Spatiotemporal controls of nutrients concentration-discharge relationships

Speaker: Dr. Camille Minaudo, Physics of Aquatic Systems Laboratory, École Polytechnique Fédérale de Lausanne - EPFL, Switzerland.

Abstract: The analysis of concentration-discharge (C-Q) relationships provides useful information on the processes controlling the mobilization and delivery of chemical elements into streams as well as biogeochemical transformations in river networks. However, finding an appropriate equation linking C to Q and characterize with confidence catchment export regimes is sometimes questionable due to a large dispersion existing in C-Q plots. After explaining the causes for scattered C-Q relationships, I will present two approaches where trying to tackle this issue in the case of nitrogen and phosphorus lead to an improved understanding of the spatial and temporal controls of nutrient exports at the catchment scale. First, I will present an empirical model which considers the possibility for C-Q relationships to differentiate seasonal patterns from the ones observed at the scale of short-term hydrological events. I will highlight the potential of this model to better understand an predict the export of nutrients in catchments with different land uses and diverse hydro-morphological characteristics. Second, I will show how accounting for hysteresis in C-Q relationships at the scale of storm events improved our understanding of phosphorus mobilization and transport in agricultural catchments, and helped to significantly reduce uncertainties in phosphorus load estimations.

Prepare yourself by reading: Minaudo, C.; Dupas, R.; Gascuel-Odoux, C.; Roubeix, V.; Danis, P.; Moatar, F. Seasonal and Event-Based Concentration-Discharge Relationships to Identify Catchment Controls on Nutrient Export Regimes. Adv. Water Resour. 2019, 131, 103379. https://doi.org/10.1016/j.advwatres.2019.103379.

From theory to practice in water quality modelling

Speaker: Dr. Marieke Frassl, German Federal Institute of Hydrology (BfG), Koblenz, Germany.

Abstract: When trying to solve problems of deteriorated water quality, we are challenged by the complexity of our ecosystems. Models are great tools to better grasp that complexity, to gain new insights into the systems and to develop new research questions. In my talk, I will show examples of model applications that helped us to better understand water quality issues in aquatic systems. The examples will cover lakes, reservoirs and rivers. In most cases, these models were used to guide decision making and I will discuss some of the challenges that lie therein. I will touch on challenges of model calibration and validation and introduce a framework for model validation. Most of the examples introduced have been team work and would not have been possible without collaboration. In the second part of my talk, I will shortly introduce the topic of collaborative writing and introduce a few guidelines that we developed based on the experience of the Global Lake Ecological Observatory Network (GLEON).

Prepare yourself by reading: Frassl M.A., Hamilton D.P., Denfeld B.A., de Eyto E., Hampton S.E., Keller P.S., et al. (2018), Ten simple rules for collaboratively writing a multi-authored paper, Plot Computational Biology, 14(11), e1006508. doi:10.1371/journal.pcbi.1006508.

Using environmental tracers to study water flow processes in a steep mountain catchment

Speaker: Dr. Jana von Freyberg, SNSF PRIMA fellow, École Polytechnique Fédérale de Lausanne - EPFL, Switzerland.

Abstract: Precipitation events in steep headwater catchments often result in rapid streamflow responses with discharge rates increasing by several orders of magnitude relative to baseflow conditions. In order to better understand how streamflow is generated so quickly in those systems we need to capture environmental tracer signatures in streamwater and precipitation at a similar temporal resolution as the underlying processes. Therefore, we have installed a ‘lab in the field’ in the pre-Alpine Erlenbach research catchment in Switzerland, where we have been measuring solutes and stable water isotopes in streamwater and precipitation at 30-minute to 1-hour temporal resolution since summer 2016. I will present two studies in which the richness of this data set has enabled us to develop new ways for condensing and analyzing environmental tracer information in streamwater and precipitation.

Prepare yourself by reading: von Freyberg J., Studer B., Rinderer M., Kirchner J.W. (2018), Studying catchment storm response using event- and pre-event-water volumes as fractions of precipitation rather than discharge, Hydrology and Earth System Sciences, 22 (11), 5847-5865. doi:10.5194/hess-22-5847-2018.

Parsimonious modeling of solute transport at the catchment scale

Speaker: Dr. Paolo Benettin, Laboratory of Ecohydrology, École Polytechnique Fédérale de Lausanne - EPFL, Switzerland.

Abstract: The problem of how catchments store and release solutes has been tackled using a number of different approaches. Integrated (or “lumped”) approaches are naturally suited to deal with catchment-scale problems as they aim to reproduce the integrated response of the system at an observational point and allow building parsimonious models. While these model strongly rely on calibration to real-world data, they offer useful insights on the temporal variability of water age. Thus, in all the circumstances where the “chronology” and the “age” of the solute input are relevant, catchment-scale models based on water age are a valid complement to process-based models. Applications to real-world catchments, with conservative and reactive solutes, has helped clarify the critical role of young (i.e. days to weeks) water in controlling the tracer signature of streamflow.

Prepare yourself by reading: Benettin P., Bailey S.W., Rinaldo A., Likens G.E., McGuire K.J., Botter G. (2017), Young runoff fractions control streamwater age and solute concentration dynamics, Hydrological Processes, 31, 2982–2986. doi: 10.1002/hyp.11243