Water and solute dynamics during rainfall events in headwater catchments in the Central Swiss Alps under the influence of green alder shrubs and wetland soils

Abstract

In the Swiss Alps, shrubs (e.g. Alnus viridis (Chaix) DC) are encroaching into formerly open habitats. The shrub encroachment might affect soil hydrological properties, which in turn influence runoff generation. Moreover, alder species (Alnus spp.) are known to affect chemical soil properties (e.g. increase of nitrate concentrations in the soil solution) and can therefore alter the water quality of stream water. In our study, we investigated four small alpine headwater catchments to assess the influence of shrub encroachment and wetland soils on stream water geochemistry during storm runoff. Stream water was sampled in the growing season of 2010 at hourly intervals during one single rainfall event. Stable isotope values (δ 18 O) of stream water (ranging from À13.8 to À8.5‰) and rainfall (bulk mean δ 18O value of about À5.6‰) during the single event were used to estimate the fraction of event water in stream discharge. Continuously measured electrical conductivity in the growing seasons of 2010 and 2011 was used to infer information on runoff generation during 15 rainfall events. Riparian wetland soils were flushed by a high fraction of event water of up to 72% during peak discharge, which increased the dissolved organic carbon export during the single rainfall event. Besides the atmospheric input through nitrate in rainwater, the expected expansion of green alder shrubs in the region, associated with increasing number and intensity of summer rainfall events in the future, might increase the episodic export of nutrients such as dissolved organic carbon and NO 3 À from these catchments.

Dissolved organic carbon load variability in the rainfall season dominated its interannual variability in the snowmelt driven basin: Evidence from 41 years data of headwater streams

“…For instance, if there are frequent floods/droughts in a catchment, the discharge becomes much less stable, which also affects the stability of DOC export/import (Dawson et al, 2008). Although the reasons for variability of DOC export/import caused by hydrological extremes may be challenging (Mueller et al, 2016), characterizing the contribution of discharge variability to DOC export/import is necessary because it can enhance understanding of the possible driving mechanism for its changes under the backdrop of changing environment.…”

“…Although the reasons for variability of DOC export/import caused by hydrological extremes may be challenging (Mueller et al, 2016), characterizing the contribution of discharge variability to DOC export/import is necessary because it can enhance understanding of the possible driving mechanism for its changes under the backdrop of changing environment.…”

Response time and water origin in a steep nested catchment in the Italian Dolomites

“…Given their typical small size (<10 km 2 ) and morphological and pedological characteristics (steep hillslopes, narrow valley bottoms and shallow soils), they comprise source areas of water, sediments and solutes and, at the same time, act as transitory hydrological sinks (Payn, Gooseff, McGlynn, Bencala, & Wondzell, ; Sidle et al, ). Headwater streams are responsible of transport mechanisms for different materials including nutrients, organic matter, wood and aquatic species (Sando & Blasch, ; Wipfli, Richardson, & Naiman, ) affecting downstream water quality and ecosystem health (Bishop et al, ; Mueller, Alaoui, & Alewell, ). Mountain headwater catchments, especially those that are dominated by snowmelt and ice melt dynamics, are generally water‐rich but, often due to logistical inconveniences, are data‐poor (Beniston, ).…”

Using repeat electrical resistivity surveys to assess heterogeneity in soil moisture dynamics under contrasting vegetation types

“…The extreme volume of rainfall instigated a change in water conductivity, with the increased influence of low conductivity rainfall replacing the soil water leading to an increase of resistivity with wetness (Chambers et al, 2014;Mueller et al, 2016). The use of the measured natural water conductivity in the catchment alongside the estimation of the pore water resistivity allowed us to account for this.…”