Effects of the 2017 drought on isotopic and geochemical gradients in the Adige catchment, Italy

The year 2017 was anomalously warm and dry across the whole Italian Peninsula, and the paucity of precipitation was emphasized during the extreme summer drought of the main Italian river, i.e., the Po river, which was characterized by a discharge persistently below 600 m 3 /s (in spite of the average discharge of 1500 m 3 /s). During these extreme conditions, the Po river oxygen and hydrogen stable isotopes (δD, δ 18 O) displayed a relation (δD = 6.1*δ 18 O − 6.6) significantly different from that recorded in the previous investigation of the years 2012-2014 (δD = 7.5*δ 18 O + 6.5). The lowering of the slope and the negative intercept clearly reflect the transition toward arid conditions that characterized the investigated period. The difference is expressed by the derivative parameter Line-Conditioned excess (LC-exc), which better describes the compositional difference of Po river water in the year 2017 with respect to that of the period 2012-2014, when the system was less affected by warm or dry conditions and the river discharge was more similar to the historical trends. The isotopic anomaly observed in 2017 throughout the river is even greater in the terminal part of the river, where in the meanders of the deltaic branches, the river flow progressively slows down, suffering significant evaporation. The isotopic signature of the water appears, therefore, an appropriate tool to monitor the watershed response to evolving environmental conditions. These sensitive isotopic parameters could be interpreted as "essential climate variables" (ECV) that are physical, chemical, or biological geo-referenced parameters that critically contribute to the characterization of Earth's climate. Future research needs to find relationships between ECV (including the water stable isotopes) and the evolution of ecosystems, which especially in the Mediterranean area, appear to be fragile and severely affected by natural and anthropogenic processes.

Section: The δD-δ 18 O Variation and Inferences On Environmental Changesmentioning

confidence: 61%

Section: Introductionmentioning

confidence: 99%

The Po River Water Isotopes during the Drought Condition of the Year 2017

Marchina

Natali

Bianchini

2019

“…Knowledge of hydrological processes is a key point in applied hydrology studies, and the understanding of runoff generation mechanisms is a milestone and, moreover, a challenging task in this field of research. In particular, reliable estimation of the baseflow process and of the low flow regime is of practical importance in the management of hydrological drought issues and in general for sustainable freshwater utilization [1][2][3]. Unfortunately, to characterize the low streamflow regime, direct baseflow measurements are needed, but they are almost never available; therefore, hydrograph filtering techniques are generally adopted to perform a robust and quantitative assessment of baseflow patterns from hydrographs.…”

Section: Introductionmentioning

confidence: 99%

Regression Approaches for Hydrograph Separation: Implications for the Use of Discontinuous Electrical Conductivity Data

Longobardi

Villani

Guida

et al. 2018

Understanding of runoff generation mechanisms affects the ability to manage streamflow quantity and quality issues. Concerning the baseflow in particular, measurements are almost never available and hydrograph separation is generally applied to characterize its relevant patterns. As an alternative to well-known recursive digital filters and mass balance filtering methods, this paper deals with the use of regression approaches, based on electrical conductivity measurements, as a proxy for total dissolved solids, to separate baseflow from total flow. Particular focus is placed on their flexibility and ability to adapt to discontinuous electrical conductivity data measurements.To illustrate this, we analyze a hydrochemical dataset collected from the Ciciriello experimental catchment (Southern Italy). The main findings are as follows: A comparative analysis suggests that the performance of regressive approaches in the case of daily electrical conductivity measurements is better than that of calibrated recursive digital filters. Weekly monitored electrical conductivity data led to performances comparable to the daily scale monitoring, and even monthly observation leads to a nonsignificant reduction in regression hydrograph filter performance; this shows how spot geochemical data monitoring may present valid and operational alternatives for characterization of baseflow in poorly gauged catchments.

“…In addition, glacial influence and its temporal variation can impact runoff hydrochemistry, producing waters with different geochemical patterns depending on the water end members [22,23]. In this view, the use of dissolved ions as sulfates and silicon can be useful in distinguishing between snow, ice, and groundwater sources in headwaters [23].Stable isotopes are an additional tool used to characterize water sources [24][25][26][27][28]. δ 2 H and δ 18 O are widely used in hydrological studies of high-elevation catchments [25][26][27][28][29].…”

mentioning

confidence: 99%

“…In this view, the use of dissolved ions as sulfates and silicon can be useful in distinguishing between snow, ice, and groundwater sources in headwaters [23].Stable isotopes are an additional tool used to characterize water sources [24][25][26][27][28]. δ 2 H and δ 18 O are widely used in hydrological studies of high-elevation catchments [25][26][27][28][29]. Improvement of technological techniques, especially laser spectroscopy, helped increase the information of these tracers in different water compartments, especially in sensitive areas such as glacialized catchments, where environmental changes have the most impact [30,31].…”

mentioning

confidence: 99%

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

Marchina

Lencioni

Paoli

et al. 2020

Glaciers are shrinking due to global warming, resulting in a diminishing contribution of ice and snowmelt to headwaters and subsequent consequences to freshwater ecosystems. Within this context, we tested whether water-stable isotopes are spatio-temporal tracers of (i) water in high altitude periglacial environments, being the isotopic signature of surface water inherited from the snow/icemelt, groundwater, and rainfall; and (ii) regional (year-specific) meteorological conditions, being the isotopic signature of precipitations affected by air temperature, humidity and aqueous vapour origin, ascribing stable isotopes to the list of "essential climate variables" (ECVs). To this end, we investigated the ionic and isotopic composition (δ 18 O and δ 2 H) of six high-altitude streams and one pond in the Italian Alps (Noce and Sarca basins) during the ablation season in 2018. Differences between habitat types (pond, kryal, rhithral, krenal) were detected. More negative values of δ 18 O and δ 2 H were recorded in the kryal and glacio-rhithral sites, dominated by ice and snowmelt, in early summer. Less negative values were recorded in these sites in late summer, as well as in the krenal sites, which were dominated by groundwater and rainfall inputs. The isotopic results also show that the complex alpine orography influences air masses and moisture, ultimately resulting in isotopic differences in the precipitations of neighboring but distinct catchments (Sarca and Noce basins). On average, less negative values were recorded in the Sarca basin, characterized by a higher contribution of precipitation of Mediterranean origin. In general, isotopic results of the entire water population appeared to be strongly influenced by the regional climatic anomaly of 2018, which was anomalously warm. Therefore, the study will provide additional information for the climate change debate, proposing water isotopes as ECVs for assessing change in a warmer future.Water 2020, 12, 390 2 of 18 future, mean annual runoff is expected to progressively decrease in glacier-fed streams, and overall changes in the hydrological behavior of small-and large-scale catchments are expected [9,10].Glacier shrinking and its consequences on glacier-fed streams induce variation in the physical, chemical and biological features of freshwater ecosystems [11,12]. This profoundly affects the ecosystem services that glacier-fed rivers provide to humans, particularly the provision of water for agriculture, hydropower, and consumption [11,13,14]. This is crucial for mountain settlements in glacialized regions, where the snow and ice melt contribution, especially in spring and summer, is the most relevant water source for several uses [13][14][15]. In particular, streams draining in Alpine areas are generally identified as some of the environments most sensitive to climate change [16,17]. This is particularly true for glacier-fed streams and rivers [18]. Within this scenario, runoff changes also impact on the biological community structure [13,19]. In fact, alpine stream...