Abstract
Abstract. Alpine streams are particularly valuable for downstream water resources and of high ecological relevance; however, a detailed understanding of water storage and release in such heterogeneous environments is often still lacking. Observations of naturally occurring tracers, such as stable isotopes of water or electrical conductivity, are frequently used to track and explain hydrologic patterns and processes. Importantly, some of these hydrologic processes also create microhabitat variations in Alpine aquatic systems, each inhabited by characteristic organismal communities. The inclusion of such ecological diversity in a hydrologic assessment of an Alpine system may improve our understanding of hydrologic flows while also delivering biological information. Recently, the application of environmental DNA (eDNA) to assess biological diversity in water and connected habitats has gained popularity in the field of aquatic ecology. A few of these studies have started to link aquatic diversity with hydrologic processes but hitherto never in an Alpine system. Here, we collected water from an Alpine catchment in Switzerland and compared the genetic information of eukaryotic organisms conveyed by eDNA with the hydrologic information conveyed by naturally occurring hydrologic tracers. Between March and September 2017, we sampled water at multiple time points at 10 sites distributed over the 13.4 km2 Vallon de Nant catchment (Switzerland). The sites corresponded to three different water types and habitats, namely low-flow or ephemeral tributaries, groundwater-fed springs, and the main channel receiving water from both previous mentioned water types. Accompanying observations of typical physicochemical hydrologic characteristics with eDNA revealed that in the main channel and in the tributaries, the biological richness increases according to the change in streamflow, dq/dt, whereas, in contrast, the richness in springs increased in correlation with electrical conductivity. At the catchment scale, our results suggest that transport of additional, and probably terrestrial, DNA into water storage or flow compartments occurs with increasing streamflow. Such processes include overbank flow, stream network expansion, and hyporheic exchange. In general, our results highlight the importance of considering the at-site sampling habitat in combination with upstream connected habitats to understand how streams integrate eDNA over a catchment and to interpret spatially distributed eDNA samples, both for hydrologic and biodiversity assessments. At the intersection of two disciplines, our study provides complementary knowledge gains and identifies the next steps to be addressed for using eDNA to achieve complementary insights into Alpine water sources. Finally, we provide recommendations for future observation of eDNA in Alpine stream ecosystems.
Highlights
Alpine environments are often considered to be water towers for lowland areas (Viviroli et al, 2007) and hotspots for biodiversity (Körner, 2002) and will likely be disproportionately affected by climate change compared to other areas (Jacobsen et al, 2012; Grabherr, 2009)
Two of the between-water-type comparisons of electrical conductivity (EC) were significant (p < 0.05) in mean rank difference according to the Kruskal–Wallis test: main channel to spring (M–S) and spring to tributary (S–T); see Table S6
We found significance (p < 0.05) in the mean rank difference of δ18O between the main channel and springs (M–S) and the main channel and tributary (M–T) but not between springs and tributary (S–T)
Summary
Alpine environments are often considered to be water towers for lowland areas (Viviroli et al, 2007) and hotspots for biodiversity (Körner, 2002) and will likely be disproportionately affected by climate change compared to other areas (Jacobsen et al, 2012; Grabherr, 2009). The topography and temperature gradients translate into a landscape with an enhanced heterogeneity of potential water flow paths. These paths are governed by highly seasonal incoming water (rain or snow), which is released as a seasonal alternation of runoff from rain, stored snow, and snowmelt. There is an ongoing search for hydrologic tracers to decompose river water into its most recent storage compartment (e.g., glacier, snow, soil, groundwater) and to identify when and where it entered the stream network (Abbott et al, 2016; Blume and Van Meerveld, 2015; Williams et al, 2009; Mosquera et al, 2018)
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