Displays

In intermittent streams, microbes in the sediments are challenged by extremely low water availability during dry periods. Microbes are responsible for the retention and degradation of nutrients. Reduced retention in headwaters can lead to nutrient and DOM accumulation in receiving downstream water bodies and can lead to eutrophication and algal blooms. Some research was done in Mediterranean regions, but we found little studies from temperate regions. There, droughts and water abstraction increased over the last years and caused sensitive headwater streams to shift from perennial to intermittent. In an experiment, we measured the effects of desiccation and re-wetting on nutrients (N, P) and dissolved organic matter (DOM) uptake by biofilms in the hyporheic zone. By that, we address two questions: (1) how do intermittent and perennial reaches differ in their response to desiccation and (2) which parameters can strengthen the resilience of hyporheic processes towards desiccation?

We performed a mesocosm experiment with sediments collected from 20 streams of 4 different regions in Austria. Both historically perennial and intermittent streams were sampled in each region. The sediments were filled into up-flow reactors and connected to a water supply to mimic conditions in the hyporheic zone. After an acclimatisation phase of 2 weeks and a dry period of 7 weeks, the sediments were rewetted. During the acclimatisation and the rewetting phase, we performed N, P and DOM plateau additions to measure the retention behaviour and the influence of drying on that behaviour. N was measured as NH₄, NO₂ and NO₃, P as soluble reactive phosphate and DOM as dissolved organic carbon, via absorption parameters and via fluorescence parameters including a PARAFAC analysis. Additionally, we monitored the extracellular enzymatic activity, the water content and other sediment parameters.

We found that the low moisture content, that is left in sediments of temperate streams even after long drought periods, is sufficient for microbes to recover quickly afterwards. We measured a peak of nutrients and DOC right after rewetting. Nutrient and DOC retention was reduced immediately after rewetting, but recovered fast. We could not see any microbial adaption of historically intermittent streams to desiccation. Thus, differences between regions were much larger than those between perennial and intermittent streams. We can verify the results from our experiment by field data we collected in parallel.

Our study clearly highlights the necessity to protect hyporheic microbes from desiccation effects by ensuring enough moisture content during dry periods. Management methods, such as shading or a reasonable amount of residual flow, can ensure healthy biofilms and reduce effects of prolonged drought periods on in-stream nutrient retention.

How to cite: Pucher, M., Hein, T., and Weigelhofer, G.: Nutrient and organic matter retention in the hyporheic zone during drying and rewetting in a mesocosm experiment., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10912, https://doi.org/10.5194/egusphere-egu2020-10912, 2020

Temporary rivers are characterized by shifting habitats between flowing, non-flowing and dry phases. Despite the fact that they are currently receiving significant attention by researchers and managers, the non-flowing (standing pools) phase has been largely disregarded. However, isolated pools in temporary rivers are transitional habitats of major ecological relevance as they can act as refuges for maintaining local and regional freshwater biodiversity. Factors such as pool duration and size, local physicochemical conditions, time since disconnection, distance to other freshwater habitats or presence of predators are crucial for a comprehensive understanding of the ecology of these habitats, and compromise to work towards adequate ecological quality assessments and conservation practices in temporary rivers.

Research is ongoing focused on the development of a method for assessing the ecological status of disconnected pools, based on the relationship between the time elapsed after the pool disconnection and the characteristics of the biological communities taking into account the above-mentioned factors. The prevalence of the pool phase is assessed using the TREHS software tool through interviews with citizens as well as aerial and surface photographs examination. The time since disconnection is assessed with the help of low-cost sensors and water stable isotopes, whereas the local environmental characteristics are assessed using regular metrics. Finally, biological communities of the pools are characterized using both taxonomic and functional metrics, with the support of metabarcoding techniques, applied to diatoms, macrophytes, macroinvertebrates and fishes. This method aims to be used by water managers to improve the monitoring of the ecological status of temporary rivers, which are common around the world, harbor unique biodiversity and provide key ecosystem services.

How to cite: Bonada, N., Gallart, F., Prat, N., Bertran, G., Cañedo-Argüelles, M., Cid, N., Fortuño, P., Gomà, J., Gutiérrez-Cánovas, C., Latron, J., Llorens, P., Múrria, C., Soria, M., Verkaik, I., and Viñoles, D.: Paying attention to the isolated pools phase in temporary rivers. A challenge to the ecological quality assessment of temporary rivers., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22590, https://doi.org/10.5194/egusphere-egu2020-22590, 2020

Temporary streams are common in headwater catchments and serve as important ecological and hydrological links between these catchments and downstream perennial rivers. However, our understanding of temporary streams in headwater catchments is limited due to a lack of high spatiotemporal resolution data of the three main hydrological states of these streams: dry streambed, standing water and flowing water. In this study, we used a custom designed multi-sensor monitoring system to collect high spatiotemporal resolution state data of the temporary streams in the 0.12 km² upper Studibach catchment, a pre-alpine headwater catchment in Alptal, Switzerland. The monitoring system was installed at 30 locations in the stream network. The state data was used to determine: (1) the temporary stream regime for every monitoring location based on the permanence of each hydrological state, (2) the state change thresholds (antecedent soil moisture, precipitation amount and intensity, and discharge at the outlet) for every monitoring location, and (3) the state change patterns in the stream network during precipitation events. The temporary stream regimes, and the state change thresholds and patterns were compared to topographic, land cover and channel characteristics to determine if these factors can explain the variability in temporary stream dynamics. The results show that there are four different landscape areas with distinctive temporary stream dynamics in the catchment, and that a steep forested section with coarse streambed material often disconnects the flowing parts of the upper and lower stream network.

How to cite: Assendelft, R. and van Meerveld, I.: Spatiotemporal changes in the hydrological state of temporary streams in a pre-alpine headwater catchment, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19965, https://doi.org/10.5194/egusphere-egu2020-19965, 2020

Empirical evidence indicates that the active part of the drainage networks, i.e. that characterized by flowing water, is not static but, conversely, it experiences significant expansion/contraction dynamics produced by the interactions between hydrological and climatic variability, morphological features and soil properties in the contributing catchment. The expansion and contraction dynamics of the "wet" component of the river network can be identified in a wide range of climatic conditions, particularly in the headwaters. In these areas, the observed river network dynamics largely depend on the capacity of the upstream drainage area to concentrate surface runoff in channelized sites.

The study presents a research activity carried out in the framework of the European project "DyNET: Dynamical River Networks" (http://www.erc-dynet.it/), specifically aimed at analysing in detail the processes and agents overseeing changes in form and in the length of river networks in a Mediterranean environment. The contribution describes the first results achieved in the southernmost of the basins under investigation in the DyNET project, namely the Turbolo creek catchment (Calabria, Southern Italy). Bi-weekly surveys were conducted in two sub-catchments having a total area of more than 1 km², both during the recession (contraction) and reactivation (expansion) phases of the drainage network. The empirical data were used for the validation of a statistical model of the wet network dynamics, designed to estimate the total length of the active network over time. This length was distributed spatially on the river network in an objective way by defining a two-way relationship between active stream length and the Topographic Wetness Index (TWI). The modelling of the network contraction and expansion dynamics was possible using a few meteorological and hydrological variables. The combined use of information on the overall length of the network and the TWI led to a reasonably good representation of the drainage network dynamics over space and time.

How to cite: Senatore, A., Liotti, A., Micieli, M., Durighetto, N., Botter, G., and Mendicino, G.: Monitoring and modelling drainage network dynamics of a Mediterranean catchment, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11761, https://doi.org/10.5194/egusphere-egu2020-11761, 2020

Headwater drainage networks have a key role in the transport of water and nutrients from the uplands to the sea. The presence of intermittent and ephemeral tributaries makes the river network highly dynamical, with expansion-contraction cycles that are observed in response to precipitation variability. Both the drainage density and the dynamics of the river network, however, are spatially heterogeneous, reflecting the patterns of geomorphic and physiographic features of the contributing catchment. One of the major effects of river network dynamics is that the hydrological connectivity between a hillslope site and the outlet changes through time, with shorter unchanneled lengths and faster drainage pathways when the network is expanded.

Using the empirical data gathered in a small alpine catchment in northern Italy, we present some analyses about the heterogeneity in the river network persistence and the catchment hydrological connectivity under different flow conditions encompassing dry and wet periods. Different areas of the catchment exhibit very different drainage densities, mirroring the spatial heterogeneity in the geomorphological properties of the catchment. In particular, the most ephemeral stretches of the network are associated with thinner soil layers, steeper slopes, and shallow bedrocks, while the most persistent tributaries emerge in regions characterized by thicker soil layers and moraine deposits. The frequency distribution of the unchanneled lengths is used as a tool to characterize the hydrological connectivity between hillslope sites and the river network. Our results show that network expansion affects the length of unchanneled pathways in a very heterogeneous way, with local variations associated to changing hydrological conditions ranging from 0 to one kilometer. Furthermore, we show that the drainage density is more heterogeneous during wet conditions, with an increase in the spatial variability of the unchanneled length of about 20%. These results hint at the importance of studying intermittent and ephemeral streams to enhance the understanding of the hydrology and biogeochemistry of headwater catchments.

How to cite: Durighetto, N., Vingiani, F., Bertassello, L. E., Camporese, M., and Botter, G.: Linking spatial heterogeneity of geomorphic properties, flow persistence and hydrological connectivity, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8831, https://doi.org/10.5194/egusphere-egu2020-8831, 2020

The precise location of river streams and the characterization of their regime (intermittent or permanent) are critical to the quantification and management of water resources. Intermittent rivers are rivers that cease to flow or go completely dry at various times and places. Some studies estimated that intermittent rivers could account for more than 50% of all rivers in the world and are expected to increase in the future. There has been a growing interest in the understanding of these rivers ecosystems and the possible consequences of this increase in intermittency on the availability of water resources. In Burkina Faso in particular, a country located in West Africa and marked by a strong rainfall gradient between North and South (600 to 1200 mm/y), intermittent streams often represent, in some areas, the only significant freshwater source available for irrigation. It is therefore necessary to develop knowledge and understand the factors controlling intermittency in order to define adequate means to preserve and protect rivers. This study aims to identify non-redundant environmental variables that best explain the geographic variations of the hydrological regime of rivers, and in particular the duration of intermittency, and to discuss their interactions. For this purpose, 40 gauging stations are taken into account in the study. The catchments controlled by these stations cover more than 50% of the country territory. The mean number of dry months was used as a predictor to define several classes of intermittence, for which explicit environmental variables were identified through a Principal Component Analysis (PCA). Results suggest that lithology is a crucial and logical control of intermittency in Burkina, with some stations classified as permanent (43%) mostly located on sedimentary and carbonate rocks, whereas the remaining stations classified as intermittent are mostly located on metamorphic rocks. There is also an increasing trend in the number of dry months depending on the aridity index, although contrasted by the underlying lithology and the catchment area. This approach may subsequently be extended to other African countries in order to consolidate our results.

How to cite: Belemtougri, A., Ducharne, A., and Karambiri, H.: Influence of Lithology, Climate and Topography on the duration of flow intermittence in Burkina Faso., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3909, https://doi.org/10.5194/egusphere-egu2020-3909, 2020

Intermittent headwater catchments constitute a significant proportion of many stream networks. In semi-arid climates, intermittent headwater streams flow only following periods of sustained rainfall. There is commonly a rapid response of streamflow to rainfall; however, whether this is the input of recent rainfall or displacement of water stored in the catchments for several years is not well known. Understanding the sources and transit times of water that contribute to streamflow is important for the maintenance of stream health and predicting the response of land-use changes.

The study focuses on two intermittent streams from two contrasting land-use (pasture and forest) in southeast Australia. The native eucalyptus forests in this region were originally cleared for grazing following European settlement ^~180 years ago and then partially replaced by plantation in the last ^~15 years. Stream water and groundwater from the riparian zone adjacent to the streams were sampled between May and October 2018.

The stream water has ³H activities of 1.30 to 3.17 TU in the pasture and 1.84 to 3.99 TU in the forest, with higher activities recorded during the higher winter flows. Groundwater from the riparian zone has ³H activities of 0.16 to 0.79 TU in the pasture and 2.01 to 4.10 TU in the forest. Aside from one riparian zone groundwater sample, all ³H activities of groundwater in the riparian zone are lower than those of recent local rainfall (^~2.79 TU). The single high ³H activity in riparian zone possibly reflects recharge by winter rainfall with higher ³H activities.

The mean transit times (MTTs) of water were estimated using a range of tracer lumped parameter models. The riparian zone groundwater has greater MTTs of hundreds of years in the pasture and up to 9 years in the forest. At high streamflow, the stream water has MTTs of <6 years in the pasture and the forest. The MTTs of stream water at low streamflow vary from 15 to 42 years in the pasture and from 3 to 16 years in the forest. The long MTTs of water from streams indicate that the source water is not just recent rainfall, rather water stored in the riparian zone is mobilised at the commencement of flow and recent rainfall makes a larger contribution at higher flows. The observation is consistent with the major ion geochemistry of the stream water, which most closely represents that of the riparian zone groundwater. The differences in MTTs of stream water between two contrasting land-use imply that the streamflow has been being most likely impacted by land-use changes. Thus, it is necessary to improve the strategies for catchment management to protect stream health from land-use practices.

How to cite: Barua, S., Cartwright, I., Daly, E., and Morgenstern, U.: Understanding the sources and transit times of water contributing streamflow from intermittent headwater catchments in semi-arid areas, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2030, https://doi.org/10.5194/egusphere-egu2020-2030, 2020

Temporary rivers (TRs) are important headwater features of river flow networks, varying dynamically in space and time and providing both terrestrial and freshwater habitats.  In parts of the UK, TRs have become a source of tension between the public and regulators against a backdrop of the competing influences of natural variability, climate change and artificial influences.  Despite this importance, such systems have typically been omitted from monitoring endeavours.  Correspondingly, the occurrence, distribution and characteristics of TRs in the UK are poorly understood.  An enhanced understanding of the features of TRs has the potential to underpin more robust evidence for the protection of aquatic habitats that are vulnerable to drying.

In this study, novel approaches to the statistical modelling of TRs in the UK are adopted to enable the simulation of intermittence metrics. Addressing the challenge of limited observational data, models are trained on data from both the UK and France, drawing on their temporal and spatial advantages, respectively, to maximise their robustness and ability to extrapolate spatially. The performance of a range of statistical modelling and machine learning approaches is evaluated, and applied in simulating intermittence metrics in the UK. 

Preliminary validation results suggest that the modelling approaches are able to replicate observed intermittence metrics where data exist.  Hierarchies of modelling approaches are derived which suggest certain families of models are more effective in simulating flow intermittency in TRs.  The best performing models under validation are taken forward to simulate intermittence patterns beyond networks of observations, helping to identify core regions towards which further focus should be directed by the research and operational TR communities.

Information on the location, prevalence and intermittency of TRs is vital to enhance the efficiency of monitoring strategies with finite resources, and bolster community efforts to engage local stakeholders in gathering additional data.

How to cite: Eastman, M., Parry, S., Sefton, C., and Svensson, C.: Statistical modelling of intermittence metrics in temporary rivers of the UK, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15218, https://doi.org/10.5194/egusphere-egu2020-15218, 2020

Many streams experienced a prominent increase in proportion of cease to flow conditions during and after the multiyear drought in Australia (Millennium drought, circa 1997 – 2009). Change in zero flow occurrence frequency reflects the general transition of stream reaches from gaining to losing conditions, from losing to losing more, and ultimately to the disconnected state. We track and characterise these changes in groundwater-surface water connection using zero flow conditions as a proxy and explore the spatial and temporal patterns in flow regime transformation. The implications for upstream / downstream water availability and management of environmental flows and ecosystems are discussed in view of projected drier future climate.

How to cite: Saft, M., Peel, M., and Peterson, T.: Characterising transition towards more ephemeral streams in Australian catchments, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21214, https://doi.org/10.5194/egusphere-egu2020-21214, 2020

The potential impact of climate change on the flow regime was analyzed for the Celone River, an intermittent river system in the Apulia Region (S_E, Italy). Rainfall and temperature recorded in the past century were analyzed. Flow regime under climate projections for the future (2030–2059) and for the recent conditions (1980–2009) were compared. The Soil and Water Assessment Tool, a hydrological model, was used to simulate daily streamflow in selected river sections.

Daily climate data used to simulate future scenarios were obtained by a combination of a global circulation model (GCM, ECHAM5) and different regional models (RACMO2; RCA; REMO). The impact on the hydrological regime was estimated as a deviation from the baseline (1980–2009) by using a number of indicators of hydrological alterations.

From 1919 to 2012, a slight reduction in total annual rainfall and a decrease of the number of rainy days was recorded, hence, an increase in extreme rainfall events. From 1954 to 2012, the minimum daily temperature in January and February increased reducing the snowfall.

Under future scenarios, an increase in mean temperature was predicted for all months between 0.5–2.4 °C and a reduction in precipitation (by 4–7%). As a consequence, the flow regime moves towards drier conditions and the divergence of the flow regime from the current conditions increases in future scenarios, especially for those reaches classified as I‐D (ie, intermittent‐dry) and E (ephemeral).

Hydrological indicators showed an extension of the dry season and an exacerbation of the extreme low flow conditions with a decrease in both high flow and low flow magnitudes for various time durations. These changes are expected to have several implications for river ecosystems that have to be considered in River Basin Management and Planning.

How to cite: De Girolamo, A. M. and Lo Porto, A.: Potential flow regime alterations under climate change in an intermittent river system, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22542, https://doi.org/10.5194/egusphere-egu2020-22542, 2020

With climate change, perennial headwater streams are expected to become intermittent and intermittent rivers to dry more often due to more severe droughts, placing additional stress on aquatic life and new constraints for water management.

In this study, we quantify the changes in river flow intermittence across France over the 21st century. Using global hydrological model calibrated on gauging stations is certainly hazardous to assess changes in flow intermittence at a fine resolution (i.e. in headwater streams). Here, we suggest a modelling framework supported by field observations performed on a large number of French intermittent streams:

- we used discrete observations from the ONDE network set up by the French Biodiversity Agency recording summer low‐flow levels once a month. ONDE sites are located on headwater streams with a Strahler order strictly less than five and evenly distributed throughout France;

- a model developed by Beaufort et al. (2017) was adapted to simulate the regional probability of drying of headwater streams (RPoD) under climate change. This empirical model is based on regional relationships established between the non-exceedance frequencies of daily discharges and the proportion of drying statuses observed at ONDE sites. Calibration was performed against the discrete flow states available at 3300 ONDE sites between May and October from 2012 to 2018. The model used daily discharges simulated at 568 gauging stations by the GR6J rainfall-runoff model (Pushpalatha et al., 2011).

An ensemble of 26 high-resolution projections has been derived from GCM simulations under RCP2.6 and RCP8.5 emission scenarios, applying an advanced delta change approach (van Pelt et al., 2012). Daily discharge time series at the 568 gauging stations obtained from GR6J with the GCM-driven forcings have been used as inputs of the empirical model to estimate RPoD under future climate conditions.

Characteristics of flow intermittence between May and October have been studied over France divided into 22 Hydro-EcoRegion. Results for the periods 2021-2050 and 2071-2100 show an increase in RPoD with time. The mean RPod over the whole period May–October is 12% at the national scale under the current climate, compared to 20% and 23% on average all RCPs together for the periods 2021-2050 and 2071-2100, respectively. The changes are significant in regions with historically high probability of drying. On the other hand, no change is detected in the Alps. This last result is debatable since, in these areas and under the current climate, low flows are mostly observed in winter, the ONDE sites are sparse and the model predicting RPoD shows the worst performance.

References:

Beaufort et al.: Extrapolating regional probability of drying of headwater streams using discrete observations and gauging networks, Hydrol. Earth Syst. Sci., 22(5), 3033–3051, 2018.

Pushpalatha et al.: A downward structural sensitivity analysis of hydrological models to improve low-flow simulation, J. Hydrol., 411, 66–76, 2011.

van Pelt et al.: Future changes in extreme precipitation in the Rhine basin based on global and regional climate model simulations, Hydrol. Earth Syst. Sci., 16, 4517–4530, 2012.

How to cite: Beaufort, A., Bottet, Q., Thirel, G., and Sauquet, E.: Assessing flow intermittence in France under climate change, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9420, https://doi.org/10.5194/egusphere-egu2020-9420, 2020

Studying Intermittent Rivers and Ephemeral Streams (IRES) requires regular observations of streamflow. Unfortunately, intermittent streams are poorly monitored, particularly in temperate climates. To fill gaps in knowledge of the dynamics of intermittent streams, a pilot initiative within the SMIRES project (Datry et al., 2017, https://www.smires.eu/) was launched in April 2019. This initiative invited citizens to submit observations for a large number of European intermittent streams.

The goal was collecting datasets that can be used in robust scientific inquiries:

-             To identify IRES at the European scale. Everyone was encouraged to report the flow state for any stream in Europe at any time during 2019;

-             To investigate the dynamics of flow intermittence by repeating field observations along an IRES at least once each month and if possible at multiple locations.

The CrowdWater app (https://crowdwater.ch/en/crowdwaterapp-en/) was used to collect the observations. Each contributor was asked to take a picture of the stream and to identify the current flow state of the stream as one of six classes, from “dry” to “flowing”. The citizen science network has collected, in eight months, more than 3500 observations in ~500 river reaches across 15 countries.

In this presentation, we will discuss the benefits and the limitations of this citizen science effort (i.e., how these data complement the information provided by gauging stations, how and why the collected data were used by the main contributors, how participants can be engaged in the long-term etc.). We will compare the success of this international initiative to other regional or local scale initiatives.

References:

Datry, T., Singer, G., Sauquet, E., Jorda-Capdevilla, D., Von Schiller, D., Subbington, R., Magand, C., Pařil, P., Miliša, M., Acuña, V., Alves, M., Augeard, B., Brunke, M., Cid, N., Csabai, Z., England, J., Froebrich, J., Koundouri, P., Lamouroux, N., Martí, E., Morais, M., Munné, A., Mutz, M., Pesic, V., Previšić, A., Reynaud, A., Robinson, C., Sadler, J., Skoulikidis, N., Terrier, B., Tockner, K., Vesely, D., Zoppini, A (2017) Science and Management of Intermittent Rivers and Ephemeral Streams (SMIRES). Research Ideas and Outcomes 3: e21774. https://doi.org/10.3897/rio.3.e21774

How to cite: Sauquet, E., van Meerveld, I., Sefton, C., Fortesa, J., Ramos Ribeiro, H., Tziortzis, I., de Girolamo, A. M., England, J., Estrany, J., Fortuño, P., Munné, A., Csabai, Z., Morais, M., Alves, H., and Datry, T.: An EU-wide citizen science network to monitor hydrological conditions in intermittent rivers and ephemeral streams, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1790, https://doi.org/10.5194/egusphere-egu2020-1790, 2019