Headwaters’ Isotopic Signature as a Tracer of Stream Origins and Climatic Anomalies: Evidence from the Italian Alps in Summer 2018

Using Stable Water Isotopes to Analyze Spatiotemporal Variability and Hydrometeorological Forcing in Mountain Valley Wetlands

Wetlands in Montane and Subalpine Subregions are increasingly recognized as important hydrologic features that support ecosystem function. However, it is currently not clear how climate trends will impact wetland hydrological processes (e.g., evaporative fluxes) across spatiotemporal scales. Therefore, identifying the factors that influence wetland hydrologic response to climate change is an important step in understanding the sensitivity of these ecosystems to environmental change. We used stable water isotopes of hydrogen and oxygen (δ2H and δ18O), coupled with climate data, to determine the spatiotemporal variability in isotopic signatures of wetland source waters and understand the influence of evaporative fluxes on wetlands in the Kananaskis Valley. Our results show that the primary runoff generation mechanism changes throughout the growing season resulting in considerable mixing in wetland surface waters. We found that evaporative fluxes increased with decreasing elevation and that isotopic values became further removed from meteoric water lines during the late peak- and into the post-growing seasons. These findings suggest that a change in the water balance in favor of enhanced evaporation (due to a warmer and longer summer season than present) will not only lead to greater water loss from the wetlands themselves but may also reduce the water inputs from their catchments.

Seasonal variations in the optical characteristics of dissolved organic matter in glacial pond water

Large amounts of dissolved organic matter (DOM) are stored in mountain glaciers. However, few researches have analysed the optical characteristics of DOM in surface waters fed by mountain glaciers and their seasonal variations. In a pond fed by a glacier we observed simultaneous decreases in the dissolved organic carbon, and increases in both absorbance at 254 nm and specific absorption coefficient (SUVA₂₅₄) during the ice-free season 2015. This behaviour differs from the typical behaviour of lake/pond water in summer, and from the trends observed in a nearby pond not fed by a glacier. The trends of DOM properties, main ions and water stable isotopes at the glacier-fed pond could be attributed to transient modifications of the subglacial hydrological system. Flushing of previously isolated pools of subglacially stored water, containing terrestrial DOM derived from glacially-overridden soil and vegetation, would be driven by intense rainfall events during the melting season. These findings suggest that heavy rainfall events during the melting season have the capability to transiently modify the characteristics of DOM in a glacial pond. These events may be further exacerbated in the future, as summer rainfall events in the Alps are predicted to increase due to global warming.

Source Water Apportionment of a River Network: Comparing Field Isotopes to Hydrodynamically Modeled Tracers

Tributary source water provenance is a primary control on water quality and ecological characteristics in branching tidal river systems. Source water provenance can be estimated both from field observations of chemical characteristics of water and from numerical modeling approaches. This paper highlights the strengths and shortcomings of two methods. One method uses stable isotope compositions of oxygen and hydrogen from water in field-collected samples to build a mixing model. The second method uses a calibrated hydrodynamic model with numerical tracers released from upstream reaches to estimate source-water fraction throughout the model domain. Both methods were applied to our study area in the eastern Sacramento–San Joaquin Delta, a freshwater tidal system which is dominated by fluvial processes during the flood season. In this paper, we show that both methods produce similar source water fraction values, implying the usefulness of both despite their shortcomings, and fortifying the use of hydrodynamic tracers to model transport in a natural system.