Abstract. Transient storage is a measure of the exchange of main channel flow with subsurface hyporheic flow and surface water dead zones. Hyporheic flow, in which river water enters the channel bed and banks to reemerge downstream, promotes biochemical processes that are important for water quality and aquatic habitat. Previous studies have quantified transient storage and hyporheic flow on small streams but were not specifically developed to identify both of these processes over long reaches of large rivers. We studied transient storage on the eighth-order upper Willamette River, which flows through highporosity gravel deposits conducive to hyporheic flow. We used main channel dye tracer studies and solute transport modeling to estimate transient storage on nine study reaches in a 26-km-long study area. We also took dye measurements

Water scarcity, land use conversion and cultural and ecosystem changes threaten the way of life for traditional irrigation communities of the semi-arid southwestern United States. Traditions are strong, yet potential upheaval is great in these communities that rely on acequia irrigation systems. Acequias are ancient ditch systems brought from the Iberian Peninsula to the New World over 400 years ago; they are simultaneously gravity flow water delivery systems and shared water governance institutions. Acequias have survived periods of drought and external shocks from changing economics, demographics, and OPEN ACCESSSustainability 2012, 4 2999 resource uses. Now, climate change and urbanization threaten water availability, ecosystem functions, and the acequia communities themselves. Do past adaptive practices hold the key to future sustainability, or are new strategies required? To explore this issue we translated disciplinary understanding into a uniform format of causal loop diagrams to conceptualize the subsystems of the entire acequia-based human-natural system. Four subsystems are identified in this study: hydrology, ecosystem, land use/economics, and sociocultural. Important linkages between subsystems were revealed as well as variables indicating community cohesion (e.g., total irrigated land, intensity of upland grazing, mutualism). Ongoing work will test the conceptualizations with field data and modeling exercises to capture tipping points for non-sustainability and thresholds for sustainable water use and community longevity.

Changes in water quality that occur as water flows along hyporheic flow paths may have important effects on surface water quality and aquatic habitat, yet very few studies have examined these hyporheic processes along large gravel bed rivers. To determine water quality changes associated with hyporheic flow along the Willamette River, Oregon, we studied hyporheic flow at six-bar deposit sites positioned between the main river channel and connected lentic alcoves. We installed piezometers and wells at each site and measured water levels and water quality in river, hyporheic and alcove water. Piezometric surfaces along with substrate characteristics were used to determine hyporheic flow path direction and hyporheic flow rate. At all sites, hyporheic flow moved from the river through bar deposits into alcove surface water. Stable isotope analysis showed little influence of upwelling groundwater. At a majority of sites, hyporheic dissolved oxygen and ammonium decreased relative to river water, and hyporheic specific conductance, nitrate and soluble reactive phosphorous increased relative to river water. At three sites, hyporheic temperature decreased 3-78C relative to river water; there was less temperature change at the other three sites. At the two sites with the highest hyporheic flow rates, hyporheic cooling was propagated into the alcove surface water. Hyporheic changes had the greatest effect on alcove water quality at sites with highly permeable substrates and high-hyporheic flow rates. The best approach to enhancing hyporheic flows and associated water quality functions is through restoring fluviogeomorphic channel processes that create and maintain high-permeability gravel deposits conducive to hyporheic flow.

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Agriculture-based irrigation communities of northern New Mexico have survived for centuries despite the arid environment in which they reside. These irrigation communities are threatened by regional population growth, urbanization, a changing demographic profile, economic development, climate change, and other factors. Within this context, we investigated the extent to which community resource management practices centering on shared resources (e.g., water for agricultural in the floodplains and grazing resources in the uplands) and mutualism (i.e., shared responsibility of local residents to maintaining traditional irrigation policies and upholding cultural and spiritual observances) embedded within the community structure influence acequia function. We used a system dynamics modeling approach as an interdisciplinary platform to integrate these systems, specifically the relationship between community structure and resource management. In this paper we describe the background and context of acequia communities in northern New Mexico and the challenges they face. We formulate a Dynamic Hypothesis capturing the endogenous feedbacks driving acequia community vitality. Development of the model centered on major stock-and-flow components, including linkages for hydrology, ecology, community, and economics. Calibration metrics were used for model evaluation, including statistical correlation of observed and predicted values and Theil inequality statistics. Results indicated that the model reproduced trends exhibited by the observed system. Sensitivity analyses of socio-cultural processes identified absentee decisions, cumulative income effect on time in agriculture, and land use preference due to time allocation, community demographic effect, effect of employment on participation, and farm size effect as key determinants of system behavior and response. Sensitivity analyses of biophysical parameters revealed that several key parameters (e.g., acres per animal unit or percentage of normal acequia ditch seepage) which created less variable system responses but which utilized similar pathways to that of the socio-cultural processes (e.g., socio-cultural or physical parameter change → agricultural profit → time in spent in agriculture → effect on socio-cultural or physical processes). These processes also linked through acequia mutualism to create the greatest variability in system outputs compared to the remainder of tests. Results also point to the important role of community mutualism in sustaining linkages between natural and human systems that increase resilience to stressors. Future work will explore scenario development and testing, integration with upland and downstream models, and comparative analyses between acequia communities with distinct social and landscape characteristics.