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Does river restoration affect diurnal and seasonal changes to surface water quality? A study along the Thur River, Switzerland.
Journal article

Does river restoration affect diurnal and seasonal changes to surface water quality? A study along the Thur River, Switzerland.

  • Chittoor Viswanathan V Eawag, Swiss Federal Institute of Aquatic Science and Technology, Department of Water Resources and Drinking Water, Überlandstrasse 133, 8600 Dübendorf, Switzerland; Université de Neuchâtel, Centre d'Hydrogéologie et de Géothermie (CHYN), Rue Emile-Argand 11, CH-2000 Neuchâtel, Switzerland.
  • Molson J Université Laval, Département de Géologie et Génie Géologique, Québec City, Québec, Canada.
  • Schirmer M Eawag, Swiss Federal Institute of Aquatic Science and Technology, Department of Water Resources and Drinking Water, Überlandstrasse 133, 8600 Dübendorf, Switzerland; Université de Neuchâtel, Centre d'Hydrogéologie et de Géothermie (CHYN), Rue Emile-Argand 11, CH-2000 Neuchâtel, Switzerland.
  • 2015-06-10
Published in:
  • The Science of the total environment. - 2015
Diurnal cycles
River restoration
Seasonal changes
Summer storm event
Water quality
English Changes in river water quality were investigated along the lower reach of the Thur River, Switzerland, following river restoration and a summer storm event. River restoration and hydrological storm events can each cause dramatic changes to water quality by affecting various bio-geochemical processes in the river, but have to date not been well documented, especially in combination. Evaluating the success of river restoration is often restricted in large catchments due to a lack of high frequency water quality data, which are needed for process understanding. These challenges were addressed in this study by measuring water quality parameters including dissolved oxygen (DO), temperature, pH, electrical conductivity (EC), nitrate and dissolved organic carbon (DOC) with a high temporal frequency (15 min-1h) over selected time scales. In addition, the stable isotopes of water (δD and δ(18)O-H2O) as well as those of nitrate (δ(15)N-NO3(-) and δ(18)O-NO3(-)) were measured to follow changes in water quality in response to the hydrological changes in the river. To compare the spatial distribution of pre- and post-restoration water quality, the sampling stations were chosen upstream and downstream of the restored section. The diurnal and seasonal changes were monitored by conducting 24-hour campaigns in three seasons (winter, summer and autumn) in 2012 and 2013. The amplitude of the diurnal changes of the various observed parameters showed significant seasonal and spatial variability. Biological processes--mainly photosynthesis and respiration--were found to be the major drivers of these diurnal cycles. During low flow in autumn, a reduction of nitrate (attributed to assimilation by autotrophs) in the pre-dawn period and a production of DOC during the daytime (attributed to photosynthesis) were observed downstream of the restored site. Further, a summer storm event was found to override the influence of these biological processes that control the diurnal changes. High frequency daily monitoring of key water quality parameters over different seasons is shown to be essential in evaluating river restoration success.
Language
  • English
Open access status
closed
Identifiers
Persistent URL
https://sonar.ch/global/documents/278120
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