Storage and routing of water in the deep critical zone of a snow dominated volcanic catchment

Abstract. This study combines major ion and isotope chemistry, age tracers, fracture density characterizations, and physical hydrology measurements to understand how the structure of the critical zone (CZ) influences its function, including water routing, storage, mean water residence times, and hydrologic response. In a high elevation rhyolitic tuff catchment in the Jemez River Basin Critical Zone Observatory (JRB-CZO) within the Valles Caldera National Preserve of northern New Mexico, a periodic precipitation pattern creates different hydrologic flow regimes during spring snowmelt, summer monsoon rain, and fall storms. Hydrometric, geochemical, and isotopic analyses of surface water and groundwater from distinct stores, most notably a perched aquifer in consolidated collapse breccia and deeper groundwater in a fractured tuff aquifer, enabled us to untangle the interactions of these groundwater stores and their contribution to streamflow across one complete water year. Despite seasonal differences in groundwater response due to water partitioning, major ion chemistry indicates that deep groundwater from the highly fractured site is more representative of groundwater contributing to streamflow across the entire water year. Additionally, comparison of streamflow and groundwater hydrographs indicates hydraulic connection between the fractured welded tuff aquifer and streamflow while the perched aquifer within the collapse breccia deposit does not show this same connection. Furthermore, analysis of age tracers and stable water isotopes indicates that groundwater is a mix of modern and older waters recharged from snowmelt and downhole neutron probe surveys suggest that water moves through the vadose zone both as vertical infiltration and subsurface lateral flow, depending on lithology. We find that in complex geologic terrain like that of the JRB-CZO, differences in CZ architecture of two hillslopes within a headwater catchment control water storage and routing through the subsurface and suggest that the perched aquifer does not contribute significantly to streams while deep fractured aquifers contribute most to streamflow.



Introduction
Understanding the interconnections of groundwater and surface water is fundamental to water resource management as groundwater and surface water should be considered a single resource (Winter, 1998); however, their interactions in different hydrogeologic settings are varied and complex (Winter, 1999).Discerning stream water 35 sources and groundwater dynamics are even more important in the context of changing climate, especially in the semiarid, mountainous environment of the western United States where warming trends are expected to threaten water supply (Barnett et al., 2005).Furthermore, identifying compartmentalized groundwater stores is necessary to sufficiently account for all components of the water balance (McDonnell, 2017).Therefore, characterizing localized water stores and the hydrologic connection of those aquifers to streams in mountainous environments that act as water 40 towers (Viviroli et al., 2007) has important implications for water resource availability of large population centers downstream.
The influence of the hydrogeologic environment (i.e.geology, topography, and climate) on the groundwater flow system of a given geographic region has long been accepted as the theoretical framework used to conceptualize groundwater flow.Building on Toth's (1970) conceptual model and the understanding that one part of the framework Freeze, 1972; Kelson and Wells, 1989;Mwakalila et al., 2002) as controls of groundwater flow systems.However, subsurface heterogeneities, which can be abundant and are challenging to identify, can give rise to complex, localized groundwater stores, whose contribution to streamflow can be very difficult to discern.There is still much to learn 50 about the extent to which structural heterogeneities exist and how, specifically, they control groundwater storage, routing, and contributions to streamflow.For instance, evidence of perched aquifers transmitting shallow subsurface flow has been shown across variable rock types (Salve et al., 2012;Kim et al., 2014;Brantley et al., 2017;Kim et al., 2017;McIntosh et al., 2017).Furthermore, Brooks et al. (2015) highlighted the need to understand the influence of subsurface structure on water routing and residence time as they concluded that surface water, across several 55 catchments and flow regimes, substantially interacted with or spent time within various soil and groundwater reservoirs.
Heavily instrumented and intensively studied sites, such as Critical Zone Observatories (CZOs), which are part of a network of field-based laboratories arrayed across a variety of rock types, land uses, elevations and climates (Anderson et al., 2008), are ideal locations to examine the interplay between subsurface structure and function.

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Moreover, recent focus on characterizing the deep subsurface architecture is beginning to elicit a deeper understanding of the role of weathering, lithology, and hydrology in overall CZ function and landscape evolution (Riebe et al. 2017).
The critical zone (CZ) is the near-surface terrestrial layer of the Earth that spans from the tops of trees down to unweathered bedrock where water, rock, air, and life meet and interact (Brantley et al., 2006(Brantley et al., , 2007;;Anderson et al., 2007;Chorover et al., 2007;Kusel et al., 2016).Understanding the coupling between CZ architecture, developed over 65 geologic time scales, and CZ function on short event time scales is a primary goal of CZ science (Chorover et al., 2011;Brooks et al., 2015).In particular, there is limited knowledge about the structure of the deep CZ and its direct influence on water storage (Holbrook et al., 2014;Dralle et al., 2018) and routing, mean residence times (McGuire et al., 2005), and streamflow sources.Furthermore, Wlostowski (In Review) notes in a cross-CZO study that the lack of subsurface characterization hinders our ability to relate catchment structure and hydrologic behavior in meaningful 70 ways.Integrated studies that simultaneously examine both, CZ architecture and CZ hydrology, through hydrometric, geophysical, geochemical, and residence time analyses are needed to understand the distribution of groundwater stores, their connection to streamflow, and the underlying impact of CZ architecture on hydrologic response to climatic drivers.
A current focus of hydrology is quantifying and predicting groundwater storage (Holbrook et  and geophysics is an important tool for examining CZ architecture and its influence on water storage and movement. For example, McGuffy (2017) used seismic refraction surveys to estimate porosity and found that initial porosity plays a significant role in bedrock weathering in granitic and rhyolitic tuff CZs.Flinchum et al. (2018) took those porosity calculations a step further in using geophysics to estimate the water holding capacity of another granitic CZ; however, 80 both studies noted the strong influence of, and uncertainty associated with degree of saturation of the media.Rempe and Dietrich (2018) used downhole surveys with a neutron probe to estimate rock moisture in the CZ and Dralle et al.
(2018) used geophysics-based storage estimates from Rempe (2016) and Rempe and Dietrich (2018) to suggest differences in direct and indirect storage within the CZ from a coupled mass balance and storage-discharge function.
The complexity of these estimates and their interactions highlights the need to couple geophysical approaches with 85 subsurface interrogation, such as drilling and field characterization of hydraulic properties, to resolve this complexity, particularly in fractured heterogeneous environments.
In a headwater catchment and nested zero order basin (ZOB) within the complex volcanic Jemez River Basin Critical Zone Observatory (JRB-CZO), a considerable amount of research has been done to characterize the hydrology of the system.For instance, previous studies have explored energy limitations and topographic controls on hydrologic ).However, seasonal groundwater changes have not been previously observed here and the interaction of different stores of water within the subsurface and the timing of their connection to streamflow are not understood.

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This gap motivated the current study, which sought to relate groundwater response, geochemistry, and age tracers across a full water year to the characterization of subsurface structure, mineralogy, and hydraulic properties.We hypothesized that there will be a more dramatic hydrologic response of shallow groundwater to spring snowmelt and a more gradual, small change after summer monsoon events.This study also aimed to elucidate how multiple groundwater stores within the CZ contribute to streamflow during different seasonal hydrologic flow regimes.

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Most upland catchment studies to date have used springs as proxies for groundwater in the JRB-CZO; however, recent work by Frisbee et al. (2013) showed that while groundwater is a significant component of most springs, no springs are consistently composed entirely of groundwater.With the recent drilling of a set of nested monitoring wells in a headwater catchment at the JRB-CZO (Figure 1B), we can now directly access groundwater from several depths within the CZ (Figure 2).This enabled the geochemical and isotopic analysis of groundwater and surface water from To address these questions, we integrated several types of analyses including hydrometric, geophysical, geochemical, isotopic, and residence time tracers to examine the hydrologic response of ground and surface water and understand the connection between distinct groundwater stores and streamflow.We compared the timing of streamflow and groundwater response to climatic drivers, quantified temporal changes in subsurface water storage, defined distinct groundwater stores, inferred recharge processes from stable water isotopes and age tracers, and 125 examine how local flow processes relate to larger scale patterns.

Site description 130
The Jemez River Basin Critical Zone Observatory (JRB-CZO) within the Valles Caldera National Preserve is situated in the Jemez Mountains in northern New Mexico northwest of Albuquerque (Figure 1A).This region is located in the transition zone between the snow dominated Rocky Mountains and the North American Monsoon (NAM) dominated deserts of the southwestern United States (Broxton et al., 2009).The JRB-CZO is in a montane, continental, sub-humid to semiarid climate characterized by a bimodal precipitation pattern (Zapata-Rios et al.,

2015b
).The VCNP is in a 21 km wide caldera that formed approximately 1.25 Myr (Bailey et al., 1969;Self et al., 1986).Ongoing volcanic activity as recent as 40 kyr caused the uplift of several resurgent domes throughout the caldera (Wolff et al., 2011) of which Redondo Peak (3,432 meters above sea level, masl) is the largest.The JRB-CZO comprises several headwater catchments that drain different aspects of Redondo Peak.The geology of Redondo Peak is characterized by several faults and is dominated by Pleistocene aged Bandelier Tuff, rhyolite, and andesitic rocks 140 (Broxton et al., 2009;Vazquez-Ortega et al., 2015) that were intermixed by collapse breccias in some locations (Hulen and Nielson, 1991), which created highly heterogeneous and complex geology (Figure 1B).La Jara catchment and the Mixed Conifer Zero Order Basin (referred to as ZOB from here on), which is nested within the headwaters of La Jara, drain the eastern side of Redondo Peak (Figure 1B).La Jara catchment ranges in elevation from 2,702 to 3,429 masl with a mean slope of 15.7 o and drains an area of 2.66 km 2 (Perdrial et al., 2014).

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The ZOB consists of SE-and SW-facing slopes that are separated by a convergent zone and drains 0.15 km 2 (Vazquez-

Groundwater well completions
Nested groundwater monitoring wells were drilled to total depths ranging from 6.7 to 47.2 meters below ground surface (mbgs) at each of three locations within the ZOB in June 2016 (Figure 1B and Figure 2).At each location, wells are separated by no more than 2 m from the next well so that the well casings stand in a line.A LiBr tracer was 165 mixed with fluids injected during the drilling and well development process.Br -concentrations were measured in initial samples to ensure that drilling fluids were flushed from monitoring wells prior to analysis of groundwater samples.All screened sections of the well casing have 0.051 cm slotted intervals.All wells were drilled to depth with a diamond impregnated TT coring drill bit at an HQ3 diameter (9.6 cm annulus diameter; Supplemental Table 1).The annuli of all wells were packed with 8-12 CSS sand surrounding screened intervals and the sand packs were sealed 170 with hydrated bentonite pellets.

Water Quality and Age Tracers
Differences in well casing diameter, depth of water column, sampling frequency, and seasonal site accessibility 175 necessitated different sampling collection among wells.Groundwater samples were collected from site 1 wells using a Waterra inertial pump (Waterra USA Inc., Peshatin, WA, USA).Groundwater samples from site 2 wells were collected with a Geotech SS Geosub Pump (Geotech Environmental Equipment, Inc., Denver, CO, USA) except during times when snow accumulated leaving the site inaccessible by vehicle during which times samples were collected with a 42.1 mm stainless-steel bailer (Geotech Environmental Equipment, Inc., Denver, CO, USA).

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Approximately three borehole volumes were discarded before collecting samples from each well to ensure that formation water was retrieved.Surface water samples of La Jara and ZOB stream water were collected at flume sites as grab samples.
Groundwater and surface water samples were collected in acid washed polypropylene bottles (for cation and trace element analysis) and DI-washed, combusted amber glass bottles (for anion, carbon content, and stable water isotope 185 analysis).Bottles were triple rinsed with sample water prior to sample collection and samples were kept cold until promptly filtered at the University of Arizona.Sample splits for cations and trace elements were filtered through 0.45 m nylon filters and acidified with trace metal grade nitric acid while all other splits were filtered through 0.7 m glass fiber filters.Surface water samples were collected biweekly during dry seasons and twice daily at highest and lowest daily discharge using an automatic sampler (Teledyne, ISCO, NE, USA) during spring 2017 snowmelt.

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Groundwater samples were collected from all wells producing water on a biweekly basis during dry seasons and daily from the shallowest well (Well 2D; total depth 6.7 mbgs) during spring snowmelt using an autosampler (Teledyne ISCO, NE, USA).
All water samples were analyzed for anions (not shown here), cations, dissolved inorganic carbon (DIC), dissolved organic carbon (DOC, not shown here), and stable water isotopes.Cations were measured by inductively Tritium analysis was completed at the University of Arizona Environmental Isotope Laboratory on select groundwater and surface water samples filtered through 0.45 m nylon filters.Mean residence time (t) was calculated using the two most common lumped parameter models, the piston flow and exponential models, according to Eq. 1 and 2, respectively (Zuber and Maloszewski, 2000;Manga, 2001;Suckow, 2014;Zapata-Rios et al., 2015b) 205 where C is the measured tritium concentration (reported as tritium units, TU) in groundwater, C0 is the measured TU in local precipitation, and λ is the tritium decay constant (5.576 x 10 -2 year -1 ) based on a tritium half-life of 12.43 yr.220 where t is the uncertainty of the age calculation, Co is the uncertainty of the background tritium concentration, and C is the uncertainty in the measurement of tritium in samples in this study.
Groundwater samples from wells 2D and 2C were collected with Hydrasleeve TM (GeoInsight, Las Cruces, NM,

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USA) passive collector bags in February 2018 for 14 C analysis.Self-sealing bags were deployed in the wells and left to equilibrate for 24 h before sample retrieval.Radiocarbon analysis was completed at the University of Arizona Accelerator Mass Spectrometry (AMS) Laboratory on DIC in groundwater samples.Measured 14 C activities are expressed as percent modern Carbon (pmC) that were calculated as weighted averages of combined machine runs to reduce overall error and  13 CDIC measured values are expressed as permil.

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Uncorrected radiocarbon ages were computed following Eq. 4 for radioactive decay using a 14 C half-life of 5730 years and an initial 14 C activity (A0) of 100 pmC, according to data from the neighboring Española Basin bound to the west by the Jemez Mountains (Manning, 2009).In order to calculate corrected radiocarbon ages, the  13 CDIC value of of -24.7 ‰ (unpublished data from Tjasa Kanduc) using equilibrium constants of the carbonate system (Drever, 1997), alpha values between CO2(g) and CO2(aq) according to Vogel et al. (1970), and alpha values between HCO3 -and CO2(aq) and between HCO3 -and CO3 2-according to Mook et al. (1974).
Corrected ages were calculated using the  13 C mixing model of equations 5 and 6 following Pearson (1965), Pearson and Hanshaw (1970), and Clark and Fritz (1997) using an assumed  13 CDIC of calcite of 0 ‰, a calculated value of  13 CDIC value of the recharge water, and A0 of 100 pmC. 245 13   −  13    13  ℎ − 13    13 C Fraction from Carbonate Dissolution (5)

Streamflow and Groundwater Depths
Streamflow measurements were recorded at 15 min intervals from pressure transducers inside the stilling well of a Parshall flume at the base of the ZOB at 2996 masl and La Jara catchment at 2739 masl (flume locations shown in Figure 1B).Transducer data were calibrated by depth measurements taken by hand at the time of each sampling event.

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All monitoring wells were installed with vibrating wire piezometers (VWP) during the drilling campaign to provide nearly continuous (15 min) measurements of hydraulic head in each well.However, several piezometers failed and were replaced with Level Troll 500 (In-Situ Inc., Fort Collins, CO, USA) series pressure transducers (Site 1) and Rugged Troll 200 (In-Situ Inc., Fort Collins, CO, USA) series pressure transducers (Site 2) in October 2017 (Supplemental Table 1).In this study, time series of groundwater depths are only shown from two wells (Well 1A and 260 Well 2D) with continuous monitoring via VWPs.Electronic sounder measurements of depth to water were taken before every groundwater sampling event, converted into depth of water column above VWP, and used to calibrate VWP and transducer measurements.

Saturated hydraulic conductivity estimates 265
Nearly continuous monitoring of hydraulic head in groundwater wells enabled individual sampling events to be treated as rising-head bail-down slug tests (Butler, 2015).Aqtesolv software (Duffield, 2007) was used to curve fit aquifer response (VWP measurements of depth of water converted into normalized change in water table height against the logarithm of elapsed time) using the Kansas Geological Survey (KGS) model (Hyder et al., 1994)

Volumetric water content in soil pedons
Decagon EC-5 soil moisture sensors measured volumetric water content (VWC) in 6 instrumented soil pedons 280 within the ZOB (Figure 4) ranging from depths of 9.5 to 65 cm below ground surface (cm bgs).VWC was measured at multiple depths in four of the six pedons.VWC was recorded every 10 min.

Downhole neutron probe surveys 285
Water content profiles with depth were determined from neutron probe (Model 503DR, Campbell Pacific Nuclear, Concord, CA, USA) surveys within the vadose zone in the top 18.3 mbgs in wells 2B and 2C and the total depth of well 3B (12.9 mbgs) over four different events.Raw neutron counts were recorded by the detector using a 32 second interval.Measurements were recorded every 0.3 m and a minimum of three readings were taken at each depth.
Standard counts were measured in an acrylic sleeve before and after measurements of each well and were used to

Hydrologic response 320
Temporal analysis of the climatic parameters (daily precipitation and temperature, Figure 3A, and snow water equivalent (SWE), Figure 3B) that drive streamflow response in ZOB and La Jara surface waters (Figure 3C and While streamflow peaks were greatest in response to spring snowmelt, there were also obvious, smaller peaks in ZOB and La Jara surface waters following summer monsoons and fall storms.For example, ZOB streamflow 335 peaked at 0.00194 m 3 s -1 on 7/31/17, 0.00194 m 3 s -1 on 8/4/17, and 0.00245 m 3 s -1 on 9/30/17 while La Jara streamflow peaked several times, most notably at 0.116 m 3 s -1 on 7/31/17, 0.0926 m 3 s -1 on 9/27/17, and 0.0890 m 3 s -1 on 9/30/17.Both snowmelt and rainfall events influenced La Jara creek and ZOB streamflow leading to increases above baseflow (Figure 3C and D, respectively).However, the major driver of streamflow and groundwater depth response was spring snowmelt.

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The depth of water in wells 1A and 2D (Figure 3D 4).VWC changes across the water year at the shallowest depth in pedons 4 and 3, located in the western area of the ZOB nearest site 2 wells, were small (0.20 m 3 m -3 range in pedon 360 4 and 0.16 m 3 m -3 range in pedon 3), while VWC at greater depth in pedon 3 increased drastically and remained elevated during spring snowmelt (peaked at 0.4175 m 3 m -3 and 0.4186 m 3 m -3 for 65 and 30 cm bgs, respectively) and fall storms (peaked at 0.4116 m 3 m -3 and 0.3109 m 3 m -3 for 65 cm and 30 cm bgs, respectively).Changes in VWC at pedons 5 and 2, located in the convergent zone of the ZOB nearest site 3 wells, were most pronounced during spring snowmelt.Again, increased VWC in pedon 2 persisted longer at depth than at the near surface.In 365 contrast, soils in the eastern area of the ZOB near site 1 wells at pedons 6 and 1 did not remain wet for extended periods, but rather increases in VWC of pedons 6 and 1 were flashy while decreased VWC during NAM season was sustained.
Estimates of saturated hydraulic conductivity of wells 1A and 2D were computed to explore differences in hydrologic properties of the two aquifers following three sampling events that served as bail-down slug out tests.

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Averaging Ksat from the three events produced a mean for well 2D of 7.22 x 10 -3 m day -1 and 1.22 x 10 -4 m day -1 for well 1A (Table 1), despite fracture density of deeper site 2 wells estimated to be approximately five times less than fracture density of site 1 wells (Figure 5).However, it is important to note that fracture density could not be calculated across the water table depths of well 2D or site 1 wells because of surface instability and presence of water inhibiting downhole televiewer images.Profiles of water content with depth below ground surface in borehole 2B (Figure 6, left), reach a local maximum water content of approximately 0.32 cm 3 cm -3 at 1 mbgs during all events.At increased depth, the water 385 content recedes to an overall minimum of 0.15 cm 3 cm -3 at 2.4 mbgs in the June, August, and February measurements while the October measurement recedes to only 0.23 cm 3 cm -3 at 1.8 mbgs before spiking to 0.36 cm 3 cm -3 at 2.4 mbgs and receding slightly to 0.35 cm 3 cm -3 at 4 mbgs below which depth changes in water content are consistent across all time series.
In borehole 2C (Figure 6, center), just 2 m away from borehole 2B, differences in water content profiles are also 390 seen over time.In October, water content increases from the surface until reaching an overall maximum of 0.4 cm 3 cm -3 at 3.7 mbgs whereas profiles from the other three events peak at 0.29 cm 3 cm -3 at only 0.6 mbgs, recede to 0.08 cm 3 cm -3 at 1.2 mbgs and increase gradually to 0.12 cm 3 cm -3 at 3.4 mbgs and drastically jump up to a range of water content from 0.34 to 0.39 cm 3 cm -3 (July to Feb, respectively) at 4 mbgs.From 4 to 15.5 mbgs, the water content profiles for all events are relatively consistent between 0.28 cm 3 cm -3 and 0.30 cm 3 cm -3 (June and August 395 identical, October 0.1 greater than summer profiles, and Feb 0.1 greater than October).
Finally, water content profiles with depth in borehole 3B (Figure 6, right) are nearly identical across all measurement events and show three peaks in water content of 0.36 cm 3 cm -3 , 0.33 cm 3 cm -3 , and 0.25 cm 3 cm -3 at 1.2, 8.5, and 11.6 mbgs, respectively.400

Contribution of distinct groundwater stores to streamflow
In a volcanic setting such as the Valles Caldera, silicate mineral weathering is the primary driver of stream water The primary groundwater cations from each monitoring well are Ca 2+ , Na + , and Mg 2+ (Table 2); however, the percentages (in terms of µeq/L) of each cation differ between sites (Sites 1 and 2).Major ion concentrations also differ with depth between site 2 wells while site 1 groundwaters (Wells 1A and 1B) are geochemically similar to one another 420 (Supplemental Fig. 1).These differences in cation concentration are used in further analysis to distinguish streamflow sources.
Temporal analysis of major cation concentrations in groundwater and surface water over WY 2017 (Figure 7) again shows clear separation of groundwater concentrations between the two sites.Ca 2+ and DIC concentrations are highest in the perched aquifer (Well 2D), where calcite is known to be present, and all site 2 groundwater Ca 2+ and

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DIC concentrations are considerably greater than surface and site 1 waters year-round (Figure 7).Furthermore, Ca 2+   and DIC concentrations are most variable in wells 2D and 2C, which change together in time, suggesting a connection between the two water stores.Finally, both Ca 2+ and DIC concentrations of shallow groundwater increase simultaneously, which is consistent with calcite dissolution, at the time that La Jara streamflow increases above baseflow during snowmelt.In contrast, Ca 2+ and DIC concentrations of La Jara surface waters do not change 430 markedly as streamflow increases while Ca 2+ and DIC concentrations of ZOB surface waters decrease slightly during this time.Mg 2+ concentrations are greatest in the deepest well (Well 2A) and decrease with decreasing depth at site 2, are lower still in site 1 groundwater, and lowest in La Jara stream water (Table 2).Na + concentrations of the perched aquifer increase steadily at the onset of snowmelt while La Jara and ZOB surface water Na + concentrations decrease slightly (Figure 7).Unfortunately, the lack of site 1 groundwater data during snowmelt 435 makes it impossible to determine if the variability of site 1 groundwater chemistry resembles that of surface waters; however, surface water concentrations of major ions are generally closer in magnitude to those of site 1 groundwaters throughout the remainder of the water year.
Comparison of Ca 2+ /Mg 2+ molar ratios with Na + concentrations (Figure 8A) and DIC concentrations (Figure 8B), which can differentiate between weathering of Ca 2+ rich and Mg 2+ rich silicate minerals, also show distinct 440 groupings of groundwater between sites and depths.The Ca 2+ /Mg 2+ molar ratios of the perched aquifer are greater than those of the deeper waters.The Ca 2+ /Mg 2+ molar ratios of surface waters overlap in space with those of deeper groundwater.The DIC concentrations clearly differentiate between sites 1 and 2 and the surface waters plot with similar DIC concentrations as site 1 groundwater, which indicates that deeper groundwater from site 1 is more representative of streamflow in La Jara catchment.

Mix of old and young snowmelt dominated waters
Stable water isotopes of groundwaters and surface waters plot together in space and plot closer to the lower isotope values of snow than to those of summer precipitation (Figure 9) indicating that snowmelt is the dominant  and 2C (Table 3).As expected, there is more tritium present in the shallowest groundwater compared to deeper waters from site 2 wells; however, the deepest site 2 groundwater from well 2A has more tritium than the shallower wells 2B and 2C.Differences in tritium content (Table 3) across similar depths from sites 1 and 2 (Figure 2) indicate the 465 presence of separate groundwater stores of water within the ZOB.
Radiocarbon age calculations were computed for the shallowest groundwater of the perched aquifer from well 2D and groundwater beneath the perched aquifer from well 2C based on 14 C activity and  13 C of DIC of the two wells.
The 14 C activity of DIC from well 2D was 75.34 ± 0.19 pmC while the  13 CDIC was -13.1 ‰, which corresponds to a corrected radiocarbon age of 621 years.The 14 C activity of DIC from well 2C was 60.02 ± 0.17 pmC and the  13 CDIC 470 was -12.4 ‰, which corresponds to a corrected radiocarbon age of 2050 years (Table 3).As expected, there is less modern 14 C-DIC in the deeper groundwater (Well 2C) indicating longer residence times at greater depth.

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This study seeks to understand the seasonal hydrologic response of groundwater as a function of depth below ground surface at sites 1 and 2 and to explore how CZ architecture influences seasonal groundwater contribution to streamflow in La Jara catchment.Contrasting CZ architecture and lithology in sites 1 and 2, along with time series of shallow and deep groundwater from both sites and surface water from the catchment outlet, enable us to decipher 480 geochemical signatures of deep groundwater from a highly fractured aquifer and shallow groundwater from a perched aquifer.The following sections discuss the dynamics of seasonal hydrologic response, water routing, recharge and water residence times, major ion chemistry, and CZ architecture to investigate streamflow contributions over time.

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Site 1 wells are situated in highly fractured welded tuff with maximum fracture density of approximately 5000 m -2 .This contrasts with highly weathered volcanic breccia in the top 15 mbgs at site 2 wells that corresponds with a caldera collapse breccia deposit overlying more consolidated, less fractured welded tuff with maximum fracture density of approximately 1000 m -2 at depth (Figure 5).We hypothesize that the differences in subsurface structure,

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presence of a confining layer, and greater fracture density of site 1 wells compared to site 2 wells (Figure 5) influences the different hydrologic response of the two sites (Figure 3).Well 1A responds rapidly to snowmelt, reaching its first peak on the same day as La Jara streamflow's first peak, and responds gradually to summer monsoon events.Well 2D has a muted response to snowmelt with the first inflection point occurring on the same day as the first ZOB discharge peak while the first well 2D water table maximum occurs 45 days after the onset of 495 snowmelt and does not respond to summer monsoon events at all.
Mean Ksat values from both wells are lower than Ksat estimates of the same Tshirege member of Bandelier Tuff from nearby Los Alamos National Lab that range from 7.6 x 10 -2 to 1.12 m day -1 (Rogers and Gallaher, 1995; Smyth and Sharp, 2006) and 9.3 x 10 -1 to 1.6 x 10 1 m day -1 (Kearl et al., 1990;Smyth and Sharp, 2006).This may be, in part, because slug tests provide localized estimates of the hydraulic conductivity directly surrounding the screened interval 500 of the well in contrast to pumping tests that provide larger scale volumetric averages of hydraulic properties.Butler (2015) notes that hydraulic conductivity estimates from slug tests should be viewed as lower bounds of the conductivity in the vicinity of the well.Furthermore, the degree of welding and presence of alteration may account for the discrepancies in conductivity estimates as Rogers and Gallaher (1995) noted that the degree of welding of the Bandelier Tuff was greatest closer to the Valles Caldera, the tuff's volcanic source and site of this study.

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Surprisingly, the mean Ksat of the perched aquifer (Well 2D) is more than one order of magnitude greater than that of the deep well 1A (7.22 x 10 -3 m day -1 and 1.22 x 10 -4 m day -1 , respectively, Table 1).Many more fractures are present at site 1 relative to site 2 (Figure 5A), which generates a fracture density approximately 5 times greater at site 1 wells than site 2 wells (Figure 5B).Unfortunately, it is not possible to directly compare the fracture density across the screened intervals from which hydraulic conductivity estimates were made because downhole images 510 could not be captured within either well at those depths, but we expect that the general trend of dense fractures at site 1 and few fractures at site 2 would persist.The lower mean Ksat of well 1A could suggest that fractures may be backfilled by mineral precipitates and weathering rinds decreasing the ability of fractures to act as preferential flowpaths.It is noteworthy, however, that such a mechanism is not clearly supported by the downhole images or core samples; these images and cores do not show obvious evidence of backfilled fractures.

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Despite unexpected Ksat differences between the two wells, the very similar shape and timing of well 1A's hydrograph compared to those of La Jara stream and ZOB surface water (Figure 3) is a function of pressure propagation and indicates hydraulic connection between the fractured aquifer and streamflow and (Sophocleous, 1991a;Welch et al., 2013).The rapid pressure pulse transfer between site 1 groundwater and the stream suggests that the fractured welded tuff aquifer has low specific storage and high transmissivity.Worthington (2015) noted 520 much more rapid changes in head in low storage fractured bedrock aquifers compared to granular aquifers and Sophocleous (1991a) found that the hydraulic diffusivity is the major control of the extent and speed of pressure pulse propagation.
The rapid response of the welded tuff aquifer (Well 1A) contrasts with the muted response of the perched aquifer (Well 2D), which does not show evidence of pressure pulse propagation between shallow groundwater and 525 the ZOB and La Jara surface waters.The slower response of groundwater levels in well 2D suggests that the perched aquifer is not directly hydraulically connected to the stream likely because of the confining layer separating it from deeper groundwater and the significantly lower fracture density of site 2 wells (Figure 5).The comparison of site 1 and 2 groundwater hydrographs to surface water hydrographs bears a striking resemblance to the juxtaposition of stream-flood wave propagation in monitoring wells drilled into buried river channels (similar to well 1A) and the 530 absence of pressure pulses in monitoring wells not associated with buried channels (similar to well 2D) seen in the Great Bend alluvial aquifer in Kansas (Sophocleous, 1991a).Furthermore, the cubic shape of the rising water table in the perched aquifer, as well as the rapid rise after inflection point in well 2D is indicative of groundwater recharge (Sophocleous, 1988(Sophocleous, , 1991a(Sophocleous, , 1991b)).Further analysis of the rates of increase before and after the well 2D hydrograph

545
The less pronounced hydrologic response to summer monsoons, compared to snowmelt and fall rain, in shallow groundwater of site 2 and deeper groundwater at site 1 is likely a function of drier antecedent soil moisture conditions at the onset of the NAM season, as indicated by decreased VWC in shallow soils from 6 instrumented pedons in the ZOB immediately before monsoon storms began compared to wetter soils during spring snowmelt and fall storms (Figure 4).This agrees with previous studies in the VCNP, which found that soil moisture was lowest in 550 early summer after soil moisture from snowmelt had receded and it increased after the arrival of monsoon storms (Vivoni et al., 2008;Molotch et al., 2009).Furthermore, Zapata-Rios et al. (2015a) found that NDVI in the VCNP increased during the NAM season suggesting that precipitation was partitioned to plant use during monsoon rains and was not available to recharge groundwater stores.Furthermore, smaller, sporadic precipitation during summer monsoon storms and increased evapotranspiration due to higher temperatures (Figure 3A) and increased plant use 555 create a wetting and drying effect in shallow soils that can be seen as small fluctuations in VWC (Figure 4).This  Neutron probe surveys show small shifts in water content with depth that are likely associated with small scale heterogeneities in bulk density created by the lithologic discontinuities in volcanic collapse breccia deposits, variable degrees of ash consolidation, welding, and secondary mineral precipitation, which are evident in

585
surveys in weathered argillite were strongly linked to changes in material properties with depth, which suggested different flow processes through the unsaturated zone.Here, lenses of increased water content (like that from 9 to 11 mbgs in well 2B) above layers of relatively lower water content (like that of 12 to 13.5 mbgs in well 2B) are indicative of subsurface lateral flow through more saturated, more conductive media that can be seen in Figure 6.
Evidence of vertical infiltration is also seen in the site 2 wells.The marked change in shape (increased water 590 content from 1 to 4 mbgs) of the October water content profile suggests vertical infiltration and subsequent recharge to the perched aquifer.Analysis of well 2D hydrograph (Figure 3F) confirms that this October neutron probe survey was completed while the perched aquifer water table was rising.Despite similar perched aquifer water table depths for all four surveys (2.7 mbgs on 6/27/17, 2.9 mbgs on 8/15/17, 2.9 mbgs on 10/12/17, and 3.2 mbgs on 2/6/18), the October survey was the only survey that corresponds with a rising rather than receding water table (Figure 3F) and is

595
the only water content profile that captured vertical infiltration of recharge to the perched aquifer.Furthermore, the wet October profile returns to dry conditions within the top 4 m in February and February water content beneath 4 m exceeds that of previous surveys, which suggests that water drains vertically at depths greater than 4 mbgs in February.that site 3 wells were drilled immediately next to (possibly within) the fault zone, which coincides with the convergent outlet of the ZOB (Figure 1).This is likely why site 3 wells did not produce water in the time period of this study (Figure 2).Furthermore, water content is nearly identical across all four measurement events in borehole 3B (Figure 6).Despite being located in a convergent zone subjected to seasonal wetland saturated conditions at the land surface, neutron probe surveys do not indicate that water infiltrates vertically in site 3. Rather, data suggest that 605 water moves laterally in the subsurface as indicated by the three lenses of increased water content seen in Figure 6.

615
of shallow groundwater (Well 2D).However, surface water concentrations of other major ions (Ca 2+ , Na + , Mg 2+ , Mn, and SO4 2-) did not coincidentally rise despite higher shallow groundwater concentrations of those ions compared to Si, which suggests, instead, a deeper source of groundwater to La Jara streams.Herein, we present further evidence that the deep groundwater source to La Jara and ZOB surface water is the deep welded tuff aquifer found throughout the greater La Jara catchment and represented at site 1 wells.

620
High Ca 2+ /Mg 2+ molar ratios of shallow groundwater from the perched aquifer (Well 2D) are a function of calcite dissolution, which is only present in the shallow subsurface at site 2 and leads to increased Ca 2+ concentrations but does not impact Mg 2+ concentrations.The clear separation of Ca 2+ /Mg 2+ molar ratios in shallow (Well 2D) and deep groundwater (Wells 1A, 1B, 2A, 2B, and 2C) and the overlap of surface water Ca 2+ /Mg 2+ molar ratios with those of deeper groundwater suggests that the perched aquifer does not contribute substantial volumes to surface flow, but 625 instead deep groundwater is the dominant source of streamflow.
The dissolution of calcite in the perched aquifer also leads to higher DIC concentrations in waters in the ZOB (Table 2; Appelo and Postma, 2005).Higher DIC concentrations in all site 2 waters is consistent with vertical connection between site 2 wells that, in turn, suggests the confining layer beneath the perched aquifer acts as more of an aquitard than aquiclude.The Ca 2+ /Mg 2+ molar ratios and DIC concentrations of surface waters are very similar to 630 those of site 1 groundwaters, which again indicates that deep groundwater from site 1 wells is more representative of groundwaters that contribute to La Jara stream.The welded tuff rock type (Figure 1) of site 1 wells is also more representative of the geology, by volume, throughout the greater La Jara catchment.
Temporal analysis of major ion chemistry indicates that deep groundwater from fractured tuff (Site 1) sustains stream baseflow as streamflow concentrations and trends in concentrations over time are consistent with site 1 635 groundwater concentrations.In contrast, pronounced changes in shallow site 2 groundwater (Wells 2D and 2C) major In summary, we propose a schematic model (Figure 10) to conceptualize the details of hydrologic structure and hydrologic function at two contrasting hillslopes within the ZOB (Sites 1 and 2).Site 2 has multiple, separate stores of groundwater across depth that are distinct from each other and distinct from deep groundwater stores at site 1.All groundwater is recharged via snowmelt and seasonal differences in hydrologic response to precipitation inputs exist 645 at both sites with less pronounced response to summer monsoons at both sites linked to drier antecedent shallow soil moisture at the onset of NAM season.There is evidence of vertical infiltration and subsurface lateral flow at site 2 and a mix of young and older waters, which are expected to persist across all groundwater stores.The fracture density at site 1 is approximately 5 times greater than at site 2 and the CZ structure and architecture of site 1 is most representative of the greater La Jara catchment.Deep groundwater from the fractured aquifer at site 1 is 650 hydrologically connected to streamflow and site 1 deep groundwater chemistry is most representative of water contributing to streamflow while the distinct chemical signature of shallow groundwater from site 2 is not seen in streamflow.

Mix of old and young snowmelt dominated waters 655
The grouping of most stable water isotopes in Figure 9 indicates that snowmelt is the dominant source of recharge to all groundwater stores in this study as the stable water isotope signatures of surface and groundwater plot much closer to the volume weighted mean (VWM) of snow (Gustafson, 2008) 10).However, radiocarbon analysis of wells 2D and 2C also indicates the presence of much older waters (corrected ages of 621 and 2050, respectively) in these shallow aquifers (Figure 10).The detection of tritium and less than 100 pmC in these 665 wells suggests a mixture of old and young waters (Bethke and Johnson, 2008;Jasechko et al., 2017); that is expected to persist in each groundwater store.
Decreasing tritium content with depth from 2D to 2C to 2B (Table 3) agrees with previous studies that have suggested residence times increase with depth (Zapata-Rios et al., 2015b).This trend along with the distinct Ca 2+ /Mg 2+ molar ratios and DIC concentrations from the presence of shallow calcite deposits in site 2 wells is consistent with a 670 vertical connection between the three shallowest site 2 wells.However, increased tritium content in well 2A (closer to that of site 1 than other site 2 wells) suggests that 2A is not vertically connected to the above site 2 wells and, instead, is likely laterally connected to younger waters upgradient.

90
partitioning and water transit times(Zapata-Rios et al., 2015a, 2015b).Other studies used carbon pool and rare earth elements and ytrrium (REY) as biogeochemical tracers of streamflow generation(Perdrial et al., 2014; Vazquez-  Ortega et al., 2015, 2016) and estimated groundwater contributions using end member mixing analyses(Liu et al., 2008a(Liu et al., , 2008b)).The most recent JRB-CZO studies explored concentration-discharge relationships to study seasonal shifts of hydrologic flow paths (McIntosh et al., 2017) and identify the hydrochemical processes governing the 95 transport behavior of five distinct groups of solutes (Olshansky et al., 2018).Furthermore, studies agree that there is little overland flow contribution to streamflow in headwater catchments (Liu et al., 2008b; Perdrial et al., 2014; Zapata-Rios et al., 2015a) and subsurface flow is the primary contributor to streamflow (Liu et al., 2008a, 2008b; Perdrial et al., 2014; Vazquez-Ortega et al., 2015; Zapata-Rios et al., 2015a; McIntosh et al., 2017; Olshansky et al., 2018; Wlostowski et al., In Review). 100 Studies spanning several water years have shown that spring snowmelt and summer monsoons induce different surface water flow regimes.More specifically, groundwater recharge appears to be restricted to winter snowmelt (McIntosh et al., 2017) and large evaporative fluxes diminish streamflow in summer months (Zapata-Rios et al., 2015a 115 the JRB-CZO to answer the following research questions: 1) What is the seasonal hydrologic response of groundwater as a function of depth below ground surface in two hillslopes with contrasting lithology and CZ architecture?2) How does CZ architecture, such as fracture density, lithology, and mineralogy control seasonal groundwater contribution to streams? 120 Hydrol.Earth Syst.Sci.Discuss., https://doi.org/10.5194/hess-2019-140Manuscript under review for journal Hydrol.Earth Syst.Sci. Discussion started: 24 April 2019 c Author(s) 2019.CC BY 4.0 License. 160 195 coupled plasma mass spectrometry (ICP-MS) at the University of Arizona Laboratory for Emerging Contaminants Hydrol.Earth Syst.Sci.Discuss., https://doi.org/10.5194/hess-2019-140Manuscript under review for journal Hydrol.Earth Syst.Sci. Discussion started: 24 April 2019 c Author(s) 2019.CC BY 4.0 License.(ALEC).Dissolved inorganic carbon was measured with a Shimadzu TOC-VCSH carbon analyzer in ALEC.Stable water isotopes ( 18 O and  2 H) were measured with a DLT-100 Laser Spectrometer at the University of Arizona.Analytical precision (1) for all samples was 0.4 permil for  2 H and 0.1 permil for  18 O.Stable isotope data from several previous studies at the JRB-CZO and surrounding locations were also incorporated (Vuataz and Goff, 1986; 200 Longmire et al., 2007; Gustafson, 2008; Broxton et al., 2009; Zapata-Rios et al., 2015b).

210
Tritium analysis of precipitation in Albuquerque, NM (70 km from the study site) was measured monthly from 1962 to 2005 and are available as part of the Global Network of Isotopes in Precipitation (GNIP) through their Water Isotope System for data analysis, visualization, and Electronic Retrieval (WISER) database.Eastoe et al. (2012) found that volume weighted mean (VWM) tritium concentrations in Albuquerque precipitation have remained stable since the early 1990s and are similar to local prebomb atmospheric tritium concentrations.Zapata-Rios et al. (2015b) used SWE 215 data from the previously described Quemazon station to calculate a VWM of background tritium (8.6 TU from 1992 to 2005) that is used as C0 in mean residence time calculations herein.The uncertainty of age calculations was computed according to Eq. 3 following Bevington and Robinson (1992), Scanlon (2000), and Zapata-Rios et al. (2015b) Hydrol.Earth Syst.Sci.Discuss., https://doi.org/10.5194/hess-2019-140Manuscript under review for journal Hydrol.Earth Syst.Sci. Discussion started: 24 April 2019 c Author(s) 2019.CC BY 4.0 License. the recharge water (-16.13‰) was first calculated based on an assumed temperature of recharge of 9.6 o C (the average temperature of soil water from the ZOB over the last year of consecutive measurements, 2011), pH of 7.51 (the average 235 pH of soil water from the ZOB over the last year of consecutive measurements, 2011), and a  13 CCO2 of ZOB vegetation of the polyline fracture traces without the underlying downhole image was used as the input file for FracPaQ (Healy et al., 2017), which extracted the x and y fracture-trace coordinates from the file.Fracture density is defined as the number of fractures per unit area and has the units of m -2 (Dershowitz and Herda, 1992).FracPaQ (Healy et al., 2017) calculates fracture density from the fracture segment network as m/2r 2 according to Mauldon et al. (2001) where m is the number of trace endpoints in circle of radius r by resampling the exposed traces using circular scan windows 315 that eliminate orientation, censoring, and length biases.

Figure
Figure3D, respectively) and groundwater from the fractured tuff (Well 1A, Figure3E) and shallow perched aquifers (Well 2D, Figure3F) are used to examine seasonal hydrologic responses.Snow water equivalent peaked at 213 mm during WY 2017 while annual cumulative precipitation was 673.5 mm for water year 2017.The average

3753. 2
Water routing in unsaturated zoneSoil moisture content in two site 2 boreholes (Wells 2B and 2C) and one site 3 borehole (Well 3B) were estimated from a neutron probe soil moisture gauge that was run downhole on four dates.Due to the textural shifts and 380 complexity of mineral composition as a function of depth at each site and across sites (Moravec et al., In Review), Hydrol.Earth Syst.Sci.Discuss., https://doi.org/10.5194/hess-2019-140Manuscript under review for journal Hydrol.Earth Syst.Sci. Discussion started: 24 April 2019 c Author(s) 2019.CC BY 4.0 License.water content estimates are used to qualitatively examine changes in water content with depth and over time within each respective borehole.
chemical fluxes (McIntosh et al., 2017) and larger concentrations of base cations have been found in waters with longer flow paths as mineral dissolution fluxes increase with increasing water transit times (Zapata-Rios et al., 2015b).405Quantitativemineralogy of cores collected during the June 2016 drilling campaign in the ZOB (Moravec et al., In Review) found that quartz, potassium feldspar, plagioclase, volcanic glass, and smaller percentages of mica are the primary minerals ubiquitous in site 1 and 2 cores.Smectite, iron oxides, illite, and magnesite, as well as diagenetically altered minerals like Ca-zeolites (clinoptilolite and mordenite), are present in smaller percentages within the top 15 mbgs of site 1, along with some 2:1 clays from 15 to 17 mbgs and 20 to 26 mbgs.Ca-zeolites, smectite, illite, iron 410 oxides, and trace talc and tremolite are also found throughout site 2 cores, as well as secondary minerals like calcite and illite in the top 15 mbgs.Greater percentages of 2:1 clays are also found throughout site 2 cores, especially from 12 to 16 mbgs and 22 to 30 mbgs.Previous analysis of saturation indices of ZOB groundwater found that well 2D shallow groundwater was saturated with respect to calcite (Olshanksy et al., 2018) while previous work by Zapata-Rios et al. (2015b) found that springs across the JRB-CZO were undersaturated with respect to calcite, albite, and 415 sanidine; therefore, interaction with those minerals is expected to influence groundwater and surface chemistry in the ZOB and La Jara catchment.Hydrol.Earth Syst.Sci.Discuss., https://doi.org/10.5194/hess-2019-140Manuscript under review for journal Hydrol.Earth Syst.Sci. Discussion started: 24 April 2019 c Author(s) 2019.CC BY 4.0 License.

450
source of recharge to groundwaters and surface waters in the ZOB and La Jara catchment.The majority of samples plot along the local meteoric water line (LMWL; from Broxton et al. (2009)), showing consistency in stable water isotopes over time.However, several surface waters and a few samples of deep groundwater from site 1 wells and Hydrol.Earth Syst.Sci.Discuss., https://doi.org/10.5194/hess-2019-140Manuscript under review for journal Hydrol.Earth Syst.Sci. Discussion started: 24 April 2019 c Author(s) 2019.CC BY 4.0 License.shallowgroundwater from well 2D have higher  18 O and  2 H values that plot to the right of the LMWL, along an enrichment line with slope of 3.4 (Figure9).

455
Tritium was detected in groundwater from each sampled well, which indicates that there is a component of modern recharge to all groundwater stores(Manning, 2009).Tritium content from wells analyzed in June 2017 and February 2018 are within two standard errors of one another indicating little difference between the tritium content of groundwater stores between the summer dry season and the winter.The highest tritium content (4.4 TU in February 2018) and therefore shortest residence time waters (12 and 17 years according to piston flow and exponential models, 460 respectively) are those of the perched aquifer while the lowest tritium content (0.7 TU in February 2018) and longest residence times (45 and 202 years, according to piston flow and exponential models, respectively) are from wells 2B Hydrol.Earth Syst.Sci.Discuss., https://doi.org/10.5194/hess-2019-140Manuscript under review for journal Hydrol.Earth Syst.Sci. Discussion started: 24 April 2019 c Author(s) 2019.CC BY 4.0 License.
effect likely inhibits infiltration of water into the subsurface and agrees with Langston et al. (2015)'s model of unsaturated zone flow in two seasonally snow covered hillslopes in Colorado which found that episodic recharge inhibited fluid flow down to the water table because of the need for shallow soil to re-wet after each precipitation event.

5604. 2
Water routing in unsaturated zone Hydrol.Earth Syst.Sci.Discuss., https://doi.org/10.5194/hess-2019-140Manuscript under review for journal Hydrol.Earth Syst.Sci. Discussion started: 24 April 2019 c Author(s) 2019.CC BY 4.0 License.Precipitation inputs differ before each neutron probe measurement (2.54 mm one day prior to July measurement, 2.03 mm one day prior to August measurement, 5.08 mm six days prior and 0.25 mm one day prior to 565 October measurement, and no precipitation over 106 days prior to the February measurement; Figure 6 top);however, water content is nearly identical in the top 4 mbgs in three of the four profiles for site 2 wells and in all site 3 data collection events (Figure6bottom).We hypothesize that the response seen at site 2 in the October survey is a function of both, the slightly larger precipitation depth prior to this survey and the wetter shallow soil conditions preceding the survey as compared to the conditions preceding the other three surveys.Higher frequency sampling 570 during wet season are needed to determine the impact of precipitation depth and the potential for precipitation thresholds to induce vertical flow.Perhaps temporal changes in water content with depth were missed because of the sporadic timing of neutron probe surveys due to the arduous transportation and permitting issues involved with the use of this instrument.While it does not appear that water content profiles with depth captured progressive enrichments in rock moisture as seen bySalve et al. (2012) and Rempe and Dietrich (2018), they do indicate that the 575 minimum dry season rock moisture storage is consistent across dry seasons, suggest differences in water routing, and identify lithologic discontinuities in the subsurface.
Hydrol.Earth Syst.Sci.Discuss., https://doi.org/10.5194/hess-2019-140Manuscript under review for journal Hydrol.Earth Syst.Sci. Discussion started: 24 April 2019 c Author(s) 2019.CC BY 4.0 License.Geologic maps of the Valles Caldera (Goff et al., 2011) indicate that a blind fault bisects the ZOB and it appears 600 This is further supported by high clay content (up to 50%) observed below 1.5 m depth at site 3 (Moravec et al.In Review), which likely impedes vertical infiltration and induces lateral flow in the subsurface.4.3 Contribution of distinct groundwater stores to streamflow 610In the same headwater catchment in the JRB-CZO, Olshansky et al. (2018) observed temporal changes in major ion concentrations of soil, surface, and ground water during spring snowmelt 2017 and found positive Si concentration pulses during the falling limb of surface water hydrographs that were hypothesized to result from increasing groundwater contributions during receding surface flows because surface water Si concentrations were similar to those Hydrol.Earth Syst.Sci.Discuss., https://doi.org/10.5194/hess-2019-140Manuscript under review for journal Hydrol.Earth Syst.Sci. Discussion started: 24 April 2019 c Author(s) 2019.CC BY 4.0 License.ion chemistry are not reflected in streamflow concentrations over time, which suggests that shallow groundwater represents only a small volumetric contribution to streamflow.Furthermore, recent work by Olshansky et al. (2018) found that soil water was an important contributor to surface water during spring snowmelt 2017 and may explain the subtle trends in Ca 2+ and DIC concentrations of surface waters, particularly ZOB surface water which was correlated 640 with soil PCO2 concentrations, at the onset of snowmelt.

Figure 2 :
Figure 2: Profile of the nested groundwater wells within the ZOB showing surface topography, depth of wells, and seasonal changes in water column heights between maximum (dotted) and minimum (solid) in meters above sea level.Lines capped with square ends represent the base of each well.It is important to note the different rock type at each site, the presence of a perched aquifer in well 2D, the disconnection between site 1 and 2 wells

Figure 3 :Figure 4 .
Figure 3: A) Daily averaged precipitation falls down from top axis.Average daily temperature is shown in red when temperatures are above zero and blue at or below zero degrees Celsius.B) Snow water equivalent (SWE) for WY 2017 reaches a maximum of 213 mm.C) Fifteen-min discharge of ZOB flume for WY 2017.D) Fifteenmin discharge of La Jara flume for WY 2017.E) Well 1A depth of water below ground surface from vibrating wire piezometer placed at 41.5 m below ground surface in fifteen-min intervals.Drops in water depth

Figure 5 :
Figure 5: A) Fracture density of sites 1 (left) and 2 (right) in m -2 .Notice that fracture density is approximately

Figure 6 :
Figure 6: Daily precipitation in mm from Redondo Weather Station above profiles of water content with depth in meters below ground surface for wells 2B, 2C, and 3B.Colors of profiles correspond to timing shown on precipitation figure above.It is important to note that the elevation above sea level of site 2 (3024 masl) and 3 (2989 masl) wells are different.

Figure 7 :Figure 8 :
Figure 7: Time series of Na + , Ca 2+ , and DIC over WY 2017 for surface waters from La Jara flume and ZOB

Figure 10 .
Figure 10.Schematic of intricacies of hydrologic structure and function across two contrasting sites within the ZOB (Sites 1 and 2).Site 2 has multiple, separate stores of groundwater across depth that are distinct from each other and distinct from deep groundwater stores at site 1.All groundwater is recharged via snowmelt and al., 2014; 75 McDonnell, 2017, Rempe and Dietrich, 2018; Dralle et al., 2018; Bhanja et al., 2018; Wlostowski et al., In Review) Ortega et al., 2016).The convergent zone of the ZOB, just above the ZOB flume, is characterized by boggy land in which standing water is present during the wettest parts of the year.Further evidence of near surface saturation in this area is the presence of marshy plants in standing water areas (e.g.broad-leaf cattails [Typha latifolia], rocky mountain irises [Iris missouriensis] and skunk cabbage [Veratrum californicum]), which contrast with those in the surrounding Hydrol.Earth Syst.Sci.Discuss., https://doi.org/10.5194/hess-2019-140Manuscript under review for journal Hydrol.Earth Syst.Sci. Discussion started: 24 April 2019 c Author(s) 2019.CC BY 4.0 License.east of Redondo Peak.Cumulative precipitation depths are summed over one water year (from October 1 to September 30 of the next year).

8 Fracture Traces and Density Estimates 300
(Gardner et al., 2000;Rempe, 2016)f the Am-241:Be source.Wet and dry calibrations were completed by measuring neutron counts within a 55-gallon drum filled with Viton sand surrounding a PVC casing (same material as well casing).The calibration between neutron counts and water content is generally linear up to water contents of 0.4 (Rempe, 2016), which is greater than the maximum water contents measured here; however, neutron probe counts are sensitive to changes in bulk density and variable solid phase chemical composition(Gardner et al., 2000;Rempe, 2016).Because 295 of the highly heterogeneous geology and mineralogy in the JRB-CZO ZOB (Moravec et al., In Review), one calibration material (Viton sand) was used for all wells and all depths, which limits the interpretation of neutron probe surveys to comparison over time at the same site.2.3 wells because the boreholes had to be immediately cased over their entire depth to control the highly pressurized sands encountered during drilling at this site.Because of the variable mineralogy and corresponding color transitions in the boreholes, a node file of fracture locations was needed and was created by tracing fractures onto a new layer over optical televiewer images from wells 1A and 2A in Adobe IllustratorTM.The scalable vector graphics (.SVG) file 310 Hydrol.Earth Syst.Sci.Discuss., https://doi.org/10.5194/hess-2019-140Manuscript under review for journal Hydrol.Earth Syst.Sci. Discussion started: 24 April 2019 c Author(s) 2019.CC BY 4.0 License.
Water depths in well 2D (Figure3F) did not have pronounced, sharp maxima and minima in response to snowmelt dynamics like those seen in surface waters and site 1 groundwater.Instead, water depths in well 2D 350 continued rising, with slight changes in rate on 3/21/17 and 4/4/17, while temperatures dropped below freezing again and a second snowpack accumulated and melted before well 2D water depths peaked on 4/22/17.Well 2D water depths did not respond to summer monsoons and, instead, continuously decreased from their spring snowmelt peak at 4/22/17 until reaching a minimum after summer monsoons on 10/4/17.However, well 2D gradually increased in response to fall storms until reaching peak water depths on 10/25/17.It appears that water slowly 355 infiltrated into the perched aquifer and recharged the near surface groundwater store.
and a second snowpack developed, well 1A depth of water receded until 4/6/17 after which it quickly rose to a second local maximum on 4/11/17 four days before ZOB streamflow reached a second max and six days before La 345 Jara streamflow reached its second peak.Well 1A water depths also peaked sharply on 10/2/17 in response to fall Hydrol.Earth Syst.Sci.Discuss., https://doi.org/10.5194/hess-2019-140Manuscript under review for journal Hydrol.Earth Syst.Sci. Discussion started: 24 April 2019 c Author(s) 2019.CC BY 4.0 License.precipitation.Conversely, well 1A water depths reached one gradual peak during NAM season on 8/16/17, despite several smaller La Jara streamflow peaks in response to summer monsoon storms.Volumetric water content (VWC) in ZOB soils from six pedons ranging from 9.5 to 65 cm bgs also varied seasonally with generally higher VWC during spring snowmelt, lower VWC at the onset of NAM season, and intermediate VWC during fall storms (Figure inflection point can be found in Olshansky et al. (2018).Hydrologic response to incoming precipitation exhibits strong dependence on season, as indicated by differences following spring snowmelt, summer monsoons, and fall precipitation.Specifically, well 1A groundwater responds rapidly to spring snowmelt (water table peaks 35.4 mbgs on 3/22/17) and fall precipitation (water table peaks 35.4 mbgs on 10/2/17); however, the welded tuff aquifer's response to summer monsoon rain is smaller and much more gradual (peaking at 36.4 mbgs on 8/16/17), suggesting that spring snowmelt and fall precipitation induce a different 540 hydrologic flow regime than that of summer monsoons.Different hydrologic flow regimes across seasons also exist in the perched aquifer (Well 2D).While all changes in the perched aquifer water table are gradual, spring snowmelt and fall precipitation produce water table peaks of 2.3 mbgs on 4/22/17 and 2.7 mbgs on 10/25/17 while the perched aquifer water table steadily decreased during summer monsoons indicating no water table changes induced by summer storms.
than to the VWM of summer precipitation (Zapata-Rios et al., 2015b).Furthermore, the detection of tritium in groundwater from each sampled 660 well indicates a component of modern recharge to each groundwater store, which agrees with previous work that found springs surrounding Redondo Peak are composed of modern water (Zapata-Rios et al., 2015b).The presence of tritium in groundwater suggests that snowmelt slowly infiltrates into all groundwater stores (Figure

Table 2 : Number of samples (n) and average concentrations of major ions and pH of surface and groundwaters. Standard deviations are shown in italicized parentheses.
Hydrol.Earth Syst.Sci.Discuss., https://doi.org/10.5194/hess-2019-140Manuscript under review for journal Hydrol.Earth Syst.Sci. Discussion started: 24 April 2019 c Author(s) 2019.CC BY 4.0 License.