Primary Productivity of lakes and rivers

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• Primary Productivity of lakes and rivers
• 1.) Of whole water columns (no container)
• Diurnal O2 method
• 2.) Of phytoplankton (bottles in situ)
• Dark and light bottle O2 method
• 14C uptake method

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Mid-day
Nightime
Dashed line 100 O2 saturation
Oxygen profiles for lake water columns daytime
vs nighttime
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Dark and light bottle technique for phytoplankton
primary production
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Van Dorn water samplerencloses a water sample
from a given depth
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• Changes in Dissolved Oxygen
• Water samples from various depths are enclosed in
  light (transparent) and dark (completely opaque)
  1 L bottles,
• For each depth initial readings of dissolved O2
  are taken (IB) and
• the light (LB) and dark (DB) samples are
  incubated for a period long enough to produce
  measurable changes in O2.
• During the incubation, we expect that the initial
  DO concentration (IB) at a given depth will
  decrease to a lower concentration in the dark
  bottles (DB) due to respiration of phytoplankton.
  
• Conversely, we expect light bottle (LB) should
  increase from their initial values (IB).

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• Calculations
• Gross photosynthesis (LB - DB) 1000 0.375
  / (PQ D t)
• Net photosynthesis (LB - IB) 1000 0.375 /
  (PQ D t)
• Respiration (IB - DB) RQ 1000 0.375 / D
  t
• Gross and net photosynthesis and respiration are
  expressed as mg C/m3/h
• LB, DB, and IB are dissolved oxygen
  concentrations in mg/L
• D t is the incubation period in hours
• 1000 converts L to m3 (1 L 1000 cm3)
• 0.375 converts mass of oxygen to mass of carbon
  and is a ratio of moles of carbon to moles of
  oxygen (12 mg C/32 mg O2 0.375)

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The Secchi diska simple way to estimate light
extinction
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Light extinction --Light enters from above and
its intensity (I) is sharply attenuated with
depth (z)absorption by water or solute molecules
or scattered by particles
Section 10.6
Iz
z 50
Photic zone
z 10
z 1
z
Page 144 in text
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Depth profile of photosynthesishow to obtain
areal estimate from volumetric
mgC/m3/d
1.0
primary production decreases at highest light
intensity
o
1.0
o
m
medium light intensity, highest primary
production
o
o
Low light intensity, low primary production
o