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Comparison of light in six New York lakes Amanda Davis Lauren Jetty Jennifer Mokos Justen Walker.

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Presentation on theme: "Comparison of light in six New York lakes Amanda Davis Lauren Jetty Jennifer Mokos Justen Walker."— Presentation transcript:

1 Comparison of light in six New York lakes Amanda Davis Lauren Jetty Jennifer Mokos Justen Walker

2 Why study light in lakes? Light drives photosynthesis. Light heats the lake. (thermal structure) Light regulates biota. (orientation, predation) Light can damage biota.

3 Absorption and scattering attenuate light within the water column Light is absorbed (transferred to heat) with depth. Light is scattered by particles within the water column.

4 The decrease in the amount of light with depth is determined by: I z = I 0 e -kz Where: I 0 = light intensity at the lake surface I z = light intensity at depth z k = attenuation coefficient z = depth (m)

5 Determine light attenuation using a light meter Deck probe measures surface irradiance Spherical probe measures irradiance at depth z http://www.cnr.vt.edu/fisheries/afs/AFS_education_fisheries_techniques_visuals_chap_4_add.htm

6 Correct irradiance for surface readings Deck o = 1964 Deck 1 = 2047 Spherical 1 = 175.8 For I at depth z = 1: Deck 1 / Deck o * Spherical 1 = 2047 / 1694 * 175.8 = 183.23

7 Convert to a linear plot by taking the log of both sides ln I z = ln I o - kz How do we determine k? y = mx +b k is the slope of the line.

8 Use regression analysis to determine k for each lake.

9

10 Light attenuation in lakes (highest to lowest) Catlin Lake Arbutus Lake Rich Lake Onondaga Lake Oneida Lake Green Lake

11 What affects light attenuation? Scattering due to water (K water ) Dissolved organics - humic & fulvic acids (K dissolved organics ) Particulates - tripton & phytoplankton (K particulates ) K = (K water ) + (K dissolved organics ) + (K particulates )

12 Are particulates responsible for light attenuation patterns?

13 Secchi Depth Inexpensive estimate of light attenuation Average between depth disc vanishes and depth it reappears Roughly estimates 10% of surface light

14

15 Secchi depth in lakes (lowest to highest) Onondaga Lake Oneida Lake Arbutus Lake Rich Lake Catlin Lake Green Lake http://www.cnr.vt.edu/fisheries/afs/AFS_education_fisheries_techniques_visuals_chap_4_add.htm

16 Summary

17 Bonus: Who’s behind the secchi disc?

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