Biological Cycles in Aquaria: An Introduction

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Biological Cycles in Aquaria An Introduction

• Timothy A. Hovanec, Ph.D.
• Chief Science Officer
• Marineland Aquatic Research Labs
• 6100 Condor Cr.
• Moorpark, CA 93021
• 805.553.4446 fax [phone]
• hovanec_at_marineland.com

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The Nitrogen Cycle
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Nitrification - the traditional scheme
Ammonia (NH )
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Nitrite (NO )
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Nitrosomonas
Nitrate (NO )
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Nitrobacter
NOT EXACTLY --- But we will come back to this
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Chemical Process

• Ammonia Oxidation
• NH3 O2 H20 2e- ---gt NH2OH H2O
• NH2OH H20 ---gt NO2- 5H H2O
• Nitrite Oxidation
• NO2- H2O ---gt NO3- 2H 4e-

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Denitrification - An Anaerobic Process

• Almost all are facultative, denitrification is a
  second choice
• Researchers use various ways to measure and
  report oxygen conc.
• Ps. denitrificans lt 0.2 ppm
• Ps. aeruginosa lt 0.4 mM O2/L/min

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Potential Problems

• Incomplete denitrification
• stops at nitrite
• toxic to fish
• toxic to nitrifying bacteria
• Goes wrong way
• get ammonia production
• High levels of dissolved organic carbon
• promotes heterotrophic bacteria
• compete with the nitrifiers
• inhibits the nitrifiers
• Build-up of sulfide
• can be lead to H2S harmful to fish nitrifiers

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Anammox ProcessAnaerobic Oxidation of Ammonium

• NH4 NO2- -----gt N2 2H2O
• Nitrate reduction to nitrite and a coupling of
  the ammonium and nitrite by Planctomycetes
• Anaerobic process but organics not needed
• Carbon is from carbon dioxide
• Energetically more efficient than denitrification
• Offshore marine sediments dominated over
  denitrification
• Nearshore (bays) denitrification dominated
• Nature 400446-449 AEM 611246-1251 AEM
  681312-1318
• http//www.anammox.com/research.html

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Silicon

• Always found combined with oxygen
• Silicon dioxide (SiO2) or Silica
• Presence/Absence effects composition of plankton
• 100x fold reduce few diatoms and radiolaria
• requirement for some deep sea sponges
• In Ocean amorphous silica is usually the weak
  acid Silicic Acid
• Conc. ranges from lt1 umol/Kg to 210 umol/kg
• At pH of 8.2 only about 5 ionized

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Choose Your Poison??

• Diatoms can cover the displays
• Cyanobacteria can form carpets over everything
• Green algae can turn the water and displays into
  soup
• Since these organisms are benthic UV, ozone, etc
  cannot eradicate them - is there a biological
  solution?

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Relationship of NP

• Dr. David Karl Univ. of Hawaii Aloha Station
  Research
• Cyanobacteria fix dinitrogen from the air so by
  removing all the nitrogen in water may promote
  cyanobacteria
• Redfield ratio of 161 NP molar ratio
• If ratio greater than 161 - cyanobacteria will
  dominate
• However, if allow phosphorus than green algae
  will dominate rather than the cyanobacteria
• Measure TP, TN and TOC not just SRP and inorganic
  nitrogen

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Sulfur Cycle

• Sulfate is a general concern
• produce hydrogen sulfide (H2S)
• In ocean is 2.7 g/Kg SO42-
• Sulfate can be an oxidant (electron acceptor)
  like oxygen
• Transformations are mediated by bacteria and
  usually involve oxidation of organic matter
• Sulfur Reduction (facultative anaerobes) - Steps
  reduce sulfate to sulfur to sulfide
• Sulfur oxidation (aerobes and anaerobes) - Steps
  oxidize sulfide to sulfur to sulfate

colorless sulfur bacteria at the
aerobic/anaerobic interface
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Carbon Cycling - Follow the Energy
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TOC Analysis

• Oceanographers
• have been arguing for decades
• not settled on a concentration
• not settled on a method
• doubled the value once, then cut is back in half

Recommend Pilson, M.E.Q. An Introduction to the
Chemistry of the Sea Chapter 11
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What is DOC in the Ocean?

• The Answer - No one knows!
• Only about 20-30 of the TOC has been determined
• lt5 is particulate. The rest is dissolved - DOC
• Contains vitamins biotin, thiamine and B12.
  Which are from cells in the water, can persist in
  the water.
• Volatile carbon dioxide, dimethyl sulfide,
  methane, ethene
• Fatty acids, lipids, amino acids, sugars less
  than 1 of the DOC. Does contain fructose,
  galactose and glucose
• Humic Acids - not the same as those in soils or
  freshwater. May be 20-40 of the total DOC but
  there are analytical problems. Probably mostly
  nonpolar and anionic.

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Coral Reef Carbon Production and Recycling
Wild et al. 2004 Nature 42866-70
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Mahalo to the Lab Staff
Dr. Paul Burrell Julia Sears-Hartley Carol
Phalanx Les Wilson Jennifer Coshland Jason
Niemans Lindsay Woodward Theresa McGrath Matt
Hovanec