Simulations of stream-subsurface water exchange (hyporheic exchange) using a three-dimensional steady state groundwater flow model and a particle tracking model in unconstrained and constrained reaches of small (2nd-order) and intermediate (5th-order) mountain streams were conducted to estimate the effects of geomorphic features on the extent, volume and residence time of...
Changes in the concentrations of dissolved ammonia (NH4+1), nitrate (NO3-1), organic nitrogen (DON) were monitored along ground water flow paths to determine the importance of the ground water system to the stream nitrogen budget. The study site was located on a wide floodplain along a fourth-order
stream in the Oregon...
Stream chemistry studies conducted in the forested Watershed 1 of the HJ Andrews Experimental Forest show a contribution of CO2 from the hyporheic zone. Hyporheic CO₂ concentrations, measured as pCO₂, have a seasonal trend as well as a responsiveness to storm events. Concentrations are highest at the end of the...
Freshwater systems are an important component of the global carbon cycle as they outgas disproportionately large quantities of carbon compared to the terrestrial landscape. Of particular importance are headwater streams, which represent roughly 90% of the channel network by length and have been conservatively estimated to outgas roughly 36% of...
Streams and rivers play a critical role in global carbon (C) cycling by processing, storing, and transporting C. Headwater streams which make up more than 95% of the length of streams and rivers worldwide have disproportionate influence on fluvial C dynamics. The hyporheic zone (HZ) of headwater streams is a...
Pacific salmon (Oncorhynchus spp.) face numerous challenges associated with climate change. Most research has emphasized the potential effects of elevated summer water temperatures; however, climatic changes are also projected to significantly alter incubation and rearing habitats during the late autumn, winter, and spring months ("the incubation period"). Along the southern...
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Steven M. Wondzell
Pacific salmon (Oncorhynchus spp.) face numerous challenges associated
Rangelands span over 50% of the globe and approximately 70% of the United States. Although livestock production is an important use of rangelands, the benefits of rangelands are highly diverse. Humans find intrinsic value in protecting these unique and variable landscapes for wildlife, vegetation, and recreation enthusiasts. Woodland plant encroachment...
Streams across the western United States are impaired from human alterations that have reduced freshwater habitat by simplifying channel complexity and disconnecting floodplains (Knox et al., 2022; Waples et al., 2008; Wohl, 2014). Climate change is likely to continue exacerbating these risks by warming summer surface stream temperatures (Crozier et...
The rapid pace of climate change is increasing tree mortality and highlighting the need to improve the mechanistic understanding of plant function under increased water stress. However, the processes that control soil moisture availability in steep mountainous terrain are poorly understood, as are the relative effects of atmospheric and soil...
This study investigated carbon dynamics in the hyporheic zone of a steep, forested catchment in the Cascade Mountains of western Oregon, USA. Water samples were collected monthly from a headwater stream and well network during baseflow conditions from July to December 2013 and again in March 2014. We also sampled...
Ecological resources available to freshwater fish shift spatially, temporally and across life stages. To better understand how spatial-temporal availability of resources influence fish, I examined the phenologies of hatching and emergence of Coho Salmon (Oncorhynchus kisutch) in streams with contrasting and strongly defined seasonal thermal variability. The study streams included...
The specific objectives of this dissertation are to determine subsurface flow
behaviors across different antecedent wetness conditions from a top-down perspective
and to mechanistically assess the hydrological controls on DOC and N transport at the
hillslope and catchment scale. The study area is a small catchment where hillslopes
issue directly...
We examined the spatial and temporal variability of stream carbon dioxide (CO₂) and the drivers of these variations in a headwater catchment. To examine temporal variation and drivers, we measured stream and hyporheic pCO₂ at high temporal resolution over 11 months in a 95.9-ha forested headwater catchment in the Western...
Hyporheic zones are important regions that reside below and along the sides of streams. Within this region, several ecosystem services are provided including stream temperature regulation, habitats for a large variety of species, pollutant removal, and nutrient cycling. Exchange between the hyporheic zone and stream occurs across multiple scales, but...
The feedbacks between hydrology and biogeochemical cycling of nitrogen (N) are of critical importance to global bioavailable N budgets. Human activities are dramatically increasing the amount of bioavailable N in the biosphere, which is causing increasingly frequent and severe impacts on ecosystems and human welfare. Streams are important features in...
The glaciated coastal mountain watersheds that drain into the Gulf of Alaska (GOA) provide a model laboratory to explore the challenges of hydrological modeling and study the impact of climate and glacier cover change on regional hydrology. The region is data-sparse and contains a complex assemblage of topography and land...
Low-tech habitat restoration techniques, including Stage 0 treatments, are increasingly applied but often lack robust evaluation of their effects. In 2018, one kilometer of the South Fork McKenzie (SFMK) River, OR was modified to the Stage 0 condition for the benefit of ESA-listed Chinook by raising the incised channel to...
Studies of the effects of forest harvest on streams and fish have a long history in the Pacific Northwest. Results of this work have prompted development of new forest harvest practices that are more protective of these resources, but the effectiveness of these new practices has not been fully evaluated....
Land use and climate change occur simultaneously around the globe. Fully understanding their separate and combined effects requires a mechanistic understanding at the local scale where their effects are ultimately realized. Here we applied an individual-based model of fish population dynamics to evaluate the role of local stream variability in...
Water transient storage zones are hotspots for metabolic activity in streams although the contribution of different types of transient storage zones to the whole-reach metabolic activity is difficult to quantify. In this study we present a method to measure the fraction of the transient storage that is metabolically active (MATS)...