LAKE ECOLOGY

1. LAKE ECOLOGY Unit 1: Module 2/3 Part 4 – Spatial and Temporal variabilityJanuary 2004

2. Modules 2/3 overview • Goal – Provide a practical introduction to limnology • Time required – Two weeks of lecture (6 lectures) and 2 laboratories • Extensions – Additional material could be used to expand to 3 weeks. We realize that there are far more slides than can possibly be used in two weeks and some topics are covered in more depth than others. Teachers are expected to view them all and use what best suits their purposes.

3. Modules 2/3 outline • Introduction • Major groups of organisms; metabolism • Basins and morphometry • Spatial and temporal variability – basic physical and chemical patchiness (habitats) • Major ions and nutrients • Management – eutrophication and water quality

4. 4. Spatial & temporal variability – basic physical and chemical patchiness (habitats)

5. 4. Spatial & temporal variability – basic physical and chemical patchiness (habitats) • Physical structure – morphometric features • Physical properties – vertical patterns of light, temperature and density • Density stratification effects on chemistry • O2 • pH, EC25 (specific conductivity/salinity) • nutrients (in section 5)

6. The size and shape of the lake matter • Shoreline development • Habitat • Aquatic plants • Water movement • Erosion potential • Privacy for people • Here’s 40 acre Ice Lake compared to 14,500 acre Lake Minnetonka

7. Lakes: spatial variability 1 • How might water quality vary between site 1 and site 2? • How might their aquatic organism communities differ? • Fish • Zooplankton • Algae • Plants

8. Lakes: spatial variability 2 • How might water quality vary between sites 1, 2 and 3? • How might aquatic organism communities differ? Fish Zooplankton Algae Plants

9. Lakes: spatial variability 3 • How might water quality vary across this lake? • How might aquatic communities differ? • Fish • Zooplankton • Algae • Plants Minnesota or Wisconsin bass-bluegill lake

10. California bass-bluegill lake Lakes: spatial variability 4 Here’s a western US reality check Z-max ~ 4 m Area ~ 10 acres Watershed - ?? (urban runoff) Wind & water flow – westerly What are major sources of variation for this system ? Water Quality Fish Zooplankton Algae Plants

11. Riverlake, Sacramento, CA • Price: $798,000 (Sep ’03) • Sq Ft: 3511 • Year Built: 1990 • Bedrooms: 4 … an upscale community … commenced development in 1987… Currently, it consists of 11 villages comprising approximately 1,000 home sites (incl. 150 lake front lots),… “…Just minutes from downtown, you'll feel like you are living at a resort in the city! Dynamic architecture brings the lake view to all major rooms”.

12. Horizontal variations from physical factors • Duluth • Persistent seasonal and short-term longshore currents in Lake Superior • Upwelling and downwelling regions • Sediment transport from shoreline erosion and deepwater resuspension • Where do you sample ? How might water quality and aquatic communities vary spatially and temporally ? • Where do stormwater and sewage overflows from Duluth go ?

13. credit: www.aquatic.uoguelph.ca/lakes/waves Water movements- currents and waves • Waves consist of the rise and fall of water particles, with some oscillation but no net flow • Currents consist of net unidirectional flows of water

14. Surface waves • Surface waves are wind-driven. Regular patterns of smooth, rounded waves are called swells. • Capillary waves have wavelengths less than 6 cm and are restored to equilibrium due to the surface tension of the water • Gravity waves have wavelengths greater than 6 cm and fall due to the force of gravity

15. Resuspension of nutrients and sediments • Resuspension important particularily in shallow lakes but also in deep lakes

16. Standing waves - surface seiches • Generated by steady wind • Surface water driven downward • Water piles up on the lee shore • Water flows back due to gravity • Standing wave rocks back and forth with decreasing motion = "surface seiches" • Sloshes at resonant frequencies based on basin shape • Can also result from landslides, air pressure, and earthquakes

17. Standing waves - surface seiches cont.

18. www.northernimages.com St. Louis River – Lake Superior seiches • The St. Louis River enters western L. Superior at the Duluth Aerial Lift Bridge • The site is influenced not only by river water flowing downstream but also occasionally by Lake Superior water flowing upstream due to the lake's seiche

19. St. Louis River – Duluth inlet data • Brown stripes are periods when water flows out into the lake • Blue indicates “negative” velocity when the lake is sloshing back into the bay • Which water body has higher EC ? • What factors influence the turbidity plot ?

20. LITTORAL ZONE LIMNETIC ZONE Major Lake Zones Horizontal & vertical variability • How do light, temperature, sediments vary across these zones ? • How do plants, periphyton, invertebrates, fish and algae vary ?

21. NRRI image Littoral Zone • Littoral zone – usually shallow, nearshore region where sufficient light can penetrate to the bottom for plants to grow (~ 1% of midday surface light intensity) • Often estimated as that area of the lake’s surface either <10 ft (3m) or <15 ft (~5 m) deep • Where the majority of aquatic plants are found; a primary habitat for young fish

22. A "natural" shoreline An altered shoreline WI DNR WI DNR Shorelines

23. Secchi depth • Nutrients N or P • Bottomwater- O2 fall winter spring summer winter Temporal variations - seasonality • Can you explain each seasonal pattern ? • What might cause the mid-summer nutrient spikes ? • Is this likely to be a stratified or unstratified lake and why ?

24. Lake Ecology Module – light, temp, density, O2 • The following slides represent the temperature, density, dissolved oxygen, and stratification portion of the Lake Ecology introductory lecture module 3+4, subtopic 4 • Additional explanatory information is available by viewing the attached Notes for each slide

25. Density, Thermal and Oxygen Stratification • Temperature and oxygen levels are major factors regulating aquatic organisms • The layering of lake waters due to density differences is a major factor structuring the ecosystem and creating distinct habitats • The seasonal pattern of turbulent mixing is also a critical determinant of ecosystem function and community structure

26. A Review of Some Basic H2O Physics DENSITY • The warmer the water, the better it floats, but ice floats too • Water becomes less dense as it warms • The difference in density per degree of warming increases as temperatures rise SO ….

27. Density layering Surface water is very buoyant because of the big density difference between it and cold bottom water (leading to stable thermal stratification) Bottom water is colder than the surface in summer (and a bit warmer in winter)

28. Temp (o C) Temp (o F) O2- Sol (mg/L) 0 32 15 5 41 13 10 50 11 15 59 10 20 68 9 25 77 8 Gas Solubility • Warmer water holds less gas (warm beer goes flat) • As 100% air-saturated water warms, it loses O2

29. Plotting profiles - light Light Depth x x x x

30. Heat and Light • Light intensity decreases exponentially with depth in a lake • Which curve is the clear lake – blue or black ? • What shape would you expect for the profile of temperature ?

31. Vertical light extinction Light intensity decreases exponentially with depth and is well described by the Beer-Bouguer-Lambert Law which states that: I(z) = I(0) * [ e-kz ] Where: I(z) = intensity of light as a function of depth z I(0) = intensity of light at the surface (0 m) k = the vertical extinction or attenuation coefficient.

32. Wind: turbulent mixing Heat, as indicated by temperature would also be expected to decrease exponentially with depth, BUT …. • The lake surface is exposed to the wind, which mixes the surface water, but the turbulent energy from the wind dissipates with depth, having less impact further down. • The greater the density difference (mostly from temperature) between layers of water, the harder it is to mix them together.

33. Wind mixing links • Also see slides in Section 5 (Water Chemistry) of this module that discuss gases (O2, N2,CO2 and H2S)

34. Temperature – calm day Depth The Temperature profile would look just like the light profile – at least on a perfectly calm day Temperature x x x x

35. Temperature – windy day • But when the wind blows, it mixes the surface water with deeper water • And its energy dissipates with depth Temperature x x x x Depth x x

36. Temperature Depth 0oC

37. Temperature Depth 0oC

38. Temperature Depth 0oC

39. Temperature 10oC Depth 0oC

40. Temperature 10oC Depth 0oC

41. Temperature 10oC 20oC Depth 0oC

42. Mid-summer thermal stratification • Bottom water colder than surface in summer • Surface water is very buoyant • BIG density difference between surface and cold bottom water = resistance to mixing

43. Temperature 10oC Depth 0oC

44. Temperature 10oC Depth 0oC

45. Temperature Depth Fall Turnover 0oC

46. Temperature Depth 0oC

47. time Thermal stratification sequences • Ice Lake, MN • Apr 23 – Jun 3, 2003 • Shagawa Lake, MN • May 7 – Jun 24, 2003 • Lake Independence, MN • Apr 12 – Jun 29, 1999 • Temperature (o C)

48. Oxygen • What are the sources of oxygen to a lake? • What are the sinks for oxygen in a lake?

49. Two Major Sources of O2 Wind energy Photosynthesis

50. O2 O2 O2 Major Sinks (losses) Diffusion Water column respiration Sediment respiration (bacteria and benthos)