Mini-conf OSUR


 AHLeGall    07/03/2017 : 22:55

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Nous profitons de la venue de collègues étrangers pour proposer une séquence de mini-conférences le mardi 7 mars de 16h à 18h dans la salle de conférence de l'OSUR

Nous profitons de la venue de collègues étrangers pour proposer une séquence de mini-conférences le mardi 7 mars de 16h à 18h dans la salle de conférence de l'OSUR

Long-term monitoring of river basins: strengths and weaknesses, opportunities and threats

Tim Burt, Nicholas Howden & Fred Worrall

In this talk, we briefly explore the importance of long water quality records. What can we learn from them? What is the science behind this work? Why bother with old data when modern techniques allow big data sets to be quickly acquired?  Why bother with old data when modelling can achieve so much? Here we briefly consider some answers: i) Detecting long-term trends - subtle change in noisy systems
- rare events - complex system response; ii) Calculation of catchment (and  larger-scale) export rates; iii) Forecasting future conditions; iv) Catchment management; v) Context for experimental and modelling studies; vi) Generating new ideas and testing hypotheses

 

 

A chemostatic world? Catchment heterogeneity as a modulator of emergent archetype concentration -discharge patterns

Andreas Musolff, Jan H. Fleckenstein, P. Suresh C. Rao & James W. Jawitz

Catchments spatially integrate diverse water flow paths that connect solute sources to the stream. The emergent patterns of in-stream concentrations (C) of problematic solutes, such as nutrients and pesticides, and discharge (Q) are affected by land management with adverse consequences for downstream water quality. Understanding the controls of C-Q patterns in catchments under stochastic hydro-climatic forcing is a pre-requisite for robust predictions and mitigation strategies. Here, we combine a synthesis of observational records from 61 catchments and 8 solutes (n = 411) with a stochastic modeling approach to test if C-Q patterns are explained by spatial heterogeneity in solute sources. We implement in the model spatially implicit catchment-scale source-zone heterogeneity on the basis of solute-source strength and its correlation to travel-time distributions. The model indicates that structured source heterogeneity, in terms of solute source strength correlation to travel time, was the dominant driver of emergent C-Q pattern archetypes. We find that further deconvolution of the spatially integrated signals (chemographs) observed in streams can be problematic because different model parameter combinations produce similar C-Q patterns. However, regardless of the C-Q pattern, the dominant solute export regime was chemostatic, implying that the variance in exported loads (L) is determined primarily by variance of Q rather than C. The analysis further reveals that homogenization of solute sources, consistent with anthropogenic land-use intensification, leads to the observed prevalence of chemostatic export regimes. Our findings suggest that strategies to improve water quality and to recover ecological integrity in streams should lead away from source homogenization in managed catchments.

 

How does catchments retain and release stored water? An explicit exploration of flowpaths and transit times in a till hillslope

Kevin Bishop and Ali Ameli

Swedish University of Agricultural Sciences, University of Western Ontario 

The stable isotopes of water have served science well as hydrological tracers which have demonstrated that there is often a large component of “old” water in stream runoff. It has been more problematic to define the full transit time distribution of that stream water. Non-linear mixing of previous precipitation signals that is stored for extended periods and slowly travel through the subsurface before reaching the stream results in a large range of possible transit times. No single hydrological tracer can be used to fully represent this, especially if all that one has is data on the precipitation input and stream runoff. In this paper we explicitly characterize the flow paths and transition times of water using a novel, quasi-steady physically-based model based on the well-studied S-Transect hillslope in Sweden where the concentration of oxygen-18 in the subsurface has been measured. We explore how the subsurface conductivity profile impacts the characteristics of transit time distributions in runoff and then test these scenarios against the observed dynamics of conservative hydrological tracers in both the stream and subsurface. This work explores how celerity and velocity differ with landscape structure with a focus on relating the riparian situation to upslope source areas. 





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