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Primary Productivity of lakes and rivers 1.) Of whole water columns (no container)

Primary Productivity of lakes and rivers 1.) Of whole water columns (no container) Diurnal O 2 method 2.) Of phytoplankton (bottles in situ ) Dark and light bottle O2 method 14 C uptake method. Nightime. Mid-day. mg/L O 2. mg/L O 2. 2. 2. 4. 4. 8. 8. 10. 10. 6. 6. 5. 5.

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Primary Productivity of lakes and rivers 1.) Of whole water columns (no container)

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  1. 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

  2. Nightime Mid-day mg/L O2 mg/L O2 2 2 4 4 8 8 10 10 6 6 5 5 Depth m Depth m 10 10 Dashed line 100% O2 saturation Oxygen profiles for lake water columns –daytime vs nighttime

  3. Dark and light bottle technique for phytoplankton primary production

  4. Van Dorn water sampler—encloses a water sample from a given depth

  5. 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).

  6. 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)

  7. The Secchi disk—a simple way to estimate light extinction

  8. 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

  9. Depth profile of photosynthesis—how 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

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