Interactive influences of climate change and ... - Wiley Online Library

Interactive influences of climate change and agriculture on aquatic habitat in a Pacific Northwestern watershed Sandra J. DeBano,1,† David E. Wooster,1 Jonathan R. Walker,2 Laura E. McMullen,2,4 and Donald A. Horneck3,5 1Department

of Fisheries and Wildlife, Hermiston Agricultural Research and Extension Center, Oregon State University, 2121 South First Street, Hermiston, Oregon 97838 USA 2ICF International, 615 Southwest Alder Street, Portland, Oregon 97205 USA 3Department of Crop and Soil Science, Hermiston Agricultural Research and Extension Center, Oregon State University, 2121 South First Street, Hermiston, Oregon 97838 USA Citation: DeBano, S. J., D. E. Wooster, J. R. Walker, L. E. McMullen, and D. A. Horneck. 2016. Interactive influences of climate change and agriculture on aquatic habitat in a Pacific Northwestern watershed. Ecosphere 7(6):e01357. 10.1002/ ecs2.1357

Abstract. Climate change and agricultural intensification are two potential stressors that may pose sig-

nificant threats to aquatic habitats in the inland Pacific Northwest over the next century. Climate change may impact running water through numerous pathways, including effects on water temperature and stream flow. In certain regions of the Pacific Northwest, agricultural activities, such as crop production, may become more profitable if water projects result in more irrigation water. If so, riparian buffers in these areas may be converted into cropland, which may in turn affect aquatic habitats through increases in sediment and agrochemical runoff into streams. We used currently available downscaled temperature and hydrology data in combination with a habitat quality framework developed for Pacific salmon and trout (Oncorhynchus spp.) to predict how different levels of each stressor, alone and in combination, may impact aquatic habitats in an inland Pacific Northwest watershed dominated by high-value agriculture— the Umatilla Subbasin. We developed spatially explicit predictions for how changes in stream flow and water temperature associated with three climate change scenarios and loss of riparian buffers in two agricultural intensification scenarios may impact aquatic habitats. We also examined the cumulative effects of the interaction of extreme climate change and agricultural intensification scenarios. Our results show that all three climate change scenarios are expected to primarily impact aquatic habitat in the upper Subbasin. In contrast, agricultural intensification scenarios did not have large impacts on temperature, but are predicted to affect other water quality variables in the lower Subbasin. A moderate scenario of agricultural intensification had relatively little effect on aquatic habitat, whereas the removal of all riparian buffers in agriculturally viable areas had a substantially negative effect on sediment, embeddedness, and large woody debris in the lower Subbasin. Interactions between the most extreme climate change and agricultural intensification scenarios reflected a complementarity of effects, with climate change primarily affecting the upper Subbasin and agricultural intensification primarily impacting the lower Subbasin. This work suggests that the Umatilla Subbasin and similar watersheds will present a challenging habitat for warm water-and pollution-intolerant species in the coming century.

Key words: agricultural intensification; climate change; low stream flow; Oncorhynchus; Pacific Northwest; runoff; stream temperature; Umatilla River. Received 9 October 2015; revised 27 January 2016; accepted 10 February 2016. Corresponding Editor: W. Cross. Copyright: © 2016 DeBano et al. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. 4 Present address: Columbia Gorge Community College, 400 East Scenic Drive, The Dalles, Oregon 97058 USA. 5 Deceased. † E-mail: [email protected]

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Introduction

increased air temperatures and to changes in precipitation amounts and patterns (Mantua et al. 2010, Isaak et al. 2012, Wu et al. 2012). The specific response of a basin’s hydrology will be influenced by the type of precipitation that currently drives its hydrograph. Pacific Northwest basins have been classified as snowmelt dominant, rain dominant, or transient (a mix of rain and snow) (Hamlet et al. 2013). The hydrology of rain and snow mixed basins, the dominant type of basin in mid-elevation areas (1000–2000 m) of the inland Pacific Northwest, has been predicted by some to be most strongly impacted by climate change as rain replaces snow as the dominant winter precipitation (Elsner et al. 2010, Dalton et al. 2013). In response, the annual hydrologic peak will occur earlier, resulting in lower summer stream flows (Elsner et al. 2010). Low stream flows may be exacerbated by increased evapotranspiration associated with higher air temperatures and by changes in summer precipitation, which may decline by up to 20–40% by the 2080s (Mote and Salathé 2010). Changes in stream temperature and flow are expected to negatively impact aquatic habitat quality for coldwater species (e.g., Poff et al. 2002, Heino et al. 2009, Wenger et al. 2011b). Indeed, several large-scale, regional studies suggest that Pacific salmon (Oncorhynchus spp.) will be particularly vulnerable to climate-induced changes in habitat (e.g., Mantua et al. 2010, Beechie et al. 2013). However, while these studies provide essential information on regional trends, they provide little resolution at the local watershed level. The complex and heterogeneous habitats of local watersheds require higher resolution predictions of the thermal and hydrologic impacts of climate change to guide management and restoration efforts (Mantua et al. 2010, Lawrence et al. 2014). In addition, with few exceptions (Wenger et al. 2011b, Walters et al. 2013, Lawrence et al. 2014), our knowledge of how climate change will interact with future changes of other stressors is limited. Stressors occurring at the local and regional level may exacerbate potential impacts of climate change (e.g., Walters et al. 2013). In response to a higher demand for food and biofuels from an expanding global population (Rosegrant et al. 2009), momentum is growing in the Pacific Northwest to increase agricultural production. In

Rivers and streams are key providers of multiple ecosystem services, including drinking water, food, transportation, and irrigation of agricultural crops (MEA 2005). Rivers and streams also serve as habitat for a variety of economically and culturally significant plant and animal life, and in the Pacific Northwest, USA, this includes several species of threatened and endangered salmonids (Huppert and Kantor 1998). Numerous human activities have negatively influenced water quality in the region over the last several hundred years, including logging, urban and suburban development, and agriculture (NRC 1996). The future of aquatic systems in the Pacific Northwest is predicted to continue to be heavily influenced by many of these locally generated stressors. However, global drivers, such as climate change, may pose even more substantial threats to aquatic habitats (Rieman and Isaak 2010) and may interact with local-scale stressors in ways that compound their effects (e.g., Walters et al. 2013). Climate change is expected to have profound impacts on various factors, including water temperatures and the hydrologic cycle, that influence the ability of aquatic systems to provide services (Frederick and Gleick 1999, Poff et al. 2002, CCSP 2008, Lettenmaier 2008). Evidence suggests that regional warming is already occurring in the Pacific Northwest (Mote 2003, Hamlet et al. 2007) and predictions from downscaled global models suggest that air temperatures will continue to rise (Mote and Salathé 2010, Beechie et al. 2013, Dalton et al. 2013). Elevated air temperatures are expected to lead to increased stream temperatures. Indeed, water temperatures in some streams in the Pacific Northwest have already shown detectable increases. For example, Isaak et al. (2012) found air temperature to be a strong driver of warming trends in more than 80% of unregulated rivers they examined. Increased stream temperatures are predicted to have multiple effects on aquatic life, not only impacting development, behavior, and mortality, but also by changing distributions of plant and animal communities with which aquatic organisms interact (Poff et al. 2002, Heino et al. 2009, Ruesch et al. 2012). Hydrological cycles are also expected to be impacted by climate change, both in response to v www.esajournals.org

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addition to increasing overall acreage of farming, there is also interest in converting dryland production systems to irrigated agriculture, which has much higher crop values relative to dryland production. These higher crop values not only result from increased yield of crops already grown in those areas, but irrigation also allows farmers to shift from relatively low-value crops (e.g., wheat) to crops that are an order of magnitude or greater in value (e.g., watermelon) (Howell 2001). Because of the economic benefits associated with irrigated crop production, increasing water availability for agriculture in the inland Pacific Northwest is a high priority. Indeed, recent efforts have focused on increasing the use of Columbia River water for irrigation in the region. In July 2015, the Oregon Legislature passed HB 5005 that provides $50 million in funding for water projects, including $11 million for pumps and equipment to provide water for increasing irrigated agriculture in one inland watershed, the Umatilla Subbasin, with resulting economic benefits for the region being estimated to exceed $1 billion a year (OWC 2015, Plaven 2015). As more water for agriculture is made available and if commodity prices continue to increase, then more land is expected to be farmed given the potential opportunity costs of not farming. This increase in agricultural intensification in the Pacific Northwest has the potential to continue to increase even in the face of the challenges associated with climate change (e.g., increased evapotranspiration, longer growing seasons), as relatively little of the Columbia River flow is allocated to agriculture (6%) compared to many of the nation’s major rivers (FCRPS 2001). Uncultivated lands, such as many riparian buffers in arid agroecosystems, may potentially be converted to cropland. In this case, streams and rivers may be negatively impacted through loss of riparian vegetation, which filters pollutants, shades water, and provides organic input into streams (Gregory et al. 1991). Given the likelihood that climate change and agricultural intensification may impact many rivers in the Pacific Northwest, it is imperative to understand how each acts singly and in combination to impact aquatic habitats in these watersheds. Thus, the objective of our study was to use locally derived data and expert opinion obtained through the last decade in combination with downscaled results from global climate models v www.esajournals.org

(GCMs) to examine how climate change and agricultural intensification may impact aquatic habitats in a watershed heavily dominated by high- value agriculture. We framed these efforts in the context of how these stressors may affect habitat of one of the region’s most sensitive groups, Pacific salmon and trout (Oncorhynchus spp.).

Methods The Umatilla Subbasin: present and future scenarios

The Umatilla Subbasin is a 5931 km2 watershed located within Umatilla and Morrow Counties in northeastern Oregon (DeBano and Wooster 2004, Fig. 1). The mainstem Umatilla River is 143 km, originating in the Blue Mountains at an elevation of 1768 m and emptying into the Columbia River at 79 m. The Subbasin experiences strong seasonal fluctuations in both temperature and precipitation with warm days, cool nights and little precipitation in the summer and colder winters, with average temperatures often only slightly above freezing. Most precipitation occurs during the fall, winter and spring. The climate of the Subbasin is also strongly influenced by elevation, with warm and dry conditions existing in the northwestern, low elevation portion of the Subbasin, where precipitation falls mainly as rain (~12 cm annually), whereas up to 140 cm of precipitation falls in high elevation areas of the Blue Mountains, primarily as snowfall. Approximately 42% of the area in the Subbasin is cropland, 42% is rangeland, 13% is forest, and 3% is urban. Agriculture is a major economic driver in the Subbasin, with the two counties ranking second and third in farm sales in the state and gross farm and ranch sales exceeding $480 million annually (ODA 2014). Irrigated crops raised in the lower Subbasin are of very high value compared to dryland crops of the upper Subbasin. Currently, only ~27% of all crop land in the Umatilla Subbasin is irrigated (DeBano and Wooster 2004). Historically, the Umatilla River supported populations of spring and fall Chinook salmon (O. tshawytscha), steelhead trout (O. mykiss), and coho salmon (O. kisutsh) (see Appendix S1 for a description of life stages). With the advent of large-scale irrigated agriculture in the early 1900s, all native anadromous salmonids except for steelhead were extirpated from the Umatilla Subbasin

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Fig. 1. Location of the Umatilla Subbasin in northeastern Oregon, USA, stream gauges, and land uses associated with stream reaches.

is believed to have been substantially reduced in the lower river due to channel engineering (DeBano and Wooster 2004). Thus, the resulting loss in discharge and increased water temperature associated with water withdrawal in the lower river not only make the river unsuitable habitat for juvenile salmonids (Appendix S1), but also have a major influence on the entire aquatic community (Miller et al. 2007, Brown et al. 2012, Wooster et al. 2016). In the future, agricultural intensification in the Umatilla Subbasin is expected to occur in concert with climate change, resulting in a heightened risk of losing multiple ecosystem services associated with aquatic systems located in its agroecosystems. As more water is made available in the future for local growers through water development projects like those recently funded by the Oregon Legislature, dryland production areas are expected to be converted to irrigated crop production (OWC 2015, Plaven

(Philips et al. 2000). A series of large water exchanges and restoration projects improved river conditions in the 1980–1990s, and Chinook and coho were reintroduced (Philips et al. 2000). All salmonid stocks in the Umatilla Subbasin are currently supplemented with hatchery production. While major improvements were made in the 1980–1990s and ongoing efforts at habitat improvement and restoration continue, salmonids and the aquatic systems of the Umatilla River are still of concern. Steelhead of the Umatilla River were listed as threatened in 1998, and although the lower river no longer completely dries during the irrigation season, up to 99% of stream flow is lost in the lower river in summer (Miller et al. 2007). Since much of the lower Umatilla River is alluvial, low flow conditions related to irrigation diversions may be exacerbated in some reaches where water is lost to the hyporheic zone, and ameliorated in others where water returns to the surface. However, hyporheic exchange v www.esajournals.org

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we examined interactions of the most extreme climate change and agricultural intensification scenarios. More specifics on each scenario are described below.

2015). When this occurs, dryland wheat producers may be able to earn more than ten times that amount by converting to irrigated agriculture (e.g., the value of wheat is ~$200–400 per acre compared to over $10,000 per acre for watermelon; Connor et al. 2002, Galinato et al. 2014, ODA 2014). In such a case, the incentive for farming any uncultivated area will greatly increase, potentially resulting in fewer agricultural producers implementing or maintaining riparian buffers on their land. To understand how climate change and agricultural intensification may impact aquatic habitats in the Umatilla Subbasin, both individually and in concert, we examined how changes in stream flow and water temperature associated with three climate change scenarios (high, moderate, and low impact scenarios) and riparian buffer loss associated with two agricultural intensification scenarios (one extreme and one moderate) impacted aquatic habitats. Salmonids in the Umatilla Basin are expected to be sensitive to both climate change and agricultural intensification, with juvenile stages being particularly vulnerable (Appendix S1). In addition, to understand the range of effects that may result if both stressors occur, from best case to worst case,

Environmental attributes examined

Because of their conservation concern and the key role that salmonids play in Pacific Northwest watersheds, we chose to focus on environmental attributes known to impact salmonids at various life stages (Appendix S1). Specifically, we selected nine of 45 environmental attributes used in the Ecosystem Diagnosis and Treatment model (EDT), a spatially explicit model used to simulate salmonid responses to restoration and other human activities (Lichatowich et al. 1995, Lestelle et al. 2004). We selected attributes we believed would be most strongly affected by climate change and agricultural intensification (Table 1; Appendix S2), and used those attributes as a general surrogate for stream condition, since conditions associated with suitable salmonid habitat are also likely to support other biota in aquatic systems not heavily impacted by humans (Pess et al. 2002, Feist et al. 2003). In addition, the EDT attribute rating system was used in a Subbasin planning effort

Table 1. Environmental attributes used to describe current conditions in the Umatilla Subbasin in eastern Oregon, USA and conditions under different climate and agricultural intensification scenarios (see Appendix S2 for details on estimating values for each attribute). An “X” in the column indicates that the attribute was included in the scenario development. Climate change

Environmental attribute and brief description Dissolved oxygen (DO)†—average dissolved oxygen within the water column Embeddedness (Emb)‡—extent that larger cobbles or gravel are surrounded by or covered by fine sediment Fine sediment (FnSedi)‡—% substrate comprised of fine sediment Low flow (FlwLow)§—average daily flow during the normal low flow period Metals/pollutants in sediments/soils (MetSedSis)†—the extent of heavy metals and other toxic pollutants within the stream sediment and/or soils adjacent to the stream channel Riparian function (RipFunc)‡—intactness of stream and floodplain linkages Summer water temperature (TmpMonMx)§—a function of the maximum water temperatures during the summer and the length of time those temperatures are above certain thresholds Turbidity (Turb)†—the severity of suspended sediment episodes within the stream reach Wood (WdDeb)‡—the amount of large woody debris within the reach

Agricultural intensification

Both

X X X

X X X

X

X X

† Attributes not previously estimated. ‡ Attributes estimated using values established through group consensus of local scientists and land managers in 2004. § Attributes previously estimated, but re-estimated using new methods described in the text.


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for the Northwest Power and Conservation Council (NWPCC) completed in 2004 (DeBano and Wooster 2004). At that time, local scientists and managers worked together to divide the Subbasin into 284 discrete reaches and to characterize each reach relative to most environmental attributes used in the EDT. Decisions on values for each reach were made on available data and consensus of professional judgment (described in DeBano and Wooster 2004). EDT environmental attributes are characterized by ranks that represent different levels of habitat suitability for salmonids. We used the EDT ranking system for all variables except for low flow. For low flow estimates, we used flow values generated by the variable infiltration capacity (VIC) hydrological model (described in more detail below) and calculated percent change compared to current conditions. Attributes are briefly described in Table 1, with more descriptions of attribute rating scales in Appendix S2, Lestelle (2005), and Lestelle et al. (2004). Of nine attributes examined, we used values estimated for current conditions in the previous Subbasin planning effort for four attributes (Table 1). For two attributes, low flow (FlwLow) and summer water temperature rank (TempMonMx), which had been estimated in the previous effort, we used new methods to establish current values and to predict future conditions (described below). The three remaining attributes had not been previously defined. We quantified reach- specific values for each attribute in Table 1 for current conditions and future scenarios (as described below), and calculated means and coefficients of variation for each attribute and mapped results using ArcGIS 10.1.

between the magnitude of low flow and high temperature in western North American streams. Although increases in winter and spring flooding events are also an important factor influencing aquatic habitat (Mantua et al. 2010), we chose to focus on summer flow because of its current limiting role in the Subbasin (DeBano and Wooster 2004). For stream temperatures, we used the EDT ranking system because it takes into account both the mean maximum daily temperature and the number of days above certain threshold temperatures (Appendix S2). Salmonids, as well as other aquatic life, are not only sensitive to temperature extremes, but also the length of time those extremes are encountered. Prolonged exposure to temperatures above this threshold can lead to higher mortality, faster growth rates, altered life histories, and smaller sizes in salmonids and other aquatic life (Richter and Kolmes 2005, Brown et al. 2012). Stream flow.—To characterize low flow, we used the Western US Stream Flow Metric Dataset to predict mean summer flow for current and future climate scenarios. To avoid including spring snow melt in summer values, the data set defines the beginning of summer individually for each stream segment and each year as the first day after June 1 when flows fell below the mean annual value. Summer periods ended on September 30, regardless of the starting date. Flow values were generated using the VIC macroscale hydrologic model (http://www.fs.fed. us/rm/boise/AWAE/projects/modeled_stream_ flow_metrics.shtml), which predicts several aspects of the hydrologic regime in the Pacific Northwest, including mean summer flows (Wenger et al. 2010). VIC uses meteorological data from GCMs associated with the A1B greenhouse gas emissions trajectory, which assumes moderate accumulation of atmospheric greenhouse gases (IPCC 2007). We used current (1978–1997) and six climate change scenarios. A scenario with the composite of 10 IPCC models for 2040 and 2080 was used to represent a moderate scenario (referred to hereafter as “Mod 2040” and “Mod 2080”). The 10 models used in the ensemble had the lowest bias in simulating observed climate change in the Pacific Northwest (Littell et al. 2011). A scenario with the MIROC.3.2 GCM for 2040 and 2080 projects a more severe

Developing climate scenarios

We characterized aquatic environments under climate change scenarios by altering two attributes, FlwLow and TempMonMx (Table 1). We chose low flow to be the primary hydrological variable of interest because, in our area, as in much of the western United States, low flows occur in summer and are limiting for many forms of aquatic life (Harvey et al. 2006, Dewson et al. 2007). Low flows can exacerbate passage barriers, increase pollutant concentrations, and raise water temperatures. In fact, Arismendi et al. (2013) found a strong negative relationship v www.esajournals.org

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scenario in the Pacific Northwest, with warmer and drier summers than the ensemble mean (referred to hereafter as “High 2040” and “High 2080”). The PCM1 GCM projects the least severe climate change scenario for the Pacific Northwest as a whole, with cooler and wetter summers than the ensemble mean (referred to hereafter as “Low 2040” and “Low 2080”). Flow metric files were used in combination with stream segments defined in the National Hydrography Dataset Plus (www.horizon-systems.com/nhdplus/) for analyses, and we used data at 1/8th of a degree. Historical data produced by VIC were “ground-truthed” using information available about flows in the Umatilla Subasin, including expert knowledge and flow data collected by the Bureau of Reclamation (www.usbr.gov/pn/ hydromet/umatilla/umatea.html). For example, VIC does not take into account human diversion activities, which heavily impact the lower 50 km of the Umatilla River (Miller et al. 2007, Brown et al. 2012). In cases where reach-level values generated by the VIC model were contradicted by current knowledge of the system, future values generated by VIC were not used given that they would be based on inaccurate current values. Instead, for modeling water temperature (see Stream Temperature Modeling section), we used estimated values for 26 reaches based on gauging stations on the Umatilla River and expert knowledge to replace inaccurate VIC values. Butter Creek was the only tributary with no gauges, but flows on the lower sections are known to be subsurface during summer (DeBano and Wooster 2004). Flow values for these 26 reaches were kept constant in regression modeling of water temperatures for all future climate scenarios because reaches are either currently completely dry in summer and thus will not worsen under climate change scenarios (e.g., lower Butter Creek) or because water management practices involving reservoirs and exchanges are likely to result in similar flow levels in the future (e.g., the lower Umatilla River). For all other reaches, predicted values under different climate change scenarios are expressed as percent decreases relative to current conditions. Stream temperature modeling.—We estimated water temperatures for each reach by developing a multiple regression model following Isaak et al. (2010). However, instead of using parametric v www.esajournals.org

regression, we used a nonparametric multiple regression technique (NPMR) (Hyperniche Version 2.0, McCune and Mefford 2009) to develop a model to estimate the EDT summer water temperature rank (TempMonMx) for each reach based on four independent variables: air temperature, radiation, flow, and elevation. NPMR is better suited for addressing ecological phenomena than other commonly used models that are additive and often assume linear or sigmoid response shapes (e.g., multiple linear regression or logistic regression) (McCune 2006). In fact, the relationship between air and stream temperature is often better described by nonlinear functions, especially at higher air temperatures, when linear regressions may overestimate stream responses to climate change (Mohseni and Stefan 1999, Mohseni et al. 1999, Mayer 2012). Unlike traditional regression approaches, NPMR effect ively models responses to multiple environmental variables using nonparametric curve-fitting techniques, with the effect of each variable depending on the value of other variables (McCune 2006). Instead of arriving at a global model, in which coefficients are derived in a fixed mathematical equation assumed to apply throughout the sample space, nonparametric multiplicative regression relies on the data to generate local models, with the model form specified using a local multiplicative smoothing function (McCune 2011). For our data, we used a local mean estimator and Gaussian weighting function in a forward step-wise regression, in which data points closer to the target point received greater weight. A cross-validated R2 (xR2) was used to evaluate model fit; xR2 is more conservative than traditional R2 because, when calculating the residual sums of squares, each individual data point is not used for calculating the estimate of the response of that point (McCune 2011). When developing the regression model, we used 57 reaches in the Umatilla Subbasin that are equipped with one or more continuously recording water temperature gauges (http://data. umatilla.nsn.us/waterquality/temperature.aspx) (Fig. 1). For reaches with multiple gauges, averages among gauges were used. Data were downloaded and TempMonMx ranks were established based on an algorithm that takes into account the maximum daily temperature, as well as the 7


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uration of temperatures above certain threshd olds during July and August for all years for which data were available (see Appendix S2 for a description of temperature ranks). Values for reach-specific independent variables used in the temperature regression were determined both for current conditions (for developing the model) and for future conditions (for predicting water temperature under future scenarios). Downscaled air temperatures for the Umatilla Subbasin were obtained from the University of Idaho (http://nimbus.cos.uidaho.edu/ MACA/) through their Multivariate Adaptive Constructed Analogs (MACA) Statistical Downscaling Method project (Abatzoglou and Brown 2012). The MACA project has downscaled model output from 14 GCMs of the Coupled Intermodel Comparison Project 5 (CMIP5). Output is downscaled to 4 km resolution for historical GCM forcings (1950–2005) and for future Representative Concentration Pathways (rcp) scenarios (2006–2100). Because the models and their method of incorporating emission scenarios are different than those used for the VIC modeling, we used the visualization tool on the MACA website to select three models that give low, medium, and high temperature predictions for our region. The inmcm4 model was selected to simulate low warming, the bcc-csm1-1 model was selected to simulate moderate warming, and the HadGEM2-CC model was selected to simulate high warming. Data were available for two emission scenarios, a low scenario (RCP4.5) and high scenario (RCP8.5). We selected the high emission scenario (RCP8.5), which represents a future with no climate action and high emissions. Current conditions were characterized using “historical data” generated with the moderate GCM (bcc-csm1-1) as a monthly average. Data generated were the mean monthly daily maximum air temperatures (tasmax) in a vector format with temperature points dispersed evenly across the study area. For the multiple regression, tasmax for July was used; the mean for 1985–2005 was used to describe current conditions, the mean from 2030–2050 was used to describe 2040 conditions, and the mean from 2070–2090 was used to describe 2080 conditions. Radiation for each reach was estimated using the approach described by Nagel et al. (2009), with reach-specific radiation being dependent v www.esajournals.org

upon (1) shading by vegetation within the focal reach and the focal reach’s catchment size (which reflects the role of stream width in affecting radiation) and (2) accumulating effects of shading of upstream reaches on the focal reach. Details are described in Appendix S3. We used mean summer flow obtained from the VIC model (described above) to characterize current conditions. Reach-specific elevation was determined using the most recent version of the USGS Digital Elevation Model (http://ned.usgs. gov/). We selected the NPMR model that explained the most variation in TempMonMx, regardless of the number of independent variables (1–4), as long as the model explained >5% of variation than a simpler model. This model was then used as a predictor model to estimate water temperature for each reach in the Umatilla Subbasin.

Developing agricultural intensification scenarios

We modeled two future agricultural scenarios. One, which we term the Doomsday Scenario, was designed to investigate what we consider to be the most extreme agricultural intensification scenario that could impact riparian areas in the Umatilla Subbasin. In this scenario, increased value of agricultural commodities results in all uncultivated areas in currently farmed lands, including woody and herbaceous riparian buffers, becoming cultivated. We limited the conversion of riparian areas to currently farmed areas (Fig. 1) because the primary reasons why certain areas are not cultivated in the Subbasin relate to a combination of low rainfall, the expense of transporting water to the area, topography, soil depth, and landownership (e.g., federal, state, and tribal lands). These factors make it unlikely that many areas in the upper watershed would be cultivated, even with increased value of crops. Although it may be unrealistic to assume that all riparian buffers would be removed in currently farmed areas, the Doomsday Scenario is designed to provide an estimate of the value of existing buffers in terms of stream condition by understanding what conditions would be if no buffers were present. We also modeled a less extreme scenario of agricultural intensification, the 75% Agricultural Intensification Scenario. In this scenario, as in the Doomsday Scenario, increasing value of

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agricultural commodities provides an incentive for farmers to convert 75% of their existing riparian buffers to cropland. This reduction is incorporated into the model as a change of width, rather than length, because of the difficulty of cultivating land at the very edge of the stream. As with the Doomsday Scenario, the reduction in buffer width only occurs on land currently farmed. Attributes examined and current conditions.—We examined eight attributes related to agricultural intensification (Table 1). Of these, current reach- specific estimates were available for four attributes, riparian function (RipFunc), woody debris (WdDeb), embeddedness (Emb), and fine sediment (FnSedi), as part of the subbasin planning effort (DeBano and Wooster 2004). Current summer water temperature rank (TmpMonMx) was determined using the regression technique described above. Three attributes were not defined for the Umatilla Subbasin in previous efforts: dissolved oxygen (DO), metals and pollutants in sediments and soils (MetSedSis), and turbidity (Turb). We estimated current conditions of these attributes, which all relate to agriculturally derived chemical inputs, by considering five factors: slope, precipitation, production type, an index of the intensity of the production system, and the estimated current riparian function. See Appendix S4 for a description of methods. Estimating conditions under future agricultural scenarios.—As stated above, attributes under future agricultural scenarios were only changed for reaches located in agricultural areas. To estimate the future conditions for RipFunc under the Doomsday Scenario, we assumed that the conversion of all riparian buffers to cropland will result in all current riparian function being lost in agricultural areas in the Subbasin. Thus all RipFunc values were changed to the worst case rank of “4” for reaches located in agricultural areas (Lestelle 2005). For the 75% Scenario, we decreased function by increasing the current RipFunc values by one rank (Lestelle 2005). Any values greater than 4 were truncated to 4. To estimate the future conditions for WdDeb under the Doomsday Scenario, we assumed that the conversion of all riparian buffers to cropland will result in the loss of all large woody debris in agricultural areas in the Subbasin. Thus v www.esajournals.org

all WdDeb values were changed to the worst case rank of 4 for reaches located in agricultural areas (Lestelle 2005). Although some woody debris may move into the lower subbasin from the upper subbasin, we assume that most woody debris contributions will come from more nearby areas. We estimated future conditions under the 75% Scenario for large woody debris by taking the midpoint between current conditions and the Doomsday Scenario. To estimate the future conditions under the Doomsday Scenario for the three variables associated with agrochemical inputs (DO, MetSedSis, Turb), we assumed that all current riparian function would be lost in agricultural areas in the Subbasin, so we simply used the values for the estimated stream conditions in the absence of filtering effects that we calculated in establishing current conditions (See Appendix S4). As with WdDeb, we estimated future conditions under the 75% Scenario for these four variables by taking the midpoint between current conditions and the Doomsday Scenario. We chose not to use simple linear relationships to describe the effect of buffer reduction on these attributes because past work has suggested that the relationship between riparian buffer width and variables associated with stream condition are not linear, with large effects not necessarily manifested until large reductions of width occur (Castelle and Johnson 2000, Dosskey 2001, Wooster and DeBano 2006). Future reach-level conditions for the Doomsday Scenario for Emb and FnSedi were estimated based on current values of the attributes and current and future values of riparian condition (See Appendix S5). As with WdDeb, we estimated conditions under the 75% Scenario for Emb and FnSedi by taking the midpoint between current conditions and the Doomsday Scenario conditions. Any values under either scenario that were greater than 4 were truncated to 4. We expected TmpMonMx to increase under the Doomsday Scenario because the removal of all riparian vegetation would result in the loss of woody vegetation in riparian areas that currently shade streams. Increases in solar radiation should lead to increased water temperature. To estimate changes in water temperatures, we used the same multiple regression model described in the climate change scenario section, but changed 9


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the solar radiation term through manipulation of shade for the Doomsday Scenario only. The 75% Scenario will not result in water temperature changes because the change is in buffer width, so that 25% of the current buffers closest to the stream (and providing the shading effect) will remain intact.

extent of flow decreases, and High 2040 showed the greatest range in reach-level low flow values (Table 2; Fig. 2). All 2080 scenarios showed larger reach-level flow reductions compared to 2040 scenarios, but Low 2080 showed the largest mean decrease in low flow and the widest spatial distribution of reduced flow (Table 2; Fig. 2). For all scenarios, most reaches with losses of flow greater than 10% were located in the upper portion of the Subbasin (Fig. 2).

Interaction scenarios

We examined four climate change × agricultural intensification interaction scenarios: Low 2080 × 75% Scenario, High 2080 × 75% Scenario, Low 2080 × Doomsday, and High 2080 × Doomsday. In the two climate change × Doomsday interaction scenarios, water temperature was impacted by changes in both radiation and air temperature. We used the NPMR model described above to model the effect that changes in radiation and air temperature had on water temperature ranks. For interactions involving the 75% Scenario, water temperatures took on the values associated with the interacting climate change scenario, since there was no loss of shading effect of the 75% Scenario, and therefore no changes in solar radiation input.

Predicted effects of climate change on stream temperature

Four variables input into the NPMR model to predict stream temperature were air temperature, radiation, flow, and elevation. The MACA downscaled data showed air temperatures increasing basin-wide under all climate change scenarios, with more extreme scenarios associated with higher temperatures and more warming occurring in 2080 as compared to 2040 (Table 3, Fig. 3). Mean increase at the reach level ranged from 1.9°C in the Low 2040 scenario to 7.7°C in the High 2080 scenario (Table 3). Solar radiation estimates for current conditions averaged 1062.9 ± 46.4 MJ·m−2·yr−1 (Fig. 4) and showed expected patterns of increased radiation in higher order reaches due to increased stream size and accumulating effects of upstream radiation. Smaller scale variation associated with shading by riparian vegetation is also evident in upper reaches of the Subbasin (Fig. 4). Reach-level elevation varied from 82 to 1211 m, with an average of 692 m. A significant NPMR model for current conditions using 57 gauging stations for stream temperature, incorporating all four predictor variables, and explaining 61% of the variation in current conditions was selected (Table 4). The selected NPMR regression model developed for current conditions was used to predict stream temperature ranks under future climate change scenarios by changing air temperature and flow, as described above. Results showed that summer water temperature at the reach level, reflected as a ranked EDT attribute, increased under all climate change scenarios (Table 5). For 2040 scenarios, Low 2040 showed the smallest increase in temperature rank, and High 2040 the largest. All 2080 scenarios showed increased stream temperature ranks compared to 2040

Results Predicted effects of climate change on stream flow

Predictions of current summer flow by the VIC historical condition scenario (Fig. 2) were consistent with observed flows in the Umatilla Subbasin with three exceptions. The lower 50 km of the mainstem Umatilla River are heavily influenced by water withdrawal (Philips et al. 2000), which were not reflected in VIC generated values (Fig. 2). In addition, flow in the lower reaches of two tributaries, Birch Creek, and Butter Creek, were overestimated by the VIC model. The lower reaches of Birch Creek and most of the lower and east fork of Butter Creek typically dry completely in summer (DeBano and Wooster 2004). VIC generated values for these reaches (delineated with an “inaccurate data” label in Fig. 2) are not reported for future scenarios since they are based on inaccurate current values. For 2040 scenarios, Low 2040 showed the largest mean decline in average summer low flow per reach compared to current conditions, whereas Mod and High 2040 showed the greatest spatial v www.esajournals.org

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Fig. 2. Mean summer low flows for current conditions, and reaches predicted to experience >10% flow reductions compared to current conditions in the Umatilla Subbasin in northeastern Oregon, USA for six climate change scenarios—a low, moderate, and high warming scenario for 2040 (Low 2040, Mod 2040, High 2040) and a low, moderate, and high warming scenario for 2080 (Low 2080, Mod 2080, High 2080). Reaches labeled as “inaccurate data” were not predicted well for current conditions under the VIC model (see text, for more detail).


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DEBANO ET AL. Table 2. Current conditions and predicted changes in mean low flow in July in the Umatilla Subbasin in eastern Oregon, USA under six climate change scenarios—a low, moderate, and high warming scenario for 2040 (Low 2040, Mod 2040, High 2040) and a low, moderate, and high warming scenario for 2080 (Low 2080, Mod 2080, High 2080). Means and CVs are calculated for the 258 reaches; 26 reaches that were not predicted well for current conditions by the VIC model are not included. See text for more detail. Scenario Current Low 2040 Mod 2040 High 2040 Low 2080 Mod 2080 High 2080

Mean (± CV) flow per reach (cfs)

Mean % decrease (± CV)†

Range in % decreases in flow†

% of reaches with declines >10%†

40.87 ± 2.43 37.44 ± 2.42 37.46 ± 2.44 37.83 ± 2.43 35.20 ± 2.44 35.96 ± 2.44 36.87 ± 2.44

… 8.59 ± 0.16 7.94 ± 0.30 7.06 ± 0.43 13.88 ± 0.17 11.63 ± 0.29 9.31 ± 0.35

… 3.72 to 12.95 −1.25 to 15.11 −6.25 to 17.32 3.75 to 21.78 −2.50 to 21.58 −6.25 to 20.14

… 8.14 20.16 18.67 92.64 75.97 37.98

† Compared to current conditions.

s cenarios (Table 5), but High 2080 and Low 2080 warming were similar. The spatial distribution of stream temperature changes shows that, for all climate change scenarios, the highest quality thermal habitat for coldwater species, located in the upper portion of the Subbasin (e.g., the upper mainstem Umatilla River, North and South Forks, Meacham Creek), have essentially disappeared with much of the Subbasin dominated by temperatures likely to lead to thermal stress or lethal conditions for sensitive coldwater species (Fig. 5). EDT ranks above 2.5 (Fig. 5) represent sub-lethal and incipient lethal ranges for salmonids, and exceed temperature criteria suitable for salmonid rearing (Appendix S2).

high temperatures are the most serious threats associated with reaches located in agricultural areas (Fig. 1). Increased agricultural intensification is expected to amplify differences between upper and lower reaches for most variables. As part of the assumptions of the scenario itself, riparian vegetation under the Doomsday Scenario is predicted to disappear in agriculturally impacted areas, leading to the worst case values for the riparian function attribute. Because woody debris is directly associated with presence of riparian vegetation, that attribute shows a concomitant decrease. However, the impact of riparian function on other attributes was variable (Fig. 6) because of the differential effect of several factors, including current conditions, how riparian function influenced input of pollutants, and the morphological and physical characteristics (e.g., substrate) of particular reaches (Appendix S5).

Predicted effects of agricultural intensification scenarios

Estimates for current conditions in the Subbasin (Fig. 6) show that sedimentation, riparian function, large woody debris, and

Table 3. Current conditions and predicted changes in reach-level mean air temperature in July in the Umatilla Subbasin in eastern Oregon, USA under six climate change scenarios—a low, moderate, and high warming scenario for 2040 (Low 2040, Mod 2040, High 2040) and a low, moderate, and high warming scenario for 2080 (Low 2080, Mod 2080, High 2080). Means and CVs are calculated for the 284 reaches. Scenario Current Low 2040 Mod 2040 High 2040 Low 2080 Mod 2080 High 2080

Mean ± CV (°C)

Mean increase ± CV (°C)

Range (°C)

29.30 ± 0.09 31.22 ± 0.08 32.05 ± 0.08 32.56 ± 0.08 34.38 ± 0.07 35.67 ± 0.07 37.05 ± 0.07

… 1.92 ± 0.02 2.75 ± 0.01 3.26 ± 0.02 5.08 ± 0.01 6.37 ± 0.02 7.75 ± 0.01

23.81–32.94 25.74–34.84 26.55–35.69 27.05–36.32 28.89–38.08 30.15–39.19 31.53–40.65


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Fig. 3. Mean air temperature for July for current conditions in the Umatilla Subbasin in northeastern Oregon, USA, and for a low warming scenario for 2040 (Low 2040) and 2080 (Low 2080) and a high warming scenario for 2040 (High 2040) and 2080 (High 2080).


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Fig. 4. Estimated radiation under (a) current conditions and (b) the Doomsday Scenario in the Umatilla Subbasin in northeastern Oregon, USA. The 75% Agricultural Intensification Scenario is not expected to impact solar radiation because only the width, not length, of buffers is expected to change.


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intensification. Only water temperature ranks could be impacted via two different mechanisms by the two stressors. For climate change, water temperature could be impacted by changes in air temperature and flow, whereas for agricultural intensification water temperature could be impacted by effects on solar radiation. However, water temperatures in the interaction scenarios (Doomsday × Low 2080 and Doomsday × High 2080) showed little difference from scenarios involving climate change only (Table 5) because of the minimal impact of riparian shading in the lower basin. The distribution of effects of the two stressors shows a high degree of spatial complementary, with effects of agricultural intensification primarily limited to the lower basin (Fig. 1) and the largest effects of climate change manifested in the upper basin (Fig. 5).

Table 4. Nonparametric multiplicative regression model results for the effect of one to four predictor variables on summer water temperature. All models are significant at P 2.5; see Appendix S2) are riparian function, large woody debris, sediment, and embeddedness (Fig. 6). Our assumption that riparian vegetation plays an important role in filtering out pollutants from agricultural runoff is supported by numerous studies (Castelle et al. 1994, Castelle and Johnson 2000, Dosskey 2001) that suggest that even very narrow buffers of riparian vegetation can substantially filter out sediment and other pollutants; for example, buffers ranging from 0.5 m to 50 m retained from 40% to 100 of sediment entering from cultivated fields (Dosskey 2001). However, the effectiveness of riparian buffers can be highly variable, depending on various factors including type of vegetation, stream size, land use legacies and instream condition (Dosskey 2001, Greenwood et al. 2012). As future research refines our knowledge of the filtering capacity of riparian vegetation in the Umatilla Subbasin, predictions can be easily modified using the algorithm and existing data set. In contrast to all other aquatic habitat variables, the conversion of riparian vegetation in agricultural areas in the lower Umatilla Subbasin had minimal effects on stream temperatures, even with the elimination of all riparian vegetation in agricultural areas that occurred with the Doomsday Scenario. Although the effect of shading provided by riparian vegetation on stream temperature can be substantial in some systems (Johnson 2004, Groom et al. 2011), other factors such as surface area of water exposed to the ambient environment and type of streambed sediment can swamp out influences of shade in stream energy budgets, making stream temperatures unresponsive even with complete removal of shading riparian vegetation (Janisch et al. 2012). In addition, shading impacts on stream temperature are expected to decline as stream order increases and less of the water’s surface is shaded by adjacent vegetation (Vannote et al. 1980). Although parts v www.esajournals.org

Interacting stressors and spatial complementarity

Few studies have examined how climate change is expected to interact with other future stressors to impact freshwater habitat in the Pacific Northwest, except for work investigating how climate change will affect the range of invasive fish species and their potential interaction with native salmonids (Wenger et al. 2011b, Lawrence et al. 2014). While several studies have examined the degree to which restoration of riparian vegetation may offset expected negative impacts of climate change on regional streams and their biota (Battin et al. 2007, Cristea and Burges 2010, Lawrence et al.

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2014), ours is the first to examine the potential negative effect of riparian buffer reduction that may result from increased agricultural intensification. Although stream restoration in the Pacific Northwest is a high priority for many stakeholders, including those in the Umatilla Subbasin, a combination of factors faced by watersheds similar to the Umatilla Subbasin may provide economic incentives for reducing or eliminating these buffers, especially in lower elevation lands suitable for cultivation that are not governed by minimum buffer regulations that apply to forested headwater streams. If water availability increases and farmers can shift from relatively low-value crops to high- value ones, the cost and benefit analysis underlying buffer creation and maintenance on private property will change to favor the conversion of buffers to crop production. If this occurs, our study suggests that agricultural intensification and climate change effects in the Umatilla Subbasin will, to a great extent, show a high degree of spatial complementarity. Like Battin et al. (2007), we found climate change impacts are expected to be most pronounced in the upper watershed; one potential mechanism underlying this pattern is that warming air temperatures at higher elevations results in both less snow accumulation in winter and earlier snowmelt which, in turn, result in lower and warmer summer flows in low-order streams (Battin et al. 2007). Meanwhile, agricultural intensification is expected to most strongly affect the lower Subbasin, a pattern common in many western US watersheds, where agricultural activity is often primarily located at lower elevation areas that are suitable for cultivation. Understanding the spatial distribution of multiple stressors in watersheds (e.g., whether they are overlapping or complementary) is key to informing management of aquatic systems (Wooster et al. 2012). Spatial complementarity of multiple stressors may indicate additive effects rather than synergistic. While complementary effects in the Umatilla Subbasin may be beneficial in the sense that no particular area of the watershed is highly degraded by both stressors, it also means that the spatial extent of human disturbance is more widespread, with virtually all parts of the watershed expected to experience declines in quality, albeit in different ways. v www.esajournals.org

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However, the lack of overlap of stressors may be beneficial to coldwater species. If the upper watershed is not converted to agriculture and riparian buffers remain intact, riparian vegetation may be able to ameliorate some of the negative effects of warming temperature. For example, Arismendi et al. (2012) observed that streams in western North America with more riparian vegetation and higher baseflows were less likely to show warming trends. Our results suggest that the reaches most likely to be influenced by climate change may also be those most likely to retain the buffering effects of riparian vegetation, potentially weakening the predicted relationship between air temperature and water temperature. With regard to the magnitude of effect of each stressor, our results suggest that aquatic habitats used by coldwater species will be more negatively impacted by climate change than by the loss of shade associated with buffer removal in the Doomsday Scenario. Steen et al. (2010) found similar results in a study of fish communities in the Great Lakes region. Although they examined the interaction of increased urbanization with climate change instead of agricultural intensification, they found warmer stream temperature associated with climate change would have larger effects on fish communities than land cover changes associated with urbanization. In our case, agricultural intensification is expected to occur in areas already fairly degraded by agriculture, and only the Doomsday Scenario involved removing all riparian buffers in these areas. Although this scenario is theoretically possible because the maintenance of riparian buffers next to streams is not regulated in nonforested lands in Oregon, it may be unlikely for several reasons, including the reluctance of farmers to cultivate land right up to the water’s edge due to bank instability and saturated soils. Thus, the likelihood of a scenario as severe as the Doomsday one occurring may be relatively small. In contrast, all climate change scenarios we examined resulted in the degradation of prime coldwater habitat in the Subbasin.

Implications for salmonids and restoration

Although the goal of our study was to examine aquatic habitat generally, we used a salmonid-based context to frame our study, both because of their predicted sensitivity to June 2016 v Volume 7(6) v Article e01357

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changes in aquatic habitat and because more is known about salmonids than any other form of aquatic life in Pacific Northwest systems. Similar to other watersheds located in the Columbia Basin, most salmonids in the Umatilla Subbasin primarily use the upper watershed for spawning and rearing (Battin et al. 2007, Appendix S1). Although affected by some stressors (e.g., railroads, channelization, road building, timber harvest), these reaches remain in relatively good condition and support spawning and rearing habitat for a number of species of concern, including threatened steelhead, bull trout (Salvelinus confluentus), spring Chinook (O. tshawytscha), and Pacific lamprey (Entosphenus tridentatus) (DeBano and Wooster 2004, Close et al. 2009). Our work is consistent with other studies in the Pacific Northwest suggesting that climate-impacted watersheds will present challenging habitat for salmonids and other coldwater species in the coming century (e.g., Battin et al. 2007, Cristea and Burges 2010, Mantua et al. 2010, Ruesch et al. 2012, Wu et al. 2012). Climate change effects on salmonids in the Umatilla Basin may be even more extreme than our analysis suggests because we did not examine other factors predicted to change that may impact aquatic habitat, including altered timing of peak runoff, flooding events, and changes in interspecific interactions (Wu et al. 2012, Beechie et al. 2013). Responses of fish to altered temperatures and hydrology may result in expansion, contraction, or movement of species ranges, with individual species responding in different ways (Wenger et al. 2011a) and more research is needed to understand how thermal and hydrological changes will impact specific salmonid species in the Umatilla Subbasin and their interspecific interactions. Our study not only predicts that salmonids will be exposed to warming summer water temperatures and low flow conditions associated with climate change in the upper subbasin, but that they may also experience negative effects under agricultural intensification in the lower subbasin if riparian buffers are reduced. Salmonids are sensitive to increases in sediment and pollutants associated with agriculture, including pesticides and fertilizers (Newcombe and Macdonald 1991, NRC 1996, Jensen et al. 2009, v www.esajournals.org

Chapman et al. 2014). Sediment input affects salmonids by decreasing spawning success, reducing prey detection and feeding rate, smothering eggs, entrapping alevins, and settling in interstitial spaces of cobble, which are used by juveniles for cover (NRC 1996, Jensen et al. 2009, Chapman et al. 2014). Sedimentation is currently a concern for the Umatilla River, which is 303(d) listed for sediment or turbidity from its mouth to its forks (ODEQ, UBWC, and CTUIR 2001), although it is more problematic in the lower subbasin (DeBano and Wooster 2004). Dryland wheat production is believed to be a major source of anthropogenically derived sedimentation in the Subbasin (DeBano and Wooster 2004). Large areas of dryland production systems, left fallow with exposed soil surfaces during the winter, have been identified as a major contributor to sediment movement to streams (NRC 1996). A shift to irrigated agriculture is unlikely to make sedimentation worse because the amount of time ground is left bare is usually reduced. This combined with the fact that two of the four anadromous salmonids spawn and rear primarily in the upper reaches may indicate that impacts on those species under agricultural intensification may be fairly limited. However, coho and fall Chinook spawn and rear in lower reaches of the mainstem Umatilla River (DeBano and Wooster 2004, Appendix S1), so agricultural intensification may pose special threats to them. As outlined by Beechie et al. (2013), modifying watershed-level restoration plans for salmonids in the face of climate change requires examining how flow and stream temperature will be affected, ideally at the highest spatial resolution possible, and then determining if those changes alter habitat that currently limits salmon recovery. Then, managers must make a qualitative assessment of whether these changes alter the effectiveness of current restoration actions. Our study suggests that focusing restoration efforts on the upper subbasin should continue to be a high priority to the degree that these actions have the best chance to counteract climate-induced warming of stream temperatures, the most limiting factor predicted for salmonids in the Umatilla Subbasin. Reconnecting floodplains with the river, creating or reconnecting side channels, removing levees and dikes, and planting riparian vegetation will increase the likelihood of producing resilient river 21


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systems and salmonid populations (Waples et al. 2009) and the expression of alternative life histories (Beechie et al. 2013). All of these actions are currently underway in the upper subbasin (Tetra Tech, CTUIR, and the USDA FS 2013). In fact, other work in the region suggests that restoration of riparian vegetation has the potential to offset predicted increases in stream temperatures associated with climate change (Lawrence et al. 2014). Although we focused on riparian buffer reductions, it is possible that even with growing economic incentives to farm more land, counterbalancing incentives in the form of policy changes or best management practices will not only prevent destruction of current buffers, but will encourage their expansion. If narrow buffers are effective in filtering agrochemicals from overland flow from agricultural lands, a supposition supported by research in the Subbasin (Wooster and DeBano 2006), then farmers considering total buffer removal could be encouraged to leave fairly narrow riparian buffers intact to reduce agrochemical runoff and increase sediment filtration. In contrast to riparian and floodplain restoration, Beechie et al. (2013) suggest that instream rehabilitation efforts such as restoring meanders of straightened channels, and adding instream structure, such as log jams and boulders, may be less effective in ameliorating temperature increases. In addition, although restoring summer base flows is feasible for the lower river and is predicted to ameliorate high water temperatures, low flows, and passage challenges, it would have no effect on the upper watershed, where climate change is expected to exert its most pronounced effects.

available data is well recognized (Kepner et al. 2012). This effort illustrates one way in which data and professional knowledge collected at the local level and often obtained in the context of publically funded natural resource management and planning efforts can be combined with downscaled hydrology and climate change modeling results to produce information that can be used to inform public decision-making. Using fairly simple decision rules to categorize reaches with regard to ranked environmental variables associated with a widely used salmonid life history model (i.e., EDT attributes) allowed us to generate spatially explicit predictions about how multiple stressors may affect a watershed. In the Umatilla Subbasin, we found that both climate change and agricultural intensification are likely to impact aquatic habitat in the future, that climate change will probably exert a stronger effect than agricultural intensification, and that these two stressors not only present different types of challenges to aquatic environments, but that the spatial distribution of their effects generally do not overlap (i.e., they are spatially complementary). This approach could be easily adapted by other subbasins, particularly in the Pacific Northwest. As an example, the NWPCC required subbasins in Oregon, Washington, and Idaho to engage in subbasin planning to be eligible for the approximately $140 million annual funding provided by the Bonneville Power Administration to mitigate and enhance fish and wildlife affected by hydropower dams and to help meet requirements of the 2000 Federal Columbia River Power System Biological Opinion. This effort resulted in plans for 58 tributary watersheds or mainstem segments of the Columbia River, making it one of the largest locally led watershed planning efforts in the United States. Most subbasins used EDT modeling for examining anadromous salmonid species, resulting in local scientists and managers collaborating to generate reach-level values for many of the environmental attributes used in the EDT. Our study provides one example of how this knowledge can be combined to gain a spatially explicit understanding of how multiple stressors are likely to impact a local watershed. Approaches like ours provide a flexible framework in which decision rules can be modified to reflect local conditions and updated with new knowledge.

Conclusions A major challenge in management related sciences is incorporating the quickly expanding availability of data in a framework that can be used by resource managers and policy makers. Many decisions that impact freshwater systems are made at regional or local levels or depend on data with local resolution. Yet most studies use only a fraction of the data and other information available to examine how global and regional processes interact together to affect regional aquatic environments. The need to couple modeling with scenario analysis in ways that capitalize on locally and regionally v www.esajournals.org

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Finally, this work highlights a number of research needs. One relates to developing subbasin-specific models that take into account the movement of woody debris, sediment, and other pollutants through the watershed so that we can improve our understanding of downstream effects of riparian management on these attributes. In addition, our knowledge of the identity, levels, and distribution of many pollutants in the Umatilla River and its tributaries is limited, as is an understanding of how these pollutants may interact with each other and other stressors to impact target species. While our study shows that multiple stressors will impact freshwater habitat in the Umatilla Subbasin, the effects of these multiple stressors on aquatic organisms are unclear. The potential of synergistic interactions of multiple stressors on aquatic organisms, especially in the face of climate change, is a continuing and urgent research need (Ormerod et al. 2010).

Arismendi, I., M. Safeeq, S. L. Johnson, J. B. Dunham, and R. Haggerty. 2013. Increasing synchrony of high temperature and low flow in western North American streams: Double trouble for coldwater biota? Hydrobiologia 712:61–70. Arismendi, I., M. Safeeq, J. B. Dunham, and S. L. Johnson. 2014. Can air temperature be used to project influences of climate change on stream temperature? Environmental Research Letters 9:084015. Battin, J., M. W. Wiley, M. H. Ruckelshaus, R. N. Palmer, E. Korb, K. K. Bartz, and H. Imaki. 2007. Projected impacts of climate change on salmon habitat restoration. Proceedings of the National Academy of Sciences 104:6720–6725. Beechie, T., et al. 2013. Restoring salmon habitat for a changing climate. River Research and Applications 29:939–960. Brown, P. D., D. Wooster, S. L. Johnson, and S. J. DeBano. 2012. Effects of water withdrawals on macroinvertebrate emergence: unexpected results for three holometabolous species. River Research and Applications 28:347–358. Caissie, D. 2006. The thermal regime of rivers: a review. Freshwater Biology 51:1389–1406. Castelle, A. J., and A. W. Johnson. 2000. Riparian vegetation effectiveness. Technical Bulletin No. 799. National Council for Air and Stream Improvement, Research Triangle Park, North Carolina, USA. Castelle, A. J., A. Johnson, and C. Conolly. 1994. Wetland and stream buffer size requirements—a review. Journal of Environmental Quality 23:878–882. CCSP (Climate Change Science Program). 2008. The effects of climate change on agriculture, land resources, water resources, and biodiversity in the United States. U.S. Department of Agriculture, Washington, D.C., USA. Chapman, J. M., C. L. Proulx, M. A. N. Veilleux, C. Levert, S. Bliss, M.-È. André, N. W. R. Lapointe, and S. J. Cooke. 2014. Clear as mud: a meta-analysis on the effects of sedimentation on freshwater fish and the effectiveness of sediment-control measures. Water Research 56:190–202. Close, D. A., K. P. Currens, A. D. Jackson, A. J. Wildbill, J. T. Hanson, J. P. Bronson, and K. Aronsuu. 2009. Lessons from the reintroduction of a non-charismatic, migratory fish: Pacific lamprey in the upper Umatilla River. Pages 1–21 in L. R. Brown, S. D. Chase, M. Mesa, R. Beamish and P. B. Moyle, editors. Biology, management, and conservation of lampreys in North America. Symposium 72. American Fisheries Society, Bethesda, Maryland, USA. Connor, J., G. Clough, and S. Herring. 2002. Enterprise budget: watermelon North Central region. Oregon State University, Extension Publication EM 8799, Corvallis, Oregon, USA.

Acknowledgments This research was funded by the US EPA’s Science to Achieve Results (STAR) Program (#RD83456601), managed by the EPA’s Office of Research and Development (ORD), National Center for Environmental Research: STAR research supports the Agency’s mission to safeguard human health and the environment. We thank Katherine Hegewisch at the Applied Climate Science Lab, Department of Geography at the University of Idaho for providing us with downscaled air temperatures under three climate scenarios for the Umatilla Subbasin. We thank Seth Wenger and one anonymous reviewer for comments that greatly improved this manuscript. Publication of this paper was supported, in part, by the Thomas G. Scott Publication Fund.

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Supporting Information Additional Supporting Information may be found online at: http://onlinelibrary.wiley.com/doi/10.1002/ ecs2.1357/supinfo

Data Availability Data associated with this paper have been deposited in the Dryad repository: http://dx.doi.org/10.5061/ dryad.564q7 (DeBano et al. 2016).


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