Transcript Lecture 3: Chemical Properties of Water MARI-5421

Conservative Water Quality
Lecture 7
Chemical Properties: dissolved
oxygen
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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)
Chemical Variables: dissolved
oxygen
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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)
Oxygen Solubility Curve
Chemical Variables: dissolved
oxygen
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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)
Oxygen Consumption vs. Size
for Channel Catfish (26oC)
O2 cons. Rate
(mg/kg/hr)
Increase in
oxygen consumption
Fish size (g)
Nonfed
Fed
2.5
880
1,230 40
100
400
620
55
500
320
440
38
1,000
250
400
60
From Lovell (1989)
from feeding (%)
Chemical Variables: dissolved
oxygen
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What might be considered
minimal levels of
maintenance of D.O.?
hard to determine due to
compounding effects (can’t
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
Chemical Variables: dissolved
oxygen
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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
Chemical Variables: dissolved
oxygen
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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
Chemical Variables: dissolved
oxygen/behavior
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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
Chemical Variables: dissolved
oxygen/behavior
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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?)--> death
Oxygen/Temperature
Interaction
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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
Chemical Variables: dissolved
oxygen/sources
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major producer of D.O. in ponds is primary
productivity (up to 80%), diffusion is low
(<3%)
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)
Oxygen Budget
Input
Photosynthesis
Inflowing water
Aeration
Diffusion
Total
Output
Overflow, drainage
Phyto respiration
Benthic respiration
Fish/shrimp resp.
Total
O2 (kg/ha)
4,130
94
99
1,050
5,373
% of total
76.9
1.7
1.8
19.6
100.0
32
3,090
1,040
1,210
5,372
0.6
57.5
19.4
22.5
100.0
Diel Oxygen Fluctuation
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Typical pattern =
oxygen max during
late afternoon
difference in
surface vs. benthic
for stratified
ponds
dry season = faster
heating at surface
and less variation
Influence of Sunlight on
Photosynthesis/O2 Production
Photorespiration: predictable
Chemical Variables: total
alkalinity
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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
Chemical Variables: total
alkalinity
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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
Chemical Variables: total
alkalinity
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total alkalinity level can be associated with
several potential problems in aquaculture:
< 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 --> low nat prod
low alkalinity = high pH
Chemical Variables: total
hardness
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total hardness: total concentration of metal
ions expressed in terms of mg/L of equivalent 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
Chemical Variables: pH
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pH: the level or intensity of a substance’s
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-
Chemical Variables: pH
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at acidic pH levels, the quantity of H+
predominates
acidic pH = pH < 7, basic = pH >7
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)
Chemical Variables: pH
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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)
Chemical Variables: carbon
dioxide
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normal component of all natural waters
sources: atmospheric diffusion,
respiration of cultured species, biological
oxidation of organic compounds
usually transported in the blood as HCO3converted to CO2 at the gill interface,
diffusion into medium
as the level of CO2 in the medium
increases, the gradient allowing diffusion is
less
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
Chemical Variables: carbon
dioxide
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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?
The Effect of pH on Carbonate
Buffering
Chemical Variables: carbon
dioxide
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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
Chemical Variable: carbon
dioxide
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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
Part II: Nitrogenous
Compounds in Water
Evolution of the Nitrogen Cycle
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Unlike carbon or oxygen, nitrogen is not
very available to life
it’s 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, Earth’s original atm was
oxygen-poor
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 Earth’s 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
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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
Nitrogen Saturation Values
Generalized Nitrogen Cycle
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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
Process 1: fixation
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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
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
Process 2: nitrification
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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!
Process 3: denitrification
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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
Aquatic Nitrogen Cycling
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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
Release of NH3
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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+ -->
NH4+)
ammonification is
heterotrophic, under
aerobic or anaerobic
conditions
ammonification
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 (Guillard’s F medium)
two step process:
NH4+ + 1.5O2  NO2- + 2H+ + H2O
NO2- + 0.5O2  NO3-
Note: these are oxygen-driven reactions
Aquatic Nitrogen Cycling
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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
Aquatic Nitrogen Cycling
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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
Nitrogen: aqueous forms
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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 NH3:NH4+ rises with pH
unfertilized ponds: TAN (NH3 +NH4+) = 0.050.075 mg/L
fertilized ponds: TAN = 0.5 mg/L, 0.075 mg
NO3-
Nitrogen Amendments
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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
Nitrogen Equillibria: NH3/NH4+
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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
More on Ammonia
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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
Ammonia Toxicity
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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
Ammonia Toxicity
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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
Ammonia Toxicity
Species
Pink salmon
Brown trout
Rainbow trout
Largemouth bass
Common carp
Channel catfish
Shrimp
96-hour LC50 (mg/L NH3)
0.08-0.1
0.50-0.70
0.16-1.10
0.9-1.4
2.2
0.50-3.8
5.71
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
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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?
-)
Nitrite (NO2
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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 can’t distinguish between NO2- and Clthus: nitrite absorption regulated by
nitrite:chloride ratio in medium
-)
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
Species
Rainbow trout
Chinook salmon
Common carp
Channel catfish
Largemouth bass
Guadeloupe bass
Shrimp, freshwater
Shrimp, saltwater
48- or 96-hr LC50 (mg/L NO2-N)
0.19-0.39
0.88
2.6
7.1-13
140
160
8.5-15.4
45-204 mg/L
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
Species
Guppy
Guadeloupe bass
Chinook salmon
Rainbow trout
Channel catfish
Bluegill
Shrimp
96-hr LC50 (mg/L NO3-N)
180-200
1,260
1,310
1,360
1,400
420-2,000
Who knows???