. By implementing necessary data preprocessing steps and machine learning routines in a R package, we aim to make these findings easily accessible and reproducible for the community. This tool provides an attractive approach for large-scale river temperature modelling, where the requirements for using process-based models are not able to be met. Future applications can include e.g. short and long term forecasting of river water temperature to find management options for balancing environmental requirements. 

How to cite: Herrnegger, M., Feigl, M., Lebiedzinski, K., and Schulz, K.: Efficient modelling of water temperature patterns in river systems – benchmarking a set of machine learning approaches, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19090, https://doi.org/10.5194/egusphere-egu2020-19090, 2020.

Water temperature modelling has become an essential tool in the management of ectotherm species downstream of dams in North American rivers. The main objective of this project is to compare different datasets and their ability to adequately simulate water temperatures in the Nechako River, (B.C., Canada) downstream of a major dam where the flow is not managed for hydroelectric production, but spills are programmed to cool the downstream reaches. This will ultimately lead to a reassessment of water management in the context of climate change to ensure the survival of fish migrating or living in the reaches located downstream of the dam during warm periods.

Water in the Nechako River stems from the Nechako reservoir at the Skins lake spillway and flows into river through a series of lakes prior to reaching Finmoore, where federal regulations stipulate that water temperatures must be maintained below 20 °C. The river has multiple tributaries on it’s 250 km journey including the Nautley river. The river flow is simulated using a 1D unsteady flow simulation and lateral inflows using HEC-RAS.

Water temperature simulations are then conducted using different datasets. The first is a series of observed meteorological data spanning from 2017 to present day from two different weather stations near the river. The second dataset is ERA5, a reanalysis product that’s gridded every 0.25°. Eleven stations nearest to the river were extracted over the same period as the observations. Both datasets were used to calibrate five parameters (dust coefficient, three wind function parameters and the Richardson number) three times using the mean absolute error (MAE), Nash-Sutcliffe coefficient (NS) and root mean squared error (RMSE) by comparing the observed and simulated temperatures near Finmoore.

Individual calibrations were performed over each available summer from early June to late August and then validated over the rest of the data to ensure the robustness of the results.

Overall, the reanalysis dataset outperformed the available observations for thermal representation of the river.

To further understand the thermal model, a sensitivity analysis was performed on the different inputs (inflow water temperature, air temperature, wind speed, etc.). The model showed very little sensitivity to the characteristics of the inflow (temperature, volume) as the point of interest was so far downstream. In fact, environmental factors such as air temperature had a greater impact on water temperature than upstream conditions at the reservoir spillway. This effect seems to be mostly attributable to Cheslatta Lake with its long water residence time that can reach upwards of three days.

The potential effects of climate change on water temperature were then investigated by modifying existing weather data like air temperature with the delta method on a monthly basis using the RCP8.5 emission scenario. Water temperatures increased throughout by roughly 2.5°C downstream, near Finmoore.

How to cite: Gatien, P.: Evaluating and modelling the impacts of climate change and reference datasets on river water temperatures for a hydropower system with two outlets, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3791, https://doi.org/10.5194/egusphere-egu2020-3791, 2020.

Human activities and natural processes are the main drivers of the spatio-temporal variability of thermal regime. Despite a few local studies on the thermal regime variability, regional assessments are scarce in the scientific literature. However, regional assessments allow tracing systematic human-induced changes emerging from some types of anthropogenic structures like dams or ponds and identifying the locations of highly influenced reaches.

In the current study, we propose a framework to detect the influence of dams and ponds on stream temperature. We use observational data from 526 evenly distributed hourly stream temperature stations in the Loire River catchment, France (110,000 km²). The data consist of unbalanced time series of natural and altered thermal regimes that contain at least 80 summer days from 2000–2018. By comparing time series of observed stream temperature and air temperature, we define five indicators to distinguish different patterns of thermal regime. Three of them are based on weekly stream-air temperature linear regressions (slope; intercept; and coefficient of determination). The remaining two indicators compare monthly air and stream temperature regime: 1) the proportion of times stream temperature is greater than air temperature from March–October (“frequency”), and 2) the lag time between the annual peak in air temperature and annual peak in stream temperature (“shift”).

K-means clustering partitioned stations into three clusters: 1) pond-like, 2) dam-like 3) and natural, with 164, 37, and 316 stations, respectively. Supporting this cluster analysis, 93% of stations in pond-like cluster have upstream ponds, and 55% of stations in dam-like cluster have upstream large dams. Pond-like stations have the greatest slope between weekly stream and air temperatures (slope = 0.4) and have stream temperatures greater than air temperatures more frequently (68%) than other clusters. In contrast, dam-like stations have the lowest correlations between weekly stream and air temperatures (mean R²=0.3, compared to 0.7 for the other two clusters). Dam-like stations also exhibit the largest shifts in stream thermal regime relative to air temperature (mean shift = 30 days). Impounded runoff index (IRI), the ratio of reservoir volume to annual discharge, best explaines variability within the dam-like cluster. For pond-like stations, catchment areas and mean upstream ponded surface area best explain the within-cluster variability, particularly for the frequency indicator, although this relationship is sensitive to interannual air temperature regime.

These findings support modelers in quantifying the downstream impacts of different types of anthropogenic structures and managers in surveying and monitoring stream networks through identification of critical reaches.

How to cite: Seyedhashemi, H., Moatar, F., Vidal, J.-P., Beaufort, A., Chandesris, A., and Valette, L.: Identifying the influence of dams and ponds on the thermal regime at regional scale: The case of Loire catchment, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15120, https://doi.org/10.5194/egusphere-egu2020-15120, 2020.

River regulation by the construction of reservoirs represents one of the greatest challenges to the natural hydrological regime and ecological health of riverine systems. The Danjiangkou (DJK) Reservoir is the largest reservoir on the Hangjiang River and started operation in 1967 and was upgraded in 2012 to provide water resource for the South-North water transfer project through central China. However, the effect of the reservoir operation on the downstream hydrological regime and ecological health of the Hanjiang River after the upgrade (increase in dam wall height) has not been examined thus far. The daily discharge series from four stations along the main stem of the Hanjiang River, including a control site were examined from 1950-2017.  the study period was divided into three periods based on the different stages of the reservoir operation: i)1950-1966, ii) 1967-2012 and iii) 2012-2017. The nature of the hydrological alteration and the ecological risk of diversity (Shannon diversity index) during different periods were investigated. The result clearly indicate that the DJK reservoir has significantly modified the hydrological regime in the middle and downstream section of the Hanjiang River, with most significant modifications recorded immediately downstream of the reservoir. Using the Range of Variability Approach, after the increase of reservoir capacity at Huangjiagang the river ecological flow requirements could not be fully guaranteed and the frequency and intensity of ecodeficit increased. Biodiversity downstream of the dam was significantly reduced at Huangjiagang (Huangzhuang) and there was an increased risk of ecosystem degradation during both the second and third time period.

How to cite: Yu, M., Wood, P., Liu, X., and Li, Q.: Assessment of potential ecological risk due to hydrological flow regime modification in the Hanjiang River basin 1950-2017, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3942, https://doi.org/10.5194/egusphere-egu2020-3942, 2020.

Understanding how summer low flows in a Mediterranean climate are influenced by climate and land use is critical for managing both water resources and in-stream ecohydrological health. The Eucalyptus forest ecosystems of southwestern Australia are experiencing a drying and warming climate, with a regional step decline in rainfall in the mid-1970s.  Reductions in catchment water storage may be exacerbated by the deep rooting habit of key overstorey species (>30 m has been reported), which can buffer against drought during dry years. Root exploitation of deep soil moisture reserves and/or groundwater can accelerate the long term decline in summer low flows, with a trend towards more ephemeral flow regimes. In contrast, conversion of forests to agricultural land in some catchments can lead to counter-trends of increased low flows due to a rise in groundwater pressure.  These are invariably associated with an increase in stream salinity as regolith stores of salt are mobilized. There has also been extennsive reforestation of farmland in some catchments. 

In this study we perform a detailed analysis of changes to annual summer seven day low flow trends in perennial catchments and flow duration curves in ephemeral catchments across 39 catchments in south-western Australia that have long term records of runoff, rainfall and land cover.  Results showed that 15% of catchments exhibited increased low flows and 85% decreased flows or decreased flow days since the 1970s.  Significant downward step changes in low flows were observed in 17 catchments (44%). The earliest downward step changes occurred in three catchments between 1981-82 (a lag of one decade after the rainfall decline), with the most recent step changes for five catchments occurring in 2001-2004 (three decades after rainfall decline).  Eleven catchments were already ephemeral in the 1970s, but exhibited continued declines in the number of annual flow days over subsequent decades.  Step changes occur when groundwater becomes disconnected or reconnected to the stream invert, with disconnection associated with rainfall decline and vegetative water use.  

The statistical methods we used in this study can be applied to any catchment in order to aid land and water managers assess the impact of climate change and land cover manipulation on low flow response.

How to cite: Smettem, K., Liu, N., Harper, R., and Ruprecht, J.: Spatiotemporal changes to low flow and catchment storage following a step change rainfall decline in Southwest Western Australia, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3214, https://doi.org/10.5194/egusphere-egu2020-3214, 2020.

Interventions of risk mitigation from floods can no longer be separated from the evaluation and improvement of river ecological status. Specific reference is made to the European framework on water quality 2000/60/CE which in turn, in Italy, has been applied in the so-called Management Plan of the Po basin (2015-2021).

The Pellice River is the recipient of the first multi-objective interventions in Italy that respond to this innovative vision of water courses. It is therefore a pilot case that distinguishes from previous design approaches. The areas of intervention have been identified at institutional level (AIPO, Regional and River Basin Authority), selecting the zones where sediment management and flood defense interventions also include habitat improvement. The working group had the task to prepare the detailed design in order to respond to the need to recreate natural conditions of the river environment and hydraulic risk mitigation.

For this purpose, the Pellice River has been studied for a length of about 20 km from the geological, hydrological, hydrogeological, geomorphological and ecological point of view, thanks to the collaboration of a multidisciplinary group, composed by engineers, biologists, ecologists, foresters, ichthyologist and river vegetation specialists. An analysis of the aquifer levels and a monitoring of the aquatic habitat were also carried out, i.e., through the identification of trout spawning. In this first phase, the aim of the study was to reach adequate information to photograph the morphological, ecological and vegetational status of the watercourse in the intervention areas.

In a second phase, the analysis has been completed by means of mono and two-dimensional hydraulic modeling not only of the flood events but also with a 1- year return time event. This is necessary to evaluate the reactivation of designed secondary channels, the effectiveness of sediment management interventions and the realization of flow diversion structures made with natural elements that can also act as a refuge for animals. These results together with the maximum and minimum depth of the aquifer made it possible to design improved aquatic animal and vegetation habitats.

Finally, some geomorphological indicators have been coupled with vegetational and ecological ones in order to propose a practical instrument for the evaluation of interventions effectiveness over time.

How to cite: Perucca, E., Gibelli, G., Peres, F., Tarchiani, J., and Telò, R.: Ecohydrological integrative approach to restoration interventions on Pellice River (Piedmont Region, Italy), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7337, https://doi.org/10.5194/egusphere-egu2020-7337, 2020.

Anthropogenically modified hydrological processes shape the Prek agroecosystem in the Cambodian part of the Mekong delta. Preks are trapezoidal channels that were initially constructed during the French protectorate for land raising purposes and extending agriculture in the low-lying Cambodian floodplain, which they connect to the river courses. These channels have become an integral part of the landscape. They are an essential vector for both flooding and drainage, and local communities are deeply organized in relation to these structures. However, with the lack of wide-ranging maintenance work, sedimentation and erosion have modified the functionalities of many of these Preks, a priori reducing the environmental amenities provided to the rural communities. In response to this, various development agencies have sought to rehabilitate several of these Preks in recent years, mostly with the objective to further intensify an already intensive agroecosystem.

 The purpose of the present study is thus to assess the actual effects of these rehabilitations on ecohydrological services. To this end, a comparison has been carried out of inundation and vegetation patterns, as well as ecosystem services, between areas where Preks have been the subject of rehabilitation projects and areas where they have not. For this purpose, remote sensing analyses, hydrological modelling and sociological methods have been employed. To begin with, an analysis of flood dynamics and vegetation structures in the study area has been carried out in the cloud computing platform Google Earth Engine using Sentinel-1 and 2 data. Furthermore, semi-structured interviews with stakeholders (farmers, village chiefs, staff from sectoral ministries) were conducted in the field to scope ecosystem services and find indicators to integrate these services into a numerical model.  

The analysis describes hydrological, ecological and agricultural dynamics that are currently at play in the area, and will further study how Preks rehabilitation could influence these dynamics by comparing areas with and without rehabilitation. Among the processes considered are shifting water availability for irrigation, agricultural intensification, modifications in small-scale habitats, changes in the use of pesticides and herbicides with resulting impacts on soil structure, and alterations in vegetation patterns. Furthermore, several aspects that have caused problems in the rehabilitation process will be considered - such as operational difficulties of sluice gates, bank collapses blocking the water flow in channels, an underestimation of multiple uses of water and a lack of understanding of the complex river flows in the area. The analysis leads to identifying the eco-hydrological processes and indicators to implement in a process-based hydrological model aiming at exploring alternative scenarios of rehabilitation. 

How to cite: Orieschnig, C. A., Belaud, G., Massuel, S., and Venot, J.-P.: Irrigation canal systems of the Cambodian Mekong delta: Assessing changes in ecosystem services for rural communities after wide-ranging rehabilitation plans., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2732, https://doi.org/10.5194/egusphere-egu2020-2732, 2020.

Dongting Lake is the largest lake in the middle reaches of the Yangtze River in China. After the completion of the Three Gorges Project, the relationship between the Yangtze River and Dongting Lake has a significant change with the decreased diversion ratio. Besides, due to the overexploitation of local human activities, some dry-up reaches appeared in the Dongting Lake region, especially in the polders with high strength  human activities. In order to scientifically understand the evolution law of water resources in those protective embankments in lakeside areas, and understand the relationship between human activities and ecosystem stability, the study works on the ecological water demand that coupled with the ecological capacity of the environment. As a typical polder, the Yule polder is selected as a case study in the Dongting Lake region. The objective is to obtain the ecological water demand process which can maintain the requirements of water quantity and quality of water to maintain water ecological needs under the condition of significant human impacts. Based on the actual situation of vegetation coverage, aquatic organism growth status and protection goals, and water demand of the industrial and agricultural population, taking the satisfaction degree of ecological water demand as an indicator, healthy of local water ecology is to be evaluated. Combining the hydrological situation of entire Yangtze River basin, the temporal distribution characteristics of ecological water demand in the Yule polder is analyzed, and also the feasibility of measures such as diverting Yangtze River water to alleviate the fragility of water ecology in the Dongting Lake region is discussed. These results could provide experience for solving similar problems in other regions.

How to cite: Cai, Y., Tang, L., Tian, D., and Xu, X.: Ecological water demand in the typical polder of Dongting Lake, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7057, https://doi.org/10.5194/egusphere-egu2020-7057, 2020.

Dynamic internal feedbacks and stochastic external shocks drive the spatial organization and heterogeneity of patchy habitats, and thus the temporal variability of patch suitability and accessibility. Such spatiotemporal shifts impact species dispersal among patches and metapopulation persistence. Here, we extended the widely recognized concepts of patch-occupancy and metapopulation capacity from static to dynamic patchy habitats, with isolated wetlands embedded in uplands as the case study. We present a new metapopulation modeling approach by linking a hydrological model for wetland variability with a dynamic stochastic patch-occupancy model. In two case study wetlandscapes, we evaluate (1) spatiotemporal dynamics of wetland hydrologic regimes, and patch suitability and connectivity driven by stochastic hydroclimatic forcing, and (2) spatiotemporal patterns of patch occupancy and metapopulation dispersal dynamics. Our modeling results reveal the importance of specific connected patches that serve as persistent hubs and form the backbone of dispersal corridors to support species dispersal in fragmented dynamic landscapes. Our analyses reveal that the interplay between stochastic hydroclimatic forcing and patchy habitat structure could drive species to extinction when specific thresholds are crossed.

How to cite: Bertassello, L. E., Jawtiz, J., Bertuzzo, E., Botter, G., Hoverman, J., and Rao, S.: Stochastic Spatiotemporal Patterns of Metapopulation Occupancy in Dynamic Wetlandscapes, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10869, https://doi.org/10.5194/egusphere-egu2020-10869, 2020.

As one of the world's three major ecosystems, the study of wetland health has global environmental implications. Vegetative biomass has emerged as one of the most valuable indicators of wetland health. The ongoing development of remote sensing techniques, coupled with improved data processing and modeling, creates new possibilities to monitor and understand wetlands. Multiple regression model types were employed to find the best fit between Landsat-8 images, vegetation indices, and field measured biomass in the Yellow River Delta Nature Reserve. Then, these models were used to estimate the spatial distribution of wetland vegetative biomass. Further, the relationship between wetland vegetative biomass and soil factors (organic matter, nitrogen, phosphorus, potassium, water soluble salt, pH, and moisture) was correlated and modelled. It was discovered that the Landsat-8 images and vegetative indices are better at predicting biomass when dry weight data is used rather than fresh weight data. Using multiple regression model types, we were able to achieve higher correlation and higher fit accuracy with vegetative indices and Bands 1-5 as independent variables and biomass dry weight as the dependent variable. Several soil factors were discovered, such as soil moisture and salt concentrations, which affect spatial distribution patterns of biomass in this wetland. Continued research using and improving upon these techniques will yield new insights into how to better promote wetland health.

How to cite: Han, M.: Wetland biomass inversion and space differentiation – Using the Yellow River Delta Nature Reserve as an example, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3577, https://doi.org/10.5194/egusphere-egu2020-3577, 2020.

rimary soilIditches during short but intense storms. Furthermore, these man made ditches provide valuable habitat for fauna and flora, but the spread of the weed could be limited by preserving existing hydraulic structures or maintaining areas where the density of terrestrial vegetation is sufficient to enhance seed retention downstream.

How to cite: Vinatier, F., Rudi, G., Belaud, G., and Bailly, J.-S.: Patterns of hydrochorous dispersal in agricultural channels, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5599, https://doi.org/10.5194/egusphere-egu2020-5599, 2020.

The rate of biogeochemical processing associated with natural degradation and transformation processes in the hyporheic zone (HZ) is one of the largest uncertainties in predicting nutrient fluxes. We present a lumped parameter (LPM) model that can be used to quantify the mass loss for nitrate in the HZ operating at the scale of river reaches to entire catchments. The model is based on using exposure times (ET) to account for the effective timescales of reactive transport in the HZ. Reach scale ET distributions are derived by removing the portion of hyporheic residence times (RT) associated with flow through the oxic zone. The model was used to quantify nitrate removal for two scenarios: 1) a 100 m generic river reach and 2) a small agricultural catchment in Brittany (France). For the field site hyporheic RT are derived from measured in-stream ²²²Rn activities and mass balance modelling. Simulations were carried out using different types of RT distributions (exponential, power-law and gamma-type) for which ET were derived. Mass loss of nitrate in the HZ for the field site ranged from 0-0.45 kg d^-1 depending on the RT distribution and the availability of oxygen in the streambed sediments. Simulations with power law ET distribution models only show very little removal of nitrate due to the heavy weighting towards shorter flow paths that are confined to the oxic sediments.  Based on the simulation results, we suggest that ET likely lead to more realistic estimates for nutrient removal.

How to cite: Frei, S., Gilfedder, B., Durejka, S., Thomas, Z., and Le Lay, H.: Quantification of Hyporheic Nitrate Removal at the Reach Scale: Exposure Times versus Residence Times, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5040, https://doi.org/10.5194/egusphere-egu2020-5040, 2020.

The purpose of the essay was analysis and evaluation of the load generated by pollutants in the Russian part of the catchment area directly entering the Baltic Sea, as well as consideration of pro-rata contribution of all sources in the formation of factual biogenous load at the catchment areas of rivers flowing into the Gulf of Finland.

The assessment of biogenous load was made on the basis of observation data, statistical reporting data, mathematical modelling data and additional monitoring data for bodies of water in previously uncontrolled areas. To assess the amount of biogenous input from uncontrolled tributaries of the Gulf of Finland, field observations of the discharge and concentration of pollutants over a number of past years were analyzed and generalized.

It is noted that there has been a tendency towards reduction of pollutants for a number of substances in the last decade, as shown by the analysis. It is demonstrated that a significant decrease is due to reduced load from point sources that discharge pollutants directly to the Baltic Sea and its bays. Some proposals are presented for improving the Russian system of monitoring the load exerted on water bodies.

How to cite: Voronov, N., Victorova, N., and Shilov, D.: Assessment of biogenous load on the Gulf of Finland exerted from the Russian territory, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7643, https://doi.org/10.5194/egusphere-egu2020-7643, 2020.

Bacterial communities are essential to the biogeochemical cycle in riverine ecosystems. However, the integrated biogeography and assembly process of planktonic and sedimentary bacterial communities in large rivers is still poorly understood. Here, the study provided the spatiotemporal pattern of bacterial communities in the Yangtze River of 4300 km continuum, which is the largest river in Asia. We found that the taxa in sediments are the main contributors to the bacterial diversity of the river ecosystem since sediments sub-group took 98.8% of the total 38, 904 Operational Taxonomic Units (OTUs) observed in 280 samples. Seasonal differences in bacterial communities were statistically significant in water, whereas bacterial communities in both water and sediment were geographically clustered according to five types of landforms: mountain, foothill, basin, foothill-mountain, and plain. Interestingly, the presence of two huge dams resulted in a drastic fall of bacterial taxa in sediment immediately downstream due to severe riverbed scouring. The integrity of the biogeography was satisfactorily interpreted by the combination of neutral and species sorting perspectives in meta-community theory for bacterial communities in flowing water and sediment. Although deterministic process had dominant influence on assembly processes in water and sediment communities, homogeneous selection was the main contributor in water, while combination of homogeneous selection and variable selection contributed selection process in sediment. In addition, homogenizing dispersal played more important role in community assembly process in sediment than water. Our study fills a gap in understanding of biogeography and assembly process of bacterial communities in one of the world’s largest river and highlights the importance of both planktonic and sedimentary communities to the integrity of bacterial biogeographic patterns in a river subject to varying natural and anthropogenic impacts.

How to cite: Liu, T., Wang, J., Liu, S., Chen, Q., Zheng, C., and Ni, J.: Integrated biogeography and assembly process of planktonic and sedimentary bacterial communities in the Yangtze River, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4567, https://doi.org/10.5194/egusphere-egu2020-4567, 2020.

Although global models of nitrogen (N) cycling typically focus on nitrate of ecosystem N saturation, dissolved organic nitrogen (DON) is the dominant form of nitrogen export from many watersheds. In previous hypotheses, DON dynamics in the watersheds was treated as being functionally equivalent to inorganic N forms. However, unlike inorganic N, the dynamics of N contained within organic molecules is controlled not only by direct biological demand for N, but also by heterotrophic demand for the reduced C, to which N is attached. During 2016-2018, we evaluated the DON release hypothesis and the passive carbon vehicle hypothesis by comparing streamwater DON, DOC, and DIN concentrations across Fushan experimental forested watershed in the northeast Taiwan. We found that (1) the export of the Fushan Experimental Forest (FEF) is N saturated and (2) the altering nature of the DON release hypothesis and passive carbon vehicle hypothesis between non-event days and typhoon events. Results show that DON concentrations change systematically with increasing nitrate concentrations in all surveys. Among which, DON concentration correlates negatively with nitrate concentration in non-event days but positively during typhoon events. Our results support the coupling between DIN, DON, and DOC concentrations in forested watersheds that are subject to high rates of anthropogenic N loading. In non-event days, the N-containing dissolved organic matter may be in a labile form of carbon. Thus, alleviating heterotrophic N limitation may result in a decrease in DON export (passive carbon vehicle hypothesis), while during typhoon events, DON losses increase as demand for labile N forms attenuates (DON release hypothesis). These hypotheses are not mutually exclusive but represent the potentially contrasting roles of DON within C and N cycles. Our study suggests that bioavailability assays and addition experiments will present variations in the direct biological demand for N and heterotrophic demand for the reduced C, which is informative and necessary for characterizing the processes controlling DON export.

Keywords: DON, DIN, N saturation, DON release hypothesis, passive carbon vehicle hypothesis

How to cite: Yu, Y.-L., Huang, J.-C., Hsu, T.-C., and Lin, T.-C.: Role of DIN and DON in nitrogen cycle in a humid subtropical forest catchment in northeast Taiwan, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21160, https://doi.org/10.5194/egusphere-egu2020-21160, 2020.

Olive groves are one of the most extensive crops in the Mediterranean region, hence, their management practices can result in significant environmental, social, and economic impacts. Given the generalized water stress conditions across the Mediterranean region, irrigation is usually applied to increase olive crop yield. In Spain, the country with the largest olive crop extension, 29% of the olive cultivated area is irrigated. Cover cropping (i.e. the maintenance of annuals and perennials in between tree rows) can be considered as one of the most widespread conservation practices. It is being increasingly adopted as a sustainable strategy to increase soil organic carbon content and mitigate soil degradation problems caused by soil erosion, apart from other benefits such as the increase of microfauna biodiversity. On the other hand, cover crops may also increase evapotranspiration and, consequently, water demand in olive production systems. While the influence of cover crops on carbon sequestration capacity of olive groves has been previously demonstrated to be positive, their effects on evapotranspiration and water use efficiency, defined as the ratio between carbon uptake and evapotranspiration, remain uncertain.

In this study, we aim to assess the effect of cover crops on microclimate conditions, carbon sequestration, evapotranspiration and water use efficiency of an irrigated olive grove located in Jaén (SE Spain), where two adjacent areas were subjected to two different treatments: 1) weed-free treatment, in which a glyphosate-based herbicide is applied annually to avoid spontaneous weed growth (generally in early spring), and 2) weed-cover treatment (i.e. cover crop), where spontaneous weed cover was kept from autumn to spring. Both treatments are equipped with a wide range of environmental sensors to characterize short- and long-term variations in ambient conditions (e.g. air temperature, relative humidity, precipitation, incoming/reflected short- and long-wave radiation, soil moisture and temperature, soil heat flux). In addition, two eddy covariance towers allow the direct measurement of atmosphere-ecosystem exchanges of water, heat, carbon dioxide and momentum at a high temporal resolution (<1h). This study was carried out over three consecutive hydrological years from October 2015 to September 2018.

Preliminary results, based on data of the first hydrological year (2015-2016), show that cover crops increase ecosystem evapotranspiration. However, the net carbon uptake was higher in the weed-cover treatment compared to the weed-free treatment, leading to a net increase in ecosystem water use efficiency. Further, the Bowen ratio – conceived as the ratio between sensible and latent heat fluxes – was lower in the weed-cover than in the weed-free treatment. Therefore, despite the fact that cover crops increase water loss through evapotranspiration, they mitigate the carbon footprint of the agrosystem, likely having a positive effect on crop water use efficiency by maximizing the ratio of carbon assimilation to water loss.

How to cite: López Ballesteros, A., Chamizo, S., Meijide, A., Aranda-Barranco, S., Sánchez-Canete, E. P., Kowalski, A. S., and Serrano-Ortiz, P.: The influence of cover cropping on carbon sequestration and water use efficiency in an irrigated Mediterranean olive agrosystem, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18868, https://doi.org/10.5194/egusphere-egu2020-18868, 2020.

In many parts of the tropics, the increased demand for cocoa and its products has led to the development of new plantations. The soil properties in these young plantations may differ from older plantations or natural forests, which may affect soil water flow. As cocoa trees are very shallow rooted, the growth and survival of trees can be prone to changes in soil hydrology. We monitored the soil properties, soil water repellency and hydraulic conductivity in a 5, 12 and >30 year old cocoa plantation. During the dominant wet period, soil water repellency was absent in all stands while the hydraulic conductivity showed no significant differences among them. This suggests that water movement in the wet was not impacted by stand age. However, during the dry season, the water drop penetration times at the 5 (4.1 hours) and 12 (4.4 hours) year old stands were twice as long as the >30 year old plantation (2.1 hours). The extreme repellency in the younger stands were expected to reduce infiltration rates; however, higher rates were recorded in the 5 and 12 year old stands. We suggest that the higher infiltration rates in the younger stands are due to a combination of a highly repellent soil matrix and the presence of large, deep soil cracks which enhanced preferential flow. With the degree of repellency not being correlated with soil properties, we hypothesised that the high grass/sedge cover and high temperatures in the 5 and 12 year old stands enhanced it. While further research is needed to investigate the roll that grass and sedges play in developing repellent conditions and affecting soil water flow, managing their cover may prove beneficial for the growth and survival of young cocoa trees.

How to cite: Farrick, K. and Gittens, D.: The Influence of Tree and Stand Age on Soil water movement in Theobroma cacao plantations , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10216, https://doi.org/10.5194/egusphere-egu2020-10216, 2020.

As climate is changing, future functionality and resilience of terrestrial ecosystems are expected to change in numerous ways. However, these projected changes remain uncertain. One of the major sources of uncertainty is the representation of vegetation dynamics which directly respond to increased temperature and ambient CO2 concentrations and thereby alter transpiration. Many of the existing hydrologic models representing components of the water cycle have a very simplified representation of vegetation dynamics that are not able to represent this link.  In this study we aim to augment the existing mesoscale Hydrologic Model (mHM) with a low complexity dynamic vegetation model (DVM). This will provide the model with improved capabilities to represent the coupled water and carbon fluxes. Our analyses focus on representing the vegetation (i.e. biomass growth) including fluxes such as gross and net primary productivity and their inter-linkages to water storage and fluxes (e.g., soil moisture and evapotranspiration) across biomes (e.g., grasslands). These inter-linkages, which are spatially and temporally variable and scale-related, are crucial for adequately representing the coupled water and carbon cycle. For example, the adequate representation of soil moisture is essential to capture the mechanistic response of plant productivity to changes in soil moisture; and vice versa especially under extreme environmental conditions. In this presentation, we will discuss the simplified structure of the DVM based on a Light Use Efficiency (LUE) model concept and couple the model components to the mHM. Furthermore, the coupled simulation results of different water and carbon fluxes will be presented for a test region in Central Germany.   

How to cite: Bahrami, B., Kumar, R., Thober, S., Rebmann, C., Fischer, R., Samaniego, L., Kleidon-Hildebrandt, A., and Attinger, S.: Augmenting the multiscale hydrologic modeling system with adequate vegetation dynamics for improved representation of coupled water and carbon cycles, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11605, https://doi.org/10.5194/egusphere-egu2020-11605, 2020.

ET partitioning is crucial to examine how water and carbon cycles are coupled and to understand the impact of climate change and human activities on ecosystems and water resources. In this study, an optimality-based ecohydrological model is validated and applied for ET partitioning in a Chihuahuan Desert shrubland site in south-eastern Arizona, USA. The ratio of transpiration to evapotranspiration is 49% for the whole period. Evaporation and plant transpiration mainly occur in growing season following the precipitation events. Evaporation responds immediately to rainfall events, while transpiration shows a lagged response of several days to those events. T/ET ratio dynamic in growing season demonstrates different patterns. Some years show low T/ET ratio at the beginning of the growing season. The peak of the T/ET ratio lags behind the rain events. Other years demonstrate stable and relatively high T/ET ratio T/ET ratio is higher than 60% during monsoon when vegetation is active. We find out that spring precipitation especially the size of the precipitation have a significant influence on shrub growth and the T/ET ratio in growing season. These years have dry spring with extremely low spring precipitation, shrubs remain inactive and there is no evident CO₂ uptake during the spring. Under such circumstance, when summer rainfall event happens, shrub has not grown yet, so the most rains are consumed by soil evaporation. In contrast, these years with high T/ET during the growing season all have high amount of spring precipitation. As a consequence, shrubs have developed a certain number of roots and leaves in spring, shrubs recover quickly after the first rain event during the growing season.

Keywords: evapotranspiration partitioning; evaoration; transpiration; spring precipitation; semiarid shrubland; Chihuahuan Desert.

How to cite: Chen, L., Hu, H., Tudaji, M., Ma, Y., and Zhao, L.: Evapotranspiration partitioning in a semiarid shrubland and its relation to spring precipitation, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21097, https://doi.org/10.5194/egusphere-egu2020-21097, 2020.

A low-cost restoration in patchy drylands aiming at recovering the ability of the ecosystem to capture and store water and nutrients is the installation of obstructions to break runoff pathways and retain these resources (hereafter, resource sinks). Field works in drylands worldwide have studied how the effectiveness of this action depends on the materials used to build the obstructions. However, the spatial pattern attributes of the resource sinks can also affect the effectiveness of the restoration and has not yet been investigated. In this work, we cover this knowledge gap by using a well-known dryland model to investigate how different initial amounts of cover and spatial distribution of installed resource sinks (i.e., random vs. regular) affects the recovery of the system. In agreement with field-work studies, our model results confirm that the installation of resource sinks can restore degraded drylands that are not able to recover naturally. More importantly, we found that a very small cover of resource sinks was sufficient to trigger the recovery of vegetation, while a high cover could lead to a complete failure of vegetation recovery. This was found for both random and regular distributions of resource sinks. However, a distribution similar to that of vegetation in the reference healthy system (i.e., regular distribution in our study system) was more effective: higher plant densities were reached for a given initial cover of resource sinks. Given the high efficiency of low covers of resource sinks suggested by our work, combined with the low-cost materials needed, the installation of resource sinks in severely degraded drylands has the potential to be a key contributor to the large restoration efforts needed to achieve land-degradation neutrality in the coming decades, particularly in developing countries.

How to cite: Garcia Mayor, A., Berghuis, P., Rietkerk, M., and Baudena, M.: The role of cover and pattern of installed resource sinks in the recovery of degraded patchy drylands , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18985, https://doi.org/10.5194/egusphere-egu2020-18985, 2020.

Terrestrial evapotranspiration (ET) is a significant part of the hydrological cycle and it couples water cycles and carbon cycles. Accurate ET estimation is of great significance to hydrological prediction. Recently, the widely used solar-induced fluorescence (SIF) for photosynthesis estimation purpose has been applied to estimate ET given the tight coupling of water and carbon cycles. Some studies have shown that SIF has the potential to predict ET when combined with other meteorological variables. However, these ET-SIF researches in the past are mostly based on empirical relationships between ET and SIF but rarely rely on the mechanistic process of carbon-water interactions. The water and carbon cycles are naturally coupled via plants’ stomata, through which plants exchange CO2 and H2O with the atmosphere. Thus, the main objective of our research is to develop SIF-based ET estimation models by coupling the water and carbon cycles. The model estimates ET by combining SIF with remote sensing products like leaf area index (LAI), photosynthetically active radiation (PAR) and vapor pressure deficit (VPD). The model is well validated by the FLUXNET2015 tower-based ET and MODIS16 ET products.

How to cite: Zhou, K., Xiong, L., and Zhang, Q.: Exploring the potential of solar-induced fluorescence for terrestrial evapotranspiration estimation, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2655, https://doi.org/10.5194/egusphere-egu2020-2655, 2020.