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The importance of fog and dew for Swiss grasslands today and in the future (Acronym: IFDewS)

English title The importance of fog and dew for Swiss grasslands today and in the future (Acronym: IFDewS)
Applicant Eugster Werner
Number 175733
Funding scheme Project funding (Div. I-III)
Research institution Institut für Agrarwissenschaften ETH Zürich
Institution of higher education ETH Zurich - ETHZ
Main discipline Climatology. Atmospherical Chemistry, Aeronomy
Start/End 01.03.2018 - 31.03.2022
Approved amount 566'762.00
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All Disciplines (6)

Discipline
Climatology. Atmospherical Chemistry, Aeronomy
Environmental Research
Hydrology, Limnology, Glaciology
Ecology
Meteorology
Agricultural and Forestry Sciences

Keywords (5)

Fog and dew water yield; Plant water status; Dew formation; Fog and dew as water sources; Climate change

Lay Summary (German)

Lead
Die Bedeutung des Taus wurde schon Ende des 18. Jahrhunderts erkannt. Wissenschaftler, die versuchten, die Tau-Erträge in Bezug auf Niederschlag zu quantifizieren, schätzten, dass Tau rund 16% zum hydrologischen Budget von England und Wales beitrug. Obwohl wir aufgrund der Fortschritte in der Wissenschaft wissen und verstehen, dass solch hohe Schätzungen der Tau-Erträge unrealistisch sind, sind wir ziemlich sicher, dass sowohl Tau als auch Nebel eine Auswirkung auf das Pflanzenwachstum haben und darauf, wie Pflanzen Trockenperioden ohne oder mit geringem Niederschlag bewältigen können.
Lay summary

In unserem SNF-geförderten Projekt wollen wir untersuchen, wie sich Tau und Nebel auf das Wachstum typischer Grünlandpflanzenarten in der Schweiz auswirken. Ist die Wirkung direkt über das Tau- und Nebelwasser, welches den Wassergehalt in den Pflanzenzellen erhöht und so den potenziellen Trockenstress reduziert? Oder ist es eher eine indirekte Wirkung, dass Tau- oder Nebeltröpfchen, die nachts von den Pflanzen gesammelt werden, die Pflanzenblattoberfläche in den ersten Morgenstunden nach Sonnenaufgang abkühlen, wenn das Wasser verdunstet und somit die Blätter bei niedrigen Temperaturen hält, was wiederum die Photosyntheseleistung begünstigt?

Es wird ein kleines Netzwerk unter Einbezug bestehender Standorte der Langzeit- und Ökosystemforschung der ETH Zürich und der WSL Birmensdorf eingerichtet, in Höhenlagen vom Schweizer Mittelland bis in die alpine Stufe. An diesen Standorten wird die Häufigkeit von Nebel und Tau bestimmt und die Wassergewinne an Gräsern und Kräutern unter solchen Bedingungen werden quantifiziert. Mit stabilen Wasser-Isotopen untersuchen wir schliesslich, welcher Anteil von Tau- und Nebelwasser das Blattwasser der Pflanzen direkt beeinflusst. Sobald wir das notwendige Prozessverständnis erlangt haben, können wir hypothetisieren, wie sich die Relevanz von Tau und Nebel mit dem Klimawandel ändert, insbesondere im Sommer bei längeren und wärmeren Trockenperioden.

Direct link to Lay Summary Last update: 31.01.2018

Lay Summary (English)

Lead
The importance of dew was already recognised at the end of the 18th century. Scientists who tried to quantify dew yields in relation to rainfall estimated that dew contributed with 16% to the hydrological budget of England and Wales. Although with the progress in science we know and understand that such high dew yield estimates are unrealistic, we are quite certain that dew and fog have an effect on plant growth and how plants can cope with dry periods with no or low rainfall.
Lay summary

In our SNF funded project we plan to investigate, how dew and fog affect the growth of typical grassland plant species in Switzerland. Is it directly via dew and fog water increasing the plant cell water and thus reducing potential drought stress? Or is it rather indirect in a way that dew or fog droplets collected by the plants during the night cool the plant leaf surface in the first morning hours after sunrise, when the water evaporates and keeps leaves at low temperatures, which in turn benefits photosynthesis?

In detail, a small network collocated with existing long-term ecosystem research sites from ETH Zürich and WSL Birmensdorf at elevations from the Swiss Plateau up to an alpine pasture will be established to measure the frequency of fog and dew, and to quantify the water gains on grass swards under such conditions. Using stable isotopes in water we will then investigate the pathways from dew and fog water to plant water in order to quantify the share of dew and fog water that directly affects plant leaf water. Once we have gained the necessary process understanding, we will be able to hypothesize how the relevance of dew and fog will change with climate change, namely under summer conditions with longer and warmer dry spells or drought periods.

Direct link to Lay Summary Last update: 31.01.2018

Responsible applicant and co-applicants

Employees

Associated projects

Number Title Start Funding scheme
55554 Fog Interception and Nutrient Inputs to Montane-Subalpine Areas in Switzerland (FINIMSAS) 01.04.1999 Project funding (Div. I-III)
63484 Fog Interception and Nutrient Inputs to Montane-Subalpine Areas in Switzerland (FINIMSAS), Part II 01.04.2001 Project funding (Div. I-III)

Abstract

Overall Aim - My proposed research project aims at (1) quantifying the amount of fog and dew water that a grassland ecosystem gains under today's climate conditions in Switzerland, (2) how fog and dew affect the plant performance of grassland, and (3) how the relevance of fog and dew may increase in the future.Working Hypotheses - We will test three working hypotheses:(1) During summer fair weather and drought periods nocturnal dew formation or fog droplet deposition under conditions with shallow radiation ground fog has a measurable and nonnegligible quantitative effect on the plant water status of representative grasslands in Switzerland. (2) This quantitative effect of fog and dew is more pronounced at higher elevations in the pre-Alps and the Alps than at lower elevations in the Alpine foreland and on the Swiss plateau.(3) The role of fog and dew for temperate ecosystems will become more important with anticipated climate change with an expected reduction in summer precipitation using the most recent regionalized A1B, A2 and RCP3PD scenarios for Switzerland.Methodical Approach - Our project foresees fieldwork to address hypotheses 1 and 2, on which the scientific work in the laboratory/in silicio to address hypothesis 3 will be based. The work will be grouped into two subproject with one Ph.D. student each: (1) Fog and dew input quantification and process understanding; and (2) Quantifying the net effect of fog and dew water on grassland plant species using artificially enriched stable isotope tracers.Field work relies on three key methods:1. Micrometeorological and microclimatic measurements at existing long-term meteorological field sites that are complemented with microlysimeters, visibility and leaf wetness sensors to quantify nocturnal fog and dew yield during the project duration.2. Stable isotopes of water will be used to quantify the share of fog or dew water taken up by typical grassland plants. We will use a highly enriched stable isotope tracer (enriched in both 18O and 2H) which will be applied to the vegetation in the evening before an expected fog or dew event to increase the signal of the water building up overnight on plant leaves that will be sampled in the morning. Destructive sampling of representative leaves to extract the leaf water in the laboratory will be used.3. Leaf water potential measurements using a physical pressure system known as Scholander bomb will be carried out at pre-dawn and at regular intervals after sunrise during the time period when fog and dew water normally evaporates from grassland. Measurements will consider both plants that were normally exposed to fog and dew as well as control plants where a foil hood was placed in the evening to prevent the formation of dew and deposition of fog droplets. The difference of such replicated sampling will be a measure of the quantitative effect of fog and dew on grassland plant performance under presence/absence of fog and dew.While micrometeorological measurements are carried out at 10 sites (9 localities) forming an elevational and north-south transect across eastern Switzerland, the field work with tracer experiments and plant water potential measurements will focus on three Swiss FluxNet grasslands where >10 years of continuous (or seasonal in case of the highest elevation) eddy covariance turbulent flux measurements are available. These turbulent flux measurements will be important to address hypothesis 2.Methods to address hypotheses 2 and 3 are of statistical nature to find and parameterize functional relationships that allow a quantitative estimation of fog and dew yield based on conventional long-term micrometeorological measurements (hypothesis 2) and based on the newest detailed climate change scenarios (hypothesis 3). Geostatistical methods will be used for spatial interpolation of functional relationships to generate a quantitative map of fog and dew yields for Switzerland for today and for the future.Importance and Impact - Although it is known since the late 18th century that dew (and possibly fog) might be a relevant component for the hydrological budget of a site, fog and dew have not been considered in a quantitative way in ecohydrological studies in Switzerland and many other regions with a temperate climate. Our expectation based on climate scenarios is that fog and dew will become more relevant in the future. Our project aims at providing the necessary knowledge and understanding to assess the importance of fog and dew for grassland ecosystems.
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