Exploring water cycle dynamics by sampling multiple stable water isotope pools in a developed landscape in Germany

Abstract

Abstract. A dual stable water isotope (δ 2 H and δ 18 O) study was conducted in the developed (managed) landscape of the Schwingbach catchment (Germany). The 2-year weekly to biweekly measurements of precipitation, stream, and groundwater isotopes revealed that surface and groundwater are isotopically disconnected from the annual precipitation cycle but showed bidirectional interactions between each other. Apparently, snowmelt played a fundamental role for groundwater recharge explaining the observed differences to precipitation δ values.A spatially distributed snapshot sampling of soil water isotopes at two soil depths at 52 sampling points across different land uses (arable land, forest, and grassland) revealed that topsoil isotopic signatures were similar to the precipitation input signal. Preferential water flow paths occurred under forested soils, explaining the isotopic similarities between top-and subsoil isotopic signatures. Due to human-impacted agricultural land use (tilling and compression) of arable and grassland soils, water delivery to the deeper soil layers was reduced, resulting in significant different isotopic signatures. However, the land use influence became less pronounced with depth and soil water approached groundwater δ values. Seasonally tracing stable water isotopes through soil profiles showed that the influence of new percolating soil water decreased with depth as no remarkable seasonality in soil isotopic signatures was obvious at depths > 0.9 m and constant values were observed through space and time. Since classic isotope evaluation methods such as transfer-function-based mean transit time calculations did not provide a good fit between the observed and calculated data, we established a hydrological model to estimate spatially distributed groundwater ages and flow directions within the Vollnkirchener Bach subcatchment. Our model revealed that complex age dynamics exist within the subcatchment and that much of the runoff must has been stored for much longer than event water (average water age is 16 years). Tracing stable water isotopes through the water cycle in combination with our hydrological model was valuable for determining interactions between different water cycle components and unravelling age dynamics within the study area. This knowledge can further improve catchment-specific process understanding of developed, human-impacted landscapes.

Ephemeral kettle hole water and sediment temporal and spatial dynamics within an agricultural catchment

“…Another explanation of the relatively enriched stream isotopic values might be the spatial distribution of water age (Orlowski, Kraft, Pferdmenges, & Breuer, 2016). Water tends to remain in storage until sufficient through-flow is achieved, usually occurring during high rainfall events (Hrachowitz et al, 2016).…”

A new instrument for stable isotope measurements of <sup>13</sup>C and <sup>18</sup>O in CO<sub>2</sub> – instrument performance and ecological application of the Delta Ray IRIS analyzer

“…As a result of the continuous isotopic exchange with air masses in the cloud, raindrops do not carry the very depleted isotopic composition within the cloud, whereas for snow, the isotopic exchange between the falling snowflakes and the air masses in the cloud does not take place, resulting in a more depleted precipitation (Gat, 1996). For example, Orlowski et al (2016) reported a maximal difference of approximately 15.5 ‰ between the δ 18 O values of rain and snow over a 2-year measurement period at a field site at an approximately 160 km air-line distance from our field site. A smaller maximal difference of approximately 9 ‰ between the δ 18 O of snow and the corresponding monthly means for rain was reported by Wenninger et al (2011), based on 2 years of measurements at two catchments in a German black forest at a 414 km air-line distance from our field site.…”

Spatial variability in specific discharge and streamwater chemistry during low flows: Results from snapshot sampling campaigns in eleven Swiss catchments

“…For example, Rossi et al (2015) showed that the combination of snapshot sampling and multivariate statistical methods facilitated classification of boreal springs with respect to water quality and quantity and thus assessment of their vulnerability to changes in land use. Other studies used data from snapshot campaigns for endmember mixing analysis (Barthold et al, 2008;Inamdar et al, 2013;Selle, Schwientek, & Lischeid, 2013) or for analysing how various landscape characteristics, such as land use or land cover (Fischer et al, 2015;Lefebvre et al, 2007;Orlowski, Kraft, Pferdmenges, & Breuer, 2016;Wayland et al, 2003;Whitehead et al, 2015), topography (Likens & Buso, 2006;Lyon et al, 2012;Singh, Emanuel, & McGlynn, 2016;Uchida & Asano, 2010), geology, and soil type (Hindshaw et al, 2011;Kim, Dietrich, Thurnhoffer, Bishop, & Fung, 2017;Soulsby et al, 2007;Zimmer et al, 2013), affect streamwater chemistry.…”