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• 1. [Article] Scenario Development and Analysis of Freshwater Ecosystem Services under Land Cover and Climate Change in the Tualatin and Yamhill River Basins, Oregon

  Humans make decisions within ecosystems to enhance their well-being, but choices can lead to unintended consequences. The ecosystem services (ES) approach supports decision-making that considers all environmental ...

  Citation × Citation Citation Abstract Copy Title: Scenario Development and Analysis of Freshwater Ecosystem Services under Land Cover and Climate Change in the Tualatin and Yamhill River Basins, Oregon Author: Hoyer, Robert Wesley Year: 2013 Humans make decisions within ecosystems to enhance their well-being, but choices can lead to unintended consequences. The ecosystem services (ES) approach supports decision-making that considers all environmental goods and services. Many challenges remain in the implementation of the ES approach like how specific ES vary through space and time. We address this research problem using the Tualatin and Yamhill river basins in northwestern Oregon as a study area. Freshwater ES are quantified and mapped with the spatially-explicit ES modeling tool, Integrated Valuation of Ecosystem Services and Tradeoffs (InVEST). In chapter II, we develop a simple urban land cover change modeling approach with selected stakeholder input. The products of this analysis are used in part to answer the question of how the freshwater ES of water yield, nutrient retention, and sediment retention will change in the future, and how their distribution potentially will change? In chapter III, these ES are modeled in InVEST using the land cover scenarios and three downscaled global climate models. The base period is 1981 to 2010 and the future period is 2036 to 2065. The models are calibrated to empirical estimates, and display different sensitivities to inputs. Water yield increases with higher rainfall but decreases with the highest temperature scenario. Nutrient export and retention estimates are positively correlated. In the Tualatin basin, more urban lands generally lead to increases in nutrient exports and retention. The effect is reversed in the Yamhill basin from much larger agricultural exports. Sediment exports and retention increase with higher winter rainfall but are negatively spatially correlated due to topographic effects. Simulation of a landscape scale installation of riparian buffers leads to decreases in exports and increases in retention. The distribution of the provision of freshwater ES remains unchanged throughout the scenarios. With few parameters in each InVEST model, all display a high degree of sensitivity. Parameterization is subject to high uncertainty even with calibrated values. We discuss the assumptions and limitations of InVEST's freshwater models. The spatially explicit nature of InVEST is its main advantage. This work coupled with other analyses in the study area can facilitate the identification of tradeoffs amongst ES leading to better ecosystem management. Title: Scenario Development and Analysis of Freshwater Ecosystem Services under Land Cover and Climate Change in the Tualatin and Yamhill River Basins, Oregon Author: Hoyer, Robert Wesley Year: 2013 Humans make decisions within ecosystems to enhance their well-being, but choices can lead to unintended consequences. The ecosystem services (ES) approach supports decision-making that considers all environmental goods and services. Many challenges remain in the implementation of the ES approach like how specific ES vary through space and time. We address this research problem using the Tualatin and Yamhill river basins in northwestern Oregon as a study area. Freshwater ES are quantified and mapped with the spatially-explicit ES modeling tool, Integrated Valuation of Ecosystem Services and Tradeoffs (InVEST). In chapter II, we develop a simple urban land cover change modeling approach with selected stakeholder input. The products of this analysis are used in part to answer the question of how the freshwater ES of water yield, nutrient retention, and sediment retention will change in the future, and how their distribution potentially will change? In chapter III, these ES are modeled in InVEST using the land cover scenarios and three downscaled global climate models. The base period is 1981 to 2010 and the future period is 2036 to 2065. The models are calibrated to empirical estimates, and display different sensitivities to inputs. Water yield increases with higher rainfall but decreases with the highest temperature scenario. Nutrient export and retention estimates are positively correlated. In the Tualatin basin, more urban lands generally lead to increases in nutrient exports and retention. The effect is reversed in the Yamhill basin from much larger agricultural exports. Sediment exports and retention increase with higher winter rainfall but are negatively spatially correlated due to topographic effects. Simulation of a landscape scale installation of riparian buffers leads to decreases in exports and increases in retention. The distribution of the provision of freshwater ES remains unchanged throughout the scenarios. With few parameters in each InVEST model, all display a high degree of sensitivity. Parameterization is subject to high uncertainty even with calibrated values. We discuss the assumptions and limitations of InVEST's freshwater models. The spatially explicit nature of InVEST is its main advantage. This work coupled with other analyses in the study area can facilitate the identification of tradeoffs amongst ES leading to better ecosystem management. Close

• 2. [Article] Potential Economic Impacts of Zebra Mussels on the Hydropower Facilities in the Columbia River Basin

  The purpose of this study was to estimate costs to the Federal Columbia River Power System hydroelectric projects in the event of a zebra mussel infestation.

  Citation × Citation Citation Abstract Copy Title: Potential Economic Impacts of Zebra Mussels on the Hydropower Facilities in the Columbia River Basin Author: Phillips, Stephen, Darland, Tim, Sytsma, Mark Year: 2005 The purpose of this study was to estimate costs to the Federal Columbia River Power System hydroelectric projects in the event of a zebra mussel infestation. Title: Potential Economic Impacts of Zebra Mussels on the Hydropower Facilities in the Columbia River Basin Author: Phillips, Stephen, Darland, Tim, Sytsma, Mark Year: 2005 The purpose of this study was to estimate costs to the Federal Columbia River Power System hydroelectric projects in the event of a zebra mussel infestation. Close

• 3. [Article] Prioritizing Zebra and Quagga Mussel Monitoring in the Columbia River Basin

  The purpose of this report is to provide a framework for the prioritization of water bodies in the Columbia River Basin and the Greater Northwest region (surrounding areas in Oregon, Washington, California, ...

  Citation × Citation Citation Abstract Copy Title: Prioritizing Zebra and Quagga Mussel Monitoring in the Columbia River Basin Author: Wells, Steve W., Counihan, Timothy D., Puls, Amy, Sytsma, Mark, Adair, Brian Year: 2011 The purpose of this report is to provide a framework for the prioritization of water bodies in the Columbia River Basin and the Greater Northwest region (surrounding areas in Oregon, Washington, California, Nevada, Idaho, Utah, and Wyoming) for early detection monitoring for dreissenid mussels. Our ability to assess the relative risk of establishment and introduction of dreissenid mussels was confounded by significant gaps in the data necessary to rigorously predict where dreissenid mussels will become introduced and subsequently established. Consequently, local jurisdictions should evaluate the prioritized lists provided critically and make adjustments where local knowledge and additional information dictates. Further, since invasive species can be introduced and become established in areas identified with low to very low risk of establishment and introduction, monitoring these areas will increase the probability of detecting mussels before they become locally established. Title: Prioritizing Zebra and Quagga Mussel Monitoring in the Columbia River Basin Author: Wells, Steve W., Counihan, Timothy D., Puls, Amy, Sytsma, Mark, Adair, Brian Year: 2011 The purpose of this report is to provide a framework for the prioritization of water bodies in the Columbia River Basin and the Greater Northwest region (surrounding areas in Oregon, Washington, California, Nevada, Idaho, Utah, and Wyoming) for early detection monitoring for dreissenid mussels. Our ability to assess the relative risk of establishment and introduction of dreissenid mussels was confounded by significant gaps in the data necessary to rigorously predict where dreissenid mussels will become introduced and subsequently established. Consequently, local jurisdictions should evaluate the prioritized lists provided critically and make adjustments where local knowledge and additional information dictates. Further, since invasive species can be introduced and become established in areas identified with low to very low risk of establishment and introduction, monitoring these areas will increase the probability of detecting mussels before they become locally established. Close

• 4. [Article] Modeling the Bull Run River-Reservoir System

  The City of Portland, Water Bureau currently operates 2 Bull Run reservoirs, Reservoir #2 and Reservoir #1 as a water supply source in the Bull Run watershed shown in Figure 1 and Figure 2. The Water Bureau ...

  Citation × Citation Citation Abstract Copy Title: Modeling the Bull Run River-Reservoir System Author: Wells, Scott A. Year: 2000 The City of Portland, Water Bureau currently operates 2 Bull Run reservoirs, Reservoir #2 and Reservoir #1 as a water supply source in the Bull Run watershed shown in Figure 1 and Figure 2. The Water Bureau wants to operate their water supply system in order to meet both water supply objectives and fish habitat objectives downstream of the Bull Run reservoirs in Bull Run River. In addition, a third Bull Run reservoir has been proposed as an additional water supply source. This reservoir also may be used to meet water supply and fish habitat objectives in Bull Run River. This proposal addresses performing the following tasks to evaluate these objectives: Gather data to construct a computer simulation model of the Bull Run system including Bull Run River, Bull Run Reservoirs #1 through #3 and the river basin without reservoirs. Ensure that the model accurately represents the system physics, chemistry and biology. Use the model to evaluate how to meet water supply and fish habitat objectives by implementation of management scenarios. Title: Modeling the Bull Run River-Reservoir System Author: Wells, Scott A. Year: 2000 The City of Portland, Water Bureau currently operates 2 Bull Run reservoirs, Reservoir #2 and Reservoir #1 as a water supply source in the Bull Run watershed shown in Figure 1 and Figure 2. The Water Bureau wants to operate their water supply system in order to meet both water supply objectives and fish habitat objectives downstream of the Bull Run reservoirs in Bull Run River. In addition, a third Bull Run reservoir has been proposed as an additional water supply source. This reservoir also may be used to meet water supply and fish habitat objectives in Bull Run River. This proposal addresses performing the following tasks to evaluate these objectives: Gather data to construct a computer simulation model of the Bull Run system including Bull Run River, Bull Run Reservoirs #1 through #3 and the river basin without reservoirs. Ensure that the model accurately represents the system physics, chemistry and biology. Use the model to evaluate how to meet water supply and fish habitat objectives by implementation of management scenarios. Close

• 5. [Article] Spokane River in Idaho and Washington TMDL Water Quality and Hydrodynamic Modeling Quality Assurance Project Plan -- DRAFT

  The focus of this present study is to perform the following tasks: • Converting the Upper Spokane River CE‐QUAL‐W2 models (Washington and Idaho) to version 3.6 • Combining the Washington and Idaho models • ...

  Citation × Citation Citation Abstract Copy Title: Spokane River in Idaho and Washington TMDL Water Quality and Hydrodynamic Modeling Quality Assurance Project Plan -- DRAFT Author: Wells, Scott A., Berger, Chris Year: 2009 The focus of this present study is to perform the following tasks: • Converting the Upper Spokane River CE‐QUAL‐W2 models (Washington and Idaho) to version 3.6 • Combining the Washington and Idaho models • Reviewing and updating model boundary conditions • Check model calibration • Meet with stakeholders • Develop and Run Modeling Scenarios • Create reports on calibration and scenario runs Title: Spokane River in Idaho and Washington TMDL Water Quality and Hydrodynamic Modeling Quality Assurance Project Plan -- DRAFT Author: Wells, Scott A., Berger, Chris Year: 2009 The focus of this present study is to perform the following tasks: • Converting the Upper Spokane River CE‐QUAL‐W2 models (Washington and Idaho) to version 3.6 • Combining the Washington and Idaho models • Reviewing and updating model boundary conditions • Check model calibration • Meet with stakeholders • Develop and Run Modeling Scenarios • Create reports on calibration and scenario runs Close

• 6. [Article] Lower Columbia River Aquatic Nonindigenous Species Survey 2001-2004

  Rates of aquatic nonindigenous species (ANS) introductions and their social, economic, and ecological impacts are increasing. Introductions of nonnative marine organisms have increased exponentially over ...

  Citation × Citation Citation Abstract Copy Title: Lower Columbia River Aquatic Nonindigenous Species Survey 2001-2004 Author: Sytsma, Mark, Cordell, Jeffery, Chapman, John, Draheim, Robyn Year: 2004 Rates of aquatic nonindigenous species (ANS) introductions and their social, economic, and ecological impacts are increasing. Introductions of nonnative marine organisms have increased exponentially over the last two centuries and expenditures on outreach, control, and research exceed millions of dollars per species for several invaders of particular concern to the United States. These trends suggest that major changes are occurring in the freshwater, estuarine, and marine ecosystems of North America, but their magnitude is probably underestimated. Title: Lower Columbia River Aquatic Nonindigenous Species Survey 2001-2004 Author: Sytsma, Mark, Cordell, Jeffery, Chapman, John, Draheim, Robyn Year: 2004 Rates of aquatic nonindigenous species (ANS) introductions and their social, economic, and ecological impacts are increasing. Introductions of nonnative marine organisms have increased exponentially over the last two centuries and expenditures on outreach, control, and research exceed millions of dollars per species for several invaders of particular concern to the United States. These trends suggest that major changes are occurring in the freshwater, estuarine, and marine ecosystems of North America, but their magnitude is probably underestimated. Close

• 7. [Article] Tidal-Fluvial and Estuarine Processes in the Lower Columbia River: II. Water Level Models, Floodplain Wetland Inundation, and System Zones

  Spatially varying water-level regimes are a factor controlling estuarine and tidal-fluvial wetland vegetation patterns. As described in Part I, water levels in the Lower Columbia River and estuary (LCRE) ...

  Citation × Citation Citation Abstract Copy Title: Tidal-Fluvial and Estuarine Processes in the Lower Columbia River: II. Water Level Models, Floodplain Wetland Inundation, and System Zones Author: Jay, David A, Borde, Amy B., Diefenderfer, Heida Year: 2016 Spatially varying water-level regimes are a factor controlling estuarine and tidal-fluvial wetland vegetation patterns. As described in Part I, water levels in the Lower Columbia River and estuary (LCRE) are influenced by tides, river flow, hydropower operations, and coastal processes. In Part II, regression models based on tidal theory are used to quantify the role of these processes in determining water levels in the mainstem river and floodplain wetlands, and to provide 21-year inundation hindcasts. Analyses are conducted at 19 LCRE mainstem channel stations and 23 tidally exposed floodplain wetland stations. Sum exceedance values (SEVs) are used to compare wetland hydrologic regimes at different locations on the river floodplain. A new predictive tool is introduced and validated, the potential SEV (pSEV), which can reduce the need for extensive new data collection in wetland restoration planning. Models of water levels and inundation frequency distinguish four zones encompassing eight reaches. The system zones are the wave- and current-dominated Entrance to river kilometer (rkm) 5; the Estuary (rkm-5 to 87), comprised of a lower reach with salinity, the energy minimum (where the turbidity maximum normally occurs), and an upper estuary reach without salinity; the Tidal River (rkm-87 to 229), with lower, middle, and upper reaches in which river flow becomes increasingly dominant over tides in determining water levels; and the steep and weakly tidal Cascade (rkm-229 to 234) immediately downstream from Bonneville Dam. The same zonation is seen in the water levels of floodplain stations, with considerable modification of tidal properties. The system zones and reaches defined here reflect geological features and their boundaries are congruent with five wetland vegetation zones. Title: Tidal-Fluvial and Estuarine Processes in the Lower Columbia River: II. Water Level Models, Floodplain Wetland Inundation, and System Zones Author: Jay, David A, Borde, Amy B., Diefenderfer, Heida Year: 2016 Spatially varying water-level regimes are a factor controlling estuarine and tidal-fluvial wetland vegetation patterns. As described in Part I, water levels in the Lower Columbia River and estuary (LCRE) are influenced by tides, river flow, hydropower operations, and coastal processes. In Part II, regression models based on tidal theory are used to quantify the role of these processes in determining water levels in the mainstem river and floodplain wetlands, and to provide 21-year inundation hindcasts. Analyses are conducted at 19 LCRE mainstem channel stations and 23 tidally exposed floodplain wetland stations. Sum exceedance values (SEVs) are used to compare wetland hydrologic regimes at different locations on the river floodplain. A new predictive tool is introduced and validated, the potential SEV (pSEV), which can reduce the need for extensive new data collection in wetland restoration planning. Models of water levels and inundation frequency distinguish four zones encompassing eight reaches. The system zones are the wave- and current-dominated Entrance to river kilometer (rkm) 5; the Estuary (rkm-5 to 87), comprised of a lower reach with salinity, the energy minimum (where the turbidity maximum normally occurs), and an upper estuary reach without salinity; the Tidal River (rkm-87 to 229), with lower, middle, and upper reaches in which river flow becomes increasingly dominant over tides in determining water levels; and the steep and weakly tidal Cascade (rkm-229 to 234) immediately downstream from Bonneville Dam. The same zonation is seen in the water levels of floodplain stations, with considerable modification of tidal properties. The system zones and reaches defined here reflect geological features and their boundaries are congruent with five wetland vegetation zones. Close

• 8. [Article] Climate Change Impacts on Precipitation Extremes over the Columbia River Basin Based on Downscaled CMIP5 Climate Scenarios

  Hydro-climate extreme analysis helps understanding the process of spatio-temporal variation of extreme events due to climate change, and it is an important aspect in designing hydrological structures, ...

  Citation × Citation Citation Abstract Copy Title: Climate Change Impacts on Precipitation Extremes over the Columbia River Basin Based on Downscaled CMIP5 Climate Scenarios Author: Dars, Ghulam Hussain Year: 2013 Hydro-climate extreme analysis helps understanding the process of spatio-temporal variation of extreme events due to climate change, and it is an important aspect in designing hydrological structures, forecasting floods and an effective decision making in the field of water resources design and management. The study evaluates extreme precipitation events over the Columbia River Basin (CRB), the fourth largest basin in the U.S., by simulating four CMIP5 global climate models (GCMs) for the historical period (1970-1999) and future period (2041-2070) under RCP85 GHG scenario. We estimated the intensity of extreme and average precipitation for both winter (DJF) and summer (JJA) seasons by using the GEV distribution and multi-model ensemble average over the domain of the Columbia River Basin. The four CMIP5 models performed very well at simulating precipitation extremes in the winter season. The CMIP5 climate models showed heterogeneous spatial pattern of summer extreme precipitation over the CRB for the future period. It was noticed that multi-model ensemble mean outperformed compared to the individual performance of climate models for both seasons. We have found that the multi-model ensemble shows a consistent and significant increase in the extreme precipitation events in the west of the Cascades Range, Coastal Ranges of Oregon and Washington State, the Canadian portion of the basin and over the Rocky Mountains. However, the mean precipitation is projected to decrease in both winter and summer seasons in the future period. The Columbia River is dominated by the glacial snowmelt, so the increase in the intensity of extreme precipitation and decrease in mean precipitation in the future period, as simulated by four CMIP5 models, is expected to aggravate the earlier snowmelt and contribute to the flooding in the low lying areas especially in the west of the Cascades Range. In addition, the climate change shift could have serious implications on transboundary water issues in between the United States and Canada. Therefore, adaptation strategies should be devised to cope the possible adverse effects of the changing the future climate so that it could have minimal influence on hydrology, agriculture, aquatic species, hydro-power generation, human health and other water related infrastructure. Title: Climate Change Impacts on Precipitation Extremes over the Columbia River Basin Based on Downscaled CMIP5 Climate Scenarios Author: Dars, Ghulam Hussain Year: 2013 Hydro-climate extreme analysis helps understanding the process of spatio-temporal variation of extreme events due to climate change, and it is an important aspect in designing hydrological structures, forecasting floods and an effective decision making in the field of water resources design and management. The study evaluates extreme precipitation events over the Columbia River Basin (CRB), the fourth largest basin in the U.S., by simulating four CMIP5 global climate models (GCMs) for the historical period (1970-1999) and future period (2041-2070) under RCP85 GHG scenario. We estimated the intensity of extreme and average precipitation for both winter (DJF) and summer (JJA) seasons by using the GEV distribution and multi-model ensemble average over the domain of the Columbia River Basin. The four CMIP5 models performed very well at simulating precipitation extremes in the winter season. The CMIP5 climate models showed heterogeneous spatial pattern of summer extreme precipitation over the CRB for the future period. It was noticed that multi-model ensemble mean outperformed compared to the individual performance of climate models for both seasons. We have found that the multi-model ensemble shows a consistent and significant increase in the extreme precipitation events in the west of the Cascades Range, Coastal Ranges of Oregon and Washington State, the Canadian portion of the basin and over the Rocky Mountains. However, the mean precipitation is projected to decrease in both winter and summer seasons in the future period. The Columbia River is dominated by the glacial snowmelt, so the increase in the intensity of extreme precipitation and decrease in mean precipitation in the future period, as simulated by four CMIP5 models, is expected to aggravate the earlier snowmelt and contribute to the flooding in the low lying areas especially in the west of the Cascades Range. In addition, the climate change shift could have serious implications on transboundary water issues in between the United States and Canada. Therefore, adaptation strategies should be devised to cope the possible adverse effects of the changing the future climate so that it could have minimal influence on hydrology, agriculture, aquatic species, hydro-power generation, human health and other water related infrastructure. Close

• 9. [Article] Theoretical Basis for the CE-QUAL-W2 River Basin Model

  The primary objective of this research is to integrate a riverine model into the existing W2 code that would provide the capability for modeling entire watersheds. This task was accomplished by the following ...

  Citation × Citation Citation Abstract Copy Title: Theoretical Basis for the CE-QUAL-W2 River Basin Model Author: Wells, Scott A., Cole, Thomas M. Year: 2000 The primary objective of this research is to integrate a riverine model into the existing W2 code that would provide the capability for modeling entire watersheds. This task was accomplished by the following steps: • Formal derivation of governing equations and solution algorithm with general channel slope • Detailed analysis of algorithm for linking branches and smooth implementation of boundary conditions between branches • Algorithm development and changes to basic model code (including branch definitions with slope, slope correction to solution algorithm, transfer of momentum between internal branches) These tasks were performed with the following constraints and initiatives: • Utilize the same solution algorithms as the existing code for hydrodynamics and water quality for the riverine system • Allow momentum transfer between adjacent branches for internal head boundary conditions • Refine the turbulence closure hypothesis for riverine sections Title: Theoretical Basis for the CE-QUAL-W2 River Basin Model Author: Wells, Scott A., Cole, Thomas M. Year: 2000 The primary objective of this research is to integrate a riverine model into the existing W2 code that would provide the capability for modeling entire watersheds. This task was accomplished by the following steps: • Formal derivation of governing equations and solution algorithm with general channel slope • Detailed analysis of algorithm for linking branches and smooth implementation of boundary conditions between branches • Algorithm development and changes to basic model code (including branch definitions with slope, slope correction to solution algorithm, transfer of momentum between internal branches) These tasks were performed with the following constraints and initiatives: • Utilize the same solution algorithms as the existing code for hydrodynamics and water quality for the riverine system • Allow momentum transfer between adjacent branches for internal head boundary conditions • Refine the turbulence closure hypothesis for riverine sections Close

• 10. [Article] Fish Species Introductions Provide Novel Insights into the Patterns and Drivers of Phylogenetic Structure in Freshwaters

  Despite long-standing interest of terrestrial ecologists, freshwater ecosystems are a fertile, yet unappreciated, testing ground for applying community phylogenetics to uncover mechanisms of species assembly. ...

  Citation × Citation Citation Abstract Copy Title: Fish Species Introductions Provide Novel Insights into the Patterns and Drivers of Phylogenetic Structure in Freshwaters Author: Strecker, Angela L., Olden, Julian D. Year: 2014 Despite long-standing interest of terrestrial ecologists, freshwater ecosystems are a fertile, yet unappreciated, testing ground for applying community phylogenetics to uncover mechanisms of species assembly. We quantify phylogenetic clustering and overdispersion of native and non-native fishes of a large river basin in the American Southwest to test for the mechanisms (environmental filtering versus competitive exclusion) and spatial scales influencing community structure. Contrary to expectations, non-native species were phylogenetically clustered and related to natural environmental conditions, whereas native species were not phylogenetically structured, likely reflecting human-related changes to the basin. The species that are most invasive (in terms of ecological impacts) tended to be the most phylogenetically divergent from natives across watersheds, but not within watersheds, supporting the hypothesis that Darwin's naturalization conundrum is driven by the spatial scale. Phylogenetic distinctiveness may facilitate non-native establishment at regional scales, but environmental filtering restricts local membership to closely related species with physiological tolerances for current environments. By contrast, native species may have been phylogenetically clustered in historical times, but species loss from contemporary populations by anthropogenic activities has likely shaped the phylogenetic signal. Our study implies that fundamental mechanisms of community assembly have changed, with fundamental consequences for the biogeography of both native and non-native species. Title: Fish Species Introductions Provide Novel Insights into the Patterns and Drivers of Phylogenetic Structure in Freshwaters Author: Strecker, Angela L., Olden, Julian D. Year: 2014 Despite long-standing interest of terrestrial ecologists, freshwater ecosystems are a fertile, yet unappreciated, testing ground for applying community phylogenetics to uncover mechanisms of species assembly. We quantify phylogenetic clustering and overdispersion of native and non-native fishes of a large river basin in the American Southwest to test for the mechanisms (environmental filtering versus competitive exclusion) and spatial scales influencing community structure. Contrary to expectations, non-native species were phylogenetically clustered and related to natural environmental conditions, whereas native species were not phylogenetically structured, likely reflecting human-related changes to the basin. The species that are most invasive (in terms of ecological impacts) tended to be the most phylogenetically divergent from natives across watersheds, but not within watersheds, supporting the hypothesis that Darwin's naturalization conundrum is driven by the spatial scale. Phylogenetic distinctiveness may facilitate non-native establishment at regional scales, but environmental filtering restricts local membership to closely related species with physiological tolerances for current environments. By contrast, native species may have been phylogenetically clustered in historical times, but species loss from contemporary populations by anthropogenic activities has likely shaped the phylogenetic signal. Our study implies that fundamental mechanisms of community assembly have changed, with fundamental consequences for the biogeography of both native and non-native species. Close