LAKE AUBURN: THE EFFECT OF CLIMATE DRIVERS ON LAKE WATER QUALITY

Transcription

1 LAKE AUBURN: THE EFFECT OF CLIMATE DRIVERS ON LAKE WATER QUALITY Bernadette Kolb, Zachary Eichenwald and Daniel Bisson, CDM Smith John Storer, Auburn Water District* David Jones, Lewiston Water Division Kenneth Wagner, Water Resource Services *Now with the Rochester NH DPW AWRA Summer Specialty Conference: Climate Change Adaptation June 17, 2015

2 Lakes and Climate Change From Williamson et al., 2009 Lakes and reservoirs as sentinels, integrators and regulators of climate change, Limnology and Oceanography 54:

3 Lake Auburn in Auburn, Maine Principal water supply for Lewiston and Auburn, Maine Filtration avoidance determination granted in 1991 Strong watershed protection program coupled with largely undeveloped watershed has maintained excellent water quality 3

4 Lake Auburn: Water Quality Overview Historically, a clear, high quality drinking water supply with few algal problems Long-term turbidity levels average well below 1 NTU Supports cold water fishery of Togue and salmon Managed by State Department of Inland Fisheries & Wildlife Interannual variations in lake water quality have always occurred, but in 2011 & 2012: Long duration cyanobacteria blooms Record high turbidity Fish kill (2012 only)

5 Lake Auburn: Vulnerabilities to Climate Change Increased weather variability More intense storms more runoff, increases erosion, more nutrient load Strong winds disrupt stratification moves nutrients to upper waters Warmer weather warmer water temperature Decreases oxygen solubility Enhances cyanobacteria (blue-green algae) growth No or reduced ice cover Enhances stratification (strength and duration) Increases low oxygen extent in deep water Increases phosphorus release from sediments 5

6 Basic Requirements to Maintain a Filtration Avoidance Determination Maintain excellent source water quality for turbidity and bacteria Turbidity cannot exceed 5 NTU on consecutive days (an event ) unless: State determines caused by unusual/unpredictable circumstances Not more than two events in 12 months or 5 events in 120 months Meet site-specific conditions: Provide disinfection Strong source water protection program Conduct on-going inspections Meet distribution water quality requirements Not identified as source of waterborne disease outbreak 6

7 2011 Water Quality Changes Mid-August 2011, significant bloom of cyanobacteria: Gloeotrichia, followed by Microcystis and Anabaena Dissolved oxygen decreased in hypolimnion to near zero 40% of sediment surface exposed to anoxic water Turbidity levels peaked at 4.41 NTU 7

8 Water Quality Degradation Continued in 2012 Surface water temperature: above average to record warm Summer algal blooms of Gloeotrichia and Anabaena By mid-september, oxygen gone from middle and bottom waters Resulted in a fish kill with 200 dead lake trout found Turbidity levels peaked at 3.55 NTU Days Maximum Turbidity Over 1 NTU

9 Factors in 2012 Fish Kill Typical Late Summer Condition Eplimnion warm, oxygenated Metalimnion cooler, moderate DO Hypolimnion cold, some to little oxygen 2012 Conditions Eplimnion warmer, oxygenated No fish habitat Metalimnion & Hypolimnion Little to no oxygen 9

10 Implications for Lewiston and Auburn Water Utilities Measured turbidity approached waiver threshold of 5 NTU in 2011 and 2012 If water quality degradation continues: Construction of an advanced water treatment plant could be mandated Taste and odor issues could occur in distribution system Ability to support coldwater fishery could be threatened 10

11 Long-term Trend? Short-term Changes? Part of a long-term pattern Had increased development in the watershed caused higher nonpoint source loads to the lake? Had the lake reached a tipping point? Had recent occurrence of Gloeotrichia increased surface water phosphorus levels? Were climate change drivers causing ecological shift? Or due to particular within-year phenomena Anomalous storms Near record warm winter

12 Watershed: Not a Key Driver of Change Land use is little changed Strong existing watershed program has provided significant protection 2011 field survey Several new eroded areas and sediment deltas observed Some areas for improved protection identified, particularly regarding storm-driven sediment load Figure credit: Comprehensive Environmental, Inc. 12

13 Recent erosion during 2011 field inspection 13

14 Climate Forcing: Weather/Precipitation Annual Precipitation was Average Hurricane Irene in Monthly Rain was Not 14

15 Climate Forcing: Temperature 15 Annual Average Intake Temperature ( C) R² = 0.6 p <<

16 Intake Water Temperature: Record to Near Record Highs Temperature ( C) Median, J F M A M J J A S O N D 16

17 Stronger Stratification Since 1980s Schmidt Stability Index describes overall resistance to mixing Schmidt Stability (J/m 2 ) September R² = p << Longer duration and more severe bottom water anoxia Increased internal phosphorus load Increased occurrence of harmful algal blooms 17

18 Extent of Shallowest Depth with Low Oxygen in Bottom Waters Does Not Occur: 2001, , Area of lake bottom where dissolved oxygen < 2 mg/l 18

19 Increased Algal Growth After 2011: Degraded Secchi Depth Measurements 0 2 Range of Measurements Secchi Depth (m) A M J J A S O N D

20 Increasing Epilimnetic Total Phosphorus Total Phosphorus (μg/l) Desirable 2005 No data prior to 2005, A M J J A S O N D 20

21 Are Degraded Conditions Likely to Continue? Initially, difficult to determine Short-term Changes Lake responds quickly to changes in temperature 2011 and 2012 had unusual climatic conditions that may have fostered algal growth Long residence time means that short-term changes have a multi-year effect Long-term Changes Evidence of climate change impacts on lake structure Consistent annual increase in phosphorus concentration in recent years Consistent annual increase in turbidity in recent years 21

22 How to Protect Lake Auburn s Filtration Waiver? Conducted intensive data collection in 2013 Obtained approval for a contingency action, if algae and high turbidity occur again Applied for and received Maine s first ever copper sulfate algaecide permit to protect and maintain filtration waiver Started planning for a long-term management system to control phosphorus in lake Hypolimnetic oxygenation Phosphorus inactivation 22

23 Estimated In-lake Management Costs Pure Oxygen Diffusion Capital Cost 1 Range: $2.6 to 4.2 M Best estimate: $3.4 M Annual Operational Cost 1 Anticipated Longevity $68,000 to $310,000 (best est. $155,000/yr) Maintenance to replace in-lake portion of system roughly every 10 years Phosphorus Inactivation $1.8 to 6.2 million; best estimate $4.1 million None May require repeat application anytime after 10 yr, likely after 20 yr Over 20 years the total cost is about the same for both in-lake management solutions Estimated capital and operational costs include 35% for contingencies 23

24 Which Long-term Alternative to Choose, if Needed? Equal scientific merit and similar life cycle costs Selection will require consideration of Trade-off: up-front cost vs. need for annual operations Regulatory approval and stakeholder acceptance Flexibility of operation Note: options are not mutually exclusive, but cost likely precludes application of both appropriate approaches 24

25 So What Happened at Lake Auburn? 25

26 Lake Auburn in 2013 and 2014 No problematic algae no algaecide required AWD/LWD strengthened watershed protection: Amended regulations to promote LID and reduce runoff to lake Implemented enhanced monitoring program Developed public education program Construction of key, high-priority structural BMPs Days Maximum Turbidity Over 1 NTU

27 No Significant Cyanobacteria Blooms: Secchi Disk Measurements Improve Maximum/Minimum, Secchi Depth (m) A M J J A S O N D 27

28 Epilimnetic Total Phosphorus: Decreasing / 2013 Total Phosphorus (μg/l) Desirable No data prior to 2005, A M J J A S O N D 28

29 Anoxia Covers Less Sediment in 2013 and extent similar to significantly smaller in extent and only occurs late in October 29

30 Long-term Management Plan Recommendations for Lake Auburn 1. Continue to monitor water quality in lake and watershed 2. Continue to enhance watershed protection program 3. Maintain the ability to apply a copper sulfate algicide 4. Begin planning for the implementation of in-lake management system 5. If an algaecide is required then implement an in-lake management option by July of the following year Benefits of this plan to improve water quality will be: Safe, affordable drinking water A robust and healthy cold-water fishery 30

31 What are the Implications for Water Utilities Climate change may bring conditions that foster increased nuisance algal productivity: Warmer water Stronger stratification increased internal nutrient load More intense storms -- increased external nutrient load Important to prepare for these changes: Robust water quality monitoring and annual data analysis Enhanced watershed management to reduce nutrient load Identification of long-term management strategy Contingency plan if sudden degradation occurs 31

32 Image credit: