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Hydrological and thermal controls of ice formation in 25 boreal stream reaches
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. (Landscape Ecology Group)
Norwegian University of Science and Technology, Department of Hydraulic and Environmental Engineering. (Department of Hydraulic and Environmental Engineering,)
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. (Landscape Ecology Group)
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. (Landscape Ecology Group)
(English)Manuscript (preprint) (Other academic)
Abstract [en]

The Northern Hemisphere has a high density of fluvial freshwater ecosystems, many of which become ice-covered during winter. The formation and extent of ice have both ecological and socio-economic implications. For example, ice can cause freezing of riparian vegetation and fish eggs as well as influence hydropower production; however, when, where and why ice develops in small streams is poorly described. Data from 25 stream reaches were used to study the factors controlling ice formation during two consecutive winters. We addressed where in the catchment surface or anchor ice is most likely to develop, how stream morphology influences ice formation, and how climate influences ice processes. Reaches far away from lake outlets were most prone to form anchor ice, but many other factors also influenced ice formation. We found that anchor-ice was most common where water temperature and groundwater input were low and stream power high. The in-stream substrate was also important for the formation of anchor ice as well as the current velocity, which created turbulence and super-cooled conditions if high enough. We demonstrated that ice formation in the studied streams was complex, involving many variables, thus we constructed a conceptual model describing the likelihood of various ice types to develop, based on our large dataset. To our knowledge, this model is the first to describe the complexity of ice formation in steep boreal streams. As such it will be useful for practitioners and scientists working in small rivers in the Northern Hemisphere.

Keyword [en]
anchor ice, boreal, channel morphology, groundwater, ice, river ice, stream
National Category
Earth and Related Environmental Sciences Oceanography, Hydrology, Water Resources
Identifiers
URN: urn:nbn:se:umu:diva-99003OAI: oai:DiVA.org:umu-99003DiVA: diva2:785098
Funder
Swedish Research Council Formas
Available from: 2015-02-02 Created: 2015-02-02 Last updated: 2015-02-04
In thesis
1. Breaking the ice: effects of ice formation and winter floods on vegetation along streams
Open this publication in new window or tab >>Breaking the ice: effects of ice formation and winter floods on vegetation along streams
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Alternative title[sv]
Klimatförändringar och isbildning i vattendrag : effekter på biologisk mångfald
Abstract [en]

Streams in cold regions are characterized by unique hydrological processes that control flow regime and water levels. One of the most important processes is the formation, growth and melting of different types of ice in and around the stream channel during winter. River ice controls major hydrologic events such as winter floods with magnitudes and frequencies often greater than those created by open-water conditions. While river management in northern countries has already recognized high risk of ice damages, the focus of the risk assessment has been mostly aimed towards the local economy; the ecological role of river ice has been less acknowledged. Along rivers in boreal Sweden, riparian vegetation has developed specific zonation with height and age of the plants increasing the further away they are from the stream channel. On lower levels the vegetation is often comprised of short-lived plants, such as annuals and biennials whereas more permanent woody vegetation is found at higher levels. This zonation has most often been explained by the resilience of different growth forms to the inundation regimes, such as the spring flood in northern systems. Within this framework, I investigated which factors drive the ice formation and how ice and ice-induced floods affect riparian and in-stream vegetation. A 3-year survey was conducted of ice formation and vegetation along 25 stream reaches and a set of experiments were used to evaluate ice as a disturbance agent. Reaches far away from lake outlets which had a low input of groundwater and a high velocity and stream power were most prone to form anchor ice, but many other factors also influenced ice formation. Streams with anchor ice experienced more frequent flooding of the riparian vegetation during winter. Our findings suggests that ice and winter floods favour diversity and create habitat heterogeneity for riparian species. On a community level, woody plants such as evergreen dwarf shrubs are eliminated when flooded during winter, opening up patches for other species to colonize, creating a dynamic riparian understory community. Significant changes in river ice conditions could develop with projected changes in climate which would have important geomorphologic, ecological and socio-economic impacts. One implication of climate change could be less ice disturbance and consequently a riparian vegetation in cold regions that slowly changes from forb to dwarf-shrub dominated with a subsequent decrease in species richness. Changes in species diversity and abundance of groups of species related to changes in ice formation could potentially cascade into riparian and in-stream processes such as nutrient cycling, litter decomposition and organism dispersal.

Place, publisher, year, edition, pages
Umeå: Umeå universitet, 2015. 25 p.
Keyword
anchor ice, climate change, in-stream, riparian, river ice, streams, vegetation
National Category
Ecology
Identifiers
urn:nbn:se:umu:diva-99008 (URN)978-91-7601-182-9 (ISBN)
Public defence
2015-02-27, Björken, Sveriges lantbruksuniversitet, Skogsmarksgränd 901 83, Umeå, 09:30 (English)
Opponent
Supervisors
Funder
Swedish Research Council Formas
Available from: 2015-02-06 Created: 2015-02-02 Last updated: 2017-04-03Bibliographically approved

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