1. 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

2. Mid-day Nightime Depth m 24 6 810 mg/L O 2 10 5 Depth m 24 6 810 mg/L O 2 10 5 Dashed line 100% O 2 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 O 2 are taken (IB) and the light (LB) and dark (DB) samples are incubated for a period long enough to produce measurable changes in O 2. 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).

7. Calculations Gross photosynthesis = [(LB - DB) * 1000 * 0.375] / (PQ *  t) Net photosynthesis = [(LB - IB) * 1000 * 0.375] / (PQ *  t) Respiration = [(IB - DB) * RQ * 1000 * 0.375] /  t Gross and net photosynthesis and respiration are expressed as mg C/m 3 /h LB, DB, and IB are dissolved oxygen concentrations in mg/L  t is the incubation period in hours 1000 converts L to m 3 (1 L = 1000 cm 3 ) 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 O 2 = 0.375)

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

9. 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 IzIz z Photic zone z 50% z 1% z 10% Section 10.6 Page 144 in text

10. o o o o mgC/m 3 /d m Depth profile of photosynthesis—how to obtain areal estimate from volumetric 1.0 o Low light intensity, low primary production medium light intensity, highest primary production primary production decreases at highest light intensity