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\begin{document}

\title{The Wasatch Environmental Observatory: A mountain to urban research
network in the semi-arid Western US}



\author[1]{Jennifer J. Follstad Shah}%
\author[1]{Ryan Bares}%
\author[1]{Brenda B. Bowen}%
\author[1]{Gabriel J. Bowen}%
\author[1]{David P. Eiriksson}%
\author[1]{A. Gannet Hallar}%
\author[1]{John D. Horel}%
\author[1]{Sarah J. Hinners}%
\author[1]{Logan R. Jamison}%
\author[1]{John C. Lin}%
\author[1]{Diane E. Pataki}%
\author[1]{S. McKenzie Skiles}%
\author[1]{Rose M. Smith}%
\author[1]{Margaret A. Wolf}%
\author[1]{Paul D. Brooks}%
\author[1]{David R. Bowling}%
\author[1]{Benjamin Fasoli}%
\author[1]{Richard P. Fiorella}%
\author[1]{Alexander A. Jacques}%
\author[1]{Daniel L. Mendoza}%
\author[1]{Logan E. Mitchell}%
\affil[1]{University of Utah}%


\vspace{-1em}



  
  \date{May 08, 2024}


\begingroup
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\selectlanguage{english}
\begin{abstract}
The Jordan River Basin, and its seven sub-catchments of the Central
Wasatch Mountains immediately east of Salt Lake City, UT, are home to an
array of research infrastructrure that collectively form the Wasatch
Environmental Observatory (WEO). Each sub-catchment is comprised of a
wildland to urban land use gradient that spans an elevation range of
over 2000 m in a linear distance of \textasciitilde{}25km. Geology
varies across the sub-catchments, ranging from granitic, intrusive to
mixed sedimentary rocks in uplands that drain to the alluvial or
colluvial sediments of the former Lake Bonneville. Vegetation varies by
elevation, aspect, distance to stream channels, and land use.~ The sharp
elevation gradient results in a range of precipitation from 700 to 1200
mm/yr (roughly 2/3 as snow) and mean annual temperature from 3.5
\textsuperscript{o} to 6.8\textsuperscript{o} C. Spring snowmelt
dominates annual discharge. Although climate is relatively similar
across the catchments, annual water yield varies spatially by more than
a factor of 3, ranging from 0.18 to 0.63. With historical strengths in
ecohydrology, water supply, and social-ecological research, current
infrastructure supports both basic and applied research in meteorology,
climate, atmospheric chemistry, hydrology, ecology, biogeochemistry,
resource management, sustainable systems, and urban redesign. Climate
and discharge data span over a century for the seven sub-catchments of
the larger basin. These data sets, combined with multiple decades of
hydrochemistry, isotopes, ecological data sets, social survey data sets,
and high-resolution LiDAR topography and vegetation structure, provide a
baseline for long-term data collected by NEON, public agencies, and
individual research projects. The combination of long-term data with
active state of the art observing facilities allows WEO to serve as a
unique natural laboratory for addressing research questions facing
rapidly growing, seasonally snow-covered, semi-arid regions worldwide
and an excellent facility for providing student education and research
training.%
\end{abstract}%



\sloppy




\textbf{Site Description}

The Wasatch Environmental Observatory (WEO) integrates existing fixed
and mobile field-based research infrastructure in central Utah, USA (40\selectlanguage{ngerman}°
34' N, 111° 53' W). This distributed observational network supports
research and training in multiple disciplines. The WEO is managed by the
University of Utah and supported by two full-time, highly skilled
technicians. The unique geography of the region allows the WEO to span
gradients from relatively unimpacted mountain environments to
century-old urban landscapes, all of which are facing major challenges
related to global changes and a growing human population. The
integration of a city-center within the study area provides benefits to
the WEO, such as the ability to affix scientific instrumentation to mass
transit; work with community partners to construct experimental, yet
operational green infrastructure facilities; and augment WEO
infrastructure with instrumentation managed by state and federal
agencies.

WEO is named for the Central Wasatch Mountains, east of Salt Lake City,
Utah, USA (Fig. 1A). The Wasatch Range represents the western edge of
the Rocky Mountain physiographic province with the Jordan (Salt Lake)
River Basin marking the eastern boundary of the Basin and Range
province. The Wasatch fault bounds the range to the west and is
responsible for over 2200m of relief between the mountain peaks
(\textgreater{}3500m) and the valley floor (\textasciitilde{}1300m). The
mountain block is lithologically and structurally complex with rocks
ranging from Precambrian quartzites and shales to Tertiary igneous
intrusions (Bryant 1990). The Jordan River Basin is bordered by
mountains in all directions but the northwest, resulting in a geography
that promotes atmospheric inversions in summer and winter months (Lin et
al., 2018). Roughly 44\% of the 2,085 km\textsuperscript{2} Jordan River
catchment area is urban, with a human population of 1.1 million living
in Salt Lake County that is expected to reach 1.7 million by 2065
(Perlich et al., 2017). The mainstem Jordan River receives inputs from
Utah Lake at the southern extent of the basin and flows north to the
Great Salt Lake. Seven major tributaries drain the Central Wasatch
Mountains and discharge to the river after passing through several
municipalities (Fig. 1B). Each sub-catchment thus represents varying
degrees of a wildland to urban land use gradient. For example, Red Butte
Canyon includes a U.S. Forest Service Research Natural Area (RNA) in its
headwaters (Ehleringer et al., 1992), while high altitude areas of Big
and Little Cottonwood canyons are home to multiple ski resorts.

The region has a cold, semi-arid climate with strong lapse rates in mean
annual temperature (MAT) and precipitation (MAP) at the sub-catchment
scale. MAT within the Central Wasatch (1300 -- 3500 m) ranges from 3.5
-- 6.8 °C, while MAP varies between 700 -- 1300 mm. In Red Butte Creek
(1300 -- 2510 m), MAT is 6.8 °C and MAP is 850 mm (Gelderloos, 2018).

In Little Cottonwood Creek (1600 -- 3500 m), which includes the
intensively studied alpine Albion Basin, MAT is 3.5 °C, while MAP is
1300 mm. Most precipitation falls as winter snow with spring melt (April
-- July) providing both surface water runoff and regional groundwater
recharge (Hely et al., 1971; Manning \& Solomon, 2004; Bardsley, et al.
2013; Gabor et al., 2017). Numerous water diversions from tributaries
and the mainstem river combined with inputs of effluent from several
water reclamation facilities and canal return flows add hydrologic
complexity to the system (Follstad Shah et al., 2019). The fourth-order
Jordan River is on the state of Utah's 303(d) list of impaired water
bodies (U.S. Code 1313(d)(1)(A) in many of its segments due to highly
regulated river flows and excessive loading of organic matter and
nutrients (Follstad Shah et al., 2019).

WEO instrumentation combined with long-term climate and stream discharge
data provide evidence of rapid climatic and hydrologic change in the
Jordan River Basin. Mean annual air temperature in each sub-catchment
has increased by approximately 1.5 °C since 1980 (Fig. 2) (Wolf, 2020;
Jamison, 2020). Downscaled climate models suggest that more
precipitation will fall as rain rather than snow in the future and the
snow line will shift upslope by 250 m (Scalzitti et al., 2016). These
changes will create flashier hydrographs within Jordan Basin
tributaries, historically characterized as snowmelt dominated. Reduced
flows to the Great Salt Lake, induced by shifting climate and water
extraction, have already exposed more lake sediment, lending to dust
storms that substantially accelerate snow melt (Skiles et al., 2018) and
exacerbate air pollution in a region prone to high concentrations of
fine particulate matter and the formation of photochemical smog (Lin et
al., 2018; Fig. 3).

In short, hydrologic process research opportunities abound in the region
given its unique geography, rapidly growing human population that puts
pressure on water resources, hydrologic change resulting from the
climate crisis, and clear linkages between the hydrologic cycle and air
quality. We now summarize some of the major avenues of research
supported by the WEO and provide greater detail about the infrastructure
supporting these efforts.

\textbf{Research Themes \& Major Findings}

\emph{Hydrology}

Over a century of streamflow monitoring from the seven main
sub-catchments draining the Central Wasatch indicate that mean annual
water yield ranges from 18\% to 63\% with higher water yield from
colder, wetter, steeper catchments (Gelderloos, 2018; Jamison, 2020;
Wolf, 2020). Hydrochemical observations from U.S. Geology Survey (USGS)
baseline network indicate that most of this surface water discharge has
had extensive interaction with the subsurface (Godsey et al., 2009). The
evidence that snowmelt drives both surface water discharge and
groundwater recharge has led to extensive focus on surface
water-groundwater interactions using a suite of tracers (Manning \&
Solomon, 2004; Manning et al., 2005). These studies demonstrate that
mountain block recharge is large, driven by snowmelt, and that regional
groundwaters are dominated by modern water with
apparent\textsuperscript{3}H/\textsuperscript{3}He ages of 5 to 50
years. Younger waters are found close to the mountain front. Recent
findings that snowmelt is decreasing due to long-term warming (Jamison,
2020) while proceeding more rapidly due to episodic dust deposition
(Skiles et al., 2018) suggest that historical patterns in recharge and
streamflow are unlikely to predict future water supply. These results
have important implications for drinking water supply given that winter
montane precipitation is an important source for tap water in the Salt
Lake Valley (Jameel et al., 2016; 2018).

\emph{Ecohydrology}

Complementing the work on snowmelt, recharge, and streamflow, WEO has
long been a location where researchers use novel methods to understand
where plants obtain water, their susceptibility to climate and drought
stress and their distribution across the landscape. For example, early
work showed that riparian trees do not use stream water (Dawson \&
Ehleringer, 1991; Oerter et al., 2019) leading to decades of work around
the globe on understanding plant water sources. More recently,
experimental plot-based studies, observations in natural forest stands,
and landscape modeling are demonstrating how plant physiology interacts
with local to regional climate to control dormancy, growth, carbon
allocation, and drought stress (Chan \& Bowling, 2017; Zenes et al.,
2020). Analysis of high-resolution LiDAR data has illustrated how human
land use decisions interact with local hydroclimate to influence both
demography and productivity of riparian vegetation across the wildland
to urban land use gradient (Grijseels et al., in review).

\emph{Water Supply \& Water Quality}

WEO researchers have leveraged existing gradients in water isotope
values (d\textsuperscript{18}O and d\textsuperscript{2}H in surface
water, groundwater, precipitation, drinking water, and effluent) across
the Jordan River Basin and monitoring of discharge and hydrochemistry to
better understand complexities in the supply of surface water and
drinking water (Jameel et al., 2016; 2018; Follstad Shah et al., 2019),
as well as relationships between water supply and water quality (Hall et
al., 2016; Gabor et al., 2017). These studies demonstrate how water
isotopes can be a tool for public utilities to identify where to monitor
for unintended reactions within pipes receiving water from multiple
sources, isolate areas of water-related public health emergencies, and
better manage impaired waterways. Studies in Jordan River tributaries
also indicate that snowmelt-dominated groundwater is a significant
contributor to discharge along the montane to urban gradient and show
that shallow, polluted groundwater in highly urban areas as the source
of elevated stream nutrient loads (Hall et al., 2016; Gabor et al.,
2017). These results challenge the existing paradigm linking stormwater
inputs to poor water quality in urban streams.

Two facilities exist at the University of Utah that provide
opportunities for assessing the efficacy of green infrastructure to
manage stormwater inputs and retain nutrients. The Green Infrastructure
Research Facility (GIRF) is an experimental set of bioswales where
hydrologic inputs, water chemistry, and vegetation can be fully
manipulated. Work at this site has demonstrated that bioswales with
irrigated wetland vegetation and un-irrigated xeric adapted upland
vegetation retained similar amounts of phosphorus, while wetland swales
retained more nitrogen (Houdeshel et al., 2015). The Landscape Lab
(\emph{http://cepd.cap.utah.edu/landscape-lab/}) consists of eight
bioswales receiving runoff from adjacent structures and streets.
Bioswales are planted with either mesic, ornamental vegetation or
drought-adapted vegetation, with equal replication of each treatment.
The site was established through a designed experiment process (Felson
and Pickett, 2005), as both a demonstration project for stormwater
management in semi-arid regions, and a research site to address how
ecohydrology and ecology affect green infrastructure function.

\emph{Climate \& Atmospheric Science}

Decades of investment in meteorological and trace gas monitoring by the
University of Utah has provided the foundation for diverse environmental
research, served civic needs (Horel et al., 2002) and resulted in one of
the longest continuous records of urban carbon dioxide
(CO\textsubscript{2}) concentrations in the nation (Lin et al., 2018;
Bares et al., 2019). This investment has better elucidated the factors
contributing to poor air quality in the Salt Lake Valley, including
population growth (Mitchell et al., 2018) and secondary formation of
PM\textsubscript{2.5} through reactions of aerosols containing ammonium
with a variety of other pollutants emitted from local sources (Moravek
et al., 2019; Womak et al., 2019). Results from recent studies also have
provided new modeling and empirical tools for monitoring air quality and
transport processes of air pollutants (e.g., Mallia et al., 2017; Bares
et al., 2018).

\textbf{Instrumentation \& Measurements}

The WEO is comprised of several instrumentation networks, described in
detail below, that can be enhanced by measurements using relocatable,
high-precision hydrologic and atmospheric observation equipment (Fig.
4). Example deployable equipment includes scintillometers, ground
penetrating radar, neutron and time domain reflectometry, cosmic ray
probes for biomass and soil moisture, lysimeters, collars for sampling
gas flux from soils, hydrologic sondes, automated water samplers,
portable trace gas infrared analyzers, and portable aerosol
spectrophotometers. The WEO also includes databases with high resolution
LiDAR data and long-term records of environmental monitoring (e.g.,
isotopes, weather, atmospheric trace gases and chemistry, water
quality). WEO resources are augmented by hydrological, meteorological,
and ecological infrastructure managed by the USGS, US Department of
Agriculture National Resource Conservation Service (NRCS), National
Ecological Observatory Network (NEON), Inc., Utah Department of
Transportation (UDOT), and Salt Lake County.

\emph{Instrumentation Networks}

Thirty stream gages exist within the Jordan Basin, amongst those
operated by the WEO, USGS, NEON Inc., and Salt Lake County. Real-time
discharge and stage height data from each gage is available online. Some
also report water temperature. Several stormwater discharge points
within Red Butte Creek also have been instrumented with sensors
continuously monitoring discharge and water temperature. Episodic
sampling has enhanced these measurements with analysis of metals and
water isotopes in stormwater.

WEO's Gradient Along Mountain to Urban Transect (GAMUT) network,
installed as part of the 5-year (2012-2018) innovative Urban Transitions
and Arid-region Hydrosustainability (iUTAH) program
(\emph{https://iutahepscor.org/}; Jones et al., 2017) includes six
coupled terrestrial climate and stream ecohydrology stations located
along the wildland to urban land use gradient from the headwaters of Red
Butte Canyon to the Jordan River on the Salt Lake Valley floor. Since
installation, meteorological stations have continuously recorded
incoming and outgoing radiation, vapor pressure, barometric pressure,
air temperature, wind speed and direction, ground-level ozone
(O\textsubscript{3}), precipitation, snow depth, photosynthetically
active radiation (PAR), and soil moisture. Aquatic stations have since
continuously recorded stream discharge, water temperature, pH, specific
conductance, dissolved oxygen, turbidity, colored dissolved organic
matter, phycocyanin, and chlorophyll. Data from these stations have been
augmented by biweekly sampling for water chemistry (e.g., nutrient and
dissolved organic carbon concentrations) and \emph{Escherichia coli}
abundance. Periodic synoptic sampling campaigns have complemented these
measurements with analysis of isotopes from water, plant tissues, and
stream macroinvertebrate communities. Social science surveys conducted
as part of the iUTAH program have provided rich information for
understanding human perceptions of and access to regional water
resources.

One of the permanent observation sites operated by NEON Inc., is located
in the Red Butte Canyon RNA. Instrumentation at this site includes
sensors that monitor stream discharge and temperature, surface water
quality, depth to groundwater, precipitation, eddy covariance, soil
moisture, and phenology.

Green infrastructure facilities at the University of Utah have been
equipped with automated flow sensors to monitor hydrologic fluxes in and
out of bioswales, as well as soil moisture sensors.

Several long-term snowpack study plots exist in the Central Wasatch and
are managed by the NRCS and UDOT. These study sites provide information
about snowpack depth, density, and snow water equivalent, as well as
meteorological data in some cases. At the Atwater Study Plot (ASP;
40.591206 N, 111.637685 W), WEO researchers have paired measurement and
aerosol deposition to understand the effect of dust on rates of snowmelt
(Skiles et al., 2018). ASP has recently been instrumented to measure
radiation fluxes, providing the first full snow energy balance estimates
in the Central Wasatch Range. A radiometer with aerosol optical depth
measurement capability is located atop a building on the campus of the
University of Utah. Additional urban and montane sites will be equipped
with dust emission and deposition sensors in the near future.

The Utah Urban CO\textsubscript{2} Network (UUCON) includes eight trace
gas stations throughout the Salt Lake Valley that span a large
elevational gradient extending from Hidden Peak in Albion Basin to the
valley floor (Lin et al., 2018; Bares et al., 2019). All of these
stations monitor CO\textsubscript{2} concentrations, but some stations
also record other gases (CO, CH\textsubscript{4}, NO\textsubscript{x},
O\textsubscript{3}), isotopes, and fine particulate matter
(PM\textsubscript{2.5}). In addition, sensors affixed to Utah Transit
Authority's light rail system measure emissions of CO\textsubscript{2},
CH\textsubscript{4}, O\textsubscript{3}, and PM\textsubscript{2.5} in
the urban core (TRAX; Lin et al. 2018; Mitchell et al., 2018; Mendoza et
al., 2019) and a mobile lab is driven around the metropolitan area on a
regular basis measuring concentrations of CO, CO\textsubscript{2},
CH\textsubscript{4}, NO\textsubscript{x}, O\textsubscript{3} and
PM\textsubscript{2.5}. Together, UUCON and these mobile monitoring
platforms comprise the Salt Lake Valley Greenhouse Gas Monitoring System
(Lin et al., 2018). Trace gas monitoring is augmented with
meteorological data housed by the MesoWest network (Horel et al., 2002).
These meteorological data have been collected since 1997 from hundreds
of locations throughout the WEO region.

\textbf{Data Availability}

Stream discharge data collected by non-WEO entities are available at
USGS (\emph{https://waterdata.usgs.gov/nwis}) and Salt Lake County
(\emph{https://rain-flow.slco.org/}) websites. GAMUT network data can be
retrieved from Hydroshare (\emph{https://www.hydroshare.org/}),
currently managed by the Consortium of Universities for the Advancement
of Hydrologic Science, Inc. (CUAHSI). NEON Inc. manages a data portal
from which data may be downloaded
(\emph{https://data.neonscience.org/data-products/explore}). Snow study
plot data can be found at the NRCS snow telemetry (SNOTEL) website
(\emph{https://www.wcc.nrcs.usda.gov/snow/}). UUCON data can be
visualized and downloaded through the Utah Atmospheric Trace Gas and Air
Quality Laboratory (\emph{https://air.utah.edu/}). Meteorological data
and Atwater Study Plot data can be obtained through MesoWest
(http://meso2.chpc.utah.edu/aq/ and
https://mesowest.utah.edu/cgi-bin/droman/meso\_base\_dyn.cgi?stn=ATH20).
High resolution LiDAR data covering the seven catchments are available
at\emph{https://gis.utah.gov/data/elevation-terrain-data/2-meter-lidar/}.
Water isotope data can be found through WaterIstopes.org
(\emph{https://wateriso.utah.edu/waterisotopes/}).

\textbf{Acknowledgments}

WEO infrastructure has been supported through grants from the U.S.
National Science Foundation (OIA-1208732, DEB-2006308, DBI-1759730,
EAR-2012091, IOS 1450650, CZO 1331408) and financial contributions from
Salt Lake County Public Utilities and the University of Utah.

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\textbf{Figure Legends}

Figure 1. The Wasatch Environmental Observatory (WEO) network study area
encompasses the Central Wasatch Mountains and the Salt Lake Valley (A),
within which exists the Jordan River Basin and seven sub-catchments (B).
Acronyms in (B) represent the names of each sub-catchment: City Creek
(CC), Red Butte Creek (RBC), Emigration Creek (EC), Parleys Creek (PC),
Mill Creek (MC), Big Cottonwood Creek (BCC), and Little Cottonwood Creek
(LCC).

Figure 2. Mean annual temperature and streamflow for the seven
tributaries draining the Central Wasatch Mountains from the water years
(October-September) of 1900 to the present.

Figure 3. Image of an atmospheric inversion trapping air pollution
within the Salt Lake Valley. Photo credit: Jeffrey D. Allred, Associated
Press.

Figure 4. Panel showing instrumentation positioned in various locations
throughout the WEO, including the headwaters of Red Butte Creek (A,B),
the Green Infrastructure Research Facility (GIRF) on the campus of the
University of Utah (C), the mobile light rail system (D), and Albion
Basin (E).



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