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Present and future climatic trends are expected to markedly alter water fluxes and stores in the hydrologic cycle. In addition, water demand continues to grow due to increased human use and a growing population. Sustainably managing water resources requires a thorough understanding of water storage and flow in natural, agricultural, and urban ecosystems. Measurements of stable isotopes of water (hydrogen and oxygen) in the water cycle (atmosphere, soils, plants, surface water, and groundwater) can provide information on the transport pathways, sourcing, dynamics, ages, and storage pools of water that is difficult to obtain with other techniques. However, the potential of these techniques for practical questions has not been fully exploited yet. Here, we outline the benefits and limitations of potential applications of stable isotope methods useful to water managers, farmers, and other stakeholders. We also describe several case studies demonstrating how stable isotopes of water can support water management decision-making. Finally, we propose a workflow that guides users through a sequence of decisions required to apply stable isotope methods to examples of water management issues. We call for ongoing dialogue and a stronger connection between water management stakeholders and water stable isotope practitioners to identify the most pressing issues and develop best-practice guidelines to apply these techniques.

The young water fraction (Fyw), defined as the fraction of catchment outflow with transit times of less than about 2–3 months, is increasingly used in hydrological studies, replacing the widely used Mean Transit Time (MTT), which is subject to aggregation error. The use of this new metric in catchment intercomparison studies is helpful to understand and conceptualize the relevant processes controlling catchment's hydrological function. Past work has shown the remarkable and counterintuitive evidence that steep (and generally high elevation) catchments worldwide reveal small Fyw values. However, the topographic slope only partially explains the observed Fyw variance, and the mechanisms hidden behind this lowering with slope remain basically unclear. The main aim of this paper is to investigate what drives Fyw variations with elevation in Alpine catchments clarifying why Fyw is low at high altitudes. In this regard, we use a dataset composed of 27 study catchments, located both in Switzerland and in Italy, that we categorize as rainfall-dominated, hybrid or snow-dominated according to a proposed formal classification scheme that considers both a common-used monthly streamflow ratio and the snow cover regime. We analyze three not previously investigated variables that could potentially explain the Fyw elevation gradients: the fractional snow cover area (FSCA), the fraction of quaternary deposits (Fqd), and the fraction of baseflow (Fbf). We also consider a fourth variable, namely the Winter Flow Index (WFI), for comparing our results about the groundwater contribution to streamflow with those of previous scientific publications. Our results suggest that unconsolidated sediments could play a role in modulating Fyw elevation gradients via their capacity to store groundwater, but further geological information, such as the portion of fractured bedrocks, would be desirable for a complete picture of the role of geology. Based on our analysis concerning the FSCA , we develop a perceptual model that explains how the increasing duration of the snowpack promotes a progressive emptying of the groundwater storage during winter, thereby increasing the streamwater age, while ephemeral snowpack generally favors rapid flow paths that increase Fyw. Finally, our work highlights that Fbf , considered as a proxy for groundwater flow, is roughly the one's complement of Fyw. In harmony with the model, we find high Fbf during all low-flow periods, which underlines that streamflow is mainly sustained by groundwater in such flow conditions. For catchments where the winter low-flow period is long compared to the summer high-flow period, this results in low Fyw. In conclusion, our data set suggests that Fbf is the best explanatory variable of Fyw elevation gradients in Alpine catchments, implying the key-role of major groundwater storages that, with the increasing snowpack duration, are actively involved in streamflow generation processes. [ABSTRACT FROM AUTHOR]

Soil management in vineyard inter-rows has a great influence on soil hydraulic conductivity and bulk density, and, consequently, on runoff and soil erosion processes at the field scale. The maintenance of bare soil in vineyard inter-rows with tillage, as well as the tractor traffic, are known to expose the soil to compaction, reduction of soil water holding capacity and increase of runoff and erosion. The use of grass cover is one of the most common and effective practices in order to reduce such threats. It is therefore important to relate rainfall characteristics, soil properties and response in terms of runoff and soil erosion, from yearly to seasonal and to single event temporal scales. The objective of this work is to quantify the temporal variability of the effects of two different kind of inter-row management on soil hydrological properties, runoff and erosion in vineyards. For this reason two vineyard field-scale plots in the Alto Monferrato vine-growing area (Piedmont, NW Italy) were monitored in two years. The inter-rows were managed with conventional tillage (CT) and grass cover (GC), respectively. Fifteen series of infiltration tests were carried out during a 2-year period of observation (October 2012 to November 2014). In order to take into account the effect of tractors traffic, the tests were done on the track, and outside the track. Furthermore, a dataset of 29 rainfall-runoff events covering a wide range of topsoil characteristics was collected in the two plots, along with soil water content and runoff discharge monitoring, and determination of sediment yield in case of erosive events. An optical disdrometer installed in the plots provided also 1-min rainfall intensity data. In summer, just one month after tillage, CT soil showed very low hydraulic conductivity, so storms were able to cause Hortonian runoff and soil losses up to 5.7 Mg ha −1 . In autumn and winter very high saturation-excess runoff was observed in CT, that reached 83% of the precipitation. Runoff in the grass cover plot was mainly due to saturation of the topsoil, and the annual reduction of runoff in the GC plot was about 63%. Soil erosion up to 1.2 Mg ha −1 in a single event was observed in the GC vineyard in winter. In each year of observation, most of the erosion occurred during a single event, while the total annual erosion was up to 9 times higher in the CT treatment than in the GC. [ABSTRACT FROM AUTHOR]

Abstract: Wood is currently widely used in low environmental impact transverse structures for stream management and restoration. During the service life of these structures, chemical, physical, and biological processes can naturally degrade the wood fibres with a consequent increase of porosity. This typically causes wood moisture to increase with decay; however, conventional wood water content measurement instruments are calibrated for wood that has not been degraded. In this study, we analysed larch wood (Larix decidua Mill.) logs at different degradation levels by surveying their water content with the time domain reflectometry (TDR) technique. TDR has been extensively used to measure water content in soil; however, it has rarely been applied to wood materials. A laboratory analysis was first performed to calibrate the TDR measurements with those obtained with the gravimetric method. Three field campaigns were conducted in three different check dams built between 1950 and 2003 and located in the NW Italian Alps. The proposed TDR calibration curve allowed for the determination of the volumetric wood water content with satisfactory accuracy. This curve showed two distinct regression slopes: the first slope was related to volumetric water contents between 0.0 and 0.16m3 m−3, whilst the second slope was related to water contents above 0.16m3 m−3. The TDR in situ measurements showed water content values ranging from 0.08 to 0.54m3 m−3 for the old timber structures and from 0.11 to 0.45m3 m−3 for the newer structures. This agrees with the conservation state of the timber, which was influenced by the position of the logs in the structure during the life of the check dams. Finally, we found an operative way to relate the wood water content to the wood degradation level. [Copyright &y& Elsevier]