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Groundwater discharge creates hotspots of riparian plant species richness in a boreal forest stream network
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. (Arcum)
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2014 (English)In: Ecology, ISSN 0012-9658, E-ISSN 1939-9170, Vol. 95, no 3, 715-725 p.Article in journal (Refereed) Published
Abstract [en]

Riparian vegetation research has traditionally focused on channel-related processes because riparian areas are situated on the edge of aquatic ecosystems and are therefore greatly affected by the flow regime of streams and rivers. However, due to their low topographic position in the landscape, riparian areas receive significant inputs of water and nutrients from uplands. These inputs may be important for riparian vegetation, but their role for riparian plant diversity is poorly known. We studied the relationship between the influx of groundwater (GW) from upland areas and riparian plant diversity and composition along a stream size gradient, ranging from small basins lacking permanent streams to a seventh-order river in northern Sweden. We selected riparian sites with and without GW discharge using a hydrological model describing GW flow accumulation to test the hypothesis that riparian sites with GW discharge harbor plant communities with higher species richness. We further investigated several environmental factors to detect habitat differences between sites differing in GW discharge conditions. Vascular plant species richness was between 15% and 20% higher, depending on the spatial scale sampled, at riparian sites with GW discharge in comparison to non-discharge sites, a pattern that was consistent across all stream sizes. The elevated species richness was best explained by higher soil pH and higher nitrogen availability (manifested as lower soil C/N ratio), conditions which were positively correlated with GW discharge. Base cations and possibly nitrogen transported by groundwater may therefore act as a terrestrial subsidy of riparian vegetation. The stable isotopes N-15 and C-13 were depleted in soils from GW discharge compared to non-discharge sites, suggesting that GW inputs might also affect nitrogen and carbon dynamics in riparian soils. Despite the fact that many flows of water and nutrients reaching streams are filtered through riparian zones, the importance of these flows for riparian vegetation has not been appreciated. Our results demonstrated strong relationships between GW discharge, plant species richness and environmental conditions across the entire stream size gradient, suggesting that both river hydrology and upland inputs should be considered to fully understand riparian vegetation dynamics.

Place, publisher, year, edition, pages
Ecological Society of America , 2014. Vol. 95, no 3, 715-725 p.
Keyword [en]
boreal forest, groundwater discharge, Krycklan catchment, riparian zone, soil nitrogen, soil pH, species richness, terrestrial subsidy, vascular plants
National Category
Ecology Environmental Sciences
URN: urn:nbn:se:umu:diva-88681DOI: 10.1890/13-0363.1ISI: 000332823100019OAI: diva2:717617
Available from: 2014-05-16 Created: 2014-05-12 Last updated: 2016-05-27Bibliographically approved
In thesis
1. Grow with the flow: Hydrological controls of riparian vegetation in boreal stream networks
Open this publication in new window or tab >>Grow with the flow: Hydrological controls of riparian vegetation in boreal stream networks
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

What drives species diversity across landscapes is one of the most fundamental questions in ecology. Further, understanding the mechanisms underlying species diversity patterns is important not only for forming and challenging ecological theories but also essential for appropriate landscape management and effective nature conservation. This thesis focuses on patterns of vascular plant, moss and liverwort species richness and composition in relation to water flow in boreal-forest catchments, focusing mostly on riparian zones (RZs), that is terrestrial areas bordering streams and rivers. I addressed some of the most essential questions related to the ecology of riparian vegetation including the role of stream network position, groundwater (GW) flow paths, substrate availability, upland perturbations, and stream restoration. I also investigated how riparian soil processes and habitat properties relate to these factors in order to provide a holistic understanding of riparian dynamics. The results showed that the species richness and composition of riparian vascular plants, mosses and liverworts are strongly influenced by position along the stream network, GW discharge, presence of variable substrates in RZs, and by stream restoration. Generally, more species were found downstream in the network, at sites with inputs of upland GW, sites with high diversity of substrates (e.g., open mineral soil, rocks, stones, wood and bark), and along streams restored after channelization. This thesis also describes how riparian habitat properties responded to position in the landscape and human impacts, thus providing mechanistic links between plant species diversity and riparian processes across spatial scales. These ecological insights are further implemented into numerous recommendations for freshwater and upland management in boreal Sweden. Given that streams and rivers connect landscape elements both longitudinally and laterally I argue that management plans should be designed for entire catchments instead of individual river segments. Ignoring the connectivity of streams as well as the high connectivity of riparian areas to uplands via GW flows may result in failure of restoration, mitigation and/or protection actions. Further, during forestry operations more emphasis should be placed on GW discharge areas along streams and rivers, because they represent important ecological and biogeochemical hotspots in the landscape. The riparian buffers left along streams in boreal catchments affected by forestry are presently insufficiently wide and often uniform in width. This threatens the assemblages of species in GW discharge hotspots and the ecosystem services they provide. Overall, this thesis describes a holistic picture of riparian diversity patterns and riparian processes in boreal landscapes, acknowledges and elaborates on current ecological theories, presenting new patterns in biodiversity, and offers management guidelines. 

Place, publisher, year, edition, pages
Umeå: Umeå Univeristy, 2015. 27 p.
boreal forest, channelization, groundwater, Krycklan catchment, liverworts, mosses, riparian buffers, riparian vegetation, river restoration, species richness, stream network, stream size, vascular plants
National Category
urn:nbn:se:umu:diva-100217 (URN)978-91-7601-212-3 (ISBN)
Public defence
2015-03-26, Björken, Sveriges lantbruksuniversitet, Skogsmarksgränd 901 83, Umeå, 10:00 (English)
Swedish Research Council Formas
Available from: 2015-03-05 Created: 2015-02-25 Last updated: 2015-03-09Bibliographically approved

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Kuglerova, LenkaJansson, RolandMalm-Renöfält, Birgitta
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