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Zero flow: hydrology and biogeochemistry of intermittent and ephemeral streams

A large proportion of the global stream network comprises channels that cease to flow or dry periodically. These systems range from near-perennial rivers with infrequent, short periods of zero flow to rivers experiencing flow only episodically following large rainfall events. Intermittent and ephemeral rivers support a unique high-biodiversity because they are coupled aquatic-terrestrial systems that accommodate a wide range of aquatic, semi-aquatic and terrestrial flora and fauna. Extension and connection of the flowing stream network can affect the quantity and quality of water in downstream perennial rivers. In many arid conditions, they are the main source of fresh water for consumptive use. However, in many places intermittent and ephemeral rivers lack protection and adequate management. There is a clear need to study the hydrology, ecology and biogeochemistry of natural intermittent and ephemeral streams to characterize their flow regimes, to understand the main origins of flow intermittence and how this affects their biodiversity, and to assess the consequences of altered flow intermittency (both increased and decreased) in river systems.
This session welcomes all contributions on the science and management of intermittent and ephemeral streams, and particularly those illustrating:
• current advances and approaches in characterizing and modelling flow intermittency,
• the effects of flow in intermittent streams on downstream perennial streams,
• the factors that affect flowing stream network dynamics
• land use and climate change impacts on flow intermittency,
• links between flow intermittency and biogeochemistry and/or ecology.

Co-organized by BG4
Convener: E. Sauquet | Co-conveners: Anna Maria De Girolamo, Catherine Sefton
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Thu, 29 Apr, 11:45–12:30

Chairpersons: E. Sauquet, Anna Maria De Girolamo, Catherine Sefton

5-minute convener introduction

Amelie Herzog et al.

Even largely perennial rivers can fall dry during drought events. A resulting partial or full drying-up of streambeds is difficult to monitor with conventional gauging stations, but important as it heavily impacts water availability, quality and aquatic ecosystems. With a predicted tendency towards more extreme droughts, event-based intermittency is likely to increase requiring a better longitudinal quantification of water level and streamflow conditions. The Dreisam River in the south-west of Germany is a stream with a highly dynamic hydrology. In the recent extreme drought years of 2015, 2018 and 2019 the main stream and tributaries partly fell dry; whereas the main gauging station still recorded flow. Furthermore, several tributaries fell dry in 2016, 2017 and 2019.To improve the understanding of the interaction between streamflow, groundwater and water usages in low flow and zero-flow situations, a flexible longitudinal water quality and quantity monitoring network was developed. Different techniques such as QR-code-reading camera systems and ultrasound devices to log water levels as well as water temperature and electrical conductivity sensors were used. The set-up was additionally equipped with conventional capacitive water level loggers. Here, we present a comparison of the different water level monitoring techniques in order to a) evaluate the advantages and limits of the novel techniques and b) investigate any added value of longitudinal, catchment wide zero level monitoring. The results show that the choice of the measurement sites' environment, including shading of QR-codes, light reflections of the water surface and streambed topography, is crucial for a successful application of the used techniques. The distributed gauges reveal a highly variable longitudinal drying pattern within the river network that appears to be event-specific and may not be explained without consideration of all natural and altered system fluxes.

How to cite: Herzog, A., Stahl, K., Weiler, M., and Blauhut, V.: Monitoring zero water level in a drought-affected headwater stream network, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8426, https://doi.org/10.5194/egusphere-egu21-8426, 2021.

Gavin Campbell and Eric Hyslop

Temporary waters span both terrestrial and aquatic environments, though the terrestrial phase is typically understudied. A key component in the ecology of these water bodies is the length of the hydroperiod. To date, hydroperiod length in temporary waters is determined largely by site visits and camera traps. These methods of determination however, are taxing on resources at fine temporal resolutions (daily). While water level loggers are able to determine hydroperiod length, they are relatively expensive and peak at 50°C, preventing the collection of terrestrial data, particularly within the tropics.

Here we propose an alternative low-cost method for the determination of a temporary pond’s hydroperiod length using anchored HOBO pendant dataloggers of temperature and light intensity. By analysing the environmental data collected at fine temporal resolution across dry and wet seasons - corroborated by daily rainfall collection and frequent site visits - the determination of phase, whether aquatic or terrestrial, using this method was possible. This then extended to the determination of the length of the hydroperiod.

In addition to determining hydroperiod length, this method also provided data on the diurnal temperature dynamics, photoperiod and irradiation intensity of the aquatic and terrestrial phases. Trends in pond drying were also detectable using these data. In the terrestrial phase, the method provided data on soil surface temperatures, which was particularly lacking for the Caribbean. These data are important in understanding environmental stress regimes among aquatic and terrestrial ecosystems, with applications in agriculture, conservation and infrastructure.

How to cite: Campbell, G. and Hyslop, E.: The use of environmental data in detailing the hydroregime of a temporary pond, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-629, https://doi.org/10.5194/egusphere-egu21-629, 2021.

Pilar Llorens et al.

Temporary rivers, characterized by shifts between flowing water, disconnected pools and dry periods, represent over 50% of the world’s river network and future climatic projections suggest their increase. These rivers are understudied, especially when only disconnected pools remain, because gauging stations or hydrological models do not inform of what happens after the cessation of flow. In addition, most of biological indicators for water quality are designed for flowing waters and their adequacy for temporary rivers is uncertain.

The development of biological metrics adequate for the assessment of disconnected pools is difficult, because the high species replacement during and following flow cessation. For this reason, one hydrological variable of paramount importance for the assessment of ecological quality of disconected pools is the time since disconnection from the river flow.

The objective of our work is to present a methodology to estimate the time since disconnection of pools from the river flow. This methodology, following the Gonfiantini (1986) model, is based on the sampling of water stable isotopes in disconnected pools. For pools disconnected from the groundwater, knowing the isotopic modification of the water in time due to evaporation, allows to estimate the relative volume of water evaporated since the pool has been disconnected. However, this approach gets complicated when pools have relevant rainfall inputs or exchanges with groundwater.

Within the Vallcebre research area (42º12’N and 1º49’E), two artificial pools, one covered with a transparent lid to prevent the input of rainfall and another uncovered, were installed to validate this methodology in controlled conditions. From July to November 2020, water volume of these pools were weekly measured and sampled for isotopic analysis. In parallel, meteorological variables were monitored and rainfall was also sampled for water stable isotopes.

To develop and validate an operational methodology for estimating the time since disconnection, we first calculated the relative amount of evaporated water based on the variations of isotopic composition of the covered pool samples, and estimated the time since disconnection (for a given natural pool) using the potential evaporation calculated from the meteorological data. For the uncovered pool, the information of amount and isotopic composition of rainfall was added in a mass balance model. Additionally, the same estimations were calculated with standard information (i.e. the meteorological data obtained from the National Meteorological Service and precipitation isotopes data from the Global Network of Isotopes in Precipitation (GNIP) of the International Atomic Energy Agency). Finally, measured volumes changes in pools, were used to assess the limitations of the operational methodology and the sensitivity of the results to meteorological conditions.

Our approach suggests that changes in isotopic composition can be a reliable method to estimate time since disconnection of pools in temporary rivers to better assess their ecological quality.

How to cite: Llorens, P., González, S., Latron, J., Múrria, C., Bonada, N., and Gallart, F.: Using stable isotopes to estimate the time since disconnection of pools in temporary rivers , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3059, https://doi.org/10.5194/egusphere-egu21-3059, 2021.

Adam Price et al.

The paradigm of surface water flow regimes is central to the aquatic sciences, where the timing, duration, frequency, magnitude, and rate of change of flow drive physical, chemical, and biological functions in aquatic systems. However, non-perennial streams comprise the majority of the global river network and there is a need to understand not just whether or not a stream periodically dries, but how it dries. Here, we propose to flip the script on flow regimes by presenting a comprehensive 'drying regime' framework to characterize stream drying.  We then identify similar drying characteristics in streams across watersheds with a broad range of climates, physiographic regions, and land uses. Using daily streamflow from 894 U.S. Geological Survey streamflow gages we isolated over 25,000 unique drying events over a period from 1979 - 2018. From these drying events we identified and calculated streamflow metrics that describe timing, duration, magnitude, frequency, and rate of change of stream drying. Using multivariate statistics, k-means clustering, and random forest analyses we grouped drying events into distinct drying regimes and determined the drivers of the clustered regimes. K-means clustering resulted in 4 distinct drying regimes characterized by (1) more frequent drying, (2) longer no-flow duration, (3) drying occurring following low antecedent flows, and (4) flashy high frequency drying, respectively. The majority of gages had more than one drying regime present at different times within each year, suggesting that dominant flow paths or drivers varied through time  Clustered drying regimes show low event-scale spatial coherence, and while drying regimes (1) and (2) show similar frequency throughout the year, (3) and (4) are substantially more frequent during summer months. Based on random forest analysis, land cover characteristics appear to drive drying event assignment to drying regimes more than climate variables. Furthermore, increased importance of individual watershed properties shows that the structural makeup of the watershed is notably more important to how an intermittent system dries than climate or physiographic characteristics. Non-perennial systems have unique functions due to the occurrence of both flowing and dry states, yet most of the past efforts rely on frameworks built around perennial streamflow behavior. Our work presents a novel drying regime framework to allow future studies to more effectively connect river drying to the physical, chemical, and biological functioning in these systems. This framework may also aid in current sustainable river management, including engineered flow regimes that are designed to balance water allocations with ecosystem requirements.

How to cite: Price, A., Jones, C. N., Hammond, J., Zimmer, M., and Zipper, S.: The drying regimes of non-perennial rivers, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6544, https://doi.org/10.5194/egusphere-egu21-6544, 2021.

Nicola Durighetto et al.

Temporary streams (i.e. streams that temporarily cease to flow) are becoming a hot research topic in hydrology. These streams provide an invaluable contribution to riverine ecosystems, as they host a variety of habitats (from lotic to lentic and terrestrial) which sustain high biodiversity. Temporary streams can be found in different regions of the world and are characterized by strongly heterogeneous flow patterns, from flashy streams that flow only after rainfall events to rivers that episodically experience droughts. Many recent studies investigated temporary streams, originating interesting observational datasets about event-based or seasonal network dynamics. Empirical or conceptual models are usually employed for assessing the main physical drivers of network dynamics in each specific study site.
In this contribution, we develop and apply novel theoretical tools to understand how the local statistical properties of each reach of the network affect the catchment-scale variability of the active length. In particular, the Stream Length Duration Curve (SLDC) is proposed to efficiently summarize catchment-scale dynamics of the active length, providing an objective way to quantify network dynamics. The concept of SLDC is applied to a number of Italian headwater catchments, where data about temporal changes in the configuration of the flowing stream are available, providing a clue for the characterization of emergent temporal and spatial patterns of network dynamics. The Stream Length Duration Curve can facilitate comparisons across different catchments an time periods, possibly enabling and objective classification of temporary streams. 

How to cite: Durighetto, N., Senatore, A., and Botter, G.: Characterizing temporary stream dynamics: the Stream Length Duration Curve, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7897, https://doi.org/10.5194/egusphere-egu21-7897, 2021.

Dmitri Kavetski et al.

Ephemeral catchments, where streamflow is frequently zero or negligible, are common across the world yet difficult to model reliably. This paper evaluates probabilistic approaches for modelling streamflow in ephemeral catchments, with a focus on the description of predictive uncertainty using residual error models.

We compare an explicit treatment of zero flows using a censoring approach versus a simpler pragmatic approach where the lower streamflow bound of zero is applied in prediction only. Following a theoretical exposition, empirical comparisons are reported using a daily rainfall-runoff model (GR4J), four residual error schemes (based on log, log-sinh and Box-Cox (BC) transformations with power parameter L = 0.2 and 0.5), 74 Australian catchments with diverse hydroclimatology, and five performance metrics, including reliability, precision, bias and proportion of zero flow days.

The explicit approach is most beneficial in "mid-ephemeral" catchments (5-50% zero flows) where it offers substantial improvements over the pragmatic approach. The BC0.2 and BC0.5 transformations are Pareto optimal: BC0.2 achieves better characterisation of predictive uncertainty, whereas BC0.5 attains lower volumetric bias. In "low-ephemeral" catchments (<5% zero flows) the pragmatic approach is sufficient, whereas in "high-ephemeral" catchments (>50% zero flows) both approaches incur limitations and further method development is warranted. The findings provide guidance on improving probabilistic streamflow predictions in ephemeral catchments.

How to cite: Kavetski, D., McInerney, D., Thyer, M., Lerat, J., and Kuczera, G.: Improving representation of zero flows in probabilistic hydrological modelling of ephemeral catchments, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3640, https://doi.org/10.5194/egusphere-egu21-3640, 2021.

Anna Maria De Girolamo et al.

The non-perennial streams and rivers are predominant in the Mediterranean region and play an important ecological role in the ecosystem diversity in this region. This class of streams is particularly vulnerable to climate change effects that are expected to amplify further under most climatic projections. Understanding the potential response of the hydrologic regime attributes to climatic stress helps in planning better conservation and management strategies. Bouregreg watershed (BW) in Morocco, is a strategic watershed for the region with a developed non-perennial stream network, and with typical assets and challenges of most Mediterranean watersheds. In this study, a hybrid modeling approach, based on the Soil and Water Assessment Tool (SWAT) model and Indicator of Hydrologic Alteration (IHA) program, was used to simulate the response of BW's stream network to climate change during the period: 2035-2050. Downscaled daily climate data from the global circulation model CNRM-CM5 were used to force the hybrid modeling framework over the study area. Results showed that, under the changing climate, the magnitude of the alteration will be different across the stream network; however, almost the entire flow regime attributes will be affected. Under the RCP8.5 scenario, the average number of zero-flow days will rise up from 3 to 17.5 days per year in some streams, the timing of the maximum flow was calculated to occur earlier by 17 days than in baseline, and the timing of the minimal flow should occur later by 170 days in some streams. The used modeling approach in this study contributed in identifying the most vulnerable streams in the BW to climate change for potential prioritization in conservation plans.

How to cite: De Girolamo, A. M., Brouziyne, Y., Benaabidate, L., Aboubdillah, A., El Bilali, A., Bouchaou, L., and Chehbouni, A.: Modeling the response of non-perennial streams to climate change impact: The Bouregreg watershed in Morocco, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9414, https://doi.org/10.5194/egusphere-egu21-9414, 2021.

Giovanni Francesco Ricci et al.

Most of the basins in the Mediterranean Region are characterized by a large spatial gradient in rainfall and temperature and heterogeneity in lithology, soil, and land use. Such environmental factors determine a specific hydrological regime of the river systems that generally includes periods of absence of flow and flash flood events.

In the past decades, several countries in South Europe did not invest resources for the monitoring of the intermittent river systems. Currently, several basins have limited time series of streamflow and water quality data. In addition, it is not rare the case of climate stations not well distributed in the basin as well as the presence of several gaps in the time series.

The lithology and geological features are among the main factors affecting the flow regime, playing a crucial role in groundwater and surface-water interaction and water exchange for which the flow may appear and disappear along with the river network. In such a complex environment, the hydrological and water quality model set up and run may be challenging.

Through a case study, this work aims to face some challenges and to define problem-solving in simulating hydrology in Mediterranean basins. The area is characterized by (i) heterogeneity in lithology with karst areas, (ii) limited flow data availability for calibrating the model, (iii) flow intermittence in the river network. The Soil and Water Assessment Tool (SWAT) was applied to the Canale D’aiedda  (Puglia, Italy), a temporary karst river basin under the Mediterranean climate and with limited data availability. Different solutions were tested to simulate the hydrological processes in the karstic areas including both GIS elaborations and model parameters settings and modifications. Among the main parameters, infiltration and transmission losses and soil hydraulic parameters resulted in the most relevant in simulating hydrology in the karst areas. To calibrate the model, a split-in-space procedure was adopted to overcome the limited streamflow measurement availability. Finally, a zero-flow threshold was introduced to predict the number of zero-flow days in the intermittent river reaches, simulating accurately the flow intermittence and the extreme low flow.

The results show that by using specific strategies in setting-up and calibrating the model, the SWAT model is able to simulate daily streamflow with acceptable performances in complex river basins.

How to cite: Ricci, G. F., Centanni, M., Gentile, F., and De Girolamo, A. M.: Simulating streamflow in a temporary karst river system, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9555, https://doi.org/10.5194/egusphere-egu21-9555, 2021.

Michael Eastman et al.

Lack of monitoring of the IRES network limits the potential to develop current understanding of these critical landscape features. Simulation offers potential to improve the spatiotemporal extent and resolution of the available evidence, enabling further research to be performed and understanding developed. Previous research has demonstrated the potential for statistical models to accurately reconstruct the spatiotemporal dynamics of intermittent rivers.

In this study ordinal regression models were trained to simulate the hydrological regime for the first time, enabling the simulation of flowing, ponded and dry dynamics using localised environmental variables, site characteristics and seasonality. This was enabled by a dataset covering the full range of hydrological conditions of ten chalk streams in the Chiltern Hills, UK over the last 23 years.

The hydrological regime was accurately simulated using ordinal regression models, with weighted f-scores ranging from 0.759-0.955, and scores exceeding 0.935 in the six most westerly streams. This apparent west-east pattern was also present in other evaluation metrics, with probability of detection scores ranging from 0.954 to 0.973 in the westerly streams, and 0.775 to 0.908 in the east, and Correct Classification Rate ranging from 0.935 to 0.955 in the west, and 0.849 to 0.909 in the east. The apparent relationship between model performance and BFI suggests groundwater influence on the hydrological regime    

Further research provided further insights into controls on model performance, including groundwater influence, prominence of ponding and the relatively rapid response of the easterly streams. In addition to improved understanding of controls on model performance, the accurate reconstruction of hydrological regime in these rivers facilitates research from linking associated data to previously unavailable hydrological state data, to investigating climate change impacts and influence of abstraction pressures on these invaluable ecosystems.

How to cite: Eastman, M., Parry, S., Sefton, C., Park, J., and England, J.: Statistical modelling of intermittence metrics in temporary rivers of the UK, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12641, https://doi.org/10.5194/egusphere-egu21-12641, 2021.

Izabela Bujak et al.

Many headwater catchments are characterized by temporary streams that flow only seasonally or during rainfall events. As a result, the network of flowing streams is a dynamic system that periodically expands and contracts. This dynamic is likely to affect water flow and composition: the expansion of the stream network enhances the hydrologic connectivity of hillslopes to the streams, which facilitates shorter transit times. Also, the onset of flow in previously dry streambeds can cause flushing of sediments and nutrients. However, our knowledge of the relationships between flowing stream network dynamics and water quantity and quality in headwater catchments is still limited because experimental data remain sparse.

Within the TempAqua project we investigate the processes that drive stream network dynamics by relating measurements of stream network geometry to changes in catchment water storage and stream water quality. For this, we monitored the flow state, discharge, groundwater levels, soil moisture, and precipitation in three (3-7 ha) headwater catchments in the northern Swiss pre-Alps (Alptal catchment) in summer and fall 2020 using a wireless sensor network. To obtain high-resolution data of the dynamic stream network, we did multiple mapping surveys using a self-developed mobile phone application. Moreover, we sampled streamwater and precipitation at an hourly resolution during rainfall events at multiple locations to quantify the short-term changes in water quality when the stream network expands. We will present our research activities in the Alptal catchment and discuss the initial results obtained from the combined monitoring of the flowing stream network and hydrometric and hydrochemical variables.

How to cite: Bujak, I., Rinaldo, A., van Meerveld, I., Käslin, F., and von Freyberg, J.: Linking the dynamic expansion and contraction of stream networks to changes in water storage and water quality in a pre-Alpine catchment, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10767, https://doi.org/10.5194/egusphere-egu21-10767, 2021.

Marc Diego-Feliu et al.
Fluxes of nutrients, metals, contaminants, among others dissolved compounds transported from land to oceans have a direct impact on coastal biogeochemical cycles. One of these land-ocean interaction mechanisms, recently recognized as an important source of these compounds, is the flow of groundwater from continental margins to the coastal ocean, commonly known as Submarine Groundwater Discharge (SGD). The Mediterranean coastline is characterized by the presence of ephemeral streams, geomorphological settings that act as preferential flow paths for both runoff and groundwater towards the sea. The Mediterranean Basin is highly influenced by strong precipitation events (>50 mm) that commonly occur during fall and spring seasons such as isolated depression at high levels events, locally named ‘gota-freda’. In such situations, runoff causes several social and environmental impacts along ephemeral streams that have been long recognized. However, when the surface water flow ceases, the subterranean part of ephemeral streams may continue supplying water and solutes to the coastal ocean via SGD. This process and its effects for coastal ecosystems have been largely overlooked. In this study, we evaluated the influence of a ‘gota-freda’ event on both the role of ephemeral streams as preferential areas for groundwater discharge and on the magnitude of SGD and SGD-derived nutrient fluxes. To do so, three seawater sampling campaigns were performed in a Mediterranean coastal region dominated by ephemeral streams (Maresme, Catalunya) after heavy rainfall events (~50 mm) and in baseflow conditions. Results of this study indicate that SGD flows are between 5 and 7 times higher after a strong precipitation event than in baseflow conditions indicating that the supply of nutrients and other dissolved compounds to the Mediterranean Sea is highly dependent on these events. This study highlights that this mechanism is a relevant process for coastal biogeochemical cycles of semi-arid regions such as the Mediterranean basin.

How to cite: Diego-Feliu, M., Rodellas, V., Alorda-Kleinglass, A., Domínguez-Gabarró, J., Saaltink, M., Folch, A., and Garcia-Orellana, J.: Ephemeral Streams: An overlooked permanent source of groundwater and Nutrients to the Mediterranean Sea, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15871, https://doi.org/10.5194/egusphere-egu21-15871, 2021.

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