Giulia Zuecco | Università degli Studi di Padova (original) (raw)

Papers by Giulia Zuecco

ABSTRACT The hydrological functioning of forested catchments in mountain regions is complex due t... more ABSTRACT The hydrological functioning of forested catchments in mountain regions is complex due to spatially and temporally variable hydrological processes. As such, the main sources of water contributing to streamflow and the dominant controls governing the runoff response still need to be identified more clearly. We therefore used stable isotope and electrical conductivity (EC) data, and hydrometric measurements in a small forested catchment in the North-Eastern Italian Pre-Alps to assess: i) the fraction of pre-event and event water during rainfall-runoff events; ii) the spatial sources of stream water during events; and iii) the temporal dynamics of groundwater. The measurements were taken during late summer and early autumn of 2011 and 2012 in the 2-ha Ressi catchment. The area is densely vegetated with broad-leaf trees. Hydrometric measurements include precipitation at two rain gauges, discharge at a V-notch weir, soil moisture at four locations along a riparian-hillslope transect, and groundwater levels in four piezometers. We collected samples on a weekly basis from bulk precipitation, groundwater and soil water (using suction lysimeters). Stream water samples were taken by an automatic sampler at a variable frequency. Additionally, samples were collected at a high temporal resolution during seven rainfall-runoff events. The deuterium and oxygen-18 isotopic composition was determined by laser absorption spectroscopy and EC was measured in the field using a portable conductivity meter. Since summer 2012, EC and water temperature in the stream are measured continuously. Two-component hydrograph separation shows that pre-event water dominates the stream response, as observed in many other forested catchments worldwide. The fraction of pre-event water for the different events ranged between 71% and 97% based on deuterium data and between 65% and 97% based on oxygen-18 data. The runoff coefficient and the groundwater peak increased linearly and the fraction of event water decreased linearly with increasing pre-event soil moisture conditions. This suggests that for small storms during dry conditions that result in low runoff coefficients, event water is mainly derived from channel interception and rainfall falling on the riparian area. These events are characterized by a quick streamflow response and large event water contributions during the initial storm response. Conversely, larger storms during wet conditions result in higher runoff coefficients and have larger contributions of pre-event water. Three-component hydrograph separation and mixing analysis revealed that the flood hydrograph mainly consists of groundwater; soil water and precipitation have smaller and similar contributions. The role of groundwater on the storm response was confirmed by the strong correlation between EC in stream water and peak water table. For summer storm events water table peaks occurred after the discharge peaked, whereas for longer and larger autumn storms the opposite was observed. This highlights the importance of groundwater contributions to streamflow, especially during wet periods. Keywords: water stable isotopes, electrical conductivity, groundwater, soil water.

ABSTRACT Rain gauges, weather radars, satellite sensors and modelled data from weather centres ar... more ABSTRACT Rain gauges, weather radars, satellite sensors and modelled data from weather centres are used operationally for estimating the spatial-temporal variability of rainfall. However, the associated uncertainties can be very high, especially in poorly equipped regions of the world. Very recently, an innovative method, named SM2RAIN, that uses soil moisture observations to infer rainfall, has been proposed by Brocca et al. (2013) with very promising results when applied with in situ and satellite-derived data. However, a thorough analysis of the physical consistency of the SM2RAIN algorithm has not been carried out yet. In this study, synthetic soil moisture data generated from a physically-based soil water balance model are employed to check the reliability of the assumptions made in the SM2RAIN algorithm. Next, high quality and multiyear in situ soil moisture observations, at different depths (5-30 cm), and rainfall for ten sites across Europe are used for testing the performance of the algorithm, its limitations and applicability range. SM2RAIN shows very high accuracy in the synthetic experiments with a correlation coefficient, R, between synthetically generated and simulated data, at daily time step, higher than 0.940 and an average Bias lower than 4%. When real datasets are used, the agreement between observed and simulated daily rainfall is slightly lower with average R-values equal to 0.87 and 0.85 in the calibration and validation periods, respectively. Overall, the performance is found to be better in humid temperate climates and for sensors installed vertically. Interestingly, algorithms of different complexity in the reproduction of the underlying hydrological processes provide similar results. The average contribution of surface runoff and evapotranspiration components amounts to less than 4% of the total rainfall, while the soil moisture variations (63%) and subsurface drainage (30%) terms provide a much higher contribution. Overall, the SM2RAIN algorithm is found to perform well both in the synthetic and real data experiments, thus offering a new and independent source of data for improving rainfall estimation, and consequently enhancing hydrological, meteorological and climatic studies.

The redistribution of rainfall in the forest canopy affects many hydrological and biogeochemical ... more The redistribution of rainfall in the forest canopy affects many hydrological and biogeochemical processes. Although many studies have focused on the quantification of throughfall, the controls on the spatial variability and temporal persistence of throughfall patterns are still poorly understood. This study therefore aims to: i) quantify throughfall at the plot scale for a pre-Alpine forested hillslope in Italy; ii) assess measurement differences between two different throughfall collectors; and iii) investigate the spatial and temporal variability of throughfall patterns and their relation to canopy characteristics.

We used a dual stable isotope approach ( 2 H and 18 O) and electrical conductivity data in combin... more We used a dual stable isotope approach ( 2 H and 18 O) and electrical conductivity data in combination with hydrometric measurements to trace water fluxes in the soil, stream and trees in a small forested watershed in the Italian Pre-Alps. The aim was to understand the main water sources for plant transpiration and runoff generation. The data were collected between events and during rainfall events in order to assess the sources of tree uptake under different conditions. Sampling and analysis are still continuing but preliminary results show that the isotopic composition of tree water was similar to soil water and rain water but statistically different from streamflow and groundwater. This suggests that trees used predominantly soil water, rather than groundwater, during the study period. No marked difference was found between the isotopic composition of the sap of trees in the riparian zone and the sap of trees on the hillslope. However, during dry conditions sap in riparian trees slowly became more similar to deep soil water and groundwater, indicating a possible switch in water uptake from shallow to deeper soil water. In contrast to the quick response of the stream, the composition of tree water did not change immediately after a rainfall event, even though the composition of shallow soil water had changed, which may be caused by storage of water in the tree and the low vapor pressure deficit that suppressed transpiration after the rainfall event. Future work will be carried out to monitor the seasonal variability in water uptake and its response to rainfall events in more detail.

Hydrology and Earth System Sciences, 2012

This study evaluated between-sample memory in isotopic measurements of δ 2 H and δ 18 O in water ... more This study evaluated between-sample memory in isotopic measurements of δ 2 H and δ 18 O in water samples by laser spectroscopy. Ten isotopically depleted water samples spanning a broad range of oxygen and hydrogen isotopic compositions were measured by three generations of offaxis integrated cavity output spectroscopy and cavity ringdown spectroscopy instruments. The analysis procedure encompassed small (less than 2 ‰ for δ 2 H and 1 ‰ for δ 18 O) and large (up to 201 ‰ for δ 2 H and 25 ‰ for δ 18 O) differences in isotopic compositions between adjacent sample vials. Samples were injected 18 times each, and the betweensample memory effect was quantified for each analysis run. Results showed that samples adversely affected by betweensample isotopic differences stabilised after seven-eight injections. The between-sample memory effect ranged from 14 % and 9 % for δ 2 H and δ 18 O measurements, respectively, but declined to negligible carryover (between 0.1 % and 0.3 % for both isotopes) when the first ten injections of each sample were discarded. The measurement variability (range and standard deviation) was strongly dependent on the isotopic difference between adjacent vials. Standard deviations were up to 7.5 ‰ for δ 2 H and 0.54 ‰ for δ 18 O when all injections were retained in the computation of the reportable δ-value, but a significant increase in measurement precision (standard deviation in the range 0.1 ‰-1.0 ‰ for δ 2 H and 0.05 ‰-0.17 ‰ for δ 18 O) was obtained when the first eight injections were discarded. In conclusion, this study provided a practical solution to mitigate between-sample memory effects in the isotopic analysis of water samples by laser spectroscopy.

Hydrology and Earth System Sciences, 2012

This study evaluated between-sample memory in isotopic measurements of δ 2 H and δ 18 O in water ... more This study evaluated between-sample memory in isotopic measurements of δ 2 H and δ 18 O in water samples by laser spectroscopy. Ten isotopically depleted water samples spanning a broad range of oxygen and hydrogen isotopic compositions were measured by three generations of offaxis integrated cavity output spectroscopy and cavity ringdown spectroscopy instruments. The analysis procedure encompassed small (less than 2 ‰ for δ 2 H and 1 ‰ for δ 18 O) and large (up to 201 ‰ for δ 2 H and 25 ‰ for δ 18 O) differences in isotopic compositions between adjacent sample vials. Samples were injected 18 times each, and the betweensample memory effect was quantified for each analysis run. Results showed that samples adversely affected by betweensample isotopic differences stabilised after seven-eight injections. The between-sample memory effect ranged from 14 % and 9 % for δ 2 H and δ 18 O measurements, respectively, but declined to negligible carryover (between 0.1 % and 0.3 % for both isotopes) when the first ten injections of each sample were discarded. The measurement variability (range and standard deviation) was strongly dependent on the isotopic difference between adjacent vials. Standard deviations were up to 7.5 ‰ for δ 2 H and 0.54 ‰ for δ 18 O when all injections were retained in the computation of the reportable δ-value, but a significant increase in measurement precision (standard deviation in the range 0.1 ‰-1.0 ‰ for δ 2 H and 0.05 ‰-0.17 ‰ for δ 18 O) was obtained when the first eight injections were discarded. In conclusion, this study provided a practical solution to mitigate between-sample memory effects in the isotopic analysis of water samples by laser spectroscopy.

The hydrological response of high elevation catchments is strongly influenced by snowmelt process... more The hydrological response of high elevation catchments is strongly influenced by snowmelt processes. Moreover, in alpine periglacial environments, the presence of permafrost (generally discontinuous and frequently associated to landforms such as rock glaciers) makes even more difficult to identify the origin of surface and subsurface waters and the main contributors to stream runoff. Based on the use of isotopic (deuterium and 18-oxygen), electrical conductivity and water temperature data, this study aims to: i) identify which environmental tracer(s) could be used as indicator(s) of the possible influence of permafrost on groundwater and stream water; ii) investigate the role of snowmelt and rainfall on the seasonal runoff response in a periglacial catchment.

We used a dual stable isotope approach ( 2 H and 18 O) and electrical conductivity data in combin... more We used a dual stable isotope approach ( 2 H and 18 O) and electrical conductivity data in combination with hydrometric measurements to trace water fluxes in the soil, stream and trees in a small forested watershed in the Italian Pre-Alps. The aim was to understand the main water sources for plant transpiration and runoff generation. The data were collected between events and during rainfall events in order to assess the sources of tree uptake under different conditions. Sampling and analysis are still continuing but preliminary results show that the isotopic composition of tree water was similar to soil water and rain water but statistically different from streamflow and groundwater. This suggests that trees used predominantly soil water, rather than groundwater, during the study period. No marked difference was found between the isotopic composition of the sap of trees in the riparian zone and the sap of trees on the hillslope. However, during dry conditions sap in riparian trees slowly became more similar to deep soil water and groundwater, indicating a possible switch in water uptake from shallow to deeper soil water. In contrast to the quick response of the stream, the composition of tree water did not change immediately after a rainfall event, even though the composition of shallow soil water had changed, which may be caused by storage of water in the tree and the low vapor pressure deficit that suppressed transpiration after the rainfall event. Future work will be carried out to monitor the seasonal variability in water uptake and its response to rainfall events in more detail.

Understandin challenge in h at 0-30 cm de Italy) by mea grapevine pla characteristic variability.... more Understandin challenge in h at 0-30 cm de Italy) by mea grapevine pla characteristic variability. Ex the influence systematically mean and the and evapotran the two sites. The model is variability.

ABSTRACT The hydrological functioning of forested catchments in mountain regions is complex due t... more ABSTRACT The hydrological functioning of forested catchments in mountain regions is complex due to spatially and temporally variable hydrological processes. As such, the main sources of water contributing to streamflow and the dominant controls governing the runoff response still need to be identified more clearly. We therefore used stable isotope and electrical conductivity (EC) data, and hydrometric measurements in a small forested catchment in the North-Eastern Italian Pre-Alps to assess: i) the fraction of pre-event and event water during rainfall-runoff events; ii) the spatial sources of stream water during events; and iii) the temporal dynamics of groundwater. The measurements were taken during late summer and early autumn of 2011 and 2012 in the 2-ha Ressi catchment. The area is densely vegetated with broad-leaf trees. Hydrometric measurements include precipitation at two rain gauges, discharge at a V-notch weir, soil moisture at four locations along a riparian-hillslope transect, and groundwater levels in four piezometers. We collected samples on a weekly basis from bulk precipitation, groundwater and soil water (using suction lysimeters). Stream water samples were taken by an automatic sampler at a variable frequency. Additionally, samples were collected at a high temporal resolution during seven rainfall-runoff events. The deuterium and oxygen-18 isotopic composition was determined by laser absorption spectroscopy and EC was measured in the field using a portable conductivity meter. Since summer 2012, EC and water temperature in the stream are measured continuously. Two-component hydrograph separation shows that pre-event water dominates the stream response, as observed in many other forested catchments worldwide. The fraction of pre-event water for the different events ranged between 71% and 97% based on deuterium data and between 65% and 97% based on oxygen-18 data. The runoff coefficient and the groundwater peak increased linearly and the fraction of event water decreased linearly with increasing pre-event soil moisture conditions. This suggests that for small storms during dry conditions that result in low runoff coefficients, event water is mainly derived from channel interception and rainfall falling on the riparian area. These events are characterized by a quick streamflow response and large event water contributions during the initial storm response. Conversely, larger storms during wet conditions result in higher runoff coefficients and have larger contributions of pre-event water. Three-component hydrograph separation and mixing analysis revealed that the flood hydrograph mainly consists of groundwater; soil water and precipitation have smaller and similar contributions. The role of groundwater on the storm response was confirmed by the strong correlation between EC in stream water and peak water table. For summer storm events water table peaks occurred after the discharge peaked, whereas for longer and larger autumn storms the opposite was observed. This highlights the importance of groundwater contributions to streamflow, especially during wet periods. Keywords: water stable isotopes, electrical conductivity, groundwater, soil water.

ABSTRACT Rain gauges, weather radars, satellite sensors and modelled data from weather centres ar... more ABSTRACT Rain gauges, weather radars, satellite sensors and modelled data from weather centres are used operationally for estimating the spatial-temporal variability of rainfall. However, the associated uncertainties can be very high, especially in poorly equipped regions of the world. Very recently, an innovative method, named SM2RAIN, that uses soil moisture observations to infer rainfall, has been proposed by Brocca et al. (2013) with very promising results when applied with in situ and satellite-derived data. However, a thorough analysis of the physical consistency of the SM2RAIN algorithm has not been carried out yet. In this study, synthetic soil moisture data generated from a physically-based soil water balance model are employed to check the reliability of the assumptions made in the SM2RAIN algorithm. Next, high quality and multiyear in situ soil moisture observations, at different depths (5-30 cm), and rainfall for ten sites across Europe are used for testing the performance of the algorithm, its limitations and applicability range. SM2RAIN shows very high accuracy in the synthetic experiments with a correlation coefficient, R, between synthetically generated and simulated data, at daily time step, higher than 0.940 and an average Bias lower than 4%. When real datasets are used, the agreement between observed and simulated daily rainfall is slightly lower with average R-values equal to 0.87 and 0.85 in the calibration and validation periods, respectively. Overall, the performance is found to be better in humid temperate climates and for sensors installed vertically. Interestingly, algorithms of different complexity in the reproduction of the underlying hydrological processes provide similar results. The average contribution of surface runoff and evapotranspiration components amounts to less than 4% of the total rainfall, while the soil moisture variations (63%) and subsurface drainage (30%) terms provide a much higher contribution. Overall, the SM2RAIN algorithm is found to perform well both in the synthetic and real data experiments, thus offering a new and independent source of data for improving rainfall estimation, and consequently enhancing hydrological, meteorological and climatic studies.

The redistribution of rainfall in the forest canopy affects many hydrological and biogeochemical ... more The redistribution of rainfall in the forest canopy affects many hydrological and biogeochemical processes. Although many studies have focused on the quantification of throughfall, the controls on the spatial variability and temporal persistence of throughfall patterns are still poorly understood. This study therefore aims to: i) quantify throughfall at the plot scale for a pre-Alpine forested hillslope in Italy; ii) assess measurement differences between two different throughfall collectors; and iii) investigate the spatial and temporal variability of throughfall patterns and their relation to canopy characteristics.

We used a dual stable isotope approach ( 2 H and 18 O) and electrical conductivity data in combin... more We used a dual stable isotope approach ( 2 H and 18 O) and electrical conductivity data in combination with hydrometric measurements to trace water fluxes in the soil, stream and trees in a small forested watershed in the Italian Pre-Alps. The aim was to understand the main water sources for plant transpiration and runoff generation. The data were collected between events and during rainfall events in order to assess the sources of tree uptake under different conditions. Sampling and analysis are still continuing but preliminary results show that the isotopic composition of tree water was similar to soil water and rain water but statistically different from streamflow and groundwater. This suggests that trees used predominantly soil water, rather than groundwater, during the study period. No marked difference was found between the isotopic composition of the sap of trees in the riparian zone and the sap of trees on the hillslope. However, during dry conditions sap in riparian trees slowly became more similar to deep soil water and groundwater, indicating a possible switch in water uptake from shallow to deeper soil water. In contrast to the quick response of the stream, the composition of tree water did not change immediately after a rainfall event, even though the composition of shallow soil water had changed, which may be caused by storage of water in the tree and the low vapor pressure deficit that suppressed transpiration after the rainfall event. Future work will be carried out to monitor the seasonal variability in water uptake and its response to rainfall events in more detail.

Hydrology and Earth System Sciences, 2012

This study evaluated between-sample memory in isotopic measurements of δ 2 H and δ 18 O in water ... more This study evaluated between-sample memory in isotopic measurements of δ 2 H and δ 18 O in water samples by laser spectroscopy. Ten isotopically depleted water samples spanning a broad range of oxygen and hydrogen isotopic compositions were measured by three generations of offaxis integrated cavity output spectroscopy and cavity ringdown spectroscopy instruments. The analysis procedure encompassed small (less than 2 ‰ for δ 2 H and 1 ‰ for δ 18 O) and large (up to 201 ‰ for δ 2 H and 25 ‰ for δ 18 O) differences in isotopic compositions between adjacent sample vials. Samples were injected 18 times each, and the betweensample memory effect was quantified for each analysis run. Results showed that samples adversely affected by betweensample isotopic differences stabilised after seven-eight injections. The between-sample memory effect ranged from 14 % and 9 % for δ 2 H and δ 18 O measurements, respectively, but declined to negligible carryover (between 0.1 % and 0.3 % for both isotopes) when the first ten injections of each sample were discarded. The measurement variability (range and standard deviation) was strongly dependent on the isotopic difference between adjacent vials. Standard deviations were up to 7.5 ‰ for δ 2 H and 0.54 ‰ for δ 18 O when all injections were retained in the computation of the reportable δ-value, but a significant increase in measurement precision (standard deviation in the range 0.1 ‰-1.0 ‰ for δ 2 H and 0.05 ‰-0.17 ‰ for δ 18 O) was obtained when the first eight injections were discarded. In conclusion, this study provided a practical solution to mitigate between-sample memory effects in the isotopic analysis of water samples by laser spectroscopy.

Hydrology and Earth System Sciences, 2012

This study evaluated between-sample memory in isotopic measurements of δ 2 H and δ 18 O in water ... more This study evaluated between-sample memory in isotopic measurements of δ 2 H and δ 18 O in water samples by laser spectroscopy. Ten isotopically depleted water samples spanning a broad range of oxygen and hydrogen isotopic compositions were measured by three generations of offaxis integrated cavity output spectroscopy and cavity ringdown spectroscopy instruments. The analysis procedure encompassed small (less than 2 ‰ for δ 2 H and 1 ‰ for δ 18 O) and large (up to 201 ‰ for δ 2 H and 25 ‰ for δ 18 O) differences in isotopic compositions between adjacent sample vials. Samples were injected 18 times each, and the betweensample memory effect was quantified for each analysis run. Results showed that samples adversely affected by betweensample isotopic differences stabilised after seven-eight injections. The between-sample memory effect ranged from 14 % and 9 % for δ 2 H and δ 18 O measurements, respectively, but declined to negligible carryover (between 0.1 % and 0.3 % for both isotopes) when the first ten injections of each sample were discarded. The measurement variability (range and standard deviation) was strongly dependent on the isotopic difference between adjacent vials. Standard deviations were up to 7.5 ‰ for δ 2 H and 0.54 ‰ for δ 18 O when all injections were retained in the computation of the reportable δ-value, but a significant increase in measurement precision (standard deviation in the range 0.1 ‰-1.0 ‰ for δ 2 H and 0.05 ‰-0.17 ‰ for δ 18 O) was obtained when the first eight injections were discarded. In conclusion, this study provided a practical solution to mitigate between-sample memory effects in the isotopic analysis of water samples by laser spectroscopy.

The hydrological response of high elevation catchments is strongly influenced by snowmelt process... more The hydrological response of high elevation catchments is strongly influenced by snowmelt processes. Moreover, in alpine periglacial environments, the presence of permafrost (generally discontinuous and frequently associated to landforms such as rock glaciers) makes even more difficult to identify the origin of surface and subsurface waters and the main contributors to stream runoff. Based on the use of isotopic (deuterium and 18-oxygen), electrical conductivity and water temperature data, this study aims to: i) identify which environmental tracer(s) could be used as indicator(s) of the possible influence of permafrost on groundwater and stream water; ii) investigate the role of snowmelt and rainfall on the seasonal runoff response in a periglacial catchment.

We used a dual stable isotope approach ( 2 H and 18 O) and electrical conductivity data in combin... more We used a dual stable isotope approach ( 2 H and 18 O) and electrical conductivity data in combination with hydrometric measurements to trace water fluxes in the soil, stream and trees in a small forested watershed in the Italian Pre-Alps. The aim was to understand the main water sources for plant transpiration and runoff generation. The data were collected between events and during rainfall events in order to assess the sources of tree uptake under different conditions. Sampling and analysis are still continuing but preliminary results show that the isotopic composition of tree water was similar to soil water and rain water but statistically different from streamflow and groundwater. This suggests that trees used predominantly soil water, rather than groundwater, during the study period. No marked difference was found between the isotopic composition of the sap of trees in the riparian zone and the sap of trees on the hillslope. However, during dry conditions sap in riparian trees slowly became more similar to deep soil water and groundwater, indicating a possible switch in water uptake from shallow to deeper soil water. In contrast to the quick response of the stream, the composition of tree water did not change immediately after a rainfall event, even though the composition of shallow soil water had changed, which may be caused by storage of water in the tree and the low vapor pressure deficit that suppressed transpiration after the rainfall event. Future work will be carried out to monitor the seasonal variability in water uptake and its response to rainfall events in more detail.

Understandin challenge in h at 0-30 cm de Italy) by mea grapevine pla characteristic variability.... more Understandin challenge in h at 0-30 cm de Italy) by mea grapevine pla characteristic variability. Ex the influence systematically mean and the and evapotran the two sites. The model is variability.