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

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 Photo: Simon Fraser University Photo: PBS Photo: Wikipedia

Mohseni et al Evaporative Cooling Evaporative Concentration River & stream salinity

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

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?

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

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

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

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 Climate model: NCAR Community Climate System Model v3.0 Land use / Land cover From Sohl et al USGS FORE-SCE model

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

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

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

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

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)

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

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 Photo: Simon Fraser University

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

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

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

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

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

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

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

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

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

Natural Background Salinity