Forschungs- & Entwicklungsinformationsdienst der Gemeinschaft - CORDIS


VEWA Berichtzusammenfassung

Project ID: 335910
Gefördert unter: FP7-IDEAS-ERC
Land: United Kingdom

Mid-Term Report Summary - VEWA (Ve-Wa:Vegetation effects on water flow and mixing in high-latitude ecosystems–Capability of headwater catchments to mediate potential climate change)

The upper latitudes of the Northern hemisphere cover a significant proportion of the Earth’s land surface and are energy-limited areas where snow is an important component of the annual water balance. Our ability to predict the impact of climate change on water resources in these regions is still limited, though they are highly sensitive to climatic warming: small differences in temperature determine the status of frozen ground and the magnitude and timing of snow accumulation and melt. These changes will affect plant communities in terms of natural succession and management of crops exploiting the milder climate. It is unknown, how such vegetation changes will feedback to affect the water balance and how plants will influence water availability.

VeWa is an interdisciplinary project investigating water uptake by plants and consequent water availability along a cross-regional climate gradient to understand responses to change in high-latitude uplands. The six VeWa catchments are located in Canada, Sweden, US and Scotland. Much of the complexity of northern landscapes is a consequence of moisture and temperature gradients, which in turn affect the timing and rates of snowpack accumulation and melt and ecosystem productivity. Within VeWa, we have conducted a catchment comparison to (1) characterise the water balance and hydrological function of the sites; (2) use stable isotope data to assess the influence of landscape characteristics on water partitioning and runoff processes; and (3) examine whether changes in isotopic signals during water flow through the catchment observed in the stream water can be used to infer the influence of plants on partitioning of waters in the catchments. We have also developed a tracer-aided, spatially distributed rainfall-runoff model to conceptualise and integrate flow paths, storage dynamics and mixing processes at the catchment scale.

First results show that the sites selected in VeWa exhibit many commonalities that reflect the distinct hydrological characteristics of northern catchments despite differences in hydroclimate and catchment characteristics. Plant canopy cover had a large influence on the quantity and distribution of interception and throughfall. Whilst temporal variability in soil water isotopes was mainly driven by throughfall or snowmelt in wet periods, the effects of soil evaporation was dominant in soils during the dry periods, with the effects of evaporative fractionation evident in in the upper 10cm of the soils. At some sites, this evaporative fractionation in the rooting zone seemed to explain the isotopic composition of plant water. Despite these processes affecting the partitioning of isotopes in the soils, catchment scale modelling showed that these differences have limited influence on stream water isotopes. Using a coupled flow-tracer model, we could model stream and soil isotope dynamics during most periods simply on the basis of mixing along the dominant flow paths without having to consider evaporative effects. The model allowed us to estimate the age distributions of internal stores, water fluxes and stream flow. Such an integrated framework using stable isotopes and modelling is providing an insightful basis for addressing the many open questions on hydrological functioning of northern environments. Importantly, the unique characteristics of northern colder regions mean that dominant paradigms and theories derived from temperate zone hydrology do not necessarily transfer to northern landscapes.

Reported by

United Kingdom
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