Freshwater Ecology - the finer details

Orthograde

• Summer
• Oligotrophic Lake
• Oxygen is high in hypolimnion
• Water is cold (4C)
• Lake has low productivity, therefore minimal decomposition,higher D.O.

Clinograde

• Summer
• Eutrophic Lake
• Oxygen is high in epilimnion (photosynthesis)
• Water is cold (4C)
• Lake has high productivity, therefore lots of decomposition,lower D.O.

Negative Heterograde• Summer
• Any lake
• Oxygen is consumed in metalimnion (bacteria, zooplankton)
• Water is at preferred temp for these organisms, lower
D.O. in metalimnion

Positive Heterograde

• Summer
  • Any lake
  • Oxygen is produced in metalimnion (phytoplankton)
  • Water is at preferred temp for these organisms, higher
  D.O. in metalimnion
  
  A.K.A. “Metalimnetic Oxygen Maxima

Key things of the nitrogen cycle

• We need diazotrophs - 2 groups of bacteria

• N.S bacteria and N.B bacteria

• NH4-NH3 is aerobic

• Denitrfication = anaerobic

Dissociation of FePo4

• dissociates when D.O is low

• Bonds when D.O is high

What is the link between Alkalinity
and lake productivity?

• As alkalinity increases so does lake productivity
• 1. Buffering compounds reduce the toxic fatal effects of low pH
• 2. Sedimentary rock that holds buffering ions is also higher in all nutrients such as nitrogen and phosphorus

How to rehabilitate lakes that are
becoming acidified?

Solve the symptom... Lake liming, adding calcium carbonate to lakes to capture free H+ ions, increase pH, and reduce acidity

• Reduce NOx and SOx pollution...
• 1991 U.S.-Canada Air Quality Agreement
• The 1994 Oslo Protocol on Further Reduction of Sulphur Emissions