Salt Dynamics in prairie wetlands under changing climate Uri Nachshon Andrew Ireson Garth van der Kamp Howard Wheater Ryan Davies GIWS, University of Saskatchewan GIWS, University of Saskatchewan Environment Canada University of Saskatchewan Imperial College London www.usask.ca/water
www.usask.ca/water Outline: Problem: Question: Hypotheses: Prairie agriculture is vulnerable to salinization What are the climatic drivers of surface salinization in the prairies? Wet conditions associated with extreme snow do not lead to signficant salinization Wet conditions associated with summer rainfall lead to severe salinization I will present various observed data to support the
www.usask.ca/water 2011: Prepare for white stuff this spring: saline soil Wetter-than-normal soil over much of the Prairies may worsen soil salinity problems this year. Soil salinization occurs when the water table is close enough to the soil s surface to allow a wicking action to carry the salty ground water to the surface dirt. http://www.producer.com/2011/02/prepare-for-white-stuff-this-spring-saline-soil/
www.usask.ca/water 2013: Wet weather worsens salinity issues recent years of wetter weather have given rise to salinity problems in places where they hadn t previously been seen. As well, farmers may have even more to deal with because of snow conditions across much of the Prairies that indicate high runoff and a potentially high water table. http://www.producer.com/2013/04/wet-weather-worsens-salinity-issues/
St Denis, Saskatchewan www.usask.ca/water
www.usask.ca/water Past prairie climate variability Pond water levels at St Denis, SK
www.usask.ca/water Past prairie climate variability Pond water levels at St Denis, SK 2000 2004 saw an extremely bad drought
www.usask.ca/water Past prairie climate variability Pond water levels at St Denis, SK 2007 saw the highest water levels up to that point
www.usask.ca/water Past prairie climate variability Pond water levels at St Denis, SK This level was exceeded in 2011
www.usask.ca/water Past prairie climate variability Pond water levels at St Denis, SK And the 2011 level was exceeded again in 2012
Past prairie climate variability www.usask.ca/water
Wet conditions Pond water levels at St Denis, SK Average year Extreme snow Extreme summer rain Extreme antecedent wetness www.usask.ca/water
Change over summer Salinity (EC and salt mass) Pond water volume [m 3 ] A normal year Normal Wet (snow) Wet (snow) Wet (rain) Wet (antecedent) Wet (rain) WATER: Spring melt fills pond Pond empties due to ET and infiltration SALTS: Salt concentration (EC) rises due to ET Salt mass (M salt ) reduces due to infiltration CHANGES OVER SUMMER: Reduction in pond volume and salt mass Increase in salt concentration 1994 1997 2007 2010 2011 2012 www.usask.ca/water
Change over summer Salinity (EC and salt mass) Pond water volume [m 3 ] High snowpack years Normal Wet (snow) Wet (snow) Wet (rain) Wet (antecedent) Wet (rain) WATER: Same pattern as normal years, but with a higher snowmelt peak SALTS: Same pattern as normal years Only a negligible increase in salt mass Basically nothing happens! CHANGES OVER SUMMER: Directions are same as a normal years 1994 1997 2007 Magnitude of water loss is larger 2010 2011 2012 www.usask.ca/water
Change over summer Salinity (EC and salt mass) Pond water volume [m 3 ] High summer rainfall years Normal Wet (snow) Wet (snow) WATER: Levels continue to rise throughout the summer months, post melt Wet (rain) Wet (rain) SALTS: Salt concentration and salt mass increase orders of magnitude above anything previously observed CHANGES OVER SUMMER: Everything increases! 1994 1997 2007 2010 2011 2012 www.usask.ca/water
Change over summer Salinity (EC and salt mass) Pond water volume [m 3 ] High antecedent wetness Normal Wet (snow) Wet (snow) WATER: Same pattern as normal years snowmelt dominated hydrograph Wet (rain) Wet (antecedent) Wet (rain) SALTS: Salt mass and concentration rise CHANGES OVER SUMMER: Water level drops Salt mass and concentration increases Evidence of groundwater exfiltration 1994 1997 2007 2010 2011 2012 www.usask.ca/water
Change over summer Salinity (EC and salt mass) Pond water volume [m 3 ] Observations of pond salinity Normal Wet (snow) Wet (snow) Wet (rain) Wet (antecedent) Wet (rain) 1994 1997 2007 2010 2011 2012 www.usask.ca/water
Different pond responses www.usask.ca/water
www.usask.ca/water The prairie salt cycle Basics: Salts of geological origin dissolve into the water and move with flow, accumulating only in evaporation front locations. Intimately linked to, and diagnostic of, the hydrology. Most prairie basins are closed, comprising fill-and-spill sequences of ponds, ending in a terminal pond, so salts are internally recycled minimal export of salts from the basin most years.
www.usask.ca/water The prairie water cycle Weathered oxidized zone (high K due to fractures) Unoxidized zone (low K)
www.usask.ca/water The prairie water cycle Snowpack builds over winter
www.usask.ca/water The prairie water cycle Snowmelt fills depressions
www.usask.ca/water The prairie water cycle Post-thaw depression focused recharge Surficial isolated aquifer
www.usask.ca/water The prairie water cycle PE > Rainfall (normally) Minimal net infiltration Surficial isolated aquifer
Prairie salt distributions www.usask.ca/water
www.usask.ca/water Prairie salt distributions Shallow salt belt High solubility salts GENERAL PATTERN Low solubility salts Saline ring
Prairie salt distributions Magnitude of salinity depends on direction of exchanges with deep GW Low salinity recharge pond www.usask.ca/water
Prairie salt distributions Magnitude of salinity depends on direction of exchanges with deep GW High salinity discharge pond www.usask.ca/water
www.usask.ca/water The prairie salt cycle Winter through to melt: Summer: Snowmelt runoff Diffusion and bioturbation (?) Evapotranspiration/ capillary flow
www.usask.ca/water Prairie wet extremes Extreme snow pack Extreme summer rainfall Snowmelt runoff Subsurface flows reversed Diffusion and bioturbation (?) Evapotranspiration/ capillary flow
Pond-groundwater exchanges www.usask.ca/water
20 m 107 108A
Transect response to rainfall www.usask.ca/water
Conclusions The past decade has seen extreme variations in climate in the prairies, including a drought, extreme high snow, and extreme high rainfall Snowmelt and rain tend to activate different hydrological processes Extreme high snowmelt over frozen soils has almost no impact on salts Extreme high summer rainfall flushes salts from the subsurface back into the ponds, from where it www.usask.ca/water