Groundwater discharge creates hotspots of riparian plant species richness in a boreal forest stream network

• Published in: Ecology
• Main Authors: Kuglerova, Lenka, Jansson, Roland, Ågren, Anneli, Laudon, Hjalmar, Malm-Renöfält, Birgitta
• Format: Article in Journal/Newspaper
• Language: English
• Published: Umeå universitet, Institutionen för ekologi, miljö och geovetenskap 2014
• Subjects: boreal forest; groundwater discharge; Krycklan catchment; riparian zone; soil nitrogen; soil pH; species richness; terrestrial subsidy; vascular plants; Ecology; Ekologi; Environmental Sciences; Miljövetenskap; Northern Sweden
• Online Access: http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-88681; https://doi.org/10.1890/13-0363.1

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 ...