1. Current and future effects of land use and climate change on river and stream salinity John Olson Desert Research Institute Society for Freshwater Science Annual Meeting 23 May 2016

2. River & stream salinity Varies over four orders of magnitude, specific electrical conductivity (EC) from 12,000 µS/cm Human activities can increase salinity, to greater than seawater (> 54,000 µS/cm) Photo: Wikipedia Photo: Kalfka et al. 2001 Photo: Simon Fraser University Photo: PBS Photo: Wikipedia

3. Mohseni et al. 2003 Evaporative Cooling Evaporative Concentration River & stream salinity

4. USEPA 2011 Proportion of Invertebrate Genera EC (µS/cm) River & stream salinity >3,000 µS/cm unsuitable: Irrigation Industry human consumption Loss of water resources Ecosystem impairment Loss of low salinity habitat : ↓ freshwater biodiversity Alters ecosystems function

5. To effectively address this challenge, we need to know: How much has salinity in streams already been altered by human activities? How much more alteration is likely with increasing development and climate change?

6. 1.Model natural background: Natural EC = f(geology, climate, …) 2.Compare to current salinity: Observed – Natural = EC Alteration 3.Model salinity alteration: EC Alteration = f(urban, ag, mining, …) 4.Predict salinity in 2100: f(future climate, urban, ag, …) = Future EC Runoff Water Rock Weathering Soil Biota Climate & Atmospheric Inputs Objectives Human

7. Models based on in situ EC measurements at minimally impacted sites by multiple agencies Response Data 1935 sites Measurements made at “base- flow”

8. Geochemical Geophysical Topography Deposition Soils Predictor Data Watershed averages of 24 static predictors

9. Predictor Data Watershed averages of 12 dynamic predictors from published climate & land use projections IPCC A2 mid-high emission scenario Current (2010) and end of century (2100) Climate From Hawkins et al. 2013 Climate model: NCAR Community Climate System Model v3.0 Land use / Land cover From Sohl et al. 2014 USGS FORE-SCE model

10. Dynamically downscaled (WRF Regional Climate Model) Statistically downscaled (PRISM Climate Data) Corrects GCM biases, incorporates topography Predictor Data Climate

11. Predictor Data FORE-SCE model spatially allocates land use change using logistic regression models Based on biogeophysical and socioeconomic conditions Spatial Allocation (FORE-SCE) IPCC scenarios Suitability Surface Historical Land Cover Protective Status Forest Age Annual LU/LC Maps Land use / Land cover 2005 2100

12. Natural Background Salinity Model RMSE = 67 µS/cm R 2 = 0.78 Random Forest Model Performance

13. Natural Background Salinity Model Rock % CaOMax TempMin PrecipYearly Precip Atm Ca Dep Rock % SRck Strength% Conifer Random Forest Model Predictors

14. 2,001 sites, part of the U.S. EPA’s National River and Stream Assessment Sites chosen using a probability-based sample design Statistically represent U.S. streams Change from Natural Background Salinity Current Observed EC (µS/cm)

15. Predicted Natural Background EC (µS/cm) Current Observed EC (µS/cm) Change from Natural Background Salinity

16. Absolute change in µS/cm Percent change Change from Natural Background EC Alteration → Response Data Photo: PBS Photo: Wikipedia Change from Natural Background Salinity Kaushal et al. 2005 Photo: Simon Fraser University

17. Salinity Alteration Model Random Forest Model Performance RMSE = 604 µS/cm R 2 = 0.60

18. Min PrecipRock % SAtm Ca Dep% Crops % Urban Rck Strength% MiningSoil Bulk D Random Forest Model Predictors Salinity Alteration Model

19. End of Century Salinity Current Observed EC (µS/cm) Predicted End of Century EC (µS/cm) Natural background model: Natural EC = f(geology, climate) Alteration model : EC Alteration = f(urban, ag) Projected Climate Land use

20. End of Century Salinity Absolute change in µS/cm Percent change Change in EC from current to 2100

21. Change in Salinity Median: 214 µS/cm Median: 319 µS/cm Median: 524 µS/cm Human use threshold > 3,000 µS/cm Currently - 3% of sites 2100 – 11% of sites

22. Change in Salinity Invertebrate Extirpation Thresholds < 300 µS/cm [5% Extirpation] Background – 65% of sites Currently – 48% of sites 2100 – 26% of sites < 2000 µS/cm [50% Extirpation] Background – 100% of sites Currently – 93% of sites 2100 – 88% of sites

23. Change in Salinity We calculated the effects of climate change on salinity separate from the total change Climate change accounts for < 10% of changes in salinity in 2100

24. Conclusions Still work to be done: Quantify uncertainty Better parse climate & LU impacts Assess vulnerability Human activities have already increased median salinity by > 100 µS/cm, potentially doubled by end of century Climate change only accounts for < 10% of change by itself Half of remaining low salinity habitat may be lost by end of century

25. Questions? Acknowledgments: GIS analysis: Megan Dettenmaier, Ben Poulsen, and Nate McPherron Funding: Sulo and Aileen Maki Endowment

26. Natural Background Salinity