Climate Change and Lakes: What You Really Need to Know. Ken Wagner, PhD, CLM, Water Resource Services

Transcription

1 Climate Change and Lakes: What You Really Need to Know Ken Wagner, PhD, CLM, Water Resource Services

2 Climate change is ongoing I am going to show you a lot of illustrative graphics, but this is the one you will remember! Courtesy of Hans Paerl of UNC, possibly the simplest proof of global warming

3 Climate change is ongoing History replete with examples of shifting climate Causes are debatable, recent ones likely by us Not rapidly reversible, have to learn to adjust Source: Source: graphics-climate-change

4 The statistics of average and variance Variance is often tied to the mean as a % of it (CV) CV higher for biology than chemistry than physics Increased average translates into increased variation Relationship between mass of P in surficial sediment and depth at which the sample was taken

5 The statistics of average and variance High variance results in a need for more data to detect trends Have to look at many factors to sort out what is going on Declining snowpack evident, but high variability, greater range in winter months Source:

6 Variation over geography Climate change does not affect all areas equally Southwest getting drier, northeast and midwest getting wetter, southeast and rockies not changing much in terms of total precipitation But the timing and magnitude of storms are changing Change since 1901 Source:

7 What we expect in New England Slight increase in amount of precipitation Warmer winters lead to more rain, less snow Shorter period of ice cover Fewer but more intense storms Warmer summers lead to warmer water Greater variation

8 What have we seen in New England? Winnipesaukee ice out date; trend(s) over time

9 What have we seen in New England? Surface water temperature in the ocean at Woods Hole, MA, Cooling trend until post- WWII, then warming trend Change is 1-2 C o over 50 years (since about 1960) Increased variation not extreme Hey, when did ice out date really start getting earlier in Winnipesaukee? Source: Nixon et al A 117 year coastal water temperature record from Woods Hole, MA. Estuaries 27:

10 What have we seen in New England? Winnipesaukee ice out date; emphasis on post-1960

11 Influenced lake features and processes Flushing rate Water level Nutrient loading Establishment of stratification Sediment oxygen demand Plankton dynamics Survival of plants through winter

12 What could happen in your lake Variable flushing Sometimes everything will stagnate, while at other times the change will be rapid Another Wellesley MA pond with a big watershed after a short but intense storm A Wellesley, MA pond with a watershed 417 times the size of the pond in summer 2016; not enough flow to flush complete cover by watermeal

13 What could happen in your lake Variable water level Dry vs wet years may have drastically different affects on water level. Situation may be exacerbated where there are withdrawals that are not scaled down during drought Major impacts possible in the nearshore zone A pond in Winchester MA in August 2016 and 2017

14 What could happen in your lake Variable nutrient loading Nonpoint source loading will rise with more precipitation Internal loading likely to increase Mix of intense storms and prolonged dry periods will induce variation Drought could increase clarity (ME in 2016)

15 What could happen in your lake Stratification Depth at which thermocline forms will vary with spring weather and could have major consequences for algae impacts Two successive years in a Cape Cod pond. The bloom came to the surface in 2009 and killed 2 million mussels

16 What could happen in your lake Oxygen demand Increased temperature leads to increased metabolism, faster decay, more oxygen demand Low oxygen can lead to greater P release from sediment Small changes could have big consequences

17 What could happen in your lake Plankton dynamics Different algae groups prefer different temperatures Cyanobacteria prefer warmest temperatures

18 What could happen in your lake Winter plant survival Lakes are freezing 1 day later per decade Plants can survive longer into the fall or even winter with less ice. As we are not swimming after about September, this may go unnoticed, but may allow for expansion of populations that grow by vegetative means (e.g. milfoil) Source:

19 What could happen in your lake Winter plant survival Lakes thawing on average 1 day earlier per decade The earlier start for growth can lead to denser plant assemblages by summer. Benson, B.J., J.J. Magnuson, O.P. Jensen, V.M. Card, G. Hodgkins, J. Korhonen, D.M. Livingstone, K.M. Stewart, G.A. Weyhenmeyer, and N.G. Granin Extreme events, trends, and variability in Northern Hemisphere lake-ice phenology ( ). Climatic Change 112(2):

20 Summary from an internat l conference Main changes to expect: Increases in external and internal loading Higher frequency of extreme events Changes induced by higher temperature More variable water level Most critical action to take? Reduce nutrient loading (control sources, improve trapping capacity)

21 Countering effects of climate change Protective watershed management control as many sources as possible Runoff storage capacity provide containment for as much runoff as possible P inactivation treatments can counter the effects of climate change Circulation/oxygenation more oxygen is always a good thing in lakes Weed control efforts we are going to need every technique we can get, but prevention is critical for invasive species

22 Countering effects of climate change Protective watershed management

23 Countering effects of climate change Runoff storage capacity

24 Countering effects of climate change P inactivation

25 Countering effects of climate change Circulation/oxygenation

26 Countering effects of climate change Weed control efforts

27 Questions and Comments