Conservative Water Quality Lecture 7

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Conservative Water QualityLecture 7
2
Chemical Properties dissolved oxygen

• Remember, along with temperature, dissolved
  oxygen (D.O.), is paramount in metabolic
  regulation
• D.O. and temp. both determine the environmental
  niche aquatic organisms occupy
• occupation of niches is controlled by a complex
  set of behavioral and physiological activities
  (acclimation)
• acclimation is slow wrt D.O. (hours, weeks)

3
Chemical Variables dissolved oxygen

• Although O2 is rather abundant in the atm (21),
  it is only marginally soluble in water (6 ppm is
  not much)
• What are the implications to fish/invertebrates?
• Even metabolic rates of aqua-communities can
  effect rapid changes in D.O.
• this effect increases with temp (interaction)
• solubility decreases with increased temp/sal
• other factors BP (direct), altitude (indirect),
  impurities (indirect)

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Oxygen Solubility Curve
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Chemical Variables dissolved oxygen

• factors affecting D.O. consumption
• water temperature (2-3x for every 10oC)
• environmental (medium) D.O. concentration
  (determines lower limit)
• fish size (Rc greater for small vs. large)
• level of activity (resting vs. forced)
• post-feeding period, etc. (2x, 1-6 hrs post
  feeding)

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Oxygen Consumption vs. Sizefor Channel Catfish
(26oC)
O2 cons. Rate Increase in
(mg/kg/hr) oxygen consumption Fish size
(g) Nonfed Fed from feeding () 2.5 880 1,230 40
100 400 620 55 500 320 440 38 1,000 250 400
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From Lovell (1989)
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Chemical Variables dissolved oxygen

• What might be considered minimal levels of
  maintenance of D.O.?
• hard to determine due to compounding effects
  (cant standardize conditions)
• major factor exposure time
• for most species
• long-term 1.5 mg/L
• medium term 1.0 mg/L
• short-term 0.3 mg/L

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Chemical Variables dissolved oxygen

• In general warm-water species are more tolerant
  of low D.O. concentrations
• Ictalurus punctatus adults/1.0 mg/L,
  fingerlings 0.5 mg/L
• Procamberus clarkii adults/2.0 mg/L,
  juveniles/1.0 mg/L
• Litopenaeus vannamei adults/0.5-0.8 mg/L
• Litopenaeus stylirostris adults/1.2-1.4 mg/L

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Chemical Variables dissolved oxygen

• Many practical aquaculturists will recommend that
  D.O. concentrations do not drop below 6.0 mg/L
• this is an impractical guideline in that this
  level can seldom be achieved at night
• a more practical guideline might be to maintain
  D.O. levels around 90 saturation
• no lower than 25 saturation for extended periods

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Chemical Variables dissolved oxygen/behavior

• if D.O. levels in the medium are adequate, fish
  meet increased demands due to locomotion or
  post-feeding by increased rate of ventilation or
  large gulps of water
• declining D.O. seek zones of higher D.O.,
  reduce activity (reduced MR), stop consumption of
  feed
• compensatory point when D.O. demand cannot be
  met by behavioral or physiological responses

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Chemical Variables dissolved oxygen/behavior

• upon reaching compensatory point gaping at
  surface, removal of oxygen from surface
• shown in both fish and invertebrates
• small aquatic animals are more efficient
• some oxygen provided by glycolysis or anaerobic
  metabolism, but blood pH drops
• pH drop in blood reduces carrying capacity of
  hemoglobin (hemocyanin?)--gt death

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Oxygen/Temperature Interaction

• Oxygen consumption increases with temperature
  until a maximum is achieved
• peak consumption rate is maintained over a small
  temp range
• consumption rate decreases rapidly as temp
  increases
• lethal temperature finally achieved

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Chemical Variables dissolved oxygen/sources

• major producer of D.O. in ponds is primary
  productivity (up to 80), diffusion is low (lt3)
• incoming water can often be deficient depending
  upon source water conditions
• major consumers primary productivity, aquatic
  species (density dependent), COD
• diel fluctuation
• indirect relationships (algae, secchi)

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Oxygen Budget
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Diel Oxygen Fluctuation

• Typical pattern oxygen max during late
  afternoon
• difference in surface vs. benthic for stratified
  ponds
• dry season faster heating at surface and less
  variation

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Influence of Sunlight on Photosynthesis/O2
Production
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Photorespiration predictable
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Chemical Variables total alkalinity

• total alkalinity the total amount of titratable
  bases in water expressed as mg/L of equivalent
  CaCO3
• alkalinity is primarily composed of the
  following ions CO3-, HCO3-, hydroxides,
  ammonium, borates, silicates, phosphates
• alkalinity in ponds is determined by both the
  quality of the water and bottom muds
• calcium is often added to water to increase its
  alkalinity, buffer against pH changes

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Chemical Variables total alkalinity

• thus, a total alkalinity determination of 200
  mg/L would indicate good buffering capacity of a
  water source
• natural freshwater alkalinity varies between 5
  mg/L (soft water) to over 500 mg/L (hard water)
• natural seawater is around 115-120 mg/L
• seldom see pH problems in natural seawater
• water having alkalinity reading of less than 30
  mg/L are problematic

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Chemical Variables total alkalinity

• total alkalinity level can be associated with
  several potential problems in aquaculture
• lt 50 mg/L copper compounds are more toxic,
  avoid their use as algicides
• natural waters with less than 40 mg/L alkalinity
  as CaCO3 have limited biofiltration capacity, pH
  independent
• low alkalinity low CO2 --gt low nat prod
• low alkalinity high pH

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Chemical Variables total hardness

• total hardness total concentration of metal ions
  expressed in terms of mg/L of equiva- lent CaCO3
• primary ions are Ca2 and Mg2, also iron and
  manganese
• total hardness approximates total alkalinity
• calcium is used for bone and exoskeleton
  formation and absorbed across gills
• soft water molt problems, bone deformities

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Chemical Variables pH

• pH the level or intensity of a substances
  acidic or basic character
• pH the negative logarithm of the hydrogen ion
  concentration (activity) of a substance
• pH -log(1/H)
• ionization of water is low (1x10-7 moles of H/L
  and 1x10-7 moles OH-/L)
• neutral pH similar levels of H and OH-

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Chemical Variables pH

• at acidic pH levels, the quantity of H
  predominates
• acidic pH pH lt 7, basic pH gt7
• most natural waters pH of 5-10, usually 6.5-9
  however, there are exceptions
• acid rain, pollution
• can change due to atm CO2, fish respiration
• pH of ocean water is stable (carbonate buffering
  system, later)

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Chemical Variables pH

• Other sources of change
• decay of organic matter
• oxidation of compounds in bottom sediments
• depletion of CO2 by phytoplankton on diel basis
• oxidation of sulfide containing minerals in
  bottom soils (e.g., oxidation of iron pyrite by
  sulfide oxidizing bacteria under anaerobic
  conditions)

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Chemical Variables carbon dioxide

• normal component of all natural waters
• sources atmospheric diffusion, respiration of
  cultured species, biological oxidation of organic
  compounds
• usually transported in the blood as HCO3-
• converted to CO2 at the gill interface, diffusion
  into medium
• as the level of CO2 in the medium increases, the
  gradient allowing diffusion is less

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Chemical Variables carbon dioxide

• this causes blood CO2 levels to increase,
  lowering blood pH
• with lower blood pH, carrying capacity of
  hemoglobin decreases, also binding affinity for
  oxygen to hemoglobin
• this phenomenon is known as the Bohr-Root effect
• CO2 also interferes with oxygen uptake by eggs
  and larvae

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CO2 Level Affects Hemoglobin Saturation
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Chemical Variables carbon dioxide

• in the marine environment, excesses of CO2 are
  mitigated by the carbonate buffering system
• CO2 reacts with water to produce H2CO3, carbonic
  acid
• H2CO3 reacts with CaCO3 to form HCO3-
  (bicarbonate) and CO32- (carbonate)
• as CO2 is used for photosynthesis, the reaction
  shifts to the left, converting bicarbonates back
  to CO2
• what large-scale implications does this have?

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The Effect of pH on Carbonate Buffering
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Chemical Variables carbon dioxide

• Concentrations of CO2 are small, even though it
  is highly soluble in water
• inverse relationship between CO2 and
  temperature/salinity
• thus, CO2 solubility depends upon many factors

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Chemical Variable carbon dioxide

• CO2 is not particularly toxic to fish or
  invertebrates, given sufficient D.O. is available
• maximum tolerance level appears to be around 50
  mg/L for most species
• good working level of around 15-20 mg/L
• diel fluctuation opposite to that of D.O.
• higher levels in warmer months of year

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Part II Nitrogenous Compounds in Water
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Evolution of the Nitrogen Cycle

• Unlike carbon or oxygen, nitrogen is not very
  available to life
• its conversion requires biological activity
• nitrogen cycle is required by life, but also
  driven by it
• cycle is rather complex and has evolved as the
  atmosphere became oxygenated
• as we know, Earths original atm was oxygen-poor

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Evolution of the Nitrogen Cycle

• Earliest forms of nitrogen-reducing bacteria had
  to have been anaerobic
• other option NH4 already existed in some form
• today these ancient N-fixers either only exist in
  anaerobic environments or the N-fixing apparati
  are carefully guarded from intracellular oxygen

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Evolution of the Nitrogen Cycle

• As Earths atmosphere became more O2-rich, more
  NO3 became available
• this created niches occupied by organisms that
  could reduce NO3 to NH3 (many higher plants can
  do this)
• converting NO3 back to N2 (denitrification) is an
  arduous process and has evolved more recently

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Gaseous Nitrogen

• Nitrogen is the major gas in the atmosphere
• after oxygen, second limiting factor
• constitutes 78.1 of total gases in air
• solubility in water is largely dependent upon two
  physio-chemical factors temperature and
  salinity
• at saturation/equillibrium it has higher values
  than oxygen or CO2?

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Nitrogen Saturation Values
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Generalized Nitrogen Cycle

• Nitrogen dynamics in the environment involves
  some fairly complex cycling
• N is relatively unreactive as an element
• cyclic conversions from one form to another are
  mainly mediated by bacteria
• Cycle occurs in both aerobic and anaerobic
  environments

nitrogen cycle
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Process 1 fixation

• Nitrogen fixation refers to the conversion of N2
  to either NO3 or NH4 by bacteria
• terrestrial systems soil bacteria in root
  nodules of legumes
• aquatic systems blue green algae
• biological, meteorological, industrial
  transformations also occur

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Nitrogen Fixation
Type of Fixation N2 fixed (1012 g per year)
Non-biological
industrial About 50
combustion About 20
lightning About 10
Total About 80
Biological
Agricultural land About 90
Forest nonag land About 50
Sea About 35
Total About 175
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Process 2 nitrification

• The term nitrification refers to the conversion
  of ammonium to nitrate (pathway 3-4 opposite)
• Responsible nitrifying bacteria known as
  chemoautotrophs
• These bacteria gain their energy by oxidizing
  NH3, while using CO2 as a source of carbon to
  synthesize organic compounds

The nitrogen cycle, once more!
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Process 3 denitrification

• By this process, NO3 in soil or water is
  converted into atm N2, nitric oxide or nitrous
  oxide
• this must occur under anaerobic conditions
  (anaerobic respiration)
• presence of O2 can reverse the reaction
• again, mediated by bacteria (Pseudomonas sp.,
  Alkaligenes sp. and Bacillus sp.)

Denitrification step 5, above
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Aquatic Nitrogen Cycling

• For aquaculturists, cycling transforms usually
  begin with the decomposition of organic matter
  from either plant or animal sources
• major source in aquaculture feeds
• ultimately excreted as amine groups on amino
  acids or excreted in soluble form primarily as
  NH3/NH4, other compounds

amino acid
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Release of NH3

• NH3 separated from organic protein via microbial
  activity
• Process referred to as deaminification or
  ammonification
• NH3 is released to water column (mineralization)
  and assimilated into primary productivity (NH3
  H --gt NH4)
• ammonification is heterotrophic, under aerobic or
  anaerobic conditions

ammonification
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Aquatic Nitrogen Cycling

• NH3 and NH4 are both either assimilated by
  aquatic plants for growth or nitrified (oxidized)
  to NO3- (nitrate)
• nitrate can also be used as a growth substrate
  (Guillards F medium)
• two step process
• NH4 1.5O2 ? NO2- 2H H2O
• NO2- 0.5O2 ? NO3-
• Note these are oxygen-driven reactions

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Aquatic Nitrogen Cycling

• Conversion of ammonia (NH3) to nitrate (NO3-) is
  via chemoautotrophic bacteria
• first step by Nitrosomonas sp.
• second step by Nitrobacter sp.
• Both steps/reactions use NH4 and NO2- as an
  energy source, CO2 as a carbon source
• this is a non-photosynthetic type of growth

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Aquatic Nitrogen Cycling

• Reaction runs best at pH 7-8 and 25-30oC
• however under low DO, it runs in reverse
• NO3- is converted to NO2 and other forms
• can go all the way backwards to NH3
• occurs in the hypolimnion under eutrophic
  (stagnant) conditions
• REM nitrogen also fixed by leguminous plants,
  free living bacteria, blue-green algae
• magnitude of this transform not well studied

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Nitrogen aqueous forms

• Gaseous form of nitrogen (N2) is most prevalent
• followed by nitrite, nitrate, ammonia or
  ammonium
• nitrite is seldom a problem unless DO levels are
  low (to be discussed later)
• ratio of NH3NH4 rises with pH
• unfertilized ponds TAN (NH3 NH4) 0.05-0.075
  mg/L
• fertilized ponds TAN 0.5 mg/L, 0.075 mg NO3-

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Nitrogen Amendments

• Nitrogen added as fertilizer to ponds urea
• Immediately upon addition, it starts to decline
• only small portion detectable from metabolic
  processes
• plants typically take it up, die, mud deposit
• inorganic nitrogen typically denitrified in the
  hypolimnion
• high afternoon pH increased volatization

urea
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Nitrogen Equillibria NH3/NH4

• ammonia (NH3) is toxic to fish/inverts
• pH affects proportion of NH3/NH4
• as pH increases, NH3 increases
• calculation example TAN 1.5 mg/L, 26oC, pH
  8.6
• answer 0.35 mg NH3/L

Affect of pH/temp on NH3/NH4 equillibria
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More on Ammonia

• As mentioned, initial source feed, direct
  source excretion
• can calculate daily dosage/loading if you know
  NPU and protein in feed
• NPU is 0.4 (approx.) for most aquaculture feeds
• equ. (1.0 - NPU)(pro/6.25)(1000) g NH3/kg
  feed
• for 1.0 ha pond receiving 100 kg of 30 protein
  feed/day, loading is 1,920 g NH3
• dilution in 10 x 106 L is 0.192 mg NH3/L
• if NPU stays constant, NH3 production increases
  with increased feeding

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Ammonia Toxicity

• Both NH3 and NH4 are toxic to fish/inverts
• as medium NH3 increases, ability to excrete
  internal NH3 decreases (fighting gradient)
• blood/tissue NH3 increases causes increase in
  blood pH
• result imbalance in enzyme activity, reduced
  membrane stability
• increased O2 consumption by tissues, gill damage,
  reduced O2 transport (Root/Bohr, but other
  direction)
• reduced growth, histological changes in
  gills/other organs

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Ammonia Toxicity

• Short term exposure toxic at 0.7-2.4 mg/L
• 96 hr LC50 varies from 0.5-3.8 mg/L for most fish
• toxicity tolerance varies due to biological
  variability of different strains of species
• eggs are most tolerant (fish)
• larvae least tolerant, older more tolerant
• same probably holds true for inverts

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Ammonia Toxicity
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Ammonia Toxicity in Ponds

• NH3 is more toxic when DO levels are low
• however, toxic effect is probably nullified by
  resultant increase in CO2
• thus, increased CO2 decreased NH3
• increased CO2 decreased pH
• in some cases, fish have been shown to acclimate
  to increases in NH3

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Nitrite (NO2-) Toxicity

• Nitrite reacts with hemoglobin to form
  methemoglobin
• in process, iron converted from ferrous (Fe2) to
  ferric (Fe3) form
• ferric form of iron cannot bind with oxygen
• blood changes from red to brown, appears anemic
• those fish having methemoglobin reductase enzyme
  can convert iron moeity back to ferrous
• maybe same for crustaceans?

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Nitrite (NO2-) Toxicity

• Recovery from nitrite toxicity usually occurs
  when fish are transferred to better water
• complete recovery can occur in 24 h
• how does it get into system in first place?
• Nitrite is quickly transported across gill
  membrane by lamellar chloride cells
• cells cant distinguish between NO2- and Cl-
• thus nitrite absorption regulated by
  nitritechloride ratio in medium

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Nitrite (NO2-) Toxicity

• Nitrite is about 55 times more toxic in
  freshwater vs. 16 ppt seawater
• Question Can you add NaCl to water to reverse
  nitrite toxicity?
• 24 hr LC50 values vary tremendously in fish
• safe bet authors say 4.5 mg/L

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Nitrite (NO3-) Toxicity
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Nitrate (NO3-) Toxicity

• Nitrate builds up in ponds, like nitrite, when
  ponds are cooler
• Nitrobacter does not function well under cool or
  cold water conditions
• however, nitrates are least toxic form of soluble
  nitrogen
• effects are similar to nitrite toxicity, but
  values of levels are much higher

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Nitrate Toxicity