The influence of climate change on reservoir water quality and mixing Dr Lee Bryant, Lecturer Dept. of Architecture and Civil Engineering University of Bath, UK Institute of Water Autumn Forum, October 15, 2019 UoB PGR: M. Amani, D. Birt, J. Waterhouse Bristol Water: R. Luckwell1 Just like we need air to breathe, oxygen (O) is one of most important elements controlling water quality and contaminant transport. Mn River Thames Univ. of Bath duck Fe pond Bath Spa Hotel How does engineered aeration affect mixing and O2 dynamics in lakes and reservoirs? Bubble plume mixers Surface aerators (e.g., ResMix) 3 Drinking water utilities use different aeration strategies internationally, but have the same key problems: Mn and algae 4 Water quality and corresponding ecosystem health are significantly and negatively influenced by climate change via: • Increased water temperature as air temperatures rise • Decreased dissolved oxygen • Elevated stress on aquatic species reliant on oxygen • Accelerated microbial reaction rates • Increased runoff pollution • Enhanced nutrient loading • Decreased dissolved oxygen • Other?! Rastogi et al. 2015. doi:10.3389/fmicb.2015.01254 • Reservoirs currently estimated to contribute 7% of global annual greenhouse gas (GHG) emissions (1.3% estimated as anthropogenic; i.e., ~as much as Canada’s total GHG) • Impact of reservoirs on GHG predicted to increase due to methane release • CH4 produced via microbial degradation of sediment organic matter UK GHG estimates Lower (1) and upper (2) bounds for UK water bodies St. Louis et al. 2009 St. Louis et al. 2000. Reservoir surfaces as sources of greenhouse gases to the atmosphere: a global estimate, Biogeosciences 50(9) www.sciencemag.org/news/2016/09/hundreds-new-dams-could-mean-trouble-our-climate. UK GHG data in figure courtesy of W. Millar-Smith. Oxygen saturation (%) decreases as water temperature increases. http://www.cotf.edu/ete/modules/waterq3/WQassess3f.html, unisense.com Growth rate of bacteria (e.g., microbes responsible for metal reduction and methane production) as a function of temperature http://www.cotf.edu/ete/modules/waterq3/WQassess3f.html Annual variations temperature, Bubble plumes installed 25 algae and Mn of Blagdon Lake C) ° Temperature ( Temperature 0 1 km Historical time series data courtesy of Bristol Water Blagdon Lake • Mendip Hills • Volume = 8260 ML • Surface Area = 170 Ha • Main inflows = Rivers Yeo, Butcombe • 7 bubble plumes operated mid- April through mid-September Field-based approach to evaluate oxygen, metal and nutrient dynamics in freshwater and marine systems Water quality: Sediment chemistry : • Total and soluble Mn (ICP-MS), DO • Total manganese (acid (Winkler titration) digestion; ICP-MS) • Multi-parameter profiling (YSI EXO3) • Temperature chains (RBR, Hobo) Methodology EXO transects Multi-parameter water quality profiling (YSI EXO3) 2018 • Dissolved oxygen • Oxidation/Reduction Potential • pH • Temperature • Conductivity • Total algae • Blue green algae 15 Results Dissolved Oxygen (mg/l) Reverse color scheme on legend!! Temperature (°C) Results Temperature (°C) Results Results • Stratification exists near sediment when honing into fine-scale changes in temperature Temperature (°C) Summer 2019 temperature Air temperature @ 5m above reservoir surface (°C; surface @ 0m) Reservoir temperature near outtake/dam (°C; surface @ 0m) Using coupled catchment-reservoir modelling to evaluate water quality Model 2: Model 1: Catchment Reservoir CE-QUAL-W2 Coupling methodology Model 1: Catchment Model 2: CE-QUAL-W2 • 2D, laterally averaged, finite-difference equation-based model developed by USACoE (Cole & Wells, 2016) • Hydrodynamic and water quality capabilities • Gridded, cellular water body representation • Well-proven model for water quality issues in reservoirs and estuaries (Debele et al, 2008) Study Area: Blagdon Lake • DEM (OS 5m) • Land-Use (CEH LCM 2015) • Soil Cover (LANDIS) • Slope Angle (Calculated) • Cloud Cover (MIDAS) • Solar Radiation (MIDAS) • Wind Speed (MIDAS) • Precipitation (CEH GEAR) Study Area: Blagdon Lake Study Area: Blagdon Lake Get equivalent plots for summer 2017!! Air temp @ 5m above reservoir surface (°C) Reservoir temp (°C; surface @ 0m) AM3D model of reservoir surface temperature during June 2017 AM3D modelled future prediction of reservoir surface temperature in 2090 Conclusions to date • Reduced dissolved oxygen and increased mixing shown to: • Increased sediment resuspension • Enhanced release of reduced chemicals (e.g., Mn) from sediment • Increased algal growth (due to additional light penetration, sediment nutrients?) • Observed correlation in data between increased mixing/destratification and homogeneous reservoir temperatures • Increased temperatures measured throughout water column, to sediment surface • Potential effects on sediment microbial metabolism and corresponding oxygen demand • Reservoir surface temperatures predicted to increase significantly by 2090 per modelled solar radiation and mixing 33.