Ecohydrologic Connections in Semiarid Rangeland Ecosystems in Oregon

An improved understanding of the ecohydrologic relationships in semiarid rangelands is imperative for the development of effective rehabilitation and land management practices. This thesis addresses the ecohydrologic relationships of two significant issues concerning semiarid rangeland ecosystems: western juniper encroachment and increasing stream temperatures. This thesis is divided into two chapters; each chapter is a manuscript reflecting a separate research site and project. The first chapter compares the use of ground and UAV-based measurements to assess vegetation and juniper characteristics in a juniper-dominated ecosystem. The second chapter describes the results of a preliminary investigation into stream temperature relationships of a semiarid riparian system in northcentral Oregon. Both manuscripts are currently being prepared for journal submission. Western juniper encroachment is a concern across many areas of the western United States and is associated with ecohydrological changes such as increased erosion and reduced intercanopy vegetation. The first research study took place at the Camp Creek Paired Watershed Study (CCPWS), as part of a long-term research project into the ecohydrological impacts of juniper encroachment and removal. The study sought to assess differences in vegetation cover between two watersheds with different densities of western juniper and to examine the accuracy of data collected using low-altitude Unmanned Aerial Vehicles (UAVs) to characterize canopy cover and vegetation cover. Based on ground-based measurements, some significant differences in vegetation cover were found between the two watersheds. Shrub cover was higher in the treated watershed than in the untreated watershed, although bare ground was similar. Herbage production in the treated watershed was also significantly greater in the treated watershed. Canopy cover estimates using UAV-based data were similar to ground estimates when multispectral vegetation indices were used. Additionally, supervised classification that utilized multispectral imagery and Normalized Difference Vegetation Index (NDVI) values yielded more accurate indications of overall vegetation cover than using multispectral imagery alone, but was only successful at differentiating between juniper from other vegetation when fall imagery was used. The second chapter of this thesis addresses stream temperature, a concern in many regions of the world because of its impact on cold-water species and biochemical processes. However, published research regarding stream temperature dynamics in arid or semiarid rangeland systems is limited. The research for the second manuscript took place in a semiarid rangeland system in northcentral Oregon along Fifteenmile Creek, which has been found to exceed suggested maximum stream temperatures. This study took place between 2014 and 2017, and examined stream temperature relationships associated with riparian shade, groundwater inflows, and ambient conditions. Stream temperatures generally followed the longitudinal gradient, with higher stream temperatures corresponding to lower elevations. During the summer, a difference of up to 5°C in the 7-day moving average stream temperature was observed between the highest and lowest elevation sites, while stream temperatures during the fall and winter seasons were more similar between sites. Air temperature was shown to be highly correlated to both shaded (r=0.960) and non-shaded (r=0.961) stream temperatures. In general, no significant difference was found between areas with riparian shading and non-shaded areas. Shallow groundwater temperatures showed less variability than stream temperatures. Groundwater was also generally cooler in the summer and warmer in the winter when compared to surface flow conditions. Differences between shallow groundwater temperatures and stream temperatures of up to 8°C in the summer and 10°C in the winter were observed, indicating that shallow groundwater inputs may have a moderating input on stream temperatures. Ecohydrologic connectivity, particularly concerning the relationship of vegetation and hydrologic characteristics, was an important consideration in both research studies. While additional research is necessary, this research provides insight into an improved understanding of how these connections can influence semiarid rangeland ecosystems

Ecohydrologic Connections of Rangeland Ecosystems in Central and Eastern Oregon, USA

In light of water scarcity and the impacts of climate change, there is an increased need to understand the interaction between land use characteristics and ecohydrologic processes in semiarid regions. Additionally, many semiarid and arid regions face various land management challenges, including woody plant encroachment, decreased snowpack, and increased stream temperatures. Therefore, a more comprehensive understanding of these processes is necessary for informing short-term land management approaches and long-term planning to help protect the resiliency of these systems. The overarching goal of the studies presented here was to examine the ecohydrologic connections and environmental characteristics at two semiarid watersheds. The research for this dissertation sought to assess these connections in the context of two significant land management concerns: western juniper encroachment and increasing stream temperatures. This dissertation is divided into four chapters. The research for the first two chapters of this dissertation took place at the Camp Creek Paired Watershed Study (CCPWS) in central Oregon, USA. This is a long-term study site established in 1993 in order to research the ecohydrologic impacts of western juniper (Juniperus occidentalis) encroachment and removal. The first chapter compares the seasonal water balance of a western juniper-dominated watershed to that of a sagebrush-dominated watershed over a period of eight years. The second chapter examines multiple approaches to estimating evapotranspiration (ET) and characterizes the relationship between two vegetation indices [Normalized Difference Vegetation Index (NDVI) and the Normalized Difference Moisture Index (NDMI)] and soil moisture, ET, and springflow characteristics. CCPWS consists of two adjacent watersheds of similar size and orientation and a riparian valley site located downstream of both watersheds. The majority of western juniper was removed from one watershed in 2005 and 2006 (‘Mays WS’), and big sagebrush (Artemisia tridentata) is the dominant overstory vegetation. Western juniper is the dominant overstory in the other watershed (‘Jensen WS’). Western juniper encroachment has been linked to reduced herbaceous productivity, altered soil moisture characteristics, altered streamflow timing, and soil erosion. Additionally, western juniper is costly and labor-intensive to remove. Cattle grazing is a key land use in central OR. In many semiarid regions of OR, reductions in herbaceous vegetative production and water availability can have ecological and economic impacts. In order to better understand the potential hydrologic impacts of western juniper at this study site, a seasonal water balance approach was used. Eight years of streamflow, springflow, soil moisture, shallow groundwater levels, and meteorological data (precipitation, air temperature, and solar radiation) were measured. The Water Table Fluctuation Method was used to calculate shallow aquifer recharge. The Hargreaves-Samani equation was used to calculate potential evapotranspiration (PET). Seasonal ET was calculated using PET and as the sink term in the water balance approach. ET accounted for the largest portion of the water budget for both watersheds, although springflow and streamflow were greater at the sagebrush-dominated watershed compared to the juniper-dominated watershed. For both watersheds, greater groundwater recharge occurred and deep percolation occurred in snow-dominated years compared to rain-dominated years, even when total annual precipitation amounts were similar. Specific data regarding ET are very limited in this region and in many semiarid areas. For the second chapter, satellite-based remote sensing data and readily available sources were used to examine monthly ET, PET, NDVI, and NDMI for both watersheds at CCPWS. Additionally, the Soil and Water Assessment Tool (SWAT) was used to model monthly ET for both watersheds. Environmental indicators, specifically springflow, soil moisture, NDVI, and NDMI, related to ET were also examined. . A small unpiloted aerial vehicle (UAV) was used to collect thermal infrared and multispectral imagery (red, green, blue, near-infrared, and red-edge wavelengths) at a small plot in each watershed, which was used to calculate ET and NDVI at an hourly scale for a small plot at each watershed. Considerable variability in seasonal and annual ET patterns and totals was found across the different watershed-scale ET models examined in this study. In general, ET rates peaked in May and June, but this was not the case for all models. For most of the watershed-scale ET models examined, total ET was greater at Jensen WS than Mays WS. A significant correlation was found between SWAT-modeled ET and NDMI, NDVI, and volumetric water content at Jensen WS. At Mays WS, a significant correlation was found between SWAT-modeled ET and volumetric water content, springflow, NDMI, and NDVI. A significant correlation was found between plot-scale hourly NDVI and ET. NDVI and springflow were also found to be significant predictors of ET at the plot scale. Research for the third chapter also sought to characterize aspects of the water balance. Multiple land use practices and land cover types are present at this study site. Sagebrush steppe, including western juniper and perennial grasses, accounts for a large portion of the watershed. Ponderosa pine and mixed conifer forests dominate in the middle reaches of the watershed. Cattle grazing and forestry are two primary land use practices at this study site. For the third manuscript, SWAT was used to model the monthly water balance for a 1280 ha watershed in eastern OR. A combination of on-site weather measurements (precipitation, air temperature, relative humidity, and solar radiation) and PRISM datasets were used to create the SWAT model. Two years were used as a “warm up” period for the model. A 10 m DEM was used for watershed delineation, National Land Cover Database (NLCD) data were used for land cover classification, and State Soil Geographic (STATSGO) data were used for soil type identification. The SWAT-calibration and uncertainty program (SWAT-CUP) was used for calibration, sensitivity analysis, and validation. Streamflow data from 2021 and plant available water content (PAWC) from 2018, 2019, and 2021 were used for calibration. Streamflow data were limited and therefore only PAWC measurements were used for validation. Sensitivity analysis was conducted for calibration simulations using streamflow only, streamflow and PAWC, and PAWC only data. Mean annual precipitation across the watershed from 2018 through 2021 was 377 mm yr⁻¹. ET accounted for the majority of the output of the water balance at 253 mm yr⁻¹, followed by water yield (123 mm yr⁻¹). Total modeled aquifer recharge was 10 mm yr⁻¹. Based on the sensitivity analysis, parameters related to snow cover, canopy cover, soil characteristics, and curve number were among the most influential parameters. The fourth chapter characterizes stream temperature dynamics along a small spring-fed stream and tributary and builds upon the previous research in land cover and water balance characterization at the study site in eastern Oregon. In the Pacific Northwest of the U.S., increased stream temperatures are of particular concern because of their negative impacts on cold-water fish (such as salmonids). While the link between land cover change and stream temperature has been widely researched, particularly in more humid regions, more information is needed to understand these interactions in semiarid climates. Stream temperature measurements were taken along the longitudinal gradient. Both the stream and tributary originate at a small spring. The daily mean, minimum, and maximum stream temperature were calculated along with the seven-day moving average (7DA), the seven-day moving average of the daily maximum (7DADM), and the diurnal range of stream temperatures. Land cover classification was performed using an object-oriented support vector machine approach. The land cover type (forested, sagebrush/shrubland, herbaceous, or non-vegetated) was examined within a 30 m buffer along the stream. A support vector regression (SVR) approach was used to examine the relationship between stream temperature characteristics (specifically the 7DADM and the diurnal range) and environmental characteristics (mean air temperature, dew point temperature, vapor pressure deficit, SWAT-modeled springflow, and land cover characteristics). Excluding the headwater sites, stream temperatures were generally greater at lower elevation sites compared to higher elevation sites, but this did not hold true for all seasons or all locations. Water temperatures at the headwater springs varied very little across seasons or years. The average diurnal range in stream temperature of other sites varied between 1.8 and 5.8 °C and did not demonstrate an association with elevation. The SVR models indicated that air temperature, followed by sagebrush steppe land cover and forest cover were the primary predictors for 7DADM or diurnal stream temperatures. The SVR model for 7DADM (R²=0.83) performed better overall than the SVR model for diurnal stream temperature (R²=0.55). The research profiled in this dissertation addresses the need for more research into the ecohydrologic processes in semiarid regions. Additionally, this research examined multiple approaches that can be applied in data-limited environments. The use of readily available data, such as PRISM, remote sensing imagery, or ET datasets, can help address these gaps in data, particularly when combined with in situ data. Results of this study contribute to the existing body of knowledge regarding the relationship between ecohydrologic processes and land use characteristics, which can provide insight into future research and land management decisions

The Seasonal Water Balance of Western-Juniper-Dominated and Big-Sagebrush-Dominated Watersheds

The combined impacts of woody plant encroachment and climate variability have the potential to alter the water balance in many sagebrush steppe ecosystems in the Western USA, leading to reduced water availability in these already water-scarce regions. This study compared the water-balance characteristics of two adjacent semiarid watersheds in central Oregon, USA: one dominated by big sagebrush and one dominated by western juniper. Precipitation, springflow, streamflow, shallow groundwater levels, and soil moisture were measured. The potential evapotranspiration was calculated using the Hargreaves–Samani method. Potential evapotranspiration and a water-balance approach were used to calculate seasonal actual evapotranspiration. The shallow aquifer recharge was calculated using the Water-Table-Fluctuation-Method. Evapotranspiration, followed by deep percolation, accounted for the largest portion (83% to 86% of annual precipitation) of water output for both watersheds. Springflow and streamflow rates were generally greater at the sagebrush-dominated watershed. Snow-dominated years showed greater amounts of groundwater recharge and deep percolation than years where a larger portion of precipitation fell as rain, even when total annual precipitation amounts were similar. This study’s results highlight the role of vegetation dynamics, such as juniper encroachment, and seasonal precipitation characteristics, on water availability in semiarid rangeland ecosystems

The Seasonal Water Balance of Western-Juniper-Dominated and Big-Sagebrush-Dominated Watersheds

The combined impacts of woody plant encroachment and climate variability have the potential to alter the water balance in many sagebrush steppe ecosystems in the Western USA, leading to reduced water availability in these already water-scarce regions. This study compared the water-balance characteristics of two adjacent semiarid watersheds in central Oregon, USA: one dominated by big sagebrush and one dominated by western juniper. Precipitation, springflow, streamflow, shallow groundwater levels, and soil moisture were measured. The potential evapotranspiration was calculated using the Hargreaves–Samani method. Potential evapotranspiration and a water-balance approach were used to calculate seasonal actual evapotranspiration. The shallow aquifer recharge was calculated using the Water-Table-Fluctuation-Method. Evapotranspiration, followed by deep percolation, accounted for the largest portion (83% to 86% of annual precipitation) of water output for both watersheds. Springflow and streamflow rates were generally greater at the sagebrush-dominated watershed. Snow-dominated years showed greater amounts of groundwater recharge and deep percolation than years where a larger portion of precipitation fell as rain, even when total annual precipitation amounts were similar. This study’s results highlight the role of vegetation dynamics, such as juniper encroachment, and seasonal precipitation characteristics, on water availability in semiarid rangeland ecosystems

The Use of Low-Altitude UAV Imagery to Assess Western Juniper Density and Canopy Cover in Treated and Untreated Stands

Monitoring vegetation characteristics and ground cover is crucial to determine appropriate management techniques in western juniper (Juniperus occidentalis Hook.) ecosystems. Remote-sensing techniques have been used to study vegetation cover; yet, few studies have applied these techniques using unmanned aerial vehicles (UAV), specifically in areas of juniper woodlands. We used ground-based data in conjunction with low-altitude UAV imagery to assess vegetation and ground cover characteristics in a paired watershed study located in central Oregon, USA. The study was comprised of a treated watershed (most juniper removed) and an untreated watershed. Research objectives were to: (1) evaluate the density and canopy cover of western juniper in a treated (juniper removed) and an untreated watershed; and, (2) assess the effectiveness of using low altitude UAV-based imagery to measure juniper-sapling population density and canopy cover. Ground- based measurements were used to assess vegetation features in each watershed and as a means to verify analysis from aerial imagery. Visual imagery (red, green, and blue wavelengths) and multispectral imagery (red, green, blue, near-infrared, and red-edge wavelengths) were captured using a quadcopter-style UAV. Canopy cover in the untreated watershed was estimated using two different methods: vegetation indices and support vector machine classification. Supervised classification was used to assess juniper sapling density and vegetation cover in the treated watershed. Results showed that vegetation indices that incorporated near-infrared reflectance values estimated canopy cover within 0.7% to 4.1% of ground-based calculations. Canopy cover estimates at the untreated watershed using supervised classification were within 0.9% to 2.3% of ground-based results. Supervised classification applied to fall imagery using multispectral bands provided the best estimates of juniper sapling density compared to imagery taken in the summer or to using visual imagery. Study results suggest that low-altitude multispectral imagery obtained using small UAV can be effectively used to assess western juniper density and canopy cover

Water Use and Soil Moisture Relationships on Western Juniper Trees at Different Growth Stages

An enhanced understanding of plant water uptake is critical for making better-informed management decisions involving vegetative manipulation practices aimed to improve site productivity. This is particularly true in arid and semiarid locations where water is a scarce, yet precious commodity. In this project, we evaluated the interannual and seasonal variability of soil moisture and transpiration in sapling, juvenile, and mature western juniper (Juniperus occidentalis) trees in a semiarid rangeland ecosystem of central Oregon, USA. Transpiration levels were greatest in mature juniper trees in an untreated juniper watershed (Jensen WS), while the lowest transpiration levels were observed in juniper saplings in a treated watershed (Mays WS) where most mature juniper trees were removed in 2005. Significant differences (p ≤ 0.05) in leaf water potential levels observed between predawn and midday readings for all juniper growth stages indicated water is lost over the course of the day. Results showed seasonal precipitation was highly variable over the course of the study (2017 through 2019) and this was reflected in soil water available for tree uptake. This resulted in considerable intra- and inter-annual variation in transpiration. In years with greater winter precipitation amounts (2017 and 2019), juniper transpiration rates were highest during the summer, followed by spring, autumn, and winter. On average, transpiration rates during the summer in the wettest (329 mm) year 2017 were 115 and 2.76 L day−1 for mature and sapling trees, respectively. No data were collected for juvenile trees in 2017. In the drier (245 mm) year 2018, higher transpiration rates were observed in the spring. On average, spring transpiration rates were 72.7, 1.61, and 1.00 L day−1 for mature, juvenile, and sapling trees, respectively. Study results highlight the sensitivity of western juniper woodlands to variations in seasonal precipitation and soil moisture availability

Novel Opioid Safety Clinic Initiative to Deliver Guideline-Concordant Chronic Opioid Therapy in Primary Care

Objective: To develop and evaluate a novel Opioid Safety Clinic (OSC) initiative to enhance adherence to guidelines on the assessment and monitoring of patients prescribed chronic opioid therapy (COT). Patients and Methods: The OSC was developed at an urban Federally Qualified Health Center to provide guideline-concordant care for COT, standardize workflows, and efficiently use clinic staff. We evaluated the OSC using a matched cohort study. Five hundred thirty-nine patients participated in the clinic between July 1, 2014, and March 31, 2016. Of these, 472 clinic participants were matched to 472 nonparticipants by sex and age on the date of the OSC visit. The OSC was evaluated by its completion rates of standardized pain assessments, urine toxicology, and naloxone dispensings. We conducted logistic regression comparing OSC participants to OSC nonparticipants. Results: A total of 539 patients attended an OSC visit, representing approximately 53% of patients in the chronic opioid registry. The OSC participants were more likely than nonparticipants to have completed a pain assessment (adjusted odds ratio [aOR], 169.8; 95% CI, 98.3-293.5), completed a urine toxicology (aOR, 46.1; 95% CI, 30.4-69.9), or had naloxone dispensed (aOR, 2.8; 95% CI, 1.9-4.3) over 12 months of follow-up. Conclusion: The OSC model improved adherence to guideline-concordant COT in primary care. Future research is needed to assess the impact of these interventions on pain, quality of life, and adverse events from opioid analgesics